tag:theconversation.com,2011:/global/topics/continents-13115/articlesContinents – The Conversation2024-02-21T13:13:10Ztag:theconversation.com,2011:article/2232092024-02-21T13:13:10Z2024-02-21T13:13:10ZEarth’s early evolution: fresh insights from rocks formed 3.5 billion years ago<figure><img src="https://images.theconversation.com/files/576464/original/file-20240219-24-5de047.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Barberton Makhonjwa Mountains look peaceful today - but 3.5 billion years ago the earth there was roiled by volcanoes. </span> <span class="attribution"><span class="source">Instinctively RDH/Shutterstock</span></span></figcaption></figure><p>Our Earth is <a href="https://www.amnh.org/exhibitions/darwin/the-world-before-darwin/how-old-is-earth#:%7E:text=Today%2C%20we%20know%20from%20radiometric,have%20been%20taken%20more%20seriously.">around 4.5 billion years old</a>. Way back in its earliest years, vast oceans dominated. There were frequent volcanic eruptions and, because there was no free oxygen in the atmosphere, there was no ozone layer. It was a dynamic and evolving planet.</p>
<p>Scientists know all of this – but, of course, there are still gaps in our knowledge. For instance, while we know what kind of rocks were being formed on different parts of the planet 3.5 billion years ago, we are still understanding which geological processes drove these formations. </p>
<p>Luckily the answers to such questions are available. Evidence is preserved in ancient volcanic and sedimentary rocks dating back to the <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/archean-eon#:%7E:text=Thus%2C%20the%20Archean%20Eon%20is,continental%20plates%20began%20to%20form.">Archaean age</a>, between 4 billion and 2.5 billion years ago.</p>
<p>These rocks are found in the oldest parts of what are today the continents, called cratons. Cratons are pieces of ancient continents that formed billions of years ago. Studying them offers a window into how processes within and on the surface of Earth operated in the past. They host a variety of different groups of rocks, including greenstones and granites.</p>
<p>One example is the <a href="https://www.sciencedirect.com/science/article/abs/pii/S0012825222000782">Singhbhum Craton</a>, in the Daitari Greenstone Belt in the state of Odisha in eastern India. This ancient part of the Earth’s crust has been found in previous research to date back to 3.5 billion years ago. The craton’s oldest rock assemblages are largely volcanic and sedimentary rocks also known as greenstone successions. Greenstones are rock assemblages made up mostly of sub-marine volcanic rocks with minor sedimentary rocks. </p>
<p>My research team and I recently published <a href="https://www.sciencedirect.com/science/article/pii/S0301926823000372">a study</a> in which we compared the Singhbhum Craton to cratons in South Africa and Australia. We chose these sites because they preserve the same kinds of rocks, in the same condition (not intensely deformed or metamorphosed), from the same time period – about 3.5 billion years ago. They are the best archives to study early Earth surface processes.</p>
<p>Our key findings were that explosive-style volcanic eruptions were common in what are today India, South Africa and Australia around 3.5 billion years ago. These eruptions mostly occurred under oceans, though sometimes above them.</p>
<p>Understanding these early Earth processes is vital for piecing together the planet’s evolutionary history and the conditions that may have sustained life during different geological epochs. This kind of research is also a reminder of the ancient geological wonders that surround us – and that there is much more to discover to understand the story of our planet.</p>
<h2>The research</h2>
<p>We sampled some rocks from the Singhbhum Craton so we could study them in our laboratory. Existing data from the same site, as well as sites in South Africa and India, were used for comparison purposes.</p>
<p>Our detailed field-based studies were complemented by <a href="https://link.springer.com/referenceworkentry/10.1007/978-94-007-6326-5_193-1">uranium-lead (U-Pb) radiometric-age dating</a>. This common and well-established method provides information as to when a magma crystallised; in other words, it tells us when a rock formed. In this way we were able to establish key geological timelines to illustrate what processes were underway and when.</p>
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<p>We also found that the geology of this area shares stark similarities with the greenstone belts documented in South Africa’s <a href="https://www.sciencedirect.com/science/article/abs/pii/S0301926816300663">Barberton</a> and <a href="https://www.sciencedirect.com/science/article/abs/pii/S1342937X11002504?via%3Dihub">Nondweni</a> areas and the <a href="https://www.nature.com/articles/375574a0">Pilbara Craton</a> in western Australia. </p>
<p>Most particularly, all these areas experienced widespread submarine mafic – meaning high in magnesium oxide – volcanic eruptions between 3.5 and 3.3 billion years ago, preserved as pillowed lava and komatiites.</p>
<p>This differs from silicic (elevated concentration of silicon dioxide) volcanism, which research <a href="https://www.sciencedirect.com/science/article/abs/pii/S0040195100000585">has shown</a> was prevalent around 3.5 billion years ago.</p>
<p>These findings enrich our understanding of ancient volcanic and sedimentary processes and their significance in the broader context of Earth’s geological as well as biological evolution.</p>
<h2>Our planet’s formative years</h2>
<p>Our discoveries are pivotal for several reasons. First, they offer a clearer picture of Earth’s early tectonic activities during the Archaean times, contributing to our understanding of the planet’s formative years. </p>
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<p>Second, the Singhbhum Craton’s unique geological features, including its greenstone belts, provide invaluable information about Earth’s surface and atmospheric processes. This is crucial for hypothesising early habitable conditions and the emergence of life on Earth. </p>
<p>Additionally, comparing the Singhbhum Craton with similar cratons in South Africa and Australia allows us to construct a more comprehensive model related to geological processes that operated during the Archaean. This can help to shed light on ancient geodynamic processes that were prevalent across different parts of the young Earth.</p>
<p>This research emphasises the need for further exploration into the geological history of ancient cratons worldwide. Understanding these early Earth processes is vital for piecing together the planet’s evolutionary history and the conditions that may have sustained life.</p><img src="https://counter.theconversation.com/content/223209/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jaganmoy Jodder received funding from the DSI-NRF Centre of Excellence (CoE) for Integrated Mineral and Energy Resource Analysis (CIMERA) and Genus DSI-NRF Centre of Excellence in Palaeosciences.</span></em></p>Cratons are pieces of ancient continents that formed billions of years ago.Jaganmoy Jodder, Post-doctoral researcher, University of the WitwatersrandLicensed 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">
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<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">
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<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/1856062022-08-10T20:11:56Z2022-08-10T20:11:56ZWhat created the continents? New evidence points to giant asteroids<figure><img src="https://images.theconversation.com/files/478446/original/file-20220810-26-3rlh9u.jpeg?ixlib=rb-1.1.0&rect=22%2C22%2C4920%2C3467&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-illustration/large-meteor-burning-glowing-hits-earths-488993764">Solarseven / Shutterstock</a></span></figcaption></figure><p>Earth is the <a href="https://doi.org/10.1029/GL010i011p01061">only planet we know of with continents</a>, the giant landmasses that provide homes to humankind and most of <a href="https://www.pnas.org/doi/10.1073/pnas.1711842115">Earth’s biomass</a>.</p>
<p>However, we still don’t have firm answers to some basic questions about continents: how did they come to be, and why did they form where they did? </p>
<p>One theory is that they were formed by giant meteorites crashing into Earth’s crust long ago. This <a href="https://www.nature.com/articles/210669a0">idea</a> has been proposed <a href="https://doi.org/10.1130/L371.1">several times</a>, but until now there has been little evidence to support it.</p>
<p>In <a href="https://www.nature.com/articles/s41586-022-04956-y">new research published in Nature</a>, we studied ancient minerals from Western Australia and found tantalising clues suggesting the giant impact hypothesis might be right.</p>
<h2>How do you make a continent?</h2>
<p>The continents form part of the lithosphere, the rigid rocky outer shell of Earth made up of ocean floors and the continents, of which the uppermost layer is the crust. </p>
<p>The crust beneath the oceans is thin and made of dark, dense basaltic rock which contains only a little silica. By contrast, the continental crust is thick and mostly consists of granite, a less dense, pale-coloured, silica-rich rock that makes the continents “float”. </p>
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<a href="https://images.theconversation.com/files/478466/original/file-20220810-26-xxv7j6.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/478466/original/file-20220810-26-xxv7j6.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/478466/original/file-20220810-26-xxv7j6.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=371&fit=crop&dpr=1 600w, https://images.theconversation.com/files/478466/original/file-20220810-26-xxv7j6.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=371&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/478466/original/file-20220810-26-xxv7j6.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=371&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/478466/original/file-20220810-26-xxv7j6.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=466&fit=crop&dpr=1 754w, https://images.theconversation.com/files/478466/original/file-20220810-26-xxv7j6.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=466&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/478466/original/file-20220810-26-xxv7j6.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=466&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">The internal structure of Earth.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Internal_structure_of_Earth#/media/File:Earth_poster.svg">Kelvin Song / Wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<p>Beneath the lithosphere sits a thick, slowly flowing mass of almost-molten rock, which sits near the top of the mantle, the layer of Earth between the crust and the core.</p>
<p>If part of the lithosphere is removed, the mantle beneath it will melt as the pressure from above is released. And impacts from giant meteorites – rocks from space tens or hundreds of kilometres across – are an extremely efficient way of doing exactly that!</p>
<h2>What are the consequences of a giant impact?</h2>
<p>Giant impacts blast out huge volumes of material almost instantaneously. Rocks near the surface will melt for hundreds of kilometres or more around the impact site. The impact also releases pressure on the mantle below, causing it to melt and produce a “blob-like” mass of thick basaltic crust. </p>
<p>This mass is called an oceanic plateau, similar to that beneath present-day Hawaii or Iceland. The process is a bit like what happens if you are hit hard on the head by a golf ball or pebble – the resulting bump or “egg” is like the oceanic plateau.</p>
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<p>Our research shows these oceanic plateaus could have evolved to form the continents through a process known as crustal differentiation. The thick oceanic plateau formed from the impact can get hot enough at its base that it also melts, producing the kind of granitic rock that forms buoyant continental crust.</p>
<h2>Are there other ways to make oceanic plateaus?</h2>
<p>There are other ways oceanic plateaus can form. The thick crusts beneath Hawaii and Iceland formed not through giant impacts but “mantle plumes”, streams of hot material rising up from the edge of Earth’s metallic core, a bit like in a lava lamp. As this ascending plume reaches the lithosphere it triggers massive mantle melting to form an oceanic plateau. </p>
<p>So could plumes have created the continents? Based on our studies, and the balance of different oxygen isotopes in tiny grains of the mineral zircon, which is commonly found in tiny quantities in rocks from the continental crust, we don’t think so.</p>
<p>Zircon is the <a href="https://www.nature.com/articles/35051550">oldest known crustal material</a>, and it can survive intact for billions of years. We can also determine quite precisely when it was formed, based on the decay of the radioactive uranium it contains.</p>
<p>What’s more, we can find out about the environment in which zircon formed by measuring the relative proportion of <a href="https://doi.org/10.2113/0530343">isotopes of oxygen</a> it contains. </p>
<p>We looked at zircon grains from one of the oldest surviving pieces of continental crust in the world, the Pilbara Craton in Western Australia, which started forming more than 3 billion years ago. Many of the oldest grains of zircon contained more light oxygen isotopes, which indicate shallow melting, but younger grains contain a more mantle-like balance isotopes, indicating much deeper melting. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/470442/original/file-20220623-51670-yjaqlb.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/470442/original/file-20220623-51670-yjaqlb.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/470442/original/file-20220623-51670-yjaqlb.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=441&fit=crop&dpr=1 600w, https://images.theconversation.com/files/470442/original/file-20220623-51670-yjaqlb.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=441&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/470442/original/file-20220623-51670-yjaqlb.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=441&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/470442/original/file-20220623-51670-yjaqlb.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=555&fit=crop&dpr=1 754w, https://images.theconversation.com/files/470442/original/file-20220623-51670-yjaqlb.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=555&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/470442/original/file-20220623-51670-yjaqlb.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=555&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 δ18O (‰) vs age (Ma) for individual dated magmatic zircon grains from the Pilbara Craton. The horizontal grey band shows the array of δ18O in mantle zircon (5.3 +/– 0.6‰, 2 s.d.). The vertical grey bands subdivide the data into three stages, as discussed in the paper. The pink boxes represent the age of deposition of high-energy impact deposits (spherule beds) from the Pilbara Craton and more widely.</span>
</figcaption>
</figure>
<p>This “top-down” pattern of oxygen isotopes is what you might expect following a giant meteorite impact. In mantle plumes, by contrast, melting is a “bottom-up” process.</p>
<h2>Sounds reasonable, but is there any other evidence?</h2>
<p>Yes, there is! The zircons from the Pilbara Craton appear to have been formed in a handful of distinct periods, rather than continuously over time. </p>
<p>Except for the earliest grains, the other grains with isotopically-light zircon have the same age as spherule beds in the Pilbara Craton and elsewhere. </p>
<p>Spherule beds are deposits of droplets of material “splashed out” by meteorite impacts. The fact the zircons have the same age suggests they may have been formed by the same events.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/477934/original/file-20220806-34973-us5oq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/477934/original/file-20220806-34973-us5oq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/477934/original/file-20220806-34973-us5oq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/477934/original/file-20220806-34973-us5oq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/477934/original/file-20220806-34973-us5oq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/477934/original/file-20220806-34973-us5oq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/477934/original/file-20220806-34973-us5oq.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 sun sets in the Pilbara, and the hunt for firewood is on.</span>
<span class="attribution"><span class="source">Chris Kirkland, 2021.</span></span>
</figcaption>
</figure>
<p>Further, the “top-down” pattern of isotopes can be recognised in other areas of ancient continental crust, such as in Canada and Greenland. However, data from elsewhere have not yet been carefully filtered like the Pilbara data, so it will take more work to confirm this pattern.</p>
