tag:theconversation.com,2011:/us/topics/earths-crust-7262/articlesEarth's crust – The Conversation2023-08-17T12:34:23Ztag:theconversation.com,2011:article/2069132023-08-17T12:34:23Z2023-08-17T12:34:23ZNASA’s Psyche mission to a metal world may reveal the mysteries of Earth’s interior<figure><img src="https://images.theconversation.com/files/539847/original/file-20230727-19-gbh5t6.jpg?ixlib=rb-1.1.0&rect=5%2C11%2C3982%2C2646&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An illustration of the asteroid Psyche, orbiting between Mars and Jupiter.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/psyche-asteroid-in-space-royalty-free-image/1286927980?phrase=Psyche&adppopup=true">24K-Production/iStock via Getty Images Plus</a></span></figcaption></figure><p>French novelist Jules Verne delighted 19th-century readers with the tantalizing notion that a <a href="https://etc.usf.edu/lit2go/222/the-journey-to-the-center-of-the-earth/">journey to the center of the Earth</a> was actually plausible. </p>
<p>Since then, scientists have long acknowledged that Verne’s literary journey was only science fiction. The extreme temperatures of the Earth’s interior – around 10,000 degrees Fahrenheit (5,537 Celsius) at the core – and the accompanying crushing pressure, which is millions of times more than at the surface, <a href="https://www.youtube.com/watch?v=NXFBJr8XRlQ">prevent people from venturing down very far</a>. </p>
<p>Still, there are a few things <a href="https://education.nationalgeographic.org/resource/core/">known about the Earth’s interior</a>. For example, geophysicists discovered that the core consists of a solid sphere of iron and nickel that comprises 20% of the Earth’s radius, surrounded by a shell of molten iron and nickel that spans an additional 15% of Earth’s radius.</p>
<p>That, and the rest of our knowledge about our world’s interior, was learned indirectly – either by studying <a href="https://climate.nasa.gov/news/3105/earths-magnetosphere-protecting-our-planet-from-harmful-space-energy/">Earth’s magnetic field</a> or the way earthquake waves <a href="https://www.snexplores.org/article/explainer-seismic-waves-come-different-flavors">bounce off different layers</a> below the Earth’s surface. </p>
<p>But indirect discovery has its limitations. How can scientists find out more about our planet’s deep interior?</p>
<p><a href="http://jimbell.sese.asu.edu/">Planetary scientists like me</a> think the best way to learn about inner Earth is in outer space. NASA’s <a href="https://www.jpl.nasa.gov/missions/psyche">robotic mission to a metal world</a> is scheduled for liftoff on Oct. 5, 2023. That mission, the spacecraft traveling there, and the world it will explore all have the same name – Psyche. And for six years now, I’ve been <a href="https://psyche.asu.edu/mission/the-team/">part of NASA’s Psyche team</a>.</p>
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<figcaption><span class="caption">It’s a mission of ‘firsts.’</span></figcaption>
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<h2>About the asteroid Psyche</h2>
<p><a href="https://solarsystem.nasa.gov/asteroids-comets-and-meteors/asteroids/overview/?">Asteroids are small worlds</a>, with some the size of small cities and others as large as small countries. They are the leftover building blocks from our solar system’s early and violent period, <a href="https://solarsystem.nasa.gov/solar-system/our-solar-system/in-depth/#:%7E:">a time of planetary formation</a>. </p>
<p>Although most are rocky, icy or a combination of both, perhaps 20% of asteroids are worlds made of metal, and similar in composition to the Earth’s core. So it’s tempting to imagine that these metallic asteroids are pieces of the cores of once-existing planets, ripped apart by ancient cosmic collisions with each other. Maybe, by studying these pieces, scientists could find out directly what a planetary core is like. </p>
<p><a href="https://solarsystem.nasa.gov/asteroids-comets-and-meteors/asteroids/16-psyche/in-depth/">Psyche</a> is the largest-known of the metallic asteroids. Discovered in 1852, Psyche has the width of Massachusetts, a squashed spherical shape reminiscent of a pincushion, and an orbit between Mars and Jupiter in the main asteroid belt. An amateur astronomer can see Psyche with a backyard telescope, but it appears only as a pinpoint of light.</p>
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<figcaption><span class="caption">An artist’s rendition of Psyche, a spectacular metallic world.</span></figcaption>
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<h2>About the Psyche mission</h2>
<p>In early 2017, NASA approved the US$1 billion <a href="https://www.nasa.gov/psyche">mission to Psyche</a>. To do its work, there’s no need for the uncrewed spacecraft to land – instead, it will orbit the asteroid repeatedly and methodically, starting from 435 miles (700 kilometers) out and then going down to 46 miles (75 km) from the surface, and perhaps even lower. </p>
<p>Once it arrives in August 2029, the probe will spend 26 months mapping the asteroid’s geology, topography and gravity; it will search for evidence of a magnetic field; and it will compare the asteroid’s composition with what scientists know, or think we know, about Earth’s core.</p>
<p>The central questions are these: Is Psyche really an exposed planetary core? Is the asteroid one big bedrock boulder, a rubble pile of smaller boulders, or something else entirely? Are there clues that the previous outer layers of this small world – the crust and mantle – were violently stripped away long ago? And maybe the most critical question: Can what we learn about Psyche be extrapolated to solve some of the mysteries about the Earth’s core? </p>
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<a href="https://images.theconversation.com/files/542041/original/file-20230809-23-wqfx53.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Technicians, inside a clean room and dressed in white garb, examine the Psyche spacecraft." src="https://images.theconversation.com/files/542041/original/file-20230809-23-wqfx53.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/542041/original/file-20230809-23-wqfx53.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/542041/original/file-20230809-23-wqfx53.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/542041/original/file-20230809-23-wqfx53.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/542041/original/file-20230809-23-wqfx53.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/542041/original/file-20230809-23-wqfx53.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/542041/original/file-20230809-23-wqfx53.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">NASA’s Psyche spacecraft, undergoing final tests in a clean room at a facility near Florida’s Kennedy Space Center.</span>
<span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/catalog/PIA25952">NASA/Frank Michaux</a></span>
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<h2>About the spacecraft Psyche</h2>
<p>The probe’s body is about the same size and mass as a large SUV. Solar panels, stretching a bit wider than a tennis court, power the cameras, spectrometers and other systems. </p>
<p>A SpaceX Falcon Heavy rocket will <a href="https://techcrunch.com/2020/02/28/spacex-wins-the-117-million-launch-contract-to-explore-psyches-heavy-metal-asteroid/">take Psyche off the Earth</a>. The rest of the way, Psyche will <a href="https://www.nasa.gov/feature/jpl/solar-electric-propulsion-makes-nasa-s-psyche-spacecraft-go">rely on ion propulsion</a> – the gentle pressure of ionized xenon gas jetting out of a nozzle provides a continuous, reliable and low-cost way to propel spacecraft out into the solar system.</p>
<p>The journey, a slow spiral of 2.5 billion miles (4 billion km) that includes a gravity-assist flyby past Mars, <a href="https://www.cnn.com/2023/06/05/world/nasa-psyche-mission-october-launch-scn/index.html">will take nearly six years</a>. Throughout the cruise, the Psyche team at NASA’s Jet Propulsion Laboratory in Pasadena, California, and here at Arizona State University in Tempe, will stay in regular contact with the spacecraft. Our team will send and receive data using <a href="https://www.nasa.gov/directorates/heo/scan/services/networks/deep_space_network/about">NASA’s Deep Space Network</a> of giant radio antennas. </p>
<p>Even if we learn that Psyche is not an ancient planetary core, we’re bound to significantly add to our body of knowledge about the solar system and the way planets form. After all, Psyche is still unlike any world humans have ever visited. Maybe we can’t yet journey to the center of the Earth, but robotic avatars to places like Psyche can help unlock the mysteries hidden deep inside the planets – including our own.</p><img src="https://counter.theconversation.com/content/206913/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jim Bell works for Arizona State University, the lead academic institution responsible for the Pyche mission. He is also a member of the Board of Directors of The Planetary Society. He receives funding from NASA.</span></em></p>Liftoff to the distant asteroid is scheduled for Oct. 5, 2023 – the beginning of a six-year journey to one of the most unusual objects in the solar system.Jim Bell, Professor of Earth and Space Exploration, Arizona State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2104212023-07-26T16:51:04Z2023-07-26T16:51:04ZWe’ve discovered how diamonds make their way to the surface and it may tell us where to find them<figure><img src="https://images.theconversation.com/files/539502/original/file-20230726-21-jcon90.jpg?ixlib=rb-1.1.0&rect=17%2C0%2C5773%2C3820&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/natural-diamond-nestled-kimberlite-1608584494">Bjoern Wylezich / Shutterstock</a></span></figcaption></figure><p>“A diamond is forever.” That iconic slogan, coined for a <a href="https://www.thedrum.com/news/2016/03/31/1948-de-beers-diamond-forever-campaign-invents-the-modern-day-engagement-ring">highly successful advertising campaign in the 1940s</a>, sold the gemstones as a symbol of eternal commitment and unity. </p>
<p>But our new research, carried out by researchers in a variety of countries and <a href="https://www.nature.com/articles/s41586-023-06193-3">published in Nature</a>, suggests that diamonds may be a sign of break up too – of Earth’s tectonic plates, that is. It may even provide clues to where is best to go looking for them. </p>
<p>Diamonds, being the <a href="https://pursuit.unimelb.edu.au/articles/diamonds-the-hard-facts">hardest naturally-occurring stones</a>, require intense pressures and temperatures to form. These conditions are only achieved deep within the Earth. So how do they get from deep within the Earth, up to the surface? </p>
<p>Diamonds are carried up in molten rocks, or magmas, called <a href="https://www.britannica.com/science/kimberlite">kimberlites</a>. Until now, we didn’t know what process caused kimberlites to suddenly shoot through the Earth’s crust having spent millions, or even billions, of years stowed away under the continents.</p>
<h2>Supercontinent cycles</h2>
<p>Most geologists agree that the explosive eruptions that unleash <a href="https://www.science.org/doi/abs/10.1126/science.1206275">diamonds happen in sync</a> with the supercontinent cycle: a recurring pattern of landmass formation and fragmentation that has defined billions of years of Earth’s history. </p>
<p>However, the exact mechanisms underlying this relationship are debated. Two main theories have emerged. </p>
<p>One proposes that kimberlite magmas <a href="https://www.sciencedirect.com/science/article/abs/pii/S0024493709002758">exploit the “wounds”</a> created when the Earth’s crust is stretched or when the slabs of solid rock covering the Earth – known as tectonic plates – split up. The other theory <a href="https://www.nature.com/articles/s41467-019-13871-2#:%7E:text=Using%20inferences%20from%20older%2C%20smooth,dense%20lower%20lithosphere%2C%20so%20that">involves mantle plumes</a>, colossal upwellings of molten rock from the core-mantle boundary, located about 2,900km beneath the Earth’s surface.</p>
<figure class="align-center ">
<img alt="Structure of the Earth." src="https://images.theconversation.com/files/539551/original/file-20230726-21-tgwt8l.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/539551/original/file-20230726-21-tgwt8l.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=418&fit=crop&dpr=1 600w, https://images.theconversation.com/files/539551/original/file-20230726-21-tgwt8l.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=418&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/539551/original/file-20230726-21-tgwt8l.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=418&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/539551/original/file-20230726-21-tgwt8l.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=526&fit=crop&dpr=1 754w, https://images.theconversation.com/files/539551/original/file-20230726-21-tgwt8l.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=526&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/539551/original/file-20230726-21-tgwt8l.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=526&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A representation of the internal structure of the Earth.</span>
<span class="attribution"><a class="source" href="https://www.usgs.gov/media/images/earth-cross-section">USGS</a></span>
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<p>Both ideas, however, are not without their problems. Firstly, the main part of the tectonic plate, <a href="https://education.nationalgeographic.org/resource/lithosphere/">known as the lithosphere</a>, is incredibly strong and stable. This makes it difficult for fractures to penetrate, enabling magmas to flush through. </p>
<p>In addition, many kimberlites don’t display the chemical “flavours” we’d expect to find in rocks derived from mantle plumes.</p>
<p>In contrast, kimberlite formation is thought to involve exceedingly low degrees of mantle rock melting, often less than 1%. So, another mechanism is needed. Our study offers a possible resolution to this longstanding conundrum.</p>
<p>We deployed statistical analysis, including machine learning – an application of artificial intelligence (AI) – to forensically examine the link between continental breakup and kimberlite volcanism. The results of our global study showed the eruptions of most kimberlite volcanoes occurred 20 to 30 million years after the tectonic breakup of Earth’s continents. </p>
<p>Furthermore, our regional study targeting the three continents where most kimberlites are found – Africa, South America and North America – supported this finding. It also added a major clue: kimberlite eruptions tend to gradually migrate from the continental edges to the interiors over time at a rate that is uniform across the continents.</p>
<p>This begs the question: what geological process could explain these patterns?
To address this question, we employed multiple computer models to capture the complex behaviour of continents as they experience stretching, alongside the convective movements within the underlying mantle.</p>
<h2>Domino effect</h2>
<p>We propose that a domino effect can explain how breakup of the continents eventually leads to formation of kimberlite magma. During <a href="https://egusphere.copernicus.org/preprints/2022/egusphere-2022-139/">rifting</a>, a small region of the continental root – areas of thick rock located under some continents – is disrupted and sinks into the underlying mantle. </p>
<p>Here, we get sinking of colder material and upwelling of hot mantle, causing a process called <a href="https://www.sciencedirect.com/science/article/abs/pii/S0012821X98000892">edge-driven convection</a>. Our models show that this convection triggers a chain of similar flow patterns that migrate beneath the nearby continent. </p>
<p>Our models show that while sweeping along the continental root, these disruptive flows remove a substantial amount of rock, tens of kilometres thick, from the base of the continental plate. </p>
<p>Various other results from our computer models then advance to show that this process can bring together the necessary ingredients in the right amounts to trigger just enough melting to generate gas-rich kimberlites. Once formed, and with great buoyancy provided by carbon dioxide and water, the magma can rise rapidly to the surface carrying its precious cargo. </p>
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<img alt="Eruption on western vent in Halema‘uma‘u crater, at the summit of Kīlauea." src="https://images.theconversation.com/files/539520/original/file-20230726-19-y5r0d0.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/539520/original/file-20230726-19-y5r0d0.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/539520/original/file-20230726-19-y5r0d0.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/539520/original/file-20230726-19-y5r0d0.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/539520/original/file-20230726-19-y5r0d0.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/539520/original/file-20230726-19-y5r0d0.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/539520/original/file-20230726-19-y5r0d0.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">It hasn’t been clear how the molten rock carrying diamonds got to the surface from deep within the Earth.</span>
<span class="attribution"><a class="source" href="https://www.usgs.gov/media/images/close-view-west-vent-halemaumau-kilauea-october-5-2021">N. Deligne / USGS</a></span>
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<h2>Finding new diamond deposits</h2>
<p>This model doesn’t contradict the spatial association between kimberlites and mantle plumes. On the contrary, the breakup of tectonic plates may or may not result from the warming, thinning and weakening of the plate caused by plumes. </p>
<p>However, our research clearly shows that the spatial, time-based and chemical patterns observed in most kimberlite-rich regions can’t be adequately explained solely by the presence of plumes.</p>
<p>The processes triggering the eruptions that bring diamonds to the surface appear to be highly systematic. They start on the edges of continents and migrate towards the interior at a relatively uniform rate.</p>
<p>This information could be used to identify the possible locations and timings of past volcanic eruptions tied to this process, offering insights that could enable the discovery of diamond deposits and other rare elements needed for the green energy transition. </p>
<p>If we are to look for new deposits, it’s worth bearing in mind that there are currently efforts by campaign groups to try to eliminate from world markets those diamonds that are <a href="https://fpi.ec.europa.eu/what-we-do/kimberley-process-fight-against-conflict-diamonds_en">used to fund wars</a> (conflict diamonds) or those coming from mines with poor conditions for workers.</p>
<p>Diamonds may or may not be forever, but our work shows that new ones have been repeatedly created over long periods in the history of our planet.</p><img src="https://counter.theconversation.com/content/210421/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Thomas Gernon receives funding from the WoodNext Foundation and the Natural Environment Research Council (NERC). </span></em></p>Scientists were not previously certain how the precious stones arrived at the Earth’s surface.Thomas Gernon, Associate Professor in Earth Science, University of SouthamptonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1932772023-01-23T13:24:30Z2023-01-23T13:24:30ZHow has the inside of the Earth stayed as hot as the Sun’s surface for billions of years?<figure><img src="https://images.theconversation.com/files/504323/original/file-20230112-43582-jetsqy.jpg?ixlib=rb-1.1.0&rect=0%2C21%2C4685%2C3672&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The slice you see cut out of the Earth reveals its core, depicted here in bright yellow.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/earth-section-royalty-free-image/174700926">fhm/E+ via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
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<blockquote>
<p><strong>How does the inside of the Earth stay boiling hot for billions of years? Henry, age 11, Somerville, Massachusetts</strong></p>
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<hr>
<p>Our Earth is structured sort of like an onion – it’s one layer after another. </p>
<p>Starting from the top down, there’s the crust, which includes the surface you walk on; then farther down, the mantle, mostly solid rock; then even deeper, the outer core, made of liquid iron; and finally, the inner core, made of solid iron, and with a radius that’s 70% the size of the Moon’s. The deeper you dive, the hotter it gets – parts of the core are as hot as the surface of the Sun.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/504301/original/file-20230112-52283-32zsaz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An illustration that shows the structure of the Earth: its crust, mantle, inner core and outer core." src="https://images.theconversation.com/files/504301/original/file-20230112-52283-32zsaz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/504301/original/file-20230112-52283-32zsaz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=405&fit=crop&dpr=1 600w, https://images.theconversation.com/files/504301/original/file-20230112-52283-32zsaz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=405&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/504301/original/file-20230112-52283-32zsaz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=405&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/504301/original/file-20230112-52283-32zsaz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=509&fit=crop&dpr=1 754w, https://images.theconversation.com/files/504301/original/file-20230112-52283-32zsaz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=509&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/504301/original/file-20230112-52283-32zsaz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=509&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 illustration depicts the four sections beneath the Earth’s surface.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/the-structure-of-planet-earth-royalty-free-illustration/1256173927">eliflamra/iStock via Getty Images Plus</a></span>
</figcaption>
</figure>
<h2>Journey to the center of the Earth</h2>
<p>As a <a href="https://scholar.google.com/citations?user=DpHUpCwAAAAJ&hl=en&oi=ao">professor of earth and planetary sciences</a>, I study the insides of our world. Just as a doctor can use a technique called <a href="https://blog.radiology.virginia.edu/ultrasound-definition-kids-imaging/">sonography</a> to make pictures of the structures inside your body with ultrasound waves, scientists use a similar technique to image the Earth’s internal structures. But instead of ultrasound, geoscientists use <a href="https://easyscienceforkids.com/seismic-waves/">seismic waves</a> – sound waves produced by earthquakes. </p>
<p>At the Earth’s surface, you see dirt, sand, grass and pavement, of course. <a href="https://www.amnh.org/learn-teach/curriculum-collections/earth-inside-and-out/inge-lehmann-discoverer-of-the-earth-s-inner-core">Seismic vibrations reveal what’s below that</a>: rocks, large and small. This is all part of the crust, which may go down as far as 20 miles (30 kilometers); it floats on top of the layer called the mantle. </p>
<p>The upper part of the mantle typically moves together with the crust. Together, they are called <a href="https://education.nationalgeographic.org/resource/lithosphere">the lithosphere</a>, which is about 60 miles (100 kilometers) thick on average, although it can be thicker at some locations. </p>
