tag:theconversation.com,2011:/us/topics/geochemistry-2691/articlesGeochemistry – The Conversation2023-03-23T19:06:07Ztag:theconversation.com,2011:article/2023342023-03-23T19:06:07Z2023-03-23T19:06:07ZA new study on Australian volcanoes has changed what we know about explosive ‘hotspot’ volcanism<figure><img src="https://images.theconversation.com/files/517090/original/file-20230323-22-f6yeod.jpg?ixlib=rb-1.1.0&rect=116%2C59%2C2166%2C1313&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Warrumbungle national park.</span> <span class="attribution"><span class="source">colinslack/Shutterstock</span></span></figcaption></figure><p>Our new study published in <a href="https://www.nature.com/articles/s41561-023-01156-9">Nature Geoscience</a> on an ancient chain of Australian volcanoes is helping to change our understanding of “hotspot” volcanism. </p>
<p>You may be surprised to learn eastern Australia hosts the <a href="https://www.nature.com/articles/nature14903">longest chain of continental hotspot volcanoes</a> on Earth. These volcanoes erupted during the last 35 million years (for 1 to 7 million years each), as the Australian continent moved over an area of heat (a hotspot) inside the planet, also known as a fixed heat anomaly or mantle plume.</p>
<p>But it appears <a href="https://www.tandfonline.com/doi/abs/10.1080/08120099.2015.997796?journalCode=taje20">the Australian hotspot waned with time</a>. And we have found the volcanoes’ inner structure and eruptions changed as a result. Our new findings show hotspot strength has key impacts on the evolution of volcanoes’ inner structure, along with their location and lifespan.</p>
<h2>Hotspots change Earth’s surface</h2>
<p>Hotspot volcanoes can produce very large volumes of lava and have an important role in Earth’s evolution and atmosphere. Today, famously active hotspot volcanoes include the Hawaiian volcanoes in the Pacific Ocean and the Canary Islands in the Atlantic Ocean. These are known as <a href="https://theconversation.com/there-she-blows-the-internal-magma-filter-that-prompts-ocean-island-volcanoes-to-erupt-167358">ocean island volcanoes</a>. </p>
<p>The Australian hotspot chain provides a continental perspective and covers the life cycle of a hotspot – a unique opportunity to better understand how hotspot volcanoes work, why they erupt, and how they evolve with time.</p>
<p>We found the strength of the hotspot and magma supply controls the duration, make-up and explosiveness of volcanoes at the surface. Around 35 to 27 million years ago, the early Australian hotspot was strong and generated enormous, long-lasting volcanoes across Queensland where magma (molten rock) took a direct route to the surface.</p>
<p>In contrast, the more recent (20 to 6 million years ago) New South Wales volcanoes are smaller and had shorter lifetimes, suggesting the hotspot lost strength with time. Interestingly, reduced supply made the magma’s journey to the surface more complicated, with many stops (magma chambers) and more explosive eruptions.</p>
<p>The tipping point occurred at the stunning <a href="https://en.wikipedia.org/wiki/Tweed_Volcano">Tweed</a>-Wollumbin (<a href="https://en.wikipedia.org/wiki/Mount_Warning">Mount Warning</a>) volcanic landscape, which formed 21–24 million years ago at today’s border between Queensland and New South Wales.</p>
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<a href="https://images.theconversation.com/files/517087/original/file-20230323-22-b5ui1s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A green valley with a lake in the distance and several jagged mountain peaks jutting into the sky" src="https://images.theconversation.com/files/517087/original/file-20230323-22-b5ui1s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/517087/original/file-20230323-22-b5ui1s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/517087/original/file-20230323-22-b5ui1s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/517087/original/file-20230323-22-b5ui1s.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/517087/original/file-20230323-22-b5ui1s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/517087/original/file-20230323-22-b5ui1s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/517087/original/file-20230323-22-b5ui1s.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>
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<span class="caption">A view of the volcanic Tweed Valley with Wollumbin (Mount Warning) in the foreground.</span>
<span class="attribution"><span class="source">Jiri Viehmann/Shutterstock</span></span>
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<h2>The secret journey of magma</h2>
<p>To discover the journey of magma inside the volcano, and the stops it made on its way to eruption, we analysed <a href="https://theconversation.com/volcano-crystals-could-make-it-easier-to-predict-eruptions-90558">volcanic crystals</a>. These are the little heroes that make it all the way to the surface. Mainly composed of silicate minerals like <a href="https://www.minerals.net/mineral/olivine.aspx">olivine</a>, <a href="https://www.mindat.org/min-9767.html">pyroxene</a> and <a href="https://en.wikipedia.org/wiki/Plagioclase#:%7E:text=Plagioclase%20is%20the%20primary%20aluminium,is%20the%20first%20to%20crystallize.">plagioclase</a>, the crystals grow in the guts of the volcano at high temperature, and register what happens before eruptions start. </p>
<p>These crystals are quite simple in northern volcanoes like <a href="https://www.sciencedirect.com/science/article/pii/S0024493718300136">Buckland</a> in Queensland, which means they travel through few, simple magma chambers. In contrast, the crystals become very complex in southern volcanoes like <a href="https://academic.oup.com/petrology/article/63/3/egac015/6535683">Nandewar</a> and <a href="https://academic.oup.com/petrology/article/59/6/1035/5033659">Warrumbungle</a> in New South Wales, which means they had a complicated journey through lots of busy magma chambers – lots of stops. </p>
<p>Importantly, when magma stops in a chamber, it cools down and becomes more viscous and difficult to erupt – a bit like cold toothpaste, instead of hot coffee. This thick, lazy magma may need new, hotter magma (caffeinated!) to come and push it to erupt.</p>
<p>If that happens, the gases trapped in the colder magma may not be able to escape, since the magma is so thick. This results in a pressure buildup, eventually exploding like a shaken bottle of fizzy drink – an explosive volcanic eruption.</p>
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Read more:
<a href="https://theconversation.com/volcano-crystals-could-make-it-easier-to-predict-eruptions-90558">Volcano crystals could make it easier to predict eruptions</a>
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<h2>A special clock</h2>
<p>The cold and hardened lava flows we see in the form of volcanic rocks contain a special clock – radioactive chemical elements have slowly broken down into stable daughter products that accumulate and increase in concentration as time passes.</p>
<p>The beauty of this process is that we know how fast it occurs. By measuring the ratio of the radioactive element and its stable daughter product we can calculate the age of a volcanic rock. By measuring the age of each lava flow from the bottom to the top of the volcano, we can measure its lifetime. </p>
<p>Our study shows the relevance of Australian volcanoes, even if mostly extinct, in better understanding eruptions that have shaped the evolution of our planet. We demonstrate the fundamental role of hotspot strength and magma supply on Earth’s landscape, as well as the eruption styles and lifetimes of volcanoes.</p>
<p>This breakthrough makes it possible to visualise the inner structure of hotspot volcanoes, and their evolution, uniquely easily accessible in the ancient, exposed Australian landscape.</p>
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Read more:
<a href="https://theconversation.com/scientists-just-revealed-the-most-detailed-geological-model-of-earths-past-100-million-years-200898">Scientists just revealed the most detailed geological model of Earth's past 100 million years</a>
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<img src="https://counter.theconversation.com/content/202334/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Al-Tamini Tapu received RTP PhD Scholarship from UQ.</span></em></p><p class="fine-print"><em><span>Paulo Vasconcelos received ARC Equipment grant to construct the UQ AGES lab. </span></em></p><p class="fine-print"><em><span>Teresa Ubide received funding from the ARC, UQ and AuScope-NCRIS</span></em></p>As continents grind across ‘hotspots’ in Earth’s mantle, we can get volcanoes erupting on the surface. Studying these can reveal much about our planet’s evolution.Al-Tamini Tapu, Geoscientist, The University of QueenslandPaulo Vasconcelos, Professor, The University of QueenslandTeresa Ubide, Associate Professor - Igneous Petrology/Volcanology, The University of QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2017842023-03-16T01:58:55Z2023-03-16T01:58:55ZWe used to think diamonds were everywhere. New research suggests they’ve always been rare<figure><img src="https://images.theconversation.com/files/515344/original/file-20230314-4604-sz23ty.JPG?ixlib=rb-1.1.0&rect=13%2C6%2C2195%2C1642&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Kimberlite volcanic rock with mantle crystals (green olivine and purple and orange garnet) and fragments of country rock (light grey).</span> <span class="attribution"><span class="license">Author provided</span></span></figcaption></figure><p>New research is shedding light on the tumultuous processes that give rise to diamonds, by homing in on a distinct purple companion found alongside them.</p>
<p>Diamonds are highly prized for their qualities but also for their rarity. One way to look for them is to search for associated minerals that occur more commonly, such as the chromium-rich pyrope garnet.</p>
<p>This vibrant purple garnet is easily found by diamond exploration companies, in sediment downstream from potentially diamond-bearing volcanic pipes, and within the pipes themselves. The presence of purple garnet is an indicator diamonds may also be present.</p>
<p>Moreover, this garnet isn’t just found near diamonds, but is also consistently found inside them. So by enhancing our understanding of pyrope garnet, and how it forms, we can also enhance our understanding of diamond formation. </p>
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Read more:
<a href="https://theconversation.com/perfectly-imperfect-the-discovery-of-the-second-largest-pink-diamond-has-left-the-world-in-awe-what-gives-diamonds-their-colour-187852">Perfectly imperfect: the discovery of the second-largest pink diamond has left the world in awe. What gives diamonds their colour?</a>
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<p>It was <a href="https://www.sciencedirect.com/science/article/abs/pii/S0024493704001331">previously thought</a> this type of garnet could not form very deep in the Earth. The theory went that it originated from a different chromium-rich mineral, called spinel, which formed at a shallow depth in the mantle and was then pushed down where temperatures and pressures were higher – leading to the garnet’s formation. </p>
<p>Our latest research, <a href="https://www.nature.com/articles/s41586-022-05665-2">published today</a> in Nature, uses a new model to revisit an old theory that suggests these pyrope garnets are actually formed much deeper in the mantle, about 100km-250km below the present surface. It also suggests diamonds may be rarer than we think.</p>
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<a href="https://images.theconversation.com/files/515665/original/file-20230316-20-allg6u.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A bright purple pyrope garnet against a great background." src="https://images.theconversation.com/files/515665/original/file-20230316-20-allg6u.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/515665/original/file-20230316-20-allg6u.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=444&fit=crop&dpr=1 600w, https://images.theconversation.com/files/515665/original/file-20230316-20-allg6u.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=444&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/515665/original/file-20230316-20-allg6u.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=444&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/515665/original/file-20230316-20-allg6u.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=558&fit=crop&dpr=1 754w, https://images.theconversation.com/files/515665/original/file-20230316-20-allg6u.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=558&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/515665/original/file-20230316-20-allg6u.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=558&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">Pyrope garnets range in colour from lilac to violet. Their colour reflects high metal chromium content.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
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<h2>How diamonds and pyrope garnet form</h2>
<p>Diamond is the crystalline form of elemental carbon, stable at very high pressures and relatively low temperatures – accidentally brought to the surface through powerful volcanic eruptions. </p>
<p>The necessary conditions to form diamond at great depth in the Earth’s mantle are only met in a few places. The geographic distribution of diamond is very uneven, with notable concentrations in southern Africa, the Congo, Tanzania, Canada, Siberia and Brazil. All of these places are characterised by ancient continental crust between 2.5 and 3.5 billion years old.</p>
<p>This crust is underlain by deep solid “roots” – like the keel of an iceberg – made of mantle which has become highly chemically depleted through intense melting over time. </p>
<p>It’s here in this depleted mantle, which extends as deep as 250km into the hotter, stirring mantle below it, that diamonds have the best opportunity to form. So what about their chromium-rich companions?</p>
<p>Using a thermodynamic computer model, we were able to demonstrate that pyrope garnets can form very deep in the Earth, at the same depths as diamonds. Specifically, these garnets would have formed during intense heating events with extreme pressures and temperatures in excess of 1,800°C.</p>
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<strong>
Read more:
<a href="https://theconversation.com/more-than-just-a-sparkling-gem-what-you-didnt-know-about-diamonds-101115">More than just a sparkling gem: what you didn't know about diamonds</a>
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<h2>How the continents grew their roots</h2>
<p>Although this is a very exciting finding in itself, what makes it more relevant is that it informs two other significant theories. </p>
<p>The first relates to why the continents formed the way they did – a point experts have long speculated about. </p>
<p>As mentioned above, pyrope garnets formed in extreme heat upwellings coming from great depths. Our findings suggest these upwellings then melted the upper mantle into place, forming the stable base of the continents. </p>
<p>In other words, the “roots” which help continents remain stable for billions of years are leftovers from the same mantle melting events that produced pyrope garnets.</p>
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<strong>
Read more:
<a href="https://theconversation.com/land-ahoy-study-shows-the-first-continents-bobbed-to-the-surface-more-than-3-billion-years-ago-171391">Land ahoy: study shows the first continents bobbed to the surface more than 3 billion years ago</a>
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<h2>Diamond rarity</h2>
<p>The second major inference relates to the rarity of diamonds.</p>
<p>Some <a href="https://www.sciencedirect.com/science/article/abs/pii/S0012821X98000648">researchers believe</a> diamonds were not originally rare, but that many were destroyed as the mantle root was eroded and modified due to continental plates moving over the globe. Our model offers the alternative perspective that diamonds may have actually always been rare.</p>
<p>How can we evaluate whether the necessary cradles of diamond – bits of highly depleted mantle in the continental roots – were once common and became rare over time, or whether they have always been rare? </p>
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<a href="https://images.theconversation.com/files/515667/original/file-20230316-14-gmme4l.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/515667/original/file-20230316-14-gmme4l.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/515667/original/file-20230316-14-gmme4l.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=275&fit=crop&dpr=1 600w, https://images.theconversation.com/files/515667/original/file-20230316-14-gmme4l.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=275&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/515667/original/file-20230316-14-gmme4l.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=275&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/515667/original/file-20230316-14-gmme4l.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=346&fit=crop&dpr=1 754w, https://images.theconversation.com/files/515667/original/file-20230316-14-gmme4l.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=346&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/515667/original/file-20230316-14-gmme4l.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=346&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 kaleidoscopic image is a diamond cradle rock under a microscope. In this view, the garnet is the black mineral.</span>
<span class="attribution"><span class="license">Author provided</span></span>
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<p>When intense melting events happened on the early Earth, the melts themselves erupted at the continental surface as very fluid lavas called “komatiites”. These lavas are preserved and are widely analysed. They have varying compositions, and our model predicts which of these could have formed alongside chromium-rich pyrope garnet. </p>
<p>We know from tens of thousands of chemical analyses of komatiite, that the particular composition associated with this pyrope garnet is very rare. That’s because in order for it to form, magma must interact with exceptionally depleted mantle that has gone through many melting events. Only between 8%-28% of komatiite fits this bill.</p>
<p>From this, we can infer that both the pyrope garnets, and the very depleted mantle domains they come from, have always been rare – even back on the early Earth. And because diamonds have an affinity for these particular rocks, they too must have always been rare – making them all the more remarkable.</p><img src="https://counter.theconversation.com/content/201784/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Carl Walsh holds a QUT postgraduate research award (PRA) scholarship.</span></em></p><p class="fine-print"><em><span>Balz Kamber receives funding from the Australian Research Council for Discovery Grant DP220100136 for work that will build on the model predictions explained in this piece.</span></em></p><p class="fine-print"><em><span>Emma Tomlinson receives funding from the European Union through an ERC consolidator grant ERC-COG-2021/101044276 to work Archaean lithosphere formation. Views and opinions expressed are however those of the author only and do not necessarily reflect those of the European Union or European Research Council. Neither the European Union nor the granting authority can be held responsible for them.</span></em></p>Diamonds form alongside a distinct purple companion. We studied it to reach a conclusion about how rare they might actually be.Carl Walsh, PhD Candidate, Queensland University of TechnologyBalz Kamber, Professor of Petrology, Queensland University of TechnologyEmma Tomlinson, Associate Professor, Trinity College DublinLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1787812022-03-18T10:24:59Z2022-03-18T10:24:59ZPowerful X-rays reveal the birth of giant rare earth element deposits – and may give clues for sustainable mining<figure><img src="https://images.theconversation.com/files/452383/original/file-20220316-19-kqp431.jpeg?ixlib=rb-1.1.0&rect=8%2C6%2C1466%2C1013&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">NASA</span></span></figcaption></figure><p>More than ten years ago, the so-called “<a href="https://www.technologyreview.com/2011/04/19/195225/the-rare-earth-crisis/">rare earth crisis</a>” highlighted the fragility of the supply chain of these metals, which are <a href="https://theconversation.com/critical-minerals-are-vital-for-renewable-energy-we-must-learn-to-mine-them-responsibly-131547">crucial for the transition to a carbon-neutral economy</a>. Most of the world’s supply of these minerals comes from a handful of giant ore deposits, but we still know little about how these deposits formed.</p>
<p>Despite the name, the rare earths are relatively widespread in Earth’s crust, compared with elements such as gold and platinum. Large, concentrated deposits suitable for mining, however, are much more scarce.</p>
<p>To understand how these deposits form, we recreated the hellish temperatures, pressures and chemical environments that occur kilometres below Earth’s surface, and used intense X-rays to probe the behaviour of rare earth elements down to the molecular level.</p>
<p><a href="https://www.nature.com/articles/s41467-022-28943-z">We discovered a previously unknown process</a> whereby rare earth elements can bind to a common chemical called carbonate in hot fluids at high pressure. This provides hints about how rare earth deposits form, and also about how we can reverse-engineer the process to extract these rare metals in a more sustainable way.</p>
<h2>What does it take to form a giant rare earth deposit?</h2>
