tag:theconversation.com,2011:/id/topics/early-earth-102235/articlesEarly Earth – The Conversation2024-03-11T16:59:03Ztag:theconversation.com,2011:article/2237182024-03-11T16:59:03Z2024-03-11T16:59:03ZStrange rock formations beneath the Pacific Ocean could change our understanding of the early Earth<figure><img src="https://images.theconversation.com/files/580557/original/file-20240307-18-xfnp9o.jpg?ixlib=rb-1.1.0&rect=21%2C70%2C922%2C475&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">NASA</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Our world may seem fragile, but Earth has been around for a very long time. If we ventured far back into the past, would we reach a time when it looked fundamentally different? </p>
<p>The answer lies in some of the earliest extensive relics of Earth’s surface, found in a remote corner of southern Africa’s highveld – a region known to geologists as the Barberton Greenstone Belt.</p>
<p>The geological formations in this region have proved difficult to decipher, despite many attempts. But our <a href="https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G51997.1/635654/Large-scale-submarine-landslides-in-the-Barberton">new research</a> has shown the key to cracking this code lies in geologically young rocks laid down on the seafloor of the Pacific Ocean off the coast of New Zealand.</p>
<p>This has opened up a new perspective on what our planet looked like when it was still young.</p>
<p>Our work began with a new, detailed geological map (by Cornel de Ronde) of part of the Barberton Greenstone Belt. This has revealed a fragment of the ancient deep seafloor, created some 3.3 billion years ago.</p>
<p>There was, however, something very strange about this seafloor, and it has taken our study of rocks laid down in New Zealand, at the other end of the Earth’s long history, to make sense of it. </p>
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Read more:
<a href="https://theconversation.com/earths-early-evolution-fresh-insights-from-rocks-formed-3-5-billion-years-ago-223209">Earth’s early evolution: fresh insights from rocks formed 3.5 billion years ago</a>
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<p>We argue that the widely held view of the early Earth as a hotter place, free of earthquakes and with a surface so weak it was unable to form rigid plates is wrong. </p>
<p>Instead, the young Earth was continually rocked by large earthquakes, triggered as one tectonic plate slid beneath another in a subduction zone as part of plate tectonics – just like New Zealand today.</p>
<figure class="align-center ">
<img alt="Landscape of Barberton Makhonjwa mountains in southern Africa" src="https://images.theconversation.com/files/580285/original/file-20240306-24-1gta3e.jpg?ixlib=rb-1.1.0&rect=17%2C41%2C3904%2C1263&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/580285/original/file-20240306-24-1gta3e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=197&fit=crop&dpr=1 600w, https://images.theconversation.com/files/580285/original/file-20240306-24-1gta3e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=197&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/580285/original/file-20240306-24-1gta3e.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=197&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/580285/original/file-20240306-24-1gta3e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=248&fit=crop&dpr=1 754w, https://images.theconversation.com/files/580285/original/file-20240306-24-1gta3e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=248&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/580285/original/file-20240306-24-1gta3e.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=248&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">The geological formations of the Barberton Greenstone Belt have proved difficult to decipher.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/landscape-barberton-makhonjwa-mountains-2100809914">Shutterstock/Instinctively RDH</a></span>
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<h2>Jumbled rocks</h2>
<p>Geologists have long found it hard to interpret the ancient rocks of the Barberton Greenstone Belt.</p>
<p>Layers that formed on land or in shallow water – for example, beautiful crystals of barite that had crystallised as evaporites, or the remains of bubbling mud pools – are found sitting on top of rocks that accumulated on the deep seafloor. Blocks of volcanic rock, chert, sandstone and conglomerate lie topsy turvy and jumbled up. </p>
<figure class="align-center ">
<img alt="A block of black chert found in the Barberton Makhonjwa mountains." src="https://images.theconversation.com/files/580332/original/file-20240307-28-ngeq8t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/580332/original/file-20240307-28-ngeq8t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/580332/original/file-20240307-28-ngeq8t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/580332/original/file-20240307-28-ngeq8t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/580332/original/file-20240307-28-ngeq8t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/580332/original/file-20240307-28-ngeq8t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/580332/original/file-20240307-28-ngeq8t.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">
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<span class="caption">Blocks of black chert can be found in the Barberton mountains.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/black-chert-ancient-rock-barberton-makhonjwa-1601619364">Shutterstock/Beate Wolter</a></span>
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<p>We realised this map looked remarkably similar to a geological map (by Simon Lamb) made of the aftermath of much more recent submarine landslides. These were triggered by great earthquakes along New Zealand’s largest fault, the megathrust in the Hikurangi subduction zone.</p>
<p>The bedrock is made of a jumble of sedimentary rocks, originally laid down on the seafloor off the coast of New Zealand some 20 million years ago. This region lay on the edges of the deep oceanic trench, where the Pacific tectonic plate is sliding down in a subduction zone triggering frequent large earthquakes. </p>
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<img alt="A sketch profile through the New Zealand subduction zone" src="https://images.theconversation.com/files/577706/original/file-20240224-18-ml4f75.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/577706/original/file-20240224-18-ml4f75.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=266&fit=crop&dpr=1 600w, https://images.theconversation.com/files/577706/original/file-20240224-18-ml4f75.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=266&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/577706/original/file-20240224-18-ml4f75.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=266&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/577706/original/file-20240224-18-ml4f75.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=334&fit=crop&dpr=1 754w, https://images.theconversation.com/files/577706/original/file-20240224-18-ml4f75.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=334&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/577706/original/file-20240224-18-ml4f75.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=334&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">This sketch profile through the New Zealand subduction zone shows how the bedrock in the shallow shelf region is sliding down into deeper water, where huge blocks pile up on top of each other.</span>
<span class="attribution"><span class="source">Simon Lamb</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
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<p>The rocks in New Zealand are the key to reading the geological record in the Barberton Greenstone Belt.</p>
<p>What was once thought to be untranslatable turns out to be a remnant of a gigantic landslide containing sediments deposited both on land or in very shallow water, jumbled with those that accumulated on the deep seafloor. </p>
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<img alt="A detail of a new map by Cornel de Ronde of the Barberton Greenstone Belt shows jumbled rocks with the remains of underwater landslides consisting of huge slide blocks." src="https://images.theconversation.com/files/577704/original/file-20240224-20-tpnf6e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/577704/original/file-20240224-20-tpnf6e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=439&fit=crop&dpr=1 600w, https://images.theconversation.com/files/577704/original/file-20240224-20-tpnf6e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=439&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/577704/original/file-20240224-20-tpnf6e.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=439&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/577704/original/file-20240224-20-tpnf6e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=552&fit=crop&dpr=1 754w, https://images.theconversation.com/files/577704/original/file-20240224-20-tpnf6e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=552&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/577704/original/file-20240224-20-tpnf6e.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=552&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">This detail of a new map by Cornel de Ronde of the Barberton Greenstone Belt shows jumbled rocks with the remains of underwater landslides consisting of huge slide blocks. We think it is the inevitable consequence of one tectonic plate sliding beneath another in a subduction zone, periodically rocked by great earthquakes.</span>
<span class="attribution"><span class="source">Cornel de Ronde</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
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<p>The importance of this lies in the fact that New Zealand’s geological record is uniquely created by the profound effects of large earthquakes in a subduction zone. This is still happening today, most recently in November 2016, when the magnitude 7.8 Kaikoura earthquake set off vast submarine landslides and debris avalanches that flowed down into deep water.</p>
<p>We found the oldest record of these earthquakes, hidden in the highveld of southern Africa.</p>