<p>The next step of our research is to reanalyse these ancient rocks from elsewhere to confirm what we suspect – that the continents grew at the sites of giant meteorite impacts. Boom.</p><img src="https://counter.theconversation.com/content/185606/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tim Johnson receives funding from Curtin University and through an Australian Research Council Discovery project (DP200101104). </span></em></p>Giant meteorite impacts may have created the land we live onTim Johnson, Associate Professor, Curtin UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1713912021-11-08T21:58:46Z2021-11-08T21:58:46ZLand ahoy: study shows the first continents bobbed to the surface more than 3 billion years ago<figure><img src="https://images.theconversation.com/files/430723/original/file-20211108-48235-1iw24v8.png?ixlib=rb-1.1.0&rect=10%2C55%2C2446%2C1575&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption"></span> <span class="attribution"><span class="license">Author provided</span></span></figcaption></figure><p>Most people know that the land masses on which we all live represent just 30% of Earth’s surface, and the rest is covered by oceans. </p>
<p>The emergence of the continents was a pivotal moment in the history of life on Earth, not least because they are the humble abode of most humans. But it’s still not clear exactly when these continental landmasses first appeared on Earth, and what tectonic processes built them.</p>
<p>Our research, <a href="https://www.pnas.org/cgi/doi/10.1073/pnas.2105746118">published</a> in Proceedings of the National Academy of Sciences, estimates the age of rocks from the most ancient continental fragments (called cratons) in India, Australia and South Africa. The sand that created these rocks would once have formed some of the world’s first beaches.</p>
<p>We conclude that the first large continents were making their way above sea level around 3 billion years ago – much earlier than the 2.5 billion years estimated by previous research.</p>
<h2>A 3-billion-year-old beach</h2>
<p>When continents rise above the oceans they start to erode. Wind and rain break rocks down into grains of sand, which are transported downstream by rivers and accumulate along coastlines to form beaches. </p>
<p>These processes, which we can observe in action during a trip to the beach today, have been operating for billions of years. By scouring the rock record for signs of ancient beach deposits, geologists can study episodes of continent formation that happened in the distant past.</p>
<p>The Singhbhum craton, an ancient piece of continental crust that makes up the eastern parts of the Indian subcontinent, contains several formations of ancient sandstone. These layers were originally formed from sand deposited in beaches, estuaries and rivers, which was then buried and compressed into rock.</p>
<p>We determined the age of these deposits by studying microscopic grains of a mineral called zircon, which is preserved within these sandstones. This mineral contains tiny amounts of uranium, which very slowly turns into lead via radioactive decay. This allows us to estimate the age of these zircon grains, using a technique called <a href="https://en.wikipedia.org/wiki/Uranium%E2%80%93lead_dating">uranium-lead dating</a>, which is well suited to dating very old rocks.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/430725/original/file-20211108-10108-1cbfduv.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Sandstone and zircon grains" src="https://images.theconversation.com/files/430725/original/file-20211108-10108-1cbfduv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/430725/original/file-20211108-10108-1cbfduv.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=348&fit=crop&dpr=1 600w, https://images.theconversation.com/files/430725/original/file-20211108-10108-1cbfduv.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=348&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/430725/original/file-20211108-10108-1cbfduv.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=348&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/430725/original/file-20211108-10108-1cbfduv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=438&fit=crop&dpr=1 754w, https://images.theconversation.com/files/430725/original/file-20211108-10108-1cbfduv.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=438&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/430725/original/file-20211108-10108-1cbfduv.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=438&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Left: sandstone formations (with ruler for scale); right: microscopic images of zircon grains.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The zircon grains reveal that the Singhbhum sandstones were deposited around 3 billion years ago, making them some of the oldest beach deposits in the world. This also suggests a continental landmass had emerged in what is now India by at least 3 billion years ago. </p>
<p>Interestingly, sedimentary rocks of roughly this age are also present in the oldest cratons of Australia (the Pilbara and Yilgarn cratons) and South Africa (the Kaapvaal Craton), suggesting multiple continental landmasses may have emerged around the globe at this time.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/whats-australia-made-of-geologically-it-depends-on-the-state-youre-in-83575">What's Australia made of? Geologically, it depends on the state you're in</a>
</strong>
</em>
</p>
<hr>
<h2>Rise above it</h2>
<p>How did rocky continents manage to rise above the oceans? A unique feature of continents is their thick, buoyant crust, which allows them to float on top of Earth’s mantle, just like a cork in water. Like icebergs, the top of continents with thick crust (typically more than 45km thick) sticks out above the water, whereas continental blocks with crusts thinner than about 40km remain submerged.</p>
<p>So if the secret of the continents’ rise is due to their thickness, we need to understand how and why they began to grow thicker in the first place. </p>
<p>Most ancient continents, including the Singhbhum Craton, are made of granites, which formed through the melting of pre-existing rocks at the base of the crust. In our research, we found the granites in the Singhbhum Craton formed at increasingly greater depths between about 3.5 billion and 3 billion years ago, implying the crust was becoming thicker during this time window. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/430727/original/file-20211108-9872-18vgwir.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Granite formation with pen for scale." src="https://images.theconversation.com/files/430727/original/file-20211108-9872-18vgwir.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/430727/original/file-20211108-9872-18vgwir.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=728&fit=crop&dpr=1 600w, https://images.theconversation.com/files/430727/original/file-20211108-9872-18vgwir.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=728&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/430727/original/file-20211108-9872-18vgwir.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=728&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/430727/original/file-20211108-9872-18vgwir.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=914&fit=crop&dpr=1 754w, https://images.theconversation.com/files/430727/original/file-20211108-9872-18vgwir.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=914&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/430727/original/file-20211108-9872-18vgwir.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=914&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Granites are some of the least dense and most buoyant types of rock (pen included for scale).</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Because granites are one of the least dense types of rock, the ancient crust of the Singhbhum Craton would have become progressively more buoyant as it grew thicker. We calculate that by around 3 billion years ago, the continental crust of the Singhbhum Craton had grown to be about 50km thick, making it buoyant enough to begin rising above sea level.</p>
<p>The rise of continents had a profound influence on the climate, atmosphere and oceans of the early Earth. And the erosion of these continents would have provided chemical nutrients to coastal environments in which early photosynthetic life was flourishing, leading to a <a href="https://www.sciencedirect.com/science/article/abs/pii/S0012821X16307117">boom in oxygen production</a> and ultimately helping to create the <a href="https://www.pnas.org/content/118/33/e2107511118">oxygen-rich atmosphere</a> in which we thrive today.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-floor-is-lava-after-1-5-billion-years-in-flux-heres-how-a-new-stronger-crust-set-the-stage-for-life-on-earth-151276">The floor is lava: after 1.5 billion years in flux, here's how a new, stronger crust set the stage for life on Earth</a>
</strong>
</em>
</p>
<hr>
<p>Erosion of the early continents would have also helped in sequestering carbon dioxide from the atmosphere, leading to global cooling of the early Earth. Indeed, the earliest glacial deposits also happen to <a href="https://www.sciencedirect.com/science/article/pii/S0012825220303445#bb0765">appear in the geological record</a> around 3 billion years ago, shortly after the first continents emerged from the oceans.</p><img src="https://counter.theconversation.com/content/171391/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Priyadarshi Chowdhury receives funding from Australian Research Council Grant No FL160100168. </span></em></p><p class="fine-print"><em><span>Jack Mulder receives funding from Australian Research Council grant FL160100168</span></em></p><p class="fine-print"><em><span>Oliver Nebel receives funding from the Australian Research Council Grant No DP180100580. </span></em></p><p class="fine-print"><em><span>Peter Cawood receives funding from Australian Research Council grant FL160100168</span></em></p>Dating of rocks that once formed some of the world’s first beaches suggests the first large continents grew large enough to rise above sea level roughly 3 billion or so years ago.Priyadarshi Chowdhury, Postdoctoral research fellow, Monash UniversityJack Mulder, Research Associate, The University of QueenslandOliver Nebel, Associate Professor, Monash UniversityPeter Cawood, Professor and ARC Laureate Fellow, Monash UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1705562021-11-01T18:38:23Z2021-11-01T18:38:23ZThe science everyone needs to know about climate change, in 6 charts<figure><img src="https://images.theconversation.com/files/428635/original/file-20211026-23-1ky80w7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Scientific instruments in space today can monitor hurricane strength, sea level rise, ice sheet loss and much more.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/gsfc/48698288003">Christina Koch/NASA</a></span></figcaption></figure><p><em><a href="https://theconversation.com/las-nociones-cientificas-sobre-el-cambio-climatico-que-todos-deberiamos-conocer-en-seis-graficos-171149">Leer en español</a></em></p>
<p>With the United Nations’ climate conference in Scotland turning a spotlight on climate change policies and the impact of global warming, it’s useful to understand what the science shows.</p>
<p>I’m an <a href="https://cires.colorado.edu/research/research-groups/elizabeth-weatherhead-group">atmospheric scientist</a> who has worked on global climate science and assessments for most of my career. Here are six things you should know, in charts.</p>
<h2>What’s driving climate change</h2>
<p>The primary focus of the negotiations is on carbon dioxide, a greenhouse gas that is released when fossil fuels – coal, oil and natural gas – are burned, as well as by forest fires, land use changes and natural sources.</p>
<p>The Industrial Revolution of the late 1800s started an enormous increase in the burning of fossil fuels. It powered homes, industries and opened up the planet to travel. That same century, scientists <a href="https://theconversation.com/scientists-understood-physics-of-climate-change-in-the-1800s-thanks-to-a-woman-named-eunice-foote-164687">identified carbon dioxide’s potential</a> to <a href="https://www.rsc.org/images/Arrhenius1896_tcm18-173546.pdf">increase global temperatures</a>, which at the time was considered a possible benefit to the planet. Systematic measurements started in the mid-1900s and have shown a steady increase in carbon dioxide, with <a href="https://www.ipcc.ch/assessment-report/ar6/">the majority of it directly traceable</a> to the combustion of fossil fuels.</p>
<p><iframe id="kkVw7" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/kkVw7/23/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>Once in the atmosphere, carbon dioxide tends to stay there for a very long time. A portion of the carbon dioxide released through human activities is taken up by plants, and some is absorbed directly into the ocean, but <a href="https://public.wmo.int/en/media/press-release/greenhouse-gas-bulletin-another-year-another-record">roughly half</a> of all carbon dioxide emitted by human activities today stays in the atmosphere — and it <a href="https://tos.org/oceanography/article/an-accounting-of-the-observed-increase-in-oceanic-and-atmospheric-co2-and-a">likely will remain there for hundreds of years</a>, influencing the climate globally.</p>
<p>During the <a href="https://www.iea.org/articles/global-energy-review-co2-emissions-in-2020">first year of the pandemic in 2020</a>, when fewer people were driving and some industries briefly stopped, carbon dioxide emissions from fuels fell by roughly 6%. But it <a href="https://essd.copernicus.org/articles/12/3269/2020/">didn’t stop the rise in the concentration of carbon dioxide</a> because the amount released into the atmosphere by human activities far exceeded what nature could absorb.</p>
<p>If civilization stopped its carbon dioxide-emitting activities today, it would <a href="https://tos.org/oceanography/article/an-accounting-of-the-observed-increase-in-oceanic-and-atmospheric-co2-and-a">still take many hundreds of years</a> for the concentration of carbon dioxide in the atmosphere to fall enough naturally to bring the planet’s carbon cycle back into balance because of carbon dioxide’s long life in the atmosphere.</p>
<p><iframe id="dE1UL" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/dE1UL/8/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<h2>How we know greenhouse gases can change the climate</h2>
<p>Multiple lines of scientific evidence point to the increase in greenhouse emissions over the past century and a half as a driver of long-term climate change around the world. For example:</p>
<ul>
<li><p>Laboratory measurements <a href="https://www.rsc.org/images/Arrhenius1896_tcm18-173546.pdf">since the 1800s</a> have repeatedly verified and quantified the absorptive properties of carbon dioxide that allow it to trap heat in the atmosphere.</p></li>
<li><p><a href="https://esd.copernicus.org/articles/12/545/2021/esd-12-545-2021-discussion.html">Simple models</a> based on the warming impact of carbon dioxide in the atmosphere <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017MS001038">match historical changes in temperature</a>.</p></li>
<li><p>Complex climate models, recently acknowledged in <a href="https://theconversation.com/winners-of-2021-nobel-prize-in-physics-built-mathematics-of-climate-modeling-making-predictions-of-global-warming-and-modern-weather-forecasting-possible-169329">the Nobel Prize for Physics</a>, not only indicate a warming of the Earth due to increases in carbon dioxide but also <a href="https://gmd.copernicus.org/articles/9/3461/2016/">offer details of the areas of greatest warming</a>.</p></li>
</ul>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/429261/original/file-20211029-26-whwkeu.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/429261/original/file-20211029-26-whwkeu.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/429261/original/file-20211029-26-whwkeu.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=353&fit=crop&dpr=1 600w, https://images.theconversation.com/files/429261/original/file-20211029-26-whwkeu.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=353&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/429261/original/file-20211029-26-whwkeu.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=353&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/429261/original/file-20211029-26-whwkeu.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=444&fit=crop&dpr=1 754w, https://images.theconversation.com/files/429261/original/file-20211029-26-whwkeu.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=444&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/429261/original/file-20211029-26-whwkeu.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=444&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">When carbon dioxide levels have been high in the past, evidence shows temperatures have also been high.</span>
<span class="attribution"><a class="source" href="https://link.springer.com/chapter/10.1007/978-3-319-46939-3_1">Based on Salawitch et al., 2017, updated with data to the end of 2020</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<ul>