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<a href="https://images.theconversation.com/files/452659/original/file-20220317-8345-1s9mrrx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/452659/original/file-20220317-8345-1s9mrrx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/452659/original/file-20220317-8345-1s9mrrx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=373&fit=crop&dpr=1 600w, https://images.theconversation.com/files/452659/original/file-20220317-8345-1s9mrrx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=373&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/452659/original/file-20220317-8345-1s9mrrx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=373&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/452659/original/file-20220317-8345-1s9mrrx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=468&fit=crop&dpr=1 754w, https://images.theconversation.com/files/452659/original/file-20220317-8345-1s9mrrx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=468&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/452659/original/file-20220317-8345-1s9mrrx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=468&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">Rare earth elements have unique electromagnetic properties that make them essential for strong alloys and magnets used in wind turbines and electric vehicle motors, as well as smartphone screens and audio.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
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<p>The <a href="https://theconversation.com/what-are-rare-earths-crucial-elements-in-modern-technology-4-questions-answered-101364">rare earth elements</a> are a group of 15 soft, silvery heavy metals found at the bottom of the periodic table (from lanthanum to lutetium). Two more elements (scandium and yttrium) are also often included in the group, because of similarities in their chemical behaviour.</p>
<p>Today’s giant deposits of rare earth elements are associated with unusual types of molten rock called carbonatite and alkaline magmas. These magmas do not contain much silicon (the second-most abundant element in the Earth’s crust after oxygen), but instead include a lot of alkali metals (sodium and potassium), calcium and volatile elements such as carbon, fluorine or phosphorus. </p>
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Read more:
<a href="https://theconversation.com/what-are-rare-earths-crucial-elements-in-modern-technology-4-questions-answered-101364">What are rare earths, crucial elements in modern technology? 4 questions answered</a>
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<p>All rocks around us contain significant amounts of rare earth elements, but they become concentrated in these exotic magmas through slow crystallisation in Earth’s crust. This is usually not enough to make an ore deposit, which consists of millions of tonnes of rock made up of between 5 and 50% by weight of rare earth elements. A second step of concentration is required. </p>
<p>In giant deposits such as Bayan Obo in Inner Mongolia, hot fluids loaded with carbonate appear to have undergone this extra concentration step. But exactly how has been a mystery. </p>
<h2>A safe ticket to Hades, with X-ray vision</h2>
<p>We think rare earth ores formed kilometres below Earth’s surface. Millions of years ago, high temperatures (200-800°C) and pressures (hundreds to thousands of times greater than atmospheric pressure) transformed pre-existing concentrations of rare earth elements into valuable ores.</p>
<p>There is no way for geologists to go and watch ore forming, but we tried to do the next best thing.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/452837/original/file-20220317-25-12sjo57.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/452837/original/file-20220317-25-12sjo57.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/452837/original/file-20220317-25-12sjo57.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/452837/original/file-20220317-25-12sjo57.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/452837/original/file-20220317-25-12sjo57.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/452837/original/file-20220317-25-12sjo57.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/452837/original/file-20220317-25-12sjo57.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/452837/original/file-20220317-25-12sjo57.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">Joël Brugger installing a new sample in the autoclave for X-ray measurements at high pressure and temperature at the ESRF synchrotron in Grenoble, France.</span>
<span class="attribution"><span class="source">Denis Testemale, CNRS</span></span>
</figcaption>
</figure>
<p>We were able to recreate and study something like the conditions that reigned during ore formation, using the French Absorption Spectroscopy Beamline (FAME) at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. </p>
<p>We used a specially designed autoclave (a geological cooking pot) to create temperatures up to 600°C and pressures up to 200 megapascals, which corresponds to depths of about 7km in Earth’s crust.</p>
<p>At the ESRF synchrotron, which is effectively a giant X-ray gun 100 billion times more powerful than a hospital X-ray device, we can probe the composition and molecular structure of fluids and dissolved materials inside the cooking pot. A safe ticket to Hades provided by X-ray vision! </p>
<p>Specifically, we probed how rare earth elements bonded with chlorine, fluorine, hydroxide or carbonate present in fluids at high pressures and temperatures. Reactions between the rare earth elements and these so-called “ligands” are responsible for the solubility of rare earth minerals. </p>
<h2>New ways to extract rare earth elements</h2>
<p>The results were unexpected. First, we discovered that fluids rich in carbonate can carry large amounts of rare earth elements. Second, adding fluorine had little effect on the fluids’ ability to carry rare earth elements. </p>
<p>This means that hot carbonate-rich fluids could transport rare earth elements and fluorine together – so common ore minerals such as bastnaesite (which is made of rare earth elements, carbonate and fluorine) could precipitate out of the fluid when it cools. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/452331/original/file-20220315-23-rh5rbh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/452331/original/file-20220315-23-rh5rbh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=352&fit=crop&dpr=1 600w, https://images.theconversation.com/files/452331/original/file-20220315-23-rh5rbh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=352&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/452331/original/file-20220315-23-rh5rbh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=352&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/452331/original/file-20220315-23-rh5rbh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=442&fit=crop&dpr=1 754w, https://images.theconversation.com/files/452331/original/file-20220315-23-rh5rbh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=442&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/452331/original/file-20220315-23-rh5rbh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=442&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Fluids rich in carbonate and fluorine can carry large amounts of rare earth elements, depositing them in high grade deposits of economic ore.</span>
<span class="attribution"><span class="source">Diagram: Joël Brugger / Bastnaesite photo: Mischa Crumbach</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Our experiments also show that carbonate-rich fluids will concentrate more light rare earths (such as lanthanum) or heavy ones (such as gadolinium and ytterbium) at different temperatures. This is important for determining the economic value of ores, as some rare earth elements are more expensive than others.</p>
<p>Most importantly, the economic and environmental costs of rare earth element mining are strongly affected by the difficulty of separating the different elements. Many ores also contain radioactive elements such as uranium and thorium, which need to be dealt with.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/critical-minerals-are-vital-for-renewable-energy-we-must-learn-to-mine-them-responsibly-131547">Critical minerals are vital for renewable energy. We must learn to mine them responsibly</a>
</strong>
</em>
</p>
<hr>
<p>Our results reveal a new avenue for rare earth element processing: using environmentally benign carbonate solutions to leach rare earth elements from ore at high temperatures.</p>
<p>In this way, we may be able to reverse-engineer the ore-forming process to extract the metals needed to sustain the world’s transition to a carbon-neutral economy.</p><img src="https://counter.theconversation.com/content/178781/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Joël Brugger receives funding from public (Australian Research Council) and private (mining companies) organisations.</span></em></p><p class="fine-print"><em><span>Marion Louvel receives funding from DFG (German Research Foundation) and EU Horizon 2020.</span></em></p><p class="fine-print"><em><span>Barbara Etschmann 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>A new geochemical discovery could lead to a cleaner way to extract the rare earth elements needed for the transition to renewable energy.Joël Brugger, Professor of Synchrotron Geosciences, Monash UniversityBarbara Etschmann, Research officer, Monash UniversityMarion Louvel, Earth science researcher, Centre national de la recherche scientifique (CNRS)Licensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1676782021-09-20T10:48:34Z2021-09-20T10:48:34ZA giant space rock demolished an ancient Middle Eastern city and everyone in it – possibly inspiring the Biblical story of Sodom<figure><img src="https://images.theconversation.com/files/421903/original/file-20210917-27-aguoxh.jpg?ixlib=rb-1.1.0&rect=6%2C0%2C710%2C608&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist's evidence-based depiction of the blast, which had the power of 1,000 Hiroshimas.</span> <span class="attribution"><span class="source">Allen West and Jennifer Rice</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>As the inhabitants of an ancient Middle Eastern city now called Tall el-Hammam went about their daily business one day about 3,600 years ago, they had no idea an unseen icy space rock was speeding toward them at about 38,000 mph (61,000 kph).</p>
<p>Flashing through the atmosphere, the rock exploded in a massive fireball about 2.5 miles (4 kilometers) above the ground. The blast was around 1,000 times more powerful than the Hiroshima atomic bomb. The shocked city dwellers who stared at it were blinded instantly. Air temperatures rapidly rose above 3,600 degrees Fahrenheit (2,000 degrees Celsius). Clothing and wood immediately burst into flames. Swords, spears, mudbricks and pottery began to melt. Almost immediately, the entire city was on fire.</p>
<p>Some seconds later, a massive shockwave smashed into the city. Moving at about 740 mph (1,200 kph), it was more powerful than the <a href="https://en.wikipedia.org/wiki/Tornado_records">worst tornado ever recorded</a>. The deadly winds ripped through the city, demolishing every building. They sheared off the top 40 feet (12 m) of the 4-story palace and blew the jumbled debris into the next valley. None of the 8,000 people or any animals within the city survived – their bodies were torn apart and their bones blasted into small fragments. </p>
<p>About a minute later, 14 miles (22 km) to the west of Tall el-Hammam, winds from the blast hit the biblical city of Jericho. Jericho’s walls came tumbling down and the city burned to the ground. </p>
<p>It all sounds like the climax of an edge-of-your-seat Hollywood disaster movie. How do we know that all of this actually happened near the Dead Sea in Jordan millennia ago? </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/421905/original/file-20210917-31825-1drwpso.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Satellite image showing the area with Tall el-Hammam about 7 miles (12 kilometers) northeast of the Dead Sea" src="https://images.theconversation.com/files/421905/original/file-20210917-31825-1drwpso.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/421905/original/file-20210917-31825-1drwpso.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=384&fit=crop&dpr=1 600w, https://images.theconversation.com/files/421905/original/file-20210917-31825-1drwpso.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=384&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/421905/original/file-20210917-31825-1drwpso.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=384&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/421905/original/file-20210917-31825-1drwpso.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=483&fit=crop&dpr=1 754w, https://images.theconversation.com/files/421905/original/file-20210917-31825-1drwpso.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=483&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/421905/original/file-20210917-31825-1drwpso.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=483&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Now called Tall el-Hammam, the city is located about 7 miles northeast of the Dead Sea in what is now Jordan.</span>
<span class="attribution"><span class="source">NASA</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Getting answers required nearly 15 years of painstaking excavations by hundreds of people. It also involved detailed analyses of excavated material by more than two dozen scientists in 10 states in the U.S., as well as Canada and the Czech Republic. When our group finally <a href="https://doi.org/10.1038/s41598-021-97778-3">published the evidence</a> recently in the journal Scientific Reports, the 21 co-authors included archaeologists, geologists, geochemists, geomorphologists, mineralogists, paleobotanists, sedimentologists, cosmic-impact experts and medical doctors.</p>
<p>Here’s <a href="https://doi.org/10.1038/s41598-021-97778-3">how we built up this picture</a> of devastation in the past.</p>
<h2>Firestorm throughout the city</h2>
<p>Years ago, when archaeologists looked out over excavations of the ruined city, they could see a dark, roughly 5-foot-thick (1.5 m) jumbled layer of charcoal, ash, melted mudbricks and melted pottery. It was obvious that an intense firestorm had destroyed this city long ago. This dark band came to be called the destruction layer.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/421904/original/file-20210917-48847-shp2wx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Excavators stand in a dry landscape with ruins of ancient walls" src="https://images.theconversation.com/files/421904/original/file-20210917-48847-shp2wx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/421904/original/file-20210917-48847-shp2wx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/421904/original/file-20210917-48847-shp2wx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/421904/original/file-20210917-48847-shp2wx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/421904/original/file-20210917-48847-shp2wx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/421904/original/file-20210917-48847-shp2wx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/421904/original/file-20210917-48847-shp2wx.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">Researchers stand near the ruins of ancient walls, with the destruction layer about midway down each exposed wall.</span>
<span class="attribution"><span class="source">Phil Silvia</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>No one was exactly sure what had happened, but that layer wasn’t caused by a volcano, earthquake or warfare. None of them are capable of melting metal, mudbricks and pottery. </p>
<p>To figure out what could, our group used the <a href="https://impact.ese.ic.ac.uk/ImpactEarth/ImpactEffects/">Online Impact Calculator</a> to model scenarios that fit the evidence. Built by impact experts, this calculator allows researchers to estimate the many details of a cosmic impact event, based on known impact events and nuclear detonations.</p>
<p>It appears that the culprit at Tall el-Hammam was a small asteroid similar to the one that <a href="https://doi.org/10.1117/12.462399">knocked down 80 million trees</a> <a href="https://theconversation.com/mystery-solved-meteorite-caused-tunguska-devastation-15154">in Tunguska, Russia in 1908</a>. It would have been a much smaller version of the <a href="https://theconversation.com/more-bad-news-for-dinosaurs-chicxulub-meteorite-impact-triggered-global-volcanic-eruptions-on-the-ocean-floor-91053">giant miles-wide rock that pushed the dinosaurs into extinction</a> 65 million ago.</p>
<p>We had a likely culprit. Now we needed proof of what happened that day at Tall el-Hammam.</p>
<h2>Finding ‘diamonds’ in the dirt</h2>
<p>Our research revealed a remarkably broad array of evidence.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/421943/original/file-20210917-31825-1vbrfje.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="magnified images of tiny quartz grains" src="https://images.theconversation.com/files/421943/original/file-20210917-31825-1vbrfje.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/421943/original/file-20210917-31825-1vbrfje.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=618&fit=crop&dpr=1 600w, https://images.theconversation.com/files/421943/original/file-20210917-31825-1vbrfje.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=618&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/421943/original/file-20210917-31825-1vbrfje.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=618&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/421943/original/file-20210917-31825-1vbrfje.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=776&fit=crop&dpr=1 754w, https://images.theconversation.com/files/421943/original/file-20210917-31825-1vbrfje.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=776&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/421943/original/file-20210917-31825-1vbrfje.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=776&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Electron microscope images of numerous small cracks in shocked quartz grains.</span>
<span class="attribution"><span class="source">Allen West</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>At the site, there are finely fractured sand grains called shocked quartz that only form at 725,000 pounds per square inch of pressure (5 gigapascals) – imagine six <a href="https://man.fas.org/dod-101/sys/land/m1.htm">68-ton Abrams military tanks</a> stacked on your thumb.</p>
<p>The destruction layer also contains tiny <a href="https://doi.org/10.1086/677046">diamonoids</a> that, as the name indicates, are as hard as diamonds. <a href="https://doi.org/10.1086/677046">Each one is smaller</a> <a href="https://doi.org/10.1016/j.chroma.2016.08.056">than a flu virus</a>. It appears that wood and plants in the area were instantly turned into this diamond-like material by the fireball’s high pressures and temperatures.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/421909/original/file-20210917-27-7y1o9c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/421909/original/file-20210917-27-7y1o9c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/421909/original/file-20210917-27-7y1o9c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=446&fit=crop&dpr=1 600w, https://images.theconversation.com/files/421909/original/file-20210917-27-7y1o9c.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=446&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/421909/original/file-20210917-27-7y1o9c.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=446&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/421909/original/file-20210917-27-7y1o9c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=561&fit=crop&dpr=1 754w, https://images.theconversation.com/files/421909/original/file-20210917-27-7y1o9c.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=561&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/421909/original/file-20210917-27-7y1o9c.jpg?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">Diamonoids (center) inside a crater were formed by the fireball’s high temperatures and pressures on wood and plants.</span>
<span class="attribution"><span class="source">Malcolm LeCompte</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Experiments with laboratory furnaces showed that the bubbled pottery and mudbricks at Tall el-Hammam liquefied at temperatures above 2,700 F (1,500 C). That’s hot enough to <a href="https://www.onlinemetals.com/en/melting-points">melt an automobile</a> within minutes.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/421942/original/file-20210917-27-5s3b15.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="magnified view of spherical shapes" src="https://images.theconversation.com/files/421942/original/file-20210917-27-5s3b15.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/421942/original/file-20210917-27-5s3b15.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=594&fit=crop&dpr=1 600w, https://images.theconversation.com/files/421942/original/file-20210917-27-5s3b15.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=594&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/421942/original/file-20210917-27-5s3b15.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=594&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/421942/original/file-20210917-27-5s3b15.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=746&fit=crop&dpr=1 754w, https://images.theconversation.com/files/421942/original/file-20210917-27-5s3b15.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=746&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/421942/original/file-20210917-27-5s3b15.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=746&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Spherules made of melted sand (upper left), palace plaster (upper right) and melted metal (bottom two).</span>
<span class="attribution"><span class="source">Malcolm LeCompte</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>The destruction layer also contains tiny balls of melted material smaller than airborne dust particles. <a href="https://doi.org/10.1073/pnas.1301760110">Called spherules</a>, they are made of vaporized iron and sand that melted at about 2,900 F (1,590 C).</p>
<p>In addition, the surfaces of the pottery and meltglass are speckled with tiny melted metallic grains, including iridium with a <a href="https://www.rsc.org/periodic-table/element/77/iridium">melting point of 4,435 F</a> (2,466 C), platinum that <a href="https://www.rsc.org/periodic-table/element/78/platinum">melts at 3,215 F</a> (1,768 C) and <a href="https://en.wikipedia.org/wiki/Zirconium(IV)_silicate">zirconium silicate at 2,800 F</a> (1,540 C).</p>
