tag:theconversation.com,2011:/ca/topics/earths-core-7486/articlesEarth's core – The Conversation2023-11-10T13:28:44Ztag:theconversation.com,2011:article/2170312023-11-10T13:28:44Z2023-11-10T13:28:44ZIs some of the body that collided with Earth to form the Moon still recognisable inside our planet?<p>Scientists have dated <a href="https://www.science.org/doi/10.1126/science.1253338">the birth of the Solar System</a> to about 4.57 billion years ago. About 60 million years later <a href="https://theconversation.com/how-old-is-our-moon-71036">a “giant impact”</a> collision between the infant Earth and a Mars-sized body called Theia created the Moon. </p>
<p>Now, <a href="https://www.nature.com/articles/s41586-023-06589-1">new research</a> suggests that the remains of the large object that collided with the young Earth to form the Moon are still identifiable deep within the planet as two large lumps. These lumps make up about 8% of the volume <a href="https://education.nationalgeographic.org/resource/mantle/">of the Earth’s mantle</a>, which is the rocky zone between the Earth’s iron core and its crust.</p>
<p>The new study, led by Qian Yuan of Arizona State University and Caltech, argues that the heat generated by this collision was not enough to melt the whole of the Earth’s mantle, so the innermost mantle remained solid. </p>
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<figcaption><span class="caption">A high resolution computer simulation of Theia colliding with the Earth to form the Moon.</span></figcaption>
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<p>Consequently, the researchers say, the melted mantle of Theia didn’t completely mix with Earth’s mantle. That would have made the Theia remnants indistinguishable from Earth’s mantle as a whole. Instead, a lot of Theia’s mantle ended up as two continent-sized lumps that now sit on top of the Earth’s core-mantle boundary.</p>
<h2>Large low-velocity provinces</h2>
<p>Yuan argues that these lumps correspond to, and can explain, the existence of the two <a href="https://www.nature.com/articles/s41467-021-22185-1">large low-velocity provinces</a> (LLVPs), that were discovered decades ago: one below the Pacific and another below Africa and the eastern Atlantic. </p>
<p>This discovery was thanks to the observation that the vibrations emanating from earthquakes, known as seismic waves, travel through these regions slightly more slowly than through “normal” lower mantle.</p>
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<img alt="" src="https://images.theconversation.com/files/557774/original/file-20231106-15-xc9gun.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/557774/original/file-20231106-15-xc9gun.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=425&fit=crop&dpr=1 600w, https://images.theconversation.com/files/557774/original/file-20231106-15-xc9gun.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=425&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/557774/original/file-20231106-15-xc9gun.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=425&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/557774/original/file-20231106-15-xc9gun.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=534&fit=crop&dpr=1 754w, https://images.theconversation.com/files/557774/original/file-20231106-15-xc9gun.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=534&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/557774/original/file-20231106-15-xc9gun.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">
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<span class="caption">The Earth’s internal layers.</span>
<span class="attribution"><span class="source">NASA (Adapted from Goddard Media Studios)</span></span>
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<p>Previous explanations of the LLVPs include that each is a deep accumulation of <a href="https://www.usgs.gov/news/science-snippet/earthword-subduction">subducted oceanic plates</a> (where plate tectonics has dragged the ocean floor down beneath a continent). Or that they are a place where anomalously hot lower mantle is beginning to rise as a “<a href="https://www.britannica.com/science/superplume">superplume</a>” (huge jets of partially molten rock). </p>
<p>However, neither of those models can account for a peculiar enrichment in volatile elements such as helium and xenon in lava that has erupted at oceanic islands above LLVPs. Yuan argues these are “fingerprints” of Theia’s growth within the <a href="https://www.jpl.nasa.gov/news/mysteries-of-the-solar-nebula">gas and dust</a> surrounding the young Sun before it collided with Earth. </p>