<li><p>Long-term records from <a href="https://doi.org/10.1038/s41586-018-0172-5">ice cores</a>, <a href="https://www.nytimes.com/2019/04/30/science/tree-rings-climate.html">tree rings</a> and <a href="https://www.aims.gov.au/docs/research/climate-change/climate-history/climate-history.html">corals</a> show that when carbon dioxide levels have been high, temperatures have also been high.</p></li>
<li><p>Our neighboring planets also offer evidence. Venus’ atmosphere is thick with carbon dioxide, and it is the <a href="https://doi.org/10.1029/95JE03862">hottest planet</a> in our solar system as a result, even though Mercury is closer to the sun. </p></li>
</ul>
<h2>Temperatures are rising on every continent</h2>
<p>The rising temperatures are evident in records from every continent and over the oceans.</p>
<p>The temperatures aren’t rising at the same rate everywhere, however. A variety of factors affect local temperatures, including land use that influences how much solar energy is absorbed or reflected, local heating sources like <a href="https://scied.ucar.edu/learning-zone/climate-change-impacts/urban-heat-islands">urban heat islands</a>, and pollution.</p>
<p>The Arctic, for example, is warming about <a href="https://www.nilu.com/2021/05/amap-increase-in-arctic-temperature-is-three-times-higher-than-the-global-average/">three times faster than the global average</a> in part because as the planet warms, snow and ice melt makes the surface more likely to absorb, rather than reflect, the sun’s radiation. Snow cover and sea ice recede even more rapidly as a result. </p>
<p><iframe id="yV1Al" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/yV1Al/12/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<h2>What climate change is doing to the planet</h2>
<p>Earth’s climate system is interconnected and complex, and even small temperature changes can have large impacts – for instance, with snow cover and sea levels.</p>
<p>Changes are already happening. Studies show that rising temperatures are <a href="https://www.ipcc.ch/assessment-report/ar6/">already affecting</a> precipitation, glaciers, weather patterns, tropical cyclone activity and severe storms. A number of studies show that the <a href="https://www.epa.gov/climate-indicators/climate-change-indicators-heat-waves">increases in frequency</a>, severity and duration of heat waves, for example, <a href="https://www.science.org/doi/10.1126/science.1098704">affect ecosystems, human lives</a>, commerce and agriculture.</p>
<p>Historical records of ocean water level have shown mostly consistent increases over the past 150 years as glacier ice melts and rising temperatures expand ocean water, with some local deviations due to sinking or rising land.</p>
<p><iframe id="AYpRq" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/AYpRq/6/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>While extreme events are often due to complex sets of causes, some are exacerbated by climate change. Just as coastal flooding can be made worse by rising ocean levels, heat waves are more damaging with higher baseline temperatures.</p>
<p>Climate scientists work hard to estimate future changes as a result of increased carbon dioxide and other expected changes, such as world population. It’s clear that temperatures will increase and precipitation will change. The exact magnitude of change depends on many interacting factors. </p>
<figure class="align-center ">
<img alt="Models of future temperature and precipitation in map form" src="https://images.theconversation.com/files/429867/original/file-20211103-21-1omk71v.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/429867/original/file-20211103-21-1omk71v.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=721&fit=crop&dpr=1 600w, https://images.theconversation.com/files/429867/original/file-20211103-21-1omk71v.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=721&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/429867/original/file-20211103-21-1omk71v.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=721&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/429867/original/file-20211103-21-1omk71v.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=906&fit=crop&dpr=1 754w, https://images.theconversation.com/files/429867/original/file-20211103-21-1omk71v.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=906&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/429867/original/file-20211103-21-1omk71v.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=906&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Based on SSP3-7.0, a high-emissions scenario.</span>
<span class="attribution"><a class="source" href="https://esd.copernicus.org/articles/12/253/2021/">Claudia Tebaldi, et al., 2021</a></span>
</figcaption>
</figure>
<h2>A few reasons for hope</h2>
<p>On a hopeful note, scientific research is improving our understanding of climate and the complex Earth system, identifying the most vulnerable areas and guiding efforts to reduce the drivers of climate change. Work on renewable energy and alternative energy sources, as well as ways to capture carbon from industries or from the air, are producing more options for a better prepared society. </p>
<p>At the same time, people are learning about how they can reduce their own impact, with the growing understanding that a globally coordinated effort is required to have a significant impact. <a href="https://www.bts.gov/data-spotlight/electric-vehicle-use-grows">Electric vehicles, as well as solar and wind power, are growing</a> at previously unthinkable rates. More people are showing a <a href="https://theconversation.com/pews-new-global-survey-of-climate-change-attitudes-finds-promising-trends-but-deep-divides-167847">willingness to adopt new strategies</a> to use energy more efficiently, consume more sustainably and choose renewable energy. </p>
<p>Scientists increasingly recognize that shifting away from fossil fuels has <a href="https://www.sciencedirect.com/science/article/abs/pii/S0269749107002849">additional benefits</a>, including <a href="https://books.google.com/books?hl=en&lr=&id=YmNnDwAAQBAJ&oi=fnd&pg=PP4&dq=World+Health+Organization,+2018,+Health,+environment+and+climate+change:+report+by+the+Director-General&ots=zQRnV6VGzD&sig=hsqdBTGjE45iZB-ECYP4HNlIQWc">improved air quality</a> for human health and ecosystems.</p>
<figure class="align-right ">
<img alt="COP26: the world’s biggest climate talks" src="https://images.theconversation.com/files/424739/original/file-20211005-17-cgrf2z.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/424739/original/file-20211005-17-cgrf2z.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/424739/original/file-20211005-17-cgrf2z.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/424739/original/file-20211005-17-cgrf2z.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/424739/original/file-20211005-17-cgrf2z.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/424739/original/file-20211005-17-cgrf2z.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/424739/original/file-20211005-17-cgrf2z.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
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<p><strong>This story is part of The Conversation’s coverage of COP26, the Glasgow climate conference, by experts from around the world.</strong>
<br><em>Amid a rising tide of climate news and stories, The Conversation is here to clear the air and make sure you get information you can trust. <a href="https://theconversation.com/us/cop26">Read more of our U.S.</a> and <a href="https://page.theconversation.com/cop26-glasgow-2021-climate-change-summit/">global coverage</a>.</em></p><img src="https://counter.theconversation.com/content/170556/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Betsy Weatherhead 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>Take a closer look at what’s driving climate change and how scientists know CO2 is involved, in a series of charts examining the evidence in different ways.Betsy Weatherhead, Senior Scientist, University of Colorado BoulderLicensed 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>
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<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/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>
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<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">
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<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>
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<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>
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<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>
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<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>
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<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>
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</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>
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</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/1512762020-12-02T19:07:29Z2020-12-02T19:07:29ZThe floor is lava: after 1.5 billion years in flux, here’s how a new, stronger crust set the stage for life on Earth<figure><img src="https://images.theconversation.com/files/372474/original/file-20201202-16-1e1t98o.jpg?ixlib=rb-1.1.0&rect=83%2C83%2C7904%2C7904&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>Our planet is unique in the Solar system. It’s the only one with active plate tectonics, ocean basins, continents and, as far as we know, life. But Earth in its current form is 4.5 billion years in the making; it’s starkly different to what it was in a much earlier era. </p>
<p>Details about how, when and why the planet’s early history unfolded as it did have largely eluded scientists, mainly because of the sparsity of preserved rocks from this geological period. </p>
<p>Our research, <a href="https://www.nature.com/articles/s41586-020-2976-3">published today in Nature</a>, reveals Earth’s earliest continents were entities in flux. They disappeared and reappeared over 1.5 billion years before finally gaining form. </p>
<h2>Early Earth: a strange new world</h2>
<p>The first 1.5 billion years of Earth’s history were a tumultuous period that set the stage for the rest of the planet’s journey. Several key events took place, including the formation of the first continents, the emergence of land and the development of the early atmosphere and oceans. </p>
<p>All of these events were the result of the changing dynamics of Earth’s interior. They were also catalysts to the first appearances of <a href="https://www.livescience.com/18565-life-building-blocks-chemical-evolution.html">primitive life</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/372488/original/file-20201202-14-34n0dy.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Zircon crystal" src="https://images.theconversation.com/files/372488/original/file-20201202-14-34n0dy.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/372488/original/file-20201202-14-34n0dy.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=430&fit=crop&dpr=1 600w, https://images.theconversation.com/files/372488/original/file-20201202-14-34n0dy.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=430&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/372488/original/file-20201202-14-34n0dy.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=430&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/372488/original/file-20201202-14-34n0dy.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=541&fit=crop&dpr=1 754w, https://images.theconversation.com/files/372488/original/file-20201202-14-34n0dy.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=541&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/372488/original/file-20201202-14-34n0dy.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=541&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 almost 4.4 billion-year-old zircon crystal, retrieved from Western Australia’s Pilbara region, is one of the oldest rock fragment ever found. In reality it’s smaller than the head of a pin.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The preserved record of Earth’s first 500 million years is limited to just a few tiny crystals of the mineral <a href="https://www.livescience.com/43584-earth-oldest-rock-jack-hills-zircon.html">zircon</a>. Over the next billion or so years, kilometre-long (and larger) fragments of rock were generated and preserved. These would go on to forge the cores of major continents.</p>
<p>Scientists know about the properties of rocks and the chemical reactions that must occur for their constituent minerals to be made. Based on this, we know early Earth boasted very high temperatures, hundreds of degrees hotter than today’s.</p>
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<p>
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<strong>
Read more:
<a href="https://theconversation.com/earths-rock-solid-connections-between-canada-and-australia-contain-clues-about-the-origin-of-life-130380">Earth's rock-solid connections between Canada and Australia contain clues about the origin of life</a>
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<h2>An epic metamorphosis</h2>
<p>Earth’s crust today is made of thick, buoyant continental crust that stands proud above the sea. Meanwhile, below the oceans are thin but dense oceanic crusts. </p>
<p>The planet is also broken into a series of plates that move around in a process called “continental drift”. In some places, these plates drift apart and in other they converge to form mighty mountains. </p>
<p>This dynamic movement of Earth’s <a href="https://www.livescience.com/37706-what-is-plate-tectonics.html">tectonic plates</a> is the mechanism by which heat from its interior is released into space. This results in volcanic activity focused mainly at the plate boundaries. A good example is the <a href="https://www.nationalgeographic.org/encyclopedia/ring-fire/">Ring of Fire</a> — a path along the Pacific Ocean where volcanic eruptions and earthquakes are frequent. </p>
<p>To unravel the processes that operated on early Earth, we developed computer models to replicate its once much hotter conditions. These conditions were driven by large amounts of internal “<a href="https://link.springer.com/referenceworkentry/10.1007%2F978-3-642-11274-4_1274">primordial heat</a>”. This is the heat left over from when Earth first formed.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/372481/original/file-20201202-15-n6vq58.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Diagram of Earth's structure" src="https://images.theconversation.com/files/372481/original/file-20201202-15-n6vq58.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/372481/original/file-20201202-15-n6vq58.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/372481/original/file-20201202-15-n6vq58.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/372481/original/file-20201202-15-n6vq58.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/372481/original/file-20201202-15-n6vq58.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/372481/original/file-20201202-15-n6vq58.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/372481/original/file-20201202-15-n6vq58.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Today, Earth has a silica-rich continental crust above sea level and a thin (but dense) silica-poor crust in the ocean.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>Our modelling shows the release of primordial heat during Earth’s early stages (which was three to four times hotter than today’s) caused extensive melting in the upper mantle. This is the mostly solid region below the crust, between 10km and 100km deep.</p>
<p>This internal melting created magma which, through a plumbing system, was thrust out as lava onto the crust. The shallow mantle left behind, dry and rigid, became welded to the crust and formed the first continents.</p>
<h2>The pulse of first life</h2>
<p>Our research revealed a lag between the formation of Earth’s first crust and the development of the mantle keels at the base of the first continents. </p>
<p>The first formed crust, which was present between 4.5 billion and 4 billion years ago, was weak and prone to destruction. It progressively became stronger over the next billion years to form the core of modern continents.</p>
<p>This process was crucial to continents becoming stable. When magma was purged from Earth’s interior, rigid rafts formed in the mantle beneath the new crust, shielding it from further destruction.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/372483/original/file-20201202-21-bjic2p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Bands in rock representing early continental activity." src="https://images.theconversation.com/files/372483/original/file-20201202-21-bjic2p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/372483/original/file-20201202-21-bjic2p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/372483/original/file-20201202-21-bjic2p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/372483/original/file-20201202-21-bjic2p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/372483/original/file-20201202-21-bjic2p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/372483/original/file-20201202-21-bjic2p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/372483/original/file-20201202-21-bjic2p.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">Pictured is banded igneous rock built up from multiple layers of magma. This rock is from Western Australia’s Pilbara Region.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Moreover, the rise of these rigid continents ultimately led to weathering and erosion, which is when rocks and minerals break down or dissolve over long periods to eventually be carried away and deposited as sediment.</p>