<p>Together, all this evidence shows that temperatures in the city rose higher than those of volcanoes, warfare and normal city fires. The only natural process left is a cosmic impact.</p>
<p>The same evidence is found at known impact sites, such as <a href="https://theconversation.com/mystery-solved-meteorite-caused-tunguska-devastation-15154">Tunguska</a> and the <a href="https://theconversation.com/more-bad-news-for-dinosaurs-chicxulub-meteorite-impact-triggered-global-volcanic-eruptions-on-the-ocean-floor-91053">Chicxulub crater</a>, created by the asteroid that triggered the dinosaur extinction.</p>
<p>One remaining puzzle is why the city and over 100 other area settlements were abandoned for several centuries after this devastation. It may be that high levels of salt deposited during the impact event made it impossible to grow crops. We’re not certain yet, but we think the explosion may have vaporized or splashed toxic levels of Dead Sea salt water across the valley. Without crops, no one could live in the valley for up to 600 years, until the minimal rainfall in this desert-like climate washed the salt out of the fields. </p>
<h2>Was there a surviving eyewitness to the blast?</h2>
<p>It’s possible that an oral description of the city’s destruction may have been handed down for generations until it was recorded as the story of Biblical Sodom. The Bible <a href="https://sarata.com/bible/chapter/Genesis.19.html#19:24">describes the devastation of an urban center</a> near the Dead Sea – <a href="https://www.biblegateway.com/passage/?search=Luke+17%3A28%E2%80%9330&version=NRSV">stones and fire fell from the sky</a>, more than one city was destroyed, thick smoke rose from the fires and city inhabitants were killed.</p>
<p>Could this be an ancient eyewitness account? If so, the destruction of Tall el-Hammam may be the second-oldest destruction of a human settlement by a cosmic impact event, after the village of <a href="https://doi.org/10.1038/s41598-020-60867-w">Abu Hureyra in Syria about 12,800 years ago</a>. Importantly, it may the first written record of such a catastrophic event.</p>
<p>[<em>Over 110,000 readers rely on The Conversation’s newsletter to understand the world.</em> <a href="https://theconversation.com/us/newsletters/the-daily-3?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=100Ksignup">Sign up today</a>.]</p>
<p>The scary thing is, it almost certainly won’t be the last time a human city meets this fate.</p>
<figure>
<img src="https://d2pn8kiwq2w21t.cloudfront.net/images/imagesasteroid20180723main-animation-16.width-1320.gif">
<figcaption><span class="caption">Animation depicting the positions of known near-Earth objects at points in time for the 20 years ending in January 2018. <i>Credit: NASA/JPL-Caltech</i></span></figcaption>
</figure>
<p>Tunguska-sized airbursts, such as the one that occurred at Tall el-Hammam, can devastate entire cities and regions, and they pose a severe modern-day hazard. As of September 2021, there are <a href="https://cneos.jpl.nasa.gov/stats/totals.html">more than 26,000 known near-Earth asteroids</a> and a hundred short-period near-Earth comets. One will inevitably crash into the Earth. Millions more remain undetected, and some may be headed toward the Earth now.</p>
<p>Unless orbiting or ground-based telescopes detect these rogue objects, the world may have no warning, just like the people of Tall el-Hammam.</p>
<p><em>This article was co-authored by research collaborators archaeologist <a href="https://www.researchgate.net/profile/Phillip-Silvia">Phil Silvia</a>, geophysicist <a href="https://www.researchgate.net/profile/Allen-West">Allen West</a>, geologist <a href="https://www.researchgate.net/profile/Ted-Bunch-2">Ted Bunch</a> and space physicist <a href="https://www.researchgate.net/profile/Malcolm-Lecompte">Malcolm LeCompte</a>.</em></p><img src="https://counter.theconversation.com/content/167678/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christopher R. Moore 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>New research suggests that fire from the sky in the form of a small asteroid annihilated a city near the Dead Sea 3,600 years ago.Christopher R. Moore, Archaeologist and Special Projects Director at the Savannah River Archaeological Research Program and South Carolina Institute for Archaeology and Anthropology, University of South CarolinaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1649522021-08-13T22:21:30Z2021-08-13T22:21:30ZLight and shade: how the natural ‘glazes’ on the walls of Kimberley rock shelters help reveal the world the artists lived in<figure><img src="https://images.theconversation.com/files/415981/original/file-20210813-21-28293z.JPG?ixlib=rb-1.1.0&rect=15%2C155%2C5160%2C3003&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>The Kimberley region is host to <a href="https://theconversation.com/this-17-500-year-old-kangaroo-in-the-kimberley-is-australias-oldest-aboriginal-rock-painting-154181">Australia’s oldest known rock paintings</a>. But people were carving engravings into some of these rocks before they were creating paintings. </p>
<p>Rock art sites on Balanggarra Country in the northeast Kimberley region are home to numerous such engravings. The oldest paintings are at least 17,300 years old, and the engravings are thought to be even older — but they have so far proved much harder to date accurately.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/414463/original/file-20210804-20-17dho34.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/414463/original/file-20210804-20-17dho34.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/414463/original/file-20210804-20-17dho34.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/414463/original/file-20210804-20-17dho34.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/414463/original/file-20210804-20-17dho34.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/414463/original/file-20210804-20-17dho34.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/414463/original/file-20210804-20-17dho34.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">Cupules, or circular man-made hollows, ground into a dark mineral coating at a rock art site on the Drysdale River, Balanggarra country.</span>
<span class="attribution"><span class="source">Photo by Damien Finch</span></span>
</figcaption>
</figure>
<p>But in research <a href="https://advances.sciencemag.org/lookup/doi/10.1126/sciadv.abf3632">published today in Science Advances</a>, we report on a crucial clue that could help date the engravings, and also reveal what the environment was like for the artists who created them. </p>
<p>Some of the rocks themselves are covered with natural, glaze-like mineral coatings that can help reveal key evidence. </p>
<h2>What are these glazes?</h2>
<p>These dark, shiny deposits on the surface of the rock are less than a centimetre thick. Yet they have detailed internal structures, featuring alternating light and dark layers of different minerals.</p>
<p>Our aim was to develop methods to reliably date the formation of these coatings and provide age brackets for any associated engravings. However, during this process, we also discovered it is possible to match layers found in samples collected at rock shelters up to 90 kilometres apart. </p>
<p>Radiocarbon dating suggests these layers were deposited around the same time, showing their formation is not specific to particular rock shelters, but controlled by environmental changes on a regional scale. </p>
<p>Dating these deposits can therefore provide reliable age brackets for any associated engravings, while also helping us better understanding the climate and environments in which the artists lived.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/414914/original/file-20210805-27-fl3od0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/414914/original/file-20210805-27-fl3od0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/414914/original/file-20210805-27-fl3od0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=425&fit=crop&dpr=1 600w, https://images.theconversation.com/files/414914/original/file-20210805-27-fl3od0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=425&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/414914/original/file-20210805-27-fl3od0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=425&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/414914/original/file-20210805-27-fl3od0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=534&fit=crop&dpr=1 754w, https://images.theconversation.com/files/414914/original/file-20210805-27-fl3od0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=534&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/414914/original/file-20210805-27-fl3od0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=534&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Marsupial tracks scratched into a glaze like coating at a rock art shelter in the north east Kimberley.</span>
<span class="attribution"><span class="source">Photo by Cecilia Myers/Dunkeld Pastoral Company; illustration by Pauline Heaney/Rock Art Australia</span></span>
</figcaption>
</figure>
<h2>Microbes and minerals</h2>
<p>Our research supports <a href="https://onlinelibrary.wiley.com/doi/10.1002/gea.1021">earlier findings</a> that layers within the glaze structure represent alternating environmental conditions in Kimberley rock shelters, that repeated over thousands of years. </p>
<p>Our model suggests that during drier conditions, bush fires produce ash, which builds up on shelter surfaces. This ash contains a range of minerals, including carbonates and sulphates. We suggest that under the right conditions, these minerals provided nutrients that allowed microbes to live on these shelter surfaces. In the process of digesting these nutrients, the microbes excrete a compound called oxalic acid, which combines with calcium in the ash deposits to form calcium oxalate. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/414950/original/file-20210806-19-18wbcl7.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/414950/original/file-20210806-19-18wbcl7.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/414950/original/file-20210806-19-18wbcl7.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=395&fit=crop&dpr=1 600w, https://images.theconversation.com/files/414950/original/file-20210806-19-18wbcl7.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=395&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/414950/original/file-20210806-19-18wbcl7.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=395&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/414950/original/file-20210806-19-18wbcl7.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=496&fit=crop&dpr=1 754w, https://images.theconversation.com/files/414950/original/file-20210806-19-18wbcl7.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=496&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/414950/original/file-20210806-19-18wbcl7.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=496&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: dark coloured, smooth mineral coating at a Kimberley rock shelter; B: alternating layering, as seen in the field; C: alternating layering as seen in a cross-sectioned coating under a microscope.</span>
<span class="attribution"><span class="source">Photos by Cecilia Myers; microscope image by Helen Green</span></span>
</figcaption>
</figure>
<p>As this process repeats over millennia, the minerals become cemented together in alternating layers, with each layer creating a record of the conditions in the rock shelter at that time.</p>
<p>Samples of the glazes were collected for analysis in close collaboration and consultation with local Traditional Owners from the Balanggarra native title region, who are partners on our research project. Using a laser, we vaporised tiny samples from the coatings to study the chemical composition of each layer. The dark layers were mostly made of calcium oxalate, while lighter layers contained mainly sulphates. We propose darker layers represent a time when microbes were more active and lighter layers represent drier periods. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-climate-change-is-erasing-the-worlds-oldest-rock-art-159929">How climate change is erasing the world’s oldest rock art</a>
</strong>
</em>
</p>
<hr>
<h2>Linking the layers</h2>
<p>These dark calcium oxalate layers also contain carbon that was absorbed from the atmosphere and digested by the microbes that created these deposits. This meant we could use a technique called <a href="https://theconversation.com/explainer-what-is-radiocarbon-dating-and-how-does-it-work-9690">radiocarbon dating</a> to determine the age of these individual layers. </p>
<p>Using a tiny drill, we removed samples from distinct dark layers in nine glazes collected from different rock shelters across the northeast Kimberley.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/414912/original/file-20210805-15-jsprpt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/414912/original/file-20210805-15-jsprpt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/414912/original/file-20210805-15-jsprpt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=260&fit=crop&dpr=1 600w, https://images.theconversation.com/files/414912/original/file-20210805-15-jsprpt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=260&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/414912/original/file-20210805-15-jsprpt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=260&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/414912/original/file-20210805-15-jsprpt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=327&fit=crop&dpr=1 754w, https://images.theconversation.com/files/414912/original/file-20210805-15-jsprpt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=327&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/414912/original/file-20210805-15-jsprpt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=327&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: micro-drilling samples from individual layers for radiocarbon dating; B: Laser ablation maps showing the distribution of the element calcium within the different layers; C: radiocarbon dating of individual layers identified four key growth periods.</span>
<span class="attribution"><span class="source">Photo by Andy Gleadow; illustration by Pauline Heaney</span></span>
</figcaption>
</figure>
<p>Despite coming from different locations, these layers all seem to have been deposited at the same time, during four key intervals spanning the past 43,000 years.</p>
<p>This suggests the formation of each layer was determined mainly by shifts in environmental conditions throughout the Kimberley, rather than by the distinct conditions in each particular rock shelter.</p>
<p>The records held by these glazes over such a large time period - including the most recent ice age - means they could help us better understand the environmental changes that directly affected human habitation and adaptation in Australia.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/414952/original/file-20210806-17-bkibgr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/414952/original/file-20210806-17-bkibgr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/414952/original/file-20210806-17-bkibgr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=459&fit=crop&dpr=1 600w, https://images.theconversation.com/files/414952/original/file-20210806-17-bkibgr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=459&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/414952/original/file-20210806-17-bkibgr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=459&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/414952/original/file-20210806-17-bkibgr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=577&fit=crop&dpr=1 754w, https://images.theconversation.com/files/414952/original/file-20210806-17-bkibgr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=577&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/414952/original/file-20210806-17-bkibgr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=577&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Hypothetical example of how layered mineral coatings can be used to date engraved rock art in Kimberley rock shelters.</span>
<span class="attribution"><span class="source">Pauline Heaney</span></span>
</figcaption>
</figure>
<h2>Stories in stone</h2>
<p>Research we <a href="https://www.nature.com/articles/s41562-020-01041-0">published earlier this year</a> shows how the subjects painted in early Kimberley rock art changed from mostly animals and plants around 17,000 years ago, to mostly decorated human figures about 12,000 years ago. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/this-17-500-year-old-kangaroo-in-the-kimberley-is-australias-oldest-aboriginal-rock-painting-154181">This 17,500-year-old kangaroo in the Kimberley is Australia's oldest Aboriginal rock painting</a>
</strong>
</em>
</p>
<hr>
<p><a href="https://www.sciencedirect.com/science/article/pii/S1040618216305018?via%3Dihub">Other</a> <a href="https://doi.org/10.1016/j.quascirev.2017.11.030">researchers</a> have discovered that during this 5,000-year period there were rapid rises in sea level, in particular around 14,500 years ago, as well as increased rainfall. </p>
<p>We interpret the change in rock art styles as a response to the social and cultural adaptations triggered by the changing climate and rising sea levels. Paintings of human figures with new technologies such as spear-throwers might show us how people adapted their hunting style to the changing environment and the availability of different types of food.</p>
<p>By dating the natural mineral coatings on the rock surfaces that acted as a canvas for this art, we can hopefully better understand the world in which these artists lived. Not only will this give us more certainty about the position of particular paintings within the overall <a href="https://rockartaustralia.org.au/rock-art/rock-art-sequence/">Kimberley stylistic rock art sequence</a>, but can also tell us about the environments experienced by First Nations people in the Kimberley. </p>
<hr>
<p><em>We thank the Balanggarra Aboriginal Corporation, the Centre for Accelerator Science at the Australian National Science and Technology Organisation, Rock Art Australia and Dunkeld Pastoral Co for their collaboration on this research.</em>_</p><img src="https://counter.theconversation.com/content/164952/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>receives funding from the Australian Research Council, Rock Art Australia, The Ian Potter Foundation and an Australian Postgraduate Award and the Australian Institute of Nuclear Science and Engineering .</span></em></p><p class="fine-print"><em><span>Damien Finch receives funding from the Australian Research Council, Rock Art Australia, an Australian Postgraduate Award and the Australian Institute of Nuclear Science and Engineering .</span></em></p>Indigenous artists have been engraving rock shelters for millennia - long before the Kimberley’s celebrated rock art paintings. Now the rocks’ natural coatings are yielding clues to the engravings’ creation.Helen Green, Research Fellow, The University of MelbourneDamien Finch, Research fellow, The University of MelbourneLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1618192021-06-27T19:48:55Z2021-06-27T19:48:55ZNot so foolish after all: ‘fool’s gold’ contains a newly discovered type of real gold<figure><img src="https://images.theconversation.com/files/408340/original/file-20210625-13-h5xcss.jpeg?ixlib=rb-1.1.0&rect=8%2C0%2C5982%2C4491&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Uoaei1/Wikimedia Commons</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>The mineral pyrite was historically nicknamed <a href="https://www.britannica.com/science/pyrite">fool’s gold</a> because of its deceptive resemblance to the precious metal. The term was often used during the California gold rush in the 1840s because inexperienced prospectors would claim discoveries of gold, but in reality it would be pyrite, composed of worthless iron disulfide (FeS₂). </p>
<p>Ironically, pyrite crystals can contain small amounts of real gold, although it is notoriously hard to extract. Gold hiding within pyrite is sometimes referred to as “invisible gold”, because it is not observable with standard microscopes, but instead requires sophisticated scientific instruments. </p>
<p>It wasn’t until the 1980s when <a href="https://www.researchgate.net/profile/Louis-Cabri/publication/258209241_The_nature_of_invisible_gold_in_arsenopyrite/links/02e7e5273cded2849f000000/The-nature-of-invisible-gold-in-arsenopyrite.pdf">researchers discovered</a> that gold in pyrite can come in different forms – either as particles of gold, or as an alloy, in which the pyrite and gold are finely mixed.</p>
<p>In our new research, <a href="https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G49028.1/604581/A-new-kind-of-invisible-gold-in-pyrite-hosted-in">published in Geology</a>, my colleagues and I discovered a third, previously unrecognised way that gold can lurk inside pyrite. When the pyrite crystal is forming under extreme temperature or pressure, it can develop tiny imperfections in its crystal structure that can be “decorated” with gold atoms.</p>
<h2>What are these ‘crystal defects’?</h2>
<p>The atoms within a crystal are arranged in a characteristic pattern called an atomic lattice. But when a mineral crystal such as pyrite is growing inside a rock, this lattice pattern can develop imperfections. Like many minerals, pyrite is tough and hard at Earth’s surface, but can become more twisty and stretchy when forming deep in the Earth, which is also where gold deposits form. </p>
<p>When crystals stretch or twist, the bonds between neighbouring atoms are broken and remade, forming billions of tiny imperfections called “dislocations”, each roughly 100,000 times smaller than the width of a human hair, or 100 times smaller than a virus particle.</p>
<p>The chemistry of these atomic-scale imperfections is notoriously difficult to study because they are so small, so any impurities are present in absolutely minuscule quantities. Detecting them requires a specialised instrument called an <a href="http://youtube.com/watch?v=CXiDO4vjfVg">atom probe</a>.</p>
<p>An atom probe can analyse materials at extremely high resolution, but its main advantage over other methods is that it allows us to build a 3D map showing the precise locations of impurities within a crystal — something that was never possible before.</p>