<h2>Melting or not melting the whole mantle?</h2>
<p>Computer models run by Yuan’s team suggest that the giant impact that formed the Moon would have not delivered enough energy to melt the whole of the Earth’s mantle. Instead, the melted remains of Theia’s mantle, which was slightly richer in iron (making it denser than Earth’s mantle) ended up at the base of the temporary magma ocean created by the collision. </p>
<p>Later, after the magma ocean had solidified, the Theia material was drawn into the lower part of Earth’s mantle by <a href="https://en.wikipedia.org/wiki/Mantle_convection">convection currents</a>, which flow at rates of centimetres per year even within the solid mantle.</p>
<p>It may have taken billions of years for these convection currents to heap up the Theia material into the LLVPs that we see today. Even if this is true, they should not be thought of as vast chunks of Theia’s mantle that survived the impact. Rather, they are made of initially dispersed Theia mantle material that has been gathered up again.</p>
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<figcaption><span class="caption">Caltech’s Qian Yuan explains by means of computer simulations.</span></figcaption>
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<h2>Is it true?</h2>
<p>Most scientists will take a lot of convincing when it comes to this theory. Yuan predicts that if his hypothesis is correct, samples of the Moon’s mantle, collected by <a href="https://www.nasa.gov/specials/artemis/">future missions</a>, will match the geochemical fingerprints found in volcanic rock from the LLVPs. I think that that proof will be a long time coming. </p>
<p>I also note that Yuan’s modelling seems to be silent on the fate of Theia’s core. Scientists usually assume Theia’s core merged with Earth’s core in the <a href="https://www.nasa.gov/solar-system/collision-may-have-formed-the-moon-in-mere-hours-simulations-reveal">hours after the collision</a>. </p>
<p>It is not clear how that could have happened if the lower part of Earth’s mantle remained solid. On the other hand, Theia’s impact happened so soon after the Earth itself was formed (probably by a series of separate collisions) that the Earth’s interior could still have been hot and molten in the aftermath of those events.</p>
<p>The implications of Yuan’s model are worth thinking about. For one thing, would the slow heaping up of Theia mantle material into the LLVPs have had any effect of on the pattern of plate tectonics high above? Possibly we would not have had an Atlantic ocean today had Theia not slammed into the proto-Earth four and a half billion years ago. </p>
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<a href="https://theconversation.com/how-the-moon-formed-new-research-133204">How the moon formed – new research</a>
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<p class="fine-print"><em><span>David Rothery is co-leader of the European Space Agency's Mercury Surface and Composition Working Group, and a Co-Investigator on MIXS (Mercury Imaging X-ray Spectrometer) that is now on its way to Mercury on board the European Space Agency's Mercury orbiter BepiColombo. He has received funding from the UK Space Agency and the Science & Technology Facilities Council for work related to Mercury and BepiColombo, and from the European Commission under its Horizon 2020 programme for work on planetary geological mapping. He is author of Planet Mercury - from Pale Pink Dot to Dynamic World, Moons: A Very Short Introduction and Planets: A Very Short Introduction. </span></em></p>The Moon was formed when it collided with Earth billions of years ago.David Rothery, Professor of Planetary Geosciences, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2149172023-11-02T12:33:11Z2023-11-02T12:33:11ZNASA’s robotic prospectors are helping scientists understand what asteroids are made of – setting the stage for miners to follow someday<figure><img src="https://images.theconversation.com/files/557153/original/file-20231101-25-cep1ng.jpg?ixlib=rb-1.1.0&rect=11%2C5%2C3982%2C2233&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Mining an asteroid probably won't look exactly like mining does on Earth, but some principles will stay the same. </span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/mining-and-extraction-of-raw-materials-on-the-royalty-free-image/1433072451?phrase=asteroid+mining&adppopup=true">posteriori/iStock via Getty Images</a></span></figcaption></figure><p>The cars, cellphones, computers and televisions that people in the U.S. use every day require metals like copper, cobalt and platinum to build. Demand from the electronics industry for these metals is only rising, and companies are constantly searching for new places on Earth to mine them.</p>