<p>Early erosion would have changed the composition of Earth’s atmosphere. It would have also provided nutrients to the oceans, seeding the development of life. </p>
<p>From our observations, we conclude the breaking of Earth’s early crust was necessary to make way for a sturdier replacement. And had this not happened, we would not have the continents, nor life, as we know it.</p>
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<strong>
Read more:
<a href="https://theconversation.com/magnetism-of-himalayan-rocks-reveals-the-mountains-complex-tectonic-history-148404">Magnetism of Himalayan rocks reveals the mountains' complex tectonic history</a>
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<img src="https://counter.theconversation.com/content/151276/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Fabio A Capitanio receives funding from the Australian Research Council</span></em></p><p class="fine-print"><em><span>Oliver Nebel receives funding from the Australian Research Council. </span></em></p><p class="fine-print"><em><span>Peter Cawood receives funding from Australian Research Council (grant FL160100168). </span></em></p>In what could be described as a rather difficult adolescence, Earth earliest continents remained in flux — disappearing and reappeared over 1.5 billion years before finally gaining form.Fabio A Capitanio, Lecturer in Geophysics, Monash UniversityOliver Nebel, Associate Professor, Monash UniversityPeter Cawood, Professor and ARC Laureate Fellow, Monash UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1487722020-10-27T21:12:37Z2020-10-27T21:12:37ZGiant ‘toothed’ birds flew over Antarctica 40 million to 50 million years ago<figure><img src="https://images.theconversation.com/files/365550/original/file-20201026-21-t2z6hk.png?ixlib=rb-1.1.0&rect=9%2C14%2C3249%2C2013&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Fossil remains indicate these birds had a wingspan of over 20 feet.</span> <span class="attribution"><span class="source">Brian Choo</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span></figcaption></figure><p>Picture Antarctica today and what comes to mind? Large ice floes bobbing in the Southern Ocean? Maybe a remote outpost populated with scientists from around the world? Or perhaps colonies of penguins puttering amid vast open tracts of snow?</p>
<p>Fossils from Seymour Island, just off the Antarctic Peninsula, are painting a very different picture of what Antarctica looked like 40 to 50 million years ago – a time when the ecosystem was lusher and more diverse. Fossils of <a href="https://doi.org/10.1038/s41598-020-61973-5">frogs</a> and <a href="https://doi.org/10.1080/03115518.2011.565214">plants</a> such as ferns and conifers indicate Seymour Island was much warmer and less icy, while fossil remains from <a href="https://doi.org/10.7717/peerj.8268">marsupials and distant relatives of armadillos and anteaters</a> hint at the previous connections between Antarctica and other continents in the Southern Hemisphere.</p>
<p>There were also birds. Penguins were present then, as they are now, but fossil relatives of <a href="http://dx.doi.org/10.13679/j.advps.2019.0014">ducks, falcons and albatrosses</a> have also been found in Antarctica. My <a href="https://scholar.google.com/citations?user=5CGShQUAAAAJ&hl=en&oi=ao">colleagues</a> and <a href="https://scholar.google.com/citations?user=XlyfD9QAAAAJ&hl=en&oi=ao">I</a> published an <a href="https://doi.org/10.1038/s41598-020-75248-6">article in 2020</a> revealing new information about the fossil group that would have dwarfed all the other birds on Seymour Island: the pelagornithids, or “bony-toothed” birds. </p>
<h2>Giants of the sky</h2>
<p>As their name suggests, these ancient birds had sharp, bony spikes protruding from sawlike jaws. Resembling teeth, these spikes would have helped them catch squid or fish. We also studied another remarkable feature of the pelagornithids – their imposing size.</p>
<p>The largest flying bird alive today is the <a href="https://www.nationalgeographic.com/animals/birds/group/albatrosses/">wandering albatross</a>, which has a wingspan that reaches 11 ½ feet. The Antarctic pelagornithids fossils we studied have a wingspan nearly double that – about 21 feet across. If you tipped a two-story building on its side, that’s about 20 feet.</p>
<p>Across Earth’s history, very few groups of vertebrates have achieved powered flight – and only two reached truly giant sizes: birds and a group of <a href="https://www.amnh.org/exhibitions/pterosaurs-flight-in-the-age-of-dinosaurs/what-is-a-pterosaur">reptiles called pterosaurs</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/365561/original/file-20201026-23-p2l76b.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A model of an enormous prehistoric bird is mounted outdoor in the middle of a river. The wingspan reaches from bank to bank." src="https://images.theconversation.com/files/365561/original/file-20201026-23-p2l76b.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/365561/original/file-20201026-23-p2l76b.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/365561/original/file-20201026-23-p2l76b.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/365561/original/file-20201026-23-p2l76b.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/365561/original/file-20201026-23-p2l76b.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/365561/original/file-20201026-23-p2l76b.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/365561/original/file-20201026-23-p2l76b.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">Full-size model of a Quetzalcoatlus on display at JuraPark in Baltow, Poland.</span>
<span class="attribution"><a class="source" href="https://upload.wikimedia.org/wikipedia/commons/5/5c/Kecalkoatl_%28Quetzalcoatlus%29_-_Baltow_%281%29.JPG">Aneta Leszkiewicz/Wikimedia</a></span>
</figcaption>
</figure>
<p>Pterosaurs ruled the skies during the Mesozoic Era (252 million to 66 million years ago), the same period that dinosaurs roamed the planet, and they reached hard-to-believe dimensions. <a href="https://www.wired.com/2013/11/absurd-creature-of-the-week-quetz/">Quetzalcoatlus</a> stood 16 feet tall and had a colossal 33-foot wingspan.</p>
<h2>Birds get their opportunity</h2>
<p>Birds originated while dinosaurs and pterosaurs were still roaming the planet. But when an <a href="https://www.smithsonianmag.com/science-nature/dinosaur-killing-asteroid-impact-chicxulub-crater-timeline-destruction-180973075/">asteroid struck the Yucatan Peninsula 66 million years ago</a>, dinosaurs and pterosaurs both perished. Some <a href="https://www.audubon.org/news/how-birds-survived-asteroid-impact-wiped-out-dinosaurs">select birds survived</a>, though. These survivors diversified into the thousands of bird species alive today. Pelagornithids evolved in the period right after dinosaur and pterosaur extinction, when competition for food was lessened. </p>
<p><a href="https://doi.org/10.1002/spp2.1284">The earliest pelagornithid remains</a>, recovered from 62-million-year-old sediments in New Zealand, were about the size of modern gulls. The first giant pelagornithids, the ones in our study, <a href="https://doi.org/10.1038/s41598-020-75248-6">took flight over Antarctica about 10 million years later</a>, in a period called the Eocene Epoch (56 million to 33.9 million years ago). In addition to these specimens, fossilized remains from other pelagornithids have been found on every continent. </p>
<p>Pelagornithids lasted for about 60 million years before going extinct just before the Pleistocene Epoch (2.5 million to 11,700 years ago). No one knows exactly why, though, because few fossil records have been recovered from the period at the end of their reign. Some paleontologists cite <a href="https://doi.org/10.1080/02724634.2011.562268">climate change as a possible factor</a>.</p>
<h2>Piecing it together</h2>
<p>The fossils we studied are fragments of whole bones collected by paleontologists from the University of California at Riverside in the 1980s. In 2003, the specimens were transferred to Berkeley, where they now reside in the <a href="https://ucmp.berkeley.edu/">University of California Museum of Paleontology</a>. </p>
<p>There isn’t enough material from Antarctica to rebuild an entire skeleton, but by comparing the fossil fragments with similar elements from more complete individuals, we were able to assess their size. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/365552/original/file-20201026-17-1koc1h3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Photo of a fossil fragment of a jawbone section that has worn toothlike projections. Line drawing around it illustrates where in the jaw it would have fit." src="https://images.theconversation.com/files/365552/original/file-20201026-17-1koc1h3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/365552/original/file-20201026-17-1koc1h3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=573&fit=crop&dpr=1 600w, https://images.theconversation.com/files/365552/original/file-20201026-17-1koc1h3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=573&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/365552/original/file-20201026-17-1koc1h3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=573&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/365552/original/file-20201026-17-1koc1h3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=720&fit=crop&dpr=1 754w, https://images.theconversation.com/files/365552/original/file-20201026-17-1koc1h3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=720&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/365552/original/file-20201026-17-1koc1h3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=720&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">In life, the pelagornithid would have had numerous ‘teeth,’ making it a formidable predator.</span>
<span class="attribution"><span class="source">Peter Kloess</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span>
</figcaption>
</figure>
<p>We estimate the pelagornithid’s skull would have been about 2 feet long. A fragment of one bird’s lower jaw preserves some of the “pseudoteeth” that would have each measured up to an inch tall. The spacing of those “teeth” and other measurements of the jaw show this fragment came from an individual as big as, if not bigger than, the largest known pelagornithids. </p>
<p>[<em>Deep knowledge, daily.</em> <a href="https://theconversation.com/us/newsletters/the-daily-3?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=deepknowledge">Sign up for The Conversation’s newsletter</a>.]</p>
<p>Further evidence of the size of these Antarctic birds comes from a second pelagornithid fossil, from a different location on Seymour Island. A section of a foot bone, called a tarsometatarsus, is the largest specimen known for the entire extinct group. </p>
<p>These pelagornithid fossil findings emphasize the importance of natural history collections. Successful field expeditions result in a wealth of material brought back to a museum or repository – but the time required to prepare, study and publish on fossils means these institutions typically <a href="https://theconversation.com/digitizing-the-vast-dark-data-in-museum-fossil-collections-102833">hold many more specimens than they can display</a>. Important discoveries can be made by collecting specimens on expeditions in remote locations, no doubt. But equally important discoveries can be made by simply processing the backlog of specimens already on hand.</p><img src="https://counter.theconversation.com/content/148772/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Peter A. Kloess 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>Paleontologists have discovered fossil remains belonging to an enormous ‘toothed’ bird that lived for a period of about 60 million years after dinosaurs.Peter A. Kloess, Doctoral Candidate, Integrative Biology, University of California, BerkeleyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1424512020-07-28T12:16:34Z2020-07-28T12:16:34ZMarie Tharp pioneered mapping the bottom of the ocean 6 decades ago – scientists are still learning about Earth’s last frontier<figure><img src="https://images.theconversation.com/files/349770/original/file-20200727-35-1udrgwj.jpg?ixlib=rb-1.1.0&rect=0%2C17%2C1198%2C883&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Tharp with an undersea map at her desk. Rolled sonar profiles of the ocean floor are on the shelf behind her.</span> <span class="attribution"><a class="source" href="https://www.ldeo.columbia.edu/news-events/join-us-celebrating-marietharp100">Lamont-Doherty Earth Observatory and the estate of Marie Tharp</a></span></figcaption></figure><p>Despite all the deep-sea expeditions and samples taken from the seabed over the past 100 years, humans still know very little about the ocean’s deepest reaches. And there are good reasons to learn more. </p>
<p>Most <a href="https://www.noaa.gov/education/resource-collections/ocean-coasts/tsunamis">tsunamis</a> start with earthquakes under or near the ocean floor. The seafloor provides habitat for fish, corals and <a href="https://ocean.si.edu/ocean-life/invertebrates/hydrothermal-vent-creatures">complex communities</a> of microbes, crustaceans and other organisms. Its topography controls currents that <a href="https://oceanexplorer.noaa.gov/facts/climate.html#:%7E:text=Ocean%20currents%20act%20as%20conveyer,influencing%20both%20weather%20and%20climate.&text=The%20ocean%20doesn't%20just,distribute%20heat%20around%20the%20globe.">distribute heat</a>, helping to regulate Earth’s climate.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/349478/original/file-20200726-29-189de0o.jpg?ixlib=rb-1.1.0&rect=31%2C4%2C2968%2C1715&q=45&auto=format&w=1000&fit=clip"><img alt="Map showing geographic features of world's oceans" src="https://images.theconversation.com/files/349478/original/file-20200726-29-189de0o.jpg?ixlib=rb-1.1.0&rect=31%2C4%2C2968%2C1715&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/349478/original/file-20200726-29-189de0o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=347&fit=crop&dpr=1 600w, https://images.theconversation.com/files/349478/original/file-20200726-29-189de0o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=347&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/349478/original/file-20200726-29-189de0o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=347&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/349478/original/file-20200726-29-189de0o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=436&fit=crop&dpr=1 754w, https://images.theconversation.com/files/349478/original/file-20200726-29-189de0o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=436&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/349478/original/file-20200726-29-189de0o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=436&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Hand-painted rendition of Heezen-Tharp 1977 ‘World ocean floor’ map, by Heinrich Berann.</span>
<span class="attribution"><a class="source" href="https://www.loc.gov/resource/g9096c.ct003148/">Library of Congress, Geography and Map Division</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p><a href="https://www.ldeo.columbia.edu/news-events/remembered-marie-tharp-pioneering-mapmaker-ocean-floor">Marie Tharp</a>, born in 1920, was a geologist and oceanographer who created maps that changed the way people imagine two-thirds of the world. Beginning in 1957, Tharp and her research partner, Bruce Heezen, began publishing the first comprehensive maps that showed the main features of the ocean bottom – mountains, valleys and trenches. </p>
<p><a href="https://scholar.google.com/citations?user=ruUF3z4AAAAJ&hl=en">As a geoscientist</a>, I believe Tharp should be as famous as Jane Goodall or Neil Armstrong. Here’s why.</p>
<h2>Traversing the Atlantic</h2>
<p>Well into the 1950s, many scientists assumed the seabed was featureless. Tharp showed that it contained rugged terrain, and that much of it was laid out in a systematic way. </p>