<h2>The key to other mysteries</h2>
<p>Our work may have unlocked other mysteries, too, because subduction zones are also associated with explosive volcanic eruptions. </p>
<p>In January 2022, Tonga’s Hunga Tonga-Hunga Ha’apai volcano erupted with the energy of a 60 Megaton atomic bomb, sending a vast cloud of ash into space. Over the next 11 hours, more than 200,000 lightning strikes flashed through this cloud.</p>
<p>In the same volcanic region, underwater volcanoes are erupting an extremely rare type of lava called boninite. This is the closest modern example of a lava that was common in the early Earth. </p>
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Read more:
<a href="https://theconversation.com/origin-of-life-lightning-strikes-may-have-provided-missing-ingredient-for-earths-first-organisms-157343">Origin of life: lightning strikes may have provided missing ingredient for Earth's first organisms</a>
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<p>The vast amounts of volcanic ash found in the Barberton Greenstone Belt may be an ancient record of similar volcanic violence. Perhaps the associated lightning strikes created the crucible for life where the basic organic molecules were forged.</p>
<p>Hidden deep in the south-west Pacific are echoes of our planet not long after it was created. They provide unexpected clues about the origins of the world we know today, and possibly life itself. The key to this turns out to be the subduction of tectonic plates.</p><img src="https://counter.theconversation.com/content/223718/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Simon Lamb receives funding from Victoria University of Wellington, New Zealand. </span></em></p><p class="fine-print"><em><span>Cornel de Ronde 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>New research comparing the geology of southern Africa with the deep seafloor near New Zealand challenges conventional views of how the planet behaved when it was very young.Simon Lamb, Associate Professor in Geophysics, Te Herenga Waka — Victoria University of WellingtonCornel de Ronde, Principal Scientist, GNS ScienceLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1978802023-02-20T13:19:21Z2023-02-20T13:19:21ZWere viruses around on Earth before living cells emerged? A microbiologist explains<figure><img src="https://images.theconversation.com/files/507461/original/file-20230131-26-ml6jvg.jpg?ixlib=rb-1.1.0&rect=0%2C3%2C2305%2C1292&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Maybe the first life on Earth was part of an 'RNA world.'</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/molecule-illustration-royalty-free-illustration/1359392488">Artur Plawgo/Science Photo Library via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
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<blockquote>
<p><strong>Were there already viruses on Earth when the first living cells appeared billions of years ago? – Aayush A., age 16, India</strong></p>
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<p>How life on Earth started has puzzled scientists for a long time. And it still does.</p>
<p>Fossils provide very important evidence about the evolution of plants and animals. Unfortunately, there are <a href="https://ucmp.berkeley.edu/bacteria/bacteriafr.html">very few fossils of ancient microbes available</a>, so scientists rely on modern microbes to devise theories about how life started. I studied bacteria and another type of microbe called archaea from hot environments <a href="https://scholar.google.com/citations?user=pN5i54IAAAAJ&hl=en">for many years</a> to learn how they might have evolved on early Earth, but I still have so many unanswered questions.</p>
<p>Based on the fossil evidence we have, single-celled microbes appeared on Earth before larger cellular life like plants and animals. But which kinds of microbes were the very first kind of life?</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/de1hiS_XjWg?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Some scientists think hydrothermal vents are the cradle of early life on Earth.</span></figcaption>
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<h2>Which microbes are considered alive?</h2>
<p>Microbes are living, single-celled creatures surrounded by a membrane. They consume and convert nutrients into biological molecules or energy and are too small to be seen without a microscope.</p>
<p>By this definition, bacteria, archaea and single-celled eukaryotes are microbes. <a href="https://bio.libretexts.org/Courses/University_of_California_Davis/BIS_2A%3A_Introductory_Biology_(Easlon)/Readings/02.2%3A_Bacterial_and_Archaeal_Diversity">Bacteria and archaea</a> are single-celled creatures that lack internal membrane-enclosed structures, like a nucleus to hold their genetic material. Single-celled eukaryotes have a nucleus and may have other membrane-enclosed structures.</p>
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<a href="https://images.theconversation.com/files/507680/original/file-20230201-8834-kxai71.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Diagram comparing a eukaryotic and prokaryotic cell" src="https://images.theconversation.com/files/507680/original/file-20230201-8834-kxai71.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/507680/original/file-20230201-8834-kxai71.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/507680/original/file-20230201-8834-kxai71.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/507680/original/file-20230201-8834-kxai71.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/507680/original/file-20230201-8834-kxai71.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/507680/original/file-20230201-8834-kxai71.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/507680/original/file-20230201-8834-kxai71.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1131&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Unlike prokaryotic cells, eukaryotic cells have membrane-enclosed structures like a nucleus and mitochondria.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/eukaryotic-vs-prokaryotic-cells-educational-royalty-free-illustration/1201105509">VectorMine/iStock via Getty Images Plus</a></span>
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<p>Some scientists <a href="https://www.genome.gov/genetics-glossary/Virus">consider viruses</a> to be microbes made of genetic material enclosed in a protein coat. They are unable to replicate on their own and hijack the machinery of other cells to make copies of themselves. Because they don’t have many <a href="https://www.khanacademy.org/test-prep/mcat/cells/viruses/a/are-viruses-dead-or-alive">features of living cells</a>, they are <a href="https://microbiologysociety.org/publication/past-issues/what-is-life/article/are-viruses-alive-what-is-life.html">not technically alive</a>.</p>
<h2>Evidence for early life on Earth</h2>
<p>Fossils can provide scientists with clues as to when life started, but they best record hard things like bones and teeth. Microbes are made of soft materials that do not fossilize well. However, some live together in very large groups of cells that can accumulate minerals and leave behind quite large fossils. </p>
<p>For example, cyanobacteria formed large structures called <a href="https://theconversation.com/ancient-microbial-life-used-arsenic-to-thrive-in-a-world-without-oxygen-146533">stromatolites</a> in the oceans of early Earth. Scientists have found fossil stromatolites that date back to <a href="https://www.sciencedaily.com/releases/2022/11/221107135817.htm">3.48 billion years ago</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/510650/original/file-20230216-759-docyl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Stromatolites near a river" src="https://images.theconversation.com/files/510650/original/file-20230216-759-docyl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/510650/original/file-20230216-759-docyl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/510650/original/file-20230216-759-docyl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/510650/original/file-20230216-759-docyl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/510650/original/file-20230216-759-docyl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/510650/original/file-20230216-759-docyl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/510650/original/file-20230216-759-docyl.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>
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<span class="caption">Stromatolites can provide information about life on early Earth.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/stromatolites-found-by-the-ottawa-river-rock-royalty-free-image/1176691303">Jana Kriz/Moment via Getty Images</a></span>
</figcaption>
</figure>
<p>Other scientists found what they believe are <a href="https://www.the-scientist.com/news-opinion/microbial-fossils-found-in-3-4-billion-year-old-subseafloor-rock-68975">fossilized archaea</a> in rocks from a 3.4 billion-year-old hot seafloor. The Earth became habitable about 4 billion years ago, so bacteria and archaea must have appeared between 3.5 billion and 4 billion years ago.</p>
<p>Looking at the chemical reactions that cells carry out can also provide clues. The reactions that make biological molecules and generate energy make up what’s called the cell’s metabolism. Scientists have found evidence that some metabolic reactions were occurring at least <a href="https://newsroom.ucla.edu/releases/life-on-earth-likely-started-at-least-4-1-billion-years-ago-much-earlier-than-scientists-had-thought">4.1 billion years ago</a>. These reactions may have been occurring on their own <a href="https://news.ncbs.res.in/research/unravelling-origin-life">before cells had evolved</a>, perhaps on the surfaces of <a href="https://doi.org/10.3390/life11080795">clays or minerals</a>.</p>
<h2>Theories about how life started on Earth</h2>
<p>Cells copy their genetic material, made of DNA and RNA, to pass it on to new generations. Although DNA is the form of genetic material most living organisms use today, some scientists believe that RNA was the <a href="https://news.ncbs.res.in/research/unravelling-origin-life">first information storage molecule</a> on early Earth because it can make copies of itself. </p>