<p>The lithosphere is divided into several <a href="https://www.kidsdiscover.com/wp-content/uploads/2012/12/KIDS-DISCOVER-Plate-Tectonics.pdf">large blocks called plates</a>. For example, the Pacific plate is beneath the whole Pacific Ocean, and the North American plate covers most of North America. Plates are kind of like puzzle pieces that fit roughly together and cover the surface of the Earth.</p>
<p>The plates are not static; instead, they move. Sometimes it’s the tiniest fraction of inches over a period of years. Other times, there’s more movement, and it’s more sudden. This sort of movement is what triggers earthquakes and volcanic eruptions. </p>
<p>What’s more, plate movement is a critical, and probably essential, factor driving the evolution of life on Earth, because the moving plates change the environment and <a href="https://theconversation.com/plate-tectonics-may-have-driven-the-evolution-of-life-on-earth-44571">force life to adapt to new conditions</a>. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/3FoSAHk7DMA?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">You’ll be amazed at all the life happening below your feet.</span></figcaption>
</figure>
<h2>The heat is on</h2>
<p>Plate motion requires a hot mantle. And indeed, as you go deeper into the Earth, the temperature increases. </p>
<p>At the bottom of the plates, around 60 miles (100 kilometers) deep, the temperature is about 2,400 degrees Fahrenheit (1,300 degrees Celsius). </p>
<p>By the time you get to the boundary between the mantle and the outer core, which is 1,800 miles (2,900 kilometers) down, the temperature is nearly 5,000 F (2,700 C). </p>
<p>Then, at the boundary between outer and inner cores, the temperature doubles, to nearly 10,800 F (over 6,000 C). That’s the part that’s <a href="https://www.livescience.com/29054-earth-core-hotter.html">as hot as the surface of the Sun</a>. At that temperature, virtually everything – metals, diamonds, human beings – vaporizes into gas. But because the core is at such high pressure deep within the planet, the iron it’s made up of remains liquid or solid. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/DI6SemRT2iY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Without plate tectonics, human beings probably would not exist.</span></figcaption>
</figure>
<h2>Collisions in outer space</h2>
<p>Where does all that heat come from? </p>
<p>It is not from the Sun. While it warms us and all the plants and animals on Earth’s surface, sunlight can’t penetrate through miles of the planet’s interior.</p>
<p>Instead, there are two sources. One is the heat that Earth inherited during its formation 4.5 billion years ago. The Earth was made <a href="https://solarsystem.nasa.gov/solar-system/our-solar-system/in-depth/#:%7E">from the solar nebula</a>, a gigantic gaseous cloud, amid endless collisions and mergings between bits of rock and debris <a href="https://www.universetoday.com/35974/planetesimals/">called planetesimals</a>. This process took tens of millions of years.</p>
<p>An enormous amount of heat was produced during those collisions, enough to melt the whole Earth. Although some of that heat was lost in space, the rest of it was locked away inside the Earth, where much of it remains even today. </p>
<p>The other heat source: the decay of radioactive isotopes, distributed everywhere in the Earth. </p>
<p>To understand this, first imagine an element <a href="https://www.ducksters.com/science/chemistry/radiation_and_radioactivity.php">as a family with isotopes as its members</a>. Every atom of a given element has the same number of protons, but different isotope cousins have varying numbers of neutrons. </p>
<p><a href="https://kids.britannica.com/students/article/radioactive-isotope/628328#:%7E">Radioactive isotopes</a> are not stable. They release a steady stream of energy that converts to heat. Potassium-40, thorium-232, uranium-235 and uranium-238 are four of the radioactive isotopes keeping Earth’s interior hot. </p>
<p>Some of those names may sound familiar to you. Uranium-235, for example, is used as a <a href="https://www.eia.gov/energyexplained/nuclear/the-nuclear-fuel-cycle.php#:%7E">fuel in nuclear power plants</a>. Earth is in no danger of running out of these sources of heat: Although most of the <a href="https://www.ducksters.com/science/chemistry/radiation_and_radioactivity.php#:%7E">original uranium-235 and potassium-40 are gone</a>, there’s enough thorium-232 and uranium-238 to last for billions more years. </p>
<p>Along with the hot core and mantle, these energy-releasing isotopes provide the heat to drive the motion of the plates. </p>
<h2>No heat, no plate movement, no life</h2>
<p>Even now, the moving plates keep changing the surface of the Earth, constantly making <a href="https://www.quantamagazine.org/why-earths-cracked-crust-may-be-essential-for-life-20180607/">new lands and new oceans over millions and billions of years</a>. The plates also affect the atmosphere over similarly lengthy time scales. </p>
<p>But without the Earth’s internal heat, the plates would not have been moving. The Earth would have cooled down. Our world would likely have been uninhabitable. You wouldn’t be here.</p>
<p>Think about that, the next time you feel the Earth under your feet.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p><img src="https://counter.theconversation.com/content/193277/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Shichun Huang 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>Starting at the surface, you would have to dig nearly 2,000 miles before reaching the Earth’s core. No one could survive that trip – and the 10,000-degree F heat once there would vaporize you anyway.Shichun Huang, Associate Professor of Earth and Planetary Sciences, University of TennesseeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1881582022-08-24T03:19:00Z2022-08-24T03:19:00ZScientists have traced Earth’s path through the galaxy via tiny crystals found in the crust<figure><img src="https://images.theconversation.com/files/479303/original/file-20220816-24-ywqf10.jpg?ixlib=rb-1.1.0&rect=1274%2C67%2C4513%2C2491&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>“To see a world in a grain of sand”, the opening sentence of the poem by <a href="https://www.poetryfoundation.org/poems/43650/auguries-of-innocence">William Blake</a>, is an oft-used phrase that also captures some of what geologists do.</p>
<p>We observe the composition of mineral grains, smaller than the width of a human hair. Then, we extrapolate the chemical processes they suggest to ponder <a href="https://eos.org/science-updates/earths-continents-share-an-ancient-crustal-ancestor">the construction of our planet</a> itself.</p>
<p>Now, we’ve taken that minute attention to new heights, connecting tiny grains to Earth’s place in the galactic environment.</p>
<h2>Looking out to the universe</h2>
<p>At an even larger scale, astrophysicists seek to understand the universe and our place in it. They use laws of physics to develop models that describe the orbits of astronomical objects.</p>
<p>Although we may think of the planet’s surface as something shaped by processes entirely within Earth itself, our planet has undoubtedly felt the effects of its cosmic environment. This includes <a href="https://www.nature.com/scitable/knowledge/library/milankovitch-cycles-paleoclimatic-change-and-hominin-evolution-68244581/">periodic changes in Earth’s orbit</a>, variations in the Sun’s output, gamma ray bursts, and of course meteorite impacts.</p>
<p>Just looking at the Moon and its pockmarked surface should remind us of that, given Earth is more than 80 times more massive than its grey satellite. In fact, recent work has pointed to the importance of meteorite impacts in the <a href="https://www.nature.com/articles/s41586-022-04956-y">production of continental crust on Earth</a>, helping to form buoyant “seeds” that floated on the outermost layer of our planet in its youth.</p>
<p>We and our international team of colleagues have now identified a rhythm in the production of this early continental crust, and the tempo points to a truly grand driving mechanism. This work has just been published <a href="https://doi.org/10.1130/G50513.1">in the journal Geology</a>.</p>
<figure class="align-center ">
<img alt="A swirling spiral of blue and white glowing stars on a dark background" src="https://images.theconversation.com/files/477930/original/file-20220806-35739-ito9l9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/477930/original/file-20220806-35739-ito9l9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=648&fit=crop&dpr=1 600w, https://images.theconversation.com/files/477930/original/file-20220806-35739-ito9l9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=648&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/477930/original/file-20220806-35739-ito9l9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=648&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/477930/original/file-20220806-35739-ito9l9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=814&fit=crop&dpr=1 754w, https://images.theconversation.com/files/477930/original/file-20220806-35739-ito9l9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=814&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/477930/original/file-20220806-35739-ito9l9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=814&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Residing inside the Milky Way galaxy makes it impossible to picture, but our galaxy is thought to be similar to other barred spiral galaxies, like NGC 4394.</span>
<span class="attribution"><span class="source">ESA/Hubble & NASA</span></span>
</figcaption>
</figure>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/what-created-the-continents-new-evidence-points-to-giant-asteroids-185606">What created the continents? New evidence points to giant asteroids</a>
</strong>
</em>
</p>
<hr>
<h2>The rhythm of crust production on Earth</h2>
<p>Many rocks on Earth form from molten or semi-molten magma. This magma is derived either directly from the mantle – the predominantly solid but slowly flowing layer below the planet’s crust – or from recooking even older bits of pre-existing crust. As liquid magma cools, it eventually freezes into solid rock.</p>
<p>Through this cooling process of magma crystallisation, mineral grains grow and can trap elements such as uranium that decay over time and produce a sort of stopwatch, <a href="https://www.gsoc.org/news/2020/12/07/zircon">recording their age</a>. Not only that, but crystals can also trap <a href="https://www.nature.com/articles/srep38503">other elements</a> that track the composition of their parental magma, like how a surname might track a person’s family.</p>
<p>With these two pieces of information – age and composition – we can then reconstruct a timeline of crust production. Then, we can decode its main frequencies, using the mathematical wizardry of the <a href="https://betterexplained.com/articles/an-interactive-guide-to-the-fourier-transform/">Fourier transform</a>. This tool basically decodes the frequency of events, much like unscrambling ingredients that have gone into the blender for a cake.</p>
<p>Our results from this approach suggest an approximate 200-million-year rhythm to crust production on the early Earth.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/ancient-earth-had-a-thick-toxic-atmosphere-like-venus-until-it-cooled-off-and-became-liveable-150934">Ancient Earth had a thick, toxic atmosphere like Venus – until it cooled off and became liveable</a>
</strong>
</em>
</p>
<hr>
<h2>Our place in the cosmos</h2>
<p>But there is another process with a similar rhythm. Our Solar System and the four spiral arms of the Milky Way are both spinning around the supermassive black hole at the galaxy’s centre, yet they are moving at different speeds.</p>
<p>The spiral arms orbit at 210 kilometres per second, while the Sun is speeding along at 240km per second, meaning our Solar System is surfing into and out of the galaxy’s arms. You can think of the spiral arms as dense regions that slow the passage of stars much like a traffic jam, which only clears further down the road (or through the arm).</p>
<figure class="align-center ">
<img alt="Geological events on the orbit of the solar system in the Milky Way galaxy" src="https://images.theconversation.com/files/477931/original/file-20220806-35905-yvr1i6.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/477931/original/file-20220806-35905-yvr1i6.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/477931/original/file-20220806-35905-yvr1i6.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/477931/original/file-20220806-35905-yvr1i6.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/477931/original/file-20220806-35905-yvr1i6.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/477931/original/file-20220806-35905-yvr1i6.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/477931/original/file-20220806-35905-yvr1i6.png?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">Geological events, including major crust formation events highlighted on the transit of the Solar System through the galactic spiral arms.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech/ESO/R. Hurt (background image)</span></span>
</figcaption>
</figure>
<p>This model results in approximately 200 million years between each entry our Solar System makes into a spiral arm of the galaxy.</p>
<p>So, there seems to be a possible connection between the timing of crust production on Earth and the length of time it takes to orbit the galactic spiral arms – but why?</p>
<h2>Strikes from the cloud</h2>
<p>In the distant reaches of our Solar System, a cloud of icy rocky debris named the <a href="https://solarsystem.nasa.gov/solar-system/oort-cloud/overview%5D">Oort cloud</a> is thought to orbit our Sun.</p>
<p>As the Solar System periodically moves into a spiral arm, interaction between it and the Oort cloud is proposed to dislodge material from the cloud, sending it closer to the inner Solar System. Some of this material may even strike Earth.</p>
<figure class="align-center ">
<img alt="A glowing image of a spiral galaxy with blue arms and pale golden centre" src="https://images.theconversation.com/files/479311/original/file-20220816-26-hmqoph.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/479311/original/file-20220816-26-hmqoph.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/479311/original/file-20220816-26-hmqoph.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/479311/original/file-20220816-26-hmqoph.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/479311/original/file-20220816-26-hmqoph.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/479311/original/file-20220816-26-hmqoph.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/479311/original/file-20220816-26-hmqoph.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">Milky Way’s structure and Solar System’s orbit through it may be important in controlling the frequency of some large impacts on Earth, which in turn may have seeded crust production on the early Earth.</span>
<span class="attribution"><span class="source">jivacore/Shutterstock</span></span>
</figcaption>
</figure>
<p>Earth experiences relatively frequent impacts from the rocky bodies of the asteroid belt, which on average arrive at speeds of 15km per second. But comets ejected from the Oort cloud arrive much faster, on average 52km per second.</p>
<p>We argue it is these periodic high-energy impacts that are tracked by the record of crust production preserved in <a href="https://knowablemagazine.org/article/physical-world/2021/keeping-time-zircons">tiny mineral grains</a>. Comet impacts excavate huge volumes of Earth’s surface, leading to decompression melting of the mantle, not too dissimilar from popping a cork on a bottle of fizz.</p>
<p>This molten rock, enriched in light elements such as silicon, aluminium, sodium and potassium, effectively floats on the denser mantle. While there are many other ways to <a href="https://theconversation.com/just-add-mantle-water-new-research-cracks-the-mystery-of-how-the-first-continents-formed-156845">generate continental crust</a>, it’s likely that <a href="https://www.nature.com/articles/s41467-019-08467-9">impacting</a> on our early planet formed buoyant seeds of crust. Magma produced from later geological processes would adhere to those early seeds.</p>
<h2>Harbingers of doom, or gardeners for terrestrial life?</h2>
<p>Continental crust is vital in most of Earth’s natural cycles – it interacts with water and oxygen, forming new weathered products, hosting most metals and biological carbon.</p>
<p>Large meteorite impacts are cataclysmic events that <a href="https://theconversation.com/more-bad-news-for-dinosaurs-chicxulub-meteorite-impact-triggered-global-volcanic-eruptions-on-the-ocean-floor-91053">can obliterate life</a>. Yet, impacts may very well have been key to the development of the continental crust we live on.</p>
<p>With the recent passage of <a href="https://theconversation.com/mysterious-alien-cigar-asteroid-is-actually-an-interstellar-lump-of-ice-not-a-space-ship-89322">interstellar asteroids</a> through the Solar System, some have even gone so far as to suggest they <a href="https://www.daviddarling.info/encyclopedia/P/panspermia.html">ferried life across the cosmos</a>.</p>
<p>However we came to be here, it is awe-inspiring on a clear night to look up at the sky and see the stars and the structure they trace, and then look down at your feet and feel the mineral grains, rock and continental crust below – all linked through a very grand rhythm indeed.</p><img src="https://counter.theconversation.com/content/188158/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Kirkland receives funding from the Australian Research Council.</span></em></p><p class="fine-print"><em><span>Phil Sutton does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>There’s a curious 200-million-year rhythm to Earth’s crust production. Now, it seems like our very place in the galaxy is tied to it.Chris Kirkland, Professor of Geology, Curtin UniversityPhil Sutton, Senior Lecturer in Astrophysics, University of LincolnLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1730762021-12-02T14:54:42Z2021-12-02T14:54:42ZHow plankton helped create the Earth’s mountains 2 billion years ago<figure><img src="https://images.theconversation.com/files/435296/original/file-20211202-17-eiblss.jpg?ixlib=rb-1.1.0&rect=12%2C0%2C3669%2C1510&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Himalayas.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/magnificent-blossoms-rhododendrons-on-background-white-582993493">Liudmila Kotvictchkaia/Shutterstock</a></span></figcaption></figure><p>A world without the great mountain ranges – the <a href="https://www.pbs.org/wnet/nature/the-himalayas-himalayas-facts/6341/">Himalayas</a>, the <a href="https://wwf.panda.org/discover/knowledge_hub/where_we_work/alps/">Alps</a>, the <a href="https://www.britannica.com/place/Rocky-Mountains">Rockies</a>, the <a href="https://www.britannica.com/place/South-America/The-Andes-Mountains">Andes</a> – is unimaginable, but they were not always a part of the Earth’s geography. Mountains didn’t start forming widely until <a href="https://www.seismosoc.org/news/seismic-signs-of-earliest-subduction-network-found-in-china/">2 billion years ago</a>, half way through the planet’s history. Now our <a href="https://www.nature.com/articles/s43247-021-00313-5">research</a> has revealed how primitive life played a key role in their introduction to the planet.</p>
<p>While the formation of mountains is usually associated with the collision of tectonic plates causing huge slabs of rock to be thrust skywards, our study has shown that this was triggered by an abundance of nutrients in the oceans 2 billion years ago which caused an explosion of planktonic life.</p>
<figure class="align-center ">
<img alt="A diagram showing the timeline of mountains on Earth." src="https://images.theconversation.com/files/435299/original/file-20211202-23-7gvpo4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/435299/original/file-20211202-23-7gvpo4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=402&fit=crop&dpr=1 600w, https://images.theconversation.com/files/435299/original/file-20211202-23-7gvpo4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=402&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/435299/original/file-20211202-23-7gvpo4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=402&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/435299/original/file-20211202-23-7gvpo4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=505&fit=crop&dpr=1 754w, https://images.theconversation.com/files/435299/original/file-20211202-23-7gvpo4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=505&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/435299/original/file-20211202-23-7gvpo4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=505&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Timeline for the formation of mountains on Earth.</span>
<span class="attribution"><span class="source">J Johnston/University of Aberdeen</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>Making mountains</h2>
<p>Mountains are not just a beautiful backdrop for recreation, they are essential to the way the world works, through their influence on weather, climate, the distribution of fresh water and the erosion of rock to make cultivable soil. </p>
<p>Before there were mountains, the plate movements that reshape the distribution of oceans and continents only occurred on a limited scale. But the movement of these plates are essential to making mountains. The pressure of one plate pushing against another – typically an ocean plate hitting a continental plate – causes slabs of ocean rock to break off and stack up on top of each other as they are pushed from behind.</p>
<p>Over millions of years the stack of rocks builds up, creating mountains, just as the Himalayas were built from ocean rocks between India and Eurasia, pushed northwards until the ocean disappeared and its remains were left piled high.</p>
<p>We know these mountains came originally from the ocean by the sea fossils found on the Tibetan plateau, thousands of metres above sea level. But piling up huge slabs of rock on such a scale needs serious lubrication, otherwise friction would stop them. That lubricant is carbon, which became part of the ocean rock when dead plankton fell to the ocean floor and became buried.</p>
<p>Plankton have lived in our oceans for over 3 billion years, but 2 billion years ago their numbers exploded when abundant nutrients entered the water. At the time, life was no more complex than their single cells. But the cells became much bigger, and they contained more carbon.</p>
<p>When they died they sank quickly and were buried in mud which created rock with unprecedented amounts of carbon, which was turned into graphite by heat and pressure. Graphite makes a great lubricant. Locks, hinges, gears, wheels and even zips all move more easily with graphite – and so do rocks. </p>
<figure class="align-center ">
<img alt="Diagram showing how mountains are formed by tectonic pressure and carbon." src="https://images.theconversation.com/files/435301/original/file-20211202-25-6wgoof.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/435301/original/file-20211202-25-6wgoof.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=369&fit=crop&dpr=1 600w, https://images.theconversation.com/files/435301/original/file-20211202-25-6wgoof.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=369&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/435301/original/file-20211202-25-6wgoof.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=369&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/435301/original/file-20211202-25-6wgoof.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=463&fit=crop&dpr=1 754w, https://images.theconversation.com/files/435301/original/file-20211202-25-6wgoof.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=463&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/435301/original/file-20211202-25-6wgoof.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=463&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Slabs of rock stacked up by lubricating carbon, which creates mountains when tectonic plates collide; precise geometry is much more complex, and slabs may stack in the opposite direction.</span>