<p>Our research reveals that dislocations within pyrite crystals can be “decorated” with gold atoms. This is particularly common where the crystals have been twisted during their history; here, gold can be present at concentrations several times higher than in the rest of the crystal.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/404402/original/file-20210604-15-ferqh6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Impurities in pyrite crystal" src="https://images.theconversation.com/files/404402/original/file-20210604-15-ferqh6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/404402/original/file-20210604-15-ferqh6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=765&fit=crop&dpr=1 600w, https://images.theconversation.com/files/404402/original/file-20210604-15-ferqh6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=765&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/404402/original/file-20210604-15-ferqh6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=765&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/404402/original/file-20210604-15-ferqh6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=961&fit=crop&dpr=1 754w, https://images.theconversation.com/files/404402/original/file-20210604-15-ferqh6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=961&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/404402/original/file-20210604-15-ferqh6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=961&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Gold (Au) atoms hiding within a pyrite crystal, alongside other imperfections including nickel, copper and bismuth. Scale bar indicates 20 nanometres.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>A potential goldmine</h2>
<p>Why should anyone care about something so tiny? Well, it gives interesting insights into how mineral deposits form, and is also a potential boon for the gold mining industry.</p>
<p>Previously, it was suspected that gold in anomalously rich pyrite crystals was in fact made of gold particles formed during a multi-step process, suggesting the pyrite and gold crystallised at different times and then became clumped together. But our discovery that gold can decorate these crystal imperfections suggests that even pyrite crystals with relatively high gold content can form in a single process.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/eureka-x-ray-vision-can-find-hidden-gold-17432">Eureka! X-ray vision can find hidden gold</a>
</strong>
</em>
</p>
<hr>
<p>Our discovery may also help gold miners more efficiently extract gold from pyrite, potentially reducing greenhouse emissions. To extract the gold, the mineral is usually oxidised in large reactors, which uses considerable amounts of energy.</p>
<p>Dislocation sites within crystals could potentially offer an enhanced partial leaching or a target for bacteria to attack and break down the crystal, releasing the gold in a process known as “bio-leaching”, thus potentially reducing energy consumption necessary for extraction. This idea is still untested, but definitely merits investigation.</p>
<p>If it helps pave the way for more sustainable gold-mining methods, then perhaps fool’s gold isn’t so foolish after all.</p>
<p>Perhaps pyrite still lives up to its historic reputation of “fool’s gold” until better, more environmentally sustainable ore processing techniques are developed.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-gold-rushes-helped-make-the-modern-world-91746">How gold rushes helped make the modern world</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/161819/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Denis Fougerouse is affiliated with the School of Earth and Planetary Sciences and The Institute for Geoscience Research at Curtin University. He receives funding from the Australian Research Council. </span></em></p>Fool’s gold, or pyrite, is made of worthless iron disulfide, but can contain tiny amounts of the real thing. Using an ‘atom probe’, research has uncovered a new way gold atoms can hide in pyrite crystals.Denis Fougerouse, Research Fellow, School of Earth and Planetary Sciences, Curtin UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1605122021-05-12T18:01:12Z2021-05-12T18:01:12ZTeeth of fallen soldiers hold evidence that foreigners fought alongside ancient Greeks, challenging millennia of military history<figure><img src="https://images.theconversation.com/files/399507/original/file-20210507-23-1eu9oap.JPG?ixlib=rb-1.1.0&rect=309%2C154%2C4179%2C2840&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The ruins of the Temple of Victory in Himera, which was constructed to commemorate the first battle in 480 B.C.</span> <span class="attribution"><span class="source">Katherine Reinberger</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>Ancient historians loved to write about warfare and famous battles. While these millennia-old stories still feed modern imaginations – Homer’s “<a href="https://www.gutenberg.org/files/2199/2199-h/2199-h.htm">Iliad</a>” provides the plot for the movie “<a href="https://www.imdb.com/title/tt0332452/">Troy</a>,” while Herodotus’ “<a href="https://www.livius.org/sources/content/herodotus/herodotus-on-thermopylae/">Histories Book VII</a>” inspired the film “<a href="https://www.imdb.com/title/tt0416449/">300</a>,” for instance – there’s rarely any physical evidence that the events they describe really happened.</p>
<p>But in 2008 a team of Italian archaeologists began to excavate outside the ancient city wall at Himera, a Greek colony on the north-central coast of Sicily, Italy. In the western necropolis, or cemetery, they found several mass graves dating to the early fifth century B.C. All the individuals in the graves were male, and many had violent trauma or even weapons lodged in their bones.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/400135/original/file-20210511-15-9k4vqn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="map of Sicily with a cutout showing the Himera archaeological site" src="https://images.theconversation.com/files/400135/original/file-20210511-15-9k4vqn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/400135/original/file-20210511-15-9k4vqn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=424&fit=crop&dpr=1 600w, https://images.theconversation.com/files/400135/original/file-20210511-15-9k4vqn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=424&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/400135/original/file-20210511-15-9k4vqn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=424&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/400135/original/file-20210511-15-9k4vqn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=533&fit=crop&dpr=1 754w, https://images.theconversation.com/files/400135/original/file-20210511-15-9k4vqn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=533&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/400135/original/file-20210511-15-9k4vqn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=533&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 plan of the Greek colony town of Himera, its location in Sicily among other sites and within the larger Mediterranean. The mass graves were found in the western necropolis.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.1371/journal.pone.0248803">Reinberger KL, Reitsema LJ, Kyle B, Vassallo S, Kamenov G, Krigbaum J (2021) Isotopic evidence for geographic heterogeneity in Ancient Greek military forces. PLoS ONE 16(5): e0248803.</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The evidence strongly suggests these men could have been soldiers who fought in 480 B.C. and 409 B.C. in the <a href="https://archive.archaeology.org/1101/features/himera.html">Battles of Himera</a>, written about by ancient Greek historians. <a href="https://scholar.google.com/citations?hl=en&user=OO0U40kAAAAJ">I’m part of</a> <a href="https://scholar.google.com/citations?hl=en&user=Z6Epx_oAAAAJ">an interdisciplinary</a> <a href="https://www.unco.edu/hss/anthropology/about/faculty/britney-kyle.aspx">team of</a> <a href="https://scholar.google.com/citations?hl=en&user=ZyNk8ysAAAAJ">anthropologists</a>, <a href="https://sicilia.academia.edu/StefanoVassallo">archaeologists</a> <a href="https://scholar.google.com/citations?user=c3IARDcAAAAJ&hl=en&oi=ao">and geologists</a> who <a href="https://doi.org/10.1371/journal.pone.0248803">analyzed the teeth of these people</a> who lived more than 2,400 years ago to figure out who they were and where they came from. It looks like early historians didn’t pass down the whole story, and our findings might rewrite parts of what’s known about Greek military history.</p>
<h2>A chance to fact-check ancient history</h2>
<p>Herodotus and another historian, Diodorus Siculus, both wrote about the Battles of Himera. They describe the first battle in 480 B.C. as <a href="https://www.perseus.tufts.edu/hopper/text?doc=Diod.+11.21&fromdoc=Perseus%3Atext%3A1999.01.0084">a victory of an alliance of Greeks from all across Sicily</a> over an invading Carthaginian force from modern-day Tunisia. Three generations later, the second battle in 409 B.C. was more chaotic. The historians report that Carthage besieged the city of Himera, which <a href="https://www.perseus.tufts.edu/hopper/text?doc=Diod.+13.62&fromdoc=Perseus%3Atext%3A1999.01.0084">this time had little outside assistance</a>.</p>
<p>These ancient accounts tell of grand generals, political alliances and sneaky military tactics such as the Greek cavalry who pretended to be friendly aid to get into the Carthaginian camp. </p>
<p>The 21st-century discovery of what looked like the remains of soldiers from around the times of these two famous battles provided a rare opportunity. Once Italian researchers had done initial studies on the skeletal remains of the 132 individuals, including estimating their age at death and looking for signs of disease, I was able to travel to Sicily with the Bioarchaeology of the Mediterranean Colonies Project, co-directed by <a href="https://scholar.google.com/citations?hl=en&user=Z6Epx_oAAAAJ">Laurie Reitsema</a> and <a href="https://www.unco.edu/hss/anthropology/about/faculty/britney-kyle.aspx">Britney Kyle</a>, to collect samples for isotope analysis.</p>
<p>My colleagues and I were interested in figuring out whether the soldiers’ remains told the same story as the ancient historians. The historical sources say they were likely all Greeks, with some possibly from other cities in Sicily, like Syracuse or Agrigento. Where had these soldiers really come from?</p>
<h2>Teeth record your origin story</h2>
<p>Luckily, chemistry provides a way to answer this question.</p>
<p>Different places on Earth have signature ratios of elemental isotopes in their land and water. Isotopes are versions of elements that have the standard number of protons but various amounts of neutrons.</p>
<p>The trick is that as you consume these characteristic isotopes in your food and drink, your body incorporates them into your bones and teeth. Researchers know that the type of <a href="https://doi.org/10.1111/1475-4754.00047">strontium in your body reflects the underlying geology or bedrock</a> where the plants and animals you ate grew. The oxygen isotopes come from your water source. These elements become a physical record of your origins.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/400368/original/file-20210512-17-dgd3xy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="cross-section diagram of a human tooth" src="https://images.theconversation.com/files/400368/original/file-20210512-17-dgd3xy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/400368/original/file-20210512-17-dgd3xy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=715&fit=crop&dpr=1 600w, https://images.theconversation.com/files/400368/original/file-20210512-17-dgd3xy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=715&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/400368/original/file-20210512-17-dgd3xy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=715&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/400368/original/file-20210512-17-dgd3xy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=898&fit=crop&dpr=1 754w, https://images.theconversation.com/files/400368/original/file-20210512-17-dgd3xy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=898&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/400368/original/file-20210512-17-dgd3xy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=898&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Enamel is the tough but thin outer covering of a tooth.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/adult-human-molar-cross-section-of-an-adult-human-molar-news-photo/143065363">Encyclopaedia Britannica/Universal Images Group via Getty Images</a></span>
</figcaption>
</figure>
<p>While bones are constantly growing – and incorporating elements from your environment throughout life – tooth enamel is like a time capsule. Scientists can use this outer layer of the tooth to figure out where an individual grew up, because it forms when you’re a child and doesn’t change over time.</p>
<p>The strontium and oxygen isotopes we measured on 62 of the individuals were incorporated into the soldiers’ teeth in childhood and preserved there, even after thousands of years in the ground. We used the combination of these elements to determine whether these soldiers were from Himera or not by comparing them to samples we collected to create a local isotopic profile for the city.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/400144/original/file-20210511-13-1dbr947.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="masked scientist holding various test tubes" src="https://images.theconversation.com/files/400144/original/file-20210511-13-1dbr947.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/400144/original/file-20210511-13-1dbr947.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=903&fit=crop&dpr=1 600w, https://images.theconversation.com/files/400144/original/file-20210511-13-1dbr947.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=903&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/400144/original/file-20210511-13-1dbr947.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=903&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/400144/original/file-20210511-13-1dbr947.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1135&fit=crop&dpr=1 754w, https://images.theconversation.com/files/400144/original/file-20210511-13-1dbr947.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1135&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/400144/original/file-20210511-13-1dbr947.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1135&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Katherine Reinberger performed chemical analysis on the samples back in the lab.</span>
<span class="attribution"><span class="source">Katherine Reinberger</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Interestingly, when we ran these analyses, we found that the majority of soldiers from the first battle in 480 B.C. were not local. Remember, that was the fight that reportedly had allied support from all over Sicily. These soldiers had such high strontium values and low oxygen values compared to what we’d expect in a Himera native that my colleagues and I think they were from even more distant places than just other parts of Sicily. Based on their teeth’s elemental isotope ratios, the soldiers likely had diverse geographic origins ranging through the Mediterranean and probably beyond.</p>
<p>On the other hand, the majority of soldiers from the later battle in 409 B.C. were in fact local. That finding supports the ancient sources that said the Himerans were mostly left unaided in the second fight, which allowed the Carthaginian force to overpower them. </p>
<h2>The unknown role of foreign mercenaries</h2>
<p>The case of the soldiers from 480 B.C. suggests that Greek armies were more diverse than previously thought. Our results challenge earlier interpretations based on historical documents that the soldiers were Greek and points to the omission of foreign mercenaries in the historians’ accounts.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/400367/original/file-20210512-18-10chtju.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Ancient Greek soldier with battle gear" src="https://images.theconversation.com/files/400367/original/file-20210512-18-10chtju.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/400367/original/file-20210512-18-10chtju.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=799&fit=crop&dpr=1 600w, https://images.theconversation.com/files/400367/original/file-20210512-18-10chtju.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=799&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/400367/original/file-20210512-18-10chtju.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=799&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/400367/original/file-20210512-18-10chtju.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1004&fit=crop&dpr=1 754w, https://images.theconversation.com/files/400367/original/file-20210512-18-10chtju.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1004&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/400367/original/file-20210512-18-10chtju.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1004&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Artist’s rendition of a heavy infantry hoplite soldier, with helmet, armor and shield.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/two-greek-soldiers-hoplite-heavy-infantry-with-helmet-news-photo/601071378">PHAS/Universal Images Group via Getty Images</a></span>
</figcaption>
</figure>
<p><a href="https://doi.org/10.1515/9781400846306-012">Modern historians</a> know Greek soldiers frequently served as paid career soldiers, or mercenaries, in foreign armies. But there is little evidence that foreign soldiers fought for Greek armies.</p>
<p>Greek armies at this time were mostly the classic hoplite soldiers: heavily armed foot soldiers. They often fought in groups based on the town they were from, where part of being a citizen meant serving in the military when needed. </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>
<p>The large variation in isotope values between the soldiers from our study strongly implies that there may have been foreign soldiers who joined the Greek side. Hiring foreign mercenaries could have changed the composition of communities in the Classical period, possibly providing outsiders a pathway to citizenship not otherwise available.</p>
<p>While the populations of Greek colonies were likely diverse because of interactions with other groups of people, not all residents of the colony would have been eligible for citizenship. Citizenship meant having a role in political life and was often reserved for wealthier men with Greek heritage. It was rare for foreigners to have a way into this highly esteemed position because, traditionally, one had to be Greek. </p>
<p>Not only does the discovery of foreign mercenary forces change the history of the first battle of Himera, it also transforms our understanding who had power and privilege in Sicily during the Classical period.</p><img src="https://counter.theconversation.com/content/160512/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Katherine Reinberger received funding for this research from the University of Georgia Graduate School (Innovative and Interdisciplinary Research Grant, Dean's Award), the University of Georgia Willson Center for Humanities & Arts Graduate Research Award, and the University of Georgia Center for Archaeological Science Norman Herz Grant for Student Research. Other funding for this project includes a Research Experience for Undergraduates from the National Science Foundation awarded to Katherine Reinberger's co-authors LJR and BK (<a href="https://www.nsf.gov/funding/pgm_summ.jsp?pims_id=5517">https://www.nsf.gov/funding/pgm_summ.jsp?pims_id=5517</a>), award numbers 1560227 and 1560158</span></em></p>Are the descriptions of war passed down by ancient historians accurate? A site in Sicily provided a rare chance to fact-check stories told about two battles from more than 2,400 years ago.Katherine Reinberger, Ph.D. Candidate in Anthropology, University of GeorgiaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1562412021-03-02T15:50:45Z2021-03-02T15:50:45ZA billion years from now, a lack of oxygen will wipe out life on Earth<figure><img src="https://images.theconversation.com/files/387012/original/file-20210301-12-pyj8jo.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5309%2C2280&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Triff / shutterstock</span></span></figcaption></figure><p>Earth will not be able to support and sustain life forever. Our oxygen-rich atmosphere may only last another billion years, according to a new study in <a href="https://dx.doi.org/10.1038/s41561-021-00693-5">Nature Geoscience</a>. </p>
<p>As our Sun ages, it is becoming more luminous, meaning that in the future Earth will receive more solar energy. This increased energy will affect the surface of the planet, speeding up the <a href="https://theconversation.com/an-effective-climate-change-solution-may-lie-in-rocks-beneath-our-feet-142462">weathering of silicate rocks</a> such as basalt and granite. When these <a href="https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/JC086iC10p09776">rocks weather</a> the greenhouse gas carbon dioxide is pulled out of the atmosphere and through chemical reactions locked in carbonate minerals. In theory, the Earth should start to cool down as carbon dioxide levels fall, but in around 2 billion years this effect will be negated by the ever-harshening glare of the Sun.</p>
<p>Carbon dioxide, along with water, is one of the key ingredients that plants need to perform <a href="https://www.rsb.org.uk/images/15_Photosynthesis.pdf">photosynthesis</a>. With falling carbon dioxide levels, less photosynthesis will occur and some types of plant may die out altogether. Less photosynthesis means less oxygen production, and gradually oxygen concentrations in Earth’s atmosphere will drop, creating a crisis for other forms of future life.</p>
<p>So, when will this happen? To find this out <a href="https://dx.doi.org/10.1038/s41561-021-00693-5">researchers from Japan and the US</a> used computer simulations to model the future evolution of the carbon, oxygen, phosphorous and sulphur cycles on the surface of the Earth. They also considered climate evolution and how the surface of the Earth (the crust, oceans and atmosphere) interacts with the planet’s interior (the mantle).</p>