<p>Scientists estimate that lots of these metals exist thousands of miles beneath Earth’s surface, in its molten core, but that’s far <a href="https://www.youtube.com/watch?v=NXFBJr8XRlQ">too deep and hot to mine</a>. Instead, some companies hope to one day search for deposits that are literally out of this world — on asteroids.</p>
<p>The commercialization of asteroid mining is still a ways off, but in October 2023, NASA launched a scientific mission to explore the <a href="https://science.nasa.gov/mission/psyche">metal-rich asteroid Psyche</a>. The <a href="https://theconversation.com/nasas-psyche-mission-to-a-metal-world-may-reveal-the-mysteries-of-earths-interior-206913">main goal of the mission</a> is studying the composition and structure of this asteroid, which could tell scientists more about Earth’s core since the two objects might have a similar makeup. </p>
<p>Both likely contain platinum, nickel, iron and possibly even gold – materials of commercial interest.</p>
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<figcaption><span class="caption">Experts need to know what’s out there on asteroids before considering whether they’re worth mining. NASA’s Psyche mission could answer some of these questions.</span></figcaption>
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<p><a href="https://valeriepayre.weebly.com/">I am a planetary geologist</a> whose work explores other planets and astronomical objects like Mars, Venus and the Moon. I will be following the Psyche mission closely, as this is the first time that scientists will be able to learn about the composition and structure of <a href="https://www.jpl.nasa.gov/missions/psyche">a possible piece of a planetary core similar to the Earth’s</a>, without indirect seismic or magnetic measurements, or replicating the pressure and temperature conditions of the Earth’s core in our labs. </p>
<p>With the spacecraft estimated to arrive at the asteroid’s orbit in 2029, the findings from the Psyche mission will provide unique insights into the type of metals present on the asteroid’s surface, as well as their amount, and the minerals containing these metals. This data is essential both for scientists like me exploring the formation and evolution planetary bodies, as well as for companies investigating the possibility of asteroid mining.</p>
<h2>Asteroid formation</h2>
<p>Asteroids come in a <a href="https://science.nasa.gov/solar-system/asteroids/facts/">variety of sizes</a>. Some are the size of a town, while others are the size of a state. Most asteroids are made of rocks and represent the leftovers from the early <a href="https://science.nasa.gov/solar-system/facts/">formation of our solar system</a> around 4.6 billion years ago.</p>
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<a href="https://images.theconversation.com/files/554412/original/file-20231017-29-nm2shd.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An artist's illustration of a gray asteroid with some yellow-ish surfaces, and two large circular craters." src="https://images.theconversation.com/files/554412/original/file-20231017-29-nm2shd.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/554412/original/file-20231017-29-nm2shd.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=533&fit=crop&dpr=1 600w, https://images.theconversation.com/files/554412/original/file-20231017-29-nm2shd.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=533&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/554412/original/file-20231017-29-nm2shd.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=533&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/554412/original/file-20231017-29-nm2shd.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=670&fit=crop&dpr=1 754w, https://images.theconversation.com/files/554412/original/file-20231017-29-nm2shd.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=670&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/554412/original/file-20231017-29-nm2shd.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=670&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">The Psyche asteroid.</span>
<span class="attribution"><a class="source" href="https://science.nasa.gov/solar-system/asteroids/16-psyche/">NASA/JPL-Caltech/ASU</a></span>