<p>Her images were critical to the development of <a href="https://www.britannica.com/science/plate-tectonics">plate tectonic theory</a> – the idea that plates, or large sections of Earth’s crust, interact to generate the planet’s seismic and volcanic activity. Earlier researchers – <a href="https://www.livescience.com/37529-continental-drift.html">particularly Alfred Wegener</a> – noticed how well the coastlines of Africa and South America fit together and proposed the continents had once been connected; Tharp identified mountains and a rift valley in the center of the Atlantic Ocean where the two continents could have been ripped apart.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/349739/original/file-20200727-63428-1lb6xwh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="sketch of undersea profile" src="https://images.theconversation.com/files/349739/original/file-20200727-63428-1lb6xwh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/349739/original/file-20200727-63428-1lb6xwh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=296&fit=crop&dpr=1 600w, https://images.theconversation.com/files/349739/original/file-20200727-63428-1lb6xwh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=296&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/349739/original/file-20200727-63428-1lb6xwh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=296&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/349739/original/file-20200727-63428-1lb6xwh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=371&fit=crop&dpr=1 754w, https://images.theconversation.com/files/349739/original/file-20200727-63428-1lb6xwh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=371&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/349739/original/file-20200727-63428-1lb6xwh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=371&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Tharp’s East-West profiles across the North Atlantic.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.1130/SPE65-p1">The Floors of the Ocean, 1959</a></span>
</figcaption>
</figure>
<p>Thanks to Tharp’s hand-drawn renditions of the ocean floor, I can imagine a walk across the Atlantic Ocean bottom from New York City to Lisbon. The journey would take me out along the continental shelf. Then downward towards the <a href="https://www.britannica.com/place/Sohm-Abyssal-Plain">Sohm Abyssal Plain</a>. I’d need to detour around underwater mountains, called <a href="https://oceanservice.noaa.gov/facts/seamounts.html">seamounts</a>. Then I’d start a slow climb up the <a href="https://www.britannica.com/place/Mid-Atlantic-Ridge">Mid-Atlantic Ridge</a>, a submerged north-south mountain range. </p>
<p>After ascending to 8,200 feet (2,500 meters) below sea level to the ridge’s peak, I would descend several hundred feet, cross the ridge’s central rift valley and proceed up over the ridge’s eastern edge. Then back down to the ocean floor, until I began trekking up the European continental slope to Lisbon. The total walk would be about 3,800 miles (6,000 kilometers) – almost twice the length of the Appalachian Trail.</p>
<h2>Mapping the unseen</h2>
<p>Born in Ypsilanti, Michigan, Tharp studied English and music in college. But then in 1943 she enrolled in a University of Michigan master’s degree program designed to train women to be petroleum geologists during World War II. “Girls were needed to fill the jobs left open because the guys were off fighting,” <a href="https://www.whoi.edu/news-insights/content/marie-tharp/">Tharp later recalled</a>.</p>
<p>After working for an oil company in Oklahoma, Tharp sought a geology job at Columbia University in 1948. Women couldn’t go on research ships, but Tharp could draft, and was hired to assist male graduate students.</p>
<p>Tharp worked with Bruce Heezen, a grad student who gave her seafloor profiles to draft. These are long paper rolls that show the depth of the seafloor along a linear path, measured from a ship using sonar.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/349741/original/file-20200727-15-69lzu4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="sketches of undersea features based on sonar" src="https://images.theconversation.com/files/349741/original/file-20200727-15-69lzu4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/349741/original/file-20200727-15-69lzu4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=967&fit=crop&dpr=1 600w, https://images.theconversation.com/files/349741/original/file-20200727-15-69lzu4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=967&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/349741/original/file-20200727-15-69lzu4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=967&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/349741/original/file-20200727-15-69lzu4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1216&fit=crop&dpr=1 754w, https://images.theconversation.com/files/349741/original/file-20200727-15-69lzu4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1216&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/349741/original/file-20200727-15-69lzu4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1216&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 illustration of Marie Tharp’s mapping process. (a) shows the position of two ship tracks (A, B) moving across the surface. (b) plots depth recordings as profiles, exaggerating their height to make features easier to visualize. (c) sketches features shown on the profiles.</span>
<span class="attribution"><a class="source" href="http://mirrorservice.org/sites/gutenberg.org/4/9/0/6/49069/49069-h/49069-h.htm">The Floors of the Ocean, 1959, Fig. 1</a></span>
</figcaption>
</figure>
<p>Starting with a large blank sheet of paper, Tharp marked lines of latitude and longitude. Then she’d carefully mark where the ship had traveled. Next she’d read the depth at each location off the sonar profile, mark it on the ship’s track and create her own condensed profile, showing the depth to the ocean floor versus the distance the ship had traveled. </p>
<p>One of her important innovations was creating sketches depicting what the seafloor would look like. These views made it easier to visualize the ocean floor’s topography and create a physiographic map.</p>
<p>Tharp’s careful plotting of six east-to-west profiles across the North Atlantic revealed something no one had ever described before: a cleft in the center of the ocean, miles wide and hundreds of feet deep. Tharp suggested that it was a rift valley – a type of long trough that was known to exist on land.</p>
<p>Heezen <a href="https://www.whoi.edu/news-insights/content/marie-tharp/">called this idea “girl talk</a>” and told Tharp to recalculate and redraft. When she did, the rift valley was still there. </p>
<p>Another research assistant was plotting locations of earthquake epicenters on a map of the same size and scale. Comparing the two maps, Heezen and Tharp realized that the earthquake epicenters fell inside the rift valley. This discovery was critical to the development of plate tectonic theory: It suggested that movement was occurring in the rift valley, and that the continents might actually be drifting apart.</p>
<p>This insight was revolutionary. When Heezen, as a newly-minted Ph.D., gave a talk at Princeton in 1957 and showed the rift valley and epicenters, geology department chair <a href="https://www.whoi.edu/news-insights/content/marie-tharp/">Harry Hess replied</a>, “You have shaken the foundations of geology.” </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/bGye6vlOpbY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Exploring mid-ocean ridges provides vast amounts of information about life on Earth.</span></figcaption>
</figure>
<h2>Tectonic resistance</h2>
<p>In 1959 the Geological Society of America published “<a href="https://doi.org/10.1130/SPE65-p1">The Floors of the Oceans: I. The North Atlantic</a>” by Heezen, Tharp and “Doc” Ewing, director of the Lamont Observatory, where they worked. It contained Tharp’s ocean profiles, ideas and access to Tharp’s physiographic maps. </p>
<p>Some scientists thought the work was brilliant, but most didn’t believe it. French undersea explorer Jacques Cousteau was determined to prove Tharp wrong. Sailing aboard his research vessel, the Calypso, he purposely crossed the mid-Atlantic Ridge and lowered an underwater movie camera. To Cousteau’s surprise, the film showed that a rift valley existed.</p>
<p>“There’s truth to the old cliché that a picture is worth a thousand words and that seeing is believing,” Tharp observed in a <a href="https://www.whoi.edu/news-insights/content/marie-tharp/">1999 retrospective essay</a>.</p>
<p>What could have created the rift? Princeton’s Hess proposed some ideas <a href="http://scilib.ucsd.edu/sio/hist_oceanogr/hess-history-of-ocean-basins.pdf">in a 1962 paper</a>. It postulated that hot magma rose from inside the Earth at the rift, expanded as it cooled and pushed two adjoining plates further apart. This idea was a key contribution to plate tectonic theory, but Hess failed to reference the critical work presented in “The Floors of the Oceans” – one of the few publications that included Tharp as a co-author. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/349691/original/file-20200727-25-1kaavmd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Portrait of Marie Tharp in 2001" src="https://images.theconversation.com/files/349691/original/file-20200727-25-1kaavmd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/349691/original/file-20200727-25-1kaavmd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/349691/original/file-20200727-25-1kaavmd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/349691/original/file-20200727-25-1kaavmd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/349691/original/file-20200727-25-1kaavmd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/349691/original/file-20200727-25-1kaavmd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/349691/original/file-20200727-25-1kaavmd.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">Marie Tharp in July 2001.</span>
<span class="attribution"><span class="source">Bruce Gilbert, Lamont-Doherty Earth Observatory</span></span>
</figcaption>
</figure>
<h2>Still surveying</h2>
<p>Tharp continued working with Heezen to bring the ocean floor to life. Their collaboration included an <a href="https://www.lib.uchicago.edu/collex/exhibits/marie-tharp-pioneering-oceanographer/1967-indian-ocean-map/">Indian Ocean map</a>, published by National Geographic in 1967, and a 1977 <a href="https://www.lib.uchicago.edu/collex/exhibits/marie-tharp-pioneering-oceanographer/1977-world-ocean-floor-map/">World Ocean Floor map</a> that is now held at the Library of Congress. </p>
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<p>After Heezen died in 1977, Tharp continued her work until her death in 2006. In October 1978, Heezen (posthumously) and Tharp were awarded the <a href="https://physicstoday.scitation.org/do/10.1063/PT.6.6.20180730a/full/">Hubbard Medal</a>, the National Geographic Society’s highest honor, joining the ranks of explorers and discoverers such as Ernest Shackleton, Louis and Mary Leakey and Jane Goodall.</p>
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<p>Today ships use a <a href="https://youtu.be/8ijaPa-9MDs">method called swath mapping</a>, which measures depth over a ribbon-like path rather than along a single line. The ribbons can be stitched together to create an accurate seafloor map.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/349692/original/file-20200727-33-wfsk35.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/349692/original/file-20200727-33-wfsk35.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/349692/original/file-20200727-33-wfsk35.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=249&fit=crop&dpr=1 600w, https://images.theconversation.com/files/349692/original/file-20200727-33-wfsk35.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=249&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/349692/original/file-20200727-33-wfsk35.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=249&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/349692/original/file-20200727-33-wfsk35.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=313&fit=crop&dpr=1 754w, https://images.theconversation.com/files/349692/original/file-20200727-33-wfsk35.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=313&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/349692/original/file-20200727-33-wfsk35.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=313&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Left. Detail of Canary Islands from Marie Tharp’s physiographic map of the North Atlantic. Right. Modern swath mapping depiction of the same area. Colors indicate depth.</span>
<span class="attribution"><span class="source">Vicki Ferrini, Lamont-Doherty Earth Observatory.</span></span>
</figcaption>
</figure>
<p>But because ships move slowly, it would take one ship 200 years to completely map the seafloor. An international effort to map the entire ocean floor in detail by 2030 is under way, using multiple ships, led by the <a href="https://www.nippon-foundation.or.jp/en/">Nippon Foundation</a> and the <a href="https://www.gebco.net/">General Bathymetric Chart of the Oceans</a>. </p>
<p>This information is critical to beginning to understand what the seafloor looks like on a neighborhood scale. Marie Tharp was the first person to show the rich topography of the ocean floor and its different neighborhoods.</p><img src="https://counter.theconversation.com/content/142451/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Suzanne OConnell 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>Born on July 30, 1920, geologist and cartographer Tharp changed scientific thinking about what lay at the bottom of the ocean – not a featureless flat, but rugged and varied terrain.Suzanne OConnell, Harold T. Stearns Professor of Earth Science, Wesleyan UniversityLicensed 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/1161682019-05-08T20:03:25Z2019-05-08T20:03:25ZHow Earth’s continents became twisted and contorted over millions of years<figure><img src="https://images.theconversation.com/files/273240/original/file-20190508-183100-1spavv4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Photographed on Kangaroo Island, this rock – called a ‘zebra schist’ – deformed from flat-lying marine sediments through being stressed by a continental collision over 500 million years ago</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/dietmardownunder/34197272884/in/album-72157681483445374/">Dietmar Muller</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p><a href="https://theconversation.com/breaking-new-ground-the-rise-of-plate-tectonics-7514">Classical plate tectonic theory</a> was developed in the 1960s. </p>
<p>It proposed that the outer layer of our planet is made up of a small number of rigid plates separated by narrow boundaries. The surface of Earth could be viewed as a simple jigsaw puzzle with just nine large plates and a bunch of much smaller ones. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/272932/original/file-20190507-103082-1rob9c6.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/272932/original/file-20190507-103082-1rob9c6.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/272932/original/file-20190507-103082-1rob9c6.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=322&fit=crop&dpr=1 600w, https://images.theconversation.com/files/272932/original/file-20190507-103082-1rob9c6.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=322&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/272932/original/file-20190507-103082-1rob9c6.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=322&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/272932/original/file-20190507-103082-1rob9c6.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=404&fit=crop&dpr=1 754w, https://images.theconversation.com/files/272932/original/file-20190507-103082-1rob9c6.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=404&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/272932/original/file-20190507-103082-1rob9c6.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=404&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Map of the Earth’s rigid plates with the major tectonic plates labelled. Narrow plate boundary zones are the thin black lines. Created using plate reconstruction software (www.gplates.org).</span>
<span class="attribution"><span class="source">Maria Seton</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/breaking-new-ground-the-rise-of-plate-tectonics-7514">Breaking new ground – the rise of plate tectonics</a>
</strong>
</em>
</p>
<hr>
<p>But what was glossed over when global plate tectonic models were first developed was the enormous deformation experienced by these seemingly rigid plates. </p>
<p><a href="https://theconversation.com/plate-tectonics-new-findings-fill-out-the-50-year-old-theory-that-explains-earths-landmasses-55424">Fifty years after</a> the plate tectonic revolution, we are pretty sure the continental parts of plates are not uniform, nor are they rigid. The giant forces that slowly move continents across the viscous mantle layer underneath, like biscuits gliding over a warm toffee ocean, stress the continents, and twist and contort the crust. This is a process that has taken place over millions of years. </p>
<p>As part of recent research, we worked with a team of international collaborators to <a href="https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018TC005462">build a computer model</a> to show just how much the continents have been deformed since the Triassic Period, about 250 million years ago. The supercontinent Pangea began breaking apart soon after, ripping along the seams between Africa and North America.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/OwBbPa1zqMU?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Animation showing the motion of the tectonic plates and the associated evolution of deformation since the breakup of the Pangea supercontinent (Credit: Sabin Zahirovic).</span></figcaption>
