tag:theconversation.com,2011:/ca/topics/rocks-10597/articlesRocks – The Conversation2023-11-20T13:15:30Ztag:theconversation.com,2011:article/2132022023-11-20T13:15:30Z2023-11-20T13:15:30ZHow do crystals form?<figure><img src="https://images.theconversation.com/files/557894/original/file-20231106-25-rk3zxx.jpg?ixlib=rb-1.1.0&rect=33%2C0%2C5595%2C3713&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Two crystalline materials together: kyanite (blue) embedded in quartz (white).</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/bladed-crystals-of-kyanite-in-quartz-from-brazil-news-photo/869774444">Photo 12/Universal Images Group via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
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<p><strong>How do crystals form? – Alyssa Marie, age 5, New Mexico</strong></p>
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<p>Scientifically speaking, the term “crystal” refers to any solid that has an <a href="https://theconversation.com/why-does-nature-create-patterns-a-physicist-explains-the-molecular-level-processes-behind-crystals-stripes-and-basalt-columns-186433">ordered chemical structure</a>. This means that its parts are arranged in a precisely ordered pattern, like bricks in a wall. The “bricks” can be <a href="https://australian.museum/learn/minerals/what-are-minerals/crystal-shapes/">cubes or more complex shapes</a>.</p>
<p>I’m <a href="https://scholar.google.com/citations?user=EqUjQbwAAAAJ&hl=en">an Earth scientist and a teacher</a>, so I spend a lot of time thinking about minerals. These are solid substances that <a href="https://www.britannica.com/science/mineral-chemical-compound">are found naturally in the ground</a> and can’t be broken down further into different materials other than <a href="https://www.youtube.com/watch?v=wzTRPlG1L0o">their constituent atoms</a>. Rocks are mixtures of different minerals. <a href="https://www.geologyin.com/2016/03/what-is-difference-between-minerals-and.html">All minerals are crystals</a>, but not all crystals are minerals. </p>
<p>Most rock shops sell mineral crystals that occur in nature. One is <a href="https://theconversation.com/not-so-foolish-after-all-fools-gold-contains-a-newly-discovered-type-of-real-gold-161819">pyrite, which is known as fool’s gold</a> because it looks like real gold. Some shops also feature showy, human-made crystals such as <a href="https://www.zmescience.com/feature-post/natural-sciences/geology-and-paleontology/rocks-and-minerals/the-bismuth-crystal-why-it-looks-so-amazingly-trippy-and-why-its-actually-a-big-deal-for-science/">bismuth</a>, a natural element that forms crystals when it is melted and cooled. </p>
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<a href="https://images.theconversation.com/files/557895/original/file-20231106-267473-4zr8g4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A dark gray rock with a large concentration of shiny yellow material covering part of its surface." src="https://images.theconversation.com/files/557895/original/file-20231106-267473-4zr8g4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/557895/original/file-20231106-267473-4zr8g4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=453&fit=crop&dpr=1 600w, https://images.theconversation.com/files/557895/original/file-20231106-267473-4zr8g4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=453&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/557895/original/file-20231106-267473-4zr8g4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=453&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/557895/original/file-20231106-267473-4zr8g4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=569&fit=crop&dpr=1 754w, https://images.theconversation.com/files/557895/original/file-20231106-267473-4zr8g4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=569&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/557895/original/file-20231106-267473-4zr8g4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=569&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Pyrite in black shale rock from a quarry in Indianapolis, Ind.</span>
<span class="attribution"><a class="source" href="https://flic.kr/p/uJq9jj">James St. John/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<h2>Why and how crystals form</h2>
<p>Crystals grow when molecules that are alike get close to each other and stick together, forming chemical bonds that act like Velcro between atoms. Mineral crystals cannot just start forming spontaneously – they need special conditions and a <a href="https://www.thoughtco.com/definition-of-nucleation-605425">nucleation site</a> to grow on. A nucleation site can be a rough edge of rock or a speck of dust that a molecule bumps into and sticks to, starting the crystallization chain reaction.</p>
<p>At or near the Earth’s surface, many molecules are dissolved in water that flows through or over the ground. If there are enough molecules in the water that are alike, they will separate from the water as solids – a process called precipitation. If they have a nucleation site, they will stick to it and start to form crystals. </p>
<p>Rock salt, which is actually <a href="https://www.britannica.com/science/halite">a mineral called halite</a>, grows this way. So does <a href="https://www.britannica.com/science/travertine">another mineral called travertine</a>, which sometimes forms flat ledges in caves and around hot springs, where water causes chemical reactions between the rock and the air. </p>
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<a href="https://images.theconversation.com/files/557876/original/file-20231106-23-phmp31.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="White rock terraces around a vent in the earth's surface releasing steam." src="https://images.theconversation.com/files/557876/original/file-20231106-23-phmp31.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/557876/original/file-20231106-23-phmp31.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=449&fit=crop&dpr=1 600w, https://images.theconversation.com/files/557876/original/file-20231106-23-phmp31.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=449&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/557876/original/file-20231106-23-phmp31.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=449&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/557876/original/file-20231106-23-phmp31.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=564&fit=crop&dpr=1 754w, https://images.theconversation.com/files/557876/original/file-20231106-23-phmp31.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=564&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/557876/original/file-20231106-23-phmp31.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=564&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Travertine ledges at Mammoth Hot Springs in Yellowstone National Park in Wyoming. Terraced pools form due to deposition of travertine from the hot spring fluids as they cool and release carbon dioxide.</span>
<span class="attribution"><a class="source" href="https://d9-wret.s3.us-west-2.amazonaws.com/assets/palladium/production/s3fs-public/thumbnails/image/P7190038.JPG">USGS</a></span>
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<p>You can make “<a href="http://www.sciencekidsathome.com/science_experiments/growing_stalactites.html">salt stalactites</a>” at home by growing salt crystals on a string. In this experiment, the string is the nucleation site. When you dissolve Epsom salts in water and lower a string into it, then leave it for several days, the water will slowly evaporate and leave the Epsom salts behind. As that happens, salt crystals precipitate out of the water and grow crystals on the string.</p>
<p>Many places in the Earth’s crust are hot enough for <a href="https://www.britannica.com/science/magma-rock">rocks to melt into magma</a>. As that magma cools down, mineral crystals grow from it, just like water freezing into ice cubes. These mineral crystals form at much higher temperatures than salt or travertine precipitating out of water. </p>
<h2>What crystals can tell scientists</h2>
<p>Earth scientists can learn a lot from different types of crystals. For example, the presence of certain mineral crystals in rocks can reveal the rocks’ age. This dating method is called <a href="https://www.britannica.com/science/geochronology">geochronology</a> – literally, measuring the age of materials from the Earth. </p>
<p>One of the most valued mineral crystals for geochronologists is <a href="https://geology.com/minerals/zircon.shtml">zircon</a>, which is so durable that it quite literally stands the test of time. The <a href="https://www.si.edu/newsdesk/releases/earths-oldest-minerals-date-onset-plate-tectonics-36-billion-years-ago">oldest zircons ever found</a> come from Australia and are about 4.3 billion years old – almost as <a href="https://www.amnh.org/exhibitions/darwin/the-world-before-darwin/how-old-is-earth">old as our planet itself</a>. Scientists use the chemical changes recorded within zircons as they grew as a reliable “clock” to <a href="https://knowablemagazine.org/article/physical-world/2021/keeping-time-zircons">figure out how old the rocks containing them are</a>.</p>
<p>Some crystals, including zircons, have growth rings, like the <a href="https://naturalsciences.org/calendar/news/science-at-home-tree-rings/">rings of a tree</a>, that form when layers of molecules accumulate as the mineral grows. These rings can tell scientists all kinds of things about <a href="https://theconversation.com/1-000-year-old-stalagmites-from-a-cave-in-india-show-the-monsoon-isnt-so-reliable-their-rings-reveal-a-history-of-long-deadly-droughts-189222">the environment in which they grew</a>. For example, changes in pressure, temperature and magma composition can all result in growth rings.</p>
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<a href="https://images.theconversation.com/files/559134/original/file-20231113-25-cx8jko.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="White rectangular feldspar crystals with faintly visible growth rings are prominent against grey granodiorite rock." src="https://images.theconversation.com/files/559134/original/file-20231113-25-cx8jko.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/559134/original/file-20231113-25-cx8jko.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=530&fit=crop&dpr=1 600w, https://images.theconversation.com/files/559134/original/file-20231113-25-cx8jko.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=530&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/559134/original/file-20231113-25-cx8jko.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=530&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/559134/original/file-20231113-25-cx8jko.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=666&fit=crop&dpr=1 754w, https://images.theconversation.com/files/559134/original/file-20231113-25-cx8jko.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=666&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/559134/original/file-20231113-25-cx8jko.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=666&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Feldspar crystals with growth rings in granodiorite rock near Squamish, British Columbia.</span>
<span class="attribution"><span class="source">Natalie Bursztyn</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<p>Sometimes mineral crystals grow as high pressure and temperatures within the Earth’s crust change rocks from one type to another in a process called <a href="https://www.amnh.org/exhibitions/permanent/planet-earth/how-do-we-read-the-rocks/three-types/metamorphic">metamorphism</a>. This process causes the elements and chemical bonds in the rock to rearrange themselves into new crystal structures. Lots of spectacular crystals grow in this way, including <a href="https://geology.com/minerals/garnet.shtml">garnet</a>, <a href="https://geology.com/minerals/kyanite.shtml">kyanite</a> and <a href="https://geology.com/minerals/staurolite.shtml">staurolite</a>.</p>
<h2>Amazing forms</h2>
<p>When a mineral precipitates from water or crystallizes from magma, the more space it has to grow, the bigger it can become. There is a <a href="https://cen.acs.org/physical-chemistry/geochemistry/Naicas-crystal-cave-captivates-chemists/97/i6">cave in Mexico full of giant gypsum crystals</a>, some of which are 40 feet (12 meters) long – the size of telephone poles.</p>
<p>Especially showy mineral crystals are also valuable as gemstones for jewelry once they are cut into new shapes and polished. The highest price ever paid for a gemstone was $71.2 million for the <a href="https://www.npr.org/sections/thetwo-way/2017/04/05/522739361/pink-star-diamond-sells-for-71-million-smashing-auction-record">CTF Pink Star diamond</a>, which went up for auction in 2017 and sold in less than five minutes.</p>
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<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/213202/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Natalie Bursztyn does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>There are a lot of myths about crystals − for example, that they are magical rocks with healing powers. An earth scientist explains some of their amazing true science.Natalie Bursztyn, Lecturer in Geosciences, University of MontanaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2134792023-11-08T13:53:29Z2023-11-08T13:53:29ZTurkana stone beads tell a story of herder life in a drying east Africa 5,000 years ago<p>On the shores of Lake Turkana in east Africa, about 5,000 to 4,000 years ago, pastoralists buried their dead in communal cemeteries that were marked by stone circles and pillars. <a href="https://doi.org/10.1073/pnas.1721975115">The north-west Kenya “pillar sites”</a> were built around the same time as Stonehenge in the UK. But these places have a different story to tell: about how mortuary traditions reflect people’s environments, behaviours and reactions to change.</p>
<p>The burial sites appeared at a time of major <a href="https://www.sciencedirect.com/science/article/pii/S027737912200021X">environmental</a> and economic <a href="https://www.sciencedirect.com/science/article/pii/S0012825217303331">change</a> in the region. The Sahara, which received enough rainfall 9,000-7,000 years ago to sustain populations of fisher-hunter-gatherers and pastoralists, was <a href="https://pastglobalchanges.org/publications/pages-magazines/pages-magazine/7413">drying</a>, causing groups of people to move east and south. Even in eastern Africa, lake levels were dropping dramatically; grassy plains were expanding. Around Lake Turkana, people began herding animals in addition to fishing and foraging. </p>
<p>At several of the pillar sites around Lake Turkana, archaeologists have found that hundreds of people were <a href="https://link.springer.com/article/10.1007/s12520-019-00914-4">ceremonially interred</a> under large, circular platform mounds. Many of those individuals were found wearing remarkable colourful stone beads, some as part of necklaces, bracelets, earrings, and other jewellery worn, for example, around the waist. These beautiful personal ornaments include blue-green amazonite, soft pink zeolite, deep red chalcedony, purple fluorite and green talc, among other minerals and rocks.</p>
<p>I study relationships between humans and their environments, especially at times of major economic transformations, using scientific techniques applied to archaeology. I recently led a team of experts in geology and archaeology of the region to conduct the first comprehensive mineralogical <a href="https://www.tandfonline.com/doi/full/10.1080/00934690.2023.2232703">analysis</a> of the Turkana stone beads. </p>
<p>The focus of our study was to discover what types of minerals and rocks the early herders had used to make adornments, and where these materials came from. </p>
<p>This kind of information can tell archaeologists about the role of artefacts in the society that used them.</p>
<h2>Wearing beads</h2>
<p>Humans have been making and wearing beads for over <a href="https://www.science.org/doi/10.1126/sciadv.abi8620">140,000 years</a>. Beads are one of the oldest forms of symbolism and are often used as <a href="https://theconversation.com/the-tiny-ostrich-eggshell-beads-that-tell-the-story-of-africas-past-128577">adornment</a> in a culture. Wearing something on your body is an expressive choice that can have many meanings, such as protection, acknowledgement of friendships and bonds, status or role in society. Personal ornaments like beads may indicate a common cultural understanding. </p>
<p>Analysis of <a href="https://theconversation.com/what-excavated-beads-tell-us-about-the-when-and-where-of-human-evolution-53695">beads in archaeological sites</a> has shown that we can learn many things from them. </p>
<p>At the Turkana pillar sites, the stone bead tradition was clearly important, partly because of the number of beads found accompanying burials, and partly because the practice persisted for hundreds of years. </p>
<p>Knowing the range of materials helps us understand landscape use in the past: where people were buried, where they watered their animals, seasonal movements for grazing, special yearly trips to significant places and other movements. Pastoralists recorded or marked their worlds by what they left behind and what they took with them. Patterns in the composition of the bead collections may indicate there was communication and exchange of objects across the region.</p>
<h2>Sorting the stone beads</h2>
<p>Of the six pillar sites that have been excavated by archaeologists, three have yielded substantial assemblages of stone beads: Lothagam North, Manemanya and Jarigole. Our team began by sorting the stone beads by site, and by their mineral and rock types.</p>
<p>Our study identified the mineral characteristics of 806 stone beads. We looked at properties like <a href="https://www.britannica.com/science/specific-gravity">specific gravity</a>, crystal and molecular structure, and the characteristic emissions that are particular to certain minerals. </p>
<p>What we found was a strikingly diverse set of beads that varied by site. The visual characteristics of some of the beads – colour, lustre and so on – may have made them particularly valuable or had a special meaning economically, socially, spiritually or symbolically. Their source and workability may also have given them a certain value. </p>
<p>Pink zeolites and turquoise amazonites were the most common stone beads at the site of Lothagam North, comprising over three-quarters of the assemblage. This was very similar to the site of Jarigole, located across the lake. The sites are hundreds of kilometres apart, with Lake Turkana in between – suggesting a cultural connection between them.</p>
<p>In contrast, the kinds of beads at Manemanya were different: mostly softer and paler pink and off-white calcite beads that were quite large. Further, while at Lothagam North there often were just a few beads found with any individual, one person at Manemanya was buried with over 300 stone beads and over 10,000 ostrich eggshell beads. </p>
<p>This suggests that although having stone beads was a commonality across the sites, distinctions – and distinct meanings for different people – did exist. </p>
<h2>Sourcing stones</h2>
<p>We also wanted to know whether the beads were produced from local sources (within a few days’ walk) or acquired through long-distance journeys or trade. Sourcing allows us to partially reconstruct how the earliest pastoralists moved around the landscape during the year.</p>
<p>A survey of the areas west of Lake Turkana and a search of the published literature on the geology of the region identified places where these materials might have come from.</p>
<p>There are possible sources for most of these materials within about 150km of the pillar sites. Limestone rocks may have been procured easily near the lake. Some of the tougher materials, like the chalcedonies, could have been carried to the lake area by rivers, to be picked up perhaps by someone watering cattle or fetching water from a stream. Other minerals come from a specific source. The variety of bead types demonstrates that people knew their landscape well.</p>
<p>Sometimes, they went out of their way to get certain minerals, or perhaps traded for them. The closest known sources for amazonite and fluorite are, respectively, 225 km, in southern Ethiopia; and 350 km, near the modern city of Eldoret, Kenya. </p>
<p>These suggest that bead making was not just a casual affair; material selection was intentional.</p>
<h2>Local landscapes</h2>
<p>Early herders in the Turkana Basin obtained materials from both local and distant places, and shaped them into personal adornments. These stone beads were placed with the dead, in numbers and combinations that differed by individual and place. We don’t yet fully know what they meant – but future research in the Turkana Basin will continue to explore the lives and legacies of these pioneering herders as they negotiated new environmental and social landscapes.</p>
<p><em>Edits and comments for this article were provided by Late Prehistory of West Turkana project co-directors Drs. Elizabeth Hildebrand and Katherine Grillo, project minerologist Mark Helper, and Emmanuel Ndiema, who helped lead the sourcing study.</em></p><img src="https://counter.theconversation.com/content/213479/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Funding for Klehm's research on the pillar site stone beads was provided by the Wenner-Gren Foundation.</span></em></p>Mineralogical analysis of 5,000-year-old stone beads from Turkana, Kenya suggest a novel mortuary tradition by early pastoralists.Carla Klehm, Research Assistant Professor, Center for Advanced Spatial Technologies, University of ArkansasLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2033922023-05-15T12:33:42Z2023-05-15T12:33:42ZWhy don’t rocks burn?<figure><img src="https://images.theconversation.com/files/523325/original/file-20230427-232-11japl.jpg?ixlib=rb-1.1.0&rect=44%2C0%2C5000%2C3308&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Jharia coal field in India has been on fire underground since 1916.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/in-the-village-liloripathra-that-is-located-on-the-top-of-news-photo/1227824345">Jonas Gratzer/LightRocket via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p>Why don’t rocks burn? – Luke, age 4, New Market, New Hampshire</p>
</blockquote>
<hr>
<p>While many rocks don’t burn, some of them do. It depends on what the rocks are made of – and that’s related to how they were formed.</p>
<p>There are three main rock types: <a href="https://www.usgs.gov/faqs/what-are-igneous-rocks">igneous</a>, <a href="https://www.usgs.gov/faqs/what-are-sedimentary-rocks">sedimentary</a> and <a href="https://www.usgs.gov/faqs/what-are-metamorphic-rocks">metamorphic</a>. These rocks are made of minerals that all have different characteristics. Some will melt into <a href="https://www.usgs.gov/faqs/what-difference-between-magma-and-lava">magma or lava</a> – super-hot, liquid rock – when they are exposed to heat. Others will catch fire.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/7Bxw4kkeHJ8?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Rocks can look alike, but one rock is not like another.</span></figcaption>
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<p>Rocks that burn when they get heated up <a href="https://www.grc.nasa.gov/www/k-12/airplane/combst1.html">are combusting</a>. This means that elements within the rocks are reacting with oxygen in the air to produce heat and light, in the form of flames. </p>
<p>The elements <a href="https://www.rsc.org/periodic-table/element/16/sulfur">sulfur</a>, <a href="https://www.rsc.org/periodic-table/element/6/carbon">carbon</a> and <a href="https://www.rsc.org/periodic-table/element/1/hydrogen">hydrogen</a> easily react with oxygen. Rocks that contain these elements are combustible. Without these elements inside them, rocks that are exposed to enough heat will melt instead of catching fire.</p>
<h2>How rocks form</h2>
<p><a href="https://www.usgs.gov/faqs/what-are-igneous-rocks">Igneous rocks</a> are formed when magma underground or <a href="https://theconversation.com/curious-kids-how-can-we-tell-when-a-volcano-is-going-to-erupt-147703">lava from a volcano</a> cools and crystallizes into solid material. These rocks are mostly made of <a href="https://www.britannica.com/science/silicate-mineral">silicate minerals</a> that crystallize at temperatures from 1,300 degrees Fahrenheit (700 degrees Celsius) up to <a href="https://education.nationalgeographic.org/resource/magma-role-rock-cycle/">as high as 2,400 F (1,300 C)</a>.</p>
<p>Igneous rocks contain few or no combustible elements. And it’s very hard to remelt them back into magma because they crystallize at such high temperatures – it would take the kind of <a href="https://theconversation.com/why-cant-we-throw-all-our-trash-into-a-volcano-and-burn-it-up-170919">high-tech incinerator that cities use to burn waste</a> to make that happen.</p>
<p><a href="https://www.usgs.gov/faqs/what-are-sedimentary-rocks">Sedimentary rocks</a> have a very different formation story. They form from broken bits of rocks, minerals, sometimes plant or animal material, and also crystals left behind when water evaporates, like the <a href="https://www.compoundchem.com/2016/03/02/limescale/">limescale</a> that forms in teakettles and bathtubs. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/523326/original/file-20230427-14-w7d3zk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Infographic showing materials washing into the ocean and becoming compressed at depth." src="https://images.theconversation.com/files/523326/original/file-20230427-14-w7d3zk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/523326/original/file-20230427-14-w7d3zk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=423&fit=crop&dpr=1 600w, https://images.theconversation.com/files/523326/original/file-20230427-14-w7d3zk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=423&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/523326/original/file-20230427-14-w7d3zk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=423&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/523326/original/file-20230427-14-w7d3zk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=531&fit=crop&dpr=1 754w, https://images.theconversation.com/files/523326/original/file-20230427-14-w7d3zk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=531&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/523326/original/file-20230427-14-w7d3zk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=531&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Sedimentary rock forms when layers of material are compressed over time, either on land or under water.</span>
<span class="attribution"><a class="source" href="https://flic.kr/p/mGbBa2">Siyavula Education/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>There is a lot of <a href="https://www.rsc.org/periodic-table/element/16/sulfur">sulfur</a>, <a href="https://www.rsc.org/periodic-table/element/6/carbon">carbon</a> and <a href="https://www.rsc.org/periodic-table/element/1/hydrogen">hydrogen</a> in living things. In fact, these are three of the <a href="https://www.livescience.com/32983-what-are-ingredients-life.html">six essential elements of life on Earth</a>. Bits of organic matter, particularly dead plants, also are combustible and allow the rocks to burn. </p>
<p>The last group of rocks is called <a href="https://www.usgs.gov/faqs/what-are-metamorphic-rocks">metamorphic</a>, because these rocks form when a lot of heat and pressure change existing rocks into new types without melting or burning them. “Metamorphosis” comes from ancient Greek and means “transformation.” For example, marble that you might see in kitchen counters or statues came from limestone that was transformed under intense heat and pressure deep underground. </p>
<h2>The rock that humans burn: Coal</h2>
<p>Metamorphic rocks that are formed from igneous rocks won’t contain the combustible elements – the ones that burn – but metamorphic rocks made from sedimentary rocks might. One familiar example is <a href="https://www.usgs.gov/faqs/what-are-types-coal">anthracite coal</a>, which is made almost entirely of carbon. It formed when dead plants fell into swamps long, long ago, were buried by sand or mud, and eventually were compressed over <a href="https://eartharchives.org/articles/the-evolution-of-plants-part-3-the-age-of-coal/index.html">hundreds of millions of years into coal</a>. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/523327/original/file-20230427-2850-2212o2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A large chunk of anthracite coal." src="https://images.theconversation.com/files/523327/original/file-20230427-2850-2212o2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/523327/original/file-20230427-2850-2212o2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=901&fit=crop&dpr=1 600w, https://images.theconversation.com/files/523327/original/file-20230427-2850-2212o2.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=901&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/523327/original/file-20230427-2850-2212o2.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=901&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/523327/original/file-20230427-2850-2212o2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1132&fit=crop&dpr=1 754w, https://images.theconversation.com/files/523327/original/file-20230427-2850-2212o2.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1132&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/523327/original/file-20230427-2850-2212o2.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1132&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Anthracite is the hardest type of coal. It contains the most carbon and the fewest impurities of all coal types.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Anthracite#/media/File:Anthracite_chunk.JPG">Jakec/Wikipedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>There are many coal seams around the world. Sometimes the coal even <a href="https://www.smithsonianmag.com/science-nature/fire-in-the-hole-77895126/">catches fire while it’s still in the ground</a>. The cause can be natural, such as a lightning strike, or human activities like mining.</p>
<p>In Centralia, Pennsylvania, a former mining town, a coal seam has been <a href="https://www.smithsonianmag.com/science-nature/fire-in-the-hole-77895126/">burning for over 50 years</a>. There are other active coal seam fires in places around the world including <a href="https://eos.org/articles/coal-seam-fires-burn-beneath-communities-in-zimbabwe">Zimbabwe in Africa</a> and <a href="https://www.cnbc.com/2015/12/02/indias-jharia-coal-field-has-been-burning-for-100-years.html">Jharia in India</a>.</p>
<p>If carbon is compressed with even more pressure than it takes to make coal, eventually <a href="https://theconversation.com/diamonds-are-forever-whether-made-in-a-lab-or-mined-from-the-earth-106665">you get diamonds</a> – the <a href="https://theconversation.com/have-scientists-really-found-something-harder-than-diamond-52391">hardest mineral found in nature</a>. In 1772, French chemist <a href="https://www.britannica.com/biography/Antoine-Lavoisier">Antoine Lavoisier</a> proved that diamonds could combust when he <a href="https://www.wtamu.edu/%7Ecbaird/sq/2014/03/27/can-you-light-diamond-on-fire/">burned one with a magnifying glass</a>. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/1QbHRLpYc-0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Scientists burn a diamond – the hardest mineral found in nature.</span></figcaption>
</figure>
<p>With enough patience, you could <a href="https://www.wtamu.edu/%7Ecbaird/sq/2014/03/27/can-you-light-diamond-on-fire/">burn a diamond in a candle flame</a>. But since diamonds are quite expensive, it’s better to stick to <a href="https://gosciencegirls.com/magnifying-glass-fire/">burning other things made of carbon</a>, like <a href="https://gosciencekids.com/magnifying-glass-fire/">leaves under a magnifying glass</a>, or sticks and marshmallows in a campfire, instead. </p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/203392/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Natalie Bursztyn does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Some rocks will burn, and others will melt, depending on how they were formed and what minerals they contain.Natalie Bursztyn, Lecturer in Geosciences, University of MontanaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1899222022-10-30T12:21:13Z2022-10-30T12:21:13ZThe Perseverance rover is collecting rock samples from Mars to bring back to Earth<figure><img src="https://images.theconversation.com/files/487389/original/file-20220929-22-ipyz4r.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C4000%2C2250&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Concept illustration for research robots that could bring samples of Mars rocks to Earth-based labs.</span> <span class="attribution"><a class="source" href="https://mars.nasa.gov/resources/26895/mars-sample-return-concept-illustration/">(NASA/JPL-Caltech)</a></span></figcaption></figure><p>Hidden in the minerals and textures that make up rocks are clues about how and when they formed and were later altered. These changes can occur due to the presence of water-rich fluids and may also be influenced by biological processes. </p>
<p>We are planetary petrologists (rock scientists) and participating scientists on the <a href="https://mars.nasa.gov/mars2020/">Mars 2020 Perseverance rover mission</a>. Our research involves exploring and interpreting the data sent back by <a href="https://mars.nasa.gov/mars2020/mission/science/landing-site/">the Perseverance rover from its landing site in Jezero Crater</a>.</p>
<h2>A mysterious lake</h2>
<p>Orbital images show that Jezero Crater was once the site of a standing body of water. It held <a href="https://doi.org/10.1016/j.pss.2012.02.003">a lake that was fed by water from an ~170 km-long river channel</a>, and images show a delta — a fan-shaped platform of sediment — at the mouth of the channel. This delta is made up of layers of finer sediments mixed with boulder-rich layers that suggest <a href="https://doi.org/10.1126/science.abl4051">that the river flow fluctuated from relatively calm conditions to large floods</a>.</p>
<p>More of a mystery, however, were rock units exposed in Jezero Crater’s floor, where Perseverance landed on Feb. 18, 2021. Of particular interest was an enigmatic unit, identified by the presence of olivine its spectral signatures (measurements of the amount of radiation it reflects).</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/491883/original/file-20221026-12-ddozm5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="a panorama of a desert landscape" src="https://images.theconversation.com/files/491883/original/file-20221026-12-ddozm5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/491883/original/file-20221026-12-ddozm5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=127&fit=crop&dpr=1 600w, https://images.theconversation.com/files/491883/original/file-20221026-12-ddozm5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=127&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/491883/original/file-20221026-12-ddozm5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=127&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/491883/original/file-20221026-12-ddozm5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=160&fit=crop&dpr=1 754w, https://images.theconversation.com/files/491883/original/file-20221026-12-ddozm5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=160&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/491883/original/file-20221026-12-ddozm5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=160&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A panorama of Brac, captured by the Mastcam-Z camera system aboard NASA’s Perseverance Mars rover between Nov. 6 and 17, 2021. The panorama is made up of a total of 64 images stitched together after being sent back to Earth.</span>
<span class="attribution"><a class="source" href="https://mars.nasa.gov/resources/26432/mastcam-zs-view-of-the-area-around-brac-in-mars-jezero-crater/">(NASA/JPL-Caltech/ASU/MSSS)</a></span>
</figcaption>
</figure>
<h2>Evidence of history</h2>
<p>Olivine is a vitreous, green mineral (its gem variety is peridot) that usually crystallizes in high-temperature magmas. In contrast, carbonate minerals can form from high to low temperatures, usually from melts or fluids that <a href="https://doi.org/10.1029/2019JE006011">may have been favourable for life</a>. </p>
<p>The olivine-rich unit is widespread in the region beyond Jezero, <a href="https://doi.org/10.1130/G45563.1">covering approximately 70,000 square kilometres</a>, and exposed within the crater just to the north and west of Perseverance’s landing site, <a href="https://scitechdaily.com/nasa-perseverance-mars-rover-to-seitah-and-back/">in a region dubbed Séítah</a>. </p>
<p>Séítah (<a href="https://www.forbes.com/sites/davidbressan/2021/03/12/nasas-perseverance-mars-rover-mission-honors-navajo-language/">meaning “amidst the sand” in Navajo</a>) is covered by a network of sand dunes, making it difficult for the rover to navigate. However, it was considered a compelling target for understanding the history of this region of Mars and because its carbonate minerals could preserve evidence of ancient life. </p>
<p>Perseverance entered Séítah in September 2021 and readily confirmed the occurrence of olivine by its <a href="https://doi.org/10.1126/sciadv.abo3399">remote-sensing instruments</a>. The microscopic cameras saw two- to three-millimeter olivine grains, but their origin was unknown.</p>
<p>On Earth, olivine grains of this size and shape may be concentrated by various geologic ways, including as wind- or water-borne sands sourced from olivine-rich regions, explosive volcanic eruptions, material ejected by meteorite impact, or they can form as crystals in cooling magma.</p>
<p>Additional information was needed to interpret the history of the olivine, but engineering challenges initially impeded the mission’s ability to use its X-ray fluorescence (XRF) spectrometer on Séítah rocks.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/491885/original/file-20221026-13-5xpz57.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="extreme close up of a rock showing a sandy grainy surface" src="https://images.theconversation.com/files/491885/original/file-20221026-13-5xpz57.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/491885/original/file-20221026-13-5xpz57.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=448&fit=crop&dpr=1 600w, https://images.theconversation.com/files/491885/original/file-20221026-13-5xpz57.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=448&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/491885/original/file-20221026-13-5xpz57.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=448&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/491885/original/file-20221026-13-5xpz57.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=563&fit=crop&dpr=1 754w, https://images.theconversation.com/files/491885/original/file-20221026-13-5xpz57.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=563&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/491885/original/file-20221026-13-5xpz57.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=563&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A close-up of a rock named Dourbes, taken by the WATSON (Wide Angle Topographic Sensor for Operations and eNgineering) camera on the end of the robotic arm aboard NASA’s Perseverance Mars rover.</span>
<span class="attribution"><a class="source" href="https://mars.nasa.gov/resources/26433/watsons-view-of-dourbes-in-mars-jezero-crater/">(NASA/JPL-Caltech/MSSS)</a></span>
</figcaption>
</figure>
<h2>Sophisticated equipment</h2>
<p><a href="https://dx.doi.org/doi:10.1016/j.apgeochem.2016.07.003">XRF spectrometers</a> have been important instruments for determining the elemental compositions (sodium to iron, and some trace elements) of rock surfaces on Mars. </p>
<p><a href="https://doi.org/10.1029/2020JE006536">Alpha Particle X-ray Spectrometers (APXS) onboard Pathfinder</a>, the <a href="https://doi.org/10.1029/2005JE002555">two Mars Exploration Rovers Spirit and Opportunity</a>, and <a href="https://doi.org/10.1029/2020JE006536">the Mars Science Laboratory rover Curiosity</a> provided bulk chemistries of ~1.5 cm circular spots that helped geologic interpretations. </p>
<p>But for some Martian rocks, uncertainties have lingered about small-scale features and fine rock textures that are critical for interpreting what minerals are present, whether they are igneous or sedimentary, or their alteration histories. </p>
<p>The PIXL onboard Perseverance is <a href="https://doi.org/10.1007/s11214-020-00767-7">a big improvement in this regard</a>: PIXL generates ~120 micron grid maps that not only provide rock and mineral chemistries, but textures that can be used to infer the origin, processes and relative timing of the various minerals and other components present.</p>
<p>The first PIXL scan of a rock surface at <a href="https://mars.nasa.gov/resources/26432/mastcam-zs-view-of-the-area-around-brac-in-mars-jezero-crater/">a Séítah outcrop called Brac</a> <a href="https://doi.org/10.1126/science.abo2756">finally nailed the unit’s origin as igneous</a>. The olivine grains are well-formed crystals with straight edges. Other high-temperature minerals, including feldspar, and larger minerals enclose or occur in the spaces between the olivine crystals, indicating slow cooling of a magma. </p>
<p>Brac is a type of rock called an olivine cumulate that formed when olivine crystallized near the top of a magma, and settled and accumulated downward due to its higher density. Olivine cumulates are well known to form on Mars because they are found among the Martian meteorites, comprising a group <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/chassignites">known as chassignites</a>, that was ejected from Mars by an impact event and eventually fell to Earth.</p>
<p>On Earth, olivine cumulates occur in large layered intrusions, <a href="https://doi.org/10.2138/gselements.13.6.391">such as the Skaergaard Intrusion in East Greenland</a>, and in thick lava flows, <a href="https://doi.org/10.1130/SPE483">such as found in the Abitibi, Ont. area</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/yOplTCgnJFQ?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Recorded video of Mars by the Perseverance rover.</span></figcaption>
</figure>
<h2>Anticipating core samples</h2>
<p>As remarkable as the PIXL scans are, Perseverance is equipped with <a href="https://mars.nasa.gov/resources/25005/mars-2020-perseverance-rover-sample-caching-system/">a very sophisticated sampling tool</a>, which it used to collect cores of Brac. At least one of these core samples will likely be brought to Earth in the early 2030s as part of the <a href="https://mars.nasa.gov/msr/">Mars Sample Return effort</a>. </p>