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<p>Not every asteroid is the same – some, like Bennu, the target of <a href="https://science.nasa.gov/mission/osiris-rex/">NASA’s OSIRIS-REx mission</a>, are rich in carbon. These are very old, and they will teach scientists more about how planets formed and how life may have begun on Earth. </p>
<p><a href="https://theconversation.com/nasas-psyche-mission-to-a-metal-world-may-reveal-the-mysteries-of-earths-interior-206913">Others, like Psyche</a>, are made of metals and potentially result from one or more collisions between astronomical objects when the solar system was forming. These collisions left debris flying through space — including potential pieces of a planet’s metal-rich core. A NASA spacecraft will orbit and analyze the surface of Psyche.</p>
<h2>Mining in space</h2>
<p>Not every mineral deposit on Earth is mineable. Companies first look for deposits with a <a href="https://www.americangeosciences.org/critical-issues/faq/what-happens-during-and-after-mining">high level of metal purity</a>. They also investigate how affordable and feasible extracting the metal would be before choosing where to mine. </p>
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<span class="caption">Before mining, companies think about whether a deposit will yield enough metal. The same principle applies to asteroid mining.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/aerial-image-directly-above-an-industrial-machine-royalty-free-image/1443957870?phrase=mine&adppopup=true">Abstract Aerial Art/DigitalVision via Getty Images</a></span>
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<p>Similarly, before mining an asteroid, companies will have to think about all those factors, and they’ll have to come up with the infrastructure needed to mine at a distance and transport the metals they mine hundreds of millions of miles back to Earth. The technology to do that is still years away, and transporting metals would require major funding.</p>
<p>A <a href="https://builtin.com/aerospace/top-space-mining-companies">few companies</a> around the world have already started to think about what the best and lowest cost approach would be, drawing from processes similar to those used on Earth. </p>
<p>The first step would be <a href="https://doi.org/10.1007/978-3-319-90303-3_6">finding a mineable metal deposit</a>. Next, they’d drill and <a href="https://www.hou.usra.edu/meetings/acm2023/pdf/2492.pdf?ref=karmanplus.com">extract the metals on the asteroid</a>. One of the most important differences with Earth mines is that each step would be undertaken remotely with spacecrafts orbiting around the asteroid and robots landing on its surface. Then, a spacecraft would send the resulting materials back to Earth. </p>
<p>Asteroid mining plans are still at their earliest stages. A few companies like <a href="https://spacenews.com/asteroid-mining-company-planetary-resources-acquired-by-blockchain-firm/">Planetary Resources</a> and <a href="https://spacenews.com/deep-space-industries-acquired-by-bradford-space/">Deep Space Industries</a>, with goals to extract metals from space, were acquired by other companies. </p>
<p>Experts can’t quite tell yet how acquiring valuable metals from asteroids would affect the global economy, but these metals could potentially flood the market and <a href="https://hir.harvard.edu/economics-of-the-stars/">lower their values</a>.</p>
<p>The Psyche mission is a huge step in figuring out what sort of metals are out there, and it may also answer questions about the composition and properties of Earth’s core.</p><img src="https://counter.theconversation.com/content/214917/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Valerie Payré does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Upcoming NASA missions will help scientists understand the composition of asteroids – which could inform companies one day hoping to commercially mine asteroids.Valerie Payré, Assistant Professor of Earth and Environmental Sciences, University of IowaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2157072023-10-17T19:08:01Z2023-10-17T19:08:01ZNASA’s Psyche asteroid mission: a 3.6 billion kilometre ‘journey to the centre of the Earth’<figure><img src="https://images.theconversation.com/files/554157/original/file-20231017-17-gr95ww.jpg?ixlib=rb-1.1.0&rect=11%2C41%2C3982%2C3652&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/catalog/PIA24471">NASA / JPL-Caltech / ASU</a></span></figcaption></figure><p>Psyche was the Greek goddess of the soul, born a mere mortal and later married to Eros, the God of love. Who knows why the Italian astronomer Annibale de Gasparis gave her name to a celestial object he observed one night in 1852?</p>