</figure>
<p>We detail this new understanding of continent mangling in a paper published this month in the journal <a href="https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018TC005462">Tectonics</a>. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/Ns-_q_mhjxM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A model of tectonic plates moving over the viscous mantle. Blue material represents plates that are being recycled into the hot interior of the Earth. Red material represents extra hot material rising from the Earth’s core. (Credit: Maelis Arnould, see https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GC007516)</span></figcaption>
</figure>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/plate-tectonics-new-findings-fill-out-the-50-year-old-theory-that-explains-earths-landmasses-55424">Plate tectonics: new findings fill out the 50-year-old theory that explains Earth's landmasses</a>
</strong>
</em>
</p>
<hr>
<h2>Immense forces</h2>
<p>We already knew that that colossal tectonic forces act along plate boundaries. We can see this when continents collide, such as when Africa collided with Eurasia, <a href="https://theconversation.com/curious-kids-how-do-mountains-form-108246">forming mountains</a> like the Alps, or forming basins when continents are torn apart, as <a href="https://www.nationalgeographic.org/encyclopedia/rift-valley/">is happening in East Africa</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/272893/original/file-20190506-103045-19b3cq9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/272893/original/file-20190506-103045-19b3cq9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/272893/original/file-20190506-103045-19b3cq9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/272893/original/file-20190506-103045-19b3cq9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/272893/original/file-20190506-103045-19b3cq9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/272893/original/file-20190506-103045-19b3cq9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/272893/original/file-20190506-103045-19b3cq9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/272893/original/file-20190506-103045-19b3cq9.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">Folded marine sediments in the Alps (Helvetic Nappes of Switzerland), uplifted and deformed by the collision of the African and Eurasian continents.</span>
<span class="attribution"><a class="source" href="https://imaggeo.egu.eu/">Kurt Stüwe</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Our new research used geological and geophysical data to pinpoint all major zones of continental deformation, built into a global model of plate motions using our <a href="https://www.earthbyte.org/category/gplates/">GPlates software</a>.</p>
<p>We show that at least one third of all continental crust has been massively deformed since Pangea first started breaking up. That’s a whopping 75 million km<sup>2</sup>, roughly the size of North and South America and Africa combined. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/272978/original/file-20190507-103045-vm7pqv.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/272978/original/file-20190507-103045-vm7pqv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/272978/original/file-20190507-103045-vm7pqv.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=373&fit=crop&dpr=1 600w, https://images.theconversation.com/files/272978/original/file-20190507-103045-vm7pqv.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=373&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/272978/original/file-20190507-103045-vm7pqv.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=373&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/272978/original/file-20190507-103045-vm7pqv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=469&fit=crop&dpr=1 754w, https://images.theconversation.com/files/272978/original/file-20190507-103045-vm7pqv.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=469&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/272978/original/file-20190507-103045-vm7pqv.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=469&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 map showing the areas that have undergone compression or extension during the past 250 million years.</span>
<span class="attribution"><span class="source">Sabin Zahirovic</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-how-do-mountains-form-108246">Curious Kids: how do mountains form?</a>
</strong>
</em>
</p>
<hr>
<p>Deformed continental regions include large stretched and submerged continents like <a href="https://theconversation.com/explorers-probe-hidden-continent-of-zealandia-83406">Zealandia</a>, as well as crustal contraction where collisions have occurred, producing mountain belts such as the <a href="https://blogs.egu.eu/divisions/gd/2017/12/20/remarkable-regions-the-india-asia-collision-zone/">Himalayas</a>, the <a href="https://en.wikipedia.org/wiki/Alps">European Alps</a>, Iran’s <a href="https://blogs.egu.eu/geolog/tag/zagros-mountains/">Zagros Mountains</a> and the <a href="https://www.gns.cri.nz/Home/Learning/Science-Topics/Earthquakes/Earthquakes-at-a-Plate-Boundary/Plate-Collision-in-NZ">southern Alps</a> of New Zealand. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/272987/original/file-20190507-103063-e3iwek.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/272987/original/file-20190507-103063-e3iwek.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/272987/original/file-20190507-103063-e3iwek.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/272987/original/file-20190507-103063-e3iwek.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/272987/original/file-20190507-103063-e3iwek.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/272987/original/file-20190507-103063-e3iwek.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/272987/original/file-20190507-103063-e3iwek.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/272987/original/file-20190507-103063-e3iwek.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">Folded marine sediments on the Whangaparaoa Peninsula north of Auckland, New Zealand, reflecting the formation of a convergent plate boundary in northern New Zealand in the beginning of the Miocene Period, around 23 million years ago.</span>
<span class="attribution"><span class="source">Adriana Dutkiewicz</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>The cradle of humankind</h2>
<p>When crust is being thinned and stretched, the crustal contortions are usually hidden away from view because they are quickly covered up by sediments. But there are exceptions. </p>
<p>The <a href="https://www.nationalgeographic.org/encyclopedia/rift-valley/">East African Rift valley</a> is one of the most spectacular examples of crustal extension visible at the surface. It has not subsided below sea level because the region is being pushed up by a <a href="https://www.nature.com/articles/s41598-018-33117-3">mantle plume</a>, a large upwelling of hot molten material causing uplift and volcanism. </p>
<p>The rift valley is underlain by a giant fault system that is <a href="https://theconversation.com/africa-is-splitting-in-two-here-is-why-94056">splitting Africa in two</a>. The rift turned a flat landscape into one with 4km high mountains and lake basins with vegetation ranging from desert to cloud forest. This variety of surface environments paved the way for the <a href="https://www.nature.com/articles/d41586-019-00213-x">early evolution and diversification of humans</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/273248/original/file-20190508-183080-zakief.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/273248/original/file-20190508-183080-zakief.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/273248/original/file-20190508-183080-zakief.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/273248/original/file-20190508-183080-zakief.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/273248/original/file-20190508-183080-zakief.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/273248/original/file-20190508-183080-zakief.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/273248/original/file-20190508-183080-zakief.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/273248/original/file-20190508-183080-zakief.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 Rift Valley was an important site for early evolution and diversification of humans.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/beautiful-landscape-rift-valley-photographed-ethiopia-375138130?src=E-ME6PPLXxy6-IIzb-OtvA-1-1">from www.shutterstock.com</a></span>
</figcaption>
</figure>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/africa-is-splitting-in-two-here-is-why-94056">Africa is splitting in two – here is why</a>
</strong>
</em>
</p>
<hr>
<h2>The importance of stress</h2>
<p>We may not like stress in our daily lives, but the continuous stress and strain acting on continents provides us with an important record of Earth’s history. </p>
<p>Modelling the patterns of continental deformation through time allows us to explore regional patterns of earthquakes and volcanism and explain dramatic changes in Earth’s climate over time. </p>
<p>It also provides a framework based on tectonic data <a href="https://www.earthbyte.org/earthbyte-group-develops-machine-learning-recipe-to-find-copper-gold-deposits-along-the-andes">to seek mineral resources</a> such as the metals <a href="https://theconversation.com/from-cobalt-to-tungsten-how-electric-cars-and-smartphones-are-sparking-a-new-kind-of-gold-rush-100838">cobalt and tungsten</a>, which are needed for a sustainable energy future.</p><img src="https://counter.theconversation.com/content/116168/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Dietmar Müller receives funding from The University of Sydney, the Australian Research Council Industrial Transformation Research Hub for Basin Geodynamics and Evolution of Sedimentary Systems (Basin GENESIS Hub), and the Deep Carbon Observatory (DCO).</span></em></p><p class="fine-print"><em><span>Maria Seton receives funding from the Australian Research Council and has received ship time funding on Australia's Marine National Facility.</span></em></p><p class="fine-print"><em><span>Sabin Zahirovic receives funding from The University of Sydney, the Australian Research Council Industrial Transformation Research Hub for Basin Geodynamics and Evolution of Sedimentary Systems (Basin GENESIS Hub), and the Deep Carbon Observatory (DCO).</span></em></p>Giant forces slowly move continents across a viscous layer of the Earth, like biscuits gliding over a warm toffee ocean. This stresses the continents, and twists and contorts the crust.Dietmar Müller, Professor of Geophysics, University of SydneyMaria Seton, ARC Future Fellow, University of SydneySabin Zahirovic, Postdoctoral Research Associate, University of SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1074542018-11-27T12:13:32Z2018-11-27T12:13:32ZWhat planet Earth might look like when the next supercontinent forms – four scenarios<figure><img src="https://images.theconversation.com/files/247548/original/file-20181127-76752-12xd1ql.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Planet Earth.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/earth-galaxy-elements-this-image-furnished-278864093?src=Z3tU77G_ytYWIdNQI0xdzw-2-85">Triff/Shutterstock</a></span></figcaption></figure><p>The outer layer of the Earth, the solid crust we walk on, is made up of broken pieces, much like the shell of a broken egg. These pieces, the tectontic plates, move around the planet at speeds of a few centimetres per year. Every so often they come together and combine into a supercontinent, which remains for a few hundred million years before breaking up. The plates then disperse or scatter and move away from each other, until they eventually – after another 400-600 million years – come back together again. </p>
<p>The last supercontinent, <a href="http://dinosaurpictures.org/ancient-earth#240">Pangea</a>, formed around 310 million years ago, and started breaking up around 180 million years ago. It has been suggested that the next supercontinent will form in 200-250 million years, so we are currently about halfway through the scattered phase of the current supercontinent cycle. The question is: how will the next supercontinent form, and why?</p>
<p>There are four fundamental scenarios for the <a href="https://www.sciencedirect.com/science/article/pii/S0921818118302054">formation of the next supercontinent</a>: Novopangea, Pangea Ultima, Aurica and Amasia. How each forms depends on different scenarios but ultimately are linked to how Pangea separated, and how the world’s continents are still moving today. </p>
<p>The breakup of Pangea led to the formation of the Atlantic ocean, which is still opening and getting wider today. Consequently, the Pacific ocean is closing and getting narrower. The Pacific is home to a ring of subduction zones along its edges (the “<a href="https://www.nationalgeographic.org/encyclopedia/ring-fire/">ring of fire</a>”), where ocean floor is brought down, or subducted, under continental plates and into the Earth’s interior. There, the old ocean floor is recycled and can go into volcanic plumes. The Atlantic, by contrast, has a large ocean ridge producing new ocean plate, but is only home to two subduction zones: the <a href="https://www.sciencedirect.com/science/article/pii/S0012825299000690?via%3Dihub">Lesser Antilles Arc</a> in the Caribbean and the <a href="http://nora.nerc.ac.uk/id/eprint/507879/1/Global%20relevance%20of%20the%20Scotia%20Arc%20-%20AAM.pdf">Scotia Arc</a> between South America and Antarctica. </p>
<h2>1. Novopangea</h2>
<p>If we assume that present day conditions persist, so that the Atlantic continues to open and the Pacific keeps closing, we have a scenario where the next supercontinent forms in the antipodes of Pangea. The Americas would collide with the northward drifting Antarctica, and then into the already collided Africa-Eurasia. The supercontinent that would then form has been named Novopangea, or Novopangaea. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/247354/original/file-20181126-140540-1toykgt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/247354/original/file-20181126-140540-1toykgt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/247354/original/file-20181126-140540-1toykgt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/247354/original/file-20181126-140540-1toykgt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/247354/original/file-20181126-140540-1toykgt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/247354/original/file-20181126-140540-1toykgt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=369&fit=crop&dpr=1 754w, https://images.theconversation.com/files/247354/original/file-20181126-140540-1toykgt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=369&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/247354/original/file-20181126-140540-1toykgt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=369&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Novopangea.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>2. Pangea Ultima</h2>
<p>The Atlantic opening may, however, slow down and actually start closing in the future. The two small arcs of subduction in the Atlantic could potentially spread all along the east coasts of the Americas, leading to a reforming of Pangea as the Americas, Europe and Africa are brought back together into a supercontinent called <a href="https://science.nasa.gov/science-news/science-at-nasa/2000/ast06oct_1">Pangea Ultima</a>. This new supercontinent would be surrounded by a super Pacific Ocean.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/247355/original/file-20181126-140519-oi7eud.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/247355/original/file-20181126-140519-oi7eud.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/247355/original/file-20181126-140519-oi7eud.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/247355/original/file-20181126-140519-oi7eud.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/247355/original/file-20181126-140519-oi7eud.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/247355/original/file-20181126-140519-oi7eud.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=369&fit=crop&dpr=1 754w, https://images.theconversation.com/files/247355/original/file-20181126-140519-oi7eud.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=369&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/247355/original/file-20181126-140519-oi7eud.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=369&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Pangea Ultima, formed by the Atlantic closing.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>3. Aurica</h2>
<p>However, if the Atlantic was to develop new subduction zones – <a href="https://www.cambridge.org/core/journals/geological-magazine/article/future-of-earths-oceans-consequences-of-subduction-initiation-in-the-atlantic-and-implications-for-supercontinent-formation/5F0C1733CB5994BAB1A04979EE59C768">something that may already be happening</a> – both the Pacific and Atlantic oceans may be fated to close. This means that a a new ocean basin would have to form to replace them. </p>