<p>Mars Sample Return would enable researchers at Earth-based labs to examine features down to the nanoscale, which could yield information about crystallization history, water activity in the rock and how long the rock was exposed. This could provide clues about the history of life on Mars. </p>
<p>Radiometric isotopic analyses would help pinpoint the timing of crystallization. Stable isotopes (H, C, N, O) would tell us about the history of fluids on Mars. <a href="https://doi.org/10.1111/maps.13242">The list goes on and on</a>! </p>
<p>Returned samples would enable us to answer the questions that are hinted at by the the recent PIXL results. We could then provide a fuller history of the olivine and carbonate-rich rocks in Jezero, and what they tell us about Mars’ history and potential for life.</p><img src="https://counter.theconversation.com/content/189922/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mariek Schmidt receives funding from Canadian Space Agency Mars 2020 Participating Scientist Grant and from the National Science and Engineering Research Council of Canada</span></em></p><p class="fine-print"><em><span>Chris Herd receives funding from the Canadian Space Agency Mars 2020 Returned Sample Science Participating Scientist Program, and from the National Science and Engineering Research Council of Canada. </span></em></p>Sophisticated equipment on the Perseverance rover is helping answer some of the many questions researchers have about Mars’ geology over time.Mariek Schmidt, Associate Professor, Earth Sciences, Brock UniversityChris Herd, Professor, Earth & Atmospheric Sciences, University of AlbertaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1925082022-10-17T14:56:12Z2022-10-17T14:56:12ZRock stars: how a group of scientists in South Africa rescued a rare 500kg chunk of human history<figure><img src="https://images.theconversation.com/files/489753/original/file-20221014-20-d4gr05.JPG?ixlib=rb-1.1.0&rect=77%2C172%2C1362%2C905&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A helicopter, net and a long-line cable - as well as a skilled pilot - were key to the 'rescue' operation.</span> <span class="attribution"><span class="source">Richard Webb</span></span></figcaption></figure><p>Scientific breakthroughs can happen in the strangest ways and places. Alexander Fleming <a href="https://www.sciencemuseum.org.uk/objects-and-stories/how-was-penicillin-developed">discovered penicillin</a> because of mould growing on a Petri dish left out while he was on holiday. Chinese monks in the 9th century wanted to make a potion for immortality: instead, they <a href="https://editions.covecollective.org/chronologies/discovery-gunpowder">discovered gunpowder</a>.</p>
<p>Our own remarkable discovery happened on a rugged, remote stretch of coastline east of Still Bay on South Africa’s Cape south coast. It was low tide, and three members of our ichnology team (people who study tracks and traces) were in search of newly exposed <a href="https://www.livescience.com/40311-pleistocene-epoch.html">Pleistocene</a> vertebrate tracksites in aeolianites (cemented dunes). </p>
<p>Ahead we saw a large rock that had tumbled down from the cliffs above. On its surface was a pattern of linear groove features in a large triangular shape, complete with an almost perfect bisecting groove. The sides of the triangle were close to a metre in length. After extensive research, <a href="http://www.ifrao.com/wp-content/uploads/2021/04/38-1-Helm-et-al.pdf">we concluded</a> that these grooves must have been made on a dune surface of unconsolidated sand by our human ancestors in the <a href="https://doi.org/10.1093/acprof:oso/9780199679584.003.0008">Middle Stone Age</a>. The patterns are likely between <a href="https://doi.org/10.1016/j.palaeo.2007.08.005">143,000 and 91,000 years old</a>.</p>
<p>It was an important find in a significant place. Multiple <a href="https://www.sciencedirect.com/science/article/abs/pii/S0047248404001307?via%3Dihub">lines of evidence</a> on this coastline <a href="https://www.sciencedirect.com/science/article/abs/pii/S0047248410001387?via%3Dihub">indicate</a> that it’s an area where our distant ancestors became <a href="https://www.science.org/doi/10.1126/science.1175028">truly modern</a>, using fire as an engineering tool and creating abstract images.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/what-triangular-patterns-on-rocks-may-reveal-about-human-ancestors-159347">What triangular patterns on rocks may reveal about human ancestors</a>
</strong>
</em>
</p>
<hr>
<p>But there was a problem. On a followup visit we found a smaller rock close by with a similar triangular feature. Subsequently, it was destroyed, likely by storm surges or high tides buffeting and overturning it. We knew that the larger rock inevitably awaited a similar fate if we did nothing. From our perspective this is one of the most important rocks in the world: it takes us back to our roots as a species and indicates the kind of “proto-art” we were capable of creating so long ago.</p>
<p>So we staged an unusual mission: a “rescue” operation designed to get the approximately 500 kilogram rock to safety – in a museum. </p>
<h2>A coordinated mission</h2>
<p>Given the rock’s size and weight, there was only one way to remove it: with a helicopter, a skilled pilot, and a strong net attached to a long-line cable. </p>
<p>Our research team accumulated funding through our paid contributions to a book project. That money went towards hiring a private helicopter and pilot, as well as getting a ground crew in place on the day. We also obtained approval from the owner of the private land on which the rock was located. We also needed a permit from the provincial heritage authority to proceed because the rock is a precious heritage item.</p>
<figure class="align-center ">
<img alt="A large grey rock surrounded by smaller stones and coarse grains of sand. There are triangular carvings on the large rock." src="https://images.theconversation.com/files/489998/original/file-20221017-21-xg96n2.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/489998/original/file-20221017-21-xg96n2.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=458&fit=crop&dpr=1 600w, https://images.theconversation.com/files/489998/original/file-20221017-21-xg96n2.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=458&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/489998/original/file-20221017-21-xg96n2.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=458&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/489998/original/file-20221017-21-xg96n2.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=575&fit=crop&dpr=1 754w, https://images.theconversation.com/files/489998/original/file-20221017-21-xg96n2.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=575&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/489998/original/file-20221017-21-xg96n2.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=575&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The larger of the two triangular geometric features (scale bar = 10 cm).</span>
<span class="attribution"><span class="source">Charles Helm</span></span>
</figcaption>
</figure>
<p>It was a nerve-racking process. The rock might have been broken as it was being lifted from its cliffside spot, or might have fallen into the sea. But 29 September 2022 – what we’d dubbed Recovery Day – went smoothly. The ground crew and the helicopter pilot co-operated superbly. Minutes after being lifted out of the remote location the rock was safely on a pallet on a truck at the local airfield. From there, it began a very cautious journey to the <a href="https://hesva.org.za/en/blombos-museum-of-archaeology/">Blombos Museum of Archaeology</a> in nearby Still Bay. Here it was lifted and gently manoeuvred into place by a dozen volunteers. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/L9kvwi_B4TI?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">An unusual ‘rescue operation’ captured on video by Richard Webb.</span></figcaption>
</figure>
<p>The rock has subsequently been encased and placed on exhibit, with interpretive text panels. It joins similar exhibits in the museum; the grooves were an example of an <a href="https://doi.org/10.1016/j.pgeola.2019.08.004">ammoglyph</a>, a term we had coined to describe a pattern created by humans in sand that is now evident in rock that has become cemented and then re-exposed.</p>
<p>Ascribing meaning to these geometric patterns made so long ago by our distant ancestors is not within our field of expertise. Still, we could not help but notice the resemblance of the triangular shape to a <a href="https://doi.org/10.1073/pnas.1119663109">purported fertility symbol</a> found in France and dated to around 38,000 years. Should the pattern on our rock
represent the same motif, it would not be the first time that southern African discoveries had <a href="https://doi.org/10.1006/jhev.2000.0435">pushed back in time</a> what has been viewed as an Upper Palaeolithic Eurasian phenomenon. </p>
<p>Our research team now sleeps better at night, knowing that this priceless piece of our human heritage has been recovered and is available for others to see, appreciate and critique.</p>
<h2>More to discover</h2>
<p>Happily, there was an unexpected bonus. Beside the eroded remains of the second rock our ground crew noted a third rock surface which had not been evident previously. Near one edge it contained a distinct pair of grooves that met at an angle of 69 degrees, forming what may have been part of another triangular feature. </p>
<p>This is clearly an area we will return to repeatedly, in the hope that tidal forces may turn over other rocks before destroying them, and may give us an opportunity to glimpse – and perhaps recover – more ammoglyphs.</p><img src="https://counter.theconversation.com/content/192508/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Without intervention, the rock may have been destroyed by high tides and storm surges.Charles Helm, Research Associate, African Centre for Coastal Palaeoscience, Nelson Mandela UniversityJan Carlo De Vynck, Director and research fellow, African Centre for Coastal Palaeoscience, Nelson Mandela University, Nelson Mandela UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1858282022-07-18T12:27:00Z2022-07-18T12:27:00ZWhen did the first fish live on Earth – and how do scientists figure out the timing?<figure><img src="https://images.theconversation.com/files/471719/original/file-20220629-26-9ob4iv.png?ixlib=rb-1.1.0&rect=0%2C0%2C1280%2C1021&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Reconstruction of _Haikouichthys ercaicunensis_ based on fossil evidence.</span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Haikouichthys_3d.png">Talifero/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>How do you figure out how long ago fish were created? Hundreds of millions of years is a long time ago. – Josh, age 11, Ephrata, Pennsylvania</strong></p>
</blockquote>
<hr>
<p>The <a href="https://doi.org/10.1038/46965">oldest fossils of animals resembling a fish</a> date back between 518 million and 530 million years ago. Discovered in China and called <em>Haikouichthys</em>, these animals were about an inch long (2.5 cm) and had a <a href="https://doi.org/10.1038/nature01264">head with seven to eight slits at its base that looked like gills</a>. They also had a <a href="https://doi.org/10.1038/nature01264">distinct spine surrounded by muscles</a>. </p>
<p>But there are ways <em>Haikouichthys</em> did not resemble any modern fish. For example, <a href="https://www.science.org/content/article/fossils-give-glimpse-old-mother-lamprey">they didn’t have a jaw</a>. Instead, their mouth was a cone-like opening similar to the ones seen in <a href="https://nhpbs.org/wild/Agnatha.asp">modern hagfish and lampreys</a>. They also <a href="https://doi.org/10.1038/nature01264">appear not to have had side fins</a>.</p>
<p>Even though <a href="https://scholar.google.com/citations?hl=en&user=w4GYLBMAAAAJ">scientists like me</a> weren’t around to see for ourselves what was happening on Earth so long ago, we use geologic clues to figure out what animals lived when. Here’s how we sort out very ancient timelines and even put dates on fossils like <em>Haikouichthys</em>.</p>
<h2>Measuring in the millions</h2>
<p>To figure out how long ago fish first appeared on Earth you need a way to measure really, really long time intervals. Clocks measure short intervals, like seconds, minutes and hours. Calendars measure longer intervals, like days, months and years. What can you use to measure millions of years?</p>
<p><a href="https://cosmosmagazine.com/earth/earth-sciences/what-is-radiometric-dating/">Radiometric dating</a> is the method that scientists use to calculate the passage of time in millions of years. To determine the age of rocks and fossils, scientists measure the type of atoms they are made of. </p>
<p>You might know that atoms are the building blocks of <a href="https://theconversation.com/what-do-molecules-look-like-184892">molecules, which make up everything around you</a> – grass, cement, even air. While most atoms are very stable, <a href="https://kids.britannica.com/kids/article/radioactivity/399579">some, called radioactive atoms, are unstable</a>. Over long periods of time, they spontaneously break down into more stable atoms. </p>
<p>Uranium is one of these radioactive atoms. <a href="https://kids.kiddle.co/Uranium">It breaks down very slowly into lead</a>. Both uranium and lead atoms can be found <a href="https://kids.kiddle.co/Pitchblende">naturally in rocks and minerals</a> in very, very low amounts. </p>
<p>Nuclear physicists have calculated that it would take <a href="https://www.livescience.com/39773-facts-about-uranium.html">700 million years for one pound of uranium</a> to break down into half a pound of lead. This rate of decay occurs at such a predictable rate that scientists can use it to calculate fairly accurately how old rocks and fossils are.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/471720/original/file-20220629-22-xaw89m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Black and white photo of man in old style dress sitting in front of an elaborate contraption." src="https://images.theconversation.com/files/471720/original/file-20220629-22-xaw89m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/471720/original/file-20220629-22-xaw89m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=431&fit=crop&dpr=1 600w, https://images.theconversation.com/files/471720/original/file-20220629-22-xaw89m.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=431&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/471720/original/file-20220629-22-xaw89m.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=431&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/471720/original/file-20220629-22-xaw89m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=542&fit=crop&dpr=1 754w, https://images.theconversation.com/files/471720/original/file-20220629-22-xaw89m.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=542&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/471720/original/file-20220629-22-xaw89m.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=542&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Ernest Rutherford at McGill University, 1905.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Ernest_Rutherford_1905.jpg">Unknown, published in 1939 in 'Rutherford: being the life and letters of the Rt. Hon. Lord Rutherford'/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The idea for radiometric dating first occurred to <a href="https://library.si.edu/digital-library/book/radioactivit00ruth">a New Zealand scientist named Ernest Rutherford</a> in 1904. His idea was to measure the number of uranium atoms and lead atoms in a rock and compare them. He predicted that an older rock would have more lead and less uranium than a younger rock would.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/471722/original/file-20220629-22-7oc2sa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A graph illustrating how proportion of unstable atoms in a substance decreases while the proportion of stable atoms increases over time." src="https://images.theconversation.com/files/471722/original/file-20220629-22-7oc2sa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/471722/original/file-20220629-22-7oc2sa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/471722/original/file-20220629-22-7oc2sa.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/471722/original/file-20220629-22-7oc2sa.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/471722/original/file-20220629-22-7oc2sa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/471722/original/file-20220629-22-7oc2sa.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/471722/original/file-20220629-22-7oc2sa.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=603&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Unstable atoms turn into stable atoms over time at a steady and predictable pace.</span>
<span class="attribution"><a class="source" href="https://oceanexplorer.noaa.gov/edu/learning/player/lesson15/l15_la1.html">NOAA</a></span>
</figcaption>
</figure>
<p>The <a href="https://www.pbs.org/wgbh/aso/databank/entries/do07ra.html">American scientist Bertram Boltwood</a> put Rutherford’s idea to the test, <a href="https://www.lindahall.org/about/news/scientist-of-the-day/bertram-boltwood">measuring the amount of uranium and lead in different rocks</a> collected from all over the world. </p>
<p>Once a rock is formed, no new elements are added to it. So scientists can calculate how much uranium the rock started with by adding what’s left to the amount of lead that’s there now, thanks to the radioactive decay process. Then, because they know exactly how long it takes for uranium to break down into lead, they can figure out the age of the rock. Boltwood proved that Rutherford’s idea worked, establishing the field of radiometric dating in 1907.</p>
<h2>The making of the <em>Haikouichthys</em> fossil</h2>
<p><a href="https://education.nationalgeographic.org/resource/fossil">Fossils are rocks</a>. So scientists can use radiometric dating to estimate how long ago the organisms that left the fossil imprint lived on Earth. </p>
<p>Animals leave fossil imprints only under special circumstances. In order for the <em>Haikouichthys</em> to leave fossils, their dead bodies would have had to sink to the bottom of the water and be covered with sediments before microorganisms could decompose them. Then, minerals in the sediments would have seeped into the <em>Haikouichthys</em> for their remains to become fossilized. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/472572/original/file-20220705-4393-thhnx8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A close-up photograph of a Haikouichthys fossil with 'eye' and 'V shaped myomere' labeled." src="https://images.theconversation.com/files/472572/original/file-20220705-4393-thhnx8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/472572/original/file-20220705-4393-thhnx8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=273&fit=crop&dpr=1 600w, https://images.theconversation.com/files/472572/original/file-20220705-4393-thhnx8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=273&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/472572/original/file-20220705-4393-thhnx8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=273&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/472572/original/file-20220705-4393-thhnx8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=343&fit=crop&dpr=1 754w, https://images.theconversation.com/files/472572/original/file-20220705-4393-thhnx8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=343&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/472572/original/file-20220705-4393-thhnx8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=343&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A nearly complete specimen of <em>Haikouichthys</em> with the eye and zigzag-shaped muscle fibers called myomeres visible. This is one of many <em>Haikouichthys</em> fossils discovered in China.</span>
<span class="attribution"><span class="source">Dr. and Prof. Degan Shu, Shannxi Key Laborotory of Early Life and Envionment Department of Geology, Northwest University</span></span>
</figcaption>
</figure>
<p>Radiometric dating of <em>Haikouichthys</em> fossils suggests these animals were <a href="https://doi.org/10.1038/46965">swimming in Earth’s waters between 518 million and 530 million years ago</a> – and possibly longer. </p>
<h2>Earth’s age as a 24-hour day</h2>
<p>Scientists, using radiometric dating, <a href="https://education.nationalgeographic.org/resource/how-did-scientists-calculate-age-earth">estimate the Earth itself is 4.5 billion years old</a>. For a long time on Earth, there was no life at all. Then microorganisms like bacteria showed up. It’s only relatively recently that plants and animals began living on Earth.</p>
<p>In fact, if you think of Earth’s age until now as a 24-hour day, it turns out <em>Haikouichthys</em> lived 2 hours and 45 minutes before the end of the day. <a href="https://australian.museum/learn/science/human-evolution/hominid-and-hominin-whats-the-difference/">Humanlike animals</a> appeared even more recently on Earth – about <a href="https://www.smithsonianmag.com/science-nature/the-human-familys-earliest-ancestors-7372974/">5 million to 7 million years ago </a> – only a few minutes before the end of the hypothetical day. </p>
<p>Whether the <em>Haikouichthys</em> was the first fish or not remains controversial. There are very few other fishlike fossils from the same time period. But paleontologists keep digging. Who knows, maybe in a few years they will discover an even older fishlike animal that will dethrone <em>Haikouichthys</em> as the oldest fishlike creature.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
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<p class="fine-print"><em><span>Isaac Skromne receives funding from National Science Foundation and National Institute of Health. </span></em></p>A biologist explains how researchers nail down the age of ancient fossils thanks to a physical process called radioactive decay.Isaac Skromne, Assistant Professor of Biology, University of RichmondLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1860292022-07-06T12:19:30Z2022-07-06T12:19:30ZWhat’s behind the enduring popularity of crystals?<figure><img src="https://images.theconversation.com/files/472090/original/file-20220701-23-s4ooix.jpg?ixlib=rb-1.1.0&rect=579%2C36%2C4111%2C2676&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Proponents claim the stones can promote health and well-being. </span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/sisters-meditating-with-healing-crystals-rooftop-royalty-free-image/1280567102?adppopup=true">janiecbros/Getty Images</a></span></figcaption></figure><p>As New York City mayor Eric Adams attends ribbon cuttings, <a href="https://nypost.com/2022/06/12/nyc-mayor-eric-adams-booed-while-marching-in-pride-parade/">marches in parades</a> and <a href="https://autos.yahoo.com/york-mayor-bulldozes-hundreds-illegal-204200186.html">bulldozes dirt bikes</a>, he wears an <a href="https://www.nytimes.com/2021/11/03/style/eric-adams-style.html">energy stone bracelet</a> that his supporters gave him. <a href="https://www.politico.com/news/magazine/2022/03/11/eric-adams-nyc-mayor-profile-00016106">In a recent interview</a>, Adams discussed his belief that New York City has a “special energy” because it sits atop a store of rare gems and stones – the so-called “<a href="https://nypost.com/2022/06/09/mayor-eric-adams-says-healing-crystals-give-nyc-good-vibes/">Manhattan schist</a>,” which is over 450 million years old and contains over 100 minerals.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1535034393030545425"}"></div></p>
<p>Adams isn’t the only one imbuing rocks with metaphysical significance. During the first year of the pandemic, the <a href="https://www.theguardian.com/us-news/2020/oct/31/us-crystal-gem-boom-people-looking-for-healing">crystal industry boomed</a>, with customers hoping the gems might relieve their anxiety. </p>
<p>Some people might be confused about the allure of these stones. But crystal enthusiasts aren’t deviants. Current ideas about crystals come from a larger tradition called “<a href="https://yalebooks.yale.edu/book/9780300136159/republic-mind-and-spirit/">metaphysical religion</a>” that has always been part of the American spiritual landscape.</p>
<h2>More than rocks</h2>
<p>Technically, <a href="https://nature.berkeley.edu/classes/eps2/wisc/Lect4.html">a crystal</a> is any matter with a repeating pattern of atoms or molecules. The crystals for sale in shops are known as <a href="https://www.sciencedirect.com/topics/chemistry/euhedral-crystal">euhedral crystals</a> because they have well-defined surfaces, or “faces.”</p>
<p><a href="https://news.stanford.edu/2018/08/09/understanding-peoples-obsession-crystals/">For centuries</a>, people have attributed special properties to crystals. Scientist <a href="https://www.google.com/books/edition/The_Demon_haunted_World/ulqPDQAAQBAJ?hl=en&gbpv=1&dq=Sagan+OUr+Demon+Haunted+World&printsec=frontcover">Carl Sagan</a>, in his book “The Demon-Haunted World,” traces their modern popularity to a series of books written in the 1980s by Katrina Raphaell, who founded <a href="https://webcrystalacademy.com/">The Crystal Academy of Advanced Healing Arts</a> in 1986.</p>
<p>Crystals aren’t just eye-catching stones. Quartz is used in electronics because it possesses <a href="https://www.youtube.com/watch?v=wcJXA8IqYl8">piezoelectric properties</a> that cause it to release an electric charge when compressed. But, <a href="https://skepticalinquirer.org/1989/07/crystals/">as skeptics are quick to point out</a>, there is no evidence crystals can bring health, prosperity or any of the other properties that crystal enthusiasts may attribute to them. </p>
<h2>Mining the metaphysical</h2>
<p>Yet crystals are part of a broader tradition called metaphysical religion, <a href="https://yalebooks.yale.edu/book/9780300136159/republic-mind-and-spirit/">a term coined</a> by historian <a href="https://www.religion.ucsb.edu/people/emeriti/catherine-l-albanese/">Catherine Albanese</a>.</p>
<p>Metaphysical religion includes modern <a href="https://www.pewresearch.org/fact-tank/2018/10/01/new-age-beliefs-common-among-both-religious-and-nonreligious-americans/">New Age movements</a>, a nebulous milieu of alternative spiritual beliefs and practices, such as <a href="https://www.psychologytoday.com/us/basics/synchronicity">synchronicity</a> or psychic abilities. Older traditions like <a href="https://hypnosis.edu/history/the-birth-of-mesmerism">Mesmerism</a>, the idea that humans beings emit magnetic energy that can be used for healing, and <a href="https://www.austintexas.gov/sites/default/files/files/Parks/OHenry/spiritualism.pdf">Spiritualism</a>, the belief that mediums can communicate with the dead, also fall under the metaphysical umbrella.</p>
<p>Albanese ascribes four characteristics to metaphysical traditions: a preoccupation with the mind and its powers; “correspondences,” or the idea of hidden connections between things; a tendency to think in terms of energy and movement; and a yearning for salvation understood as “solace, comfort, therapy, and healing.” </p>
<h2>‘Contagious magic’</h2>
<p>Metaphysical ideas about crystals exhibit each of these characteristics.</p>
<p>While crystals are physical objects, not thoughts, many crystal enthusiasts recommend “cleansing” and “charging” crystals <a href="https://themanifestationcollective.co/how-cleanse-charge-crystals-beginner/">through visualization</a> and other meditative techniques. So the mind plays a key role in crystal spirituality, as it does in other forms of metaphysical religion.</p>
<figure class="align-center ">
<img alt="Two masked women walk through a store filled with colorful crystals." src="https://images.theconversation.com/files/472112/original/file-20220701-22-57bpnb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/472112/original/file-20220701-22-57bpnb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/472112/original/file-20220701-22-57bpnb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/472112/original/file-20220701-22-57bpnb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/472112/original/file-20220701-22-57bpnb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/472112/original/file-20220701-22-57bpnb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/472112/original/file-20220701-22-57bpnb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Crystal sales soared during the pandemic.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/cheryl-rey-center-manager-of-the-crystalarium-and-abby-news-photo/1234406149?adppopup=true">Genaro Molina/Los Angeles Times via Getty Images</a></span>
</figcaption>
</figure>
<p>Correspondence refers to the belief found in many occult traditions that ordinary things possess secret qualities or connections to other things. A classic example is <a href="https://www.theatlantic.com/health/archive/2018/01/the-new-age-of-astrology/550034/">astrology</a>, which postulates a correspondence between one’s birthday and certain personality traits. Metaphysical claims about crystals also reflect a belief in correspondences. For example, Colleen McCann, a self-described shaman affiliated with the crystal purveyor Goop, <a href="https://nypost.com/2017/10/04/spencer-pratt-and-heidi-montag-order-27k-of-crystals-for-childbirth/">described the positive qualities</a> of different crystals: bloodstones promote good health, rose quartzes help with love, and pink mangano calcites are good for sleep. </p>
<p>Modern crystal enthusiasts often use words like “energy” and “vibrations” that present their ideas in a scientific register. When enthusiasts talk about the energy of crystals – like Eric Adams did – they really mean that it exerts influence within a certain proximity. This is the principle behind <a href="https://www.elle.com/uk/beauty/body-and-physical-health/a28242635/crystal-water-bottle-wellness-trend/">crystal water bottles</a> that can be used to “charge” water with “vibrational energy.”</p>
<p>Stripped of scientific language, the logic of energy and vibrations is another form of what anthropologist <a href="https://www.britannica.com/biography/James-George-Frazer">James Frazer</a> called “<a href="https://www.gutenberg.org/files/3623/3623-h/3623-h.htm#c3section1">contagious magic</a>” found in many cultures, where simply placing one thing next to another is believed to cause an effect.</p>
<h2>A source of stigma</h2>
<p>Finally, metaphysical religion tends to focus on solving problems in this life rather than the hereafter. This includes health and prosperity, but also emotional growth and well-being. Crystal spirituality is certainly centered around these worldly goals. </p>
<p>This is a big distinction from traditions like Christianity that emphasize salvation in heaven. It is also a factor in why metaphysical ideas are stigmatized despite their popularity.</p>
<p>Protestant Christianity, with its emphasis on “sola fides” – faith alone – has historically dismissed many forms of <a href="https://www.tandfonline.com/toc/rfmr20/current">material religion</a>, or objects with religious significance, as superstition. So in a culture shaped by its historically <a href="https://religionnews.com/2021/07/08/survey-white-mainline-protestants-outnumber-white-evangelicals/">Protestant majority</a>, some Americans may be predisposed to look at crystal spirituality as foolish, greedy or even <a href="https://www.bibleinfo.com/en/questions/what-does-bible-say-about-crystals">blasphemous</a>. </p>
<p>But while claims about the hidden properties of crystals lack scientific validation, so do many of the claims of Christianity and other mainstream religions. </p>
<p>From a historical perspective, Adams’ ideas about crystals don’t make him an outlier. As a scholar of religious studies, I see him as a normal part of the American religious landscape.</p><img src="https://counter.theconversation.com/content/186029/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Joseph P. Laycock does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Crystals are part of a larger tradition of metaphysical religions that have a long history in the U.S.Joseph P. Laycock, Associate Professor of Religious Studies, Texas State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1713912021-11-08T21:58:46Z2021-11-08T21:58:46ZLand ahoy: study shows the first continents bobbed to the surface more than 3 billion years ago<figure><img src="https://images.theconversation.com/files/430723/original/file-20211108-48235-1iw24v8.png?ixlib=rb-1.1.0&rect=10%2C55%2C2446%2C1575&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption"></span> <span class="attribution"><span class="license">Author provided</span></span></figcaption></figure><p>Most people know that the land masses on which we all live represent just 30% of Earth’s surface, and the rest is covered by oceans. </p>
<p>The emergence of the continents was a pivotal moment in the history of life on Earth, not least because they are the humble abode of most humans. But it’s still not clear exactly when these continental landmasses first appeared on Earth, and what tectonic processes built them.</p>
<p>Our research, <a href="https://www.pnas.org/cgi/doi/10.1073/pnas.2105746118">published</a> in Proceedings of the National Academy of Sciences, estimates the age of rocks from the most ancient continental fragments (called cratons) in India, Australia and South Africa. The sand that created these rocks would once have formed some of the world’s first beaches.</p>
<p>We conclude that the first large continents were making their way above sea level around 3 billion years ago – much earlier than the 2.5 billion years estimated by previous research.</p>
<h2>A 3-billion-year-old beach</h2>
<p>When continents rise above the oceans they start to erode. Wind and rain break rocks down into grains of sand, which are transported downstream by rivers and accumulate along coastlines to form beaches. </p>
<p>These processes, which we can observe in action during a trip to the beach today, have been operating for billions of years. By scouring the rock record for signs of ancient beach deposits, geologists can study episodes of continent formation that happened in the distant past.</p>
<p>The Singhbhum craton, an ancient piece of continental crust that makes up the eastern parts of the Indian subcontinent, contains several formations of ancient sandstone. These layers were originally formed from sand deposited in beaches, estuaries and rivers, which was then buried and compressed into rock.</p>
<p>We determined the age of these deposits by studying microscopic grains of a mineral called zircon, which is preserved within these sandstones. This mineral contains tiny amounts of uranium, which very slowly turns into lead via radioactive decay. This allows us to estimate the age of these zircon grains, using a technique called <a href="https://en.wikipedia.org/wiki/Uranium%E2%80%93lead_dating">uranium-lead dating</a>, which is well suited to dating very old rocks.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/430725/original/file-20211108-10108-1cbfduv.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Sandstone and zircon grains" src="https://images.theconversation.com/files/430725/original/file-20211108-10108-1cbfduv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/430725/original/file-20211108-10108-1cbfduv.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=348&fit=crop&dpr=1 600w, https://images.theconversation.com/files/430725/original/file-20211108-10108-1cbfduv.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=348&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/430725/original/file-20211108-10108-1cbfduv.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=348&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/430725/original/file-20211108-10108-1cbfduv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=438&fit=crop&dpr=1 754w, https://images.theconversation.com/files/430725/original/file-20211108-10108-1cbfduv.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=438&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/430725/original/file-20211108-10108-1cbfduv.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=438&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Left: sandstone formations (with ruler for scale); right: microscopic images of zircon grains.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The zircon grains reveal that the Singhbhum sandstones were deposited around 3 billion years ago, making them some of the oldest beach deposits in the world. This also suggests a continental landmass had emerged in what is now India by at least 3 billion years ago. </p>
<p>Interestingly, sedimentary rocks of roughly this age are also present in the oldest cratons of Australia (the Pilbara and Yilgarn cratons) and South Africa (the Kaapvaal Craton), suggesting multiple continental landmasses may have emerged around the globe at this time.</p>
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<strong>
Read more:
<a href="https://theconversation.com/whats-australia-made-of-geologically-it-depends-on-the-state-youre-in-83575">What's Australia made of? Geologically, it depends on the state you're in</a>
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<h2>Rise above it</h2>
<p>How did rocky continents manage to rise above the oceans? A unique feature of continents is their thick, buoyant crust, which allows them to float on top of Earth’s mantle, just like a cork in water. Like icebergs, the top of continents with thick crust (typically more than 45km thick) sticks out above the water, whereas continental blocks with crusts thinner than about 40km remain submerged.</p>
<p>So if the secret of the continents’ rise is due to their thickness, we need to understand how and why they began to grow thicker in the first place. </p>
<p>Most ancient continents, including the Singhbhum Craton, are made of granites, which formed through the melting of pre-existing rocks at the base of the crust. In our research, we found the granites in the Singhbhum Craton formed at increasingly greater depths between about 3.5 billion and 3 billion years ago, implying the crust was becoming thicker during this time window. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/430727/original/file-20211108-9872-18vgwir.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Granite formation with pen for scale." src="https://images.theconversation.com/files/430727/original/file-20211108-9872-18vgwir.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/430727/original/file-20211108-9872-18vgwir.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=728&fit=crop&dpr=1 600w, https://images.theconversation.com/files/430727/original/file-20211108-9872-18vgwir.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=728&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/430727/original/file-20211108-9872-18vgwir.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=728&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/430727/original/file-20211108-9872-18vgwir.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=914&fit=crop&dpr=1 754w, https://images.theconversation.com/files/430727/original/file-20211108-9872-18vgwir.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=914&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/430727/original/file-20211108-9872-18vgwir.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=914&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Granites are some of the least dense and most buoyant types of rock (pen included for scale).</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Because granites are one of the least dense types of rock, the ancient crust of the Singhbhum Craton would have become progressively more buoyant as it grew thicker. We calculate that by around 3 billion years ago, the continental crust of the Singhbhum Craton had grown to be about 50km thick, making it buoyant enough to begin rising above sea level.</p>
<p>The rise of continents had a profound influence on the climate, atmosphere and oceans of the early Earth. And the erosion of these continents would have provided chemical nutrients to coastal environments in which early photosynthetic life was flourishing, leading to a <a href="https://www.sciencedirect.com/science/article/abs/pii/S0012821X16307117">boom in oxygen production</a> and ultimately helping to create the <a href="https://www.pnas.org/content/118/33/e2107511118">oxygen-rich atmosphere</a> in which we thrive today.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-floor-is-lava-after-1-5-billion-years-in-flux-heres-how-a-new-stronger-crust-set-the-stage-for-life-on-earth-151276">The floor is lava: after 1.5 billion years in flux, here's how a new, stronger crust set the stage for life on Earth</a>
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<hr>
<p>Erosion of the early continents would have also helped in sequestering carbon dioxide from the atmosphere, leading to global cooling of the early Earth. Indeed, the earliest glacial deposits also happen to <a href="https://www.sciencedirect.com/science/article/pii/S0012825220303445#bb0765">appear in the geological record</a> around 3 billion years ago, shortly after the first continents emerged from the oceans.</p><img src="https://counter.theconversation.com/content/171391/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Priyadarshi Chowdhury receives funding from Australian Research Council Grant No FL160100168. </span></em></p><p class="fine-print"><em><span>Jack Mulder receives funding from Australian Research Council grant FL160100168</span></em></p><p class="fine-print"><em><span>Oliver Nebel receives funding from the Australian Research Council Grant No DP180100580. </span></em></p><p class="fine-print"><em><span>Peter Cawood receives funding from Australian Research Council grant FL160100168</span></em></p>Dating of rocks that once formed some of the world’s first beaches suggests the first large continents grew large enough to rise above sea level roughly 3 billion or so years ago.Priyadarshi Chowdhury, Postdoctoral research fellow, Monash UniversityJack Mulder, Research Associate, The University of QueenslandOliver Nebel, Associate Professor, Monash UniversityPeter Cawood, Professor and ARC Laureate Fellow, Monash UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1687302021-10-07T18:02:28Z2021-10-07T18:02:28ZPerseverance’s first major successes on Mars – an update from mission scientists<figure><img src="https://images.theconversation.com/files/424652/original/file-20211005-27-ihwlyw.jpg?ixlib=rb-1.1.0&rect=194%2C986%2C9772%2C8278&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Perseverance took a selfie next to its biggest accomplishment yet – the two small drill holes where the rover took samples of Martian rocks.