<span class="attribution"><span class="source">J Bowie/University of Aberdeen</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>Lubrication</h2>
<p>The plentiful graphite that accumulated beneath the ocean floor had a profound effect, by lubricating the building of mountains. While it has long been known that tectonic processes were lubricated, our research shows that it was the sheer abundance of carbon in the ocean that played a crucial role in the thickening of the Earth’s crust that built its mountain ranges.</p>
<p>The process has continued since then, and other geological layers like salt have also played their part, but the graphite beds of 2 billion years ago were especially slippery, and some have been involved in making mountains more than once. </p>
<p>The biggest mountains on Earth, the Himalayas, are <a href="https://www.britannica.com/place/Himalayas">geologically young</a> – about 50 million years old – but rocks made in a much older ocean slid over each other to help create them. They had already slid in the first millions of years after they formed, and then after a long dormancy they slid again to help the rise of the Himalayas. They may slide again in the distant future.</p>
<p>Long after mankind is gone, those ancient plankton will continue their influence on the planet. The mountains made 2 billion years ago are worn down now, but we can still see their roots in places like Scotland, for example.</p>
<p>Our study looked at 20 cases of mountain building around the world from that time, from Australia to China, South America to the Arctic and in north-west Scotland, where we can see the slip surfaces in graphite-bearing rocks in Harris, Iona and Gairloch, formed during earthquakes that accompanied the earliest mountain building. The island of Tiree is one of the flattest places in Britain, but the seabirds that run over its sandy beaches cross the foundations of huge, long-gone mountains.</p>
<figure class="align-center ">
<img alt="A beach fringing turquoise waters on the Hebridean island of Tiree off the West Coast of Scotland." src="https://images.theconversation.com/files/435306/original/file-20211202-19-1qorakp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/435306/original/file-20211202-19-1qorakp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/435306/original/file-20211202-19-1qorakp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/435306/original/file-20211202-19-1qorakp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/435306/original/file-20211202-19-1qorakp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/435306/original/file-20211202-19-1qorakp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/435306/original/file-20211202-19-1qorakp.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">The Hebridean island of Tiree is now utterly flat, its 2 billion-year-old mountains worn away.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/picture-taken-caolas-beach-on-scottish-368446253">Alistair MacLean/Shutterstock</a></span>
</figcaption>
</figure>
<h2>Graphite resources</h2>
<p>In each of the 20 ancient mountain ranges that were studied, exceptional amounts of graphite were recorded. In many cases the graphite is abundant enough to have been mined as a resource.</p>
<p>Graphite is now a hot commodity, as it is needed in the batteries that are central to green technology (far more graphite is required than lithium in a lithium ion battery). Many of the largest graphite deposits in the world were formed about 2 billion years ago. The graphite that helped bring us mountains may prove critical to the planet once more, and play a key role in its preservation for future generations.</p>
<p>Without the carbon from countless cells of plankton, the distribution of tectonic plates may have evolved rather differently, and we would not have mountains as we know them. Ours is a planet fundamentally shaped by life.</p><img src="https://counter.theconversation.com/content/173076/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Parnell receives funding from NERC.</span></em></p>Mountains can’t be created without lubricant, and 2 billion years ago that lubricant was graphite produced by the carbon broken down from layers of dead plankton on the ocean floor.John Parnell, Professor of Geology and Petroleum Geology, University of AberdeenLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1718332021-11-22T15:29:22Z2021-11-22T15:29:22ZCurious Kids: Why are there so few impact craters on Earth?<figure><img src="https://images.theconversation.com/files/431908/original/file-20211115-21-g451m1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An illustration shows how, about 65 million years ago, a large asteroid collided with Earth. It hit what is today Mexico and created the Chicxulub crater.</span> <span class="attribution"><span class="source">Mark Garlick/Science Photo Library/Getty Images</span></span></figcaption></figure><p><em>Curious Kids is <a href="https://theconversation.com/africa/topics/curious-kids-36782">a series</a> for children in which we ask experts to answer questions from kids.</em></p>
<p><strong>Why are there so few craters on Earth? (Ivon, 11, Butterworth, South Africa)</strong></p>
<p>Thank you for the great question, Ivon. Scientists call these “impact craters”: a bowl-shaped depression in the rocky crust of a planet, moon or asteroid that is caused by another rocky piece of space debris slamming into it really fast. This high-speed collision – over 36000 kilometres per hour! – releases a huge amount of energy that causes a lot of destruction. </p>
<p>I am a geoscientist who studies impact sites in Africa and on other continents. Scientists like me have identified the remains of around 200 impact craters across our planet. Some people might think that 200 is quite a big number, but you are right – compared to the Moon and the other rocky planets and moons in our solar system, it is exceptionally low. There are several reasons for this.</p>
<h2>Understanding Earth</h2>
<p>The first reason is that Earth’s surface is continuously changing because we live on a geologically active planet. Impact craters are relatively shallow, so these “dents” in Earth’s rocky crust (the surface bit we can see with our eyes) can be easily buried or wiped out by erosion. For instance, the giant, 160-km-wide <a href="https://www.nationalgeographic.com/science/article/last-day-dinosaurs-reign-captured-stunning-detail">Chicxulub crater</a> in Mexico that wiped out most of the dinosaurs and many other species 65 million years ago is only 1-2 km deep and is hidden beneath younger layers of sediment. In contrast, the much older, equally famous, <a href="https://whc.unesco.org/en/list/1162/">Vredefort crater</a> in South Africa has experienced millions of years of erosion by rivers or glaciers so that the crater itself has been erased. Fortunately, ring-shaped patterns in the rocks indicate that something very violent and unusual happened in the distant past. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/431909/original/file-20211115-13-17nd3qw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/431909/original/file-20211115-13-17nd3qw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=395&fit=crop&dpr=1 600w, https://images.theconversation.com/files/431909/original/file-20211115-13-17nd3qw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=395&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/431909/original/file-20211115-13-17nd3qw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=395&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/431909/original/file-20211115-13-17nd3qw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=497&fit=crop&dpr=1 754w, https://images.theconversation.com/files/431909/original/file-20211115-13-17nd3qw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=497&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/431909/original/file-20211115-13-17nd3qw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=497&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Barringer Meteor Crater near Winslow, Arizona.</span>
<span class="attribution"><span class="source">Independent Picture Service/Universal Images Group via Getty Images</span></span>
</figcaption>
</figure>
<p>The next reason is that two-thirds of Earth’s rocky crust is hidden beneath the oceans. We actually know less about many parts of the deep ocean floor than the surfaces of other planets in the solar system. Could there be lots of craters hidden beneath the oceans? We don’t know the answer for sure, but probably not, because there is something unusual about Earth’s oceanic crust: it is much, much younger than the continental crust on which we live and the crusts of the Moon and other planets. </p>
<p>Let me explain. Since the 1960s we have known that new ocean crust is being created almost continuously along giant rifts (called mid-ocean ridges). At the same time, other parts of this basalt crust are sinking back into the mantle along subduction zones. This is like a conveyor belt and is part of what we call <a href="https://www.nationalgeographic.org/encyclopedia/plate-tectonics/">plate tectonics</a>. The key point is that we can’t find any oceanic crust that is older than 200 million years. This means that any crater that formed more than 200 million years ago in an ocean has been destroyed. That sounds like a long time, right? But it’s a very small time window compared with the <a href="https://www.nationalgeographic.org/topics/resource-library-age-earth/">4.6 billion years</a> that Earth and the other planets have existed. </p>
<p>The presence of so much deep water on Earth means many smaller asteroids that would definitely make impact craters on dry land do not produce craters in the oceanic crust. This is because the water column absorbs all or most of the impact energy, maybe creating a short-lived tsunami but leaving no other trace. </p>
<p>Earth’s atmosphere also plays a role in reducing the number of impact craters. One of the remarkable observations from the Apollo programme that studied the moon was that every single sample showed signs of high-speed impacts, down to micro-craters. Up until the 1970s many scientists thought the reason there were so few craters on Earth compared to the Moon was because our atmosphere caused the small asteroid debris to burn up (as meteors) and slow down as it passed through the atmosphere so that it didn’t have enough energy left to blast a crater in the crust. </p>
<p>In some cases the atmosphere even “bounced” asteroids back into outer space, much like you can skip a stone across a pool of water. As there will be many more smaller craters – because there are many smaller asteroids – we can see that the atmosphere acts as both a filter and a shield to reduce the number of impacts.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/why-the-moon-is-such-a-cratered-place-118842">Why the Moon is such a cratered place</a>
</strong>
</em>
</p>
<hr>
<h2>Looking for impact craters</h2>
<p>Finally, we need to consider our own role in your question: how good are scientists and ordinary people at recognising impact craters? There are thousands of craters on Earth, but craters can also be formed in other ways, such as volcanic eruptions and sinkholes. </p>
<p>So, geoscientists need to carefully collect and examine all the evidence before they can confirm that a crater (or, rather, what’s left of it) was formed by impact. Impact crater studies didn’t really exist until about 60 years ago. Up until then, most of the craters on Earth were thought to be caused by volcanic eruptions. </p>
<p>Then scientists working on underground military nuclear explosions started looking into the physics of shock waves in rocks caused by the nuclear explosions. Others began scrutinising the thousands of craters on the Moon as preparation for the <a href="https://www.britannica.com/science/Apollo-space-program">Apollo moon landings</a>. When they went looking for similar craters on Earth, they started to find unusual evidence that the rocks in and around some craters had been affected by exceptional shock pressures and temperatures that could not be explained by volcanic eruptions. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/what-a-moroccan-crater-reveals-about-a-rare-double-whammy-from-the-skies-61406">What a Moroccan crater reveals about a rare double whammy from the skies</a>
</strong>
</em>
</p>
<hr>
<p>So geoscientists have to be a bit like detectives: we need to collect evidence to prove that a crater was caused by an impact rather than by anything else. Every few years another crater is added to the list as the proof is presented to, and accepted by, the international geoscientific community. </p>
<p>There are many hundreds of possible, or suspected, impact craters on Earth that await confirmation or rejection, including dozens <a href="https://books.google.co.za/books?hl=en&lr=&id=cn6jLdR-DtoC&oi=fnd&pg=PA6&dq=Reimold,+W.U.+%26+Gibson,+R.L.+2009.+Meteorite+Impact!&ots=8MnBv5Po9T&sig=rBknaBFMQCYzEeZHQkJZ710p7WI#v=onepage&q&f=false">right here</a> on the African continent where we live. Even though it’s really big, Africa still has only 20 confirmed impact sites and is definitely underrepresented in the <a href="http://passc.net/EarthImpactDatabase/New%20website_05-2018/Index.html">global list</a>. This may be partly because of its geology but it is also because too few African geoscientists are looking for impact craters in Africa – maybe one day you can join us, Ivon, and help in the search!</p><img src="https://counter.theconversation.com/content/171833/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Roger Lawrence Gibson has previously received research funding from the National Research Foundation. </span></em></p>Impact craters are relatively shallow, so these bowl-shaped “dents” in Earth’s rocky crust can be easily buried or erased by erosion.Roger Lawrence Gibson, Professor of Structural Geology and Metamorphic Petrology, University of the WitwatersrandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1635782021-07-14T04:20:41Z2021-07-14T04:20:41Z5 rocks any great Australian rock collection should have, and where to find them<figure><img src="https://images.theconversation.com/files/411135/original/file-20210714-25-17z85xl.jpg?ixlib=rb-1.1.0&rect=5%2C11%2C3928%2C2607&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>Road tripping with a geologist is a little different. While you’re probably reading road signs and dodging roadkill, we’re reading road cuttings and deciphering the history of the area over the previous millions — or even billions — of years. </p>
<p>Geology has shaped the Australian landscape. In Victoria where I live, for example, the western plains are pockmarked by <a href="https://www.tandfonline.com/doi/full/10.1080/08120099.2013.806954">Australia’s youngest volcanoes</a>, while the east of the state has been <a href="https://www.annualreviews.org/doi/abs/10.1146/annurev.earth.28.1.47">pushed up</a> to form the mountains of the Great Dividing Range. </p>
<p>Along the southern margin of the state are fossilised braided rivers, relics of when <a href="https://www.tandfonline.com/doi/abs/10.1046/j.1440-0952.1999.00757.x">Australia drifted away from Antarctica</a>. Evidence of this event extends into Tasmania, where dolerite, <a href="https://core.ac.uk/download/pdf/156738663.pdf">a rock that signifies this rift</a>, looms in enormous columns over Hobart from Mount Wellington.</p>
<p>This probably won’t surprise anyone who knows me, but I have rocks peppered around my house that I’ve collected on my travels. Every time I look at them, I not only think about how the rocks were formed, I’m also reminded of the trip when I collected them.</p>
<p>With international and even state borders set to remain closed for a while longer, this is the perfect time to take a great Australian road trip, become a rock detective, and build up your rock collection while you’re at it. </p>
<p>To help you get started, I’ve listed five rocks any great Australian rock collection should have.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/411149/original/file-20210714-19-12ucjmr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Green, volcanic crater" src="https://images.theconversation.com/files/411149/original/file-20210714-19-12ucjmr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/411149/original/file-20210714-19-12ucjmr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=339&fit=crop&dpr=1 600w, https://images.theconversation.com/files/411149/original/file-20210714-19-12ucjmr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=339&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/411149/original/file-20210714-19-12ucjmr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=339&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/411149/original/file-20210714-19-12ucjmr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=426&fit=crop&dpr=1 754w, https://images.theconversation.com/files/411149/original/file-20210714-19-12ucjmr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=426&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/411149/original/file-20210714-19-12ucjmr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=426&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The crater of an erupted volcano near Mount Gambier in Victoria.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>1. Mantle xenoliths</h2>
<p><em>Western Victoria</em></p>
<p>The youngest rocks in Australia are those that erupted out of Australia’s <a href="https://www.biodiversitylibrary.org/page/41319502#page/12/mode/1up">youngest volcano</a> in Mount Gambier, South Australia, 4,000 to 8,000 years ago. That volcano is the culmination of an enormous field of volcanoes that span central and western Victoria.</p>
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<strong>
Read more:
<a href="https://theconversation.com/photos-from-the-field-the-stunning-crystals-revealing-deep-secrets-about-australian-volcanoes-161176">Photos from the field: the stunning crystals revealing deep secrets about Australian volcanoes</a>
</strong>
</em>
</p>
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<p>In western Victoria, the volcanoes were formed from magma that ascended from the Earth’s mantle — the layer between the Earth’s core and crust. While the magma was rising, it tore off chunks of the surrounding mantle rock and transported it to the surface. We can find these chunks of the mantle — or <a href="https://www.sciencedirect.com/science/article/pii/S0012821X97000587?via%3Dihub">mantle xenoliths</a> (xeno = foreign, lith = rock) — in cooled lava today in western Victoria. </p>
<p>At first, these rocks look like any other piece of black or brown basalt, but then you turn them over or crack them open and there’s <a href="https://theconversation.com/photos-from-the-field-the-stunning-crystals-revealing-deep-secrets-about-australian-volcanoes-161176">a blob of bright green rock</a> staring back at you. The mantle rock inside is comprised mainly of olivine, which is a green mineral, and some black/brown pyroxene.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/411142/original/file-20210714-25-1olsmws.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Green rock blob encased in black rock" src="https://images.theconversation.com/files/411142/original/file-20210714-25-1olsmws.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/411142/original/file-20210714-25-1olsmws.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=397&fit=crop&dpr=1 600w, https://images.theconversation.com/files/411142/original/file-20210714-25-1olsmws.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=397&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/411142/original/file-20210714-25-1olsmws.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=397&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/411142/original/file-20210714-25-1olsmws.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=499&fit=crop&dpr=1 754w, https://images.theconversation.com/files/411142/original/file-20210714-25-1olsmws.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=499&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/411142/original/file-20210714-25-1olsmws.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=499&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Green mantle xenolith (xeno = foreign, lith = rock) encased in cooled basaltic lava from Mount Shadwell, Victoria.</span>
<span class="attribution"><span class="source">Dr Melanie Finch</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Mantle xenoliths are a great place to start your rock collection because not only will they be your very own piece of Earth’s mantle, but you can find them yourself through a bit of fossicking around some of the volcanoes in western Victoria.</p>
<h2>2. Meteorites</h2>
<p><em>The Nullarbor Desert, South Australia and Western Australia</em></p>
<p>The Nullarbor is a desert plain region which straddles the border of South Australia and Western Australia. </p>
<p>The dry environment is ideal for preserving meteorites that fall to Earth, and the light colour of the limestone country rock and lack of vegetation means the black and brown meteorites are easier to see.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/411144/original/file-20210714-21-i1bpv1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/411144/original/file-20210714-21-i1bpv1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/411144/original/file-20210714-21-i1bpv1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/411144/original/file-20210714-21-i1bpv1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/411144/original/file-20210714-21-i1bpv1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/411144/original/file-20210714-21-i1bpv1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/411144/original/file-20210714-21-i1bpv1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/411144/original/file-20210714-21-i1bpv1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A black meteorite standing out against the white limestone of the Nullarbor Plain.</span>
<span class="attribution"><span class="source">Professor Andy Tomkins</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Even if you don’t have a great eye for spotting meteorites hiding in plain sight, you can do as the geologists do and use a magnet on a stick to help you. Most meteorites are iron-rich, so wandering around with a magnet hovering over the surface is a good way to pick them up. </p>
<p>Thousands of meteorites have been found in the Nullarbor, <a href="https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1945-5100.2010.01289.x">some up to 40,000 years old</a>.</p>
<h2>3. Metamorphic rocks</h2>
<p><em>Broken Hill, New South Wales</em></p>
<p>You’ve probably heard of Broken Hill because of the large silver, lead and zinc mine there. But the geological conditions that created the ore deposit around <a href="https://pubs.geoscienceworld.org/gsa/geology/article/32/7/589/29483/Subseafloor-origin-for-Broken-Hill-Pb-Zn-Ag">1.7 billion years ago</a> also made some beautiful rocks.</p>
<p>A visit to Broken Hill’s <a href="https://www.brokenhill.nsw.gov.au/Facilities/Albert-Kersten-Mining-and-Minerals-Museum">Albert Kersten Mining and Minerals Museum</a> will demonstrate the vast array of unusual minerals found in the region, some of them described for the first time at this locality. </p>