<p>In this scenario the Pan-Asian rift currently cutting through Asia from west of India up to the Arctic opens to form the new ocean. The result is the formation of <a href="https://www.cambridge.org/core/journals/geological-magazine/article/the-future-of-earths-oceans-consequences-of-subduction-initiation-in-the-atlantic-and-implications-for-supercontinent-formation/5F0C1733CB5994BAB1A04979EE59C768">the supercontinent Aurica</a>. Because of <a href="https://www.nytimes.com/2016/09/24/world/what-in-the-world/australia-continental-drift-location-gps.html?_r=1">Australia’s current northwards drift</a> it would be at the centre of the new continent as East Asia and the Americas close the Pacific from either side. The European and African plates would then rejoin the Americas as the Atlantic closes.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/VqjHmtZ9240?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<h2>4. Amasia</h2>
<p>The fourth scenario predicts a completely different fate for future Earth. Several of the tectonic plates are currently moving north, including both Africa and Australia. This drift is <a href="https://www.nature.com/articles/nature10800">believed to be driven</a> by anomalies left by Pangea, deep in the Earth’s interior, in the part called the mantle. Because of this northern drift, one can envisage a scenario where the continents, except Antarctica, keep drifting north. This means that they would eventually gather around the North Pole in a <a href="https://www.sciencemag.org/news/2012/02/meet-amasia-next-supercontinent">supercontinent called Amasia</a>. In this scenario, both the Atlantic and the Pacific would mostly remain open.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/247356/original/file-20181126-140528-r0g50t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/247356/original/file-20181126-140528-r0g50t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/247356/original/file-20181126-140528-r0g50t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/247356/original/file-20181126-140528-r0g50t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/247356/original/file-20181126-140528-r0g50t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/247356/original/file-20181126-140528-r0g50t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=369&fit=crop&dpr=1 754w, https://images.theconversation.com/files/247356/original/file-20181126-140528-r0g50t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=369&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/247356/original/file-20181126-140528-r0g50t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=369&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Amasia, the fourth scenario.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Of these four scenarios we believe that Novopangea is the most likely. It is a logical progression of present day continental plate drift directions, while the other three assume that another process comes into play. There would need to be new Atlantic subduction zones for Aurica, the reversal of the Atlantic opening for Pangea Ultima, or anomalies in the Earth’s interior left by Pangea for Amasia. </p>
<p>Investigating the Earth’s tectonic future forces us to push the boundaries of our knowledge, and to think about the processes that shape our planet over long time scales. It also leads us to think about the Earth system as a whole, and raises a series of other questions – what will the climate of the next supercontinent be? How will the ocean circulation adjust? How will life evolve and adapt? These are the kind of questions that push the boundaries of science further because they push the boundaries of our imagination.</p><img src="https://counter.theconversation.com/content/107454/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mattias Green receives funding from the Natural Environmental Research Council.</span></em></p><p class="fine-print"><em><span>Hannah Davies receives funding from the Portuguese science foundation (FCT)</span></em></p><p class="fine-print"><em><span>Joao C. Duarte receives funding from the Portuguese Science Foundation (FCT)</span></em></p>Scientists have predicted four supercontinent scenarios - but which is the most likely?Mattias Green, Reader in Physical Oceanography, Bangor UniversityHannah Sophia Davies, PhD Researcher, Universidade de Lisboa Joao C. Duarte, Researcher and Coordinator of the Marine Geology and Geophysics Group, Universidade de Lisboa Licensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/835752017-11-20T19:15:08Z2017-11-20T19:15:08ZWhat’s Australia made of? Geologically, it depends on the state you’re in<figure><img src="https://images.theconversation.com/files/189566/original/file-20171010-19989-1qjhbav.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The continent of Australia is a mixture of land masses of differing ages. </span> <span class="attribution"><span class="source">Alan Collins</span>, <span class="license">Author provided</span></span></figcaption></figure><p>We think of Australia as a solid landmass. But it’s actually more like a jigsaw puzzle that has been put together over many millions of years. </p>
<p>The problem with working out how Australia formed is that the evidence is often buried, making access to geological materials quite difficult. </p>
<p>But now new techniques, new drill holes and the reevaluation of older samples are reshaping our understanding of how and when Australia formed.</p>
<p>And the results are not what you’d expect. An ocean and mountains once existed in the west and centre of Australia, and the eastern states are latecomers - they’re relatively new to the continent.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/a-map-that-fills-a-500-million-year-gap-in-earths-history-79838">A map that fills a 500-million year gap in Earth's history</a>
</strong>
</em>
</p>
<hr>
<h2>Australia is old, very old</h2>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/189560/original/file-20171010-17697-11g6c4m.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/189560/original/file-20171010-17697-11g6c4m.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/189560/original/file-20171010-17697-11g6c4m.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/189560/original/file-20171010-17697-11g6c4m.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/189560/original/file-20171010-17697-11g6c4m.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/189560/original/file-20171010-17697-11g6c4m.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/189560/original/file-20171010-17697-11g6c4m.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">PhD student Bo Yang examining precious rocks from deep beneath the Northern Territory in the Darwin Core store of the Northern Territory Geological Survey.</span>
<span class="attribution"><span class="source">Alan Collins</span></span>
</figcaption>
</figure>
<p>Australia has only been a unique continent for around <a href="http://www.antarctica.gov.au/about-antarctica/environment/geology/antarctic-prehistory">55 million years</a>. However, the rocks and minerals beneath us date back to an earlier time. These give clues as to the composite nature of the lands that make Australia. </p>
<p>The world’s oldest known material – some unprepossessing grains of sand – are found in Western Australia. These are <a href="http://www.abc.net.au/science/articles/2014/02/24/3950076.htm">4,374 million years old</a>, nearly as ancient as the <a href="https://theconversation.com/how-old-is-earth-a-word-to-sceptics-on-the-dating-game-5971">planet Earth itself</a>. </p>
<p>Between Perth and Kalgoorlie lies an ancient piece of the Earth called the Yilgarn craton. This is dated between <a href="http://www.sciencedirect.com/science/article/pii/S0301926804000178">3,700 and 2,600 million years old</a>. Further north, centred around the iron-ore towns of Newman and Tom Price, lies an equally old terrane called the <a href="http://www.ga.gov.au/provexplorer/provinceDetails.do?eno=464203">Pilbara craton</a>. </p>
<p>These cratons are really proto-continents, or “wannabe-continents”. They are made of the same materials continents are made of, but quite small compared to the modern landmasses. They are the earliest jigsaw puzzle pieces.</p>
<h2>Building ‘the lucky country’</h2>
<p>We now know that in Earth’s middle age, sometime between 1,800-1,300 million years ago, three contributing continents came together to form part of what we now recognise as Australia. At the time, each was still linked to rocks that are now found elsewhere in the world. </p>
<p>Surprisingly, the cratons that came from the three continents are broadly defined by our present state and territory boundaries. </p>
<p>The South Australian Craton (SAC) was connected to a big chunk of modern day Antarctica. The North Australian Craton (NAC) – matching roughly to the Northern Territory, the Kimberley and northern Queensland – was likely linked to parts of what is now northern China. The West Australian Craton (WAC) was made up of both the Yilgarn and Pilbara cratons that had collided together earlier. </p>
<p>As the ancestral plates moved around, these three continents smashed into each other and formed ancient mountain belts. These mountains are now eroded to low stumps – such as the Musgrave Ranges in central Australia – or buried beneath much later sediments, such as those that make up the vast western deserts. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/195386/original/file-20171120-18561-3wlyur.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/195386/original/file-20171120-18561-3wlyur.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/195386/original/file-20171120-18561-3wlyur.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=199&fit=crop&dpr=1 600w, https://images.theconversation.com/files/195386/original/file-20171120-18561-3wlyur.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=199&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/195386/original/file-20171120-18561-3wlyur.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=199&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/195386/original/file-20171120-18561-3wlyur.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=250&fit=crop&dpr=1 754w, https://images.theconversation.com/files/195386/original/file-20171120-18561-3wlyur.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=250&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/195386/original/file-20171120-18561-3wlyur.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=250&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"><strong>Illustration of the amalgamation of ‘ancient’ Australia</strong>. The first event is the loss of the western Mirning Ocean followed by the collision of the Western Australian Craton (WAC) with the combined South Australian Craton (SAC) and North Australian Craton (NAC). Volcanoes and mountains that formed during this period eroded to form sands that buried much of northern Australia.</span>
<span class="attribution"><span class="source">Marcella Cheng for The Conversation, modified from Yang et al</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>An ocean between states</h2>
<p>The boundary between the West Australian Craton and the other cratons lies buried beneath the Nullabor Plain in the south, and beneath the Great Sandy Desert further north. </p>
<p>Until very recently, geologists thought this collision, which brought together much of the continent, occurred <a href="http://sp.lyellcollection.org/content/424/1/47">1800 million years ago</a>. This was based on the ages of some rocks poking out of the Great Sandy Desert in remote Western Australia. </p>
<p>But intriguing recent <a href="http://hdl.handle.net/2440/106136">research</a> using new dating techniques suggests that the collision represented by these rocks is actually 500 million years younger than anyone thought.</p>
<p>New exploratory drilling by state and federal geological surveys also suggests that an ocean once separated Western Australia and South Australia until at least <a href="http://www.sciencedirect.com/science/article/pii/S0024493717300518">1,400 million years ago</a>. This ocean was named after the Mirning people who are indigenous to the region.</p>
<h2>Volcanoes along the border</h2>
<p>Closing the Mirning ocean bought Australia together for the first time, around 1,350 million years ago. Oceans close by subduction: this is the process when an oceanic plate moves beneath an overriding continent, and is similar to that occurring in the Andes, Japan, or New Zealand today. </p>
<p>This process is thought to have created volcanic mountains along the region now straddled by the South Australia-Northern Territory-Western Australia borders. Our latest <a href="http://www.sciencedirect.com/science/article/pii/S0301926817303613">research paper</a> proposes that as this mountain range formed, then eroded over time, the sediment produced was moved by rivers and deposited in a large inland sea that covered a lot of the Northern Territory under a blanket of sand and mud. This now forms the bedrock under much of the area between Tennant Creek and Katherine. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/189548/original/file-20171010-17706-1d9ply0.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/189548/original/file-20171010-17706-1d9ply0.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/189548/original/file-20171010-17706-1d9ply0.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/189548/original/file-20171010-17706-1d9ply0.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/189548/original/file-20171010-17706-1d9ply0.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/189548/original/file-20171010-17706-1d9ply0.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/189548/original/file-20171010-17706-1d9ply0.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">One of the Geological Survey of WA drillsites in the Nullabor Plain.</span>
<span class="attribution"><span class="source">Geological Survey of Western Australia</span></span>
</figcaption>
</figure>
<p>What makes this particularly exciting is that this increased volcanic erosion bought nutrients into the sea. As a result, we suggest that huge bacteria growths injected our atmosphere with oxygen. </p>
<p>When the bacteria died, they were buried, underwent decay and resulted in <a href="https://theconversation.com/a-time-capsule-containing-118-trillion-cubic-feet-of-gas-is-buried-in-northern-australia-80268">vast gas reserves encased in rocks of the region</a>.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/a-time-capsule-containing-118-trillion-cubic-feet-of-gas-is-buried-in-northern-australia-80268">A time capsule containing 118 trillion cubic feet of gas is buried in northern Australia</a>
</strong>
</em>
</p>
<hr>
<h2>The eastern states are young</h2>
<p>So these cratons, and the roots of the mountain belts that mark where they collided, make up Western Australia, South Australia, northern Queensland and the Northern Territory, but what about the eastern states? </p>
<p>Well for quite a long period of time, these areas of Australia simply did not exist. These relative newcomers consist mainly of rocks formed on the edge of old Australia as the Pacific Ocean evolved over the last 500 million years (in the last ninth of Earth history). </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>Tasmania is older and may well have been <a href="http://www.abc.net.au/catalyst/stories/4425034.htm">a part of North America</a> until within the last billion years. </p>
<p>But apart from that, mountain ranges have grown, faults have moved, but the bulk of Australia has been together for the last billion years or so, only to have broken out finally as our present landmass 55 million years ago.</p><img src="https://counter.theconversation.com/content/83575/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alan Collins receives funding from a diverse range of industry, state and federal government sources. </span></em></p><p class="fine-print"><em><span>Bo Yang receives funding from a diverse range of industry, state and federal government sources.</span></em></p><p class="fine-print"><em><span>Grant Cox receives funding from the Australian Research Council Linkage scheme.</span></em></p>The world’s oldest known material is from Western Australia. But for much of Australia’s geological past, the eastern states simply didn’t exist. They’re relative newcomers to our ancient continent.Alan Collins, Professor of Geology, University of AdelaideBo Yang, PhD candidate, University of AdelaideGrant Cox, Research Fellow, University of AdelaideLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/723142017-02-16T13:43:45Z2017-02-16T13:43:45ZWhy the discovery of a small continental fragment in the Indian Ocean matters<figure><img src="https://images.theconversation.com/files/156935/original/image-20170215-19249-1s891ue.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Mauritius beachfront view with volcanic mountains. The basaltic lavas constituting these mountains formed no older than 9 million years ago.