</span> <span class="attribution"><a class="source" href="https://mars.nasa.gov/resources/26253/perseverances-selfie-at-rochette/">NASA/JPL-Caltech/MSSS</a></span></figcaption></figure><p>In the short time since NASA’s Perseverance rover landed in Mars’ Jezero Crater on Feb. 18, 2021, it’s already made history.</p>
<p>At the moment, Mars and the Earth are on opposite sides of the Sun, and the two planets cannot communicate with each other. After working nonstop for the past 216 Martian days, the science teams are taking the first real break since the mission started.</p>
<p>We are <a href="https://mars.nasa.gov/people/profile/?id=22881#bio">two</a> <a href="https://www.eaps.purdue.edu/people/profile/briony.html">members</a> of the Perseverance team, and with the rover <a href="https://mars.nasa.gov/mars2020/mission/status/337/hunkering-down-for-solar-conjunction/">hunkered down</a> for the <a href="https://mars.nasa.gov/all-about-mars/night-sky/solar-conjunction/">20 days of conjunction</a>, it is the perfect time to step back and reflect on the mission thus far. </p>
<p>Perseverance has tested out all of its engineering capabilities, driven <a href="https://mars.nasa.gov/mars2020/mission/where-is-the-rover/">1.6 miles (2.6 kilometers)</a> over rough terrain and taken <a href="https://mars.nasa.gov/mars2020/multimedia/raw-images/">tens of thousands of photos</a> with its <a href="https://doi.org/10.1007/s11214-020-00765-9">19 cameras</a>. Of all of these incredible successes, there are three major milestones that we’re particularly excited about: collecting the first rock core samples, flying the Ingenuity helicopter and publishing our first scientific results about the Jezero Crater delta.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/424641/original/file-20211005-16-zebafp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A rock on reddish brown surface with a circular hole drilled into the top." src="https://images.theconversation.com/files/424641/original/file-20211005-16-zebafp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/424641/original/file-20211005-16-zebafp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=227&fit=crop&dpr=1 600w, https://images.theconversation.com/files/424641/original/file-20211005-16-zebafp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=227&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/424641/original/file-20211005-16-zebafp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=227&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/424641/original/file-20211005-16-zebafp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=285&fit=crop&dpr=1 754w, https://images.theconversation.com/files/424641/original/file-20211005-16-zebafp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=285&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/424641/original/file-20211005-16-zebafp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=285&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Perseverance has already cached two samples of Martian rocks after drilling cores out of a rock, the first of which is the hole seen here.</span>
<span class="attribution"><a class="source" href="https://mars.nasa.gov/resources/26209/perseverances-navigation-camera-captures-sample-borehole/">NASA/JPL-Caltech</a></span>
</figcaption>
</figure>
<h2>Return shipping</h2>
<p>One of Perseverance’s primary objectives is to use its <a href="https://mars.nasa.gov/resources/25005/mars-2020-perseverance-rover-sample-caching-system/">sample caching system</a> to extract small rock cores – roughly the size of dry-erase markers – and seal them in special sample tubes. A future mission will then pick them up and bring them on a long, interplanetary journey back to Earth.</p>
<p>For Perserverance’s first drilling attempt in August, our team picked a nice flat rock that was easy to access with the drill. After six days of assessing the bedrock – and finally drilling into it – we were thrilled to see a hole in the ground and get confirmation that the sample tube had sealed successfully. However, the next day the rover sent photos of the inside of the tube, and we saw it was actually empty. Some of Mars’ atmosphere is trapped inside and will be useful to study, but it’s not what the team was hoping for.</p>
<p>Ultimately, our team concluded that the rock itself was much softer than expected and it was completely pulverized during the act of drilling. </p>
<p>Three weeks and 1,800 feet (550 meters) later, we came across some promising-looking rocks protruding up above the red surface. This suggested that the rocks were harder and therefore easier to take a sample of. This time Perseverance successfully extracted and stored two core samples from the grayish, wind-polished rock. After collecting up to a few dozen more, it will drop the samples at a safe and easily accessible location on Mars’ surface. NASA’s <a href="https://www.jpl.nasa.gov/missions/mars-sample-return-msr">Mars Sample Return</a> mission, which is currently in development, will pick up the sample tubes in the late 2020s and bring them home.</p>
<p>But scientists don’t have to wait that long to learn about the rocks. At both sites, Perseverance used the <a href="https://mars.nasa.gov/mars2020/spacecraft/instruments/sherloc/">SHERLOC</a> and <a href="https://mars.nasa.gov/mars2020/spacecraft/instruments/pixl/">PIXL</a> spectrometers on its arm to measure the composition of the rocks. We found crystalline minerals that suggest the rocks formed in a basaltic lava flow, as well as salt minerals that could be <a href="https://mars.nasa.gov/news/9036/nasas-perseverance-rover-collects-puzzle-pieces-of-mars-history/">evidence of ancient groundwater</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/wMnOo2zcjXA?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Ingenuity’s first flight, seen in this video, showed that the helicopter could fly on Mars. Credit: NASA/JPL-Caltech.</span></figcaption>
</figure>
<h2>First in flight</h2>
<p>Perseverance may be a long way from Earth, but it has a sidekick. The <a href="https://mars.nasa.gov/technology/helicopter/#Overview">Ingenuity helicopter</a> detached from the rover shortly after they landed on Mars and became the first craft to fly in the atmosphere of another planet. </p>
<p>Ingenuity is solar powered, weighs <a href="https://mars.nasa.gov/technology/helicopter/#Tech-Specs">4 pounds (1.8 kg)</a>, and its main body is roughly the size of a grapefruit. On April 19, 2021, the helicopter took its first flight, hovering 10 feet (3 meters) above the ground for 39 seconds before coming straight down. This short hop showed that its long blades could generate enough lift to allow flight in Mars’ thin air. </p>
<p>The next flights tested the helicopter’s ability to move horizontally, and it covered longer distances each time, traveling as much as <a href="https://mars.nasa.gov/technology/helicopter/#Flight-Log">2,050 feet (625 meters)</a> in its farthest trip to date. </p>
<p>Ingenuity has now flown 13 times and has captured detailed photos of the ground to scout out the rough terrain ahead of Perseverance. These images are helping the team decide how to navigate around obstacles on the way toward the rover’s eventual destination, a large delta in Jezero Crater.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/424648/original/file-20211005-21-1j6gyi.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A satellite image showing a delta shaped rock formation on the surface of Mars." src="https://images.theconversation.com/files/424648/original/file-20211005-21-1j6gyi.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/424648/original/file-20211005-21-1j6gyi.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=568&fit=crop&dpr=1 600w, https://images.theconversation.com/files/424648/original/file-20211005-21-1j6gyi.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=568&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/424648/original/file-20211005-21-1j6gyi.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=568&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/424648/original/file-20211005-21-1j6gyi.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=714&fit=crop&dpr=1 754w, https://images.theconversation.com/files/424648/original/file-20211005-21-1j6gyi.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=714&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/424648/original/file-20211005-21-1j6gyi.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=714&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A delta in Jezero Crater, seen in this satellite image, is where Perseverance will collect the majority of its samples.</span>
<span class="attribution"><a class="source" href="https://mars.nasa.gov/resources/25264/jezero-crater-as-seen-by-esas-mars-express-orbiter/">ESA/DLR/FU-Berlin</a></span>
</figcaption>
</figure>
<h2>Zooming into the Jezero delta</h2>
<p>NASA selected <a href="https://theconversation.com/bringing-mars-rocks-back-to-earth-on-feb-18-perseverance-rover-landed-safely-on-mars-a-lead-scientist-explains-the-tech-and-goals-153851">Jezero Crater as Perseverance’s landing site</a> specifically because it gives the rover access to a large stack of rocks that sits at the end of a dry river valley. Based on <a href="https://www.jpl.nasa.gov/images/jezero-craters-ancient-lakeshore">satellite images</a>, scientists think that these rocks are made of sediment deposited by an ancient river that flowed into a lake roughly <a href="https://mars.nasa.gov/mars2020/mission/science/landing-site/">3.5 billion years ago</a>. If true, this location could have been an excellent environment for life. </p>
<p>However, the resolution of the satellite data isn’t high enough to say for sure whether the sediments were deposited slowly into a long-lived lake or whether the structure formed under drier conditions. The only way to know with certainty was to take images from the surface of Mars.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/424642/original/file-20211005-25-9p3y9l.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A small hill of red dirt and rocks." src="https://images.theconversation.com/files/424642/original/file-20211005-25-9p3y9l.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/424642/original/file-20211005-25-9p3y9l.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=321&fit=crop&dpr=1 600w, https://images.theconversation.com/files/424642/original/file-20211005-25-9p3y9l.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=321&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/424642/original/file-20211005-25-9p3y9l.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=321&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/424642/original/file-20211005-25-9p3y9l.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=403&fit=crop&dpr=1 754w, https://images.theconversation.com/files/424642/original/file-20211005-25-9p3y9l.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=403&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/424642/original/file-20211005-25-9p3y9l.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=403&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">This structure of boulders and sediment shows the geological history of the delta.</span>
<span class="attribution"><a class="source" href="https://mastcamz.asu.edu/galleries/kodiak-dawn/?back=%2Fmars-images%2Fteam-favorites%2F">NASA/JPL-Caltech/ASU/MSSS</a></span>
</figcaption>
</figure>
<p>Perseverance <a href="https://www.nasa.gov/image-feature/jpl/welcome-to-octavia-e-butler-landing">landed</a> over a mile (roughly 2 kilometers) away from the cliffs at the front of the delta. We are both on the team in charge of the <a href="https://mastcamz.asu.edu/">Mastcam-Z</a> instrument, a set of cameras with zoom lenses that would allow us to see a paper clip from the opposite side of a football field. During the first few weeks of the mission, we used Mastcam–Z to survey the distant rocks. From those panoramic views, we selected specific spots to look at in more detail with the rover’s <a href="https://supercam.cnes.fr/en/supercam-and-its-super-sensors">SuperCam</a>, a telescopic camera. </p>
<p>When the images got back to Earth, we saw tilted layers of sediments in the lower parts of the 260-foot-tall (80 meters) cliffs. Toward the top we spotted boulders, some as large as 5 feet (1.5 meters) across.</p>
<p>From the structure of these formations, our team has been able to reconstruct a geological story billions of years old, which we <a href="https://www.science.org/doi/10.1126/science.abl4051">published</a> in the journal Science on Oct. 7, 2021. </p>
<p>For a long time – potentially millions of years – a river flowed into a lake that filled Jezero Crater. This river slowly deposited the tilted layers of sediment we see in the cliffs of the delta. Later on, the river became mostly dry except for a few big flooding events. These events had enough energy to carry big rocks down the river channel and deposit them on top of the older sediment; these are the boulders we see atop the cliffs now. </p>
<p>Since then, the climate has been arid and winds have slowly been eroding away the rock.</p>
<p>Confirming that there was a lake in Jezero Crater is the first major science result of the mission. In the coming year, Perseverance will drive up to the top of the delta, studying the rock layers in microscopic detail along the way and collecting many samples. When those samples eventually make their way to Earth, we will learn if they contain signs of microbial life that may once have thrived in this ancient lake on Mars.</p>
<p>[<em>Get the best of The Conversation, every weekend.</em> <a href="https://theconversation.com/us/newsletters/weekly-highlights-61?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=weeklybest">Sign up for our weekly newsletter</a>.]</p><img src="https://counter.theconversation.com/content/168730/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Melissa Rice receives funding from NASA to participate in the Mars 2020 Mission as a member of Long-Term Planning group and as a Mastcam-Z Co-Investigator.</span></em></p><p class="fine-print"><em><span>Briony Horgan receives funding from NASA to participate in the Mars 2020 Mission as a member of Long-Term Planning group and as a Mastcam-Z Co-Investigator.</span></em></p>Perseverance and its helicopter sidekick, Ingenuity, have been on Mars for nearly nine months. The duo have taken rock samples, performed first flights and taken images of the delta in Jezero Crater.Melissa Rice, Associate Professor of Planetary Science, Western Washington UniversityBriony Horgan, Associate Professor of Planetary Science, Purdue UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1635782021-07-14T04:20:41Z2021-07-14T04:20:41Z5 rocks any great Australian rock collection should have, and where to find them<figure><img src="https://images.theconversation.com/files/411135/original/file-20210714-25-17z85xl.jpg?ixlib=rb-1.1.0&rect=5%2C11%2C3928%2C2607&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>Road tripping with a geologist is a little different. While you’re probably reading road signs and dodging roadkill, we’re reading road cuttings and deciphering the history of the area over the previous millions — or even billions — of years. </p>
<p>Geology has shaped the Australian landscape. In Victoria where I live, for example, the western plains are pockmarked by <a href="https://www.tandfonline.com/doi/full/10.1080/08120099.2013.806954">Australia’s youngest volcanoes</a>, while the east of the state has been <a href="https://www.annualreviews.org/doi/abs/10.1146/annurev.earth.28.1.47">pushed up</a> to form the mountains of the Great Dividing Range. </p>
<p>Along the southern margin of the state are fossilised braided rivers, relics of when <a href="https://www.tandfonline.com/doi/abs/10.1046/j.1440-0952.1999.00757.x">Australia drifted away from Antarctica</a>. Evidence of this event extends into Tasmania, where dolerite, <a href="https://core.ac.uk/download/pdf/156738663.pdf">a rock that signifies this rift</a>, looms in enormous columns over Hobart from Mount Wellington.</p>
<p>This probably won’t surprise anyone who knows me, but I have rocks peppered around my house that I’ve collected on my travels. Every time I look at them, I not only think about how the rocks were formed, I’m also reminded of the trip when I collected them.</p>
<p>With international and even state borders set to remain closed for a while longer, this is the perfect time to take a great Australian road trip, become a rock detective, and build up your rock collection while you’re at it. </p>
<p>To help you get started, I’ve listed five rocks any great Australian rock collection should have.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/411149/original/file-20210714-19-12ucjmr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Green, volcanic crater" src="https://images.theconversation.com/files/411149/original/file-20210714-19-12ucjmr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/411149/original/file-20210714-19-12ucjmr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=339&fit=crop&dpr=1 600w, https://images.theconversation.com/files/411149/original/file-20210714-19-12ucjmr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=339&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/411149/original/file-20210714-19-12ucjmr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=339&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/411149/original/file-20210714-19-12ucjmr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=426&fit=crop&dpr=1 754w, https://images.theconversation.com/files/411149/original/file-20210714-19-12ucjmr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=426&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/411149/original/file-20210714-19-12ucjmr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=426&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The crater of an erupted volcano near Mount Gambier in Victoria.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>1. Mantle xenoliths</h2>
<p><em>Western Victoria</em></p>
<p>The youngest rocks in Australia are those that erupted out of Australia’s <a href="https://www.biodiversitylibrary.org/page/41319502#page/12/mode/1up">youngest volcano</a> in Mount Gambier, South Australia, 4,000 to 8,000 years ago. That volcano is the culmination of an enormous field of volcanoes that span central and western Victoria.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/photos-from-the-field-the-stunning-crystals-revealing-deep-secrets-about-australian-volcanoes-161176">Photos from the field: the stunning crystals revealing deep secrets about Australian volcanoes</a>
</strong>
</em>
</p>
<hr>
<p>In western Victoria, the volcanoes were formed from magma that ascended from the Earth’s mantle — the layer between the Earth’s core and crust. While the magma was rising, it tore off chunks of the surrounding mantle rock and transported it to the surface. We can find these chunks of the mantle — or <a href="https://www.sciencedirect.com/science/article/pii/S0012821X97000587?via%3Dihub">mantle xenoliths</a> (xeno = foreign, lith = rock) — in cooled lava today in western Victoria. </p>
<p>At first, these rocks look like any other piece of black or brown basalt, but then you turn them over or crack them open and there’s <a href="https://theconversation.com/photos-from-the-field-the-stunning-crystals-revealing-deep-secrets-about-australian-volcanoes-161176">a blob of bright green rock</a> staring back at you. The mantle rock inside is comprised mainly of olivine, which is a green mineral, and some black/brown pyroxene.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/411142/original/file-20210714-25-1olsmws.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Green rock blob encased in black rock" src="https://images.theconversation.com/files/411142/original/file-20210714-25-1olsmws.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/411142/original/file-20210714-25-1olsmws.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=397&fit=crop&dpr=1 600w, https://images.theconversation.com/files/411142/original/file-20210714-25-1olsmws.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=397&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/411142/original/file-20210714-25-1olsmws.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=397&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/411142/original/file-20210714-25-1olsmws.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=499&fit=crop&dpr=1 754w, https://images.theconversation.com/files/411142/original/file-20210714-25-1olsmws.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=499&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/411142/original/file-20210714-25-1olsmws.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=499&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Green mantle xenolith (xeno = foreign, lith = rock) encased in cooled basaltic lava from Mount Shadwell, Victoria.</span>
<span class="attribution"><span class="source">Dr Melanie Finch</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Mantle xenoliths are a great place to start your rock collection because not only will they be your very own piece of Earth’s mantle, but you can find them yourself through a bit of fossicking around some of the volcanoes in western Victoria.</p>
<h2>2. Meteorites</h2>
<p><em>The Nullarbor Desert, South Australia and Western Australia</em></p>
<p>The Nullarbor is a desert plain region which straddles the border of South Australia and Western Australia. </p>
<p>The dry environment is ideal for preserving meteorites that fall to Earth, and the light colour of the limestone country rock and lack of vegetation means the black and brown meteorites are easier to see.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/411144/original/file-20210714-21-i1bpv1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/411144/original/file-20210714-21-i1bpv1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/411144/original/file-20210714-21-i1bpv1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/411144/original/file-20210714-21-i1bpv1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/411144/original/file-20210714-21-i1bpv1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/411144/original/file-20210714-21-i1bpv1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/411144/original/file-20210714-21-i1bpv1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/411144/original/file-20210714-21-i1bpv1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A black meteorite standing out against the white limestone of the Nullarbor Plain.</span>
<span class="attribution"><span class="source">Professor Andy Tomkins</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Even if you don’t have a great eye for spotting meteorites hiding in plain sight, you can do as the geologists do and use a magnet on a stick to help you. Most meteorites are iron-rich, so wandering around with a magnet hovering over the surface is a good way to pick them up. </p>
<p>Thousands of meteorites have been found in the Nullarbor, <a href="https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1945-5100.2010.01289.x">some up to 40,000 years old</a>.</p>
<h2>3. Metamorphic rocks</h2>
<p><em>Broken Hill, New South Wales</em></p>
<p>You’ve probably heard of Broken Hill because of the large silver, lead and zinc mine there. But the geological conditions that created the ore deposit around <a href="https://pubs.geoscienceworld.org/gsa/geology/article/32/7/589/29483/Subseafloor-origin-for-Broken-Hill-Pb-Zn-Ag">1.7 billion years ago</a> also made some beautiful rocks.</p>
<p>A visit to Broken Hill’s <a href="https://www.brokenhill.nsw.gov.au/Facilities/Albert-Kersten-Mining-and-Minerals-Museum">Albert Kersten Mining and Minerals Museum</a> will demonstrate the vast array of unusual minerals found in the region, some of them described for the first time at this locality. </p>
<p>If you’re seeking your own chunk of Broken Hill’s geological history, Round Hill is the place for you. Just a short way out of the town centre, you’ll find beautiful red garnets surrounded by patches of white minerals (quartz and feldspar). </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/411143/original/file-20210714-23-22ws9z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A geologist holding a rock with various colours" src="https://images.theconversation.com/files/411143/original/file-20210714-23-22ws9z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/411143/original/file-20210714-23-22ws9z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=424&fit=crop&dpr=1 600w, https://images.theconversation.com/files/411143/original/file-20210714-23-22ws9z.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=424&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/411143/original/file-20210714-23-22ws9z.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=424&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/411143/original/file-20210714-23-22ws9z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=532&fit=crop&dpr=1 754w, https://images.theconversation.com/files/411143/original/file-20210714-23-22ws9z.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=532&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/411143/original/file-20210714-23-22ws9z.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=532&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A large garnet from the Broken Hill region.</span>
<span class="attribution"><span class="source">Professor Andy Tomkins</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>These rocks started out as sand and mud, and <a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1525-1314.2005.00608.x">record the history</a> of being buried and heated to over 700°C deep below the Earth’s surface. This process caused the rock to start melting and created the striking stripey, garnet-rich rocks we find there today.</p>
<h2>4. Banded iron formation</h2>
<p><em>Western Australia</em></p>
<p>Banded iron formation is a layered sedimentary rock mainly comprised of alternating bands of chert (a sedimentary rock made of quartz) that’s often red in colour and silver to black iron oxide. It is the main host of iron ore, and can be found in several regions in Western Australia.</p>
<p>The Hamersley Province in the northwestern part of Western Australia has the <a href="https://www.sciencedirect.com/science/article/pii/S0301926815003629">thickest and most extensive</a> banded iron formations in the world. They are about <a href="https://www.tandfonline.com/doi/abs/10.1111/j.1400-0952.2004.01082.x?casa_token=QbHbov_0we0AAAAA:brBYBRIolr2lzbYRHh1CxGZ8zJDTdP02YNjrkq-wXVUfzNj5SK5c9cmcWlmmvOi2WUYd4biGz6ao">2.45 to 2.78 billion years old</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/411141/original/file-20210714-23-1kx5iq1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Red and brown bands along a rock face" src="https://images.theconversation.com/files/411141/original/file-20210714-23-1kx5iq1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/411141/original/file-20210714-23-1kx5iq1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/411141/original/file-20210714-23-1kx5iq1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/411141/original/file-20210714-23-1kx5iq1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/411141/original/file-20210714-23-1kx5iq1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/411141/original/file-20210714-23-1kx5iq1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/411141/original/file-20210714-23-1kx5iq1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Banded iron formation at Forescue Falls, WA.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/graeme/12116315164/in/photolist-7CDYgj-2j6Va2M-2jdGHSf-oEf3Dz-2jdKu3P-2jdKu2m-2dN6GRq-2dN6GBh-oUHcDh-9q1zoW-oEg6Xp-oWKg3z-9q1Ajo-h9Ze7W-oWtFjP-oEfWy6-jsFhnA-mgHSqk-gTUFeN-oWuEdP-zAzaNc-7AevFd-7AazUx-7Ae6uE-7AedRo-7Ae3iw-7AadWP-7Aahr4-7Ae5Qh-7Aai96-7Ae2ps-7AaXwr-2jWei3g-2jW9Sxi-uRHgZW">Graeme Churchard/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Geologists believe they <a href="https://onlinelibrary.wiley.com/doi/abs/10.1046/j.1365-3091.2003.00594.x">formed on a continental shelf</a>, where thick continental crust extends out into the ocean and then drops away to oceanic crust.</p>
<p>Banded iron formation is exciting because it no longer forms on Earth today, meaning it records an ancient process that we no longer see happening. </p>
<p>It is thought to have formed in ancient oceans, which were starting to increase in oxygen content at the time. It records the chemical input of these oceans, as well as sediments from the continent and volcanoes on the ocean floor.</p>
<h2>5. Dinosaur fossils</h2>
<p><em>Central and western Queensland</em></p>
<p>Oh to have been in Queensland 100 million years ago! Judging by the fossils found in parts of the state, it would have been a cornucopia of dinosaur activity.</p>
<p>From an unlikely duo of <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0006190">dinosaurs in a 98-million-year-old billabong</a> in Winton, to <a href="https://www.tandfonline.com/doi/abs/10.1080/02724634.2012.694591">fossilised evidence of a dinosaur herd</a> at Lark Quarry, Queensland is the place to go to peer back in time to the Mesozoic Era between 252 and 66 million years ago. </p>
<p>And if you’re really lucky, you might even have dinosaur bones on your property, like <a href="https://peerj.com/articles/11317/">the huge, long-necked sauropod</a> discovered just this year on a Queensland cattle farm.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/411146/original/file-20210714-27-uptilx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An outback museum with a dinosaur statue in front" src="https://images.theconversation.com/files/411146/original/file-20210714-27-uptilx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/411146/original/file-20210714-27-uptilx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/411146/original/file-20210714-27-uptilx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/411146/original/file-20210714-27-uptilx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/411146/original/file-20210714-27-uptilx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/411146/original/file-20210714-27-uptilx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/411146/original/file-20210714-27-uptilx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Australian Age of Dinosaurs Museum in Winton, Queensland, is home to the largest collection of Australian dinosaur fossils. (Note: not a real dinosaur.)</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>When building your Australian rock collection, remember to check first if <a href="https://theconversation.com/how-to-hunt-fossils-responsibly-5-tips-from-a-professional-palaeontologist-156861">fossicking is allowed in the area</a>. When you find an interesting rock, your state or territory geological survey might be able to help with identifying it. </p>
<p>Happy hunting!</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-to-hunt-fossils-responsibly-5-tips-from-a-professional-palaeontologist-156861">How to hunt fossils responsibly: 5 tips from a professional palaeontologist</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/163578/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Emily Finch has previously received funding from an Australian Postgraduate Award and a Society of Economic Geologists Graduate Student Fellowship. </span></em></p>When borders reopen, take an Aussie road trip and explore the continent’s unique geology, from meteorites in the Nullarbor Plain to rock formations that are billions of years old.Emily Finch, Beamline Scientist at ANSTO, and Research Affiliate, Monash UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1629842021-06-21T19:12:11Z2021-06-21T19:12:11ZThe surface of Venus is cracked and moves like ice floating on the ocean – likely due to tectonic activity<figure><img src="https://images.theconversation.com/files/407495/original/file-20210621-27-8cz1kb.png?ixlib=rb-1.1.0&rect=28%2C19%2C1249%2C685&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">New research suggests that Venus' crust is broken into large blocks – the dark reddish–purple areas – that are surrounded by belts of tectonic structures shown in lighter yellow–red.