<p>They modelled two theoretical scenarios: an Earth-like planet with an active biosphere, and a planet without an active biosphere. Interestingly, both scenarios produced broadly similar results: oxygen levels started to fall drastically at around 1 billion years in the future. This finding suggests that while falling levels of carbon dioxide and plant photosynthesis do affect oxygen levels, the effect of this process is secondary to long-term interactions between the mantle and surface environments. In short, it is the balance between the geochemistry of which rocks enter the mantle during subduction (see diagram below), and which gases are emitted from the mantle via volcanoes, that seems to mostly affect how long Earth’s atmosphere will remain oxygen-rich.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/387238/original/file-20210302-17-g6ays6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Diagram of subduction." src="https://images.theconversation.com/files/387238/original/file-20210302-17-g6ays6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/387238/original/file-20210302-17-g6ays6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=326&fit=crop&dpr=1 600w, https://images.theconversation.com/files/387238/original/file-20210302-17-g6ays6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=326&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/387238/original/file-20210302-17-g6ays6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=326&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/387238/original/file-20210302-17-g6ays6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=409&fit=crop&dpr=1 754w, https://images.theconversation.com/files/387238/original/file-20210302-17-g6ays6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=409&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/387238/original/file-20210302-17-g6ays6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=409&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Subduction is the process of rocks sinking into the inner Earth. But these rocks may take certain gases with them.</span>
<span class="attribution"><span class="source">stihii / shutterstock</span></span>
</figcaption>
</figure>
<p>The authors of the study conclude that our oxygen-rich atmosphere may only last around 1.08 billion more years. To put that in context, oxygen only started to accumulate in Earth’s atmosphere 2.5 billion years ago – during the <a href="https://theconversation.com/billions-of-years-ago-the-rise-of-oxygen-in-earths-atmosphere-caused-a-worldwide-deep-freeze-139722">Great Oxidation Event</a> – and it is likely that oxygen levels stayed fairly low for most of the planet’s history, only rising to near modern levels following the evolution of land plants around <a href="https://theconversation.com/breathable-atmospheres-may-be-more-common-in-the-universe-than-we-first-thought-128648">400 million years ago</a>.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/billions-of-years-ago-the-rise-of-oxygen-in-earths-atmosphere-caused-a-worldwide-deep-freeze-139722">Billions of years ago, the rise of oxygen in Earth’s atmosphere caused a worldwide deep freeze</a>
</strong>
</em>
</p>
<hr>
<p>The end of oxygen would almost certainly mark the end of Earth being able to support complex, aerobically respiring, forms of life. Though the details are debated, and other environmental factors are at play, scientists have long noted that the evolution and radiation of complex life on Earth seem tied to periods of <a href="https://www.nature.com/articles/nature13068">relative oxygen abundance</a>.</p>
<p>The authors of this study estimate that the total habitable lifetime of Earth – before it loses its surface water – is around 7.2 billion years, but they also calculate that an oxygen-rich atmosphere may only be present for around <a href="https://dx.doi.org/10.1038/s41561-021-00693-5">20%–30% of that time</a>.</p>
<p>Why does this matter? Imagine we were aliens on another world scanning the heavens for signs of life by looking for oxygen and ozone in the <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4643826/">atmospheres of exoplanets</a>. If our instruments passed over Earth 2 billion years from now, or 2 billion years ago, we might interpret a <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5399744/">false negative</a> – that such planets lacked a reliable “biosignature” – and move on with our search.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/387020/original/file-20210301-23-1q12fcx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Planets in space." src="https://images.theconversation.com/files/387020/original/file-20210301-23-1q12fcx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/387020/original/file-20210301-23-1q12fcx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=350&fit=crop&dpr=1 600w, https://images.theconversation.com/files/387020/original/file-20210301-23-1q12fcx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=350&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/387020/original/file-20210301-23-1q12fcx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=350&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/387020/original/file-20210301-23-1q12fcx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=440&fit=crop&dpr=1 754w, https://images.theconversation.com/files/387020/original/file-20210301-23-1q12fcx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=440&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/387020/original/file-20210301-23-1q12fcx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=440&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Some exoplanets may appear Earth-like now, but won’t in future.</span>
<span class="attribution"><span class="source">Jurik Peter / shutterstock</span></span>
</figcaption>
</figure>
<p>The same problem faces astronomers and planetary scientists today: what kind of exoplanets should we target, and what is a reliable biosignature of alien life? Habitability is not just a place around a star but a time in a planet’s evolution, and we must remain aware that we are limited to what we can see right now.</p>
<p>The future of our atmosphere bears a strong resemblance to its distant past: low in oxygen, rich in methane (if not carbon dioxide) with the possibility of organic hazes. As the authors of the new study suggest, using Earth as an analogue we might need to think more broadly about which gases to look for in exoplanet atmospheres and that we may need to rethink our interpretations of what those gases may indicate.</p>
<p>We need to better understand the history of our own atmosphere’s evolution over time and how the surface and interior of our planet evolved together. Only then will we be better placed to determine whether there is life living in the glare of other suns.</p><img src="https://counter.theconversation.com/content/156241/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Matthew Warke receives funding from the Carnegie Trust for the Universities of Scotland and the European Research Council. </span></em></p>This discovery will shape the hunt for life on exoplanets.Matthew Warke, Research Fellow, School of Earth & Environmental Sciences, University of St AndrewsLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1515782020-12-16T19:04:29Z2020-12-16T19:04:29ZEastern Australia has hundreds of enigmatic volcanoes. New research shows how they formed<figure><img src="https://images.theconversation.com/files/375215/original/file-20201215-15-15pzf7a.jpg?ixlib=rb-1.1.0&rect=14%2C0%2C2367%2C1350&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/q9-KwUcNNPQ">Luisa Denu / Unsplash</a></span></figcaption></figure><p>The landscape of eastern Australia is dotted with hundreds of extinct volcanoes. They gave rise to an environment to which Aboriginal people have been connected for <a href="https://theconversation.com/when-the-bullin-shrieked-aboriginal-memories-of-volcanic-eruptions-thousands-of-years-ago-81986">tens of thousands of years</a>, and the rich soils upon which modern Australia has grown in the last <a href="https://maas.museum/inside-the-collection/2016/03/31/industrial-revolution-wool/">few hundred years</a>.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/when-the-bullin-shrieked-aboriginal-memories-of-volcanic-eruptions-thousands-of-years-ago-81986">When the Bullin shrieked: Aboriginal memories of volcanic eruptions thousands of years ago</a>
</strong>
</em>
</p>
<hr>
<p>Yet until recently, these volcanoes posed a geological mystery. There are two common ways volcanoes form: at the edges of tectonic plates, or on top of blobs of hot material called “mantle plumes”, which rise from the planet’s deep interior. For most of eastern Australia’s volcanoes, however, neither of these explanations fits the bill. </p>
<p>We have now <a href="https://advances.sciencemag.org/content/6/51/eabd0953">solved the puzzle</a>. By studying the history of the eruptions and the chemical makeup of the rocks they spat out, we discovered a previously unknown geological mechanism that links volcanoes from Far North Queensland to the southern tip of Tasmania.</p>
<h2>Australia’s volcanic connection</h2>
<p>You may be surprised to learn that hundreds of volcanoes erupted along the entire eastern side of Australia over the past 100 million years. This volcanism also extended offshore to New Zealand and the <a href="https://www.9news.com.au/national/zealandia-how-the-worlds-hidden-continent-was-formed-near-australia-science/3a06ec96-fd19-421a-8422-e7dc107dd324">submerged continent of Zealandia</a>.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/what-are-lost-continents-and-why-are-we-discovering-so-many-126355">What are lost continents, and why are we discovering so many?</a>
</strong>
</em>
</p>
<hr>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/375836/original/file-20201218-17-1p83ap3.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Map showing Australia and Zealandia's volcanoes, mostly located down Australia's east coast" src="https://images.theconversation.com/files/375836/original/file-20201218-17-1p83ap3.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/375836/original/file-20201218-17-1p83ap3.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/375836/original/file-20201218-17-1p83ap3.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/375836/original/file-20201218-17-1p83ap3.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/375836/original/file-20201218-17-1p83ap3.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/375836/original/file-20201218-17-1p83ap3.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/375836/original/file-20201218-17-1p83ap3.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">There are many volcanoes across Australia and Zealandia. Highlights for volcano spotters include: (A) Sawn Rocks in New South Wales, (B) Glass House Mountains and (C) Undara Lava Tubes in Queensland, (D) Mt Gambier in South Australia, (E) Organ Pipes in Victoria and (F) The Nut in Tasmania.</span>
<span class="attribution"><span class="source">Jo Condon / Mahsa-Chitsaz / Luisa Denu / Jane Farquhar / Charles G / Nick Carson / Around Aus</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Most of the world’s volcanoes form when a process called “subduction” pushes parts of the seafloor down into Earth’s mantle, where it melts and produces volcanism at the surface. The best-known example of this kind of volcanism is the <a href="https://theconversation.com/five-active-volcanoes-on-my-asia-pacific-ring-of-fire-watch-list-right-now-90618">Ring of Fire</a> around the Pacific Ocean.</p>
<p>Alternatively, chains of volcanic islands may be built by hot material rising from the Earth’s deep interior – called “mantle plumes” – in a process that created the likes of Hawaii, Iceland, and the Galapagos Islands. These so-called “hotspot chains” track the movement of tectonic plates as new islands form over a stationary mantle plume.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/375314/original/file-20201216-21-upi7g.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/375314/original/file-20201216-21-upi7g.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/375314/original/file-20201216-21-upi7g.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=264&fit=crop&dpr=1 600w, https://images.theconversation.com/files/375314/original/file-20201216-21-upi7g.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=264&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/375314/original/file-20201216-21-upi7g.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=264&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/375314/original/file-20201216-21-upi7g.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=332&fit=crop&dpr=1 754w, https://images.theconversation.com/files/375314/original/file-20201216-21-upi7g.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=332&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/375314/original/file-20201216-21-upi7g.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=332&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Most volcanoes are clustered near subduction zones, where oceanic crust is recycled into the Earth’s mantle, or above hotspots which create chains of islands in the oceans.</span>
<span class="attribution"><span class="source">University of Saskatchewan</span></span>
</figcaption>
</figure>
<p>However, most of the volcanoes in our backyard are not related to mantle plumes and are not close to plate boundaries. So why are they here?</p>
<h2>Examining Australia’s volcanic pulse</h2>
<p>Our study, <a href="https://advances.sciencemag.org/content/6/51/eabd0953">published today</a> in Science Advances, shows the frequency of volcanic eruptions in eastern Australia and Zealandia depends on what’s happening to the seafloor some 3,000 kilometres further east.</p>
<p>Why does this happen? It’s all to do with how much water and carbon dioxide are trapped in the seafloor, which is recycled down into the mantle. </p>
<p>Over many millions of years, a reservoir of these volatile ingredients has built up in the mantle, more than 410 kilometres below the surface. This reservoir stays dormant beneath the Australian plate, until tectonic forces create bursts of movement.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/australias-volcanic-history-is-a-lot-more-recent-than-you-think-58766">Australia's volcanic history is a lot more recent than you think</a>
</strong>
</em>
</p>
<hr>
<p>As slabs of seafloor are subducted at the Tonga-Kermadec Trench, which runs from New Zealand all the way to Samoa, the vibrations reach all way to the mantle reservoir beneath eastern Australia and Zealandia. As a result, water and carbon dioxide shake loose from the reservoir and rise up to produce volcanic eruptions at the surface. </p>
<p>We found our first piece of evidence for this driving process in the deep history of volcanic eruptions in the region. There were two gradual increases in volcanism, one between 60 million years ago and 21 million years ago, and the other from 10 million years ago to 2 million years ago. These periods were separated by a brief (in geological terms) lull in eruption frequency. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/ECp63U_8gBs?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Reconstruction of volcanism and subduction in eastern Australia and Zealandia since 120 million years ago in map view, visualised in AuScope enabled GPlates software.</span></figcaption>
</figure>
<p>Both episodes were produced by major reorganisations of Earth’s tectonic plates, in which the plates rapidly change speed and direction. These changes led to the subduction of a massive pile of western Pacific seafloor, which in turn caused volcanic activity as water and carbon dioxide were shaken from their reservoir in the mantle.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/375331/original/file-20201216-13-lrijul.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Our model in section view together with a graph of volcanism through time." src="https://images.theconversation.com/files/375331/original/file-20201216-13-lrijul.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/375331/original/file-20201216-13-lrijul.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/375331/original/file-20201216-13-lrijul.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/375331/original/file-20201216-13-lrijul.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/375331/original/file-20201216-13-lrijul.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/375331/original/file-20201216-13-lrijul.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/375331/original/file-20201216-13-lrijul.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">Our new model of volcanism shown as a slice through the Earth (sectional view), visualised together with the region’s volcanism over the last 100 million years.</span>
<span class="attribution"><span class="source">Jo Condon / Ben Mather</span></span>
</figcaption>
</figure>
<h2>Fingerprinting Australia’s mystery volcanoes</h2>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/374593/original/file-20201213-15-1qvrg46.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/374593/original/file-20201213-15-1qvrg46.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/374593/original/file-20201213-15-1qvrg46.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/374593/original/file-20201213-15-1qvrg46.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/374593/original/file-20201213-15-1qvrg46.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/374593/original/file-20201213-15-1qvrg46.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/374593/original/file-20201213-15-1qvrg46.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">In 2019 we travelled aboard the CSIRO research vessel Investigator to collect rock samples from underwater volcanoes and map thousands of kilometres of seafloor.</span>
<span class="attribution"><span class="source">Supplied</span></span>
</figcaption>
</figure>
<p>This subduction process is not unique to the Australian east coast. What sets the east Australia-Zealandia region apart is that the seafloor being pushed under the continent from the western Pacific is rich in materials that contain water and carbon dioxide. </p>
<p>Not only that, but these materials seem to collect at a shallow depth in the mantle over a long period of time, rather than sink deeper into Earth’s interior. This creates a zone deep in the mantle right under the east coast of Australia that is enriched with volatile materials.</p>
<p>We examined the chemical composition of rocks produced by these ancient eruptions across the region and found the vast majority shared common chemical fingerprints. These fingerprints told us the eruptions across the eastern third of Australia and Zealandia came from a common mantle reservoir, which could only have formed from the subduction of ancient seafloor. This was the final piece of the puzzle that helped us connect seemingly random volcanoes over 100 million years of history.</p>
<h2>New ‘eyes’ to explore abroad and at home</h2>
<p>Combining the perspectives of volcanic history, tectonic plate movements and geochemistry may also help us to unlock other explosive mysteries of our natural world. We hope to test our model further in other enigmatic regions where volcanoes appear in the middle of tectonic plates, such as the western United States, eastern China, and around Bermuda.</p>
<p>In the meantime, we hope our discoveries give you a new way to look at the many beautiful volcanic hills and other features of eastern Australia. If you’re driving around the countryside this summer, here are our top five volcanic highlights for your travelling pleasure:</p>
<ul>
<li><p><a href="https://www.discovertasmania.com.au/attraction/thenut">The Nut</a>, Tasmania</p></li>
<li><p><a href="https://discovermountgambier.com.au/experience/geological-wonders/">Mount Gambier</a>, South Australia</p></li>
<li><p><a href="https://www.parks.vic.gov.au/places-to-see/parks/organ-pipes-national-park">Organ Pipes National Park</a>, Victoria</p></li>
<li><p><a href="https://www.visitnarrabri.com.au/narrabri-directory/sawn-rocks/">Sawn Rocks Narrabri</a>, New South Wales</p></li>
<li><p><a href="https://www.tropicalnorthqueensland.org.au/things-to-do/geological-wonders/lava-tubes/">Undara lava tubes</a>, Queensland</p></li>
</ul>
<hr>
<p><em>This study was carried out by researchers from the University of Sydney, <a href="https://www.monash.edu/science/schools/earth-atmosphere-environment">Monash University</a> and <a href="https://www.gns.cri.nz/">GNS Science</a> in Dunedin, New Zealand. It was enabled by Australia’s National Collaborative Research Infrastructure Strategy (<a href="https://www.education.gov.au/national-collaborative-research-infrastructure-strategy-ncris">NCRIS</a>) via <a href="https://www.auscope.org.au">AuScope</a> and <a href="https://www.chiefscientist.nsw.gov.au">The Office of the Chief Scientist and Engineer</a>, NSW Department of Industry.</em></p>
<p><em>CORRECTION: This article originally referred to Cradle Mountain in Tasmania, which is not in fact volcanic. It should have referred to <a href="https://www.discovertasmania.com.au/attraction/thenut">The Nut</a>, which is. This has been amended.</em></p><img src="https://counter.theconversation.com/content/151578/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ben Mather works for The University of Sydney, supported by funds from the Australian Research Council.</span></em></p><p class="fine-print"><em><span>Dietmar Müller receives funding from the Australian Research Council, the AuScope National Collaborative Research Infrastructure and the NSW Department of Industry.</span></em></p><p class="fine-print"><em><span>Jo Condon works for AuScope, a non-profit organisation funded by the Australian Government (NCRIS) that helped to enable this research. </span></em></p><p class="fine-print"><em><span>Maria Seton receives funding from the Australian Research Council.</span></em></p><p class="fine-print"><em><span>Oliver Nebel receives funding from the Australian Research Council</span></em></p>From far north Queensland to the southern tip of Tasmania, there is a common geological mechanism that links Eastern Australia’s volcanic history.Ben Mather, Computational Geophysicist, University of SydneyDietmar Müller, Professor of Geophysics, University of SydneyJo Condon, Honorary researcher, The University of MelbourneMaria Seton, Senior Lecturer, University of SydneyOliver Nebel, Associate Professor, Monash UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1435642020-07-29T18:04:02Z2020-07-29T18:04:02ZStonehenge: how we revealed the original source of the biggest stones<figure><img src="https://images.theconversation.com/files/349929/original/file-20200728-21-igjyf1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Andre Pattenden/English Heritage</span></span></figcaption></figure><p>Stonehenge, an icon of European prehistory that attracts more than a million visitors a year, is rarely out of the news. Yet, surprisingly, there is much we don’t know about it. Finding the sources of the stones used to build the monument is a fundamental question that has vexed antiquaries and archaeologists for over four centuries.</p>