<p>Because some modern viruses use RNA to store genetic information, some scientists believe that viruses could have <a href="https://doi.org/10.1016/j.biochi.2005.03.015">evolved from self-replicating RNAs</a>. This possibility would mean that viruses may have appeared before bacteria. But because viruses don’t leave fossils behind, there isn’t available evidence to support this idea.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/VYQQD0KNOis?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The RNA-world hypothesis proposes that self-replicating RNA evolved before DNA or proteins.</span></figcaption>
</figure>
<p>At some point, metabolic reactions and replication processes had to come together inside a membrane to make an early form of a cell: a pre-cell. Perhaps this happened when a viruslike structure infected a collection of metabolic reactions enclosed within a membrane. The pre-cell could then duplicate itself, leading to the <a href="https://doi.org/10.1098/rstb.2002.1183">evolution of the first living cell</a>. This cell would have been like today’s bacteria and archaea.</p>
<p>Maybe viruslike structures did form before cells. However, those simple viruslike structures might have been just pieces of DNA or RNA, so could they really be considered “viruses”? </p>
<p>Another popular theory states that viruses evolved from degenerated bacteria or archaea that lost most of the genetic instructions for carrying out metabolism and forming cells. There are <a href="http://www.biologyaspoetry.com/textbooks/microbes_and_evolution/symbioses_serial_endosymbiosis.html">many examples</a> of similar smaller degenerations that have occurred in the bacterial world today.</p>
<h2>Uncovering early life</h2>
<p>The surface of the Earth today is very different from <a href="https://eos.org/science-updates/rethinking-the-search-for-the-origins-of-life">what it was 4 billion years ago</a>. Some have speculated that deep under the Earth’s surface, where it is too hot for modern life, these early conditions <a href="https://www.chemistryworld.com/features/hydrothermal-vents-and-the-origins-of-life/3007088.article">might still be present</a>, allowing some protolife forms to continue to exist where they are protected from being consumed by other microbes. </p>
<p>When people can explore other planets or moons, perhaps we will find processes similar to those that were at work on early Earth. This kind of discovery could help us solve the puzzle of life’s origin here.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/197880/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Kenneth Noll previously received funding from NSF, NASA, DOE and the Office of Naval Research. </span></em></p>Fossil evidence of how the earliest life on Earth came to be is hard to come by. But scientists have come up with a few theories based on the microbes, viruses and prions existing today.Kenneth Noll, Professor Emeritus of Microbiology, University of ConnecticutLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1916732022-11-28T18:31:32Z2022-11-28T18:31:32ZWhere did the Earth’s oxygen come from? New study hints at an unexpected source<p>The amount of oxygen in the Earth’s atmosphere makes it a habitable planet.</p>
<p>Twenty-one per cent of the atmosphere consists of this life-giving element. But in the deep past — as far back as the Neoarchean era 2.8 to 2.5 billion years ago — <a href="https://doi.org/10.1126/sciadv.aax1420">this oxygen was almost absent</a>. </p>
<p>So, how did Earth’s atmosphere become oxygenated? </p>
<p><a href="https://www.nature.com/articles/s41561-022-01071-5">Our research</a>, published in <em>Nature Geoscience</em>, adds a tantalizing new possibility: that at least some of the Earth’s early oxygen came from a tectonic source via the movement and destruction of the Earth’s crust.</p>
<h2>The Archean Earth</h2>
<p>The Archean eon represents one third of our planet’s history, from 2.5 billion years ago to four billion years ago. </p>
<p>This alien Earth was a water-world, covered in <a href="https://doi.org/10.1038/ngeo2878">green oceans</a>, shrouded in a <a href="https://doi.org/10.1089/ast.2007.0197">methane haze</a> and completely lacking multi-cellular life. Another alien aspect of this world was the nature of its tectonic activity. </p>
<p>On modern Earth, the dominant tectonic activity is called plate tectonics, where oceanic crust — the outermost layer of the Earth under the oceans — sinks into the Earth’s mantle (the area between the Earth’s crust and its core) at points of convergence called subduction zones. However, there is considerable debate over whether plate tectonics operated back in the Archean era. </p>
<p>One feature of modern subduction zones is their association with <a href="https://doi.org/10.1002/9781119473206.ch3">oxidized magmas</a>. These magmas are formed when oxidized sediments and bottom waters — cold, dense water near the ocean floor — are <a href="https://doi.org/10.1073/pnas.1821847116">introduced into the Earth’s mantle</a>. This produces magmas with high oxygen and water contents. </p>
<p>Our research aimed to test whether the absence of oxidized materials in Archean bottom waters and sediments could prevent the formation of oxidized magmas. The identification of such magmas in Neoarchean magmatic rocks could provide evidence that subduction and plate tectonics occurred 2.7 billion years ago.</p>
<h2>The experiment</h2>
<p>We collected samples of 2750- to 2670-million-year-old granitoid rocks from across the Abitibi-Wawa subprovince of the Superior Province — the largest preserved Archean continent stretching over 2000 km from Winnipeg, Manitoba to far-eastern Quebec. This allowed us to investigate the level of oxidation of magmas generated across the Neoarchean era. </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/489928/original/file-20221017-23-zslasf.jpeg?ixlib=rb-1.1.0&rect=0%2C619%2C3565%2C3116&q=45&auto=format&w=1000&fit=clip"><img alt="Dr. Xuyang Meng collecting a rock sample in Rouyn-Noranda, Que." src="https://images.theconversation.com/files/489928/original/file-20221017-23-zslasf.jpeg?ixlib=rb-1.1.0&rect=0%2C619%2C3565%2C3116&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/489928/original/file-20221017-23-zslasf.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/489928/original/file-20221017-23-zslasf.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/489928/original/file-20221017-23-zslasf.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/489928/original/file-20221017-23-zslasf.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/489928/original/file-20221017-23-zslasf.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/489928/original/file-20221017-23-zslasf.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"></a>
<figcaption>
<span class="caption">The 2750- to 2670-million-year-old granitoid rocks collected from the largest preserved Archean continent may help reveal the origin story of the Earth’s oxygen.</span>
<span class="attribution"><span class="source">(Dylan McKevitt)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Measuring the oxidation-state of these magmatic rocks — formed through the cooling and crystalization of magma or lava — is challenging. <a href="https://www.nationalgeographic.com/science/article/news-earth-rocks-sediment-first-life-zircon">Post-crystallization events may have modified these rocks through later deformation, burial or heating.</a></p>
<p>So, we decided to look at the <a href="https://www.mindat.org/min-29229.html">mineral <em>apatite</em></a> which is present in the <a href="https://www.mindat.org/min-4421.html">zircon crystals</a> in these rocks. Zircon crystals can withstand the intense temperatures and pressures of the post-crystallization events. They retain clues about the environments in which they were originally formed and provide precise ages for the rocks themselves. </p>
<p>Small apatite crystals that are less than 30 microns wide — the size of a human skin cell — are trapped in the zircon crystals. They contain sulfur. By measuring the amount of sulfur in apatite, we can establish whether the apatite grew from an oxidized magma. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/489940/original/file-20221017-11-1mj81z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Map of Canada showing the location of the Superior Province in the east of the country." src="https://images.theconversation.com/files/489940/original/file-20221017-11-1mj81z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/489940/original/file-20221017-11-1mj81z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=511&fit=crop&dpr=1 600w, https://images.theconversation.com/files/489940/original/file-20221017-11-1mj81z.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=511&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/489940/original/file-20221017-11-1mj81z.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=511&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/489940/original/file-20221017-11-1mj81z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=643&fit=crop&dpr=1 754w, https://images.theconversation.com/files/489940/original/file-20221017-11-1mj81z.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=643&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/489940/original/file-20221017-11-1mj81z.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=643&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 Superior Province that stretches from central Manitoba to eastern Quebec in Canada.</span>
<span class="attribution"><span class="source">(Xuyang Meng)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>We were able to successfully measure the <a href="https://doi.org/10.1007/978-3-642-11274-4_4021">oxygen fugacity</a> of the original Archean magma — which is essentially the amount of free oxygen in it — using a specialized technique called X-ray Absorption Near Edge Structure Spectroscopy (<a href="http://www.cei.washington.edu/education/science-of-solar/xray-absorption-near-edge-spectroscopy-xanes/">S-XANES</a>) at the Advanced Photon Source synchrotron at <a href="https://www.anl.gov/">Argonne National Laboratory in Illinois</a>. </p>
<h2>Creating oxygen from water?</h2>
<p>We found that the magma sulfur content, which was initially around zero, increased to 2000 parts per million around 2705 million years. This indicated the magmas had become more sulfur-rich. Additionally, the <a href="https://doi.org/10.1093/petrology/egab079">predominance of S6+ — a type of sulfer ion — in the apatite</a> suggested that the sulfur was from an oxidized source, matching <a href="https://doi.org/10.1016/j.precamres.2021.106104">the data from the host zircon crystals.</a></p>