</span> <span class="attribution"><a class="source" href="https://astrogeology.usgs.gov/search/map/Venus/Magellan/Venus_Magellan_LeftLook_mosaic_global_75m">Paul K. Byrne/NASA/USGS</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p><em>The <a href="https://theconversation.com/us/topics/research-brief-83231">Research Brief</a> is a short take about interesting academic work.</em></p>
<h2>The big idea</h2>
<p>Much of the brittle, upper crust of Venus is broken into fragments that jostle and move – and the slow churning of Venus’ mantle beneath the surface might be responsible. My colleagues and I arrived at this finding using <a href="https://astrogeology.usgs.gov/search/map/Venus/Magellan/Venus_Magellan_LeftLook_mosaic_global_75m">decades-old radar data</a> to explore how the surface of Venus interacts with the interior of the planet. We describe it in a <a href="https://doi.org/10.1073/pnas.2025919118">new study published</a> in the Proceedings of the National Academy of Sciences on June 21, 2021.</p>
<p><a href="https://scholar.google.com/citations?user=Lb6BrKEAAAAJ&hl=en&oi=ao">Planetary scientists like me</a> have long known that Venus has <a href="https://arstechnica.com/science/2017/04/on-venus-tectonics-without-the-plates/">a plethora of tectonic landforms</a>. Some of these formations are long, thin belts where the crust has been pushed together to form ridges or pulled apart to form troughs and grooves. In many of these belts there’s evidence that pieces of the crust have moved side to side, too.</p>
<p>Our new study shows, for the first time, that these bands of ridges and troughs often mark the boundaries of flat, low-lying areas that themselves show relatively little deformation and are individual blocks of Venus’ crust that have shifted, rotated and slid past each other over time – and may have done so in the recent past. It’s a little like <a href="https://theconversation.com/plate-tectonics-new-findings-fill-out-the-50-year-old-theory-that-explains-earths-landmasses-55424">Earth’s plate tectonics</a> but on a smaller scale and more closely resembles <a href="https://www.oceanpolaire.org/en/polar-encyclopaedia/encyclopedie-polaire-en-c1/#">pack ice that floats atop the ocean</a>.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/407455/original/file-20210621-62599-1w5g1ia.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A person standing on an ice chunk with a large ridge of ice in front of them." src="https://images.theconversation.com/files/407455/original/file-20210621-62599-1w5g1ia.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/407455/original/file-20210621-62599-1w5g1ia.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/407455/original/file-20210621-62599-1w5g1ia.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/407455/original/file-20210621-62599-1w5g1ia.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/407455/original/file-20210621-62599-1w5g1ia.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/407455/original/file-20210621-62599-1w5g1ia.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/407455/original/file-20210621-62599-1w5g1ia.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Where ice chunks collide, the ice is thrust upwards to create ridges much like what researchers think happens on Venus.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Pressure_ridge_--_where_two_ice_floes_meet.jpg#/media/File:Pressure_ridge_--_where_two_ice_floes_meet.jpg">Ben Holt and Susan Digby/WikimediaCommons</a></span>
</figcaption>
</figure>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/407456/original/file-20210621-34789-1ggbcf2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An aerial photo of pack ice with large block of ice floating on the sea and small cracks showing water between chunks of ice." src="https://images.theconversation.com/files/407456/original/file-20210621-34789-1ggbcf2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/407456/original/file-20210621-34789-1ggbcf2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/407456/original/file-20210621-34789-1ggbcf2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/407456/original/file-20210621-34789-1ggbcf2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/407456/original/file-20210621-34789-1ggbcf2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/407456/original/file-20210621-34789-1ggbcf2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/407456/original/file-20210621-34789-1ggbcf2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The crust of Venus is fractured into large pieces that behave more like chunks of ice floating on the ocean.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Sea_ice_near_coast_of_Labrador_-a.jpg#/media/File:Sea_ice_near_coast_of_Labrador_-a.jpg">Endlisnis/WikimediaCommons</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Researchers have hypothesized that – <a href="https://people.earth.yale.edu/sites/default/files/files/Bercovici/17_MantlConvection-ESEG2011-2_0.pdf">just like Earth’s mantle</a> – the mantle of Venus swirls with currents as it’s heated from below. My colleagues and I modeled the sluggish but powerful movement of Venus’ mantle and showed that it is sufficiently forceful to fragment the upper crust everywhere we’ve found these lowland blocks. </p>
<h2>Why it matters</h2>
<p>A major question about Venus is whether the planet has active volcanoes and tectonic faulting today. It’s essentially the same size, composition and age as Earth – so why wouldn’t it be geologically alive?</p>
<p>But no mission to Venus has yet conclusively shown the planet to be active. There’s tantalizing but ultimately inconclusive evidence that <a href="https://www.esa.int/Science_Exploration/Space_Science/Venus_Express/Venus_is_alive_geologically_speaking">volcanic eruptions have taken place there in the geologically recent past</a> – and are perhaps even ongoing. The case for tectonic activity – the creaking, breaking and folding of the planet’s crust – is on even less solid ground.</p>
<p>Showing that Venus’ geological engine is still running would have huge implications for understanding the composition of the planet’s mantle, where and how volcanism might be taking place today and how the very crust itself is formed, destroyed and replaced. Because our study suggests that some of this jostling of the crust is geologically recent, we may have taken a big step forward in understanding if Venus really is active today.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/407309/original/file-20210619-27-tggglg.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A red–hued image of the surface of Venus showing a large darker piece of the surface surrounded by lighter colors against the backdrop of space." src="https://images.theconversation.com/files/407309/original/file-20210619-27-tggglg.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/407309/original/file-20210619-27-tggglg.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/407309/original/file-20210619-27-tggglg.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/407309/original/file-20210619-27-tggglg.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/407309/original/file-20210619-27-tggglg.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/407309/original/file-20210619-27-tggglg.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/407309/original/file-20210619-27-tggglg.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The largest block of lowlands the team found – the dark red shape in the center of this radar image – is about the size of Alaska and surrounded by ridges and deformations that show up as lighter colors.</span>
<span class="attribution"><a class="source" href="https://astrogeology.usgs.gov/search/map/Venus/Magellan/Venus_Magellan_LeftLook_mosaic_global_75m">Paul K. Byrne/NASA/USGS</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>What still isn’t known</h2>
<p>It’s not clear just how widespread these crustal fragments are. My colleagues and I have found 58 so far, but that’s almost certainly a low estimate.</p>
<p>We also don’t yet know when these crustal blocks first formed, nor how long they’ve been moving around on Venus. Determining when the crust’s fragmentation and jostling occurred is key – especially if planetary scientists want to understand this phenomenon in relation to the planet’s suspected recent volcanic activity. Figuring that out would give us vital information on how the planet’s surface features reflect the geological turmoil within.</p>
<h2>What’s next</h2>
<p>This initial study has allowed my colleagues and me to make our best guess yet about how Venus’ vast lowlands have been deformed, but we need much higher-resolution radar images and topographic data to build on this work. Luckily, that’s <a href="https://theconversation.com/nasa-is-returning-to-venus-to-learn-how-it-became-a-hot-poisonous-wasteland-and-whether-the-planet-was-ever-habitable-in-the-past-162140">exactly what scientists are going to get</a> in the coming years, with <a href="https://www.nasa.gov/press-release/nasa-selects-2-missions-to-study-lost-habitable-world-of-venus/">NASA</a> and the <a href="https://www.esa.int/Science_Exploration/Space_Science/ESA_selects_revolutionary_Venus_mission_EnVision">European Space Agency</a> both recently announcing new missions bound for Venus later this decade. It’ll be worth the wait to get a better understanding of Earth’s enigmatic neighbor.</p>
<p>[<em>The Conversation’s science, health and technology editors pick their favorite stories.</em> <a href="https://theconversation.com/us/newsletters/science-editors-picks-71/?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=science-favorite">Weekly on Wednesdays</a>.]</p><img src="https://counter.theconversation.com/content/162984/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Paul K. Byrne does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Researchers used decades-old radar data and found that some low-lying areas of Venus’ crust are moving and jostling. This evidence is some of the strongest yet of tectonic activity on Venus.Paul K. Byrne, Associate Professor of Planetary Science, North Carolina State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1539292021-02-03T18:12:27Z2021-02-03T18:12:27ZWhy is the Earth blue?<figure><img src="https://images.theconversation.com/files/381471/original/file-20210130-19353-m2fhci.jpg?ixlib=rb-1.1.0&rect=0%2C12%2C2048%2C1232&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The greenhouse effect and plate tectonics are essential for maintaining water on the Earth's surface.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/gsfc/4426654941/in/album-72157632172101342/">NASA/Goddard Space Flight Center/Reto Stöckli</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Seen from space, the Earth is blue. The Earth has been blue for over 4 billion years because of the liquid water on its surface. How has the Earth managed to sustain liquid water on its surface for such a long time?</p>
<p>There is only one known planet with permanent bodies of liquid water at its surface: ours. Earth sciences allow us to explain why the Earth has almost always been blue: it’s neither too warm nor too cold. If the Earth was first red and black, it has been blue for more than 4 billion years, with rare exceptions when it <a href="https://www.livescience.com/64692-snowball-earth.html">got too cold and turned into a white snowball</a>.</p>
<p>This incredible characteristic is due to the interactions of the water cycle with plate tectonics and the greenhouse effect, as well as the configuration of the solar system. Today, Earth’s average surface temperature is about 15°C, colder than Venus <a href="https://www.space.com/18526-venus-temperature.html">(465 °C)</a> and warmer than Mars <a href="https://www.space.com/16907-what-is-the-temperature-of-mars.html">(-60 °C on average)</a>. On Earth, at sea level, water freezes below 0°C and boils at 100°C. Earth’s surface is thus kept within a temperature range that might seem large to us, but is actually fairly narrow when compared with other planets, and it has remained so for billions of years.</p>
<h2>Greenhouse gases play their part</h2>
<p>The average temperature on a planet’s surface depends on the interaction of three parameters that can vary widely from one planet to the next: </p>
<ul>
<li><p>The <em>energy</em> arriving from the Sun.</p></li>
<li><p>The <a href="https://earthobservatory.nasa.gov/glossary/albedo"><em>albedo</em></a> of the surface, meaning how much it reflects solar radiation away.</p></li>
<li><p><a href="https://en.wikipedia.org/wiki/Greenhouse_gas"><em>Greenhouse gases</em></a>, which trap solar radiation within Earth’s atmosphere. Without greenhouse gases, Earth’s surface would be at a temperature around -15°C and probably devoid of liquid water. </p></li>
</ul>
<p>Interactions between sunlight, albedo, and greenhouse gases have maintained a fairly constant energy balance since the first oceans appeared on Earth.</p>
<p>Early in the Earth’s history, the young Sun <a href="https://astrobiology.nasa.gov/news/earth-during-a-faint-young-sun/">was less bright</a> and our planet received less energy from it. However, levels of greenhouse gases such as CO<sub>2</sub> and methane were much higher than today, which maintained surface temperatures high enough for water to be liquid.</p>
<p>The greenhouse effect decreased over time because CO<sub>2</sub> can be removed from the atmosphere by <a href="https://theconversation.com/how-humans-derailed-the-earths-climate-in-just-160-years-114021">two processes</a>. First, the acidifying effect of CO<sub>2</sub> dissolved in surface waters causes rocks to dissolve, which releases calcium. Calcium combines with the dissolved CO<sub>2</sub> to form carbonate rocks such as limestone, one of the main carbon sinks.</p>
<p>The second sink is organic carbon stored in sedimentary rocks. Organisms on land and in the ocean use CO<sub>2</sub> to build organic matter during photosynthesis, a portion of which is deposited at the bottom of the ocean when the organisms die. There, the organic matter is incorporated into sedimentary rocks, where it can be stored for millions of years.</p>
<h2>Without tectonics, no oceans; without oceans, no tectonics</h2>
<p>Although carbon sinks store CO<sub>2</sub> away from the atmosphere, volcanoes and oceanic ridges deliver CO<sub>2</sub> back into the atmosphere. This delivery is sustained through plate tectonics. Over long timescales, plate tectonics helps maintain Earth’s surface temperature in the range that allows surface waters to be liquid. The presence of liquid water and plate tectonics are thus intimately linked. How does that happen?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/381472/original/file-20210130-20464-rh136d.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Interactions with water, plate tectonics and CO₂" src="https://images.theconversation.com/files/381472/original/file-20210130-20464-rh136d.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/381472/original/file-20210130-20464-rh136d.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=218&fit=crop&dpr=1 600w, https://images.theconversation.com/files/381472/original/file-20210130-20464-rh136d.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=218&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/381472/original/file-20210130-20464-rh136d.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=218&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/381472/original/file-20210130-20464-rh136d.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=274&fit=crop&dpr=1 754w, https://images.theconversation.com/files/381472/original/file-20210130-20464-rh136d.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=274&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/381472/original/file-20210130-20464-rh136d.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=274&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Interactions with water, plate tectonics and CO₂.</span>
<span class="attribution"><span class="source">Guillaume Paris</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The ocean floor is composed of oceanic plates. They move away from oceanic ridges, the chain of submarine volcanoes that runs across the planet, and then down toward the depths of the Earth through subduction. During the hundreds of millions of years that they traverse the oceans, oceanic plates become hydrated: their minerals incorporate water, which modifies their mechanical properties. As they are subducted, oceanic plates eventually dehydrate; the released water eventually produces magmas that form granites, the bedrock of the continents. Without liquid water, there would be no tectonics and therefore, no continents!</p>
<p>Due to this recycling of older oceanic plates into the mantle, new plates are constantly being formed from material erupted at oceanic ridges. As this material rises through the mantle and to the ocean floor, it cools and releases CO<sub>2</sub>, helping sustain greenhouse gas concentrations. Water remains liquid and the Earth remains blue, as it has been for several billion years.</p>
<h2>From black and red to blue</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/363406/original/file-20201014-21-137hhpb.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/363406/original/file-20201014-21-137hhpb.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/363406/original/file-20201014-21-137hhpb.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/363406/original/file-20201014-21-137hhpb.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/363406/original/file-20201014-21-137hhpb.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/363406/original/file-20201014-21-137hhpb.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/363406/original/file-20201014-21-137hhpb.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/363406/original/file-20201014-21-137hhpb.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A trace of the oldest oceans: pillow lavas that are 3.8 billion years old (Greenland).</span>
<span class="attribution"><span class="source">Guillaume Caro</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>It has long been assumed that water-rich celestial bodies from the outer solar system brought water to the recently formed Earth. One of our team <a href="https://science.sciencemag.org/content/369/6507/1110.full">recently published</a> a study that questions this hypothesis and suggests that water – that is, hydrogen and oxygen – could have been brought instead by the rocks that formed the Earth.</p>
<p>When the Earth first formed 4.5 billion years ago, it was probably too hot for water to be liquid at the surface. In any case, if there had been oceans, they would certainly have vaporized upon the giant impact between the young Earth and a planetary body (probably as big as Mars), which melted the surface of our planet and formed the Moon <a href="https://www.sciencedirect.com/science/article/abs/pii/S0012821X17300560">4.4 billion years ago</a>.</p>
<p>As the Earth’s surface slowly cooled and solidified after the impact, it was likely covered in dark basaltic rocks, with neither life nor water. Cooling magmas release elements such as hydrogen, oxygen, and carbon as gas containing molecules such as water, carbon dioxide, and/or methane. The first oceans may therefore have formed relatively quickly after the impact. The first <a href="https://www.livescience.com/43584-earth-oldest-rock-jack-hills-zircon.html">known minerals</a> on Earth bear the chemical signature of interactions with liquid water. Thus, Earth may have been blue for almost 4.4 billion years.</p>
<p>The first indisputable proof of oceans on Earth’s surface is 3.8 billion years old, including the oldest marine sediments, found in <a href="https://en.wikipedia.org/wiki/Isua_Greenstone_Belt">Isua</a> and Akilia (Greenland) and Nuvvuagittuq (Canada), and the oldest pillow lavas, uniquely shaped rocks that form as lava cools underwater.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/363407/original/file-20201014-21-1b9cc0l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/363407/original/file-20201014-21-1b9cc0l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=362&fit=crop&dpr=1 600w, https://images.theconversation.com/files/363407/original/file-20201014-21-1b9cc0l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=362&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/363407/original/file-20201014-21-1b9cc0l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=362&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/363407/original/file-20201014-21-1b9cc0l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=455&fit=crop&dpr=1 754w, https://images.theconversation.com/files/363407/original/file-20201014-21-1b9cc0l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=455&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/363407/original/file-20201014-21-1b9cc0l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=455&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Modern pillow lavas forming underwater near Hawaii.</span>
<span class="attribution"><span class="source">NOAA</span></span>
</figcaption>
</figure>
<p>Whether 3.8 or 4.4 billion years old, the history of the oceans is linked to that of the Earth and life. Today, human activities are causing the oceans to become more acidic and warmer. Oceans won’t disappear, but the life within is endangered. Our CO<sub>2</sub> emissions exceed global volcanic emissions <a href="https://theconversation.com/co-levels-and-climate-change-is-there-really-a-controversy-119268">by a factor of 70</a>, endangering the existing balance between processes operating at the Earth’s surface and those deep within it. Our societies rely on both.</p><img src="https://counter.theconversation.com/content/153929/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Guillaume Paris has received funding from CNRS and ANR.</span></em></p><p class="fine-print"><em><span>Laurette Piani has received funding from the National Research Agency for her work on meteorite water.</span></em></p>The presence of water on the Earth’s surface is the result of a subtle balance between different mechanisms in the atmosphere and below the surface.Guillaume Paris, Géochimiste, chargé de recherche CNRS au Centre de recherches pétrographiques et géochimiques de Nancy, Université de LorraineLaurette Piani, Cosmochimiste, chargée de recherche CNRS au Centre de Recherches Pétrographiques et Géochimiques (CRPG) de Nancy, CNRS, Université de LorraineLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1484042020-11-02T20:01:34Z2020-11-02T20:01:34ZMagnetism of Himalayan rocks reveals the mountains’ complex tectonic history<figure><img src="https://images.theconversation.com/files/365671/original/file-20201026-17-199ct3j.jpg?ixlib=rb-1.1.0&rect=155%2C0%2C2993%2C1999&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Himalayan rocks hold magnetic clues about their origins.</span> <span class="attribution"><span class="source">Craig Robert Martin</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>Breathing quickly in the thin mountain air, my colleagues and I set down our equipment. We’re at the base of a jagged outcrop that protrudes upwards out of a steep gravel slope.</p>
<p>The muffled soundscape of the spectacular Himalayan wilderness is punctuated by a military convoy roaring along the Khardung-La road below. It’s a reminder how close we are to the long-disputed borders between India, Pakistan and China which lie on the ridgelines just a few miles away.</p>
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<p>This area also contains a different type of boundary, a narrow sinuous geological structure that stretches along the length of the Himalayan mountain range. Known as a suture zone, it’s only a few kilometers wide and consists of slivers of different types of rocks all sliced together by fault zones. It marks the boundary where two tectonic plates fused together and an ancient ocean disappeared.</p>
<p>Our team of geologists traveled here to collect rocks that erupted as lava more than 60 million years ago. By decoding the magnetic records preserved inside them, we hoped to reconstruct the geography of ancient landmasses – and <a href="https://doi.org/10.1073/pnas.2009039117">revise the story of the creation of the Himalayas</a>.</p>
<h2>Sliding plates, growing mountains</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/366741/original/file-20201030-23-t6znxn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="artist's rendering of two tectonic plates colliding at a subduction zone" src="https://images.theconversation.com/files/366741/original/file-20201030-23-t6znxn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/366741/original/file-20201030-23-t6znxn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=489&fit=crop&dpr=1 600w, https://images.theconversation.com/files/366741/original/file-20201030-23-t6znxn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=489&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/366741/original/file-20201030-23-t6znxn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=489&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/366741/original/file-20201030-23-t6znxn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=614&fit=crop&dpr=1 754w, https://images.theconversation.com/files/366741/original/file-20201030-23-t6znxn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=614&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/366741/original/file-20201030-23-t6znxn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=614&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">At a subduction zone, two tectonic plates collide, with one slowly sliding beneath the other.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/tectonic-plates-world-map-royalty-free-illustration/889618718">VectorMine/iStock via Getty Images Plus</a></span>
</figcaption>
</figure>
<p>Tectonic plates make up the surface of Earth, and they’re constantly in motion – drifting at the <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/tectonic-plate">imperceptibly slow pace</a> of just a few centimeters each year. Oceanic plates are colder and denser than the mantle beneath them, so they sink downward into it at subduction zones.</p>
<p>The sinking edge of the ocean plate drags the ocean floor along behind it like a conveyor belt, pulling the continents toward each other. When the entire ocean plate disappears into <a href="https://www.nationalgeographic.org/encyclopedia/mantle/">the mantle</a>, the continents on either side plow into each other with enough force to uplift great mountain belts, like the Himalayas.</p>
<p>Geologists generally thought that the Himalayas formed <a href="https://doi.org/10.1130/0016-7606(2000)112%3C324:TOTHAS%3E2.0.CO;2">55 million years ago in a single continental collision</a> – when the Neotethys Ocean plate subducted under the southern edge of Eurasia and the Indian and Eurasian tectonic plates collided. </p>
<p>But by measuring the magnetism of rocks from northwest India’s remote and mountainous Ladakh region, our team has shown that the tectonic collision that formed the world’s largest mountain range was actually a complex, multi-stage process involving at least two subduction zones.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/366500/original/file-20201029-13-1784e5k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="diagram of interior of Earth and magnetic field stretching from pole to pole" src="https://images.theconversation.com/files/366500/original/file-20201029-13-1784e5k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/366500/original/file-20201029-13-1784e5k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=646&fit=crop&dpr=1 600w, https://images.theconversation.com/files/366500/original/file-20201029-13-1784e5k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=646&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/366500/original/file-20201029-13-1784e5k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=646&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/366500/original/file-20201029-13-1784e5k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=811&fit=crop&dpr=1 754w, https://images.theconversation.com/files/366500/original/file-20201029-13-1784e5k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=811&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/366500/original/file-20201029-13-1784e5k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=811&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Earth’s magnetic field is generated by movement within the planet’s outer core. Magnetic north and south drift and sometimes flip over time.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/earth-magnetic-field-scientific-vector-royalty-free-illustration/932342344">VectorMine/iStock via Getty Images Plus</a></span>
</figcaption>
</figure>
<h2>Magnetic messages, preserved for all time</h2>
<p>Constant movement of our planet’s metallic outer core creates electric currents which in turn generate <a href="https://cosmosmagazine.com/geoscience/what-creates-earth-s-magnetic-field/">Earth’s magnetic field</a>. It’s oriented differently depending where in the world you are. The magnetic field always points toward the magnetic north or the south, which is why your compass works, and averaged over thousands of years it points toward the geographic pole. But it also slopes downward into the ground at an angle which varies depending on how far you are from the equator. </p>
<p>When lava erupts and cools to form rock, the magnetic minerals inside lock in the direction of the magnetic field of that location. So <a href="https://doi.org/10.1016/B0-12-369396-9/00106-4">by measuring the magnetization of volcanic rocks</a>, <a href="https://scholar.google.com/citations?hl=en&user=aD8WioMAAAAJ">scientists like me</a> can determine what latitude they came from. Essentially, this method allows us to unwind millions of years of plate tectonic motions and create maps of the world at different times throughout geologic history.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/365226/original/file-20201023-20-172l0hn.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Member of our research team collecting samples in Ladakh." src="https://images.theconversation.com/files/365226/original/file-20201023-20-172l0hn.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/365226/original/file-20201023-20-172l0hn.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=884&fit=crop&dpr=1 600w, https://images.theconversation.com/files/365226/original/file-20201023-20-172l0hn.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=884&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/365226/original/file-20201023-20-172l0hn.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=884&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/365226/original/file-20201023-20-172l0hn.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1111&fit=crop&dpr=1 754w, https://images.theconversation.com/files/365226/original/file-20201023-20-172l0hn.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1111&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/365226/original/file-20201023-20-172l0hn.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1111&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Geologist collects core samples using a water-cooled electric core drill.</span>
<span class="attribution"><span class="source">Craig Robert Martin</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Over multiple expeditions to the Ladakh Himalayas, our team collected hundreds of 1-inch diameter rock core samples. These rocks originally formed on a volcano active between 66 and 61 million years ago, around the time that the first stages of collision began. We used a hand-held electric drill with a specially designed diamond coring bit to drill approximately 10 centimeters down into the bedrock. We then carefully marked these cylindrical cores with their original orientation before chiseling them out of the rock with nonmagnetic tools.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/366238/original/file-20201028-15-ujjeor.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="cylindrical rock core samples with markings" src="https://images.theconversation.com/files/366238/original/file-20201028-15-ujjeor.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/366238/original/file-20201028-15-ujjeor.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=431&fit=crop&dpr=1 600w, https://images.theconversation.com/files/366238/original/file-20201028-15-ujjeor.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=431&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/366238/original/file-20201028-15-ujjeor.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=431&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/366238/original/file-20201028-15-ujjeor.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=542&fit=crop&dpr=1 754w, https://images.theconversation.com/files/366238/original/file-20201028-15-ujjeor.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=542&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/366238/original/file-20201028-15-ujjeor.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=542&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A few rock core samples, with the sample orientation line marked on their sides.</span>
<span class="attribution"><span class="source">Craig Robert Martin</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>The aim was to reconstruct where these rocks originally formed, before they were sandwiched between India and Eurasia and uplifted into the high Himalayas. Keeping track of the orientation of the samples as well as the rock layers they came from is essential to calculating which way the ancient magnetic field pointed relative to the surface of the ground as it was over 60 million years ago.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/365268/original/file-20201023-19-1igxsu8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="View of magnetometer equipment at MIT." src="https://images.theconversation.com/files/365268/original/file-20201023-19-1igxsu8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/365268/original/file-20201023-19-1igxsu8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/365268/original/file-20201023-19-1igxsu8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/365268/original/file-20201023-19-1igxsu8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/365268/original/file-20201023-19-1igxsu8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/365268/original/file-20201023-19-1igxsu8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/365268/original/file-20201023-19-1igxsu8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The magnetometer sits inside a magnetically shielded room at the MIT Paleomagnetism Laboratory.</span>
<span class="attribution"><span class="source">Craig Robert Martin</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>We brought our samples back to the <a href="http://www.benweiss.mit.edu/">MIT Paleomagnetism Laboratory</a> and, inside a special room that’s shielded from the modern-day magnetic field, we heated them in increments up to 1,256 degrees Fahrenheit (680 degrees Celsius) to slowly remove the magnetization.</p>
<p>Different mineral populations acquire their magnetization at different temperatures. Incrementally heating and then measuring the samples in this way enables us to extract the original magnetic direction by removing more recent overprints that might hide it.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/366244/original/file-20201028-17-hpwmb7.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="diagrams depicting India colliding with Eurasia either in a single stage or multiple stages" src="https://images.theconversation.com/files/366244/original/file-20201028-17-hpwmb7.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/366244/original/file-20201028-17-hpwmb7.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=239&fit=crop&dpr=1 600w, https://images.theconversation.com/files/366244/original/file-20201028-17-hpwmb7.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=239&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/366244/original/file-20201028-17-hpwmb7.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=239&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/366244/original/file-20201028-17-hpwmb7.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=301&fit=crop&dpr=1 754w, https://images.theconversation.com/files/366244/original/file-20201028-17-hpwmb7.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=301&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/366244/original/file-20201028-17-hpwmb7.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=301&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Black lines mark boundaries between tectonic plates. Black lines with triangular tick marks show subduction zones, with the direction of subduction. The Trans-Tethyan Subduction Zone is the additional subduction zone not accounted for in the single-stage collision model. The Trans-Tethyan Subduction Zone is where the volcanic island chain formed before the Indian continent collided into it and pushed it into Eurasia, forming the Himalaya.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.1073/pnas.2009039117">Martin et al 'Paleocene latitude of the Kohistan-Ladakh arc indicates multi-stage India-Eurasia collision,' PNAS 2020</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span>
</figcaption>
</figure>
<h2>Magnetic traces build a map</h2>
<p>Using the average magnetic direction of the whole suite of samples we can calculate their ancient latitude, which we refer to as the paleolatitude.</p>
<p>The original single-stage collision model for the Himalaya predicts that these rocks would have formed close to Eurasia at a latitude of around 20 degrees north, but our data shows that these rocks did not form on either the Indian or the Eurasian continents. Instead, they formed on a chain of volcanic islands, out in the open Neotethys Ocean at a latitude of about 8 degrees north, thousands of kilometers south of where Eurasia was located at the time.</p>
<p>This finding can be explained only if there were <a href="https://doi.org/10.1038/ngeo2418">two subduction zones</a> pulling India rapidly toward Eurasia, rather than just one. </p>
<p>[<em>You’re smart and curious about the world. So are The Conversation’s authors and editors.</em> <a href="https://theconversation.com/us/newsletters/weekly-highlights-61?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=weeklysmart">You can get our highlights each weekend</a>.]</p>
<p>During a geologic time period known as the Paleocene, India caught up with the volcanic island chain and collided with it, scraping up the rocks we eventually sampled onto the northern edge of India. India then continued northward before <a href="https://doi.org/10.1016/j.epsl.2013.01.023">ramming into Eurasia around 40 to 45 million years ago</a> – 10 to 15 million years later than was generally thought.</p>