<p>Our interdisciplinary team, including researchers from four UK universities (Brighton, Bournemouth, Reading and UCL) and English Heritage, has used a novel geochemical approach to examine the large “sarsen” stones at Stonehenge. <a href="https://advances.sciencemag.org/lookup/doi/10.1126/sciadv.abc0133">Our results</a> confirm that the nearby Marlborough Downs were the source region for the sarsens, but also pinpoint a specific area as the most likely place from where the stones were obtained.</p>
<p>Two main types of stone are present at Stonehenge: sarsen sandstone for the massive framework of upright stones capped by horizontal lintels; and a mix of igneous rocks and sandstones collectively known as “bluestones” for the smaller elements within the central area. </p>
<figure class="align-center ">
<img alt="Part of Stonehenge casting shadows." src="https://images.theconversation.com/files/349935/original/file-20200728-27-rvvein.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/349935/original/file-20200728-27-rvvein.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=441&fit=crop&dpr=1 600w, https://images.theconversation.com/files/349935/original/file-20200728-27-rvvein.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=441&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/349935/original/file-20200728-27-rvvein.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=441&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/349935/original/file-20200728-27-rvvein.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=554&fit=crop&dpr=1 754w, https://images.theconversation.com/files/349935/original/file-20200728-27-rvvein.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=554&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/349935/original/file-20200728-27-rvvein.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=554&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Inside the sarsen circle.</span>
<span class="attribution"><span class="source">James Davies/English Heritage</span></span>
</figcaption>
</figure>
<p><a href="https://www.cambridge.org/core/journals/antiquity/article/megalith-quarries-for-stonehenges-bluestones/AAF715CC586231FFFCC18ACB871C9F5E/core-reader?sfns=mo">Research in the last decade</a> has confirmed that the igneous bluestones were brought to Stonehenge from the Preseli Hills in Pembrokeshire, over 200km to the west. The sandstones have been tracked to eastern Wales although the exact outcrops have yet to be found. However, the origins of the sarsen stones has, until now, remained a mystery.</p>
<p>Stonehenge is a complicated and long-lived monument <a href="https://www.cambridge.org/core/journals/antiquity/article/stonehenge-remodelled/A118920A90FB7CCB2838CEEB10BE477D">constructed in five main phases</a>. The earliest, dated to about 3000BC, comprised a roughly 100m-diameter circular enclosure bounded by a bank and external ditch. Inside were various stone and timber structures, and numerous cremation burials. </p>
<p>The sarsen structures visible today were erected around 2500BC and comprised five trilithons (the doorway-like structures formed from two uprights joined by a lintel) surrounded by a circle of a further 30 uprights linked by lintels. The trilithons were arranged in a horseshoe formation with its principal axis aligned to the rising midsummer sun in the northeast and the setting midwinter sun to the southwest.</p>
<h2>Locating the sarsen source</h2>
<p>Conventional wisdom holds that the sarsens were brought to Stonehenge from the Marlborough Downs, some 30km to the north, the closest area with substantial scatters of large sarsen boulders. However, the Marlborough Downs are extensive and greater precision is needed to understand how prehistoric peoples used the landscape and its resources. </p>
<p>Our research has identified what might be termed the “geochemical fingerprint” of the Stonehenge sarsens. We started by analysing the geochemistry of all 52 remaining sarsens at Stonehenge (28 of those originally present are now missing, having been removed long ago). </p>
<p>This phase of the work involved using a non-destructive technology called portable x-ray fluorescence spectrometry (PXRF). Carrying out the PXRF analyses required access to the monument when it was closed to visitors and included several night shifts and one early morning analysing the lintel stones from a mobile scaffold tower. Data collection is never easy!</p>
<figure class="align-center ">
<img alt="Diagram of Stonehenge layout" src="https://images.theconversation.com/files/349931/original/file-20200728-29-5kkqcy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/349931/original/file-20200728-29-5kkqcy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=424&fit=crop&dpr=1 600w, https://images.theconversation.com/files/349931/original/file-20200728-29-5kkqcy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=424&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/349931/original/file-20200728-29-5kkqcy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=424&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/349931/original/file-20200728-29-5kkqcy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=533&fit=crop&dpr=1 754w, https://images.theconversation.com/files/349931/original/file-20200728-29-5kkqcy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=533&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/349931/original/file-20200728-29-5kkqcy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=533&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Most sarsens had the same chemical signature.</span>
<span class="attribution"><span class="source">David Nash, University of Brighton</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Analysis of the PXRF data showed that the geochemistry of most of the stones at Stonehenge was highly consistent, and only two sarsens (stones 26 and 160) had a statistically different chemical signature. This was an interesting result as it suggested we were looking for a single main source. </p>
<p>Then came a major stroke of luck. We were able to analyse three small samples that had been taken from one of <a href="https://www.bbc.co.uk/news/uk-england-wiltshire-48190588">the stones in 1958</a>, Stone 58, part of the group of sarsens with a consistent chemistry. Using a method known as inductively coupled plasma mass spectrometry (ICP-MS) gave a high-resolution geochemical fingerprint for the Stonehenge sarsen. Like all good detectives, we could now compare our fingerprint with those of the potential sources.</p>
<figure class="align-center ">
<img alt="Man examining stone rod." src="https://images.theconversation.com/files/349938/original/file-20200728-29-ptxuq9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/349938/original/file-20200728-29-ptxuq9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/349938/original/file-20200728-29-ptxuq9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/349938/original/file-20200728-29-ptxuq9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/349938/original/file-20200728-29-ptxuq9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/349938/original/file-20200728-29-ptxuq9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/349938/original/file-20200728-29-ptxuq9.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">David Nash examining the core from Stone 58.</span>
<span class="attribution"><span class="source">Sam Frost/English Heritage</span></span>
</figcaption>
</figure>
<p>Sarsen blocks are found widely scattered across southern Britain, broadly south of a line from Devon to Norfolk. We sampled stones from 20 areas, including six in the Marlborough Downs, and analysed them using ICP-MS. </p>
<p>Comparing the geochemical signature from Stone 58 against our resulting data revealed only one direct chemical match: the area known as West Woods to the south-west of Marlborough. We could therefore conclude that most of the Stonehenge sarsens were from West Woods.</p>
<p>Our results not only identify a specific source for most of the sarsens used to build Stonehenge, but also open up debate about many connected issues. Researchers have previously <a href="https://www.cambridge.org/core/journals/antiquity/article/stonehenge-remodelled/A118920A90FB7CCB2838CEEB10BE477D">suggested several routes</a> by which the sarsens may have been transported to Stonehenge, without actually knowing where they came from. </p>
<figure class="align-center ">
<img alt="Aerial view of Stonehenge" src="https://images.theconversation.com/files/349933/original/file-20200728-35-1e5a8up.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/349933/original/file-20200728-35-1e5a8up.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/349933/original/file-20200728-35-1e5a8up.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/349933/original/file-20200728-35-1e5a8up.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/349933/original/file-20200728-35-1e5a8up.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/349933/original/file-20200728-35-1e5a8up.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/349933/original/file-20200728-35-1e5a8up.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Many mysteries remain.</span>
<span class="attribution"><span class="source">Andre Pattenden/English Heritage</span></span>
</figcaption>
</figure>
<p>Now these can be revisited as we better appreciate the effort of moving <a href="https://research.historicengland.org.uk/Report.aspx?i=15106&ru=%252fResults.aspx%253fp%253d1%2526n%253d10%2526ry%253d2012%2526t%253dstonehenge%2526ns%253d1">boulders as long as 9m and weighing over 30 tonnes</a> some 25km across the undulating landscape of Salisbury Plain. We can feel the pain of the Neolithic people who took part in this collective effort and think about how they managed such a Herculean task. </p>
<p>We can also ask what was special about the West Woods plateaux and its sarsens. Was it simply their shape and size that attracted attention? Or was there some more deep-seated reason rooted in the beliefs and identities of the people that built Stonehenge? </p>
<p>Revealing that all the stones came from a single main source is also important and accords with the evidence that the sarsens were all erected at much the same time. But what about the two sarsens whose fingerprints differ from the main source? Where did they come from? The quest continues, and the questions just keep coming.</p><img src="https://counter.theconversation.com/content/143564/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Nash received funding for the research described in this article from the British Academy and The Leverhulme Trust.</span></em></p><p class="fine-print"><em><span>Timothy Darvill received funding for the research described in this article from the British Academy and The Leverhulme Trust.</span></em></p>How we traced the origin of the sarsen stones.David Nash, Professor of Physical Geography, University of BrightonTimothy Darvill, Professor of Archaeology, Department of Archaeology and Anthropology, Bournemouth UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1397222020-06-02T14:49:54Z2020-06-02T14:49:54ZBillions of years ago, the rise of oxygen in Earth’s atmosphere caused a worldwide deep freeze<figure><img src="https://images.theconversation.com/files/339150/original/file-20200602-133851-utuwkv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Nostalgia for Infinity / shutterstock</span></span></figcaption></figure><p>Around two and a half billion years ago the Earth was an alien world that would have been hostile to most of the complex life that surrounds us today. This was a planet where bacteria reigned, and one kind of bacteria in particular – <a href="https://ucmp.berkeley.edu/bacteria/cyanointro.html">cyanobacteria</a> – was slowly changing the world around it through photosynthesis.</p>
<p>The atmosphere of the early Earth lacked <a href="https://www.nature.com/articles/nature13068">oxygen</a>. This began to change during what’s known as the <a href="http://www.bbc.co.uk/earth/story/20150701-the-origin-of-the-air-we-breathe">Great Oxidation Event</a>, or GOE. At its broadest definition, the GOE refers to a series of chemical changes that geologists and geochemists have observed in rocks that are between 2.5 and 2.3 billion years old. These changes were the result of oxygen given off by ancient cyanobacteria. Communities of this bacteria lived in shallow seawater and were preserved in rocks as structures called <a href="https://theconversation.com/shark-bay-stromatolites-at-risk-from-climate-change-4277">stromatolites</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/339156/original/file-20200602-133902-wbgu4d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/339156/original/file-20200602-133902-wbgu4d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/339156/original/file-20200602-133902-wbgu4d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/339156/original/file-20200602-133902-wbgu4d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/339156/original/file-20200602-133902-wbgu4d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/339156/original/file-20200602-133902-wbgu4d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/339156/original/file-20200602-133902-wbgu4d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/339156/original/file-20200602-133902-wbgu4d.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">Modern stromatolites in Shark Bay, Australia.</span>
<span class="attribution"><span class="source">totajla / shutterstock</span></span>
</figcaption>
</figure>
<p>We know that the GOE was associated with a series of glaciations on Earth, at least one of which was thought to be the first <a href="https://astronomy.com/news/2019/04/the-story-of-snowball-earth">“snowball Earth” event</a> – a glaciation so severe that ice sheets extended as far as the tropics. Though this glaciation has now been dated to approximately <a href="https://www.pnas.org/content/114/8/1811">2.42 billion years ago</a>, uncertainty about the exact timing of the Great Oxidation Event has meant that it has not been possible to say which came first; was it the oxidation or the snowball Earth glaciation?</p>
<p>There have been hypotheses and arguments supporting both scenarios. If the glaciation came first, it is possible that it was because nutrients that were derived from rocks ground up by glaciers were washed into the oceans by rivers and floodwaters when the ice sheets melted. Once in the ocean these nutrients could have stimulated a cyanobacterial bloom thereby increasing <a href="https://www.pnas.org/content/102/32/11131.short#abstract-1">oxygen production</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/339200/original/file-20200602-133860-u8my01.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/339200/original/file-20200602-133860-u8my01.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/339200/original/file-20200602-133860-u8my01.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=316&fit=crop&dpr=1 600w, https://images.theconversation.com/files/339200/original/file-20200602-133860-u8my01.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=316&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/339200/original/file-20200602-133860-u8my01.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=316&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/339200/original/file-20200602-133860-u8my01.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=398&fit=crop&dpr=1 754w, https://images.theconversation.com/files/339200/original/file-20200602-133860-u8my01.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=398&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/339200/original/file-20200602-133860-u8my01.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=398&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 cyanobacterial bloom in the Baltic Sea.</span>
<span class="attribution"><span class="source">Niar / shutterstock</span></span>
</figcaption>
</figure>
<p>Conversely, oxygenation of the atmosphere during the GOE would have destabilised methane, a greenhouse gas that is thought to have been present in greater concentrations in the early atmosphere. A <a href="https://www.sciencedirect.com/science/article/pii/S0016703718302151">rapid drop in methane levels</a> would have caused a collapse of the greenhouse effect, therefore triggering a sudden and severe cooling of the climate.</p>
<h2>Searching for sulphur</h2>
<p>To investigate the timing of the Great Oxidation Event, colleagues and I examined two rock “cores” drilled from the Kola Peninsula in the far north-west of Russia, not far from Finland and Norway. These sedimentary rocks were deposited in shallow seawater between 2.50 and 2.43 billion years ago. We analysed the sulphur they contained using a new state-of-the-art technique developed at the <a href="https://www.st-andrews.ac.uk/earth-sciences/">University of St Andrews</a> in Scotland, and our results are now published in the journal <a href="https://www.pnas.org/content/early/2020/05/26/2003090117">PNAS</a>. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/339202/original/file-20200602-133855-149yold.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/339202/original/file-20200602-133855-149yold.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/339202/original/file-20200602-133855-149yold.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1091&fit=crop&dpr=1 600w, https://images.theconversation.com/files/339202/original/file-20200602-133855-149yold.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1091&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/339202/original/file-20200602-133855-149yold.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1091&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/339202/original/file-20200602-133855-149yold.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1371&fit=crop&dpr=1 754w, https://images.theconversation.com/files/339202/original/file-20200602-133855-149yold.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1371&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/339202/original/file-20200602-133855-149yold.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1371&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">2.5 billion year old rocks, containing traces of a planet with – and without – oxygen.</span>
<span class="attribution"><span class="source">Aivo Lepland</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>We looked at sulphur because sulphur isotopes – that is, atoms of sulphur with different atomic masses – are the most robust “fingerprints” of the GOE. The relative amounts of each of these sulphur isotopes is usually predictable. However, in rocks more than 2.5 billion years old this rule does not hold true, and certain unpredictable ratios, caused by photochemical reactions in the atmosphere, are preserved in rocks if the atmosphere at the time lacked oxygen. Therefore we can use the point at which <a href="https://www.annualreviews.org/doi/full/10.1146/annurev-earth-060115-012157#_i57">sulphur with this sort of unpredictable isotope ratios</a> vanishes from ancient rocks to pinpoint the GOE. </p>
<p>We found evidence in the older Russian rocks we looked at, but in the younger rocks it was absent. This is strong evidence that the GOE happened in a 70-million-year interval between 2.50 and 2.43 billion years ago. This is earlier than previous estimates of the GOE, but we argue that it is consistent with sulphur isotope records from South Africa, North America and Australia.</p>
<p>Importantly, given the age constraints on the snowball Earth deposit, we can now say the GOE preceded the most severe of the glacial episodes. We conclude, as <a href="https://advances.sciencemag.org/content/6/9/eaax1420">others have argued</a>, that it is likely that rising atmospheric oxygen concentrations lowered methane levels and weakened the greenhouse effect thereby pushing the planet into a period of major glaciation.</p>
<p>So, why does this matter? As we take greater steps to evaluating the habitability of other planets and moons in our solar system, and exoplanets beyond, it is vitally important that we understand the evolution of life in the context of the geological changes that have happened on Earth. If we were to view the ancient Earth through a telescope <a href="https://theconversation.com/breathable-atmospheres-may-be-more-common-in-the-universe-than-we-first-thought-128648">would we recognise a habitable world</a>?</p>
<p>Further, as we continue to change our atmosphere through rising anthropogenic greenhouse gas emissions, and consider schemes to mitigate climate change by directly <a href="https://www.bbc.co.uk/news/science-environment-47638586">removing greenhouse gases from the air</a>, it is important that we understand the extremes of how Earth’s climate has shifted in the distant past. The Great Oxidation Event reminds us of a time when life on Earth pumped uncontrolled levels of “waste gas” into the atmosphere. While this facilitated the eventual evolution of complex life like humans, it changed the course of Earth history forever.</p><img src="https://counter.theconversation.com/content/139722/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Matthew Warke receives funding from the European Research Council (via grant No 678812 to Dr Mark Claire) and the Carnegie Trust for the Universities of Scotland. </span></em></p>Scientists have now dated the ‘Great Oxidation Event’ to just before the planet’s first ‘snowball’ period.Matthew Warke, Research Fellow, School of Earth & Environmental Sciences, University of St AndrewsLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1255572019-12-02T04:42:29Z2019-12-02T04:42:29ZReturning to country: we should use genetics, geology and more to repatriate Aboriginal remains<figure><img src="https://images.theconversation.com/files/304605/original/file-20191202-156112-1xetq8o.jpg?ixlib=rb-1.1.0&rect=0%2C7%2C2586%2C1073&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Working out where Aboriginal remains came from will in take researchers from several disciplines working together.</span> <span class="attribution"><span class="source">Michael Westaway</span>, <span class="license">Author provided</span></span></figcaption></figure><p>The remains of thousands of Aboriginal Australians are scattered around the world in museums and universities. Many institutions accept these remains should be returned to descendant communities, but it’s not always easy to do.</p>