<p>If you’re seeking your own chunk of Broken Hill’s geological history, Round Hill is the place for you. Just a short way out of the town centre, you’ll find beautiful red garnets surrounded by patches of white minerals (quartz and feldspar). </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/411143/original/file-20210714-23-22ws9z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A geologist holding a rock with various colours" src="https://images.theconversation.com/files/411143/original/file-20210714-23-22ws9z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/411143/original/file-20210714-23-22ws9z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=424&fit=crop&dpr=1 600w, https://images.theconversation.com/files/411143/original/file-20210714-23-22ws9z.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=424&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/411143/original/file-20210714-23-22ws9z.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=424&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/411143/original/file-20210714-23-22ws9z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=532&fit=crop&dpr=1 754w, https://images.theconversation.com/files/411143/original/file-20210714-23-22ws9z.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=532&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/411143/original/file-20210714-23-22ws9z.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=532&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A large garnet from the Broken Hill region.</span>
<span class="attribution"><span class="source">Professor Andy Tomkins</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>These rocks started out as sand and mud, and <a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1525-1314.2005.00608.x">record the history</a> of being buried and heated to over 700°C deep below the Earth’s surface. This process caused the rock to start melting and created the striking stripey, garnet-rich rocks we find there today.</p>
<h2>4. Banded iron formation</h2>
<p><em>Western Australia</em></p>
<p>Banded iron formation is a layered sedimentary rock mainly comprised of alternating bands of chert (a sedimentary rock made of quartz) that’s often red in colour and silver to black iron oxide. It is the main host of iron ore, and can be found in several regions in Western Australia.</p>
<p>The Hamersley Province in the northwestern part of Western Australia has the <a href="https://www.sciencedirect.com/science/article/pii/S0301926815003629">thickest and most extensive</a> banded iron formations in the world. They are about <a href="https://www.tandfonline.com/doi/abs/10.1111/j.1400-0952.2004.01082.x?casa_token=QbHbov_0we0AAAAA:brBYBRIolr2lzbYRHh1CxGZ8zJDTdP02YNjrkq-wXVUfzNj5SK5c9cmcWlmmvOi2WUYd4biGz6ao">2.45 to 2.78 billion years old</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/411141/original/file-20210714-23-1kx5iq1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Red and brown bands along a rock face" src="https://images.theconversation.com/files/411141/original/file-20210714-23-1kx5iq1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/411141/original/file-20210714-23-1kx5iq1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/411141/original/file-20210714-23-1kx5iq1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/411141/original/file-20210714-23-1kx5iq1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/411141/original/file-20210714-23-1kx5iq1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/411141/original/file-20210714-23-1kx5iq1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/411141/original/file-20210714-23-1kx5iq1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Banded iron formation at Forescue Falls, WA.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/graeme/12116315164/in/photolist-7CDYgj-2j6Va2M-2jdGHSf-oEf3Dz-2jdKu3P-2jdKu2m-2dN6GRq-2dN6GBh-oUHcDh-9q1zoW-oEg6Xp-oWKg3z-9q1Ajo-h9Ze7W-oWtFjP-oEfWy6-jsFhnA-mgHSqk-gTUFeN-oWuEdP-zAzaNc-7AevFd-7AazUx-7Ae6uE-7AedRo-7Ae3iw-7AadWP-7Aahr4-7Ae5Qh-7Aai96-7Ae2ps-7AaXwr-2jWei3g-2jW9Sxi-uRHgZW">Graeme Churchard/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Geologists believe they <a href="https://onlinelibrary.wiley.com/doi/abs/10.1046/j.1365-3091.2003.00594.x">formed on a continental shelf</a>, where thick continental crust extends out into the ocean and then drops away to oceanic crust.</p>
<p>Banded iron formation is exciting because it no longer forms on Earth today, meaning it records an ancient process that we no longer see happening. </p>
<p>It is thought to have formed in ancient oceans, which were starting to increase in oxygen content at the time. It records the chemical input of these oceans, as well as sediments from the continent and volcanoes on the ocean floor.</p>
<h2>5. Dinosaur fossils</h2>
<p><em>Central and western Queensland</em></p>
<p>Oh to have been in Queensland 100 million years ago! Judging by the fossils found in parts of the state, it would have been a cornucopia of dinosaur activity.</p>
<p>From an unlikely duo of <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0006190">dinosaurs in a 98-million-year-old billabong</a> in Winton, to <a href="https://www.tandfonline.com/doi/abs/10.1080/02724634.2012.694591">fossilised evidence of a dinosaur herd</a> at Lark Quarry, Queensland is the place to go to peer back in time to the Mesozoic Era between 252 and 66 million years ago. </p>
<p>And if you’re really lucky, you might even have dinosaur bones on your property, like <a href="https://peerj.com/articles/11317/">the huge, long-necked sauropod</a> discovered just this year on a Queensland cattle farm.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/411146/original/file-20210714-27-uptilx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An outback museum with a dinosaur statue in front" src="https://images.theconversation.com/files/411146/original/file-20210714-27-uptilx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/411146/original/file-20210714-27-uptilx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/411146/original/file-20210714-27-uptilx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/411146/original/file-20210714-27-uptilx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/411146/original/file-20210714-27-uptilx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/411146/original/file-20210714-27-uptilx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/411146/original/file-20210714-27-uptilx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Australian Age of Dinosaurs Museum in Winton, Queensland, is home to the largest collection of Australian dinosaur fossils. (Note: not a real dinosaur.)</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>When building your Australian rock collection, remember to check first if <a href="https://theconversation.com/how-to-hunt-fossils-responsibly-5-tips-from-a-professional-palaeontologist-156861">fossicking is allowed in the area</a>. When you find an interesting rock, your state or territory geological survey might be able to help with identifying it. </p>
<p>Happy hunting!</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-to-hunt-fossils-responsibly-5-tips-from-a-professional-palaeontologist-156861">How to hunt fossils responsibly: 5 tips from a professional palaeontologist</a>
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<img src="https://counter.theconversation.com/content/163578/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Emily Finch has previously received funding from an Australian Postgraduate Award and a Society of Economic Geologists Graduate Student Fellowship. </span></em></p>When borders reopen, take an Aussie road trip and explore the continent’s unique geology, from meteorites in the Nullarbor Plain to rock formations that are billions of years old.Emily Finch, Beamline Scientist at ANSTO, and Research Affiliate, Monash UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1568452021-03-31T18:59:31Z2021-03-31T18:59:31ZJust add (mantle) water: new research cracks the mystery of how the first continents formed<figure><img src="https://images.theconversation.com/files/389406/original/file-20210314-24-1f4b7uk.jpg?ixlib=rb-1.1.0&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>Earth is an amazing planet. As far as we know, it’s the only planet in the universe where life exists. It’s also the only planet known to have continents: the land masses on which we live and which host the minerals needed to support our complex lives. </p>
<p>Experts still vigorously debate how the continents formed. We do know water was an essential ingredient for this — and many geologists have proposed this water would have come from Earth’s surface via subduction zones (as is the case now). </p>
<p>But <a href="http://doi.org/10.1038/s41586-021-03337-1">our new research</a> shows this water would have actually come from deep within the planet. This suggests Earth in its youth behaved very differently to how it does today, containing more primordial water than previously thought. </p>
<h2>How to grow a continent</h2>
<p>The solid Earth is comprised of a series of layers including a dense iron-rich core, thick mantle and a rocky outer layer called the lithosphere.</p>
<p>But it wasn’t always this way. When Earth first formed about 4.5 billion years ago, it was a ball of molten rock that was regularly pummelled by meteorites. </p>
<p>As it cooled over a period of a billion years or so, the first continents began to emerge, made of pale-coloured <a href="https://geology.com/rocks/granite.shtml">granite</a>. Exactly how they came to be has long intrigued scientists. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/392176/original/file-20210329-17-1suspmd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Earth's crust diagram" src="https://images.theconversation.com/files/392176/original/file-20210329-17-1suspmd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/392176/original/file-20210329-17-1suspmd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/392176/original/file-20210329-17-1suspmd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/392176/original/file-20210329-17-1suspmd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/392176/original/file-20210329-17-1suspmd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/392176/original/file-20210329-17-1suspmd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/392176/original/file-20210329-17-1suspmd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=377&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Earth comprises a core, mantle and outer crust.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>To make granitic continental crust capable of floating, dark volcanic rocks known as <a href="https://geology.com/rocks/basalt.shtml">basalts</a> have to be melted. Basalts, which are formed as a result of melting in the mantle, would have covered Earth when the planet was starting out.</p>
<p>However, to make continental crust from basalt requires another essential ingredient: water. Knowing how this water got into the rocks at enough depth is key to understanding how the first continents formed. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/earth-has-stayed-habitable-for-billions-of-years-exactly-how-lucky-did-we-get-153416">Earth has stayed habitable for billions of years – exactly how lucky did we get?</a>
</strong>
</em>
</p>
<hr>
<p>One mechanism of taking water to depth is through subduction. This is how most new continental crust is produced today, including the Andes mountain range in South America. </p>
<p>In subduction zones, rocky plates at the bottom of the ocean chill and become increasingly dense until they’re forced under the continents and back into the mantle below, taking ocean water with them.</p>
<p>When this water interacts with basalt in the mantle, it creates granitic crust. But Earth was much hotter billions of years ago, so many experts have argued subduction (at least in the form we currently understand) <a href="https://www.nature.com/articles/nature21383">couldn’t have operated</a>. </p>
<p>Long linear mountain belts such as the Andes contrast starkly with the structure of the granitic crust preserved in the Pilbara region of outback Western Australia. </p>
<p>This ancient crust viewed from above has a “dome-and-keel” pattern, with balloons (domes) of pale-coloured granite rising into the surrounding darker and denser basalts (the keels). </p>
<figure class="align-center ">
<img alt="Pilbara Craton Western Australia" src="https://images.theconversation.com/files/389401/original/file-20210314-15-1ac0r0o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/389401/original/file-20210314-15-1ac0r0o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=430&fit=crop&dpr=1 600w, https://images.theconversation.com/files/389401/original/file-20210314-15-1ac0r0o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=430&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/389401/original/file-20210314-15-1ac0r0o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=430&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/389401/original/file-20210314-15-1ac0r0o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=540&fit=crop&dpr=1 754w, https://images.theconversation.com/files/389401/original/file-20210314-15-1ac0r0o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=540&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/389401/original/file-20210314-15-1ac0r0o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=540&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Satellite images of the Pilbara Craton, Western Australia. Pale-coloured granite domes are surrounded by dark-coloured basalts.</span>
<span class="attribution"><span class="source">Google Earth</span></span>
</figcaption>
</figure>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/390272/original/file-20210318-21-1ipkljp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Dome-and-keel structure" src="https://images.theconversation.com/files/390272/original/file-20210318-21-1ipkljp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/390272/original/file-20210318-21-1ipkljp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=291&fit=crop&dpr=1 600w, https://images.theconversation.com/files/390272/original/file-20210318-21-1ipkljp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=291&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/390272/original/file-20210318-21-1ipkljp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=291&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/390272/original/file-20210318-21-1ipkljp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=366&fit=crop&dpr=1 754w, https://images.theconversation.com/files/390272/original/file-20210318-21-1ipkljp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=366&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/390272/original/file-20210318-21-1ipkljp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=366&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 very simplified cross section of a dome-and-keel structure.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Dome_and_Keel_Structure.pdf">Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>But where did the water needed to produce these domes come from? </p>
<h2>Tiny crystals record Earth’s early history</h2>
<p><a href="http://doi.org/10.1038/s41586-021-03337-1">Our research</a>, led by scientists at the Geological Survey of Western Australia and Curtin University, addressed this question. We analysed tiny crystals trapped in the ancient magmas that cooled and solidified to form the Pilbara’s granite domes.</p>
<p>These crystals, made of a mineral called zircon, contain uranium which <a href="https://en.wikipedia.org/wiki/Uranium%E2%80%93lead_dating">turns into lead over time</a>. We know the rate of this change, and can measure the amounts of uranium and lead contained within. As such, we can obtain a record of their age.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/389402/original/file-20210314-16-og11ln.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Zircon" src="https://images.theconversation.com/files/389402/original/file-20210314-16-og11ln.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/389402/original/file-20210314-16-og11ln.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=360&fit=crop&dpr=1 600w, https://images.theconversation.com/files/389402/original/file-20210314-16-og11ln.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=360&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/389402/original/file-20210314-16-og11ln.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=360&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/389402/original/file-20210314-16-og11ln.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=452&fit=crop&dpr=1 754w, https://images.theconversation.com/files/389402/original/file-20210314-16-og11ln.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=452&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/389402/original/file-20210314-16-og11ln.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=452&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Zircon crystals grown in an ancient magma.</span>
</figcaption>
</figure>
<p>The crystals also contain clues to their origin, which can be unravelled by measuring their oxygen isotope composition. Importantly, zircons that crystallised in molten rocks hydrated by water from Earth’s surface have different compositions to zircons that formed deep in the mantle. </p>
<p>Measurements show the water required for the most primitive ancient WA granites would have come from deep within Earth’s mantle and not from the surface.</p>
<figure class="align-center ">
<img alt="Ion microprobe used for dating zircon" src="https://images.theconversation.com/files/389001/original/file-20210311-23-d4hrrn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/389001/original/file-20210311-23-d4hrrn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/389001/original/file-20210311-23-d4hrrn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/389001/original/file-20210311-23-d4hrrn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/389001/original/file-20210311-23-d4hrrn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/389001/original/file-20210311-23-d4hrrn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/389001/original/file-20210311-23-d4hrrn.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">Chris Kirkland (left) and Tim Johnson loading samples into a secondary-ion mass spectrometer, which shoots a beam of ions into zircon crystals to determine their age and oxygen isotope composition.</span>
</figcaption>
</figure>
<h2>Is the present always the key to the past?</h2>
<p>How the first continents formed is part of a broader debate regarding one of the central tenets of the physical sciences: <a href="https://www.nps.gov/articles/geologic-principles-uniformitarianism.htm">uniformitarianism</a>. This is the idea that the processes which operated on Earth in the distant past are the same as those observed today. </p>
<p>Earth today loses heat through plate tectonics, when the ridged lithospheric plates that form the planet’s solid, outer shell move around. This helps regulate its internal temperature, stabilises atmospheric composition, and probably also facilitated the <a href="https://theconversation.com/does-a-planet-need-plate-tectonics-to-develop-life-61303">development of complex life</a>. </p>
<p>Subduction is one of the most important components of this process. But <a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/ter.12378">several lines of evidence</a> are inconsistent with subduction and plate tectonics on an early Earth. They indicate strongly that our planet behaved very differently in the first two billion years following its formation than it does today.</p>
<p>So while uniformitarianism is a useful way to think about many geological processes, the present may not always be the key to the past.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/does-a-planet-need-plate-tectonics-to-develop-life-61303">Does a planet need plate tectonics to develop life?</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/156845/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Kirkland receives funding from the Australian Research Council and the Geological Survey of Western Australia. </span></em></p><p class="fine-print"><em><span>Tim Johnson receives funding from the Australian Research Council (DP200101104) and the China University of Geosciences, Wuhan. </span></em></p><p class="fine-print"><em><span>Hugh Smithies 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>Evidence from the Pilbara region suggests Earth in its youth behaved very differently to how it does today, and had more water within it than previously thought.Chris Kirkland, Professor of Geology, Curtin UniversityHugh Smithies, Adjunct Research Fellow, Curtin UniversityTim Johnson, Associate Professor, Curtin UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1568992021-03-12T19:00:29Z2021-03-12T19:00:29ZEarth’s early magma oceans detected in 3.7 billion year-old Greenland rocks<figure><img src="https://images.theconversation.com/files/389271/original/file-20210312-13-1o4pbk9.jpg?ixlib=rb-1.1.0&rect=10%2C0%2C7252%2C4845&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">4 billion years ago, the Earth was composed of a series of magma oceans hundreds of kilometres deep.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/realistic-alien-planet-outer-space-3d-1429607681">Larich/Shutterstock</a></span></figcaption></figure><p>Earth hasn’t always been a blue and green oasis of life in an otherwise inhospitable solar system. During our planet’s first 50 million years, around 4.5 billion years ago, its surface was a hellscape of magma oceans, bubbling and belching with heat from Earth’s interior.</p>
<p>The subsequent cooling of the planet from this molten state, and the crystallisation of these magma oceans into solid rock, was <a href="https://www.nature.com/articles/nature06355">a defining stage</a> in the assembly of our planet’s structure, the chemistry of its surface, and the formation of its early atmosphere.</p>
<p>These primeval rocks, containing clues that might explain Earth’s habitability, were assumed to have been lost to the ravages of plate tectonics. But now, <a href="http://dx.doi.org/10.1126/sciadv.abc7394">my team has discovered</a> the chemical remnants of Earth’s magma oceans in 3.7 billion year-old rocks from southern Greenland, revealing a tantalising snapshot of a time when the Earth was almost entirely molten.</p>
<h2>Hell on Earth</h2>
<p>Earth is the product of a chaotic early solar system, which is believed to have featured a number of catastrophic impacts between the Earth and other planetary bodies. The formation of Earth culminated in <a href="https://www.nature.com/articles/35089010">its collision with a Mars-sized impactor planet</a>, which also resulted in the formation of Earth’s moon some 4.5 billion years ago.</p>
<p>These cosmic clashes are thought to have generated enough energy to melt the Earth’s crust and almost all of our planet’s interior (the mantle), creating planetary-scale volumes of molten rock that formed “magma oceans” hundreds of kilometres in depth. Today, in contrast, Earth’s crust is entirely solid, and the mantle is seen as a “plastic solid”: allowing slow, viscous geological movement a far cry from the liquid magma of Earth’s early mantle.</p>
<p>As the Earth recovered and cooled after its chaotic collisions, its deep magma oceans <a href="https://www.sciencedirect.com/science/article/pii/S0012821X19305771">crystallised and solidified</a>, beginning Earth’s journey to the planet we know today. The volcanic gases which bubbled out of Earth’s cooling magma oceans may have been decisive in the formation and composition of our planet’s early atmosphere – which would eventually support life. </p>
<figure class="align-center ">