<p>This final continental collision raised the volcanic islands from sea level up over 4,000 meters to their present-day location, where they form jagged outcrops along a spectacular Himalayan mountain pass.</p><img src="https://counter.theconversation.com/content/148404/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Craig Robert Martin receives funding from the National Science Foundation (NSF).</span></em></p>Earth’s magnetic field locks information into lava as it cools into rock. Millions of years later, scientists can decipher this magnetic data to build geologic timelines and maps.Craig Robert Martin, Ph.D. Student in Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology (MIT)Licensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1424622020-07-16T12:12:24Z2020-07-16T12:12:24ZAn effective climate change solution may lie in rocks beneath our feet<figure><img src="https://images.theconversation.com/files/347714/original/file-20200715-31-u81v6h.jpg?ixlib=rb-1.1.0&rect=4%2C4%2C2991%2C1989&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Weathering of rocks like these basalt formations in Idaho triggers chemical processes that remove carbon dioxide from the air.</span> <span class="attribution"><a class="source" href="https://flic.kr/p/2hMZxfS">Matthew Dillon/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Why has Earth’s climate remained so stable over geological time? The answer just might rock you. </p>
<p>Rocks, particularly the types created by volcanic activity, play a critical role in keeping Earth’s long-term climate stable and cycling carbon dioxide between land, oceans and the atmosphere.</p>
<p>Scientists have known for <a href="https://doi.org/10.1029/JC086iC10p09776">decades</a> that rock weathering – the chemical breakdown of minerals in mountains and soils – removes carbon dioxide from the atmosphere and transforms it into stable minerals on the planet’s surface and in ocean sediments. But because this process operates over millions of years, it is too weak to offset modern global warming from human activities.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/347727/original/file-20200715-37-1s7y6p6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/347727/original/file-20200715-37-1s7y6p6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/347727/original/file-20200715-37-1s7y6p6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/347727/original/file-20200715-37-1s7y6p6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/347727/original/file-20200715-37-1s7y6p6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/347727/original/file-20200715-37-1s7y6p6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/347727/original/file-20200715-37-1s7y6p6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/347727/original/file-20200715-37-1s7y6p6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1131&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Acid rain damage to buildings and monuments, like this sandstone statue in Dresden, Germany, is a form of chemical weathering.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Acid_rain#/media/File:Skulptur_aus_Sandstein,_Dresden_2012-09-06-0555.jpg">Slick/Wikipedia</a></span>
</figcaption>
</figure>
<p>Now, however, emerging science – including at the California Collaborative for Climate Change Solutions’ (C4) <a href="https://www.workinglandsinnovation.com/">Working Lands Innovation Center</a> – shows that it is possible to accelerate rock weathering rates. Enhanced rock weathering could both slow global warming and improve soil health, making it possible to grow crops more efficiently and bolster food security. </p>
<h2>Rock chemistry</h2>
<p>Many processes <a href="https://www.nationalgeographic.org/encyclopedia/weathering/">weather rocks</a> on Earth’s surface, influenced by chemistry, biology, climate and plate tectonics. The dominant form of chemical weathering occurs when carbon dioxide combines with water in the soil and the ocean to make carbonic acid. </p>
<p>About 95% of Earth’s crust and <a href="https://www.britannica.com/science/Earths-mantle">mantle</a> – the thick layer between the planet’s crust and its core – is made of <a href="https://www.britannica.com/science/silicate-mineral">silicate minerals</a>, which are compounds of silicon and oxygen. Silicates are the main ingredient in most igneous rocks, which form when volcanic material cools and hardens. Such rocks make up about 15% of Earth’s <a href="https://en.wikipedia.org/wiki/Igneous_rock#Geological_significance">land surface</a>. </p>
<p>When carbonic acid comes in contact with certain silicate minerals, it triggers a chemical process known as the <a href="https://doi.org/10.3389/fspas.2019.00062">Urey reaction</a>. This reaction pulls gaseous carbon dioxide from the atmosphere and combines it with water and calcium or magnesium silicates, producing two bicarbonate ions. Once the carbon dioxide is trapped in these soil carbonates, or ultimately washed into the ocean, it no longer warms the climate.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/347723/original/file-20200715-35-oit8oh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/347723/original/file-20200715-35-oit8oh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/347723/original/file-20200715-35-oit8oh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=333&fit=crop&dpr=1 600w, https://images.theconversation.com/files/347723/original/file-20200715-35-oit8oh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=333&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/347723/original/file-20200715-35-oit8oh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=333&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/347723/original/file-20200715-35-oit8oh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=418&fit=crop&dpr=1 754w, https://images.theconversation.com/files/347723/original/file-20200715-35-oit8oh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=418&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/347723/original/file-20200715-35-oit8oh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=418&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">When carbonic acid dissolves calcium and magnesium silicate minerals, they break down into dissolved compounds, some of which contain carbon. These materials can flow to the ocean, where marine organisms use them to build shells. Later the shells are buried in ocean sediments. Volcanic activity releases some carbon back to the atmosphere, but much of it stays buried in rock for millions of years.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Carbonate%E2%80%93silicate_cycle#/media/File:Carbon-Slicate_Cycle_Feedbacks.jpg">Gretashum/Wikipedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The Urey reaction runs at a higher rate when silicate-rich mountains such as the Himalayas expose fresh material to the atmosphere – for example, after a landslide – or when the climate becomes hotter and moister. Recent research demonstrates that humans can speed up the process substantially to help fight modern global warming.</p>
<h2>Accelerated weathering</h2>
<p>The biggest limit on weathering is the amount of silicate minerals exposed at any given time. Grinding up volcanic silicate rocks into a fine powder increases the surface area available for reactions. Further, adding this rock dust to the soil exposes it to plant roots and soil microbes. Both roots and microbes produce carbon dioxide as they decompose organic matter in the soil. In turn, this increases carbonic acid concentrations that accelerate weathering.</p>
<p>One recent study by British and Americans scientists suggests that adding finely crushed silicate rock, such as basalt, to all cropland soil in China, India, the U.S. and Brazil could trigger weathering that would remove <a href="https://doi.org/10.1038/s41586-020-2448-9">more than 2 billion tons of carbon dioxide</a> from the atmosphere each year. For comparison, the U.S. emitted <a href="https://www.nytimes.com/2019/01/08/climate/greenhouse-gas-emissions-increase.html">about 5.3 billion tons</a> of carbon dioxide in 2018. </p>
<p>[<em>Get our best science, health and technology stories.</em> <a href="https://theconversation.com/us/newsletters/science-editors-picks-71/?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=science-best">Sign up for The Conversation’s science newsletter</a>.]</p>
<h2>Farming with rocks</h2>
<p>One compelling aspect of enhanced weathering is that, in controlled-environment studies involving basalt amendments of soil, cereal grain yields are improved by <a href="https://doi.org/10.1111/gcb.15089">roughly 20%</a>. </p>
<p>As basalt weathers, it increases vital plant nutrients that can boost production and increase crops yields. Mineral nutrients such as calcium, potassium and magnesium create healthier soils. Farmers have been <a href="http://dx.doi.org/10.1590/S0001-37652006000400009">amending soil with rock minerals for centuries</a>, so the concept is nothing new. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/347717/original/file-20200715-29-x3wxdd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/347717/original/file-20200715-29-x3wxdd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/347717/original/file-20200715-29-x3wxdd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/347717/original/file-20200715-29-x3wxdd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/347717/original/file-20200715-29-x3wxdd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/347717/original/file-20200715-29-x3wxdd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/347717/original/file-20200715-29-x3wxdd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/347717/original/file-20200715-29-x3wxdd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Spreading lime on a field in Devon, England to improve soil quality.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Spreading_lime_on_a_Devon_field.jpg">Mark Robinson/Wikipedia</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>At the <a href="https://www.workinglandsinnovation.com/">Working Lands Innovation Center</a>, we are conducting perhaps the largest enhanced weathering demonstration experiment on real farms in the world. We are partnering with farmers, ranchers, government, the mining industry and Native American tribes in California on some 50 acres of cropland soil amendment trials. We are testing the effects of rock dust and compost amendments on greenhouse gas emissions from the soil, carbon capture, crop yields, and plant and microbial health. </p>
<p>Our initial results suggest that adding basalt and <a href="https://www.britannica.com/science/wollastonite">wollastonite</a>, a calcium silicate mineral, increased corn yields by 12% in the first year. Working with <a href="https://ww2.arb.ca.gov/our-work/programs/cap-and-trade-program">California’s greenhouse gas emissions trading program</a> and our state’s diverse agricultural interests, we hope to establish a pathway that would offer monetary incentives to farmers and ranchers who allow enhanced rock weathering on their lands. We aim to create a protocol for farmers and ranchers to make money from the carbon they farm into the soil and help businesses and industry achieve their carbon neutrality goals. </p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1184184454522081281"}"></div></p>
<h2>Why negative emissions matter</h2>
<p>Under the <a href="https://theconversation.com/paris-agreement-on-climate-change-the-good-the-bad-and-the-ugly-52242">2015 Paris climate agreement</a>, nations have pledged to limit global warming to less then 2 degrees Celsius above preindustrial levels. This will require massive cuts in greenhouse gas emissions.</p>
<p>Pulling carbon dioxide from the air – also known as negative emissions – is also necessary to avoid the worst climate change outcomes, because atmospheric carbon dioxide has an <a href="https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_Chapter06_FINAL.pdf">average lifespan of more than 100 years</a>. Every molecule of carbon dioxide that is released to the atmosphere through fossil fuel combustion or land clearing will remain there for many decades trapping heat and warming Earth’s surface.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/4IUQn9uL6W0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">In an even faster version of enhanced weathering, scientists pump supercritical carbon dioxide underground into basalt formations, where it reacts with minerals to form new solid rock.</span></figcaption>
</figure>
<p>Nations need a portfolio of solutions to create <a href="https://www.nap.edu/catalog/25259/negative-emissions-technologies-and-reliable-sequestration-a-research-agenda">negative emissions</a>. Enhanced weathering is poised for rapid scale-up, taking advantage of farm equipment that’s already in place, global mining operations and supply chains that currently deliver fertilizers and seeds worldwide. By addressing soil erosion and food security along with climate change, I believe rock weathering can help humans escape the hard place we find ourselves in today.</p><img src="https://counter.theconversation.com/content/142462/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Benjamin Z. Houlton receives funding from the California Strategic Growth Council</span></em></p>To avoid global warming on a catastrophic scale, nations need to reduce emissions and find ways to pull carbon from the air. One promising solution: spreading rock dust on farm fields.Benjamin Z. Houlton, Professor of Global Environmental Studies, Chancellor's Fellow and Director, John Muir Institute of the Environment, University of California, DavisLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1226172019-09-05T18:50:14Z2019-09-05T18:50:14ZFriday essay: lessons from stone – Indigenous thinking and the Law<figure><img src="https://images.theconversation.com/files/290607/original/file-20190903-175705-bbfa3t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The sacred site of Uluru. In our Law we know that rocks are sentient and contain spirit. </span> <span class="attribution"><span class="source">Dan peled/AAP</span></span></figcaption></figure><p>In Dreaming stories, Emu is often a narcissist who damages social relationships. These stories teach us about the protocols for living sustainably, and warn us about unsustainable behaviours. The basic protocols of Aboriginal society, like most societies, include respecting and hearing all points of view in a yarn. </p>
<p>Narcissists demand this right, then refuse to allow other points of view on the grounds that any other opinion somehow infringes their freedom of speech or is offensive. </p>
<p>They destroy the basic social contracts of reciprocity (which allow people to build a reputation of generosity based on sharing to ensure ongoing connectedness and support), shattering these frameworks of harmony with a few words of nasty gossip. They apply double standards and break down systems of give and take until every member of a social group becomes isolated, lost in a Darwinian struggle for power and dwindling resources that destroys everything. Then they move on to another place, another group. Feel free to extrapolate this pattern globally and historically.</p>
<p>We have stories for this behaviour, memorial stones scattered along songlines throughout the landscape, victims and transgressors transformed into rock following epic struggles to stand for all time as cautionary tales. Clancy McKellar, a Wangkumarra Songman, took me to a site where three brothers who had kidnapped women were punished and turned to stone.</p>
<p>All over that place in Tibooburra the red rocks are people turned to stone for breaking the Law or messing around too much with weather modification rituals. There is Law and knowledge of Law in stones. All Law-breaking comes from that first evil thought, “I am greater-than,” that original sin of placing yourself above the land or above other people.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/290626/original/file-20190903-175696-1bepnru.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/290626/original/file-20190903-175696-1bepnru.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/290626/original/file-20190903-175696-1bepnru.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/290626/original/file-20190903-175696-1bepnru.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/290626/original/file-20190903-175696-1bepnru.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/290626/original/file-20190903-175696-1bepnru.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/290626/original/file-20190903-175696-1bepnru.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/290626/original/file-20190903-175696-1bepnru.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Red Rocks at Tibooburra.</span>
<span class="attribution"><span class="source">Author provided</span></span>
</figcaption>
</figure>
<p>In our traditional systems of Law we remember, however, that everyone is an idiot from time to time. Punishment is harsh and swift, but afterwards there is no criminal record, no grudge against the transgressor. Perpetrators are only criminals until they are punished, and then they may be respected again and begin afresh to make a positive contribution to the group.</p>
<p>In this way, people will not lie and shift blame or avoid punishment by twisting rules to escape accountability. They can look forward to a clean slate and therefore be willing and equal participants in their own punishment and transformation, which is a learning process more than anything else.</p>
<p>This is perhaps something of value to be taken from our stone stories to make justice systems more effective and sustainable today. Those old criminals in stone all over this country are not despised figures, but respected entities who received their punishment and are now revered in their roles of keeping the Law. If we respect them and hear their stories, they can tell us how to live together better.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-the-seasonal-calendars-of-indigenous-australia-88471">Explainer: the seasonal 'calendars' of Indigenous Australia</a>
</strong>
</em>
</p>
<hr>
<h2>Albino boy</h2>
<p>But I don’t know very much about rocks. I feel more at home on open savannah and dry sclerophyll bushlands, and my Story Place has only one stone, which moves around of its own accord and so is in a different position every time you go there. It arrived from Asia, carried by a cyclone, and never quite settled down to live slowly like other rocks. So I need to yarn with somebody who really understands the way stone works. As usual, I seek the most insightful knowledge in the most marginalised point of view. I talk to a young Tasmanian Aboriginal boy called Max.</p>
<p>Max has silvery white hair and alabaster skin. He looks and talks like he’d be more at home riding a dragon than a stock horse. He’s a proper nerd, memorising hundreds of digits of pi for no particular reason, thinking his martial arts skills are much better than they really are, and carrying around an encyclopaedic knowledge of elves and hobbits and superheroes. He can also write songs in his ancestral language that make me cry.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/290603/original/file-20190903-175714-1wigy69.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/290603/original/file-20190903-175714-1wigy69.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/290603/original/file-20190903-175714-1wigy69.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=458&fit=crop&dpr=1 600w, https://images.theconversation.com/files/290603/original/file-20190903-175714-1wigy69.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=458&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/290603/original/file-20190903-175714-1wigy69.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=458&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/290603/original/file-20190903-175714-1wigy69.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=575&fit=crop&dpr=1 754w, https://images.theconversation.com/files/290603/original/file-20190903-175714-1wigy69.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=575&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/290603/original/file-20190903-175714-1wigy69.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=575&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Max.</span>
<span class="attribution"><span class="source">Author provided</span></span>
</figcaption>
</figure>
<p>We’ve spent a lot of time sparring in a traditional style that was once done with stone knives. The rules of engagement are that you can only cut your opponent on the arms, shoulders or back (extremely difficult to do) and — here’s the kicker — at the end of the fight the winner must get cut up the same as the loser, so that nobody can walk away with a grudge. </p>
<p>It’s hard enough to cut somebody on the back with a stone knife when they’re trying to do the same to you, but it’s even harder when you know that every time you cut them you’re really just cutting yourself.</p>
<p>In our yarns following these sessions we decided this kind of combat forces you to see your enemy’s point of view, and by the end of it you can no longer be opponents because you’re connected by mutual respect and understanding. More lessons from stone — but how to apply these today? Sounds like a good opportunity for a thought experiment.</p>
<p>I guess if you wanted to take a contemporary economy that is dependent on perpetual war and try to make it sustainable, you could start by applying similar rules of engagement. But in the stone-knife model, enemies are a non-renewable resource and eventually you would run out of them. It would not be sustainable at all for the war machine if everybody ended up respecting all points of view. </p>
<p>Perhaps the transferable wisdom here is simply that most young men need something a little meatier than mindfulness workshops to curtail the terrifying narcissism that overtakes them from the moment their balls drop. Maybe then they won’t grow up to be the men who start wars in the first place.</p>
<p>This brings us back to that foundational flaw, that Luciferian lie: “I am greater than you; you are lesser than me.” Because his appearance does not match some people’s idea of his cultural identity, Max faces abusive encounters grounded in that foundational flaw daily. His identity is constantly questioned by both Aboriginal and non-Aboriginal people who place themselves in a greater-than position and get a little thrill out of pronouncing judgement on his existence. Max reflects on these encounters, deciding that these people lack their own authentic identities and therefore can only find comfort in assaulting his.</p>
<p>Max may not know everything about his lineage or his culture, both of which were catastrophically disrupted by large-scale genocide, but he knows who he is, and the
fragments of cultural knowledge he carries have integrity and value. He applies the pattern in those fragments to every aspect of his life.</p>
<blockquote>
<p>I don’t know what I’d be if I didn’t have my identity, because I haven’t really known a life without it. I can’t discern parts that are Indigenous and parts that are not because all of my actions are Indigenous — the way I move through the world, my social interactions, my way of thinking about anything. It bleeds through you no matter what.</p>
</blockquote>
<p>When Max recites a hundred digits of pi he is not stepping outside of his identity; he is singing a pattern of creation from north to south. He does not need to have an Elder’s level of knowledge to do this. He needs only to perceive the pattern in what he does know.</p>
<p>Keepers of knowledge see him behaving in this way and know he is ready to be responsible for additional knowledge, so pass on story to him. This is how Indigenous Knowledge works.</p>
<h2>Strong no matter what</h2>
<p>Max teaches me about rocks, because Tasmanian people have a particular connection to rocks.</p>
<blockquote>
<p>Stones to me are the objects that parallel all life, more so than trees or mortal things because stones are almost immortal. They know things learned over deep time. Stone represents earth, tools and spirit; it conveys meaning through its use and through its resilience to the elements. At the same time it ages, cracking and eroding as time wears it down, but it is still there, filled with energy and spirit.</p>
</blockquote>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/290475/original/file-20190902-175682-1gsehn1.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/290475/original/file-20190902-175682-1gsehn1.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/290475/original/file-20190902-175682-1gsehn1.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/290475/original/file-20190902-175682-1gsehn1.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/290475/original/file-20190902-175682-1gsehn1.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/290475/original/file-20190902-175682-1gsehn1.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/290475/original/file-20190902-175682-1gsehn1.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/290475/original/file-20190902-175682-1gsehn1.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Albino Boy sacred site: a massive complex of carved standing stones in north west New South Wales.</span>
<span class="attribution"><span class="source">Author provided</span></span>
</figcaption>
</figure>
<p>We yarn about the sentience of stones and the ancient Greek mistake of identifying “dead matter” as opposed to living matter, limiting for centuries to come the potential of western thought when attempting to define things like consciousness and self-organising systems such as galaxies. They viewed space as lifeless and empty between stars; our own stories represented those dark areas as living country, based on observed effects of attraction from those places on celestial bodies. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-ancient-aboriginal-star-maps-have-shaped-australias-highway-network-55952">How ancient Aboriginal star maps have shaped Australia's highway network</a>
</strong>
</em>
</p>
<hr>
<p>Theories of dead matter and empty space meant that western science came late to discoveries of what they now call “dark matter”, finding that those areas of “dead and empty” space actually contain most of the matter in the universe.</p>
<p>This brings us back to Elder of the Nyoongar people, Uncle Noel Nannup’s, creation story of when Emu went nuts with narcissism and demanded to become the boss of creation. In that story, the pre-creation reality was that space was solid: it sat heavily upon the ground, crushing everything that attempted to come into being. Earth and sky had to be separated, the Ancestors lifting up the heavens physically. </p>
<p>Sky country is seen in our stories as tangible, having mass, in a way that reveals an understanding of dark matter. All that celestial territory is in constant communication with us, exerting forces upon us and even exchanging matter in the form of rocks crashing through our atmosphere. Our stories show our ancient understanding of the way asteroids form craters, a realisation that only entered scientific knowledge a few short decades ago.</p>
<p>Max and I yarn about how our knowledge of these things cannot have always been unique to our culture alone, as the ancient names for constellations are often the same as ours throughout the world — the seven sisters, the two brothers, the eagle, the hunter. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/290604/original/file-20190903-175696-6rhw7v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/290604/original/file-20190903-175696-6rhw7v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/290604/original/file-20190903-175696-6rhw7v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/290604/original/file-20190903-175696-6rhw7v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/290604/original/file-20190903-175696-6rhw7v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/290604/original/file-20190903-175696-6rhw7v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=500&fit=crop&dpr=1 754w, https://images.theconversation.com/files/290604/original/file-20190903-175696-6rhw7v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=500&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/290604/original/file-20190903-175696-6rhw7v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=500&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Sylvia Ken, winner of the 2019 Wynne Prize, with her painting of the Seven Sisters at the Art Gallery of NSW in May.</span>
<span class="attribution"><span class="source">Peter Rae/AAP</span></span>
</figcaption>
</figure>
<p>These are global stories and systems of knowledge that must have once been common to all people. We think something terrible must have happened in the north to make people forget, causing science to have to start all over again from scratch rather than building on what went before. What could this cataclysm have been?</p>
<p>I imagine the Black Death couldn’t have helped, but I suspect it began earlier than that. I think the Emu deception got out of hand somewhere and spread, causing more and more people to think themselves greater than the land, greater than others, greater than the women who hold our lives in their hands and bellies. Whatever it is, this cataclysm is growing and I wonder how we can stand against it.</p>
<p>Max responds:</p>
<blockquote>
<p>Stone teaches us that we should be strong no matter what tries to crack us or wear us down, keeping an unbreakable core through your culture and your beliefs. The majority of this earth is rock, and while water and plants make up its surface, the body of the earth, the part that keeps it all together, is rock. </p>
<p>You can have life and creation but it will all crumble without a solid base, same with society, companies, relationships, identities, knowledge, almost anything both tangible and intangible. Like those forests and trees sitting as a skin over the rocks of the earth — without that strength inside, without that stone, it would crumble.</p>
</blockquote>
<h2>Uluru rocks</h2>
<p>Thinking about the shape of the world Max describes and the thin skin around it, I reflect on the physics of our creation stories and the way rocks wear away over time into balls. </p>
<p>I perceive a pattern in the universe whereby the most efficient shape for holding matter together is a sphere. I might say to the growing numbers of flat-earth theorists out there, “Blow me a flat bubble and I’ll consider your theory.” But that would be placing myself in a greater-than position, so I need to check myself and pay attention to them, remembering that there is always value in marginal viewpoints.</p>
<p>So I listen to them online and realise that the sphere is not the final shape of this creation process. Our own galaxy began as a sphere and flattened into a disc and the earth is gradually flattening itself too, as it spins like a lump of clay on a wheel. It’s only flattened by just over 20 kilometres at the poles so far, but it’s getting there. It’s a good thing I didn’t dismiss the flat-earthers out of hand, otherwise I might never have understood that properly.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/290470/original/file-20190902-175700-1i4lm62.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/290470/original/file-20190902-175700-1i4lm62.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/290470/original/file-20190902-175700-1i4lm62.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=918&fit=crop&dpr=1 600w, https://images.theconversation.com/files/290470/original/file-20190902-175700-1i4lm62.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=918&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/290470/original/file-20190902-175700-1i4lm62.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=918&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/290470/original/file-20190902-175700-1i4lm62.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1153&fit=crop&dpr=1 754w, https://images.theconversation.com/files/290470/original/file-20190902-175700-1i4lm62.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1153&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/290470/original/file-20190902-175700-1i4lm62.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1153&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p>But what use could come from that kind of thinking? Well, thought experiment might yield a few applications. Packaging, for example, might make more efficient use of space and resources if we considered that you can get a hell of a lot more into a small sphere than a big box. </p>
<p>But then what would stop those spheres rolling off the shelves? The flat-earthers resolve this — just squash the spheres down a bit. Thank you, flat-earthers. That innovation could save a bit of landfill, buy us a little time.</p>
<p>Max thinks it will take a bigger shift in thinking to stave off planetary destruction, that we need to learn more about respect from the stones. I agree — the understanding that we are no greater or lesser than a rock would certainly change things if a critical mass of people all came to it at once. </p>
<p>Anyone who thinks they’re better than a rock should be turned into one — then they would find out they’re not that special, and they could finally be happy. Max suggests that in recent decades people have been becoming aware of rock spirit, reminding me of what has been going on at Uluru.</p>
<p>There is a shed there full of rocks. For a long time, tourists took stones away from that sacred site as souvenirs, then a few decades ago something strange began to happen. The tourists <a href="https://www.news.com.au/travel/australian-holidays/northern-territory/the-souvenir-from-uluru-you-should-never-take/news-story/31345382f651611f088775ae0eb16e5f">started mailing the rocks back</a> with panicked reports of weird happenings, disturbed sleep, bad luck, ghostly visitations and terrible accidents. Somehow they knew it was because of the rocks, and were sending them back with desperate apologies. So many were returned that they had to build a big storage shed to house them.</p>
<p>In our Law we know that rocks are sentient and contain spirit. You can’t just pick one up and carry it home, as you will disturb its spirit and it will disturb you in turn. If you sit at any campfire for a yarn with Aboriginal people anywhere on this continent, you will be sure to hear a cautionary tale about a relative who was silly enough to pick up a rock and take it home, who then got sick or was haunted or killed or went crazy. </p>
<p>A lot of rocks are benevolent and enjoy being used and traded, but you have to follow the guidance of the old people to know which ones you can use. Rocks are to be respected.</p>
<p>Perhaps further work needs to be done on what constitutes consciousness and what constitutes life. If the definitions of these things could include rocks as sentient beings, it would go a long way towards stemming the emu-like behaviours that are running rampant across the earth and cyberspace right now. Either that, or we could start mailing those Uluru rocks out to all the narcissists to give them a lesson in respect for others.</p>
<p><em>This is an edited extract from Tyson Yunkaporta’s Sand Talk: How Indigenous Thinking Can Save the World, Text Publishing.</em></p><img src="https://counter.theconversation.com/content/122617/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tyson Yunkaporta does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>There are memorial stones scattered along songlines throughout the Australian landscape, victims and transgressors transformed into rock following epic struggles to stand as cautionary tales.Tyson Yunkaporta, Senior Lecturer Indigenous Knowledges, Deakin UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1164292019-06-11T00:20:48Z2019-06-11T00:20:48ZCurious Kids: where do rocks come from?<figure><img src="https://images.theconversation.com/files/276702/original/file-20190528-92790-1ehkdqf.jpg?ixlib=rb-1.1.0&rect=0%2C8%2C5463%2C2506&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Rocks contain a layer-by-layer record of the history of our planet.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/86755183@N04/16485047966/">Fred Moore/flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p><em><a href="https://theconversation.com/au/topics/curious-kids-36782">Curious Kids</a> is a series for children. If you have a question you’d like an expert to answer, send it to curiouskids@theconversation.edu.au You might also like the podcast <a href="http://www.abc.net.au/kidslisten/imagine-this/">Imagine This</a>, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.</em> </p>
<hr>
<blockquote>
<p><strong>Where do rocks come from? - Claire, age 5, Perth, WA.</strong></p>
</blockquote>
<p>Wow, Claire, what a great question. Sitting in a university, I rarely get asked such brilliant questions. So, thank you. </p>
<p>As strange as it sounds, rocks are made from stardust; dust blasted out and made from exploding stars. </p>
<p>In fact, our corner of space has many rocks floating around in it. From really fine dust, to pebbles, boulders and house-sized rocks that can burn up in the night sky to make meteors or “shooting stars”. </p>
<p>The Moon and our local planets – Mars, Venus and Mercury – are just the largest rocks floating around our part of space. These are all made from space dust stuck together over billions of years.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-how-was-the-earth-made-112067">Curious Kids: how was the Earth made?</a>
</strong>
</em>
</p>
<hr>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/277790/original/file-20190604-69079-tznyh9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/277790/original/file-20190604-69079-tznyh9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/277790/original/file-20190604-69079-tznyh9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/277790/original/file-20190604-69079-tznyh9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/277790/original/file-20190604-69079-tznyh9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/277790/original/file-20190604-69079-tznyh9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/277790/original/file-20190604-69079-tznyh9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">An artist’s impression of early Earth, which was then a molten ball of lava flying through space.</span>
<span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA15808">NASA/JPL-Caltech</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>The ‘light’ rocks are on the Earth’s surface</h2>
<p>Planet Earth is a rock too, but so much has happened since it was formed from dust and small rocks that smashed and stuck together 4.543 billion years ago.</p>
<p>As the space dust hit each other to make the earth, it got super hot and melted. The Earth was, at that time, a spinning ball of red-hot lava flying through space. </p>
<p>In this melted lava planet, heavy bits of the earth sank and the light frothy bits gathered on the surface. </p>
<p>Have you ever looked closely at a glass of milky coffee at a cafe? The dark heavy coffee is at the bottom, whereas the light, frothy milk sits on the top. Well, our planet was a bit like that coffee billions of years ago. </p>
<iframe src="https://giphy.com/embed/fEZ982FPO0jIc" width="100%" height="480" frameborder="0" class="giphy-embed" allowfullscreen=""></iframe>
<p><a href="https://giphy.com/gifs/eastbay-fEZ982FPO0jIc"></a></p>
<p>We don’t see the really heavy rocks these days because they sank deep in the planet very early on. The rocks we see on the surface are like the frothy milk! They were light and rose to the top. Then, as time moved on, the planet cooled and froze to become the solid earth we have now. </p>
<p>I know most rocks are heavy. But in fact some rocks – even really big ones like Uluru – are actually much lighter than the rocks found in the deep Earth.</p>