<p>A major problem is that we often lack detailed information about where in Australia the remains came from. It has been <a href="https://www.oxfordhandbooks.com/view/10.1093/oxfordhb/9780199569069.001.0001/oxfordhb-9780199569069-e-41">estimated</a> that up to a quarter of the human remains in Australian museums have poor contextual information.</p>
<p>Recently, we completed an Australian Research Council-funded <a href="https://www.tandfonline.com/doi/full/10.1080/00438243.2019.1686418">project</a> that focused on human remains from the Cape York Peninsula of Queensland, in collaboration with several local Aboriginal communities. </p>
<p>What we found suggests no single method such as DNA testing or using geological clues will be enough to reliably determine the origin of remains – an interdisciplinary approach using all available evidence will be required.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/mungo-man-returns-home-there-is-still-much-he-can-teach-us-about-ancient-australia-87264">Mungo Man returns home: there is still much he can teach us about ancient Australia</a>
</strong>
</em>
</p>
<hr>
<h2>DNA evidence alone won’t be enough</h2>
<p>Over the past few years there has been considerable interest in the possibility that genetic testing can solve the repatriation problem. One aim of our project was to see if this approach would work in the Australian context.</p>
<p>In a <a href="https://advances.sciencemag.org/content/4/12/eaau5064">study</a> reported last year, we extracted genetic information from ancient human remains of known provenance and compared them to genomes obtained from living Aboriginal Australians.</p>
<p>We looked at two different kinds of DNA: nuclear DNA (this is the DNA that contains the genetic code for building your body) and mitochondrial DNA (the DNA of the tiny cell units called mitochondria that help to power your body’s cells).</p>
<p>When we used nuclear DNA, we were able to link ancient remains and living individuals from the same area with a high degree of accuracy. But when we only employed mitochondrial DNA from the ancient remains, the accuracy dropped markedly. The nuclear DNA analyses had a success rate of 100%, whereas the mitochondrial DNA analyses failed to identify a region of origin for 31% of the individuals and suggested the wrong region for 7% of them.</p>
<p>This is an issue because, for very old remains, it’s much more likely that we will be able to recover mitochondrial DNA than nuclear DNA. The reason is simply numbers: each cell contains hundreds or thousands of copies of the mitochondrial DNA but only one or two of the nuclear DNA.</p>
<p>There are other problems with relying solely on DNA for repatriation. The complexities of human social life (such as inter-tribal marriage) and the impacts of colonisation on Aboriginal Australians (such as displacement) mean that even full genome comparisons may not correctly identify an individual’s tribal affiliation.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/304588/original/file-20191201-156116-lvm5ey.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/304588/original/file-20191201-156116-lvm5ey.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/304588/original/file-20191201-156116-lvm5ey.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/304588/original/file-20191201-156116-lvm5ey.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/304588/original/file-20191201-156116-lvm5ey.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/304588/original/file-20191201-156116-lvm5ey.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/304588/original/file-20191201-156116-lvm5ey.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">
<figcaption>
<span class="caption">Excavating the remains of a woman buried more than 3000 years ago at Duyfken Point on Cape York revealed no nuclear DNA.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>Mapping strontium also won’t be enough</h2>
<p>Another way to get information about where human remains are from is to measure the strontium in their bones and teeth.</p>
<p>Strontium is a common element, and our bodies use it as a building block. There are different types of strontium, called isotopes, and the ratio of these isotopes in the ground varies from place to place. So, if you measure the strontium isotope ratios in some remains and have a map of the different ratios at different places, it can help you work out where the remains came from.</p>
<p>Strontium isotope ratios have been used to guide repatriation elsewhere in the world, but our research in Cape York suggests this approach also won’t solve the problem of repatriating Australian Aboriginal remains by itself.</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/304614/original/file-20191202-79485-g68ivm.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/304614/original/file-20191202-79485-g68ivm.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=788&fit=crop&dpr=1 600w, https://images.theconversation.com/files/304614/original/file-20191202-79485-g68ivm.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=788&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/304614/original/file-20191202-79485-g68ivm.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=788&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/304614/original/file-20191202-79485-g68ivm.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=990&fit=crop&dpr=1 754w, https://images.theconversation.com/files/304614/original/file-20191202-79485-g68ivm.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=990&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/304614/original/file-20191202-79485-g68ivm.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=990&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A map of strontium isotope ratios in Cape York, derived from measurements of soil, water and plants.</span>
<span class="attribution"><span class="source">Shaun Adams</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>In the course of our Cape York project, we completed the first regional scale <a href="https://onlinelibrary.wiley.com/doi/full/10.1002/gea.21728">analysis</a> of strontium isotope variability in Australia. This involved collecting a large number of water, soil, and plant samples and creating a strontium isotope map or “isoscape”.</p>
<p>We found that locations often did not have unique values. This suggests that strontium ratios can narrow down the range of possible areas to which a set of remains could be returned, but on their own they are unlikely to pinpoint the exact area.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/where-did-you-grow-up-how-strontium-in-your-teeth-can-help-answer-that-question-112705">Where did you grow up? How strontium in your teeth can help answer that question</a>
</strong>
</em>
</p>
<hr>
<h2>Genomes and isotopes together</h2>
<p>Based on the results of our studies with genomes and isotopes, we think a reliable protocol for repatriating Aboriginal remains will take more than one scientific technique. Genomics alone won’t solve the problem. Nor will isotope geochemistry.</p>
<p>Instead, we need to develop an integrated interdisciplinary approach using DNA, isotopes, and whatever other lines of evidence are available (such as detailed analysis of bones, and even linguistics).</p>
<p>In order for this approach to work, we need to avoid creating a hierarchy among the scientific disciplines involved and focus instead on how they complement each other. In addition, we need to devise mechanisms that encourage sustained interaction and knowledge transfer between scientists from different disciplines.</p>
<h2>Aiming higher</h2>
<p>We drew another major conclusion from our Cape York project: those of us involved in repatriation projects should aim higher. We need to put more time and energy into developing new techniques and assessing the accuracy of existing ones.</p>
<p>Equally importantly, we need to seek new ways of fostering collaboration among scientists from different fields and between scientists and Aboriginal communities.</p>
<p>Lastly, the repatriation of Aboriginal remains deserves the same level of rigour as the repatriation of historical military remains and modern missing person cases. Crucially, this means that we should employ the standard of proof for coronial investigations, which is “on the balance of probabilities”.</p><img src="https://counter.theconversation.com/content/125557/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mark Collard receives funding from the Canada Research Chairs Program, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, and Simon Fraser University.</span></em></p><p class="fine-print"><em><span>Michael Westaway receives funding from the Australian Research Council. </span></em></p><p class="fine-print"><em><span>Adrian Miller, Joanne Wright, and Shaun Adams 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>It’s not always easy to work out where Aboriginal remains came from, but science can help.Mark Collard, Canada Research Chair in Human Evolutionary Studies, and Professor of Archaeology, Simon Fraser UniversityAdrian Miller, Pro Vice-Chancellor Indigenous Engagement, CQUniversity AustraliaJoanne Wright, Research scientist, Griffith UniversityMichael Westaway, Australian Research Council Future Fellow, Archaeology, School of Social Science, The University of QueenslandShaun Adams, Archaeologist, Griffith UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1106522019-02-01T10:19:31Z2019-02-01T10:19:31ZPonds can absorb more carbon than woodland – here’s how they can fight climate change in your garden<figure><img src="https://images.theconversation.com/files/256636/original/file-20190131-75085-aeuuvx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/pink-water-lily-lake-goldfish-142067443?src=N7w0h3qGCNdhJ3XzsVwzPQ-1-96">NagyDodo/Shutterstock</a></span></figcaption></figure><p>Ponds are taken for granted. Perhaps it’s because most of us have seen them – and on occasion, fallen into them – and think they’re only good for goldfish. Ponds may be the number one habitat for children’s “<a href="https://www.bbc.com/bitesize/articles/z9fkwmn">minibeast</a>” hunts, but we are supposed to grow out of them in adulthood. </p>
<p>As James Clegg, <a href="https://www.nature.com/articles/170681a0">a 20th-century British naturalist wrote</a>, ponds are </p>
<blockquote>
<p>a field particularly suited to the activities of the amateur, whose humble pond-hunting, if carried out systematically and carefully, may well result in valuable contributions to science.</p>
</blockquote>
<p>But all-too often, ponds are missed out of conservation strategies which are instead fixated on larger lakes and rivers. This is a serious omission – ponds are the <a href="https://link.springer.com/article/10.1007/s10750-015-2554-0">most common and widespread habitat</a> for all plants and animals across the continents and islands of Earth, from Antarctica to the tropics. Perched on the surface of Alpine glaciers or waiting out desert droughts to refill with the rains, deep in equatorial forest or amid the city sprawl. They could well be <a href="https://www.sciencedirect.com/science/article/pii/S0921818102001273">found on Mars</a>. </p>
<p>The past 20 years have seen a blossoming of research into ponds, led in the UK by the <a href="http://www.europeanponds.org/">Freshwater Habitats Trust and, internationally, the European Pond Conservation Network</a>. These organisations bring together researchers and practitioners to help conserve pond biodiversity. Their work has revealed that ponds are biodiversity hotspots in the landscape, disproportionately rich in species when compared to rivers, streams and lakes and <a href="https://link.springer.com/chapter/10.1007/978-90-481-9088-1_2">home to many rare specialists</a>, such as <a href="https://freshwaterhabitats.org.uk/pond-clinic/identifying-creatures-pond/fairy-shrimp/">fairy</a> and <a href="https://www.theguardian.com/environment/2015/may/24/specieswatch-tadpole-shrimp-oldest-living-creature">tadpole shrimps</a>. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/256634/original/file-20190131-112389-1kwpod0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/256634/original/file-20190131-112389-1kwpod0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=436&fit=crop&dpr=1 600w, https://images.theconversation.com/files/256634/original/file-20190131-112389-1kwpod0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=436&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/256634/original/file-20190131-112389-1kwpod0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=436&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/256634/original/file-20190131-112389-1kwpod0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=548&fit=crop&dpr=1 754w, https://images.theconversation.com/files/256634/original/file-20190131-112389-1kwpod0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=548&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/256634/original/file-20190131-112389-1kwpod0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=548&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Tadpole shrimps (<em>Triops cancriformis</em>) are the world’s oldest living animals and live in ponds.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/notostraca-two-tadpole-shrimps-triops-cancriformis-55996426?src=_W05oGa4bjeIqTl6tPC8nA-1-0">Repina Valeriya/Shutterstock</a></span>
</figcaption>
</figure>
<p>Ponds benefit humans by slowing down water run-off that can cause flooding and <a href="https://link.springer.com/article/10.1007/S10750-013-1719-Y">mopping up excess nutrients</a> – a great example of what are now recognised as “<a href="https://www.sciencedirect.com/science/article/pii/S0048969718327268">small water bodies</a>” that enrich and enliven a landscape. But, globally, ponds may also be important in influencing atmospheric carbon by storing and releasing it, given the intensity of geochemical processes and the sheer number of ponds around the world. However, just how fast ponds can bury carbon is poorly understood.</p>
<h2>A carbon sink in your own backyard</h2>
<p>Measuring the rate at which ponds can store carbon is tricky, primarily because the age of many ponds is unknown. To get <a href="https://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/fee.1988">precise measurements of carbon burial rates</a> we exploited an unusual opportunity using some small, lowland pools whose age is known to the exact day. The ponds were dug out in 1994, at Hauxley Nature Reserve in north-east England. Their original purpose was to follow the <a href="https://link.springer.com/article/10.1007/s10750-011-0678-4">colonisation of plants and invertebrates</a>.</p>
<p>Two decades later they had accumulated a layer of sediment, dark and rich in organic debris, distinctly different to the underlying clay. We used sediment cores and dug out all of the sediment from some ponds, to measure the organic carbon that had accumulated. The amount of carbon in the cores was scaled up to the amount dug up from other ponds to reflect the total volume of sediment.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/256079/original/file-20190129-108367-wgrd51.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/256079/original/file-20190129-108367-wgrd51.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/256079/original/file-20190129-108367-wgrd51.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/256079/original/file-20190129-108367-wgrd51.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/256079/original/file-20190129-108367-wgrd51.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/256079/original/file-20190129-108367-wgrd51.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/256079/original/file-20190129-108367-wgrd51.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">
<figcaption>
<span class="caption">Ponds are carbon sinks which can fit well in intensively managed landscapes.</span>
<span class="attribution"><span class="source">Mike Jeffries</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The ponds’ burial rates for organic carbon ranged from 79 to 247g per square metre per year, with a mean of 142g. These rates are high – much higher than the rates of 2-5g attributed to surrounding habitats such as <a href="http://digital.csic.es/bitstream/10261/89790/1/Downing-GBC-2008-v22-GB1018.pdf">woodland or grassland</a>. Small ponds occupy a <a href="https://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/fee.1988">tiny proportion of the UK’s land area</a> – scarcely 0.0006% – compared to grassland at 36% or 2.3% for ancient woodland. But the rate of carbon burial we found would result in ponds burying half as much as the vastly greater expanse of grassland.</p>
<p>However, the role ponds play in the carbon cycle is complicated. Some ponds may be significant sources of greenhouse gases, such as <a href="https://www.nature.com/articles/s41598-018-27770-x">permafrost thaw ponds</a> in the Arctic which release even more carbon as the tundras they’re found in warm. Our Hauxley ponds can switch back and forth from being a net sink to a net source of carbon as they dry out or re-flood. Nevertheless, our ponds have accumulated plenty of carbon over their 20 years and provided a home to a wealth of animals and plants.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/256078/original/file-20190129-108342-33dvnv.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/256078/original/file-20190129-108342-33dvnv.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/256078/original/file-20190129-108342-33dvnv.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/256078/original/file-20190129-108342-33dvnv.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/256078/original/file-20190129-108342-33dvnv.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/256078/original/file-20190129-108342-33dvnv.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/256078/original/file-20190129-108342-33dvnv.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">
<figcaption>
<span class="caption">Researchers take carbon cores from ponds at Hauxley Nature Reserve.</span>
<span class="attribution"><span class="source">Mike Jeffries</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Nothing was done to engineer carbon burial in our ponds – there was no artificial enhancement of productivity to maximise carbon capture. They are small, shallow, lowland ponds among the intensively farmed landscapes typical of much of the temperate climes. Similar ponds and tiny wetlands are dotted throughout the local landscape, primarily scraped out for wildlife conservation. </p>
<p>These lowland ponds are easy to create, <a href="https://freshwaterhabitats.org.uk/pond-clinic/create-pond/">even in a back garden</a>. They can be small and temporary – clean water is the key – and the value of their wildlife is now firmly understood. No longer overlooked, the importance of ponds in the carbon cycle and in fighting climate change is becoming apparent.</p><img src="https://counter.theconversation.com/content/110652/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mike Jeffries 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>Ponds are good for more than just decorating the garden – they could be your best tool in fighting climate change.Mike Jeffries, Associate Professor, Ecology, Northumbria University, NewcastleLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/900702018-01-22T17:15:27Z2018-01-22T17:15:27ZHow comet dust has enabled us to trace the history of the Solar System<figure><img src="https://images.theconversation.com/files/201810/original/file-20180112-101514-o1dufb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The comet 67P/Churyumov-Gerasimenko, seen up close.</span> <span class="attribution"><a class="source" href="http://www.esa.int/spaceinimages/Images/2016/11/Rosetta_comet_close-ups">ESA/Rosetta/NavCam</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>We are not used to considering dust as a valuable material – unless it comes from space. And more precisely, from the comet 67P/Churyumov-Gerasimenko. An analysis of its dust has provided valuable information about this celestial object, and, more generally, on the history of the Solar System.</p>
<p>Using the <a href="http://sci.esa.int/rosetta/35061-instruments/?fbodylongid=1638">COSIMA instrument</a> aboard the European space probe Rosetta, a scientific team scrutinised the comet <a href="http://sci.esa.int/rosetta/14615-comet-67p/">67P/Churyumov-Gerasimenko</a> (67P) in great detail from August 2014 to September 2016. They were interested in the dust particles ejected from the comet’s nucleus and captured by the spacecraft, and COSIMA made it possible to study their composition. The results of their research were published in <a href="https://academic.oup.com/mnras/article/469/Suppl_2/S712/4670835">December 2017</a> by the Royal Astronomical Society.</p>
<p>The study indicates that, on average, half of the mass of each dust particle consists of carbonaceous material with a mainly <a href="https://en.oxforddictionaries.com/definition/macromolecule">macromolecular</a> organic structure; the other half being mostly composed of non-hydrated silicate minerals. How is this result important or interesting? What does it imply? Was it expected by scientists or is it a total break pre-existing theories?</p>
<p>Thanks to Rosetta and its instruments, we have been able to get a better idea of what 67P is composed. This is particularly true for the gases in its atmosphere, thanks to the <a href="http://sci.esa.int/rosetta/35061-instruments/?fbodylongid=1650">ROSINA</a> instrument. During the comet’s journey around the Sun, it continuously releases gases and dust that form a faint halo. This phenomenon is explained by the sublimation of ices that are embedded within the nucleus of the comet – they directly change from the solid to the gaseous state. As the gas escapes into the comet’s atmosphere, it bring with it small dust particles. ROSINA has characterised and quantified the gases: it’s made of water vapour, carbon dioxide, carbon monoxide, molecular oxygen and a multitude of small organic molecules mainly made of carbon, hydrogen, nitrogen and oxygen atoms.</p>