<p>Psyche was only the 16th “asteroid” ever discovered: inhabitants of the Solar System that were neither the familiar planets nor the occasional visitors known as comets. Today we know the asteroid belt between the orbits of Mars and Jupiter contains millions of space rocks, ranging in size from the dwarf planet Ceres down to tiny pebbles and grains of dust.</p>
<p>Among all these, Psyche is still special. With an average diameter of around 226km, the potato-shaped planetoid is the largest “M-type” asteroid, made largely of iron and nickel, much like Earth’s core. </p>
<p>Last week NASA <a href="https://www.jpl.nasa.gov/missions/psyche">launched a spacecraft to rendezvous with Psyche</a>. The mission will take a six-year, 3.6 billion kilometre journey to gather clues that Earth scientists like me will interrogate for information about the inaccessible interior of our own world. </p>
<h2>Natural laboratories</h2>
<p>M-type asteroids like Psyche are thought to be the remnants of planets destroyed in the early years of the Solar System. In these asteroids, heavier elements (like metals) sank toward the centre and lighter elements floated up to the outer layers. Then, due to collisions with other objects, the outer layers were torn away and most of the material was ejected into space, leaving behind the metal-rich core.</p>
<p>These metallic worlds are perfect “natural laboratories” for studying planetary cores.</p>
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Read more:
<a href="https://theconversation.com/nasas-psyche-mission-is-set-for-launch-heres-how-it-could-unveil-the-interior-secrets-of-planets-215547">Nasa's Psyche mission is set for launch – here's how it could unveil the interior secrets of planets</a>
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<p>Our current methods for studying Earth’s core are quite indirect. We sometimes get tiny glimpses into the Solar System’s early history – and hence our planet’s own history – from metallic meteorites, parts of asteroids that fall to Earth. However, this view is very limited.</p>
<p>Another way to study the core is using seismology: studying how the vibrations caused by earthquakes travel through the planet’s interior, in much the same way doctors can use ultrasound to see the inside of our bodies.</p>
<p>However, on Earth we have fewer seismographs in the oceans and in the Southern Hemisphere, which restrict what we can see of the core.</p>
<p>What’s more, the core is buried beneath the planet’s outer layers, which obscure our view even further. It is like looking at a distant object through an imperfect lens.</p>
<p>As well as seismology, we learn about the core through lab experiments attempting to recreate the high pressures and temperatures of Earth’s interior.</p>
<p>We take the observations from seismology and lab experiments and try to explain them using computer simulations. In <a href="https://www.nature.com/articles/s41467-023-41725-5">a recent paper in Nature Communications</a>, we discussed the current challenges in studying Earth’s core – and the ways forward.</p>
<h2>What the Psyche mission hopes to discover</h2>
<p>We can think of NASA’s mission to Psyche as a journey to the centre of Earth without having to travel down through the planet’s rocky crust, the slowly moving mantle and the liquid core.</p>
<p>The mission aims to find out whether Psyche really is the core of a destroyed planet, that was initially hot and molten but slowly cooled and solidified like the core of our planet. On the other hand it’s possible Psyche is made of material that was never melted at all.</p>
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Read more:
<a href="https://theconversation.com/what-are-asteroids-made-of-a-sample-returned-to-earth-reveals-the-solar-systems-building-blocks-176548">What are asteroids made of? A sample returned to Earth reveals the Solar System's building blocks</a>
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<p>NASA also wants to discover how old Psyche’s surface is, which would reveal how long ago it lost its outer layers. The mission will also investigate the asteroid’s chemical composition: whether it contains lighter elements alongside iron and nickel, such as oxygen, hydrogen, carbon, silicon and sulphur. The presence or absence of these could give us clues about our own planet’s evolution.</p>
<p>Information about Psyche’s shape, mass, and gravity distribution will also be gathered. Also, the potential for future mineral exploration should be studied.</p>