<h2>Lava and plates</h2>
<p>Those rocks on the Earth’s surface actually <a href="https://theconversation.com/a-map-that-fills-a-500-million-year-gap-in-earths-history-79838">move around</a>. Large chunks the size of continents (called “plates”) jostle each other and this can cause earthquakes. Some of them get forced under other plates and heat up and eventually melt. This forms more lava. The lava erupts from volcanoes, then cools and forms new rocks. </p>
<p>Here are some pictures of lava in the melted state and then after it has cooled down:</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/276748/original/file-20190528-42560-rvs752.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/276748/original/file-20190528-42560-rvs752.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/276748/original/file-20190528-42560-rvs752.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/276748/original/file-20190528-42560-rvs752.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/276748/original/file-20190528-42560-rvs752.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/276748/original/file-20190528-42560-rvs752.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/276748/original/file-20190528-42560-rvs752.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Volcanic lava in Etra Ale Volcano in Ethiopia in 2016. Lava emerges from volcanoes and then cools on the Earth’s surface to form rocks.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/myneur/6900576021/">Petr Meissner/flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-how-do-mountains-form-108246">Curious Kids: how do mountains form?</a>
</strong>
</em>
</p>
<hr>
<h2>Mountains and gems are also rocks</h2>
<p>Mountains form where two plates smash into each other. The rocks that get caught between two of the Earth’s plates get squashed under huge pressures and heat up. These can form really beautiful rocks. Sometimes gems form in these rocks and people try to find them to make jewellery.</p>
<p>Rain and ice break up the rocks in mountains. These form sand and mud that get washed out to form beaches, rivers and swamps. This sand and mud can get buried, squashed and heated, which eventually turns them into rocks.</p>
<p>Rocks contain a record of the history of our planet; what is has been through and what is capable of. We are only just learning how to read it. </p>
<p>So, next time you see a rock, just think what an incredible story it contains.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/273473/original/file-20190509-183086-sm9qf0.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/273473/original/file-20190509-183086-sm9qf0.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/273473/original/file-20190509-183086-sm9qf0.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/273473/original/file-20190509-183086-sm9qf0.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/273473/original/file-20190509-183086-sm9qf0.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/273473/original/file-20190509-183086-sm9qf0.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/273473/original/file-20190509-183086-sm9qf0.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Spectacular layered sedimentary rocks from Tigray, Ethiopia, where each layer represents an ancient sea bed. Rocks of these types contain the history of the surface of the planet.</span>
<span class="attribution"><span class="source">Author provided</span></span>
</figcaption>
</figure>
<hr>
<p><em>Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au</em></p>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=376&fit=crop&dpr=1 600w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=376&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=376&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=472&fit=crop&dpr=1 754w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=472&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=472&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p><em>Please tell us your name, age and which city you live in. We won’t be able to answer every question but we will do our best.</em></p><img src="https://counter.theconversation.com/content/116429/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alan Collins receives funding from a number of industry and government sources including the Australian Research Council</span></em></p>As strange as it sounds, rocks are made from stardust.Alan Collins, Professor of Geology, University of AdelaideLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1152662019-04-15T15:00:05Z2019-04-15T15:00:05ZNew technique helps identify which ancient rocks were used for cooking<figure><img src="https://images.theconversation.com/files/269015/original/file-20190412-76831-124o29c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Experimentally heated quartzite at different stages of heating.</span> <span class="attribution"><span class="source">Bentsen and Wurz, 2019, Journal of Field Archaeology</span></span></figcaption></figure><p>Fire was probably <a href="https://www.scientificamerican.com/article/quest-for-clues-to-humanitys-first-fires/">first used by humans one million years ago</a>. It was a valuable resource for light, warmth, and keeping predators at bay. It also opened up new culinary avenues: roasting meat, fish, shellfish and vegetables on charcoal or in the fire was probably early modern humans’ <a href="https://www.researchgate.net/publication/322632256_Towards_a_better_understanding_of_cooking_techniques_in_the_African_Middle_Stone_Age">main cooking technique</a>. </p>
<p>Between 50 000 and 30 000 years ago, people started producing large quantities of heat-affected rocks. Researchers think <a href="http://www.paleoanthro.org/media/journal/content/PA20150054.pdf">this signals the start of boiling and intensive bone grease rendering</a>. These cooking techniques used heated rocks to warm up liquid, adding dishes like broth and soup to the menu. Rocks were also probably used as primitive frying pans, placed in or next to fires, and as <a href="https://aswtproject.wordpress.com/category/fire-cracked-rock/">heating elements to bake or fry food in earth ovens</a>.</p>
<p>One of the ways to recognise which rocks were used for cooking is by mapping colour changes. Many rocks rubefy – develop shades of pink or red – during heating; others whiten or darken.</p>
<p>But it’s difficult to describe these colour changes in a way that makes it possible to compare the colours of different rocks in different studies. One researcher’s “dark pink” is another’s “purple”.</p>
<p>In <a href="https://www.tandfonline.com/doi/full/10.1080/00934690.2019.1591092">a new paper</a> in the Journal of Field archaeology, my co-author Sarah Wurz and I have taken some steps towards addressing this issue.</p>
<p>We heated rocks in experimental campfires and compared different colour recording methods to describe the rocks. We wanted to find the best method to describes rocks’ colour changes, and which also allows statistical analyses of these changed. This baseline study means that in future, researchers can more easily compare heated rocks from different studies and areas. </p>
<p>This is important because it helps researchers to understand the use and development of human cooking techniques. It can also help us understand other uses of heated rocks, such as in steam baths.</p>
<h2>The sample rocks</h2>
<p>One set of the rocks used in this research came from a site in South Africa’s Eastern Cape province. The <a href="https://www.thoughtco.com/klasies-river-caves-167251">Klasies River main site</a> was first excavated in the late 1960s, then again between 1984 and 1995. </p>
<p>Earlier excavations revealed that small groups of early modern humans visited Klasies River many times between 120 000 and 40 000 years ago, and sometimes stayed for a few days at a time. The groups included both children and adults; they collected or caught and ate seafood, land animals, and plants. The remains of their fires and burning marks on bones showed that they also cooked their food.</p>
<p>My co-author, Sarah Wurz from the University of the Witwatersrand, is directing a <a href="https://www.facebook.com/KlasiesRiver/">new excavation phase</a> at Klasies River main site. As part of her team, I’m excavating and analysing the site. Given my specialisation – fire use and experimental archaeology – I’m particularly interested in one of our finds: fractured and broken quartzite fragments that appear rubefied. Could these rocks have been heated, perhaps for use in cooking?</p>
<p>I knew from other studies that quartzite in other areas changed colour when exposed to heat, but it was difficult to compare those results to the rocks from Klasies River. The problem was that colours were described with words and there were limited photos. I could not be sure if the dark red or light pink described in the literature was similar to the colours I was seeing in my experiments. I also did not know how quartzite from the Klasies River area reacted to heat. </p>
<p>I decided to try and replicate the potentially heated rocks. So we collected quartzite cobbles at the beach and heated them in controlled fires. I recorded the temperatures during the fires and could see that some of the rocks in the fires fractured and changed colour during the experiment. Many of the samples did not change after the first heating episode. Some samples didn’t change even after repeated heating. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/269016/original/file-20190412-76827-1c1juao.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/269016/original/file-20190412-76827-1c1juao.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/269016/original/file-20190412-76827-1c1juao.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/269016/original/file-20190412-76827-1c1juao.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/269016/original/file-20190412-76827-1c1juao.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/269016/original/file-20190412-76827-1c1juao.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/269016/original/file-20190412-76827-1c1juao.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">One of the experimental fires, surrounded with rocks.</span>
<span class="attribution"><span class="source">Silje Evjenth Bentsen</span></span>
</figcaption>
</figure>
<p>This was just part of my work: I also tried different approaches to see how best to quantify the changes to the rocks.</p>
<h2>Technology and statistics</h2>
<p>Before the experiments, and after every heating episode, I recorded the colour of the quartzite samples. I noted the <a href="https://munsell.com/about-munsell-color/how-color-notation-works/">Munsell colour value</a> of each sample. This provides a standardised colour chart that can be used to describe colours, which makes it a little easier to compare colours across studies. Then, using statistical software, I converted the Munsell colour values to numerical values. Lastly, I photographed all the samples in controlled light before the experiments started and after every heating episode. </p>
<p>The photos were imported into Adobe Photoshop software, where I could record the digital RGB colour values of each sample. We could then conduct statistical analyses of the converted Munsell values and the digital colour values. I used the same methods to record colours of selected archaeological samples and to analyse them.</p>
<p>The digitally recorded colour values proved to be the best way to distinguish between the unheated and the repeatedly heated samples.</p>
<p>This process had two results. The first was that I was able to answer my questions about the Klasies River rocks. The quartzite from this site fractures, breaks and changes colour when heated in a campfire. It had to be quite close to the heat, and some samples needed to be repeatedly heated before they changed. </p>
<p>We could also show that the archaeological samples were probably repeatedly heated. This could, for example, have happened if the rocks were placed around the campfire and exposed to several fires. This find represents one of the earliest examples of using stones for heating or possibly cooking.</p>
<p>The second result has consequences far beyond this single study. I could show that digital colour values could be used to distinguish between unheated and repeatedly heated rocks, even when few changes were perceived by the naked eye. This provides a means to better identify heated rocks. Digital colour values also provide a measurement that is fairly independent of the researchers and allows us to compare rocks from different areas and studies.</p><img src="https://counter.theconversation.com/content/115266/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>This research has been supported by grants from the South African National Research Foundation (AOP150909141975, Grant No: 98826), the DST/NRF Centre of Excellence in Palaeosciences (CoE-Pal) (Postdoctoral Fellowship Grant No. PD2015/02SB) and the Claude Leon Foundation. Silje Evjenth Bentsen is currently a postdoctoral research fellow at the SFF Centre for Early Sapiens behaviour (SapienCE), supported by the Research Council of Norway through its Centres of Excellence funding scheme, project number 262618. Any opinion, finding and conclusion or recommendation expressed in this material is that of the author and the funding bodies does not accept any liability in this regard, nor do the opinions, findings, conclusions or recommendations in this material necessarily represent the views of the funding bodies.</span></em></p>Researchers can more easily compare heated rocks from different studies and areas.Silje Evjenth Bentsen, Postdoctor in archaeology at SapienCE, University of BergenLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1110972019-02-07T14:07:47Z2019-02-07T14:07:47ZTracks in rocks tell us where ancient animals roamed in southern Africa<figure><img src="https://images.theconversation.com/files/257240/original/file-20190205-86202-r3a0hm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Roberts Rock, before it slid into the sea, provided evidence of ancient vertebrate life.</span> <span class="attribution"><span class="source">Charles Helm</span></span></figcaption></figure><p>At first glance, they look like nothing more interesting than rocks. But to our research team, these two rocks – situated just 420 metres apart on a rugged, remote portion of South Africa’s Cape south coast – are fascinating and important pieces of ancient history.</p>
<p>The rocks are described in <a href="https://doi.org/10.17159/sajs.2019/5135">a paper</a> based on research that’s part of a decade-long multi-disciplinary study along a 350km stretch of this particular coastline. It’s been rewarding work. We’ve identified more than 130 sites containing trackways made by vertebrates during the Pleistocene era, dating back to between <a href="http://dx.doi.org/10.17159/sajs.2018/20170266">36 000 and 140 000 years ago</a>. </p>
<p>We’ve also found 40 hominin tracks on the ceiling and side walls of a coastal cave. These may represent the <a href="https://www.nature.com/articles/s41598-018-22059-5">first known example of humans jogging</a>.</p>
<p>Now we can add Roberts Rock and Megafauna Rock to the list. They contain trackways and tracks made by elephant, rhino and antelope, as well as by long-extinct buffalo and horse species, that all roamed the area hundreds of thousands of years ago. </p>
<p>Tracksites like these are scientifically important. They can be thought of as a movie that can tell stories about prehistoric humans as well as animal behaviour, and how many species were in a place at a particular point in time. They also have heritage and aesthetic value. These rocks, and similar finds, are a reminder that it’s important to regularly survey and document southern Africa’s coastlines. Fossils and trackways can be recorded through cast replicas and detailed photographs. This will allow more people to “read the rocks” and decipher our past.</p>
<h2>Ancient megafauna</h2>
<p>The rocks that sparked our latest paper lie to the east of a small town in South Africa called Still Bay. The first rock was <a href="https://www.researchgate.net/publication/222670634_Last_Interglacial_fossil_elephant_trackways_dated_by_OSLAAR_in_coastal_aeolianites_Still_Bay_South_Africa">initially described</a> in 2008; we later named it Roberts Rock in honour of Dr David Roberts, who discovered it.</p>
<p>Its 5 metre x 3.5 metre surface contained spectacular elephant trackways – the first to be reported from southern Africa. Over time we monitored its slow but steady demise. First it split in two, exposing many more tracks. By 2016 it had slumped into the sea, and was destroyed by wave action.</p>
<p>The second rock, measuring 5 metres x 5 metres x 2.5 metres, was arguably even more significant. In addition to numerous elephant tracks it contained probable single tracks of the extinct giant Cape horse (<em>Equus capensis</em>) and the extinct long-horned buffalo (<em>Syncerus antiquus</em>). We also identified a single track that was probably made by a rhinoceros. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/257241/original/file-20190205-86236-15ubnl2.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/257241/original/file-20190205-86236-15ubnl2.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/257241/original/file-20190205-86236-15ubnl2.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/257241/original/file-20190205-86236-15ubnl2.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/257241/original/file-20190205-86236-15ubnl2.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/257241/original/file-20190205-86236-15ubnl2.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/257241/original/file-20190205-86236-15ubnl2.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Tracks on Megafauna Rock reveal evidence of four of the species that once roamed there.</span>
<span class="attribution"><span class="source">Charles Helm</span></span>
</figcaption>
</figure>
<p>These four animals were all members of the megafauna – large creatures – that lived during the Pleistocene. Finding their tracks on a single rock was a surprise, and we named it Megafauna Rock.</p>
<p>The long-horned buffalo and giant Cape horse both went extinct between <a href="https://www.overbergrenosterveld.org.za/1983_fynbosmammals_program.pdf">10 000 and 12 000 years ago</a>. At the time of discovery, these were the first probable rhinoceros and giant Cape horse tracks that had been identified. We have subsequently found further such sites. The long-horned buffalo track, meanwhile, confirmed our findings from another site in our study area: the tracks of this species <a href="http://wiredspace.wits.ac.za/handle/10539/23736">are distinctive</a>, usually being wider than they are long.</p>
<p>Both rocks contained tracks on multiple layers. This suggests repeated use of an area over time, and possibly that the rocks were close to a water source. Using the results from dated samples from sites nearby, we’ve inferred that most of the tracks in this area are between 116 000 and 128 000 years old.</p>
<p>These rocks are just two highlights in an area that’s remarkably rich in trace fossils, and which preserves some of the activities of the Pleistocene fauna in exquisite detail. All this provides a glimpse of Pleistocene dune life and suggests an area teeming with large mammals.</p>
<p>Another important element to this research is that the tracks along this coastline were made at the margin of the <a href="http://dx.doi.org/10.1144/SP411.11">Palaeo-Agulhas Plain</a>, which was alternately exposed and covered by the ocean during multiple Pleistocene sea level changes. When exposed, this plain, which at times was <a href="https://doi.org/10.1016/j.quascirev.2010.01.015">up to 100 km wide</a>, could have provided <a href="https://www.researchgate.net/publication/285273001_Stone_Age_People_in_a_Changing_South_African_Greater_Cape_Floristic_Region">an east-west migration corridor</a> that supported large numbers of mammals. So, our studies can help to shed light on the climate and environmental conditions during the Pleistocene.</p>
<h2>A vanishing heritage</h2>
<p>One of the realities we’ve had to come to terms with, working on these coastal bluffs, is that the tracksites we find are ephemeral and unstable. High tides and storm surges batter the bluffs; many fragile sites are destroyed through erosion, while new ones appear.</p>
<p>An even larger rock has become exposed close to where Roberts Rock once stood. It contains multiple layers of elephant tracks, bird tracks, golden mole burrow traces and invertebrate traces – but it too is inexorably sliding down the unstable slope into the sea. There is little doubt that many other such sites have been exposed and destroyed without ever being witnessed or identified by humans.</p><img src="https://counter.theconversation.com/content/111097/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Charles Helm does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Trackways made by vertebrates during the Pleistocene era, dating back to between 36 000 and 140 000 years helps with research into ancient animals.Charles Helm, Research Associate, African Centre for Coastal Palaeoscience, Nelson Mandela UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1010022018-09-11T10:36:38Z2018-09-11T10:36:38ZWelcome to the new Meghalayan age – here’s how it fits with the rest of Earth’s geologic history<figure><img src="https://images.theconversation.com/files/235703/original/file-20180910-123110-1b0t4ht.jpg?ixlib=rb-1.1.0&rect=688%2C0%2C3771%2C2547&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">India's Mawmluh Cave, home of the reference stalagmite for the newly named age.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/breathtaking-mawmluh-cave-cherrapunji-meghalaya-india-1084380635">Abhijeet Khedgikar/Shutterstock.com</a></span></figcaption></figure><p>Jurassic, Pleistocene, Precambrian. The named times in Earth’s history might inspire mental images of dinosaurs, trilobites or other enigmatic animals unlike anything in our modern world.</p>
<p>Labels like these are part of a system scientists use to divide up Earth’s 4.6 billion year history. The biggest divisions are eons which split into eras, which break into periods, which divide into epochs and then all the way down to ages. </p>
<p><iframe id="CwVct" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/CwVct/6/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>Officially, we’re living in the Holocene epoch. Informally, people talk about our current age as the Anthropocene, melding humans with the lingo of geologic time. And now, there’s a new age with a new name – <a href="http://www.stratigraphy.org/index.php/ics-news-and-meetings/119-collapse-of-civilizations-worldwide-defines-youngest-unit-of-the-geologic-time-scale">the Meghalayan</a>. So how did the custom of dividing and categorizing time get started, and who gets to decide when there is a new age, epoch or era? </p>
<h2>Before the ages, naming the rocks</h2>
<p>The geologic time scale was not entirely intentional, at least at its start. In the early 1800s, geologists began to create maps and descriptions showing where different types of rocks occurred throughout western Europe. </p>
<p>Some of this was driven by natural curiosity. <a href="https://www.britannica.com/science/Triassic-Period">The Triassic</a> is named because the same three-part layering – carbonate-rich shale on top of fossil-rich limestone on top of red sandstone – was found throughout western Europe. To European scientists, this configuration seemed common enough to warrant a name.</p>
<p>Some labeling emerged from economic motivations. If a particular type of sandstone or limestone or coal proved useful, then people wanted to know where else to put a quarry or mine to find the same rock. </p>
<p>The study of how rocks are layered and organized became formalized as <a href="https://www.britannica.com/science/stratigraphy-geology">stratigraphy</a>. To assign a name to a particular rock, stratigraphers put criteria in place. There had to be a location where the archetype of that rock could be found. There should be a widespread geographic distribution, as for the Triassic. There might be signature fossils that only occur in that rock, or are not found in younger rocks (suggesting an extinction) or older rocks (telling us when a new species developed). </p>
<p>Names for the divisions of the rock record drew from where those rocks were first or best described – Devonian rocks in Devonshire, Cambrian rocks in Wales (Cambria, as the Romans called the region) – or from obvious characteristics. Cretaceous rocks in Europe are full of fossils that provide a rich source of chalk. Carboniferous rocks around the world include important coal resources. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/235413/original/file-20180907-90565-6dw7kb.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/235413/original/file-20180907-90565-6dw7kb.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/235413/original/file-20180907-90565-6dw7kb.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/235413/original/file-20180907-90565-6dw7kb.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/235413/original/file-20180907-90565-6dw7kb.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/235413/original/file-20180907-90565-6dw7kb.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/235413/original/file-20180907-90565-6dw7kb.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/235413/original/file-20180907-90565-6dw7kb.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Rocks near Gubbio, Italy, change in color and texture at the line indicating the Cretaceous-Paleogene extinction event that wiped out the dinosaurs 66 million years ago. A baseball hat shows scale.</span>
<span class="attribution"><span class="source">Robert DeConto and Mark Leckie, UMass Geosciences</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Rocks equal time</h2>
<p>The big mental leap came in connecting rocks with time – those Devonian rocks were formed during what came to be called Devonian time. That’s how geologic time became a convenient shorthand for major events and changes in life’s history on Earth. The Cretaceous is not just chalk. It’s a time when conditions were just right for the seas to be filled with huge populations of plankton – whose bodies sank to the ocean floor and eventually formed chalk when they died.</p>
<p>What began as a system to distinguish different rocks in western Europe has grown into a formalized, sophisticated and systematic way of thinking about life and time and the ways these are recorded in rocks.</p>
<p>The history of Earth’s atmosphere is one example. Invisible chemical proxies created by ancient organisms and preserved in sedimentary rocks record the rises and falls in oxygen and carbon dioxide over the past 600 million years. These coincide with events along the geologic timescale such as major mass extinctions, the evolution of land plants and the assembly and breakup of supercontinents.</p>
<p>Be it fossils or minerals or minute chemical signatures, the stratigraphic records reveals the interplay between life, earth and environment through time.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/235398/original/file-20180907-90553-ny3qtt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/235398/original/file-20180907-90553-ny3qtt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/235398/original/file-20180907-90553-ny3qtt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=430&fit=crop&dpr=1 600w, https://images.theconversation.com/files/235398/original/file-20180907-90553-ny3qtt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=430&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/235398/original/file-20180907-90553-ny3qtt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=430&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/235398/original/file-20180907-90553-ny3qtt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=540&fit=crop&dpr=1 754w, https://images.theconversation.com/files/235398/original/file-20180907-90553-ny3qtt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=540&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/235398/original/file-20180907-90553-ny3qtt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=540&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The official chart of geologic time over Earth’s billions of years.</span>
<span class="attribution"><a class="source" href="http://www.stratigraphy.org/index.php/ics-chart-timescale">http://www.stratigraphy.org</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<h2>Defining the Meghalayan Age</h2>
<p>Scientists still continue to refine the geologic timescale. This summer brought the <a href="https://www.qpg.geog.cam.ac.uk/news/formalsubdivisionoftheholoceneseriesgeogr18.pdf">official naming of a new age</a>: the Meghalayan.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/235694/original/file-20180910-123128-jylltf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/235694/original/file-20180910-123128-jylltf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/235694/original/file-20180910-123128-jylltf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1129&fit=crop&dpr=1 600w, https://images.theconversation.com/files/235694/original/file-20180910-123128-jylltf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1129&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/235694/original/file-20180910-123128-jylltf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1129&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/235694/original/file-20180910-123128-jylltf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1419&fit=crop&dpr=1 754w, https://images.theconversation.com/files/235694/original/file-20180910-123128-jylltf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1419&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/235694/original/file-20180910-123128-jylltf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1419&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Layers within the Indian stalagmite that defines the beginning of the Late Holocene Meghalayan Age, 4,200 years ago.</span>
<span class="attribution"><a class="source" href="http://web.csulb.edu/newsroom/collapse-of-civilizations-worldwide-defines-youngest-unit--of-the-geologic-time-scale/">Stanley C. Finney, CSULB</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p><a href="https://onlinelibrary.wiley.com/doi/abs/10.1002/jqs.2565">Numerous climate records</a> show that Earth faced an abrupt shift towards a cooler and drier climate 4,200 years ago. A team led by stratigrapher and climate scientist <a href="https://scholar.google.com/citations?user=9ad8lnkAAAAJ&hl=en&oi=sra">Mike Walker</a> proposed that this was a significant and global-scale event, best represented by climate signals found in <a href="http://www.stratigraphy.org/index.php/ics-news-and-meetings/119-collapse-of-civilizations-worldwide-defines-youngest-unit-of-the-geologic-time-scale">a stalagmite from Mawmluh Cave</a> in Meghalaya state, in northeast India. </p>
<p>The <a href="http://www.stratigraphy.org/">International Commission on Stratigraphy (ICS)</a> and its parent body, the International Union of Geological Sciences, vote on and ratify such proposals. ICS is in effect the <a href="http://www.stratigraphy.org/index.php/ics-chart-timescale">official keeper of the geologic time scale</a>. When a new time division is approved, as in the case of the Meghalayan, ICS sets the official description and adds that new detail to the geologic time scale. </p>
<p>All rocks younger than 4,200 years are now part of the Meghalayan Stage. Time since 4,200 years ago is in the Meghalayan Age. But there is a lot to unpack in these details.</p>
<h2>Splitting up the Holocene</h2>
<p>As of July 2018, the Holocene – the most recent epoch of time spanning from 11,700 years ago to the present – is divided into three ages: the Greenlandian, the Northgrippian and the Meghalayan. </p>
<p>Those first two are unusual because their type localities are not rocks. Instead, they’re layers of ice deep within the Greenland Ice Sheet. Both are defined by major, global-scale environmental change: warming in the case of the Greenlandian and ripple effects of melting ice sheets for the Northgrippian. </p>
<p>The Meghalayan, too, is unusual, and not just for its first-ever use of a stalagmite as the rock that defines the archetype. The global-scale climate change that defines the beginning of the Meghalayan coincides with a period of ongoing migration and collapse of many early human civilizations around the globe. For the first time, our stratigraphy has been defined at least in part by effects on human activities. </p>
<h2>What about the Anthropocene?</h2>
<p>Which brings us to the idea of an <a href="http://quaternary.stratigraphy.org/working-groups/anthropocene/">Anthropocene</a> – a proposed division of geologic time defined by signs of human activities in the geologic record. If human activities can be associated with divisions of geologic time – as was done for the Meghalayan – and we define geologic time based on various characteristics in rocks, then what to make of the inescapable imprint of human activities in the rock record?</p>
<p>There are good arguments to be made both <a href="https://doi.org/10.1177/2053019618784971">for and against</a> an Anthropocene.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/235704/original/file-20180910-123107-eoqe8p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/235704/original/file-20180910-123107-eoqe8p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/235704/original/file-20180910-123107-eoqe8p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=460&fit=crop&dpr=1 600w, https://images.theconversation.com/files/235704/original/file-20180910-123107-eoqe8p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=460&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/235704/original/file-20180910-123107-eoqe8p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=460&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/235704/original/file-20180910-123107-eoqe8p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=578&fit=crop&dpr=1 754w, https://images.theconversation.com/files/235704/original/file-20180910-123107-eoqe8p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=578&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/235704/original/file-20180910-123107-eoqe8p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=578&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Tiny microplastic particles are spreading across the environment, leaving a human signature in Earth’s stratigraphy.</span>
<span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/Microplastics/bc632653e02e4a56b5a222239d274cf2/2/0">AP Photo/Ted S. Warren</a></span>
</figcaption>
</figure>
<p>Human beings have clearly altered landscapes through deforestation, agriculture and industrialization, which among other things have accelerated <a href="http://www.waterencyclopedia.com/En-Ge/Erosion-and-Sedimentation.html">erosion and sediment accumulation</a>. Plastics are <a href="https://theconversation.com/far-more-microplastics-floating-in-oceans-than-thought-51974">accumulating in our oceans</a> and biosphere, leaving a global-scale marker of these synthetic materials in soils and sediments. People are causing <a href="https://theconversation.com/study-humans-causing-sixth-extinction-event-on-earth-43439">high extinction rates</a> and rapid changes in where species <a href="https://theconversation.com/can-climate-corridors-help-species-adapt-to-warming-world-61190">are found around the world</a>. And of course burning fossil fuels and human-induced climate change leave <a href="https://doi.org/10.1016/j.quaint.2014.11.045">signatures in sediment records</a> worldwide. </p>
<p>But to date, the International Commission on Stratigraphy has not approved the designation of an Anthropocene. One challenge is agreeing on when the Anthropocene should begin. While things such as plastics or carbon dioxide from fossil fuels are geologically recent, human impacts on landscapes, biodiversity and biogeography may extend back thousands of years. It is very hard to pinpoint the first moment in time when our species began to affect the Earth. </p>
<p>The new divisions of the Holocene also cut into the available time for an Anthropocene. The Meghalayan begins 4,200 years ago and continues to the present. Simply put, there is no time left over in the Holocene where we could put an Anthropocene. </p>
<p>For the Anthropocene to be included in the formal geologic time scale, stratigraphers will need to argue that its onset was global in scale, simultaneous around the world and significant in its imprint on the geologic record. </p>
<p>Or maybe these types of formal requirements no longer apply. As scientists recognize that humans are now part of stratigraphy, perhaps we need to rethink our criteria in a way that separates geologic time from human time.</p>
<hr>
<p><em>This article has been updated to correct the order of labeling in geologic time.</em></p><img src="https://counter.theconversation.com/content/101002/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Steve Petsch receives funding from National Science Foundation.</span></em></p>2018 brought the announcement of a new geologic age that covers the last 4,200 years. How do scientists divide up Earth’s timeline and what do these demarcations mean?Steve Petsch, Associate Professor of Geosciences, UMass AmherstLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1006312018-08-01T10:38:21Z2018-08-01T10:38:21ZParts of the Pacific Northwest’s Cascadia fault are more seismically active than others – imaging data suggests why<figure><img src="https://images.theconversation.com/files/229901/original/file-20180730-106514-1rqf4bf.jpg?ixlib=rb-1.1.0&rect=114%2C2%2C1652%2C1092&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">What's going on 150 kilometers below the Earth's surface?</span> <span class="attribution"><a class="source" href="https://www.goodfreephotos.com">Good Free Photos</a></span></figcaption></figure><p>The Pacific Northwest is known for many things – its beer, its music, its mythical large-footed creatures. Most people don’t associate it with earthquakes, but they should. It’s home to the <a href="http://discovermagazine.com/2012/extreme-earth/01-big-one-earthquake-could-devastate-pacific-northwest">Cascadia megathrust fault</a> that runs 600 miles from Northern California up to Vancouver Island in Canada, spanning several major metropolitan areas including Seattle and Portland, Oregon.</p>
<p>This geologic fault has been relatively quiet in recent memory. There haven’t been many widely felt quakes along the Cascadia megathrust, certainly nothing that would rival a catastrophic event like the 1989 <a href="https://earthquake.usgs.gov/earthquakes/events/1989lomaprieta/">Loma Prieta earthquake</a> along the active San Andreas in California. That doesn’t mean it will stay quiet, though. Scientists know it has the potential for large earthquakes – as big as <a href="https://www.newyorker.com/magazine/2015/07/20/the-really-big-one">magnitude 9</a>.</p>
<p>Geophysicists have known for over a decade that not all portions of the Cascadia megathrust fault behave the same. The northern and southern sections are much more seismically active than the central section – with frequent small earthquakes and ground deformations that residents don’t often notice. But why do these variations exist and what gives rise to them?</p>