<img alt="The Earth's layers in a cross-section, showing the core, mantle, and crust" src="https://images.theconversation.com/files/389270/original/file-20210312-20-8ptx8n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/389270/original/file-20210312-20-8ptx8n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/389270/original/file-20210312-20-8ptx8n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/389270/original/file-20210312-20-8ptx8n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/389270/original/file-20210312-20-8ptx8n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=500&fit=crop&dpr=1 754w, https://images.theconversation.com/files/389270/original/file-20210312-20-8ptx8n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=500&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/389270/original/file-20210312-20-8ptx8n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=500&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Earth is now composed of the inner core, the outer core, the lower mantle, the upper mantle, and the crust.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/structure-planet-earth-space-3d-rendering-1614442552">AlexLMX/Shutterstock</a></span>
</figcaption>
</figure>
<h2>Geological search</h2>
<p>Finding geological evidence for the Earth’s former molten state is extremely difficult. This is because magma ocean events are likely to have taken place over 4 billion years ago, and many of the rocks from that period of Earth’s history have since been recycled by plate tectonics. </p>
<p>But while rocks from this period no longer exist, their chemical traces may still be stored in Earth’s depths. Solidified crystals from Earth’s cooling period would have been so dense that they’d have sunk to the base of Earth’s mantle. Scientists even believe that these mineral residues may be stored in isolated zones deep within <a href="https://www.sciencedirect.com/science/article/pii/S0012821X19301797">Earth’s mantle-core boundary</a>.</p>
<p>If they do exist, these ancient crystal graveyards are inaccessible to us – hiding far too deep for us to take direct samples. And if they were to ever rise to the Earth’s surface, the magma ocean crystals would naturally undergo a process of melting and solidifying, leaving only traces of their origins in the volcanic rocks that make it to Earth’s crust.</p>
<h2>Crystal clues</h2>
<p>We knew Greenland would be a good place to search for these traces of Earth’s molten past. Our samples originate from the Isua supracrustal belt in southwestern Greenland, which is a <a href="https://royalsocietypublishing.org/doi/10.1098/rsnr.2009.0004">famous area for geologists</a>. At first glance, Isua’s rocks look just like any modern basalt you’d find on the sea floor. But these rocks some of the oldest in the world, believed to be between 3.7 and 3.8 billion years old. </p>
<p>On analysing Isua’s rocks, we discovered unique iron isotope signatures. These signatures showed that the region of the mantle from which the rocks had formed had been subjected to very high pressure, over 700 kilometres below Earth’s surface. That’s exactly where minerals formed during magma ocean crystallisation would have been located. </p>
<p>But if these rocks did indeed bear traces of crystallised magma ocean, how did they find their way to the Earth’s surface? The answer lies in how the Earth’s interior melts, producing volcanic rocks on the planet’s surface.</p>
<h2>Melting rocks</h2>
<p>When regions of the Earth’s semi-solid mantle heat up and melt, they rise buoyantly towards the Earth’s crust, ultimately producing volcanic rocks when the magma reaches the surface and cools. By studying the chemistry of these rocks on the surface, we can probe the composition of the material that melted to form them.</p>
<p>The isotopic makeup of Isua rocks revealed that their journey to Earth’s surface involved several stages of crystallisation and remelting in the interior of the planet – a kind of distillation process on their way to the surface. But the rocks that emerged, located in present-day Greenland, still retain chemical signatures that connect them to Earth’s magma-covered past. </p>
<p>The results of our work provide some of the first direct geological evidence for the signature of magma ocean crystals in volcanic rocks found on Earth’s surface. Now, we’d like to understand whether other ancient volcanic rocks across the world can tell us more about Earth’s former magma oceans, or whether we’ve instead stumbled upon a geological oddity: more of a one-off clue. </p>
<p>If other volcanoes may have spewed similar geological artefacts, we might also look to modern eruption hotspots such as Hawaii and Iceland for further <a href="https://www.pnas.org/content/117/49/30993.short">isotopic novelties</a> that speak of Earth’s ancient past. It’s possible that more primordial rocks may be found in the future which could help us understand more about the Earth’s violent, magma-covered past.</p><img src="https://counter.theconversation.com/content/156899/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Helen M Williams has received funding from NERC and the ERC. </span></em></p>The rocks provide rare evidence of a time when Earth’s surface was a deep sea of incandescent magma.Helen M Williams, Reader in Geochemistry, University of CambridgeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1465342020-12-06T10:02:39Z2020-12-06T10:02:39ZThe Atlantic: The driving force behind ocean circulation and our taste for cod<figure><img src="https://images.theconversation.com/files/372503/original/file-20201202-17-1qg6r71.jpg?ixlib=rb-1.1.0&rect=38%2C0%2C4195%2C2818&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Fishing boats coming into Le Guilvinec, Brittany, France, at the end of the day.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/homecoming-tired-fishermans-ships-approaching-after-772649248">Photoneye/Shutterstock</a></span></figcaption></figure><p>“<a href="https://www.abebooks.co.uk/first-edition/Atlantic-Close-Re-Open-Offprint-Nature-Vol/30196723457/bd">Did the Atlantic close and then reopen</a>?” That was the question posed in a 1966 paper by the Canadian geophysicist <a href="https://www.ldeo.columbia.edu/the-vetlesen-prize/past-recipients/john-tuzo-wilson">J. Tuzo Wilson</a>. </p>
<p>The answer? Yes, over millions of years. And it was the breakup of the <a href="https://www.britannica.com/place/Pangea">supercontinent Pangea</a>, starting some 180 million years ago, that began creating the Atlantic Ocean basin as we know it today.</p>
<p>Earth’s surface is made up of <a href="https://www.britannica.com/science/plate-tectonics">intersecting tectonic plates</a>. For much of our planet’s history these plates have been bumping into one another, forming chains of mountains and volcanoes, and then rifting apart, creating oceans. </p>
<p>When Pangea existed it would have been possible to walk from modern Connecticut or Georgia in the U.S. to what is now Morocco in Africa. Geologists don’t know what causes continents to break up, but we know that when rifting occurs, continents thin and pull apart. Magma intrudes into the continental rocks. </p>
<hr>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/369797/original/file-20201117-13-180ibt9.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/369797/original/file-20201117-13-180ibt9.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/369797/original/file-20201117-13-180ibt9.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/369797/original/file-20201117-13-180ibt9.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/369797/original/file-20201117-13-180ibt9.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=504&fit=crop&dpr=1 754w, https://images.theconversation.com/files/369797/original/file-20201117-13-180ibt9.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=504&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/369797/original/file-20201117-13-180ibt9.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=504&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><strong><em>This story is part of <a href="https://theconversation.com/uk/topics/oceans-21-96784">Oceans 21</a></em></strong>
<br><em><a href="https://oceans21.netlify.app/">Five profiles open our series on the global ocean</a>, delving into ancient <a href="https://theconversation.com/exploring-the-indian-ocean-as-a-rich-archive-of-history-above-and-below-the-water-line-133817">Indian Ocean</a> trade networks, <a href="https://theconversation.com/it-might-be-the-worlds-biggest-ocean-but-the-mighty-pacific-is-in-peril-150745">Pacific</a> plastic pollution, <a href="https://theconversation.com/arctic-ocean-climate-change-is-flooding-the-remote-north-with-light-and-new-species-150157">Arctic</a> light and life, <a href="https://theconversation.com/the-atlantic-the-driving-force-behind-ocean-circulation-and-our-taste-for-cod-146534">Atlantic</a> fisheries and the <a href="https://theconversation.com/an-ocean-like-no-other-the-southern-oceans-ecological-richness-and-significance-for-global-climate-151084">Southern Ocean</a>’s impact on global climate. Look out for new articles in the lead up to COP26. Brought to you by The Conversation’s international network.</em></p>
<hr>
<p>The oldest portions of crust in the Atlantic Ocean lie off of North America and Africa, which were adjacent in Pangea. They show that these two continents separated about 180 million years ago, forming the North Atlantic Ocean basin. The rest of Africa and South America rifted apart about 40 million or 50 million years later, creating what is now the South Atlantic Ocean basin. </p>
<p>Magma wells upward from beneath the ocean floor at the Mid-Atlantic Ridge, creating new crust where the plates move apart. Some of this ocean crust is younger than you or me, and more is being created today. The Atlantic is still growing.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/370161/original/file-20201118-17-39dr16.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="World map with colored zones showing age of ocean plates" src="https://images.theconversation.com/files/370161/original/file-20201118-17-39dr16.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/370161/original/file-20201118-17-39dr16.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=330&fit=crop&dpr=1 600w, https://images.theconversation.com/files/370161/original/file-20201118-17-39dr16.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=330&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/370161/original/file-20201118-17-39dr16.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=330&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/370161/original/file-20201118-17-39dr16.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=415&fit=crop&dpr=1 754w, https://images.theconversation.com/files/370161/original/file-20201118-17-39dr16.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=415&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/370161/original/file-20201118-17-39dr16.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=415&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 map shows how ocean crust rises upward at rifts between tectonic plates and spreads outward. In the Atlantic, light blue crust began forming 180 million years ago when North America and Africa rifted apart. Green crust was produced 128 million to 84 million years ago when Africa and South America rifted apart. Dark red crust is the youngest, formed up to 10 million years ago.</span>
<span class="attribution"><a class="source" href="https://www.ngdc.noaa.gov/mgg/ocean_age/data/2008/ngdc-generated_images/whole_world/2008_age_of_oceans_plates.jpg">NOAA NGDC</a></span>
</figcaption>
</figure>
<h2>Winds and currents</h2>
<p>Once the ocean basin formed after Pangea’s breakup, water entered from rain and rivers. Winds began to move the surface water. </p>
<p>Thanks to the <a href="https://www.youtube.com/watch?v=xqM83_og1Fc">unequal heating of Earth’s surface and its rotation</a>, these winds blow in different directions. The Earth is warmer at the equator than near the poles, which puts air in motion. At the equator the planet’s heat causes moist air to warm, expand and rise. At the polar regions cold, dry, heavier air descends. </p>
<p>This motion creates “cells” of rising and descending air that control global wind patterns. Earth’s rotation dictates that different parts of the globe travel at different speeds. At a pole, a molecule of air would just spin around, while a particle of air at the equator in Quito, Ecuador, would travel 7,918 miles (12,742 kilometers) in a single day. </p>
<p>This different movement causes the air cells to break up. For example, in the <a href="https://www.bbc.co.uk/bitesize/guides/zpykxsg/revision/1">Hadley Cell</a>, tropical air, which rose at the equator, cools in the upper atmosphere and descends at about 30 degrees north and south latitude – roughly, near the northern and southern tips of Africa. Earth’s rotation <a href="https://scied.ucar.edu/learning-zone/how-weather-works/global-air-atmospheric-circulation">turns this descending air</a>, creating trade winds that flow from east to west across the Atlantic and back to the equator. At higher latitudes in the North and South Atlantic, the same forces create mid-latitude cells with winds that blow from west to east.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/368418/original/file-20201109-21-1plttsv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Atmospheric circulation diagram" src="https://images.theconversation.com/files/368418/original/file-20201109-21-1plttsv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/368418/original/file-20201109-21-1plttsv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=462&fit=crop&dpr=1 600w, https://images.theconversation.com/files/368418/original/file-20201109-21-1plttsv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=462&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/368418/original/file-20201109-21-1plttsv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=462&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/368418/original/file-20201109-21-1plttsv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=581&fit=crop&dpr=1 754w, https://images.theconversation.com/files/368418/original/file-20201109-21-1plttsv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=581&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/368418/original/file-20201109-21-1plttsv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=581&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Earth’s atmospheric circulation, showing the Hadley, midlatitude and polar cells, and the wind patterns they produce.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:NASA_depiction_of_earth_global_atmospheric_circulation.jpg">NASA/Wikimedia</a></span>
</figcaption>
</figure>
<p>As air flows across the ocean’s surface, it moves water. This creates a circulating system of gyres, or rotating currents, that move clockwise in the North Atlantic and counterclockwise in the South Atlantic. These gyres are part of a <a href="https://svs.gsfc.nasa.gov/vis/a000000/a003600/a003658/">global conveyor belt</a> that transports and redistributes heat and nutrients throughout the global ocean. </p>
<p>The Gulf Stream, which follows the U.S. East Coast before heading east across the North Atlantic, is part of the North Atlantic gyre. Since the current carries warm water north, it is easy to see on false-color <a href="https://visibleearth.nasa.gov/images/54734/temperature-of-the-gulf-stream">infrared satellite images</a> as it transports heat northward. Like a river, it also meanders. </p>
<h2>Moving water masses</h2>
<p>These wind-blown surface currents are important for many reasons, including <a href="https://divediscover.whoi.edu/history-of-oceanography/benjamin-franklin-discovering-the-gulf-stream/">human navigation</a>, but they affect only about 10% of the Atlantic’s volume. Most of the ocean operates in a different system, which is called thermohaline circulation because it is driven by heat (thermo) and salt (saline).</p>
<p>Like many processes in the ocean, salinity is tied to weather and circulation. For example, trade winds blow moist air from the Atlantic across Central America and into the <a href="https://theconversation.com/it-may-be-the-worlds-biggest-deepest-ocean-but-the-mighty-pacific-is-in-peril-150406">Pacific Ocean</a>, which concentrates salinity in the Atlantic waters left behind. As a result, the Atlantic is <a href="https://earthobservatory.nasa.gov/images/78250/a-measure-of-salt">slightly saltier than the Pacific</a>. </p>
<p>This extra salinity makes the Atlantic the driving force in ocean circulation. As currents move surface waters poleward, the water cools and becomes more dense. Eventually at high latitudes this cold, salty water sinks to the ocean floor. From there it flows along the bottom and back toward the the opposite pole, creating density-driven currents with names such as <a href="https://en.wikipedia.org/wiki/North_Atlantic_Deep_Water">North Atlantic Deep Water</a> and <a href="https://en.wikipedia.org/wiki/Antarctic_bottom_water">Antarctic Bottom Water</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/368484/original/file-20201110-22-6dz8ei.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Thermohaline circulation map" src="https://images.theconversation.com/files/368484/original/file-20201110-22-6dz8ei.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/368484/original/file-20201110-22-6dz8ei.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=382&fit=crop&dpr=1 600w, https://images.theconversation.com/files/368484/original/file-20201110-22-6dz8ei.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=382&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/368484/original/file-20201110-22-6dz8ei.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=382&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/368484/original/file-20201110-22-6dz8ei.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=480&fit=crop&dpr=1 754w, https://images.theconversation.com/files/368484/original/file-20201110-22-6dz8ei.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=480&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/368484/original/file-20201110-22-6dz8ei.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=480&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Global thermohaline circulation is driven primarily by the formation and sinking of deep water. It moves heat from the equator toward the poles.</span>
<span class="attribution"><a class="source" href="https://www.grida.no/resources/5228">Hugo Ahlenius, UNEP/GRID-Arendal</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>As these deep currents move, they collect surface organisms that have died and fallen to the bottom. With time, the organisms decompose, filling the deep water with essential nutrients. </p>
<p>In some locations this nutrient-rich water rises back up to the surface, a process called upwelling. When it reaches the ocean’s sunlit zone, within 650 feet (200 meters) of the surface, tiny organisms called phytoplankton feed on the nutrients. In turn, they become food for zooplankton and larger organisms higher up the food chain. Some of the the Atlantic’s richest fishing grounds, such as <a href="https://www.newworldencyclopedia.org/entry/Grand_Banks">the Grand Banks</a> to the southeast of Newfoundland in Canada and the <a href="https://earthobservatory.nasa.gov/features/Malvinas">Falkland/Malvinas Islands</a> in the South Atlantic, are upwelling areas. </p>
<p>Much about the Atlantic remains to be discovered, especially in a changing climate. Will rising carbon dioxide levels and resulting ocean acidification disrupt marine food chains? How will a warmer ocean affect circulation and hurricane intensity? What we do know is that the Atlantic’s winds, currents and sea life are intricately connected, and disrupting them can have far-reaching effects.</p>
<h2>Atlantic cod fishing</h2>
<p>Now, let’s head back up to the surface, and into the wake of the first sailboats that set out to fish for cod along the Canadian coast. These pioneering ships paved the way for greater exploitation of the Atlantic’s wealth of fishery resources – particularly cod. Communities of people greatly benefited from these resources over the following centuries, until the threat of overfishing became impossible to ignore.</p>
<p>The history of fishing in the Atlantic is often said to trace back to the discovery of the cod-rich Canadian waters of Newfoundland, attributed to Italian navigator and explorer John Cabot, who led an English expedition there in 1497. From the 16th to the 20th centuries, cod-fishing mania swept European fleets. Between 1960 to 1976, ships from Spain, Portugal and France were responsible for <a href="https://www.nafo.int/Data/STATLANT">40% of the catch</a>. However, <a href="https://books.google.fr/books/about/Management_of_Marine_Fisheries_in_Canada.html?id=uWOmj-j0jmcC&redir_esc=y">in 1977 Canada extended its territory</a> offshore by 200 miles, taking possession of the Newfoundland cod fisheries, which accounted for 70% of cod production in the Northwest Atlantic.</p>
<figure class="align-center ">
<img alt="Fishermen aboard a boat with a haul of cod" src="https://images.theconversation.com/files/371062/original/file-20201124-15-ud1t75.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/371062/original/file-20201124-15-ud1t75.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/371062/original/file-20201124-15-ud1t75.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/371062/original/file-20201124-15-ud1t75.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/371062/original/file-20201124-15-ud1t75.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/371062/original/file-20201124-15-ud1t75.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/371062/original/file-20201124-15-ud1t75.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">Fishermen aboard a boat with a haul of cod.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/fr/image-photo/cod-fishing-lofoten-norway-fisherman-action-1261237213">Georg Kristiansen/Shutterstock</a></span>
</figcaption>
</figure>
<p>For five centuries, the only thing that mattered was the size of the catch. This drove innovations in the design and equipment of fishing boats. The sailboat cod-fishing industry in Newfoundland and Iceland <a href="https://archimer.ifremer.fr/doc/00486/59783/62917.pdf">hit its peak in the late 19th century</a>; from 1800 to 1900, France – the main fishing operator alongside Britain – outfitted more than 30,000 schooners. </p>
<p>At the end of the 19th century, the rowboat was replaced by the dory, a small (two-person) boat from North America, which sharply increased production. A plaque commenting on the new safety of the dory in the French <a href="https://www.ville-fecamp.fr/-Musee-.html">Museum of Fisheries</a>, in Normandy – dedicated to the history of commercial cod fishing – noted that the hazard of losing a man overboard was “built into the mindset of cod-fishing.” But by the early 20th century, steamers had begun to replace these boats.</p>
<p>New <a href="https://doi.org/10.1016/j.marpol.2020.103868">productivity gains</a> came with new techniques, such as <a href="https://www.sciencedirect.com/science/article/abs/pii/S0308597X07000784">using back-trawling</a> instead of side-trawling in the 1950s and 1960s, alongside reduced crew sizes.</p>
<p>The biggest cod catch, at nearly 1.9 million tons, was recorded in 1968. After that, overall production declined year after year, reaching less than a million tons in 1973. Numbers slowly picked up again in the 1980s after European fleets were excluded from the Newfoundland area, but this comeback was short-lived. On July 2, 1992, the Canadian government announced <a href="https://books.google.fr/books/about/Management_of_Marine_Fisheries_in_Canada.html?id=uWOmj-j0jmcC&redir_esc=y">a moratorium</a> on cod fishing, confirming that populations had collapsed. This collapse in the northwestern Atlantic has <a href="https://www.sciencedirect.com/science/article/abs/pii/S0308597X04000600">since become a textbook example of the risks of overfishing</a>.</p>
<h2>The wider catch</h2>
<p>Seafood production in the Atlantic went from an estimated 9 million tons in 1950 to more than 23 million tons in 1980 and 2000, and <a href="http://www.fao.org/fishery/static/Yearbook/YB2018_USBcard/navigation/index_content_capture_e.htm#C">22 million tons in 2018</a>. This overall production has remained stable since 1970. </p>