<p>These new findings indicate that oxidized magmas did form in the Neoarchean era 2.7 billion years ago. The data show that the lack of dissolved oxygen in the Archean ocean reservoirs did not prevent the formation of sulfur-rich, oxidized magmas in the subduction zones. The oxygen in these magmas must have come from another source, and was ultimately released into the atmosphere during volcanic eruptions.</p>
<p>We found that the occurrence of these oxidized magmas correlates with major gold mineralization events in the Superior Province and Yilgarn Craton (Western Australia), demonstrating a connection between these oxygen-rich sources and global world-class ore deposit formation.</p>
<figure class="align-center ">
<img alt="Oxygen" src="https://images.theconversation.com/files/497078/original/file-20221123-16-sl0vkx.jpg?ixlib=rb-1.1.0&rect=40%2C172%2C5422%2C3448&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/497078/original/file-20221123-16-sl0vkx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/497078/original/file-20221123-16-sl0vkx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/497078/original/file-20221123-16-sl0vkx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/497078/original/file-20221123-16-sl0vkx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/497078/original/file-20221123-16-sl0vkx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/497078/original/file-20221123-16-sl0vkx.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">The driving of ocean water deep into the Earth, caused by the sliding of oceanic plates under the Earth’s continental plates, may generate free oxygen as well as the mechanism to release it — volcanoes.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<p>The implications of these oxidized magmas go beyond the understanding of early Earth geodynamics. Previously, it was thought unlikely that Archean magmas could be oxidized, when the <a href="https://doi.org/10.1126/science.1078265">ocean water</a> and <a href="https://doi.org/10.1038/nature25009">ocean floor rocks or sediments</a> were not. </p>
<p>While the exact mechanism is unclear, the occurrence of these magmas suggests that the process of subduction, where ocean water is taken hundreds of kilometres into our planet, generates free oxygen. This then oxidizes the overlying mantle. </p>
<p>Our study shows that Archean subduction could have been a vital, unforeseen factor in the oxygenation of the Earth, the early <a href="https://doi.org/10.1038/ngeo2939">whiffs of oxygen 2.7 billion years ago</a> and also the <a href="https://doi.org/10.1016/B978-0-08-095975-7.01307-3">Great Oxidation Event, which marked an increase in atmospheric oxygen by two per cent 2.45 to 2.32 billion years ago</a>.</p>
<p>As far as we know, the Earth is the only place in the solar system — past or present — with plate tectonics and active subduction. This suggests that this study could partly explain the lack of oxygen and, ultimately, life on the other rocky planets in the future as well.</p><img src="https://counter.theconversation.com/content/191673/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Mole received funding from Canada First Research Excellence Fund (CFREF) and additional federal, provincial, and industry partners as part of the Metal Earth project; a Canadian geoscience research program led by Laurentian University. The $104-million dollar project started in 2016, and is transforming our understanding of the genesis of base and precious metal deposits during Earth’s evolution. This initiative has created a strategic consortium of allied Canadian and international researchers, government, and industry. The Metal Earth grant project # is CFREF-2015-00005. David currently works for Geoscience Australia, who were not involved in this work.</span></em></p><p class="fine-print"><em><span>Adam C. Simon received funding from the U.S. National Science Foundation EAR grants #2214119 and 1924142.</span></em></p><p class="fine-print"><em><span>Xuyang Meng receives funding from Canada First Research Excellence Fund (CFREF-2015-00005), Natural Science Foundation of China, U.S. National Science Foundation EAR, and a doctoral scholarship from China Scholarship Council.</span></em></p>Could tectonic processes in the early Earth have contributed to the rise of oxygen?David Mole, Postdoctoral fellow, Earth Sciences, Laurentian UniversityAdam Charles Simon, Arthur F. Thurnau Professor, Earth & Environmental Sciences, University of MichiganXuyang Meng, Postdoctoral Fellow, Earth and Environmental Sciences, University of MichiganLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1728212021-12-07T08:46:55Z2021-12-07T08:46:55ZHow changing levels of iron shaped the evolution of life on Earth – and why alien hunters should take note<figure><img src="https://images.theconversation.com/files/434722/original/file-20211130-19-ydbxib.jpg?ixlib=rb-1.1.0&rect=120%2C105%2C3375%2C2341&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Early Earth on the left, had seas infused with life-enhancing iron, whereas Earth today, seen on the right, does not.
</span> <span class="attribution"><span class="source">Credit: Image courtesy of Mark A. Garlick / markgarlick.com</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Our red blood is full of iron. We need iron for growth and for immunity. It is even added to foodstuffs, such as cereals, to ensure that <a href="https://www.thetimes.co.uk/article/how-can-i-combat-iron-deficiency-anaemia-rb0cnzgfv">there is enough</a> of this nutrient in the diet to prevent iron deficiency. </p>
<p>However, on a very different scale, during the development of life on planet Earth over billions of years, iron deficiency may have stimulated evolution. According to our new research, <a href="https://doi.org/10.1073/pnas.2109865118">published in the Proceedings of the National Academy of Sciences</a> (PNAS), rising and falling levels of iron on our planet may have enabled complex organisms to evolve from simpler forebears. </p>
<p>The terrestrial planets in our solar system – Mercury, Venus, Earth and Mars – have different amounts of iron in their rocky mantles, the layer below the outermost planetary crust. Mercury’s mantle has the least amount of iron, and Mars’ has the most. This variation is due to differences in distance from the Sun. It is also down to the varying conditions under which the planets initially formed their metallic, iron-rich cores.</p>
<p>The amount of iron in the mantle regulates several planetary processes, including the <a href="https://www.thetimes.co.uk/article/how-can-i-combat-iron-deficiency-anaemia-rb0cnzgfv">retention of surface water</a>. And without water, life as we know it <a href="https://www.youtube.com/watch?v=pTka51ky9TE">cannot exist</a>. Astronomical observations of other solar systems may <a href="https://iopscience.iop.org/article/10.3847/2041-8213/abf7ca">enable estimates</a> of a planet’s mantle iron, helping to narrow the search for planets capable of harbouring life. </p>
<p>As well as contributing to planetary habitability, iron is fundamental for the <a href="https://www.tandfonline.com/doi/pdf/10.3109/15563657108990976">biochemistry that allows life to happen</a>. Iron has a unique combination of properties, including the ability to form chemical bonds in multiple orientations and relative ease of gaining or losing one electron. As a result, iron mediates many biochemical processes in cells, especially by enabling catalysis – a process that speeds up chemical reactions. Metabolic processes <a href="https://www.nature.com/articles/s41586-019-1151-1">that are vital to life</a>, such as DNA synthesis and cellular energy generation, rely on iron.</p>
<p>In our work, we calculated the amount of iron in Earth’s seas over billions of years. We then considered the effect on evolution of enormous amounts of iron falling out of the seas.</p>
<h2>Iron through the ages</h2>
<p>The initial formative events of geochemistry evolving into biochemistry, life, took place more than 4 billion years ago. And there is an consensus that <a href="https://iubmb.onlinelibrary.wiley.com/doi/full/10.1002/iub.1632">iron was a pivotal element</a> for this process. The conditions of early Earth were very different to those now. In particular, there was almost no oxygen in the atmosphere, which meant that iron was easily soluble in water as “ferrous iron” (Fe2+). The abundance of nutritious iron in the Earth’s early seas helped life to evolve. However, this “<a href="https://doi.org/10.1016/j.bbagen.2011.08.002">ferrous paradise</a>” was not to last.</p>
<p>The <a href="https://slate.com/technology/2014/07/the-great-oxygenation-event-the-earths-first-mass-extinction.html">Great Oxygenation Event</a> resulted in the appearance of oxygen in the Earth’s atmosphere. It occurred from around 2.43 billion years ago. This changed the surface of Earth and caused a <a href="https://www.science.org/doi/10.1126/sciadv.1603076">profound loss of soluble iron</a> from the upper ocean and surface waters of the planet. A second, more recent “oxygenation event”, the Neoproterozoic, occurred between 800 to 500 million years ago. This raised oxygen concentrations yet higher. As a consequence of these two events, oxygen combined with iron and gigatons of oxidised, insoluble, “ferric iron” (Fe3+) dropped out of ocean waters, becoming unavailable to most lifeforms.</p>
<figure class="align-center ">
<img alt="Image of the Pilbara region in Western Australia known for the red earth and its vast mineral deposits in iron ore – oxygen and iron atoms bonded together into molecules." src="https://images.theconversation.com/files/435291/original/file-20211202-21-22o85a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/435291/original/file-20211202-21-22o85a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/435291/original/file-20211202-21-22o85a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/435291/original/file-20211202-21-22o85a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/435291/original/file-20211202-21-22o85a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/435291/original/file-20211202-21-22o85a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/435291/original/file-20211202-21-22o85a.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">The Pilbara region in Western Australia is known for the red earth and its vast mineral deposits in iron ore – oxygen and iron atoms bonded together into molecules.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/pilbara-region-western-australia-known-red-1921102964">electra/Shutterstock</a></span>