<p><a href="https://scholar.google.com/citations?user=67KN5e4AAAAJ&hl=en&oi=ao">Our</a> <a href="https://scholar.google.com/citations?user=SXGw77gAAAAJ&hl=en&oi=sra">research</a> tries to answer these questions by <a href="https://doi.org/10.1029/2018GL078700">constructing images of what’s happening deep within the Earth</a>, more than 100 kilometers below the fault. We’ve identified regions that are rising up beneath these active sections which we think are leading to the observable differences along the Cascadia fault.</p>
<h2>Cascadia and the ‘Really Big One’</h2>
<p>The Cascadia <a href="https://www.livescience.com/43220-subduction-zone-definition.html">subduction zone</a> is a region where two tectonic plates are colliding. The <a href="https://americastectonics.weebly.com/juan-de-fuca-explorer-and-gorda-plates.html">Juan de Fuca</a>, a small oceanic plate, is being driven under the North American plate, atop which the continental U.S. sits.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/229912/original/file-20180731-102467-1oh0x8m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/229912/original/file-20180731-102467-1oh0x8m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/229912/original/file-20180731-102467-1oh0x8m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=363&fit=crop&dpr=1 600w, https://images.theconversation.com/files/229912/original/file-20180731-102467-1oh0x8m.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=363&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/229912/original/file-20180731-102467-1oh0x8m.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=363&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/229912/original/file-20180731-102467-1oh0x8m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=456&fit=crop&dpr=1 754w, https://images.theconversation.com/files/229912/original/file-20180731-102467-1oh0x8m.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=456&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/229912/original/file-20180731-102467-1oh0x8m.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=456&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Juan de Fuca plate meets the North American plate beneath the Cascadia fault.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Cascadia_earthquake_sources.png">USGS</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Subduction systems – where one tectonic plate slides over another – are capable of producing the world’s largest known earthquakes. A prime example is the <a href="https://www.livescience.com/39110-japan-2011-earthquake-tsunami-facts.html">2011 Tohoku earthquake</a> that rocked Japan.</p>
<p>Cascadia is seismically very quiet compared to other subduction zones – but it’s not completely inactive. Research indicates the fault ruptured in a <a href="https://www.opb.org/news/series/unprepared/jan-26-1700-how-scientists-know-when-the-last-big-earthquake-happened-here/">magnitude 9.0 event in 1700</a>. That’s roughly 30 times more powerful than the largest predicted San Andreas earthquake. Researchers suggest that we are within the roughly <a href="https://projects.oregonlive.com/maps/earthquakes/timeline">300- to 500-year window</a> during which <a href="https://www.newyorker.com/magazine/2015/07/20/the-really-big-one">another large Cascadia event may occur</a>.</p>
<p>Many smaller undamaging and unfelt events take place in northern and southern Cascadia every year. However, in central Cascadia, underlying most of Oregon, there is very little seismicity. Why would the same fault behave differently in different regions? </p>
<p>Over the last decade, scientists have made several additional observations that highlight variations along the fault.</p>
<p>One has to do with <a href="https://www.ldeo.columbia.edu/%7Edjs/aleut/info_for_public.html">plate locking</a>, which tells us where stress is accumulating along the fault. If the tectonic plates are locked – that is, really stuck together and unable to move past each other – stress builds. Eventually that stress can be released rapidly as an earthquake, with the magnitude depending on how large the patch of fault that ruptures is.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/229900/original/file-20180730-106521-cc0xx3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/229900/original/file-20180730-106521-cc0xx3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/229900/original/file-20180730-106521-cc0xx3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=769&fit=crop&dpr=1 600w, https://images.theconversation.com/files/229900/original/file-20180730-106521-cc0xx3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=769&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/229900/original/file-20180730-106521-cc0xx3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=769&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/229900/original/file-20180730-106521-cc0xx3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=966&fit=crop&dpr=1 754w, https://images.theconversation.com/files/229900/original/file-20180730-106521-cc0xx3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=966&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/229900/original/file-20180730-106521-cc0xx3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=966&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A GPS geosensor in Washington.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/File:EarthScope-geosensor.jpg">Bdelisle</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Geologists have recently been able to deploy <a href="https://www.unavco.org/projects/major-projects/pbo/pbo.html">hundreds of GPS</a> monitors across Cascadia to record the subtle ground deformations that result from the plates’ inability to slide past each other. Just like historic seismicity, plate locking is more common in the <a href="http://geodesygina.com/Cascadia.html">northern and southern parts of Cascadia</a>.</p>
<p>Geologists are also now able to observe difficult-to-detect seismic rumblings known as <a href="https://pnsn.org/tremor">tremor</a>. These events occur over the time span of several minutes up to weeks, taking much longer than a typical earthquake. They don’t cause large ground motions even though they can release significant amounts of energy. Researchers <a href="https://doi.org/10.1126/science.1084783">have only discovered</a> <a href="https://doi.org/10.1126/science.1060152">these signals</a> in the <a href="https://doi.org/10.1126/science.1070378">last 15 years</a>, but permanent seismic stations have helped build a robust catalog of events. Tremor, too, seems to be more concentrated along the <a href="https://doi.org/10.1130/G23740A.1">northern and southern parts</a> of the fault. </p>
<p>What would cause this situation, with the area beneath Oregon relatively less active by all these measures? To explain we had to look deep, over 100 kilometers below the surface, into the Earth’s mantle.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/229896/original/file-20180730-106524-1kc0lc8.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/229896/original/file-20180730-106524-1kc0lc8.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/229896/original/file-20180730-106524-1kc0lc8.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=588&fit=crop&dpr=1 600w, https://images.theconversation.com/files/229896/original/file-20180730-106524-1kc0lc8.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=588&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/229896/original/file-20180730-106524-1kc0lc8.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=588&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/229896/original/file-20180730-106524-1kc0lc8.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=738&fit=crop&dpr=1 754w, https://images.theconversation.com/files/229896/original/file-20180730-106524-1kc0lc8.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=738&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/229896/original/file-20180730-106524-1kc0lc8.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=738&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Green dots and blue triangles show locations of seismic monitoring stations.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.1029/2018GL078700">Bodmer et al., 2018, Geophysical Research Letters</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Imaging the Earth using distant quakes</h2>
<p>Physicians use electromagnetic waves to “see” internal structures like bones without needing to open up a human patient to view them directly. Geologists <a href="https://www.iris.edu/hq/inclass/animation/seismic_tomography_ct_scan_as_analogy">image the Earth</a> in much the same way. Instead of X-rays, we use seismic energy radiating out from distant magnitude 6.0-plus earthquakes to help us “see” features we physically just can’t get to. This energy travels like sound waves through the structures of the Earth. When rock is hotter or partially molten by even a tiny amount, seismic waves slow down. By measuring the arrival times of seismic waves, we create 3D images showing how fast or slow the seismic waves travel through specific parts of the Earth. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/229895/original/file-20180730-106499-xy3gha.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/229895/original/file-20180730-106499-xy3gha.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/229895/original/file-20180730-106499-xy3gha.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=557&fit=crop&dpr=1 600w, https://images.theconversation.com/files/229895/original/file-20180730-106499-xy3gha.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=557&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/229895/original/file-20180730-106499-xy3gha.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=557&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/229895/original/file-20180730-106499-xy3gha.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=699&fit=crop&dpr=1 754w, https://images.theconversation.com/files/229895/original/file-20180730-106499-xy3gha.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=699&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/229895/original/file-20180730-106499-xy3gha.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=699&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Ocean bottom seismometers waiting to be deployed during the Cascadia Inititive.</span>
<span class="attribution"><span class="source">Emilie Hooft</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>To see these signals, we need records from seismic monitoring stations. More sensors provide better resolution and a clearer image – but gathering more data can be problematic when half the area you’re interested in is underwater. To address this challenge, we were part of a team of scientists that deployed hundreds of seismometers on the ocean floor off the western U.S. over the span of four years, starting in 2011. This experiment, the <a href="https://cascadia.uoregon.edu/">Cascadia Initiative</a>, was the first ever to cover an entire tectonic plate with instruments at a spacing of roughly 50 kilometers.</p>
<p><a href="https://doi.org/10.1029/2018GL078700">What we found are two anomalous regions</a> beneath the fault where seismic waves travel slower than expected. These anomalies are large, about 150 kilometers in diameter, and show up beneath the northern and southern sections of the fault. Remember, that’s where researchers have already observed increased activity: the seismicity, locking, and tremor. Interestingly, the anomalies are not present beneath the central part of the fault, under Oregon, where we see a decrease in activity.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/229899/original/file-20180730-106505-ah3ah8.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/229899/original/file-20180730-106505-ah3ah8.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/229899/original/file-20180730-106505-ah3ah8.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=446&fit=crop&dpr=1 600w, https://images.theconversation.com/files/229899/original/file-20180730-106505-ah3ah8.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=446&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/229899/original/file-20180730-106505-ah3ah8.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=446&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/229899/original/file-20180730-106505-ah3ah8.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=561&fit=crop&dpr=1 754w, https://images.theconversation.com/files/229899/original/file-20180730-106505-ah3ah8.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=561&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/229899/original/file-20180730-106505-ah3ah8.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=561&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Regions where seismic waves moved more slowly, on average, are redder, while the areas where they moved more quickly are bluer. The slower anomalous areas 150 km beneath the Earth’s surface corresponded to where the colliding plates are more locked and where tremor is more common.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.1029/2018GL078700">Bodmer et al., 2018, Geophysical Research Letters</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>So what exactly are these anomalies?</p>
<p>The tectonic plates float on the Earth’s rocky mantle layer. Where the mantle is slowly rising over millions of years, the rock decompresses. Since it’s at such high temperatures, nearly 1500 degrees Celsius at 100 km depth, it can <a href="https://www.wired.com/2012/12/why-do-rocks-melt-volcano/">melt ever so slightly</a>.</p>
<p>These physical changes cause the anomalous regions to be more buoyant – melted hot rock is less dense than solid cooler rock. It’s this buoyancy that we believe is affecting how the fault above behaves. The hot, partially molten region pushes upwards on what’s above, similar to how a helium balloon might rise up against a sheet draped over it. We believe this increases the forces between the two plates, causing them to be more strongly coupled and thus more fully locked.</p>
<h2>A general prediction for where, but not when</h2>
<p>Our results provide new insights into how this subduction zone, and possibly others, behaves over geologic time frames of millions of years. Unfortunately our results can’t predict when the next large Cascadia megathrust earthquake will occur. This will require more research and dense active monitoring of the subduction zone, both onshore and offshore, using seismic and GPS-like stations to capture short-term phenomena. </p>
<p>Our work does suggest that a large event is more likely to start in either the northern or southern sections of the fault, where the plates are more fully locked, and gives a possible reason for why that may be the case.</p>
<p>It remains important for the public and policymakers to stay informed about the potential risk involved in <a href="https://www.seattletimes.com/seattle-news/science/californias-celeb-quake-expert-says-preventing-damage-is-key-to-quick-recovery/">cohabiting with a subduction zone fault</a> and to support programs such as <a href="https://earthquake.usgs.gov/research/earlywarning/">Earthquake Early Warning</a> that seek to expand our monitoring capabilities and mitigate loss in the event of a large rupture.</p><img src="https://counter.theconversation.com/content/100631/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Doug Toomey receives funding from National Science Foundation and the United States Geological Survey. </span></em></p><p class="fine-print"><em><span>Miles Bodmer does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>A new array of seismometers provides a glimpse of what’s happening deep beneath this geologic fault. New data help explain why the north and south of the region are more seismically active than the middle.Miles Bodmer, PhD Student in Earth Sciences, University of OregonDoug Toomey, Professor of Earth Sciences, University of OregonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/951202018-04-30T10:45:46Z2018-04-30T10:45:46ZNitrogen from rock could fuel more plant growth around the world – but not enough to prevent climate change<figure><img src="https://images.theconversation.com/files/216693/original/file-20180427-135840-jpltrz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Long's Peak framed by rock outcrop, Rocky Mountain National Park, Colorado.</span> <span class="attribution"><a class="source" href="https://flic.kr/p/f8hFh4">Roy Luck</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Nitrogen is one of the most important resources for people, ecosystems and the planet. It’s found in all sorts of essential molecules, including DNA, protein and cell walls. Life - and humanity - cannot exist without adequate access to this precious nutrient.</p>
<p>For many years, researchers believed that essentially all of the nitrogen in the world’s natural plants and soils originated from the atmosphere, where it makes up about <a href="https://climate.nasa.gov/news/2491/10-interesting-things-about-air/">78 percent</a> of the air we breathe. But in a recent <a href="http://dx.doi.org/10.1126/science.aan4399">study</a>, my colleagues <a href="https://scholar.google.com/citations?user=vOrVZHoAAAAJ&hl=en">Scott Morford</a>, <a href="http://dahlgrenlab.lawr.ucdavis.edu/">Randy Dahlgren</a> and I discovered that up to a quarter of the planet’s terrestrial nitrogen originates from weathering of bedrock.</p>
<p>As a <a href="https://www.bzhoulton.com/">global environmental scientist</a> who has been <a href="https://scholar.google.com/citations?user=iZIphU4AAAAJ&hl=en">studying</a> nitrogen, climate and ecosystems for over a decade, I found this result surprising. And it has big implications for people and the planet. If there is more nitrogen available in Earth’s system than scientists have thought, it could fuel extra photosynthesis by plants, increasing the rate at which they pull carbon pollution out of the atmosphere. </p>
<p>But this isn’t a solution to climate change, contrary to what some <a href="https://www.rushlimbaugh.com/daily/2018/04/11/climate-change-news-co2-much-less-impactful-anyone-knew/">prominent pundits</a> have contended. Rock weathering is no magic answer: It simply does not supply nitrogen fast enough to radically slow warming over the next 100 years.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/216682/original/file-20180427-135817-qewqaz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/216682/original/file-20180427-135817-qewqaz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/216682/original/file-20180427-135817-qewqaz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=389&fit=crop&dpr=1 600w, https://images.theconversation.com/files/216682/original/file-20180427-135817-qewqaz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=389&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/216682/original/file-20180427-135817-qewqaz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=389&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/216682/original/file-20180427-135817-qewqaz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=489&fit=crop&dpr=1 754w, https://images.theconversation.com/files/216682/original/file-20180427-135817-qewqaz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=489&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/216682/original/file-20180427-135817-qewqaz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=489&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Traditional view of the nitrogen cycle, including human contributions from fossil fuel combustion and use of synthetic nitrogen fertilizer.</span>
<span class="attribution"><a class="source" href="https://cpo.noaa.gov/Meet-the-Divisions/Earth-System-Science-and-Modeling/AC4/Improved-understanding-of-nitrogen-cycle">NOAA</a></span>
</figcaption>
</figure>
<h2>Calculating Earth’s nitrogen budget</h2>
<p>Geologists have long known that there’s a lot of nitrogen in rocks, but our study was the first to show that this nitrogen is released quickly enough to influence plant and soil nutrient cycling on a global scale. Nitrogen inputs are critical to maintaining ecosystems because they <a href="http://msue.anr.msu.edu/news/the_nitrogen_cycle_explaining_where_your_lost_nitrogen_is_going">lose a bit of nitrogen</a> every year. Rain washes it out of soil, and bacteria convert it to gaseous forms that escape to the atmosphere. Without ongoing access to new nitrogen sources, plants eventually <a href="http://www.pnas.org/content/110/31/12733.short">would stop growing</a> and pulling carbon dioxide out of the air. </p>
<p>Our study used several different techniques to show that rocks are an important component of the planet’s nitrogen cycle. In cases where weathering rates are high and sedimentary rocks contain a decent quantity of nitrogen, they actually provide more nitrogen than the atmosphere. We pulled together decades of data on where nitrogen exists - in the atmosphere, rocks, the ocean and Earth’s mantle (the rock between its crust and its core), and used this information to build a picture of the planet’s nitrogen budget. </p>
<p>This work revealed a critical role played by rock weathering. Many processes gradually break rocks down over time, including freezing and thawing, chemical reactions, and impacts of living organisms such as lichens and tree roots. Weathering releases nitrogen, replenishing nitrogen that continental erosion carries to the ocean over millions of years.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/216684/original/file-20180427-135851-nvasi6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/216684/original/file-20180427-135851-nvasi6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/216684/original/file-20180427-135851-nvasi6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/216684/original/file-20180427-135851-nvasi6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/216684/original/file-20180427-135851-nvasi6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/216684/original/file-20180427-135851-nvasi6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/216684/original/file-20180427-135851-nvasi6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/216684/original/file-20180427-135851-nvasi6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Sandstone weathering on the shore of Puget Sound, caused when expanding salt crystals break fragments of rock, creating small holes that become larger as the process repeats over time.</span>
<span class="attribution"><a class="source" href="https://www.usgs.gov/media/images/honeycomb-weathering-limestone-formations">Collin Smith/USGS</a></span>
</figcaption>
</figure>
<p>This initial finding was supported by a suite of classic geochemical models, evidence built from our global rock nitrogen inventory, and a new global computer model that we created for this study.</p>
<p>Until now researchers had assumed that the atmosphere was the <a href="http://www.physicalgeography.net/fundamentals/9s.html">main source of nitrogen</a> for Earth’s ecosystems. But they also had <a href="https://doi.org/10.1007/s100210000029">trouble</a> explaining how so much nitrogen accumulated in ecosystems if it came solely from the atmosphere.</p>
<p>We identified bedrock as the source of this “missing nitrogen” by showing that rock weathering could help to meet nitrogen demand from plants and animals. In mountainous regions and areas with moist climates, where rocks are exposed and tend to weather quickly, we estimate that rock weathering doubles the amount of nitrogen that enters natural ecosystems. </p>
<h2>Nourishing the carbon cycle</h2>
<p>What does this mean for the carbon cycle and global climate change? Several computer simulations have <a href="http://dx.doi.org/10.1126/science.1091390">shown</a> that nitrogen affects carbon storage in a way that could substantially alter the amount of global warming that occurs in this <a href="https://doi.org/10.1029/2009GL041009">century</a>. Our past <a href="http://dx.doi.org/10.1038/nature10415">work</a> showed that ecosystems living on nitrogen-rich bedrock contained twice as much carbon in their soils and trees as those on nitrogen-poor bedrock. The nitrogen in the rock was feeding the ecosystem, allowing plants to accumulate more biomass than sites without much rock nitrogen weathering. </p>
<p>But rock nitrogen has always been a part of the planet, even if we weren’t terribly mindful of it. Our study makes explicit a process that is already affecting the planet’s carbon cycle. And it helps explain how plants and soils have absorbed roughly 30 percent of carbon emissions from human activities, even though nutrient constraints on plant growth are <a href="https://doi.org/10.1111/j.1461-0248.2007.01113.x">widespread</a>. </p>
<p>Globally, ecosystems still derive more nitrogen from the air than from rocks. Nonetheless, our findings may help make global climate models more precise and resolve some puzzling observations at higher latitudes, which tend to hold more nitrogen in rocks. For example, boreal forest zones in northern Canada and Eurasia are storing carbon at a level higher than many scientists would have predicted, and are greening in response to climate change. We expect these regions may have high levels of nitrogen from rock weathering.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/Yi8SFOJffFA?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">NASA scientists used almost 30 years of data from the NASA/U.S. Geological Survey Landsat satellites to track changes in vegetation in Alaska and Canada. Of the more than 4 million square miles, 30 percent had increases in vegetation (greening) while only 3 percent had decreases (browning).</span></figcaption>
</figure>
<h2>Rock nitrogen won’t save us from climate change</h2>
<p><a href="https://climatefeedback.org/evaluation/investors-business-daily-editorial-misrepresents-study-to-claim-plants-will-prevent-dangerous-climate-change/">Some pundits</a> have argued that our work shows scientists don’t have a firm grasp of such issues as global climate change. This view is wrong. </p>
<p>Our study highlights a role for rocks in supplying nitrogen to terrestrial ecosystems. It challenges a paradigm that was established as far back as the late 1800s, but this doesn’t make us doubt the scientific process. Instead, we recognize that questions must always drive our thinking – for example, “I wonder whether rock nitrogen matters to the planet?” </p>
<p>Others have misinterpreted our work as evidence that the risk of extreme climate change has been overblown. For example, conservative commentator Rush Limbaugh <a href="https://www.rushlimbaugh.com/daily/2018/04/11/climate-change-news-co2-much-less-impactful-anyone-knew/">opined</a>, “It’s a scientific report that carbon dioxide, CO2, that which causes the greenhouse effect, is much, much, much less impactful than anybody knew.” </p>
<p>Wrong again. Our study said no such thing, and it does not imply that curbing global climate change is less urgent. Rock nitrogen can help fertilize the carbon cycle, but there is not enough of it to stop the rapid pace of global climate change. That will require aggressively cutting greenhouse gas emissions and creating technologies that can remove carbon from the atmosphere at a large scale over the next <a href="http://dx.doi.org/10.1126/science.aah3443">few decades</a>.</p>
<p>Climate models consistently show that nature will not save us. We have to save ourselves – although rocks may provide us with a bit more cushion than we previously knew.</p><img src="https://counter.theconversation.com/content/95120/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Benjamin Z. Houlton receives funding from the National Science Foundation.</span></em></p>Scientists have long thought most nitrogen in Earth’s ecosystems comes from the air, but new research shows it also is released as rocks weather. This could boost plant growth and help sequester carbon – but not fast enough to avert climate change, as some pundits have claimed.Benjamin Z. Houlton, Professor of Global Environmental Studies, Chancellor's Fellow and Director, John Muir Institute of the Environment, University of California, DavisLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/850122017-10-16T13:11:53Z2017-10-16T13:11:53ZHow we used the Earth’s magnetic field to date rocks rich in dinosaur fossils<figure><img src="https://images.theconversation.com/files/189742/original/file-20171011-16636-s6gmqy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Barkly Pass, the stratotype for the Elliot Formation. These beautiful rocks hold ancient secrets.</span> <span class="attribution"><span class="source">Lara Sciscio</span></span></figcaption></figure><p>Covering two thirds of South Africa the <a href="http://www.sciencedirect.com/science/article/pii/S1464343X05001184">Karoo Basin</a>, visually, is a beautiful space. When looking more deeply into its rock layers, like leafing through the pages of a book, one can read about a wealth of palaeoevinromental and biological processes. </p>
<p>The Karoo Basin is an invaluable archive of information over its 120 million year depositional history. Rich in fossils, both plants and animals, the Karoo Basin records crisis periods – mass extinction events – in the distant past when many species became extinct.</p>
<p>So far, there have been five main mass extinction events globally. The biggest, the <a href="http://science.nationalgeographic.com/science/prehistoric-world/permian-extinction/">end-Permian</a>, about 252 million years ago, was the Earth’s largest ecological disaster. The Karoo Basin also holds evidence of the third largest mass extinction. This occurred at the end of the Triassic, about 200 million years ago, and heralded the rise of the dinosaurs.</p>
<p>Understanding these climate change events and their impact on biology in the Karoo Basin could influence the way we look at the sixth extinction, which is happening now: the <a href="https://www.smithsonianmag.com/science-nature/what-is-the-anthropocene-and-are-we-in-it-164801414/">Anthropocene</a>. </p>
<p>Scientists need to know when the ancient extinctions happened and for how long. These events are recorded in layers of rock. So we need to know the age of those rocks. There are certain “geological clocks” which help when dating rocks: a mineral called zircon is one. Fossil pollen and spores are others. But when these are scarce, we need another way of measuring the age of rocks. And the Earth’s own magnetic field provides a useful source.</p>
<h2>A different technique</h2>
<p>My colleagues and I were interested in the age of a specific rock unit in the Karoo Basin: the <a href="http://sajg.geoscienceworld.org/content/118/3/311">Elliot Formation</a>. Rocks of the Elliot Formation outcrop in a ring around the Drakensberg Plateau (see figure). The Elliot Formation contains many fossils that shed light on the existence and evolution of dinosaurs in southern Africa. </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/190136/original/file-20171013-11722-9mss76.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/190136/original/file-20171013-11722-9mss76.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/190136/original/file-20171013-11722-9mss76.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1113&fit=crop&dpr=1 600w, https://images.theconversation.com/files/190136/original/file-20171013-11722-9mss76.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1113&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/190136/original/file-20171013-11722-9mss76.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1113&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/190136/original/file-20171013-11722-9mss76.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1399&fit=crop&dpr=1 754w, https://images.theconversation.com/files/190136/original/file-20171013-11722-9mss76.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1399&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/190136/original/file-20171013-11722-9mss76.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1399&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">Lara Sciscio</span></span>
</figcaption>
</figure>
<p>This is especially interesting as the Formation is thought to span the end-Triassic mass extinction event. However, the age of the Elliot Formation and where this extinction event occurred within its rock layers was debated. </p>
<p>As there are no radiometric dates from zircons for the Elliot Formation, we used the Earth’s ancient geomagnetic field as a dating tool. This technique has been used globally on <a href="https://www.news.uct.ac.za/article/-2017-09-01-geological-barcodes-a-unique-way-to-date-rocks">similar aged rocks</a>. Applying it here enabled us to narrow down the age of the Elliot Formation to somewhere between about 213 million and 195 million years old. </p>
<p>These dates may help us to answer broader questions relating to the severity of the end-Triassic mass extinction and the post-extinction recovery period in southern Africa. This time line is particularly useful in measuring the diversity of dinosaurs across the bio-crisis and during a critical time in their evolution.</p>
<h2>Magnetic flips</h2>
<p>The Earth generates and sustains a <a href="http://www.physics.org/article-questions.asp?id=64">magnetic field</a> through the motion of the liquid outer core. Some minerals in rocks are able to record the Earth’s magnetic field when they are deposited. Two such minerals, hematite and maghemite, are prevalent in the Elliot Formation. In fact, they lend the Formation a distinct brick-red colour. </p>
<p>Our research <a href="http://www.sciencedirect.com/science/article/pii/S1342937X16302593?via%3Dihub">has found</a> that minerals within the rocks of the Elliot Formation are able to retain primary magnetisations: they have reliably recorded the Earth’s magnetic field at the time of their deposition. That’s important because natural processes can cause “overprinting” – wiping out the original magnetic signature.</p>
<p>This method has been used within the Karoo Basin before on older rocks, but it’s never guaranteed that rocks will retain their primary magnetic signatures. The fact that the Elliot Formation, largely, didn’t fall prey to “overprinting” is what allowed us to record the pattern of the ancient magnetic field.</p>
<h2>Pole reversal offers timing tool</h2>
<p>The Earth’s magnetic field is not constant through time. It “flips” or “reverses” at irregular intervals; on average, every few million years.</p>
<p>When this happens, the magnetic north pole is direct to the geographic south pole and vice versa. Rocks contain alternating layers of north- and south-directed minerals corresponding to every “flip” event. This creates distinct geomagnetic polarity chron(s) – a name to define a specific unit of time during reversals – for any given time period. </p>
<p>By studying the rates and number of these reversals recorded in the Elliot Formation’s rocks, we are able to get a more accurate idea of the rocks’ age. </p>
<p>The next step in pinpointing the Elliot Formation’s relative age was to build its unique magnetic polarity time scale – a log of all the reversal events.</p>
<p>This involved drilling out small samples of rock, using a portable hand-held drill, and orientating them, using a special compass in the field. Thereafter samples were processed in the <a href="https://www.uj.ac.za/faculties/science/geology/Pages/Paleomag-lab.aspx">Paleomag Lab</a> at the University of Johannesburg to recover their unique geomagnetic polarity history. </p>
<p>By doing this, we could build a composite magnetic polarity chronology for the Elliot Formation. We were then able to compare these rocks from South Africa and neighbouring Lesotho to others of a similar time period globally. In so doing, the Elliot Formation records the Earth’s magnetic field as it was about 200 million years ago.</p>
<p>We are not the only ones trying to pin down this important rock unit’s age. We hope that our work will provide a framework on which to place other kinds of information produced by others in this and related fields.</p><img src="https://counter.theconversation.com/content/85012/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Lara Sciscio receives funding from DST-NRF Centre of Excellence in Palaeosciences (CoE in Palaeosciences). </span></em></p>The earth’s own magnetic field offers a useful way to measure the age of rocks - information that can help unpack ancient events and aid our understanding of the present.Lara Sciscio, Postdoctoral Research Fellow in Geological Sciences, University of Cape TownLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/641522016-12-09T02:07:57Z2016-12-09T02:07:57ZCatching lightning in a fossil – and calculating how much energy a strike contains<figure><img src="https://images.theconversation.com/files/149316/original/image-20161208-31402-vgl94l.jpg?ixlib=rb-1.1.0&rect=229%2C9%2C1634%2C1299&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Very powerful, try to avoid.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/rickywilson/2569675373">Rick Wilson</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>For most of human history, people have been terrified by lightning. <a href="http://www.sacred-texts.com/afr/fssn/fsn21.htm">Frightening bolts from above</a>, lightning was a <a href="http://lightningsafety.com/nlsi_info/myths.html">tool of the gods</a> to smite mortals for their hubris (or their unfortunate penchant for seeking shelter from storms under trees). The discovery and implementation of <a href="https://www.fi.edu/history-resources/franklins-lightning-rod">Benjamin Franklin’s lightning rod</a> tamed this once formidable, divine weapon.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/149318/original/image-20161208-31352-1m75vph.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/149318/original/image-20161208-31352-1m75vph.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/149318/original/image-20161208-31352-1m75vph.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=897&fit=crop&dpr=1 600w, https://images.theconversation.com/files/149318/original/image-20161208-31352-1m75vph.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=897&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/149318/original/image-20161208-31352-1m75vph.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=897&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/149318/original/image-20161208-31352-1m75vph.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1127&fit=crop&dpr=1 754w, https://images.theconversation.com/files/149318/original/image-20161208-31352-1m75vph.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1127&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/149318/original/image-20161208-31352-1m75vph.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1127&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Will a lightning bolt contain enough energy to blast Marty McFly through time?</span>
</figcaption>
</figure>
<p>Nonetheless, lightning’s strength still lingers in our imagination. Hollywood considers it powerful enough to allow strangely designed cars from the early 1980s to <a href="http://www.imdb.com/title/tt0088763/">break the space-time continuum</a>. In the comic book world, it’s an ingredient in the <a href="https://en.wikipedia.org/wiki/Flash_(Barry_Allen)">formula for developing superpowers</a>. It has also been given the power to <a href="https://en.wikipedia.org/wiki/Frankenstein%27s_monster">return life to the dead</a>, though not always with the intended effect.</p>