<p>All of this will be possible with the broad-spectrum cameras, spectrometers, magnetometers, gravimeters and other instruments the spacecraft carries. Scientists like me will follow with impatience the mission’s long journey through space.</p><img src="https://counter.theconversation.com/content/215707/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Hrvoje Tkalčić receives funding from the Australian Research Council. </span></em></p>A distant lump of space rock may have a surprising amount in common with the core of our own planet.Hrvoje Tkalčić, Professor, Head of Geophysics, Director of Warramunga Array, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2069132023-08-17T12:34:23Z2023-08-17T12:34:23ZNASA’s Psyche mission to a metal world may reveal the mysteries of Earth’s interior<figure><img src="https://images.theconversation.com/files/539847/original/file-20230727-19-gbh5t6.jpg?ixlib=rb-1.1.0&rect=5%2C11%2C3982%2C2646&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An illustration of the asteroid Psyche, orbiting between Mars and Jupiter.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/psyche-asteroid-in-space-royalty-free-image/1286927980?phrase=Psyche&adppopup=true">24K-Production/iStock via Getty Images Plus</a></span></figcaption></figure><p>French novelist Jules Verne delighted 19th-century readers with the tantalizing notion that a <a href="https://etc.usf.edu/lit2go/222/the-journey-to-the-center-of-the-earth/">journey to the center of the Earth</a> was actually plausible. </p>
<p>Since then, scientists have long acknowledged that Verne’s literary journey was only science fiction. The extreme temperatures of the Earth’s interior – around 10,000 degrees Fahrenheit (5,537 Celsius) at the core – and the accompanying crushing pressure, which is millions of times more than at the surface, <a href="https://www.youtube.com/watch?v=NXFBJr8XRlQ">prevent people from venturing down very far</a>. </p>
<p>Still, there are a few things <a href="https://education.nationalgeographic.org/resource/core/">known about the Earth’s interior</a>. For example, geophysicists discovered that the core consists of a solid sphere of iron and nickel that comprises 20% of the Earth’s radius, surrounded by a shell of molten iron and nickel that spans an additional 15% of Earth’s radius.</p>
<p>That, and the rest of our knowledge about our world’s interior, was learned indirectly – either by studying <a href="https://climate.nasa.gov/news/3105/earths-magnetosphere-protecting-our-planet-from-harmful-space-energy/">Earth’s magnetic field</a> or the way earthquake waves <a href="https://www.snexplores.org/article/explainer-seismic-waves-come-different-flavors">bounce off different layers</a> below the Earth’s surface. </p>
<p>But indirect discovery has its limitations. How can scientists find out more about our planet’s deep interior?</p>
<p><a href="http://jimbell.sese.asu.edu/">Planetary scientists like me</a> think the best way to learn about inner Earth is in outer space. NASA’s <a href="https://www.jpl.nasa.gov/missions/psyche">robotic mission to a metal world</a> is scheduled for liftoff on Oct. 5, 2023. That mission, the spacecraft traveling there, and the world it will explore all have the same name – Psyche. And for six years now, I’ve been <a href="https://psyche.asu.edu/mission/the-team/">part of NASA’s Psyche team</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/y__vwRQ3PVg?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">It’s a mission of ‘firsts.’</span></figcaption>
</figure>
<h2>About the asteroid Psyche</h2>
<p><a href="https://solarsystem.nasa.gov/asteroids-comets-and-meteors/asteroids/overview/?">Asteroids are small worlds</a>, with some the size of small cities and others as large as small countries. They are the leftover building blocks from our solar system’s early and violent period, <a href="https://solarsystem.nasa.gov/solar-system/our-solar-system/in-depth/#:%7E:">a time of planetary formation</a>. </p>
<p>Although most are rocky, icy or a combination of both, perhaps 20% of asteroids are worlds made of metal, and similar in composition to the Earth’s core. So it’s tempting to imagine that these metallic asteroids are pieces of the cores of once-existing planets, ripped apart by ancient cosmic collisions with each other. Maybe, by studying these pieces, scientists could find out directly what a planetary core is like. </p>