</figcaption>
</figure>
<p>Life had developed – and maintains – an inescapable dependency on iron. The loss of access to soluble iron had major consequences for the evolution of life on Earth. Behaviour that optimised the acquisition and use of iron would have had a clear selective advantage. We can still see this in genetic analysis of infections today: bacterial variants able to efficiently scavenge iron from their hosts do better than less able competitors over a few short generations. </p>
<p>A key weapon in this battle for iron was the “<a href="https://doi.org/10.1038/%20s41579-019-0284-4">siderophore</a>” – a small molecule produced by many bacteria that captures oxidised iron (Fe3+). Siderophores became spectacularly more useful after oxygenation, enabling organisms to assimilate iron from minerals containing oxidised iron. However, siderophores also helped steal iron from other organisms, including bacteria. This switch in focus, from acquiring iron from the environment to stealing it from other lifeforms, set up a new dynamic of <a href="https://www.pnas.org/content/103/44/16502">competitive interaction</a> between pathogens and their hosts. Thanks to this process, both parties continually evolved to <a href="https://www.science.org/doi/10.1126/science.aaa2468">attack and defend their iron resources</a>. Over millions of years, this powerful competitive drive led to increasingly complex behaviour, resulting in more advanced organisms. </p>
<p>However, other strategies, besides theft, can help deal with the dependency on a sparse nutrient. One such example is symbiotic, cooperative relationships that share resources. Mitochondria are iron-rich, energy-generating machines that were originally bacteria but now <a href="https://doi.org/10.1038/s41564-020-0710-4">reside in our cells</a>. Multiple cells clumping together as complex organisms enable more efficient use of rare nutrients than single-celled organisms, such as bacteria. For example, humans <a href="https://www.sciencedirect.com/science/article/pii/S0092867416317500">recycle 25 times as much iron</a> per day as we take in from our diet. From an iron-biased view, infection, symbiosis and multicellularity provided different but elegant means for lifeforms to counteract the limitation of iron. The need for iron may have shaped evolution - including life as we know it today.</p>
<p>Earth demonstrates the importance of being ironic. The combination of both an early Earth with biologically accessible iron and the subsequent removal of iron during surface oxidation, has provided unique environmental pressures facilitating the evolution of complex life from simpler precursors.</p>
<p>These specific sets of conditions and changes over such long timescales are possibly uncommon on other planets. The likelihood of other advanced lifeforms being found in our cosmic neighbourhood may therefore be low. Yet looking at the iron abundance on other worlds could also help us find such rare worlds.</p><img src="https://counter.theconversation.com/content/172821/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Hal Drakesmith receives funding from Medical Research Council UK and the Bill and Melinda Gates Foundation.</span></em></p><p class="fine-print"><em><span>Jon Wade 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>Life doesn’t just need water and oxygen to thrive, it also needs iron.Hal Drakesmith, Professor of Iron Biology, University of OxfordJon Wade, Associate Professor of Planetary Materials, University of OxfordLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1713912021-11-08T21:58:46Z2021-11-08T21:58:46ZLand ahoy: study shows the first continents bobbed to the surface more than 3 billion years ago<figure><img src="https://images.theconversation.com/files/430723/original/file-20211108-48235-1iw24v8.png?ixlib=rb-1.1.0&rect=10%2C55%2C2446%2C1575&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption"></span> <span class="attribution"><span class="license">Author provided</span></span></figcaption></figure><p>Most people know that the land masses on which we all live represent just 30% of Earth’s surface, and the rest is covered by oceans. </p>
<p>The emergence of the continents was a pivotal moment in the history of life on Earth, not least because they are the humble abode of most humans. But it’s still not clear exactly when these continental landmasses first appeared on Earth, and what tectonic processes built them.</p>
<p>Our research, <a href="https://www.pnas.org/cgi/doi/10.1073/pnas.2105746118">published</a> in Proceedings of the National Academy of Sciences, estimates the age of rocks from the most ancient continental fragments (called cratons) in India, Australia and South Africa. The sand that created these rocks would once have formed some of the world’s first beaches.</p>
<p>We conclude that the first large continents were making their way above sea level around 3 billion years ago – much earlier than the 2.5 billion years estimated by previous research.</p>
<h2>A 3-billion-year-old beach</h2>
<p>When continents rise above the oceans they start to erode. Wind and rain break rocks down into grains of sand, which are transported downstream by rivers and accumulate along coastlines to form beaches. </p>
<p>These processes, which we can observe in action during a trip to the beach today, have been operating for billions of years. By scouring the rock record for signs of ancient beach deposits, geologists can study episodes of continent formation that happened in the distant past.</p>
<p>The Singhbhum craton, an ancient piece of continental crust that makes up the eastern parts of the Indian subcontinent, contains several formations of ancient sandstone. These layers were originally formed from sand deposited in beaches, estuaries and rivers, which was then buried and compressed into rock.</p>
<p>We determined the age of these deposits by studying microscopic grains of a mineral called zircon, which is preserved within these sandstones. This mineral contains tiny amounts of uranium, which very slowly turns into lead via radioactive decay. This allows us to estimate the age of these zircon grains, using a technique called <a href="https://en.wikipedia.org/wiki/Uranium%E2%80%93lead_dating">uranium-lead dating</a>, which is well suited to dating very old rocks.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/430725/original/file-20211108-10108-1cbfduv.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Sandstone and zircon grains" src="https://images.theconversation.com/files/430725/original/file-20211108-10108-1cbfduv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/430725/original/file-20211108-10108-1cbfduv.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=348&fit=crop&dpr=1 600w, https://images.theconversation.com/files/430725/original/file-20211108-10108-1cbfduv.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=348&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/430725/original/file-20211108-10108-1cbfduv.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=348&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/430725/original/file-20211108-10108-1cbfduv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=438&fit=crop&dpr=1 754w, https://images.theconversation.com/files/430725/original/file-20211108-10108-1cbfduv.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=438&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/430725/original/file-20211108-10108-1cbfduv.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=438&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Left: sandstone formations (with ruler for scale); right: microscopic images of zircon grains.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The zircon grains reveal that the Singhbhum sandstones were deposited around 3 billion years ago, making them some of the oldest beach deposits in the world. This also suggests a continental landmass had emerged in what is now India by at least 3 billion years ago. </p>
<p>Interestingly, sedimentary rocks of roughly this age are also present in the oldest cratons of Australia (the Pilbara and Yilgarn cratons) and South Africa (the Kaapvaal Craton), suggesting multiple continental landmasses may have emerged around the globe at this time.</p>
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Read more:
<a href="https://theconversation.com/whats-australia-made-of-geologically-it-depends-on-the-state-youre-in-83575">What's Australia made of? Geologically, it depends on the state you're in</a>
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<h2>Rise above it</h2>
<p>How did rocky continents manage to rise above the oceans? A unique feature of continents is their thick, buoyant crust, which allows them to float on top of Earth’s mantle, just like a cork in water. Like icebergs, the top of continents with thick crust (typically more than 45km thick) sticks out above the water, whereas continental blocks with crusts thinner than about 40km remain submerged.</p>
<p>So if the secret of the continents’ rise is due to their thickness, we need to understand how and why they began to grow thicker in the first place. </p>