<p>Just how much energy actually is in a lightning bolt? It may seem like this question should have been definitively answered before, but it turns out it’s difficult to answer quantitatively. In my research, we <a href="http://doi.org/10.1038/srep30586">tackled this issue in a new way</a>: We deduced how big a bolt of lightning was based on the size of rocks formed by lightning.</p>
<h2>Rough estimates</h2>
<p>Lightning is obviously powerful: One need only look at a tree that it’s splintered down the center for proof. Lightning generates temperatures hotter than the surface of the sun, <a href="http://doi.org/10.1016/0021-9169(64)90113-8">in excess of 20,000 degrees Celsius</a>, a temperature that is otherwise unrelateable to the human experience.</p>
<p>This temperature measurement provides <a href="http://doi.org/10.1029/RG022i004p00363">one way to estimate the energy of lightning</a>. It takes a certain amount of energy to heat air to a high temperature. By measuring the length of a lightning strike, multiplying it by the energy per length required to heat up the air to tens of thousands of degrees, we can calculate lightning’s energy.</p>
<p>Alternatively, we can approach the measurement of lightning energy by considering the voltage of a strike. A volt is a measurement of the amount of energy released as each pack of electrons flows from one side of an object to another – for instance, a battery. When lightning strikes, we can determine the <a href="http://doi.org/10.1109/15.249398">voltage it induces on nearby powerlines</a>; measurements range from hundreds of thousands to millions of volts. From <a href="https://en.wikipedia.org/wiki/Ohm%27s_law">Ohm’s law</a>, we can calculate the power of lightning by multiplying this by the number of electrons that move during the strike, a value known as the current. If we know the duration of this strike, we can then calculate the energy.</p>
<p>These methods have a large range of errors: not calculating the length of the lightning strike correctly, or getting the amount of gas heated per length wrong, or the temperature, or voltage, or number of electrons – all give pretty large errors for these calculations. </p>
<p>Could there be another route to calculating lightning energy that might pare down some of these errors? Florida’s unique geology provided an interesting route to answering this question.</p>
<h2>Fossilized lightning</h2>
<p>Florida tends to be a fairly boring state for a rock enthusiast. There’s sand, and there’s limestone. Not much else, and all of it is young, geologically speaking. Sometimes the sand is on top of the limestone, and sometimes it’s on the side. Sometimes the sand was deposited 15 million years ago, sometimes 5 million years ago. There’s a lot of sand. </p>
<p>Florida’s weather is a bit more interesting; it’s actually the U.S. state <a href="http://www.vaisala.com/VaisalaImages/Lightning/avg_sd_2005-2014_CONUS_2km_grid.png">most often struck by lightning</a>. A lot of times this lightning strikes the sand that covers the state. When it does so, it creates a new type of rock, called a fulgurite – a hollow tube formed as the lightning travels through the sand, vaporizing it and melting its outer edges. When the sand cools down, which happens quickly, the hollow tube is frozen in glass, recording the path the lightning traveled. By definition, a fulgurite is a metamorphic rock, changed by heat and pressure, from sand to something new.</p>
<p>Fulgurites are generally rare, unless you know where to look. Central peninsular Florida hosts several sand mines that supply the raw material for roads and cement, golf courses and playgrounds. At one site, we collected several hundred fulgurites; more than 250 lay in the field, with many more found in spoil piles, filtered out of the sand prior to its being loaded onto trucks.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/149290/original/image-20161208-31383-kx7vxr.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/149290/original/image-20161208-31383-kx7vxr.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/149290/original/image-20161208-31383-kx7vxr.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/149290/original/image-20161208-31383-kx7vxr.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/149290/original/image-20161208-31383-kx7vxr.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/149290/original/image-20161208-31383-kx7vxr.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/149290/original/image-20161208-31383-kx7vxr.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/149290/original/image-20161208-31383-kx7vxr.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The sand mine in Polk County, Florida, from which the fulgurites were collected.</span>
<span class="attribution"><span class="source">Matthew Pasek</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>These sites are not really any different than any place else in Florida – they aren’t some sort of lightning magnet – but the geologic setting was just right for keeping them around for a long time. These sand mines probably have about one million year’s worth of fulgurites buried inside of them. They’re easy to find – since glass isn’t something you want in commercial sand, the mine filters them out.</p>
<p>The fulgurites range in thickness from about the size of a baby’s little finger to about the size of man’s arm in thickness. The thicker ones had to be formed by much more energetic lightning bolts: a thicker fulgurite means more sand had to be vaporized. Most fulgurites we recovered were short fragments, though the longest ones found were a yard or two long.</p>
<h2>Calculating from the fulgurites</h2>
<p>It takes a specific amount of energy to vaporize sand into gas. First the sand has to be heated to around 1700°C, about the temperature of molten lava. At this temperature, the sand melts. The molten sand then has to heat to just shy of 3000°C, when it vaporizes. It takes about 15 megajoules of energy to heat and vaporize a kilogram of sand. That’s about the amount of energy the average U.S. household consumes in six hours, or the kinetic energy an average car would have if it were going 300 miles per hour.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/149300/original/image-20161208-31385-xczm6h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/149300/original/image-20161208-31385-xczm6h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/149300/original/image-20161208-31385-xczm6h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/149300/original/image-20161208-31385-xczm6h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/149300/original/image-20161208-31385-xczm6h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/149300/original/image-20161208-31385-xczm6h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/149300/original/image-20161208-31385-xczm6h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/149300/original/image-20161208-31385-xczm6h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The largest fulgurite found during recovery at the sand mine.</span>
<span class="attribution"><span class="source">Matt Pasek</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>After measuring our fulgurites, we determined that on average, the energy required to form these rocks was at least about one megajoule per meter of fulgurite formed. We calculated the energy per meter since, again in most cases, the fulgurites we had collected were broken. </p>
<p>So based on our calculations, how close does Hollywood come, with estimates like in “Back to the Future” of 1.21 gigawatts of power in lightning? Power is energy per time, and our measurements of fulgurites suggest that megajoules of energy make rock in thousandths to millionths of seconds. So a gigawatt is actually on the low side – lightning power may be a thousand times that, reaching into the terawatts, though the average is probably tens of gigawatts.</p>
<p>That’s enough energy to power about a billion houses, albeit only for a few millionths of a second. Unfortunately, given its sporadic and unpredictable nature, no power grid will ever be able to harness lightning effectively. But with that much power, perhaps breaking the space-time continuum in a souped-up Delorean is not so unfeasible after all….</p>
<h2>An oddity in the pattern</h2>
<p>When we looked at these fulgurites in depth, something odd came out of the data. Our energy measurements followed something called a “lognormal” trend.</p>
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<p>Rather than following the bell curve we often see in the distribution of natural phenomena – like, for instance, the heights of American men – the energy curve was less equally balanced. For heights, the same number of men are two inches above average as are two inches below. But for lightning, the large lightning strikes were much larger than the average, while the smaller strikes were not so much smaller than the average. Strikes that were twice the average were as frequent as those that were half the average.</p>
<p>Now why might this be at all interesting or useful? Measuring the energy in lightning is a way of measuring potential damage: A lightning strike can vaporize rock, so what might it do to wood or electronics? Our measurements show that the biggest lightning strikes are multiples of the average lightning strikes: A big one might be 20 times as large as the average. That’s a lot for a <a href="https://en.wikipedia.org/wiki/Lightning_rod#Lightning_protection_system">lightning protection system</a> to handle. The peak energy calculated from our rock-based method may give an idea as to the maximum damage we may expect, and may eventually allow for better preparation against the worst-case scenario.</p><img src="https://counter.theconversation.com/content/64152/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Matthew Pasek receives funding from NASA Exobiology and Evolutionary Biology (Grant NNX14AN96G)</span></em></p>Lightning strikes are powerful – but we haven’t had solid estimates of their energy until now. Researchers turned to the hollow stone tubes they create by vaporizing sand for more precise calculations.Matthew Pasek, Associate Professor of Geosciences, University of South FloridaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/652342016-09-18T00:36:37Z2016-09-18T00:36:37ZHumans can make rockfalls from earthquakes more dangerous<p>Earthquakes (including the tsunamis they generate) are <a href="http://reliefweb.int/sites/reliefweb.int/files/resources/PAND_report.pdf">Earth’s most fatal natural hazard</a>, accounting for approximately 55% of the more than 1.35 million disaster deaths in the last two decades. The <a href="https://profile.usgs.gov/myscience/upload_folder/ci2013Feb2015013642954Holzer%20Savage%20Fatalities%20EQ%20Spectra%202013.pdf">US Geological Survey predicts</a> that more than 2.5 million people will die from earthquakes this century alone.</p>
<p>So anything that can be learnt from past earthquakes to reduce death tolls and damage is welcome. </p>
<p>Most fatalities and injuries in earthquakes result from damage and collapse of buildings, houses and other urban infrastructure exposed to strong seismic ground shaking.</p>
<p>The most lethal combinations occur when large populations with vulnerable infrastructure are exposed to strong and frequent earthquakes.</p>
<p>A poignant example of a disastrous convergence of these factors is the magnitude 7 earthquake near Port-au-Prince, in Haiti, in 2010. More than <a href="http://dx.doi.org/10.1080/13623699.2010.535279">150,000 are now thought to have died</a> from the earthquake or in the following six-week period due to injuries or illness.</p>
<p>Other examples of seismologically risky ticking time bombs include <a href="http://time.com/3838716/earthquake-risk-nepal/">Tehran and Istanbul</a>, where large fatalities are expected in future earthquakes.</p>
<h2>Deadly rockfalls</h2>
<p>Landslides and other mass movements, such as rockfalls, are another important cause of earthquake fatalities. In the <a href="http://blogs.agu.org/landslideblog/2013/05/12/the-wenchuan-earthquake-five-years-on/">magnitude 7.9 Wenchuan earthquake</a> in China in 2008, landslides caused more than 20,000 of the estimated 80,000 fatalities.</p>
<p>Landslides caused approximately 26,000 fatalities in the <a href="http://currents.plos.org/disasters/article/analysis-of-landslides-triggered-by-october-2005-kashmir-earthquake/">magnitude 7.6 Kashmir earthquake</a> in 2005.</p>
<p>Of the 185 fatalities in the <a href="http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=10708024">magnitude 6.3 earthquake at Christchurch</a> in New Zealand in 2011, five were caused by rocks that hit people after falling from steep basaltic bedrock cliffs. </p>
<p>In the aftermath of the Christchurch earthquakes, the annual <a href="http://dx.doi.org/10.1193/021413EQS026M">fatality risk posed by future rockfalls</a> was calculated by a team led by <a href="http://www.gns.cri.nz/">GNS Science</a> for individuals living in areas of Christchurch susceptible to mass movements. Some residents were estimated to have a greater than 1 in 1,000 annual chance of dying from future rockfalls. </p>
<p>Following the public release of maps and reports, a thorough process was undertaken to clarify the proposed land use planning boundaries considered in the <a href="http://www.chchplan.ihp.govt.nz/">Christchurch Replacement District Plan</a>. This included <a href="http://www.chchplan.ihp.govt.nz/wp-content/uploads/2015/03/IHP_Natural-Hazards-PART_180315.pdf">panel hearings</a>, that included experts and welcomed public submissions.</p>
<p>Important elements to consider in the context of future rockfall risk include the frequency of rockfalls and the maximum distance that rocks might travel if they are dislodged from a cliff.</p>
<p>Our <a href="http://advances.sciencemag.org/content/2/9/e1600969">new research</a>, when combined with <a href="http://www.drquigs.com/wp-content/uploads/2016/09/jqs_2895_RS.pdf">other recent studies</a> in this region, examines these elements in detail and provides some interesting results.</p>
<h2>Falling boulders</h2>
<p>We have been researching the Rapaki rockfall site, where hundreds of rocks fell and rolled downslope in the 2011 Christchurch earthquakes, since 2011.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/137871/original/image-20160915-4983-1iszs99.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/137871/original/image-20160915-4983-1iszs99.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/137871/original/image-20160915-4983-1iszs99.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=452&fit=crop&dpr=1 600w, https://images.theconversation.com/files/137871/original/image-20160915-4983-1iszs99.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=452&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/137871/original/image-20160915-4983-1iszs99.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=452&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/137871/original/image-20160915-4983-1iszs99.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=568&fit=crop&dpr=1 754w, https://images.theconversation.com/files/137871/original/image-20160915-4983-1iszs99.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=568&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/137871/original/image-20160915-4983-1iszs99.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=568&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Co-author Josh Borella taking the measure of a prehistoric boulder.</span>
<span class="attribution"><span class="source">Mark Quigley</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Two PhD students, one postdoctoral researcher, many domestic and international researchers and hundreds of undergraduate students have conducted research at the site. It is now one of the most extensively studied and analysed geologic sites in all of New Zealand. </p>
<p>Using field studies, laser scans, air photos and drones, we mapped more than 1,000 individual rocks that were present on this hillslope prior to the 2011 earthquakes. </p>
<p>We measured the distances of the 2011 and pre-2011 boulders from the source cliff to determine how far they travelled. The pre-2011 boulders appear on the oldest aerial photographs of the areas and local residents claim they have been on the hillslope as long as they can remember. </p>
<p>These prehistoric rocks are partially embedded in hillslope sediment and are weathered with lichen covered surfaces. They have the same volumetric characteristics and are comprised of the same rock types that fell in 2011.</p>
<p>Geochemical and geochronological <a href="http://www.drquigs.com/wp-content/uploads/2014/10/G36149.1.full_.pdf">studies of the prehistoric rocks and the sediments</a> within which they reside indicate the most recent severe rockfall event in the Rapaki area of Christchurch occurred many thousands of years ago. Our best estimate of this timing is 6,000 to 8,000 years before present.</p>
<p>But what was perhaps most intriguing was that a significant population of the modern boulders travelled further downslope (more than 150 metres) than their most travelled prehistoric counterparts.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/137872/original/image-20160915-4944-1agrux9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/137872/original/image-20160915-4944-1agrux9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/137872/original/image-20160915-4944-1agrux9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=462&fit=crop&dpr=1 600w, https://images.theconversation.com/files/137872/original/image-20160915-4944-1agrux9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=462&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/137872/original/image-20160915-4944-1agrux9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=462&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/137872/original/image-20160915-4944-1agrux9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=581&fit=crop&dpr=1 754w, https://images.theconversation.com/files/137872/original/image-20160915-4944-1agrux9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=581&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/137872/original/image-20160915-4944-1agrux9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=581&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A comparison of rockfall for both prehistoric and modern boulders.</span>
<span class="attribution"><span class="source">Josh Borella</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>We used numerical models to simulate the trajectories of modern boulders and compared these to the prehistoric ones. To get a better fit for the prehistoric boulder locations, we added vegetation to the hillslope in our models and re-ran them. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/137874/original/image-20160915-4936-n1bgn7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/137874/original/image-20160915-4936-n1bgn7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/137874/original/image-20160915-4936-n1bgn7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=420&fit=crop&dpr=1 600w, https://images.theconversation.com/files/137874/original/image-20160915-4936-n1bgn7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=420&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/137874/original/image-20160915-4936-n1bgn7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=420&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/137874/original/image-20160915-4936-n1bgn7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=528&fit=crop&dpr=1 754w, https://images.theconversation.com/files/137874/original/image-20160915-4936-n1bgn7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=528&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/137874/original/image-20160915-4936-n1bgn7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=528&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Modelling shows the location of simulated boulders when drag force attributed to native forest is applied correlates well with mapped prehistoric boulder distributions.</span>
<span class="attribution"><span class="source">Louise Vick</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Our hypothesis is that the prehistoric rockfall events occurred when self-regenerating native forest was present on the currently deforested grassy hillslope. The impacts of falling boulders with native bush and forest slowed boulder velocities and reduced their travel distance.</p>
<p>Our extensive studies at Rapaki including radiocarbon dating reveal evidence for 17th to 20th century burning and changes in hillslope erosion rates between the prehistoric and modern rockfall events.</p>
<p>Large scale deforestation of Banks Peninsula, beginning with Maori arrival in the area and continuing during European settlement, may have inadvertently increased rockfall hazard by removing the natural vegetative barrier that previously impeded boulder travel.</p>
<h2>Lessons to be learnt</h2>
<p>The Scottish geologist <a href="https://www.britannica.com/biography/James-Hutton">James Hutton</a> is often regarded as one of the founding fathers of geology. In his 1795 work, <a href="http://sacred-texts.com/earth/toe/index.htm">In Theory of the Earth</a>, he writes:</p>
<blockquote>
<p>In examining things present, we have data from which to reason with regard to what has been; and, from what has actually been, we have data for concluding with regard to that which is to happen thereafter.</p>
</blockquote>
<p>This idea was subsequently expanded upon by fellow Scot <a href="https://www.britannica.com/biography/Sir-Charles-Lyell-Baronet">Charles Lyell</a> in his <a href="http://www.esp.org/books/lyell/principles/facsimile/">Principles of Geology</a> (1830), and now underpins what is commonly referred to in science circles as the <a href="https://www.britannica.com/science/uniformitarianism">uniformitarianism</a> principle.</p>
<p>Put simply, if things have happened in the past then they can happen again in the future in much the same way and with the same impact.</p>
<p>In seismic hazard analysis, we often use geologic records of past earthquakes and their associated phenomena to predict the most likely characteristics of future events.</p>
<p>A lesson from our Christchurch example is that we need to consider any landscape changes made in an earthquake-prone area and how these might cause future events to deviate somewhat from those of the past. This includes those landscape changes made by humans.</p>
<p>On the plus side, our study provides evidence that native revegetation of some of the slopes most affected by severe rockfalls in Christchurch has the potential to reduce the travel distance of future rockfall events.</p>
<p>A variety of other approaches including land use changes, such as red zoning the riskiest areas, and engineering solutions may also reduce rockfall risk. </p>
<p>Some of these have been well implemented in Christchurch, such as scaling off loose boulders, caging and bolting susceptible rock outcrops and building barriers such as rock cages and walls. Non-native trees such as pines have also proved somewhat effective in reducing rockfall hazard.</p>
<p>Hopefully these lessons will travel well throughout New Zealand and the world, with an aim of reducing future fatalities and loss from rockfalls caused by earthquakes.</p><img src="https://counter.theconversation.com/content/65234/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mark Quigley receives funding from the New Zealand Earthquake Commission.</span></em></p><p class="fine-print"><em><span>Josh Borella receives funding from the New Zealand Earthquake Commission.</span></em></p>A new study of the 2011 Christchurch earthquake shows boulders from rockfalls fell much further than in earlier quakes that happened before humans arrived and changed the landscape.Mark Quigley, Associate professor, The University of MelbourneJosh Borella, PhD candidate in geology, University of CanterburyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/539172016-03-04T11:17:24Z2016-03-04T11:17:24ZHow we used a century of data to create a modern, digital geologic map of Alaska<figure><img src="https://images.theconversation.com/files/113756/original/image-20160303-9486-14d0nj9.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The biggest state has a brand new map.</span> <span class="attribution"><span class="source">Geologic Map of Alaska</span></span></figcaption></figure><p>Since <a href="http://www.simonwinchester.com/map">William Smith’s publication</a> of the first geologic map of England in 1815, geologists have used maps to show the distribution and character of rocks at the Earth’s surface, and display their interpretations of the underlying geology. These maps help guide exploration for natural resources and help users understand natural hazards and ecosystems.</p>
<p>When my colleagues and I began working on a new geologic map of Alaska in the late 1990s, we decided to structure it quite differently from the previous version, published back in 1980. This time around, we’d tap into Geographic Information Systems (GIS) technology. Though what we recently released is called the <a href="http://dx.doi.org/10.3133/sim3340">Geologic Map of Alaska</a>, it’s really a database from which many different maps can be created. </p>
<p>The advent of digital methods has revolutionized mapping. Printed maps are limited in how much they can show before the amount of detail obscures meaning. They’re also restricted to a single view of the information. Digital maps can store and display a variety of information, allowing users to focus on the characteristics of interest. Using GIS and digital data, many different maps can be created and displayed, allowing users of our new Alaska database to choose which aspects to display.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/113622/original/image-20160302-25881-1xc2g61.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/113622/original/image-20160302-25881-1xc2g61.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/113622/original/image-20160302-25881-1xc2g61.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=487&fit=crop&dpr=1 600w, https://images.theconversation.com/files/113622/original/image-20160302-25881-1xc2g61.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=487&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/113622/original/image-20160302-25881-1xc2g61.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=487&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/113622/original/image-20160302-25881-1xc2g61.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=612&fit=crop&dpr=1 754w, https://images.theconversation.com/files/113622/original/image-20160302-25881-1xc2g61.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=612&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/113622/original/image-20160302-25881-1xc2g61.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=612&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A U.S. Geological Survey party in the moraines of the Malaspina Glacier in Alaska, circa 1890.</span>
<span class="attribution"><a class="source" href="http://library.usgs.gov/photo/#/item/51ddacc4e4b0f72b4471ee15">U.S. Geological Survey</a></span>
</figcaption>
</figure>
<h2>New compilation of more than a century of data</h2>
<p>The United States is divided into quadrangles for mapping purposes; in Alaska, each measures one degree of latitude by two or three degrees of longitude – about 70 by 100 miles. Alaska is composed of 153 of these quadrangles. We started compiling a database and digitizing 1:250,000-scale quadrangle geologic maps, for which about two-thirds of the 153 quadrangles had been published. Many of these geologic maps had been completed after release of the 1980 map. We also found unpublished compilations for some additional quadrangles. </p>
<p>Then we added data from other available sources – maps published at other scales, journal articles, original field notes, aerial photos, Google Earth and new fieldwork. We scoured any sources we could think of that might have geological data about Alaska for inclusion in our new map, even going back to some of the Russian writings from prior to the <a href="https://history.state.gov/milestones/1866-1898/alaska-purchase">Alaska purchase in 1867</a>.</p>
<p>Having worked in Alaska for many years, I understand how little we know about the geology of Alaska compared to the conterminous U.S., due to factors including its vast size, its low population and limited infrastructure, and the complexity of its geology. Yet I was surprised how much we <em>do</em> know, just hidden away in forgotten or obscure documents.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/113759/original/image-20160303-9507-3499ug.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/113759/original/image-20160303-9507-3499ug.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/113759/original/image-20160303-9507-3499ug.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=776&fit=crop&dpr=1 600w, https://images.theconversation.com/files/113759/original/image-20160303-9507-3499ug.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=776&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/113759/original/image-20160303-9507-3499ug.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=776&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/113759/original/image-20160303-9507-3499ug.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=976&fit=crop&dpr=1 754w, https://images.theconversation.com/files/113759/original/image-20160303-9507-3499ug.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=976&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/113759/original/image-20160303-9507-3499ug.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=976&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The back cover of the new Geologic Map of Alaska’s pamphlet gives a sense of some of the earlier maps it’s updating.</span>
<span class="attribution"><span class="source">U.S. Geological Survey</span></span>
</figcaption>
</figure>
<p>Our sources span more than 100 years of data collection by a large number of geologists, each with a particular perspective. Many of the early geologic expeditions were limited in what they could see as they traveled; in general, there was no going back if you saw something today that made you want to take another look at something you saw two days ago. Often early expeditions were also producing the topographic maps as they went.</p>
<p>Each geologist was influenced by personal experience and the paradigms of the time. Prior to the advent of radioactive dating techniques, determining the age of rock units was dependent on finding fossils and understanding the geologic structures and stratigraphy. For instance, Father Hubbard, the “<a href="http://www.marywood.edu/archives/archival-exhibits/father-bernard-hubbard.html">Glacier Priest</a>,” <a href="https://books.google.com/books?q=editions:OCLC560491739&id=w7ygnQEACAAJ">studied the geology along the Alaska Peninsula</a> in the 1930s. Noting the coal beds, he thought the chain of volcanoes along the peninsula were due to the burning of coal deep underground. The advent of plate tectonic theory explains the volcanoes as a result of subduction and fits them into larger framework. While the presence of the volcanoes hasn’t changed, how we explain them has. I had to try to get into each geologist’s head, to attempt to understand what they saw and how the clues in the data they collected in the past could be interpreted within a modern plate tectonic paradigm.</p>
<p>Other challenges included determining precise locations from hand-drawn or reconnaissance maps. These early maps might not have complete contour lines; one map area I worked on had some mountains in the wrong spots and others were even missing. Essentially sketches, they were the best that could be done at the time.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/113791/original/image-20160303-13754-qseibx.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/113791/original/image-20160303-13754-qseibx.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/113791/original/image-20160303-13754-qseibx.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=553&fit=crop&dpr=1 600w, https://images.theconversation.com/files/113791/original/image-20160303-13754-qseibx.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=553&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/113791/original/image-20160303-13754-qseibx.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=553&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/113791/original/image-20160303-13754-qseibx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=695&fit=crop&dpr=1 754w, https://images.theconversation.com/files/113791/original/image-20160303-13754-qseibx.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=695&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/113791/original/image-20160303-13754-qseibx.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=695&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A 1959 map of the Ruby quadrangle that served as source material for the new map.</span>
<span class="attribution"><span class="source">U.S. Geological Survey</span></span>
</figcaption>
</figure>
<p>We also had to deal with reconciling the many different styles of geologic maps produced over the decades, along with poorly registered illustrations and lack of sample location information in published literature. For example, an early map of the Ruby quadrangle in west central Alaska was based on a crude, exploratory-quality topographic map; we had to redraw it, trying to more accurately locate geologic features, before we could digitize it.</p>
<p>Based on local geology, we compiled over 15,000 map units from the source maps. Each map unit was defined by distinctive rock units, using characteristics such as age, rock type and environment of formation – beach deposit versus deep ocean, for instance, or lava flow versus granite. By grouping similar map units together, we were able to reduce these to 1,350 unique map units. Further reduction resulted in about 450 map units for the detailed digital release and a generalized 220 units for the eventual print version. The resulting map divides the state along geologic characteristics rather than divided into units based on longitude and latitude.</p>
<p>The published digital map allows the user to zoom from the generalized version to the detailed version. The associated database contains more than a dozen interrelated tables that make this release special; and unlike previous print-only releases, the database is designed to be updated.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/113783/original/image-20160303-9490-rnpqv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/113783/original/image-20160303-9490-rnpqv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/113783/original/image-20160303-9490-rnpqv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/113783/original/image-20160303-9490-rnpqv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/113783/original/image-20160303-9490-rnpqv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/113783/original/image-20160303-9490-rnpqv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/113783/original/image-20160303-9490-rnpqv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/113783/original/image-20160303-9490-rnpqv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Warren Coonrad of the USGS working in southwest Alaska in 1975.</span>
<span class="attribution"><span class="source">U.S. Geological Survey</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Though I drove the effort, I stood on the shoulders of giants. Current USGS staff and volunteers and nearly a dozen retired USGS staff (Emeritus) contributed to the effort. Digital support came from many, as we had to capture data, design the spatial databases and package the data for release.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/113788/original/image-20160303-9463-1vo02bz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/113788/original/image-20160303-9463-1vo02bz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/113788/original/image-20160303-9463-1vo02bz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=468&fit=crop&dpr=1 600w, https://images.theconversation.com/files/113788/original/image-20160303-9463-1vo02bz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=468&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/113788/original/image-20160303-9463-1vo02bz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=468&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/113788/original/image-20160303-9463-1vo02bz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=588&fit=crop&dpr=1 754w, https://images.theconversation.com/files/113788/original/image-20160303-9463-1vo02bz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=588&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/113788/original/image-20160303-9463-1vo02bz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=588&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Anchorage area, in the new map.</span>
<span class="attribution"><span class="source">Geologic Map of Alaska</span></span>
</figcaption>
</figure>
<h2>A geologic map for the 21st century</h2>
<p>Previous generations commonly used hand-drawn overlays to display different types of map data. To discover relationships between data types, geologists had to mentally visualize these relationships or draw new maps.</p>
<p>Today, with GIS, this process can be computer-aided. Choosing the data to display, GIS-capable users can generate derivative maps, or query the map and database for a variety of characteristics. GIS allows the user to explore relationships between data sets, test theories and otherwise use this geologic database of Alaska as an analysis tool. Users can incorporate additional data – for example, geochemical analyses – to characterize geologic units. Alternatively, a user could compare plant distributions with underlying geology to evaluate potential relationships.</p>
<p>The map and database are analogous to a map that shows the roads, but not the route. It doesn’t tell you which path to take until you figure out where you’re going. Like a spreadsheet, this map allows the user to ask questions.</p>
<p>As designed, the map is intended for a wide audience, from Alaska Native Corporations and land management agencies to academic institutions and mining and energy companies. This map provides a broad overview, as well as detailed information, which enhance a user’s ability to search for patterns and trends otherwise not apparent, and its digital form aids users in incorporating other data sets.</p><img src="https://counter.theconversation.com/content/53917/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Frederic Wilson receives funding from the U.S. Geological Survey and the National Park Service. He is a Fellow of the Geological Society of America and a member of the Alaska Geological Society</span></em></p>On printed maps, piling on the detail risks obscuring the meaning. This new digital map is really more of a database from which users can create different versions that match their own interests.Frederic Wilson, Research Geologist, US Geological SurveyLicensed as Creative Commons – attribution, no derivatives.