<p>In the North Atlantic, whiting and herring are the two most fished species by tonnage. Sardine and sardinella hold the top spots in the Central Atlantic. In the South Atlantic, mackerel and Argentine hake dominate the catch.</p>
<p>The Food and Agriculture Organization of the United Nations (FAO) has identified six production areas in the Atlantic Ocean, divided up cardinally, as shown on the map below. In 1950, these various areas accounted for <a href="http://www.fao.org/fishery/static/Yearbook/YB2018_USBcard/navigation/index_content_capture_e.htm#C">52% of the worldwide catch</a>. From 1960 to 1980, this proportion went down to 37% to 43%. Since 1990, one-quarter of global seafood production is caught by fleets operating in the Atlantic.</p>
<p>Nearly <a href="http://www.fao.org/fishery/static/Yearbook/YB2018_USBcard/navigation/index_intro_e.htm">60% of seafood production</a> now comes from fisheries in the Pacific Ocean, and 15% from the Indian Ocean.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/371046/original/file-20201124-17-1waqbvw.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/371046/original/file-20201124-17-1waqbvw.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/371046/original/file-20201124-17-1waqbvw.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=763&fit=crop&dpr=1 600w, https://images.theconversation.com/files/371046/original/file-20201124-17-1waqbvw.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=763&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/371046/original/file-20201124-17-1waqbvw.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=763&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/371046/original/file-20201124-17-1waqbvw.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=959&fit=crop&dpr=1 754w, https://images.theconversation.com/files/371046/original/file-20201124-17-1waqbvw.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=959&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/371046/original/file-20201124-17-1waqbvw.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=959&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">FAO has identified six production areas in the Atlantic Ocean.</span>
<span class="attribution"><a class="source" href="http://www.fao.org/fishery/docs/maps/world_2003.gif">Le Floc’h (adapted from FAO's map, 2003)</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p><strong>The northeastern Atlantic</strong> (FAO Area 27) covers fisheries operated by European fleets. This area is, by far, the most bountiful of the entire Atlantic zone, with a total catch of 9.6 million tons in 2018. Norway <a href="http://www.fao.org/fishery/static/Yearbook">took the lead</a> for seafood production by tonnage (2.5 million tons) in 2018, ahead of Spain (just under a million tons). It is also the most diversified zone, with more than 450 commercial species.</p>
<p><strong>The northwestern Atlantic</strong> (FAO Area 21) stretches from the Rhode Island and Gulf of Maine coastlines in the U.S. to the Canadian coasts, including the Gulf of Saint Lawrence and the waters of Newfoundland and Labrador. Cod has dominated the history of fishing in this area since the 16th century. The biggest overall catch was recorded in 1970, at more than 4 million tons. But, after 1990, that number dropped, as a consequence of the 1992 moratorium. Since 2000, the northwest area has accounted for around 10% of the Atlantic catch (1.7 million tons in 2018). There are 220 monitored species in the area.</p>
<p><strong>Eastern Central Atlantic</strong> (FAO Area 34) stretches from the Moroccan to the Zairian coasts. Species caught include sardine, anchovy and herring. In 2018, this area accounted for a quarter of the total seafood production of all six Atlantic areas. That same year, West African fisheries recorded the second biggest catches after the northeastern Atlantic. The high number of commercial species identified by the FAO sets this region apart, at nearly 300.</p>
<p><strong>Western Central Atlantic</strong> (FAO Area 31) stretches from the southern U.S. to the north of Brazil, including the Caribbean. Since 1970, catch size has remained between 1.3 million and 1.8 million tons (5% to 10% of the entire Atlantic catch). Lobster and shrimp are the target species in the Caribbean waters.</p>
<p><strong>Southeast Atlantic</strong> (FAO Area 47) connects the African coastlines of Angola, Namibia and South Africa. Production surpassed 2 million tons in 1970 and 1980, accounting for 10% of the total Atlantic catch. Since 1990, the catch has been stable, with a plateau of 1.5 million tons. It’s the least diversified region in the Atlantic, with 160 species monitored by the FAO. Mackerel, hake and anchovy make up 59% of total production.</p>
<p><strong>Southwest Atlantic</strong> (FAO Area 41), which stretches along the coastlines of Brazil, Uruguay and Argentina in South America, was the lowest-producing of the six areas until 1980. It recorded no more than 5% of the total Atlantic catch. But from 1990, fisheries produced 1.8 million to 2 million tons (8% to 10% of the overall catch). This can be attributed to investment from the Argentinian government into <a href="https://doi.org/10.4000/norois.7300">fishing fleets</a> in the 1980s. Some 225 commercial species are being statistically monitored, with 52% of total production coming from hake, shortfin squid and shrimp.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/371047/original/file-20201124-17-1exliy7.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/371047/original/file-20201124-17-1exliy7.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/371047/original/file-20201124-17-1exliy7.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=287&fit=crop&dpr=1 600w, https://images.theconversation.com/files/371047/original/file-20201124-17-1exliy7.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=287&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/371047/original/file-20201124-17-1exliy7.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=287&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/371047/original/file-20201124-17-1exliy7.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=360&fit=crop&dpr=1 754w, https://images.theconversation.com/files/371047/original/file-20201124-17-1exliy7.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=360&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/371047/original/file-20201124-17-1exliy7.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=360&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Catches in the Atlantic (1950-2018) according to the FAO areas.</span>
<span class="attribution"><a class="source" href="http://www.fao.org/fishery/statistics/fr">Le Floc’h</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<h2>Protecting the entire ecosystem</h2>
<p>At a time when scientific research predicts that all living marine resources will <a href="https://science.sciencemag.org/content/314/5800/787">be exhausted by 2048</a>, a new fisheries approach is required to avoid new tragedies, like the one that befell the cod populations in the northwestern Atlantic.</p>
<p>In this context, protecting ecosystems has become a priority. This growing acknowledgment of the impacts of fishing is a direct result of the successful work undertaken by ecological and social science researchers since the 1970s, who placed the concept of resilience at the heart of their studies.</p>
<p>This new ecosystem-based management approach, now inscribed in law in <a href="https://ec.europa.eu/environment/marine/eu-coast-and-marine-policy/marine-strategy-framework-directive/index_en.htm">Europe</a> and <a href="https://laws-lois.justice.gc.ca/eng/acts/o-2.4/">Canada</a>, has been positive. A similar <a href="https://obamawhitehouse.archives.gov/administration/eop/oceans/policy">U.S. policy</a> was revoked by President Donald Trump, but likely will be restored by incoming president Joe Biden. However, there is still work to do to tackle the main challenge – making this approach a reality in all Atlantic fisheries.</p><img src="https://counter.theconversation.com/content/146534/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The Atlantic Ocean is still growing physically, but humans are over-harvesting its rich fisheries. The most famous one – North Atlantic cod – has become a textbook example of harmful overfishing.Suzanne OConnell, Professor of Earth and Environmental Sciences, Wesleyan UniversityPascal Le Floc’h, Maître de conférences, économiste, laboratoire Amure (UBO, Ifremer, CNRS), Université de Bretagne occidentale Licensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1465762020-09-28T19:59:34Z2020-09-28T19:59:34ZRocky icebergs and deep anchors – new research on how planetary forces shape the Earth’s surface<figure><img src="https://images.theconversation.com/files/360159/original/file-20200927-20-1qx2iju.jpg?ixlib=rb-1.1.0&rect=44%2C187%2C4947%2C2552&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock/Harvepino</span></span></figcaption></figure><p>Have you ever wondered why the Earth’s surface is separated into two distinct worlds – the oceans and large tracts of land? </p>
<p>Why aren’t land and water more mixed up, forming a landscape of lakes? And why is most of the land relatively low and close to sea level, making coastal regions vulnerable to rising seas?</p>
<p>Our new <a href="https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GC009150">research</a> uncovers the fundamental forces that control the Earth’s surface. These findings will help scientists calculate how land levels will respond to the melting of ice sheets and rises in sea level, as a consequence of global warming, as well as providing insights into changes in land area throughout our planet’s history.</p>
<figure class="align-center ">
<img alt="View of Mt Cook" src="https://images.theconversation.com/files/360181/original/file-20200928-20-mmciuw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/360181/original/file-20200928-20-mmciuw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=275&fit=crop&dpr=1 600w, https://images.theconversation.com/files/360181/original/file-20200928-20-mmciuw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=275&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/360181/original/file-20200928-20-mmciuw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=275&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/360181/original/file-20200928-20-mmciuw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=345&fit=crop&dpr=1 754w, https://images.theconversation.com/files/360181/original/file-20200928-20-mmciuw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=345&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/360181/original/file-20200928-20-mmciuw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=345&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">View of Mt Cook/Aoraki, rising 3724m above sea level at the head of Lake Pukaki in New Zealand’s South Island. The mountain is underlain by crust about 45km thick.</span>
<span class="attribution"><span class="source">Shutterstock/yong922760</span></span>
</figcaption>
</figure>
<h2>Rocky icebergs</h2>
<p>The research draws on the work by an inspiring early geologist. In 1855, the British Astronomer Royal <a href="https://en.wikipedia.org/wiki/George_Biddell_Airy">George Biddell Airy</a> published what is arguably one of the <a href="https://www.jstor.org/stable/pdf/108511.pdf">most important scientific papers</a> in the earth sciences, setting out the basic understanding of what controls the elevation of the planet’s surface.</p>
<p>Airy was aware the shape of the Earth is very similar to a spinning fluid ball, distorted by the forces of rotation so that it bulges slightly at the equator and flattens at the poles. He concluded the interior of the Earth must be fluid-like.</p>
<p>His <a href="https://www.jstor.org/stable/pdf/108589.pdf">measurements of the force of gravity</a> in mine shafts showed the deep interior of the Earth must be much denser than the shallow parts. </p>
<figure class="align-right ">
<img alt="Ice berg" src="https://images.theconversation.com/files/360173/original/file-20200927-22-m3z7yx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/360173/original/file-20200927-22-m3z7yx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=750&fit=crop&dpr=1 600w, https://images.theconversation.com/files/360173/original/file-20200927-22-m3z7yx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=750&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/360173/original/file-20200927-22-m3z7yx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=750&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/360173/original/file-20200927-22-m3z7yx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=943&fit=crop&dpr=1 754w, https://images.theconversation.com/files/360173/original/file-20200927-22-m3z7yx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=943&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/360173/original/file-20200927-22-m3z7yx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=943&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">Shutterstock/Sergey Nivens</span></span>
</figcaption>
</figure>
<p>Airy then made an extraordinary leap of scientific thinking. He proposed that the outer part of the Earth, which he called the <a href="https://en.wikipedia.org/wiki/Earth%27s_crust">crust</a>, must be floating on underlying “fluid”. </p>
<p>An analogy might be an iceberg floating in water — to rise above the surface, the iceberg must have deep icy roots. </p>
<p>Applying the same principle to the Earth, Airy proposed the Earth’s crust also had iceberg-like roots, and the higher the surface elevation, the deeper these roots must be, creating thicker crust. </p>
<figure class="align-center ">
<img alt="Map of the continents" src="https://images.theconversation.com/files/359204/original/file-20200921-24-trg15b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/359204/original/file-20200921-24-trg15b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=499&fit=crop&dpr=1 600w, https://images.theconversation.com/files/359204/original/file-20200921-24-trg15b.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=499&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/359204/original/file-20200921-24-trg15b.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=499&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/359204/original/file-20200921-24-trg15b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=628&fit=crop&dpr=1 754w, https://images.theconversation.com/files/359204/original/file-20200921-24-trg15b.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=628&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/359204/original/file-20200921-24-trg15b.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=628&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The continents define large continuous areas of land separated by oceans. The Earth’s crust is much thicker beneath the continents compared to the oceans.</span>
<span class="attribution"><span class="source">Simon Lamb</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Airy’s idea provided a fundamental explanation for continents and oceans. They were regions of thick and thin crust respectively. High mountain ranges, such as the Himalaya or Andes, were underlain by even thicker crust.</p>
<h2>Tectonic plates</h2>
<p>In the 1960s, the new theory of <a href="https://www.livescience.com/37706-what-is-plate-tectonics.html">plate tectonics</a> introduced a complication. It added the concept of tectonic plates, which are colder and denser than the deeper mantle (the geological <a href="https://www.nationalgeographic.org/encyclopedia/mantle/">layer beneath the crust</a>). </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-earths-continents-became-twisted-and-contorted-over-millions-of-years-116168">How Earth's continents became twisted and contorted over millions of years</a>
</strong>
</em>
</p>
<hr>
<p>Over the past two decades, geophysicists have finally put together an accurate picture of the crust in the continents. </p>
<figure class="align-center ">
<img alt="Graphic explaining how tectonic plates add depth to the " src="https://images.theconversation.com/files/359206/original/file-20200921-18-cvgi6k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/359206/original/file-20200921-18-cvgi6k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=288&fit=crop&dpr=1 600w, https://images.theconversation.com/files/359206/original/file-20200921-18-cvgi6k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=288&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/359206/original/file-20200921-18-cvgi6k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=288&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/359206/original/file-20200921-18-cvgi6k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=362&fit=crop&dpr=1 754w, https://images.theconversation.com/files/359206/original/file-20200921-18-cvgi6k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=362&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/359206/original/file-20200921-18-cvgi6k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=362&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Airy imagined the crust as a rocky iceberg with buoyant roots holding up the surface. Plate tectonics adds a dense root of the plate that acts as an anchor.</span>
<span class="attribution"><span class="source">Simon Lamb</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>We found a surprising result – there seems to be little relation between the average elevations of the continents and the thickness of the underlying crust, except that the crust is much thicker than beneath the oceans. Most of the land area is within a few hundred metres of sea level, yet the thickness of the crust varies by more than 20km.</p>
<p>So why don’t we see the differences in crustal thickness below a continent reflected in its shape above? Our <a href="https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GC009150">research</a> shows the underlying thick tectonic plate is acting as an anchor, keeping the elevations relatively low even though the buoyant crust wants to rise higher.</p>
<p>We used measurements of the thickness of the tectonic plates, recently <a href="http://ds.iris.edu/ds/products/emc-cam2016/">determined from the speed of seismic waves</a>. The base of the continental plates reaches up to 250km deep, but most is between 100km and 200km deep. </p>
<p>We also worked out the densities of the different layers from variations in the strength of gravity. It was clear that the dense roots of the plates were capable of pulling down the surface of the Earth in exactly the way needed to explain the actual elevations.</p>
<figure class="align-center ">
<img alt="Graphic showing the relationship between the thickness of the crust and the elevation of a continent." src="https://images.theconversation.com/files/359248/original/file-20200922-24-13a7r5d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/359248/original/file-20200922-24-13a7r5d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=697&fit=crop&dpr=1 600w, https://images.theconversation.com/files/359248/original/file-20200922-24-13a7r5d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=697&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/359248/original/file-20200922-24-13a7r5d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=697&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/359248/original/file-20200922-24-13a7r5d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=876&fit=crop&dpr=1 754w, https://images.theconversation.com/files/359248/original/file-20200922-24-13a7r5d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=876&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/359248/original/file-20200922-24-13a7r5d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=876&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The average elevations of the continents are surprisingly insensitive to their average crustal thicknesses, contrary to Airy’s prediction that they float on the underlying mantle like rocky ‘icebergs’. If the effect of the deep ‘anchor’ of the underlying dense root to the plates is removed, the continents bob up, floating as the iceberg principle would predict, with a straight-line relation between crustal thickness and elevation.</span>
<span class="attribution"><span class="source">Simon Lamb</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>A balance of planetary forces</h2>
<p>Europe and Asia have very similar average elevations of around 175m above sea level. In Asia, both the crust and tectonic plate are thicker than underneath the European continent, but the weight of the extra thickness balances the tendency for the thicker crust to rise up. </p>
<p>But why is there so much land close to sea level? The answer is erosion. Over geological time, major rivers wear away the landscape, carrying rock fragments to the sea. In this way, rivers will always reduce the continents to an elevation close to sea level. </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 ">
<img alt="Image of Antarctic landscape" src="https://images.theconversation.com/files/360174/original/file-20200927-24-15xcakm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/360174/original/file-20200927-24-15xcakm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/360174/original/file-20200927-24-15xcakm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/360174/original/file-20200927-24-15xcakm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/360174/original/file-20200927-24-15xcakm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/360174/original/file-20200927-24-15xcakm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/360174/original/file-20200927-24-15xcakm.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">Antarctica is too cold for rivers to erode the landscape.</span>
<span class="attribution"><span class="source">Shutterstock/Li Hui Chen</span></span>
</figcaption>
</figure>
<p>East Antarctica is the exception that proves the rule. It has been close to the South Pole for hundreds of millions of years, with a climate too cold for large rivers to significantly erode the landscape. </p>
<p>The crust has been “protected” from the forces of erosion and is on average about 5km thicker than all the other southern continents, but it has a similar plate thickness. </p>
<p>The weight of the vast <a href="https://www.nationalgeographic.org/photo/5icesheet-cutaway/?utm_source=BibblioRCM_Row">East Antarctic ice sheet</a> is pushing down the underlying bedrock. But if all the ice melted, the surface of East Antarctica would bounce back over the following 10,000 years or so to form the highest continent of all. </p>
<p>This, of course, is no cause for comfort in our present climate predicament, with much of the world’s population living in coastal areas.</p><img src="https://counter.theconversation.com/content/146576/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Simon Lamb receives funding from New Zealand Marsden Fund, New Zealand Earthquake Commission (EQC), Victoria University of Wellington.</span></em></p>New research uncovers the fundamental factors that control the Earth’s surface, providing insights into how land levels will respond to the melting of ice sheets and sea level rise.Simon Lamb, Associate Professor in Geophysics, Te Herenga Waka — Victoria University of WellingtonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1263552019-11-24T19:05:19Z2019-11-24T19:05:19ZWhat are lost continents, and why are we discovering so many?<figure><img src="https://images.theconversation.com/files/303106/original/file-20191122-74588-1h7i1ci.jpg?ixlib=rb-1.1.0&rect=41%2C137%2C3944%2C2850&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Lord Howe Island is one of the few places where the lost continent of Zealandia is exposed above sea level. </span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/download/confirm/1383726818?src=8cdca944-3b36-41dd-a084-4fbdd2c81e59-1-0&size=huge_jpg">SHUTTERSTOCK</a></span></figcaption></figure><p>For most people, continents are Earth’s seven main large landmasses. </p>