<p>Most ancient continents, including the Singhbhum Craton, are made of granites, which formed through the melting of pre-existing rocks at the base of the crust. In our research, we found the granites in the Singhbhum Craton formed at increasingly greater depths between about 3.5 billion and 3 billion years ago, implying the crust was becoming thicker during this time window. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/430727/original/file-20211108-9872-18vgwir.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Granite formation with pen for scale." src="https://images.theconversation.com/files/430727/original/file-20211108-9872-18vgwir.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/430727/original/file-20211108-9872-18vgwir.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=728&fit=crop&dpr=1 600w, https://images.theconversation.com/files/430727/original/file-20211108-9872-18vgwir.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=728&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/430727/original/file-20211108-9872-18vgwir.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=728&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/430727/original/file-20211108-9872-18vgwir.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=914&fit=crop&dpr=1 754w, https://images.theconversation.com/files/430727/original/file-20211108-9872-18vgwir.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=914&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/430727/original/file-20211108-9872-18vgwir.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=914&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Granites are some of the least dense and most buoyant types of rock (pen included for scale).</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Because granites are one of the least dense types of rock, the ancient crust of the Singhbhum Craton would have become progressively more buoyant as it grew thicker. We calculate that by around 3 billion years ago, the continental crust of the Singhbhum Craton had grown to be about 50km thick, making it buoyant enough to begin rising above sea level.</p>
<p>The rise of continents had a profound influence on the climate, atmosphere and oceans of the early Earth. And the erosion of these continents would have provided chemical nutrients to coastal environments in which early photosynthetic life was flourishing, leading to a <a href="https://www.sciencedirect.com/science/article/abs/pii/S0012821X16307117">boom in oxygen production</a> and ultimately helping to create the <a href="https://www.pnas.org/content/118/33/e2107511118">oxygen-rich atmosphere</a> in which we thrive today.</p>
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Read more:
<a href="https://theconversation.com/the-floor-is-lava-after-1-5-billion-years-in-flux-heres-how-a-new-stronger-crust-set-the-stage-for-life-on-earth-151276">The floor is lava: after 1.5 billion years in flux, here's how a new, stronger crust set the stage for life on Earth</a>
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<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/1665652021-08-25T20:05:24Z2021-08-25T20:05:24ZWho were the Toaleans? Ancient woman’s DNA provides first evidence for the origin of a mysterious lost culture<figure><img src="https://images.theconversation.com/files/417306/original/file-20210823-19-1bucpl0.jpg?ixlib=rb-1.1.0&rect=45%2C45%2C7596%2C5030&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Stone arrowheads (Maros points) and other flaked stone implements from the Toalean culture of South Sulawesi.</span> <span class="attribution"><span class="source">Shahna Britton/Andrew Thomson</span>, <span class="license">Author provided</span></span></figcaption></figure><p>In 2015, <a href="https://arkeologi.unhas.ac.id/archeology-department/?lang=en">archaeologists</a> from the University of Hasanuddin in Makassar, on the Indonesian island of Sulawesi, uncovered the skeleton of a woman buried in a limestone cave. Studies revealed the person from Leang Panninge, or “Bat Cave”, was 17 or 18 years old when she died some 7,200 years ago.</p>
<p>Her discoverers dubbed her Bessé’ (pronounced <em>bur-sek</em>¹) — a nickname bestowed on newborn princesses among the <a href="https://www.britannica.com/topic/Bugis">Bugis</a> people who now live in southern Sulawesi. The name denotes the great esteem local archaeologists have for this ancient woman. </p>
<p>She represents the only known skeleton of one of the Toalean people. These enigmatic hunter-gatherers inhabited the island before Neolithic farmers from mainland Asia (“<a href="https://en.wikipedia.org/wiki/Austronesian_peoples">Austronesians</a>”) spread into Indonesia around 3,500 years ago. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/417311/original/file-20210823-27-1xmauxb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/417311/original/file-20210823-27-1xmauxb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/417311/original/file-20210823-27-1xmauxb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/417311/original/file-20210823-27-1xmauxb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/417311/original/file-20210823-27-1xmauxb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/417311/original/file-20210823-27-1xmauxb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/417311/original/file-20210823-27-1xmauxb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/417311/original/file-20210823-27-1xmauxb.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">Burial of a Toalean hunter-gatherer woman dated to 7,200 years ago. Bessé’ was 17-18 years old at time of death. She was buried in a flexed position and several large cobbles were placed on and around her body. Although the skeleton is fragmented, ancient DNA was found preserved in the dense inner ear bone (petrous).</span>
<span class="attribution"><span class="source">University of Hasanuddin</span></span>
</figcaption>
</figure>
<p>Our team <a href="https://protect-au.mimecast.com/s/phV2C6X1LmSr6rk8Yfp2hJb?domain=nature.com">found</a> ancient DNA that survived inside the inner ear bone of Bessé’, furnishing us with the first direct genetic evidence of the Toaleans. This is also the first time ancient human DNA has been reported from Wallacea, the vast group of islands between Borneo and New Guinea, of which Sulawesi is the largest. </p>
<p>Genomic analysis shows Bessé’ belonged to a population with a previously unknown ancestral composition. She shares about half of her genetic makeup with present-day Indigenous Australians and people in New Guinea and the Western Pacific. This includes DNA inherited from the now-extinct <a href="https://www.nationalgeographic.com/science/article/enigmatic-human-relative-outlived-neanderthals">Denisovans</a>, who were distant cousins of Neanderthals. </p>
<p>In fact, relative to other ancient and present-day groups in the region, the proportion of Denisovan DNA in Bessé’ could indicate the main meeting point between our species and Denisovans was in Sulawesi itself (or perhaps a nearby Wallacean island).</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/evolutionary-study-suggests-prehistoric-human-fossils-hiding-in-plain-sight-in-southeast-asia-157587">Evolutionary study suggests prehistoric human fossils 'hiding in plain sight' in Southeast Asia</a>
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<p>The ancestry of this pre-Neolithic woman provides fascinating insight into the little-known population history and genetic diversity of early modern humans in the Wallacean islands — the gateway to the continent of Australia.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/417309/original/file-20210823-19-1oadhuw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/417309/original/file-20210823-19-1oadhuw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/417309/original/file-20210823-19-1oadhuw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=425&fit=crop&dpr=1 600w, https://images.theconversation.com/files/417309/original/file-20210823-19-1oadhuw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=425&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/417309/original/file-20210823-19-1oadhuw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=425&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/417309/original/file-20210823-19-1oadhuw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=534&fit=crop&dpr=1 754w, https://images.theconversation.com/files/417309/original/file-20210823-19-1oadhuw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=534&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/417309/original/file-20210823-19-1oadhuw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=534&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Sulawesi is the largest island in Wallacea, the zone of oceanic islands between the continental regions of Asia and Australia. White shaded areas represent landmasses exposed during periods of lower sea level in the Late Pleistocene. The Wallace Line is a major biogeographical boundary that marks the eastern extent of the distinctive plant and animal worlds of Asia. The Toalean cave site Leang Panninge (where Bessé’ was found) is located in Sulawesi’s southwestern peninsula (see inset panel). Toalean archaeological sites have only been found in a roughly 10,000 km² area of this peninsula, south of Lake Tempe.</span>
<span class="attribution"><span class="source">Kim Newman</span></span>
</figcaption>
</figure>
<h2>Toalean culture</h2>
<p>The archaeological story of the Toaleans began more than a century ago. In 1902, the Swiss naturalists Paul and Fritz Sarasin excavated several caves in the highlands of southern Sulawesi. </p>
<p>Their digs unearthed small, finely crafted stone arrowheads known as <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0251138">Maros points</a>. They also found other distinctive stone implements and tools fashioned from bone, which they attributed to the original inhabitants of Sulawesi — the prehistoric “Toalien” people (now spelled Toalean). </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/417310/original/file-20210823-15-1wn4h00.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/417310/original/file-20210823-15-1wn4h00.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/417310/original/file-20210823-15-1wn4h00.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=737&fit=crop&dpr=1 600w, https://images.theconversation.com/files/417310/original/file-20210823-15-1wn4h00.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=737&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/417310/original/file-20210823-15-1wn4h00.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=737&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/417310/original/file-20210823-15-1wn4h00.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=926&fit=crop&dpr=1 754w, https://images.theconversation.com/files/417310/original/file-20210823-15-1wn4h00.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=926&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/417310/original/file-20210823-15-1wn4h00.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=926&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 Toalean stone arrowhead, known as a Maros point. Classic Maros points are small (roughly 2.5cm in maxiumum dimension) and were fashioned with rows of fine tooth-like serrations along the sides and tip, and wing-like projections at the base. Although this particular stone technology seems to have been unique to the Toalean culture, similar projectile points were produced in northern Australia, Java and Japan.</span>