<p>Other instruments, such as on-board cameras and the <a href="http://virtis-rosetta.lesia.obspm.fr/VIRTIS-the-instrument.html">VIRTIS</a> imaging spectrometer, studied the surface of 67P. Its structures are complex: cliffs, faults, landslides, pits and more. But above all, the comet surface is very dark and has little ice. The fact that it is so dark is possibly due to a high organic carbon content. Given that the ices and gases represent only a small fraction of the total cometary matter, the researchers rely on, among other things, the analysis of the dust grains released by the comet to learn more about the makeup of the comet’s nucleus. This dust is representative of the comet’s non-volatile composition, and the study of the dust’s chemical characteristics will reflect those of the comet’s nucleus.</p>
<h2>35,000 particles collected</h2>
<p>The COSIMA instrument is a kind of physico-chemical mini-laboratory, whose function was to collect dust particles released by the comet 67P, image them and then measure their chemical characteristics using a surface analysis method called “time-of-flight secondary ion mass spectrometry” (TOF-SIMS). During the two years spent orbiting the comet, data collection was more successful than dared hoped for by the researchers and engineers who designed the instrument about 20 years ago. Indeed, COSIMA has collected more than 35,000 particles that are up to 1 millimetre in diameter. We had expected many fewer and infinitely smaller dust grains.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/201167/original/file-20180108-83574-lhhcyu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/201167/original/file-20180108-83574-lhhcyu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=294&fit=crop&dpr=1 600w, https://images.theconversation.com/files/201167/original/file-20180108-83574-lhhcyu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=294&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/201167/original/file-20180108-83574-lhhcyu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=294&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/201167/original/file-20180108-83574-lhhcyu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=370&fit=crop&dpr=1 754w, https://images.theconversation.com/files/201167/original/file-20180108-83574-lhhcyu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=370&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/201167/original/file-20180108-83574-lhhcyu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=370&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">On the left, the surface of the cometary nucleus seen by the Rosetta probe. Condensed ice beneath the surface sublimes from the depths of the comet when it is warmed up as the comet approaches the Sun. The escaping gas entrains small dust particles that can be collected and analysed by the instruments of the Rosetta probe. On the right, a collecting target (1 cm x 1 cm) of the COSIMA instrument showing tiny fragments of the nucleus, up to a millimetre in size, that have impacted it. All these dust particles consist of an intimate mixture of 50/50 (by mass) of silicate minerals and organic material.</span>
<span class="attribution"><span class="source">Left, ESA/Rosetta/MPS for OSIRIS Team; right, ESA/Rosetta/MPS for COSIMA Team.</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The analysis and scientific interpretation of the mass spectrometric measurements made on a fraction of the particles collected (about 250) was long and challenging. The ultra-porosity of the dust, collected almost intact after ejection from the comet’s surface, has few analogues in our laboratories and the mastery of the TOF-SIMS technique, already complicated in the laboratory, had proved to be almost heroic when conducted remotely in space.</p>
<p>From these measurements, it was possible to deduce the dust particles’ main constituent elements (oxygen, carbon, silicon, iron, magnesium, sodium, nitrogen, aluminium, calcium…), as well as some information on the chemical nature of some components. From these data, the team showed that each dust particle (size ranging from ~0.05 to 1 mm in diameter) contained, on average, about 50% by mass of organic carbonaceous material. This material was mainly macromolecular, meaning that it was made of large structures put together in a totally disordered and complex fashion; the other half of the mass is mainly composed of non-hydrated silicates minerals.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/202873/original/file-20180122-182965-s6lb4b.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/202873/original/file-20180122-182965-s6lb4b.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=168&fit=crop&dpr=1 600w, https://images.theconversation.com/files/202873/original/file-20180122-182965-s6lb4b.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=168&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/202873/original/file-20180122-182965-s6lb4b.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=168&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/202873/original/file-20180122-182965-s6lb4b.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=212&fit=crop&dpr=1 754w, https://images.theconversation.com/files/202873/original/file-20180122-182965-s6lb4b.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=212&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/202873/original/file-20180122-182965-s6lb4b.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=212&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Left: the average elemental composition of the dust particles of comet 67P. Right: the average mass distribution of minerals and organic material in the dust.</span>
<span class="attribution"><span class="source">ESA/Rosetta/MPS for COSIMA Team.</span></span>
</figcaption>
</figure>
<p>According to the measurements, this dust composition is independent of the particle collection date. In other words, on average, there is no difference in composition between the dust ejected by the comet before, during or after its <a href="https://www.merriam-webster.com/dictionary/perihelion">perihelion</a>, which is when, in August 2015, 67P made its closest approach to the Sun and where its activity was the most intense. The composition of cometary dust is also not dependent on their size or morphology – “fluffy aggregates” or more “compact grains”. The analysed particles are small fragments of the nucleus, coming from its surface as well as pits that sink into the depths of the comet. Therefore, the average composition determined by COSIMA most likely reflects the overall volatile-free composition of 67P’s nucleus. Most of the cometary matter is thus formed by this intimate mixture of 50-50 by weight of minerals and solid carbonaceous material.</p>
<h2>A primitive material</h2>
<p>These results, as well as those obtained 30 years ago during the flyby of comet Halley by the <a href="https://motherboard.vice.com/en_us/article/nz7zz8/happy-anniversary-giotto-the-probe-that-flew-by-halleys-comet-30-years-ago">Giotto</a> and <a href="https://link.springer.com/article/10.1134/S0038094612070106">Vega</a> probes, prove that comets are among the most carbon-rich Solar System objects. Experts suspected this, but this is finally a direct experimental proof. The high value of the abundance ratio between carbon and silicon measured by COSIMA is very close to the abundance ratio of these elements measured in the Sun’s <a href="https://www.merriam-webster.com/dictionary/photosphere">photosphere</a>. Moreover, the silicates contained in 67P dust do not show any notable signs of alteration by liquid water. These two observations are an important proof of the primitive character of this cometary substance. It means that this material has hardly been modified since the comet’s formation, unlike most other objects in the Solar System. Studying it takes us back to the very beginning of the Solar System, nearly 4.5 billion years ago.</p>
<p>The COSIMA measurements, combined with the observations of the other Rosetta instruments, indicate that most of the cometary carbonaceous material is not found in ices and gases, but in dust, in this non-volatile macromolecular form. This result is in line with laboratory analyses of other extra-terrestrial materials that have been collected on Earth – meteorites, micrometeorites and interplanetary dust particles. With these, however, the original object from which these materials originated is rarely known. And above all, heating during the atmospheric entry alters and modifies, at least in part, their carbonaceous components. </p>
<p>COSIMA’s <em>in situ</em> measurements and its collection of dust at low speeds (a few metres per second, the pace of someone jogging) have made it possible to totally preserve the chemical information. Thus, it is possible to say today that if comets like 67P played a role in the appearance of life on Earth, especially by bringing carbon-rich material, it would have been this complex macromolecular component that dominated what was delivered.</p><img src="https://counter.theconversation.com/content/90070/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Les auteurs ne travaillent pas, ne conseillent pas, ne possèdent pas de parts, ne reçoivent pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'ont déclaré aucune autre affiliation que leur organisme de recherche.</span></em></p>Dust can be instructive. The analysis of those collected around the comet 67P/Churyumov-Gerasimenko provided new information on the history of the solar system.Donia Baklouti, Astrochimiste, Maître de Conférences à l’Institut d’Astrophysique Spatiale (IAS), Université Paris-SaclayAnaïs Bardyn, Astrochimiste, post-doctorante au Department of Terrestrial Magnetism (DTM), Carnegie ScienceHervé Cottin, Astrochimiste, Professeur au Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), Université Paris-Est Créteil Val de Marne (UPEC)Licensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/61282012-03-29T03:42:47Z2012-03-29T03:42:47ZWhat on Earth! Hot news on our planet’s formation<figure><img src="https://images.theconversation.com/files/9100/original/cjft3psj-1332983488.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">It's time we got to the core of our planet's early history.</span> <span class="attribution"><span class="source">Derringdos</span></span></figcaption></figure><p>As of today, the world might have changed forever. </p>
<p>A fundamental assumption underpinning much of modern geochemistry is that the earth has the same composition as a class of meteorites called <a href="http://en.wikipedia.org/wiki/Chondrite">chondrites</a>. These are small fragments of rock-like, primeval material that have survived from the birth of the sun with few subsequent changes.</p>
<p>So ingrained is this chondritic assumption in geochemical thinking that, as recently as three years ago, to write a paper questioning the chondritic theory would have been regarded as an act of scientific heresy. It’s unlikely any reputable scientific journal would have published it.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/9109/original/9fg8n23r-1332992351.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/9109/original/9fg8n23r-1332992351.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/9109/original/9fg8n23r-1332992351.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=454&fit=crop&dpr=1 600w, https://images.theconversation.com/files/9109/original/9fg8n23r-1332992351.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=454&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/9109/original/9fg8n23r-1332992351.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=454&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/9109/original/9fg8n23r-1332992351.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=571&fit=crop&dpr=1 754w, https://images.theconversation.com/files/9109/original/9fg8n23r-1332992351.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=571&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/9109/original/9fg8n23r-1332992351.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=571&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 collision with the young Earth changed the planet’s composition.</span>
<span class="attribution"><span class="source">Wikimedia Commons</span></span>
</figcaption>
</figure>
<p>Every professor and every textbook has been telling students for more than 40 years that the composition of Earth is chondritic. Consequently, all geochemists assume the chondritic hypothesis forms an unshakable foundation upon which we can build future advances in geochemistry. </p>
<p>But today, with <a href="http://www.nature.com/nature/journal/v483/n7391/abs/nature10901.html">a paper published in Nature</a>, we’re challenging this fundamental assumption, arguing Earth’s composition isn’t chondritic.</p>
<p>While our paper could be a turning point, geochemists have been questioning aspects of the “chondritic” hypothesis for three or four years now.</p>
<p>We know that the <a href="http://en.wikipedia.org/wiki/Argon">argon</a> content of the atmosphere is <a href="http://www.nature.com/nature/journal/v303/n5920/abs/303762a0.html">only about half that predicted by the chondritic hypothesis</a>. This insight has led to the suggestion that <a href="http://www.geokem.com/homogen.html">the earth’s mantle</a> – the rocky part between the <a href="http://pubs.usgs.gov/gip/dynamic/inside.html">iron-nickel core</a> at the centre of the earth and the surface – is divided into two layers, and only the outer layer has lost argon.</p>
<p>Our study shows this can’t be the case, but more on that in a moment.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/_mcC8kFacrk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>Our challenge to the chondritic paradigm comes from studies of <a href="http://en.wikipedia.org/wiki/Neodymium">neodymium</a> <a href="https://theconversation.com/could-iran-be-building-nuclear-weapons-a-scientific-perspective-5399">isotopes</a> in volcanic rocks and meteorites. Our studies show that the ratio of <a href="http://en.wikipedia.org/wiki/Samarium">samarium</a> to neodymium (both <a href="http://en.wikipedia.org/wiki/Rare_earth_element">“rare-earth” metals</a>) in Earth’s volcanic rocks is higher than it is in chondritic meteorites.</p>
<p>This means rare-earth elements abundant in the upper part of the earth, as seen in volcanoes, are not chondritic. The <a href="http://physics.ucr.edu/%7Ewudka/Physics7/Notes_www/node10.html">simplest explanation</a> for this observation? The composition of the Earth is not chondritic.</p>
<p>But there are other theories being proposed as an explanation of the neodymium paradox. One is that there must be a complementary hidden reservoir of material near the core-mantle boundary with a low samarium-to-neodymium ratio. This would balance out the high samarium-to-neodymium ratio of upper Earth, thereby maintaining the chondritic hypothesis.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/9108/original/67c2zpy5-1332991978.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/9108/original/67c2zpy5-1332991978.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/9108/original/67c2zpy5-1332991978.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/9108/original/67c2zpy5-1332991978.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/9108/original/67c2zpy5-1332991978.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/9108/original/67c2zpy5-1332991978.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/9108/original/67c2zpy5-1332991978.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/9108/original/67c2zpy5-1332991978.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Chondrite meteorites are among the oldest known materials in the universe. This one is more than 4.5 billion years old.</span>
<span class="attribution"><span class="source">Hypocentre</span></span>
</figcaption>
</figure>
<p>Many geochemists have found this hidden reservoir a convenient place to hide excesses or deficiencies of other elements that do not conform to the chondritic Earth hypothesis.</p>
<p>But the “hidden reservoir” hypothesis has a flaw. It requires about 40% of the mantle’s <a href="http://www.jstor.org/discover/10.2307/74932?uid=3737536&uid=2129&uid=2&uid=70&uid=4&sid=21100691664991">heat-producing elements</a> – uranium, thorium and potassium – to be concentrated near the core-mantle boundary. The problem with the hypothesis is while you can hide elements that don’t fit your theory, you can’t hide the heat they produce.</p>
<p>The only mechanism by which the heat produced by the putative hidden layer of low-samarium-to-neodymium-ratio material can be removed is through <a href="http://www.sciencedaily.com/articles/m/mantle_plume.htm">mantle plumes</a>. These are columns of hot rock that rise from the core-mantle boundary, almost 3,000km below the surface, and give rise to volcanoes such as those in Hawaii.</p>
<p>The hidden reservoir hypothesis therefore requires 40% of the mantle’s heat-loss to come from mantle plumes. This is inconsistent with <a href="http://www.mantleplumes.org/WebDocuments/Sleep1990.pdf">the observation that plumes carry less than 20% of the mantle’s heat loss</a>. Consequently the hidden layer hypothesis cannot be correct. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/9096/original/b7yfj579-1332982286.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/9096/original/b7yfj579-1332982286.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=412&fit=crop&dpr=1 600w, https://images.theconversation.com/files/9096/original/b7yfj579-1332982286.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=412&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/9096/original/b7yfj579-1332982286.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=412&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/9096/original/b7yfj579-1332982286.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=518&fit=crop&dpr=1 754w, https://images.theconversation.com/files/9096/original/b7yfj579-1332982286.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=518&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/9096/original/b7yfj579-1332982286.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=518&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"><span class="source">Wikimedia Commons</span></span>
</figcaption>
</figure>
<p>So what’s the alternative? Well, in conjunction with <a href="http://65.54.113.26/Author/19613042/herbert-palme">Professor Herbert Palme</a>, my co-author <a href="http://people.rses.anu.edu.au/oneill_h/">Professor Hugh O'Neill</a> developed an alternative hypothesis for the composition of the earth.</p>
<p>The prevailing theory holds Earth was <a href="http://myweb.tiscali.co.uk/newuniverse/real_accretion.html">formed by collisions of planetary bodies</a> of ever-increasing size. Our suggestion is that by the time the planetary bodies reached moderate size (a few hundred kilometres across), they developed an outer shell rich in heat-producing elements and with a samarium-to-neodymium ratio below the chondritic value.</p>
<p>We suggest that during the final stages of formation of the earth, the outer shell was lost by a process called collisional erosion.</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/9094/original/qvnmcf4g-1332980811.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/9094/original/qvnmcf4g-1332980811.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=490&fit=crop&dpr=1 600w, https://images.theconversation.com/files/9094/original/qvnmcf4g-1332980811.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=490&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/9094/original/qvnmcf4g-1332980811.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=490&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/9094/original/qvnmcf4g-1332980811.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=616&fit=crop&dpr=1 754w, https://images.theconversation.com/files/9094/original/qvnmcf4g-1332980811.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=616&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/9094/original/qvnmcf4g-1332980811.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=616&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Our planet was created through the collision of chondrite meteorites, similar to this one that landed in Mexico in 1969.</span>
<span class="attribution"><span class="source">jtaylor14368</span></span>
</figcaption>
</figure>
<p>This erosion produced an Earth that is depleted in heat-producing elements compared with the value predicted by the chondritic hypothesis and with a higher samarium-to-neodymium ratio.</p>
<p>Our new theory explains why the samarium-to-neodymium ratio of Earth is above the chondritic value and why the atmosphere has less argon. </p>
<p>(The collisional erosion hypothesis predicts the earth will have less potassium, and argon comes from the decay of potassium.)</p>
<p>Many of the paradoxes that have puzzled geochemists for the last 40 years are predicated on the assumption that the composition of Earth’s mantle is chondritic. If we abandon the chondritic hypothesis many of the problems that have been puzzling geochemists for years disappear. </p>
<p>If our theory is correct and Earth isn’t chondritic, then this necessitates a dramatic rethink of the way we understand the formation of Earth.</p>
<p>We might even have spent the past 40 years developing ingenious solutions to problems that didn’t even exist – problems that stemmed from the chondritic hypothesis.</p><img src="https://counter.theconversation.com/content/6128/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ian Campbell receives funding from the Australian Research council
and several mining companies, none of whom are interested in or fund the research discussed in our paper</span></em></p>As of today, the world might have changed forever. A fundamental assumption underpinning much of modern geochemistry is that the earth has the same composition as a class of meteorites called chondrites…Ian Campbell, Professor of Geochemistry, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.