<p>But geoscientists have a different take on this. They look at the type of rock a feature is made of, rather than how much of its surface is above sea level. </p>
<p>In the past few years, we’ve seen an increase in the discovery of lost continents. Most of these have been plateaus or mountains made of <a href="https://en.wikipedia.org/wiki/Continental_crust">continental crust</a> hidden from our view, below sea level. </p>
<p>One example is <a href="https://www.bbc.com/news/world-asia-39000936">Zealandia</a>, the world’s eighth continent that extends underwater from New Zealand. </p>
<p>Several smaller lost continents, called microcontinents, have also recently been discovered submerged in the <a href="http://www.cmar.csiro.au/datacentre/process/data_files/cruise_docs/ss2011_v06_summary.pdf">eastern</a> and <a href="https://www.nationalgeographic.com/news/2013/2/130225-microcontinent-earth-mauritius-geology-science/">western Indian Ocean</a>. </p>
<p>But why, with so much geographical knowledge at our fingertips, are we still discovering lost continents in the 21st century?</p>
<h2>We may have found another</h2>
<p>In August, we undertook a <a href="https://research.csiro.au/educator-on-board/category/in2019_t04/">28-day voyage</a> on the research vessel RV Investigator to explore a possible lost continent in a remote part of the Coral Sea. The area is home to a large underwater plateau off Queensland, called the <a href="https://en.wikipedia.org/wiki/Louisiade_Plateau">Louisiade Plateau</a>, which represents a major gap in our knowledge of Australia’s geology. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-the-rv-investigators-role-in-marine-science-35239">Explainer: the RV Investigator’s role in marine science</a>
</strong>
</em>
</p>
<hr>
<p>On one hand, it could be a lost continent that broke away from Queensland about 60 million years ago. Or it could have formed as a result of a massive volcanic eruption taking place around the same time. We’re not sure, because nobody had recovered rocks from there before - until now. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/300798/original/file-20191107-10940-1ejlfph.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/300798/original/file-20191107-10940-1ejlfph.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/300798/original/file-20191107-10940-1ejlfph.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=402&fit=crop&dpr=1 600w, https://images.theconversation.com/files/300798/original/file-20191107-10940-1ejlfph.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=402&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/300798/original/file-20191107-10940-1ejlfph.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=402&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/300798/original/file-20191107-10940-1ejlfph.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=505&fit=crop&dpr=1 754w, https://images.theconversation.com/files/300798/original/file-20191107-10940-1ejlfph.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=505&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/300798/original/file-20191107-10940-1ejlfph.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=505&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An extremely violent eruption formed this volcanic rock we recovered.</span>
<span class="attribution"><span class="source">Author supplied</span></span>
</figcaption>
</figure>
<p>We spent about two weeks collecting rocks from this feature, and recovered a wide variety of rock types from parts of the seafloor as deep as 4,500m. </p>
<p>Most were formed through volcanic eruptions, but some show hints that continental rocks are hiding beneath. Lab work over the next couple of years will give us more certain answers.</p>
<h2>Down to the details</h2>
<p>There are many mountains and plateaus below sea level scattered across the oceans, and these have been mapped from space. They are the lighter blue areas you can see on Google Maps. </p>
<iframe src="https://www.google.com/maps/d/u/0/embed?mid=1-BXL84yHMfY85995MPKhFQf44Ze0z8rb" width="100%" height="480"></iframe>
<hr>
<p>However, not all submerged features qualify as lost continents. Most are made of materials quite distinct from what we traditionally think of as continental rock, and are instead formed by massive outpourings of magma. </p>
<p>A good example is <a href="https://www.youtube.com/watch?v=hLGp6lRaSs0&t=">Iceland</a> which, despite being roughly the size of New Zealand’s North Island, is not considered continental in geological terms. It’s made up mainly of volcanic rocks deposited over the past 18 million years, meaning it’s relatively young in geological terms.</p>
<p>The only foolproof way to tell the difference between massive submarine volcanoes and lost continents is to collect rock samples from the deep ocean.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/300796/original/file-20191107-10905-1of0bqe.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/300796/original/file-20191107-10905-1of0bqe.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/300796/original/file-20191107-10905-1of0bqe.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=402&fit=crop&dpr=1 600w, https://images.theconversation.com/files/300796/original/file-20191107-10905-1of0bqe.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=402&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/300796/original/file-20191107-10905-1of0bqe.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=402&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/300796/original/file-20191107-10905-1of0bqe.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=505&fit=crop&dpr=1 754w, https://images.theconversation.com/files/300796/original/file-20191107-10905-1of0bqe.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=505&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/300796/original/file-20191107-10905-1of0bqe.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=505&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Plenty of soft, gloopy sediment covers the bottom of the Coral Sea.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Finding the right samples is challenging, to say the least. Much of the seafloor is covered in soft, gloopy sediment that obscures the solid rock beneath. </p>
<p>We use a sophisticated mapping system to search for steep slopes on the seafloor, that are more likely to be free of sediment. We then send a metal rock-collecting bucket to grab samples.</p>
<p>The more we explore and sample the depths of the oceans, the more likely we’ll be to discover more lost continents.</p>
<h2>The ultimate lost continent</h2>
<p>Perhaps the best known example of a lost continent is <a href="https://www.bbc.com/news/world-asia-39000936">Zealandia</a>. While the geology of New Zealand and New Caledonia have been known for some time, it’s only recently their common heritage as part of a much larger continent (which is 95% underwater) has been accepted. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explorers-probe-hidden-continent-of-zealandia-83406">Explorers probe hidden continent of Zealandia</a>
</strong>
</em>
</p>
<hr>
<p>This acceptance has been the culmination of years of painstaking research, and exploration of the geology of deep oceans through sample collection and geophysical surveys.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/300800/original/file-20191107-10973-1ve9lhc.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/300800/original/file-20191107-10973-1ve9lhc.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/300800/original/file-20191107-10973-1ve9lhc.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/300800/original/file-20191107-10973-1ve9lhc.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/300800/original/file-20191107-10973-1ve9lhc.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/300800/original/file-20191107-10973-1ve9lhc.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/300800/original/file-20191107-10973-1ve9lhc.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/300800/original/file-20191107-10973-1ve9lhc.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">Continental rocks recovered from a microcontinent in the Indian Ocean are similar to rocks found in Western Australia.</span>
<span class="attribution"><span class="source">Author supplied</span></span>
</figcaption>
</figure>
<p>New discoveries continue to be made. </p>
<p>During a 2011 expedition, we discovered <a href="https://www.nationalgeographic.com/news/2011/11/111121-dinosaurs-gondwana-ancient-rocks-science/">two lost continental fragments</a> more than 1,000km west of Perth. </p>
<p>The granite lying in the middle of the deep ocean there looked similar to what you would find around Cape Leeuwin, in Western Australia. </p>
<h2>Other lost continents</h2>
<p>However, not all lost continents are found hidden beneath the oceans. </p>
<p>Some existed only in the geological past, millions to billions of years ago, and later collided with other continents as a result of plate tectonic motions. </p>
<p>Their only modern-day remnants are small slivers of rock, usually squished up in mountain chains such as the Himalayas. One example is <a href="https://www.nationalgeographic.com.au/science/lost-continent-revealed-in-new-reconstruction-of-geologic-history.aspx">Greater Adria</a>, an ancient continent now embedded in the mountain ranges across Europe.</p>
<p>Due to the perpetual motion of tectonic plates, it’s the fate of all continents to ultimately reconnect with another, and form a supercontinent. </p>
<p>But the fascinating life and death cycle of continents is the topic of another story.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-earths-continents-became-twisted-and-contorted-over-millions-of-years-116168">How Earth's continents became twisted and contorted over millions of years</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/126355/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Maria Seton receives funding from the Australian Research Council and has received ship time funding through Australia's Marine National Facility.</span></em></p><p class="fine-print"><em><span>Joanne Whittaker receives funding from the Australian Research Council, the Australian Antarctic Division, and ship time through Australia's Marine National Facility. </span></em></p><p class="fine-print"><em><span>Simon Williams is affiliated with the University of Sydney and Northwest University, Xi'an. He receives funding from the Australian Research Council and the Natural Science Foundation of China, and ship time through Australia's Marine National Facility. </span></em></p>We undertook a 28-day voyage to explore a possible lost continent in a remote part of the Coral Sea, in an area off the coast of Queensland. Here’s what we found.Maria Seton, ARC Future Fellow, University of SydneyJoanne Whittaker, Associate Professor, University of TasmaniaSimon Williams, Research Fellow, University of SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/554242016-07-05T01:57:30Z2016-07-05T01:57:30ZPlate tectonics: new findings fill out the 50-year-old theory that explains Earth’s landmasses<figure><img src="https://images.theconversation.com/files/129030/original/image-20160701-18317-xgbe00.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Satellite image of California's San Andreas fault, where two continental plates come together.</span> <span class="attribution"><a class="source" href="http://photojournal.jpl.nasa.gov/catalog/PIA14555">NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Fifty years ago, there was a seismic shift away from the longstanding belief that Earth’s continents were permanently stationary. </p>
<p>In 1966, <a href="https://www.geolsoc.org.uk/Plate-Tectonics/Chap1-Pioneers-of-Plate-Tectonics/John-Tuzo-Wilson">J. Tuzo Wilson</a> published <a href="http://fossilhub.org/wp-content/uploads/2012/10/Wilson1966_did_Atlantic_reopen.pdf">Did the Atlantic Close and then Re-Open?</a> in the journal Nature. The Canadian author introduced to the mainstream the idea that continents and oceans are in continuous motion over our planet’s surface. Known as <a href="https://en.wikipedia.org/wiki/Plate_tectonics">plate tectonics</a>, the theory describes the large-scale motion of the outer layer of the Earth. It explains tectonic activity (things like earthquakes and the building of mountain ranges) at the edges of continental landmasses (for instance, the San Andreas Fault in California and the Andes in South America). </p>
<p>At 50 years old, with a surge of interest in where the surface of our planet has been and where it’s going, scientists are reassessing what plate tectonics does a good job of explaining – and puzzling over where new findings might fit in.</p>
<h2>Evidence for the theory</h2>
<p>Although the widespread acceptance of the theory of plate tectonics is younger than Barack Obama, German scientist <a href="https://en.wikipedia.org/wiki/Alfred_Wegener">Alfred Wegener</a> first advanced the hypothesis back in 1912.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/125595/original/image-20160607-15061-lvdpu.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/125595/original/image-20160607-15061-lvdpu.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/125595/original/image-20160607-15061-lvdpu.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=707&fit=crop&dpr=1 600w, https://images.theconversation.com/files/125595/original/image-20160607-15061-lvdpu.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=707&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/125595/original/image-20160607-15061-lvdpu.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=707&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/125595/original/image-20160607-15061-lvdpu.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=888&fit=crop&dpr=1 754w, https://images.theconversation.com/files/125595/original/image-20160607-15061-lvdpu.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=888&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/125595/original/image-20160607-15061-lvdpu.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=888&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 map of the original supercontinent, Pangaea, with modern continent outlines.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Pangaea_continents.svg">Kieff</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>He noted that the Earth’s current landmasses could fit together like a jigsaw puzzle. After analyzing fossil records that showed similar species once lived in now geographically remote locations, meteorologist Wegener proposed that the continents had <a href="https://en.wikipedia.org/wiki/Continental_drift">once been fused</a>. But without a mechanism to explain how the continents could actually “drift,” most geologists dismissed his ideas. His “amateur” status, combined with <a href="http://www.smithsonianmag.com/science-nature/when-continental-drift-was-considered-pseudoscience-90353214/?no-ist">anti-German sentiment</a> in the period after World War I, meant his hypothesis was deemed speculative at best.</p>
<p>In 1966, Tuzo Wilson built on earlier ideas to provide a missing link: the Atlantic ocean had opened and closed at least once before. By studying rock types, he found that parts of New England and Canada were of European origin, and that parts of Norway and Scotland were American. From this evidence, Wilson showed that the Atlantic Ocean had opened, closed and re-opened again, taking parts of its neighboring landmasses with it.</p>
<p>And there it was: proof our planet’s continents were not stationary.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/129045/original/image-20160701-18294-p1ohek.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/129045/original/image-20160701-18294-p1ohek.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/129045/original/image-20160701-18294-p1ohek.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=409&fit=crop&dpr=1 600w, https://images.theconversation.com/files/129045/original/image-20160701-18294-p1ohek.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=409&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/129045/original/image-20160701-18294-p1ohek.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=409&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/129045/original/image-20160701-18294-p1ohek.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=515&fit=crop&dpr=1 754w, https://images.theconversation.com/files/129045/original/image-20160701-18294-p1ohek.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=515&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/129045/original/image-20160701-18294-p1ohek.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=515&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The 15 major plates on our planet’s surface.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Plates_tect2_en.svg">USGS</a></span>
</figcaption>
</figure>
<h2>How plate tectonics works</h2>
<p>Earth’s crust and top part of the mantle (the next layer in toward the core of our planet) run about 150 km deep. Together, they’re called the <a href="https://www.geolsoc.org.uk/Plate-Tectonics/Chap2-What-is-a-Plate/Mechanical-properties-lithosphere-and-asthenosphere">lithosphere</a> and make up the “plates” in plate tectonics. We now know there are 15 major plates that cover the planet’s surface, moving at around the speed at which our fingernails grow.</p>
<p>Based on <a href="https://www.youtube.com/watch?v=phZeE7Att_s">radiometric dating</a> of rocks, we know that no ocean is more than 200 million years old, though our continents are much older. The oceans’ opening and closing process – called the <a href="https://www.youtube.com/watch?v=I_q3sAcuzIY">Wilson cycle</a> – explains how the Earth’s surface evolves. </p>
<p>A continent breaks up due to changes in the way molten rock in the Earth’s interior is flowing. That in turn acts on the lithosphere, changing the direction plates move. This is how, for instance, South America broke away from Africa. The next step is continental drift, sea-floor spreading, ocean formation – and hello, Atlantic Ocean. In fact, the Atlantic is still opening, generating new plate material in the middle of the ocean and making the flight from New York to London a few inches longer each year. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/125567/original/image-20160607-15024-19y7pwa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/125567/original/image-20160607-15024-19y7pwa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=464&fit=crop&dpr=1 600w, https://images.theconversation.com/files/125567/original/image-20160607-15024-19y7pwa.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=464&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/125567/original/image-20160607-15024-19y7pwa.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=464&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/125567/original/image-20160607-15024-19y7pwa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=583&fit=crop&dpr=1 754w, https://images.theconversation.com/files/125567/original/image-20160607-15024-19y7pwa.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=583&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/125567/original/image-20160607-15024-19y7pwa.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=583&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A simplified ‘Wilson Cycle’.</span>
<span class="attribution"><span class="source">Philip Heron</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Oceans close when their tectonic plate sinks beneath another, a process geologists call subduction. Off the Pacific Northwest coast of the United States, the ocean is slipping under the continent and into the mantle below the lithosphere, creating in slow motion Mount St Helens and the Cascade mountain range. </p>
<p>In addition to undergoing spreading (construction) and subduction (destruction), plates can simply rub up against each other - usually generating large earthquakes. These interactions, also discovered by Tuzo Wilson back in the 1960s, are termed “conservative.” All three processes occur at the edges of plate boundaries.</p>
<p>But the conventional theory of plate tectonics stumbles when it tries to explain some things. For example, what produces mountain ranges and earthquakes that occur within continental interiors, far from plate boundaries?</p>
<h2>Gone but not forgotten</h2>
<p>The answer may lie in a <a href="http://doi.org/10.1038/ncomms11834">map of ancient continental collisions</a> my colleagues and I assembled. </p>
<p>Over the past 20 years, improved computer power and mathematical techniques have allowed researchers to more clearly look below the Earth’s crust and explore the deeper parts of our plates. Globally, we find many instances of scarring left over from the ancient collisions of continents that formed our present-day continental interiors.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/129046/original/image-20160701-18291-vfhlh0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/129046/original/image-20160701-18291-vfhlh0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/129046/original/image-20160701-18291-vfhlh0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=354&fit=crop&dpr=1 600w, https://images.theconversation.com/files/129046/original/image-20160701-18291-vfhlh0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=354&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/129046/original/image-20160701-18291-vfhlh0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=354&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/129046/original/image-20160701-18291-vfhlh0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=445&fit=crop&dpr=1 754w, https://images.theconversation.com/files/129046/original/image-20160701-18291-vfhlh0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=445&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/129046/original/image-20160701-18291-vfhlh0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=445&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Present day plate boundaries (white) with hidden ancient plate boundaries that may reactivate to control plate tectonics (yellow). Regions where anomalous scarring beneath the crust are marked by yellow crosses.</span>
<span class="attribution"><a class="source" href="http://www.nature.com/ncomms/2016/160610/ncomms11834/fig_tab/ncomms11834_F1.html">Philip Heron</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>A map of ancient continental collisions may represent regions of hidden tectonic activity. These old impressions below the Earth’s crust may still govern surface processes – despite being so far beneath the surface. If these deep scarred structures (more than 30 km down) were reactivated, they would cause devastating new tectonic activity. </p>
<p>It looks like previous plate boundaries (of which there are many) may never really disappear. These <a href="https://eos.org/articles/tiny-mineral-grains-could-drive-plate-tectonics">inherited structures contribute to geological evolution</a>, and may be why we see geological activity within current continental interiors.</p>
<h2>Mysterious blobs 2,900 km down</h2>
<p>Modern geophysical imaging also shows <a href="https://en.wikipedia.org/wiki/Large_low-shear-velocity_provinces">two chemical “blobs”</a>
at the boundary of Earth’s core and mantle – thought to possibly stem from our planet’s formation. </p>