<span class="attribution"><span class="source">Shahna Britton/Andrew Thomson.</span></span>
</figcaption>
</figure>
<p>Some Toalean cave sites have since been excavated to a higher scientific standard, yet our understanding of this culture is at an early stage. The oldest known Maros points and other Toalean artefacts date to about 8,000 years ago. </p>
<p>Excavated findings from caves suggest the Toaleans were hunter-gatherers who preyed heavily on wild endemic <a href="https://sites.google.com/site/wildpigspecialistgroup/home/Sus-celebensis">warty pigs</a> and harvested edible shellfish from creeks and estuaries. So far, evidence for the group has only been found in one part of southern Sulawesi.</p>
<p>Toalean artefacts disappear from the archaeological record by the fifth century AD — a few thousand years after the first Neolithic settlements emerged on the island. </p>
<p>Prehistorians have long sought to determine who the Toaleans were, but efforts have been impeded by a lack of securely-dated human remains. This all changed with the discovery of Bessé’ and the ancient DNA in her bones.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/417312/original/file-20210823-19-1thz0l0.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/417312/original/file-20210823-19-1thz0l0.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/417312/original/file-20210823-19-1thz0l0.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/417312/original/file-20210823-19-1thz0l0.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/417312/original/file-20210823-19-1thz0l0.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/417312/original/file-20210823-19-1thz0l0.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/417312/original/file-20210823-19-1thz0l0.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/417312/original/file-20210823-19-1thz0l0.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">Toalean stone arrowheads (Maros points), backed microliths (small stone implements that may have been hafted as barbs) and bone projectile points. These artefacts are from Indonesian collections curated in Makassar and mostly comprise undated specimens collected from the ground surface at archaeological sites.</span>
<span class="attribution"><span class="source">Basran Burhan</span></span>
</figcaption>
</figure>
<h2>The ancestral story of Bessé’</h2>
<p>Our results mean we can now confirm existing presumptions the Toaleans were related to the first modern humans to enter Wallacea some <a href="https://theconversation.com/buried-tools-and-pigments-tell-a-new-history-of-humans-in-australia-for-65-000-years-81021">65,000 years ago</a> or more. These seafaring hunter-gatherers were the ancestors of Aboriginal Australians and Papuans. </p>
<p>They were also the earliest inhabitants of Sahul, the supercontinent that emerged during the Pleistocene (ice age) when global sea levels fell, exposing a land bridge between Australia and New Guinea. To reach Sahul, these pioneering humans made ocean crossings through Wallacea, but little about their journeys is known. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/island-hopping-study-shows-the-most-likely-route-the-first-people-took-to-australia-93120">Island-hopping study shows the most likely route the first people took to Australia</a>
</strong>
</em>
</p>
<hr>
<p>It is conceivable the ancestors of Bessé’ were among the first people to reach Wallacea. Instead of island-hopping to Sahul, however, they remained in Sulawesi.</p>
<p>But our analyses also revealed a deep ancestral signature from an early modern human population that originated somewhere in continental Asia. These ancestors of Bessé’ did not intermix with the forebears of Aboriginal Australians and Papuans, suggesting they may have entered the region after the initial peopling of Sahul — but long before the Austronesian expansion. </p>
<p>Who were these people? When did they arrive in the region and how widespread were they? It’s unlikely we will have answers to these questions until we have more ancient human DNA samples and pre-Neolithic fossils from Wallacea. This unexpected finding shows us how little we know about the early human story in our region.</p>
<h2>A new look at the Toaleans</h2>
<p>With funds awarded by the Australian Research Council’s Discovery <a href="https://www.arc.gov.au/grants/discovery-program/discovery-projects">program</a> we are initiating a new project that will explore the Toalean world in greater detail. Through archaeological excavations at Leang Panninge we hope to learn more about the development of this unique hunter-gatherer culture. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/417313/original/file-20210823-21-1y8qu2m.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/417313/original/file-20210823-21-1y8qu2m.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/417313/original/file-20210823-21-1y8qu2m.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/417313/original/file-20210823-21-1y8qu2m.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/417313/original/file-20210823-21-1y8qu2m.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/417313/original/file-20210823-21-1y8qu2m.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/417313/original/file-20210823-21-1y8qu2m.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/417313/original/file-20210823-21-1y8qu2m.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">Excavations at Leang Panninge cave, Mallawa, South Sulawesi.</span>
<span class="attribution"><span class="source">Leang Panninge Research Team.</span></span>
</figcaption>
</figure>
<p>We also wish to address longstanding questions about Toalean social organisation and ways of life. For example, some scholars have inferred the Toaleans became so populous that these hitherto small and scattered groups of foragers began to settle down in large sedentary communities, and possibly even domesticated wild pigs.</p>
<p>It has also recently been <a href="https://www.sciencedirect.com/science/article/abs/pii/S2352409X16300694">speculated</a> Toaleans were the mysterious Asian seafarers who visited Australia in ancient times, introducing the dingo (or more accurately, the domesticated ancestor of this now-wild canid). There is clearly much left to uncover about the long island story of Bessé’ and her kin. </p>
<hr>
<p>¹<em>The “bur” syllable is pronounced as in the English word “bursary”. The “k” is essentially a strangulated stop in the throat, akin to the “t” in the Cockney “bo'ol”, for bottle. (With thanks to Professor Campbell Macknight).</em></p><img src="https://counter.theconversation.com/content/166565/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Adam Brumm receives funding from the Australian Research Council.</span></em></p><p class="fine-print"><em><span>Adhi Agus Oktaviana is a PhD candidate in Place, Evolution and Rock Art Heritage Unit, Griffith University, Australia. </span></em></p><p class="fine-print"><em><span>Akin Duli receives funding from Universitas Hasanuddin and Universiti Sains Malaysia. He is affiliated with Archaeology Department, Universitas Hasanuddin. </span></em></p><p class="fine-print"><em><span>Basran Burhan is a PhD student at Griffith University</span></em></p><p class="fine-print"><em><span>Selina Carlhoff receives funding from the European Research Council and the Max Planck Society. </span></em></p><p class="fine-print"><em><span>Cosimo Posth 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>The first ancient human DNA from the Indonesian island of Sulawesi — and the wider Wallacea islands group — sheds light on the early human history of the region.Adam Brumm, Professor, Griffith UniversityAdhi Oktaviana, PhD Candidate, Griffith UniversityAkin Duli, Professor, Universitas HasanuddinBasran Burhan, PhD candidate, Griffith UniversityCosimo Posth, Junior Professor, University of TübingenSelina Carlhoff, Max Planck Institute of GeoanthropologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1568452021-03-31T18:59:31Z2021-03-31T18:59:31ZJust add (mantle) water: new research cracks the mystery of how the first continents formed<figure><img src="https://images.theconversation.com/files/389406/original/file-20210314-24-1f4b7uk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption"></span> <span class="attribution"><span class="license">Author provided</span></span></figcaption></figure><p>Earth is an amazing planet. As far as we know, it’s the only planet in the universe where life exists. It’s also the only planet known to have continents: the land masses on which we live and which host the minerals needed to support our complex lives. </p>
<p>Experts still vigorously debate how the continents formed. We do know water was an essential ingredient for this — and many geologists have proposed this water would have come from Earth’s surface via subduction zones (as is the case now). </p>
<p>But <a href="http://doi.org/10.1038/s41586-021-03337-1">our new research</a> shows this water would have actually come from deep within the planet. This suggests Earth in its youth behaved very differently to how it does today, containing more primordial water than previously thought. </p>
<h2>How to grow a continent</h2>
<p>The solid Earth is comprised of a series of layers including a dense iron-rich core, thick mantle and a rocky outer layer called the lithosphere.</p>
<p>But it wasn’t always this way. When Earth first formed about 4.5 billion years ago, it was a ball of molten rock that was regularly pummelled by meteorites. </p>