<p><a href="https://solarsystem.nasa.gov/asteroids-comets-and-meteors/asteroids/16-psyche/in-depth/">Psyche</a> is the largest-known of the metallic asteroids. Discovered in 1852, Psyche has the width of Massachusetts, a squashed spherical shape reminiscent of a pincushion, and an orbit between Mars and Jupiter in the main asteroid belt. An amateur astronomer can see Psyche with a backyard telescope, but it appears only as a pinpoint of light.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/TgVorJfM8BM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">An artist’s rendition of Psyche, a spectacular metallic world.</span></figcaption>
</figure>
<h2>About the Psyche mission</h2>
<p>In early 2017, NASA approved the US$1 billion <a href="https://www.nasa.gov/psyche">mission to Psyche</a>. To do its work, there’s no need for the uncrewed spacecraft to land – instead, it will orbit the asteroid repeatedly and methodically, starting from 435 miles (700 kilometers) out and then going down to 46 miles (75 km) from the surface, and perhaps even lower. </p>
<p>Once it arrives in August 2029, the probe will spend 26 months mapping the asteroid’s geology, topography and gravity; it will search for evidence of a magnetic field; and it will compare the asteroid’s composition with what scientists know, or think we know, about Earth’s core.</p>
<p>The central questions are these: Is Psyche really an exposed planetary core? Is the asteroid one big bedrock boulder, a rubble pile of smaller boulders, or something else entirely? Are there clues that the previous outer layers of this small world – the crust and mantle – were violently stripped away long ago? And maybe the most critical question: Can what we learn about Psyche be extrapolated to solve some of the mysteries about the Earth’s core? </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/542041/original/file-20230809-23-wqfx53.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Technicians, inside a clean room and dressed in white garb, examine the Psyche spacecraft." src="https://images.theconversation.com/files/542041/original/file-20230809-23-wqfx53.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/542041/original/file-20230809-23-wqfx53.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/542041/original/file-20230809-23-wqfx53.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/542041/original/file-20230809-23-wqfx53.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/542041/original/file-20230809-23-wqfx53.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/542041/original/file-20230809-23-wqfx53.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/542041/original/file-20230809-23-wqfx53.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">NASA’s Psyche spacecraft, undergoing final tests in a clean room at a facility near Florida’s Kennedy Space Center.</span>
<span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/catalog/PIA25952">NASA/Frank Michaux</a></span>
</figcaption>
</figure>
<h2>About the spacecraft Psyche</h2>
<p>The probe’s body is about the same size and mass as a large SUV. Solar panels, stretching a bit wider than a tennis court, power the cameras, spectrometers and other systems. </p>
<p>A SpaceX Falcon Heavy rocket will <a href="https://techcrunch.com/2020/02/28/spacex-wins-the-117-million-launch-contract-to-explore-psyches-heavy-metal-asteroid/">take Psyche off the Earth</a>. The rest of the way, Psyche will <a href="https://www.nasa.gov/feature/jpl/solar-electric-propulsion-makes-nasa-s-psyche-spacecraft-go">rely on ion propulsion</a> – the gentle pressure of ionized xenon gas jetting out of a nozzle provides a continuous, reliable and low-cost way to propel spacecraft out into the solar system.</p>
<p>The journey, a slow spiral of 2.5 billion miles (4 billion km) that includes a gravity-assist flyby past Mars, <a href="https://www.cnn.com/2023/06/05/world/nasa-psyche-mission-october-launch-scn/index.html">will take nearly six years</a>. Throughout the cruise, the Psyche team at NASA’s Jet Propulsion Laboratory in Pasadena, California, and here at Arizona State University in Tempe, will stay in regular contact with the spacecraft. Our team will send and receive data using <a href="https://www.nasa.gov/directorates/heo/scan/services/networks/deep_space_network/about">NASA’s Deep Space Network</a> of giant radio antennas. </p>