</span> <span class="attribution"><span class="source">Prof. Susan J. Webb, University of the Witwatersrand</span></span></figcaption></figure><p>Far beneath Mauritius’ inactive volcanoes lies an astonishing, important piece of the Earth’s history: a fragment of ancient continental crust. And no: it’s not <a href="http://www.livescience.com/23217-lost-city-of-atlantis.html">Atlantis</a>.</p>
<p>This discovery, which my colleagues and I have outlined in a newly <a href="http://rdcu.be/oVJ5">published study</a>, is extremely exciting. Discovering new pieces of continent will help geoscientists to understand the details of how continents break apart, and how the pieces can be better reconstructed to their pre-breakup configurations. This could, for example, be used as an important exploration tool for mineral deposits.</p>
<p>Our work demonstrates that continental break-up is often a complex and messy process. When continents begin to break apart, they can be stretched and fragmented, as new oceanic crust forms by continuous outpourings of magma at mid-ocean ridges. This forces the newly-formed crust to separate in opposite directions, taking the passive pieces of continent with them. Sometimes the sites of deep convection cells can suddenly shift, causing “ridge jumps”. This is how fragments of continent can become isolated, or “stranded” in many places across the ocean floor. </p>
<p>The Indian Ocean is a good place to study this, because it contains large fragments of continental crust like Madagascar, smaller ones like the Seychelles, and still smaller ones like the one now thought to underlie Mauritius.</p>
<p>Mauritius is an Indian Ocean island of volcanic origin, and lavas started forming there about 9 million years ago. Today it is dormant and most of the craters are covered with a rich variety of fauna and flora.</p>
<h2>What we found</h2>
<p>My colleagues and I suggest that during the active period, the lavas <a href="http://www.nature.com/ngeo/journal/v6/n3/abs/ngeo1736.html">erupted</a> on top of a small continental fragment that was then buried several kilometers below the new volcanic island. As the Mauritian lavas rose toward the surface, they passed through the stranded continental fragment, incorporating and dissolving some of it.</p>
<p>We were able to show that this continental fragment exists because we found tiny crystals of zircon – a mineral that can be analysed to provide age information – in a rare volcanic rock called trachyte, which is exposed at five different sites in Mauritius. We determined that the zircons were formed 2,500 to 3,000 million years ago. This is vastly older than even the earliest Mauritian volcanic rocks, which started erupting 9 million years ago. </p>
<p>The ages of the ancient zircons are also much older than the rocks present on the floor of the Indian Ocean, which all formed less than 200 million years ago. The nearest place where rocks as old as the ancient zircons can be found is in Madagascar, which is more than 700km to the west.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/o61P6ysKklM?wmode=transparent&start=94" frameborder="0" allowfullscreen=""></iframe>
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<p>The ancient zircons recovered in the new research are the only accessible remnants of the old granitic rocks which are now hidden below. We cannot specify the exact size of the buried fragment of ancient continent, but we think it might be similar to the present areal extent of Mauritius, about 2000kmsq.</p>
<p>In addition to our discovery of this previously unknown continental fragment below Mauritius, my colleagues and I suggest that there may be other pieces of ancient continent scattered elsewhere on the floor of the Indian Ocean. These are now mostly submerged and covered by lavas, coral reefs or sand banks. They include the Saya de Malha Bank, the Chagos and Cargados-Carahos shoals, the Laccadive Ridge and the Nazareth Bank. They may have once been joined together 80 to 90 million years ago, in a now fragmented continent we have named “Mauritia”.</p>
<h2>Continental break up</h2>
<p>So, where did this all begin?</p>
<p>We have known for some time that the familiar continental entities of the southern hemisphere – including Africa, South America, Madagascar, India, Australia and Antarctica – were joined together about 500 million years ago. This huge landmass was called <a href="http://www.livescience.com/37285-gondwana.html">Gondwana</a>. In fact, Gondwana was once part of an even larger “super-continent” called Pangea. </p>
<p>About 185 million years ago Gondwana began to drift apart and fragment due to plate tectonic processes that take place at the Earth’s outer shell of crustal rocks. Pieces of continent, both large and small, ride as “passengers” on newly-formed plates of oceanic crust; these continuously move away from each other at speeds of several centimetres per year. </p>
<p>The familiar present-day positions of the continents will continue to change, as plate tectonic forces drive them apart. For example, continental fragmentation appears to be starting in the East African Rift of Ethiopia, Kenya and Tanzania, where a new ocean basin might form tens of millions of years in the future, splitting East and West Africa into separate continental pieces. </p>
<p>In this sense, the idea that there are only seven continents is misleading because it is arbitrarily based on size, and would exclude substantial continental entities like Greenland and Borneo, as well as smaller ones like Madagascar, New Guinea and New Zealand. Because the sizes and shapes of continents have continuously changed over time, all continental entities can therefore be considered “fragments” of variable size.</p>
<p>It isn’t every day that someone can claim to have discovered a new piece of continent, even though the one in the new work described here is buried under a volcano and cannot be seen or touched. But its presence adds to a growing understanding of how the Earth works at present, and contributes to the question of how it worked in the past. These are the primary goals of geological science.</p><img src="https://counter.theconversation.com/content/72314/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Lewis Ashwal receives funding from the South African National Research Council and the University of the Witwatersrand.</span></em></p>Researchers have found a small piece of a “lost continent” buried underneath the lava on Mauritius.Lewis Ashwal, Professor, University of the WitwatersrandLicensed 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/333342014-10-23T16:01:49Z2014-10-23T16:01:49ZContinents may not have been created in the way we thought<figure><img src="https://images.theconversation.com/files/62626/original/fx2jb524-1414060802.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">How many continents can you count on one hand?</span> <span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-129993308/stock-photo-map-painted-on-hands-concept-of-having-the-world-in-our-hands.html?src=K9CBtfEfPR8VSCfWr9Ti4w-1-84">Chones</a></span></figcaption></figure><p>From the 1950s until recently, <a href="http://www.waterencyclopedia.com/Oc-Po/Plate-Tectonics.html">we thought</a> we had a clear idea of how continents form. Most people will have heard of plate tectonics: moving pieces on the surface of the planet that collide, pull away or slide past one another over millions of years to shape our world. </p>
<p>There are two types of crust that sit on top of these plates: oceanic crust (that beneath our oceans) and continental crust (that beneath our feet). These move across the surface of the Earth at rates of up to 10cm per year. Many are in a state of constant collision with one another. </p>
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<figcaption>
<span class="caption">Mountain range being formed by continental crusts colliding.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-140843146/stock-vector-geological-fault-mountain-up-transform-earth-cross-section.html?src=D_3DWInDZ7RLJuUtLnkXug-1-40">Daulon</a></span>
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<p>Continental crust is thicker than oceanic crust. When continents collide, they buckle upwards and sideways to form mountain ranges: the Himalayas, for example. When continental and oceanic regions collide, the oceanic crust slides beneath the continent and gets consumed back into the Earth in a process that geologists call subduction. </p>
<p>In these circumstances, the plate on top is subjected to compressing and stretching forces that can create mountain belts such as the Andes in South America. The sinking ocean plate meanwhile melts and can produce volcanoes at the surface. All of this adds new material to the continent. As the plate beneath pushes its way under the one above, large earthquakes can also be generated, like the one that struck Sumatra in 2004 and caused the <a href="http://www.thebcom.org/ourwork/reliefwork/96-the-boxing-day-tsunami-facts-and-figures.html?showall=1">Boxing Day tsunami</a>. </p>
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<a href="https://images.theconversation.com/files/62629/original/2h3kkws4-1414061560.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/62629/original/2h3kkws4-1414061560.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/62629/original/2h3kkws4-1414061560.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/62629/original/2h3kkws4-1414061560.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/62629/original/2h3kkws4-1414061560.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/62629/original/2h3kkws4-1414061560.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/62629/original/2h3kkws4-1414061560.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/62629/original/2h3kkws4-1414061560.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">Ocean crust meets continental crust.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-123695335/stock-photo-convergent-plate-boundary-created-by-two-continental-plates-that-slide-towards-each-other-digital.html?src=ND_yeUIY_GYJ8JYbPIGN4g-1-0">Andrea Danti</a></span>
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<h2>Rip it up and start again</h2>
<p>For 60 years the orthodoxy has been that these processes gradually form supercontinents, such as <a href="http://www.livescience.com/37285-gondwana.html">Gondwana</a> or <a href="http://www.princeton.edu/%7Eachaney/tmve/wiki100k/docs/Laurasia.html">Laurasia</a>, where a vast land mass is brought together before slowly breaking up and drifting away in pieces again. This has happened a number of times in cycles since the Earth was formed, collecting and then separating land over and over again.</p>
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<a href="https://images.theconversation.com/files/62631/original/cysfbpyv-1414063343.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/62631/original/cysfbpyv-1414063343.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/62631/original/cysfbpyv-1414063343.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=360&fit=crop&dpr=1 600w, https://images.theconversation.com/files/62631/original/cysfbpyv-1414063343.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=360&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/62631/original/cysfbpyv-1414063343.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=360&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/62631/original/cysfbpyv-1414063343.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=453&fit=crop&dpr=1 754w, https://images.theconversation.com/files/62631/original/cysfbpyv-1414063343.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=453&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/62631/original/cysfbpyv-1414063343.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=453&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Is it a bird, is it a plane…?</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-195323180/stock-vector-continental-drift-on-the-planet-earth-pangaea-laurasia-gondwana-modern-continents.html?src=87BNyljpTwfXStoZA4NByA-1-0">Designua</a></span>
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</figure>
<p>Now we have new information that suggests that the process is more complex than we had thought. When supercontinents break apart, small pieces of so-called “exotic continental crust” sometimes splinter off and get set adrift in newly formed oceanic crust (which is generated in places where continents break up). </p>
<p>When the oceanic crust containing the remnant fragment of continental material collides with another continent, the exotic piece of crust is too thick and buoyant to take part in the usual process of subduction. Instead of sliding beneath, it gets stuck at the margin of the continent. </p>
<p>When the surrounding zones of tectonic collision recede as the large piece of continental crust increases in size, the newly formed crust is forced to wrap itself around the exotic continental fragment. This creates a dramatic bent mountain belt called an <a href="http://gsabulletin.gsapubs.org/content/early/2013/02/21/B30765.1">orocline</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/62640/original/9x8mypzp-1414067688.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/62640/original/9x8mypzp-1414067688.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/62640/original/9x8mypzp-1414067688.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=295&fit=crop&dpr=1 600w, https://images.theconversation.com/files/62640/original/9x8mypzp-1414067688.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=295&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/62640/original/9x8mypzp-1414067688.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=295&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/62640/original/9x8mypzp-1414067688.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=371&fit=crop&dpr=1 754w, https://images.theconversation.com/files/62640/original/9x8mypzp-1414067688.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=371&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/62640/original/9x8mypzp-1414067688.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=371&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Cantabrian mountains: your starting orocline for 10.</span>
<span class="attribution"><a class="source" href="http://upload.wikimedia.org/wikipedia/commons/2/22/SotresPanorama.jpg">Wikimedia</a></span>
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<p>This theory <a href="http://www.nature.com/nature/journal/v508/n7495/full/nature13033.html#videos">was first published</a> by a group of Australian academics earlier this year, based on predictions from their 3D computer model. But the field evidence to support their findings was limited, so the race was on to demonstrate that this really does happen. </p>
<p>To confuse things further, not all oroclines are necessarily formed in this way: sometimes mountain ranges can bend for other reasons. So the likes of the Texas Orocline in eastern Australia or the Cantabrian Orocline in Iberia would be good places to look for evidence of the new theory. But their existence doesn’t tell us anything by itself. </p>
<h2>Mountains below the ground</h2>
<p>This is where my team came in. I have spent the best part of 12 years driving around the outback in eastern Australia, digging holes to bury small seismic sensors. These record earthquakes from places like Indonesia, Fiji and Japan, which through a process called seismic tomography has enabled us over time to build up a 3D image of the Earth’s crust in Australia. It is similar to the X-ray-based computerised tomography (CT-scan) that doctors use to construct internal images of parts of the human body. Over the years I planted about 700 of these sensors.</p>
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<a href="https://images.theconversation.com/files/62632/original/9jnjh7d6-1414063467.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/62632/original/9jnjh7d6-1414063467.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/62632/original/9jnjh7d6-1414063467.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=374&fit=crop&dpr=1 600w, https://images.theconversation.com/files/62632/original/9jnjh7d6-1414063467.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=374&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/62632/original/9jnjh7d6-1414063467.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=374&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/62632/original/9jnjh7d6-1414063467.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=469&fit=crop&dpr=1 754w, https://images.theconversation.com/files/62632/original/9jnjh7d6-1414063467.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=469&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/62632/original/9jnjh7d6-1414063467.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=469&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Sensor detail, eastern Australia.</span>
<span class="attribution"><span class="source">Nick Rawlinson</span></span>
</figcaption>
</figure>
<p>The sensors <a href="http://geology.gsapubs.org/content/42/9/783.full">have now enabled us</a> to prove that the theory is correct. Ironically we found what we were looking for, not in any of the world’s known bent mountain ranges but in one of the flattest places on Earth: the Hay plains in western New South Wales, a dry dusty expanse over hundreds of miles. </p>
<p>Hay is the site of an old sea that formed and receded due to variations in sea level, during which sediments were deposited on the eroded bedrock below. Our imaging shows that buried underneath it are the remains of exactly the sort of orocline the theory predicted. </p>
<h2>Now for the rethink…</h2>
<p>What does this mean for geology? It shows us that continents form in more complex ways than we thought. Scientists will now probably start testing other parts of the Earth’s crust to try and find examples elsewhere, including the oroclines that we can already see. It is very hard to say how widespread these features will turn out to be. Most likely the old version of plate tectonics will still be true in the majority of cases.</p>
<p>The discovery may give us new insights into how minerals are formed. I wouldn’t go as far as to say it will help us to find more minerals, but it should add extra sophistication to our predictive framework for saying where and how minerals form. </p>
<p>It will also make us think more about what happens when supercontinents break apart, especially smaller pieces the size of Tasmania or the UK. It could mean that a lot of them end up forming new continents through this sort of process. Previously scientists hadn’t given this much thought. Wherever the new findings take us, it may be the beginning of a new chapter in how the world fits together.</p><img src="https://counter.theconversation.com/content/33334/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nick's work has received grants from the Australian government and Australian Research Council</span></em></p>From the 1950s until recently, we thought we had a clear idea of how continents form. Most people will have heard of plate tectonics: moving pieces on the surface of the planet that collide, pull away…Nick Rawlinson, Chair in Geophysics, University of AberdeenLicensed as Creative Commons – attribution, no derivatives.