<p>As it cooled over a period of a billion years or so, the first continents began to emerge, made of pale-coloured <a href="https://geology.com/rocks/granite.shtml">granite</a>. Exactly how they came to be has long intrigued scientists. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/392176/original/file-20210329-17-1suspmd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Earth's crust diagram" src="https://images.theconversation.com/files/392176/original/file-20210329-17-1suspmd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/392176/original/file-20210329-17-1suspmd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/392176/original/file-20210329-17-1suspmd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/392176/original/file-20210329-17-1suspmd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/392176/original/file-20210329-17-1suspmd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/392176/original/file-20210329-17-1suspmd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/392176/original/file-20210329-17-1suspmd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=377&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Earth comprises a core, mantle and outer crust.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>To make granitic continental crust capable of floating, dark volcanic rocks known as <a href="https://geology.com/rocks/basalt.shtml">basalts</a> have to be melted. Basalts, which are formed as a result of melting in the mantle, would have covered Earth when the planet was starting out.</p>
<p>However, to make continental crust from basalt requires another essential ingredient: water. Knowing how this water got into the rocks at enough depth is key to understanding how the first continents formed. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/earth-has-stayed-habitable-for-billions-of-years-exactly-how-lucky-did-we-get-153416">Earth has stayed habitable for billions of years – exactly how lucky did we get?</a>
</strong>
</em>
</p>
<hr>
<p>One mechanism of taking water to depth is through subduction. This is how most new continental crust is produced today, including the Andes mountain range in South America. </p>
<p>In subduction zones, rocky plates at the bottom of the ocean chill and become increasingly dense until they’re forced under the continents and back into the mantle below, taking ocean water with them.</p>
<p>When this water interacts with basalt in the mantle, it creates granitic crust. But Earth was much hotter billions of years ago, so many experts have argued subduction (at least in the form we currently understand) <a href="https://www.nature.com/articles/nature21383">couldn’t have operated</a>. </p>
<p>Long linear mountain belts such as the Andes contrast starkly with the structure of the granitic crust preserved in the Pilbara region of outback Western Australia. </p>
<p>This ancient crust viewed from above has a “dome-and-keel” pattern, with balloons (domes) of pale-coloured granite rising into the surrounding darker and denser basalts (the keels). </p>
<figure class="align-center ">
<img alt="Pilbara Craton Western Australia" src="https://images.theconversation.com/files/389401/original/file-20210314-15-1ac0r0o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/389401/original/file-20210314-15-1ac0r0o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=430&fit=crop&dpr=1 600w, https://images.theconversation.com/files/389401/original/file-20210314-15-1ac0r0o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=430&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/389401/original/file-20210314-15-1ac0r0o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=430&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/389401/original/file-20210314-15-1ac0r0o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=540&fit=crop&dpr=1 754w, https://images.theconversation.com/files/389401/original/file-20210314-15-1ac0r0o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=540&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/389401/original/file-20210314-15-1ac0r0o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=540&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Satellite images of the Pilbara Craton, Western Australia. Pale-coloured granite domes are surrounded by dark-coloured basalts.</span>
<span class="attribution"><span class="source">Google Earth</span></span>
</figcaption>
</figure>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/390272/original/file-20210318-21-1ipkljp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Dome-and-keel structure" src="https://images.theconversation.com/files/390272/original/file-20210318-21-1ipkljp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/390272/original/file-20210318-21-1ipkljp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=291&fit=crop&dpr=1 600w, https://images.theconversation.com/files/390272/original/file-20210318-21-1ipkljp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=291&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/390272/original/file-20210318-21-1ipkljp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=291&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/390272/original/file-20210318-21-1ipkljp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=366&fit=crop&dpr=1 754w, https://images.theconversation.com/files/390272/original/file-20210318-21-1ipkljp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=366&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/390272/original/file-20210318-21-1ipkljp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=366&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A very simplified cross section of a dome-and-keel structure.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Dome_and_Keel_Structure.pdf">Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>But where did the water needed to produce these domes come from? </p>
<h2>Tiny crystals record Earth’s early history</h2>
<p><a href="http://doi.org/10.1038/s41586-021-03337-1">Our research</a>, led by scientists at the Geological Survey of Western Australia and Curtin University, addressed this question. We analysed tiny crystals trapped in the ancient magmas that cooled and solidified to form the Pilbara’s granite domes.</p>
<p>These crystals, made of a mineral called zircon, contain uranium which <a href="https://en.wikipedia.org/wiki/Uranium%E2%80%93lead_dating">turns into lead over time</a>. We know the rate of this change, and can measure the amounts of uranium and lead contained within. As such, we can obtain a record of their age.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/389402/original/file-20210314-16-og11ln.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Zircon" src="https://images.theconversation.com/files/389402/original/file-20210314-16-og11ln.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/389402/original/file-20210314-16-og11ln.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=360&fit=crop&dpr=1 600w, https://images.theconversation.com/files/389402/original/file-20210314-16-og11ln.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=360&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/389402/original/file-20210314-16-og11ln.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=360&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/389402/original/file-20210314-16-og11ln.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=452&fit=crop&dpr=1 754w, https://images.theconversation.com/files/389402/original/file-20210314-16-og11ln.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=452&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/389402/original/file-20210314-16-og11ln.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=452&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Zircon crystals grown in an ancient magma.</span>
</figcaption>
</figure>
<p>The crystals also contain clues to their origin, which can be unravelled by measuring their oxygen isotope composition. Importantly, zircons that crystallised in molten rocks hydrated by water from Earth’s surface have different compositions to zircons that formed deep in the mantle. </p>
<p>Measurements show the water required for the most primitive ancient WA granites would have come from deep within Earth’s mantle and not from the surface.</p>
<figure class="align-center ">
<img alt="Ion microprobe used for dating zircon" src="https://images.theconversation.com/files/389001/original/file-20210311-23-d4hrrn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/389001/original/file-20210311-23-d4hrrn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/389001/original/file-20210311-23-d4hrrn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/389001/original/file-20210311-23-d4hrrn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/389001/original/file-20210311-23-d4hrrn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/389001/original/file-20210311-23-d4hrrn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/389001/original/file-20210311-23-d4hrrn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Chris Kirkland (left) and Tim Johnson loading samples into a secondary-ion mass spectrometer, which shoots a beam of ions into zircon crystals to determine their age and oxygen isotope composition.</span>
</figcaption>
</figure>
<h2>Is the present always the key to the past?</h2>
<p>How the first continents formed is part of a broader debate regarding one of the central tenets of the physical sciences: <a href="https://www.nps.gov/articles/geologic-principles-uniformitarianism.htm">uniformitarianism</a>. This is the idea that the processes which operated on Earth in the distant past are the same as those observed today. </p>
<p>Earth today loses heat through plate tectonics, when the ridged lithospheric plates that form the planet’s solid, outer shell move around. This helps regulate its internal temperature, stabilises atmospheric composition, and probably also facilitated the <a href="https://theconversation.com/does-a-planet-need-plate-tectonics-to-develop-life-61303">development of complex life</a>. </p>
<p>Subduction is one of the most important components of this process. But <a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/ter.12378">several lines of evidence</a> are inconsistent with subduction and plate tectonics on an early Earth. They indicate strongly that our planet behaved very differently in the first two billion years following its formation than it does today.</p>
<p>So while uniformitarianism is a useful way to think about many geological processes, the present may not always be the key to the past.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/does-a-planet-need-plate-tectonics-to-develop-life-61303">Does a planet need plate tectonics to develop life?</a>
</strong>
</em>
</p>
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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.