<p>These hot, dense piles of material lie beneath Africa and the Pacific. Located more than 2,900 km below the Earth’s surface, they’re difficult to study. And nobody knows where they came from or what they do. When these blobs of anomalous substance interact with cold ocean floor that has subducted from the surface down to the deep mantle, they generate hot plumes of mantle and blob material that cause <a href="https://philheron.com/lips/">super-volcanoes at the surface</a>. </p>
<p>Does this mean plate tectonic processes control how these piles behave? Or is it that the deep blobs of the unknown are actually controlling what we see at the surface, by releasing hot material to break apart continents? </p>
<p><a href="http://doi.org/10.1038/ngeo2733">Answers to these questions</a> have the potential to shake the very foundations of plate tectonics.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/125581/original/image-20160607-15041-th83ur.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/125581/original/image-20160607-15041-th83ur.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=159&fit=crop&dpr=1 600w, https://images.theconversation.com/files/125581/original/image-20160607-15041-th83ur.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=159&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/125581/original/image-20160607-15041-th83ur.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=159&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/125581/original/image-20160607-15041-th83ur.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=200&fit=crop&dpr=1 754w, https://images.theconversation.com/files/125581/original/image-20160607-15041-th83ur.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=200&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/125581/original/image-20160607-15041-th83ur.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=200&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Arizona State seismology expert Ed Garnero’s summary of how far we have come in over 100 years of studying the interior of the Earth.</span>
<span class="attribution"><a class="source" href="http://garnero.asu.edu/research_images/images_interp.html">Ed Garnero</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Plate tectonics in other times and places</h2>
<p>And the biggest question of all remains unsolved: How did plate tectonics even begin?</p>
<p>The early Earth’s interior <a href="http://www.livescience.com/42373-early-earth-crust-dripped.html">had significantly hotter temperatures</a> – and therefore different physical properties – than current conditions. Plate tectonics then may not be the same as what our conventional theory dictates today. What we understand of today’s Earth may have little bearing on its earliest beginnings; we might as well be thinking about <a href="https://theconversation.com/keep-a-lid-on-it-the-controversy-over-earths-oldest-rocks-19825">an entirely different world</a>.</p>
<p>In the coming years, we may be able to apply what we discover about how plate tectonics got started here to actual other worlds – the billions of exoplanets found in the <a href="http://www.bbc.co.uk/science/space/universe/sights/habitable_zones">habitable zone</a> of our universe. </p>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/125589/original/image-20160607-15045-7a0xna.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/125589/original/image-20160607-15045-7a0xna.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/125589/original/image-20160607-15045-7a0xna.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/125589/original/image-20160607-15045-7a0xna.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/125589/original/image-20160607-15045-7a0xna.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/125589/original/image-20160607-15045-7a0xna.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/125589/original/image-20160607-15045-7a0xna.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=603&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Venus has some geologic features, but not plate tectonics.</span>
<span class="attribution"><a class="source" href="http://photojournal.jpl.nasa.gov/catalog/PIA00254">NASA/JPL</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>So far, amazingly, Earth is the only planet we know of that has plate tectonics. In our solar system, for example, <a href="https://en.wikipedia.org/wiki/Venus">Venus</a> is often considered Earth’s twin - just with a hellish climate and complete <a href="http://arstechnica.com/science/2014/04/venus-crust-heals-too-fast-for-plate-tectonics/">lack of plate tectonics</a>.</p>
<p>Incredibly, the ability of a planet to generate complex life is <a href="https://theconversation.com/does-a-planet-need-plate-tectonics-to-develop-life-61303">inextricably linked to plate tectonics</a>. A gridlocked planetary surface has helped produce Venus’ inhabitable toxic atmosphere of 96 percent CO₂. On Earth, <a href="http://doi.org/10.1038/nature13072">subduction helps push carbon down into the planet’s interior</a> and out of the atmosphere.</p>
<p>It’s still difficult to explain how <a href="https://en.wikipedia.org/wiki/Cambrian_explosion">complex life exploded all over our world 500 million years ago</a>, but the processes of removing carbon dioxide from the atmosphere is further <a href="http://www.astrobio.net/news-brief/earths-breathable-atmosphere-tied-plate-tectonics/">helped by continental coverage</a>. An exceptionally slow process starts with carbon dioxide mixing with rain water to wear down continental rocks. This combination can form carbon-rich limestone that subsequently washes away to the ocean floor. The long removal processes (even for geologic time) eventually could create a more breathable atmosphere. It just took 3 billion years of plate tectonic processes to get the right carbon balance for life on Earth.</p>
<h2>A theory works now, but what’s in the future?</h2>
<p>Fifty years on from Wilson’s 1966 paper, geophysicists have progressed from believing continents never moved to thinking that every movement may leave a lasting memory on our Earth. </p>
<p>Life here would be vastly different if plate tectonics changed its style – as we know it can. A changing mantle temperature may affect the interaction of our lithosphere with the rest of the interior, <a href="https://www.sciencenews.org/article/plate-tectonics-just-stage-earth%E2%80%99s-life-cycle">stopping plate tectonics</a>. Or those continent-sized chemical blobs could move from their relatively stable state, causing <a href="http://es.ucsc.edu/%7Ethorne/TL.pdfs/GLM_P4.pdf">super-volcanoes as they release material</a> from their deep reservoirs.</p>
<p>It’s hard to understand what our future holds if we don’t understand our beginning. By discovering the secrets of our past, we may be able to predict the motion of our plate tectonic future.</p><img src="https://counter.theconversation.com/content/55424/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Philip Heron receives funding from Natural Sciences and Engineering Research Council of Canada. He works for the University of Toronto. </span></em></p>Fifty years on from a groundbreaking paper, geophysicists have progressed from believing continents never moved to thinking that every movement may leave a lasting memory on our planet.Philip Heron, Postdoctoral Fellow in Geodynamics, University of TorontoLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/393302015-03-25T19:13:46Z2015-03-25T19:13:46ZNewly discovered layer in Earth’s mantle can affect surface dwellers too<figure><img src="https://images.theconversation.com/files/75996/original/image-20150325-14532-15qn5fr.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">No Earths were harmed in the making of this image</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/argonne/14259873660/">Johan Swanepoel/Shutterstock</a></span></figcaption></figure><p>Sinking tectonic plates get jammed in a newly discovered layer of the Earth’s mantle – and could be causing earthquakes on the surface.</p>
<p>It was previously thought that Earth’s <a href="http://www.britannica.com/EBchecked/topic/349935/lower-mantle">lower mantle</a>, which begins at a depth of around 700 km and forms the major part of the mantle, is fairly uniform and varies only gradually as it goes deeper.</p>
<p>However, our new <a href="http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2393.html">study</a> points towards a layer in the mantle characterised by a strong increase in viscosity – a finding which has strong implications for our understanding of what’s going on deep down below our feet.</p>
<h2>The deep unknown</h2>
<p>The Earth’s mantle is the largest shell inside our planet. Ranging from about 50 km to 3000 km depth, it links the hot liquid <a href="http://education.nationalgeographic.com.au/education/encyclopedia/core/?ar_a=1">outer core</a> – with temperatures higher than 5,000K – to the Earth’s surface. </p>
<p>The movement of materials within the Earth’s mantle is thought to drive <a href="http://science.nationalgeographic.com/science/earth/the-dynamic-earth/plate-tectonics-article/">plate tectonic movements</a> on the surface, ultimately leading to earthquakes and volcanoes. The mantle is also the Earth’s largest reservoir for many elements stored in mantle minerals. Throughout Earth’s history, substantial amounts of material have been exchanged between the deep mantle and the surface and atmosphere, affecting both the life and climate above ground.</p>
<p>Because mankind is incapable of directly probing the lower mantle – the <a href="http://www.slate.com/blogs/atlas_obscura/2014/05/08/kola_superdeep_borehole_is_the_world_s_deepest_hole.html">deepest man-made hole</a> is only around 12 km deep – many details of the global material recycling process are poorly understood. </p>
<p>We do know, however, that the main way materials are transferred from the Earth’s surface and atmosphere back into the deep mantle occurs when one tectonic plate <a href="http://www.livescience.com/43220-subduction-zone-definition.html">slides under another</a> and is pushed down below another into the mantle.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/75976/original/image-20150325-14515-gt7xes.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/75976/original/image-20150325-14515-gt7xes.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=444&fit=crop&dpr=1 600w, https://images.theconversation.com/files/75976/original/image-20150325-14515-gt7xes.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=444&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/75976/original/image-20150325-14515-gt7xes.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=444&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/75976/original/image-20150325-14515-gt7xes.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=558&fit=crop&dpr=1 754w, https://images.theconversation.com/files/75976/original/image-20150325-14515-gt7xes.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=558&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/75976/original/image-20150325-14515-gt7xes.png?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">
<figcaption>
<span class="caption">A strong increase in the viscosity leads to a stiff layer which catches sinking slabs.</span>
<span class="attribution"><span class="source">Hauke Marquardt</span></span>
</figcaption>
</figure>
<h2>A trap for sinking plates</h2>
<p>So far most researchers assumed that these sinking plates either stall at the boundary between the upper and lower mantle at a depth of around 700 km or sink all the way through the lower mantle to the core-mantle boundary 3,000 km down. </p>
<p>But our new <a href="http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2393.html">research</a>, published in the latest online issue of Nature Geoscience, shows that many of these sinking slabs may in fact be trapped above a previously undiscovered impermeable layer of rock within the lower mantle.</p>
<p>We found that enormous pressures in the lower mantle, which range from 25 GPa (gigapascal) to 135 GPa, can lead to surprising behaviour of matter. To picture just how high this pressure is, balancing the Eiffel Tower in your hand would create pressures on the order of 10 GPa. These pressures lead to the formation of a stiff layer in the Earth’s mantle. Sinking plates may become trapped on top of this layer, which reaches its maximum stiffness at a depth below 1,500km.</p>
<h2>Under pressure</h2>
<p>We formed this conclusion after performing laboratory experiments on ferropericlase, a magnesium/iron oxide that is thought to be one of the main constituents of the Earth’s lower mantle. We compressed the ferropericlase to pressures of almost 100 GPa in a <a href="http://www.hpdo.com/intro.html">diamond-anvil cell</a>, a high-pressure device which compresses a tiny sample the size of a human hair between the tips of two minuscule brilliant-cut diamonds. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/75982/original/image-20150325-14500-itiy2z.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/75982/original/image-20150325-14500-itiy2z.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=639&fit=crop&dpr=1 600w, https://images.theconversation.com/files/75982/original/image-20150325-14500-itiy2z.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=639&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/75982/original/image-20150325-14500-itiy2z.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=639&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/75982/original/image-20150325-14500-itiy2z.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=803&fit=crop&dpr=1 754w, https://images.theconversation.com/files/75982/original/image-20150325-14500-itiy2z.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=803&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/75982/original/image-20150325-14500-itiy2z.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=803&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A diamond-anvil cell compresses a tiny sample under high pressure between two minuscule diamonds.</span>
<span class="attribution"><span class="source">Image via Hauke Marquardt</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>While under compression, the ferropericlase was probed with high-energy x-rays to investigate how it deforms under these high pressures. We found that the ability of the material to resist irreversible deformation increased by over three times under high pressures.</p>
<p>These results were used to model the change of viscosity with depth in Earth’s lower mantle. While previous estimates have indicated only gradual variations of viscosity with depth, we found a dramatic increase of viscosity throughout the upper 900 km of the lower mantle. </p>
<p>Such a strong increase in viscosity can stop the descent of slabs and, in doing so, strongly affect the deep Earth material cycle. These new findings are supported by <a href="http://royalsocietypublishing.org/content/roypta/360/1800/2475.full.pdf">3-D imaging observations</a> based on the analysis of seismic wave speeds travelling through the Earth that also indicate that the slabs stop sinking before they reach a depth of 1500 km.</p>
<h2>Surface effects</h2>
<p>If true, the existence of this stiff layer in the Earth’s mantle has wide-ranging implications for our understanding of the deep Earth material cycle. It could limit material mixing between the upper and lower parts of the lower mantle, meaning mantle regions with previously different geochemical signatures stay isolated in separate patches instead of mixing over geologic time. </p>
<p>What’s more, a stiff mid-mantle layer could also put stress on slabs much closer to the Earth’s surface, potentially acting as a trigger of deep earthquakes.</p>
<p>We are really just at the beginning of a deeper understanding of the inner workings of our planet, many of which ultimately affect our life on its surface.</p><img src="https://counter.theconversation.com/content/39330/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Hauke Marquardt receives funding from the German Science Foundation DFG.</span></em></p>The discovery of a thickly viscous layer which traps sinking plates below Earth’s surface has wide implications, not least as a cause of earthquakes.Hauke Marquardt, Researcher in Mineral Physics, Bayreuth UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/183112013-09-23T11:50:30Z2013-09-23T11:50:30ZMeet the earthquakes that happen 600km underground<figure><img src="https://images.theconversation.com/files/31666/original/4xv3v76n-1379621304.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Earth crust cutaway</span> <span class="attribution"><span class="source">Jeremy Kemp</span></span></figcaption></figure><figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/31660/original/kkrsksbx-1379603972.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/31660/original/kkrsksbx-1379603972.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=334&fit=crop&dpr=1 600w, https://images.theconversation.com/files/31660/original/kkrsksbx-1379603972.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=334&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/31660/original/kkrsksbx-1379603972.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=334&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/31660/original/kkrsksbx-1379603972.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=420&fit=crop&dpr=1 754w, https://images.theconversation.com/files/31660/original/kkrsksbx-1379603972.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=420&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/31660/original/kkrsksbx-1379603972.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=420&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">An earthquake four times bigger than the 1906 San Francisco one struck off the coast of Siberia earlier this year, but more than 600km down.</span>
<span class="attribution"><span class="source">antiquationadmiration</span></span>
</figcaption>
</figure>
<p>A little more than 90 years ago, British geologist Herbert Hall Turner noticed some earthquake data that suggested a surprising explanation. The only way to explain it was if the quake had occurred hundreds of kilometres beneath the Earth’s surface, instead of the more commonly seen near-surface earthquakes. </p>
<p>Since Turner’s observations, deep earthquakes have fascinated seismologists. It is still unclear why they happen, but <a href="http://dx.doi.org/10.1126/science.1240206">two studies</a> just published in the journal <a href="http://dx.doi.org/10.1126/science.1242032">Science</a>, taking different approaches, conclude that they are probably a result of rapid changes in minerals at that depth.</p>
<p>Such deep earthquakes do not have immediate consequences for humans. But they hold clues about destructive quakes in the Earth’s shallower crust, making it important to understand them.</p>
<h2>Not just superficial</h2>
<p>Most earthquakes occur in the stiff, brittle outer shell that includes the Earth’s crust. This “seismogenic zone”, which causes the most devastating and dangerous earthquakes, goes down to about 15km beneath the surface.</p>
<p>As you go deeper, pressure and temperature both increase rapidly, so the nature of earthquakes changes. Rocks move slowly, speaking on geological time scales, when pushed or pulled by different forces acting on them. At depth, they appear to flow like soft toffee, rather than break like peanut brittle.</p>
<p>This is why Turner’s observations of earthquakes more than 600km below the surface were puzzling. If the rocks flow slowly, then there shouldn’t really be any sudden shocks that cause an earthquake. Rather, there should be gentle continuous readjustments to stress. </p>
<p>Suggestions have been floated in the past about what triggers such earthquakes. But Thorne Lay of University of California Santa Cruz took a step ahead to analyse a deep earthquake that occurred this year on May 24, in the Pacific Ocean beneath the Okhotsk plate. At a magnitude of 8.3, it was four times greater than the 1906 San Francisco earthquake. Indeed, it was the biggest ever recorded at a depth of more than 600km. A near-surface earthquake of the same magnitude could’ve been very destructive, but at that depth it was barely noticeable at the surface above.</p>
<p>Recent analysis of an earthquake at Bhuj, India in 2001 suggests it shared similarities to the Okhotsk event, although it was just 16km deep. In contrast, however, it caused terrible devastation, including an estimated 20,000 deaths. “There may be things we don’t understand about more shallow earthquakes that we can learn from studying these deep earthquakes,” said Bob Myhill of the University of Bayreuth.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/31666/original/4xv3v76n-1379621304.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/31666/original/4xv3v76n-1379621304.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/31666/original/4xv3v76n-1379621304.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=412&fit=crop&dpr=1 600w, https://images.theconversation.com/files/31666/original/4xv3v76n-1379621304.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=412&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/31666/original/4xv3v76n-1379621304.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=412&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/31666/original/4xv3v76n-1379621304.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=518&fit=crop&dpr=1 754w, https://images.theconversation.com/files/31666/original/4xv3v76n-1379621304.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=518&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/31666/original/4xv3v76n-1379621304.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"></a>
<figcaption>
<span class="caption">A slice through Earth.</span>
<span class="attribution"><span class="source">Jeremy Kemp</span></span>
</figcaption>
</figure>
<p>During the Okhotsk event, the Pacific plate of Earth’s crust was drawn down into the hot mantle that makes up much of the planet’s interior. What Lay found was that the seismic energy released in the event was so large that it caused fractures as great as 180km long below the surface. The rock ruptured at close to the speed of sound, which in the rock would be as much as 14,000 km/h. </p>
<p>But what caused such rapid rupture? Alexandre Schubnel of Ecole Normale Supérieure suggests an explanation, which hinges a the mineral making up the deep rock, called olivine. To be sure he designed lab experiments that could mimic deep earth.</p>
<p>Schubnel found that above a critical temperature and pressure, olivine changes into another mineral called spinel. Under stress, this sudden change creates fractures, much like those seen in the earthquake. The mineral change releases stress instantaneously, in just the same way as stress was relieved in the deep earthquake under the Pacific Ocean. </p>
<p>There is one critical difference, however. To make the experiments easier, the olivine used by Schubnel in the lab contained the element germanium instead of silicon. Germanium-olivines are known to behave slightly differently than silicon-olivines, and this may make a lot of difference 600km below the surface.</p>
<p>Still, while the mini-earthquakes seen in the lab were a million billion times smaller than what those in the earth, the reason these experiments can be trusted is because the creaks and groans of minerals in a lab show similar characteristics as that of large earthquakes. So, even though Suchbnel’s idea is not new, it confirms experimentally suggestions made by researchers before. It opens the way to studying deep earthquakes in the safety and comfort of the lab.</p><img src="https://counter.theconversation.com/content/18311/count.gif" alt="The Conversation" width="1" height="1" />
A little more than 90 years ago, British geologist Herbert Hall Turner noticed some earthquake data that suggested a surprising explanation. The only way to explain it was if the quake had occurred hundreds…Simon Redfern, Professor in Earth Sciences, University of CambridgeLicensed as Creative Commons – attribution, no derivatives.