<p>Even if we learn that Psyche is not an ancient planetary core, we’re bound to significantly add to our body of knowledge about the solar system and the way planets form. After all, Psyche is still unlike any world humans have ever visited. Maybe we can’t yet journey to the center of the Earth, but robotic avatars to places like Psyche can help unlock the mysteries hidden deep inside the planets – including our own.</p><img src="https://counter.theconversation.com/content/206913/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jim Bell works for Arizona State University, the lead academic institution responsible for the Pyche mission. He is also a member of the Board of Directors of The Planetary Society. He receives funding from NASA.</span></em></p>Liftoff to the distant asteroid is scheduled for Oct. 5, 2023 – the beginning of a six-year journey to one of the most unusual objects in the solar system.Jim Bell, Professor of Earth and Space Exploration, Arizona State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2104212023-07-26T16:51:04Z2023-07-26T16:51:04ZWe’ve discovered how diamonds make their way to the surface and it may tell us where to find them<figure><img src="https://images.theconversation.com/files/539502/original/file-20230726-21-jcon90.jpg?ixlib=rb-1.1.0&rect=17%2C0%2C5773%2C3820&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/natural-diamond-nestled-kimberlite-1608584494">Bjoern Wylezich / Shutterstock</a></span></figcaption></figure><p>“A diamond is forever.” That iconic slogan, coined for a <a href="https://www.thedrum.com/news/2016/03/31/1948-de-beers-diamond-forever-campaign-invents-the-modern-day-engagement-ring">highly successful advertising campaign in the 1940s</a>, sold the gemstones as a symbol of eternal commitment and unity. </p>
<p>But our new research, carried out by researchers in a variety of countries and <a href="https://www.nature.com/articles/s41586-023-06193-3">published in Nature</a>, suggests that diamonds may be a sign of break up too – of Earth’s tectonic plates, that is. It may even provide clues to where is best to go looking for them. </p>
<p>Diamonds, being the <a href="https://pursuit.unimelb.edu.au/articles/diamonds-the-hard-facts">hardest naturally-occurring stones</a>, require intense pressures and temperatures to form. These conditions are only achieved deep within the Earth. So how do they get from deep within the Earth, up to the surface? </p>
<p>Diamonds are carried up in molten rocks, or magmas, called <a href="https://www.britannica.com/science/kimberlite">kimberlites</a>. Until now, we didn’t know what process caused kimberlites to suddenly shoot through the Earth’s crust having spent millions, or even billions, of years stowed away under the continents.</p>
<h2>Supercontinent cycles</h2>
<p>Most geologists agree that the explosive eruptions that unleash <a href="https://www.science.org/doi/abs/10.1126/science.1206275">diamonds happen in sync</a> with the supercontinent cycle: a recurring pattern of landmass formation and fragmentation that has defined billions of years of Earth’s history. </p>
<p>However, the exact mechanisms underlying this relationship are debated. Two main theories have emerged. </p>
<p>One proposes that kimberlite magmas <a href="https://www.sciencedirect.com/science/article/abs/pii/S0024493709002758">exploit the “wounds”</a> created when the Earth’s crust is stretched or when the slabs of solid rock covering the Earth – known as tectonic plates – split up. The other theory <a href="https://www.nature.com/articles/s41467-019-13871-2#:%7E:text=Using%20inferences%20from%20older%2C%20smooth,dense%20lower%20lithosphere%2C%20so%20that">involves mantle plumes</a>, colossal upwellings of molten rock from the core-mantle boundary, located about 2,900km beneath the Earth’s surface.</p>
<figure class="align-center ">
<img alt="Structure of the Earth." src="https://images.theconversation.com/files/539551/original/file-20230726-21-tgwt8l.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/539551/original/file-20230726-21-tgwt8l.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=418&fit=crop&dpr=1 600w, https://images.theconversation.com/files/539551/original/file-20230726-21-tgwt8l.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=418&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/539551/original/file-20230726-21-tgwt8l.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=418&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/539551/original/file-20230726-21-tgwt8l.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=526&fit=crop&dpr=1 754w, https://images.theconversation.com/files/539551/original/file-20230726-21-tgwt8l.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=526&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/539551/original/file-20230726-21-tgwt8l.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=526&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A representation of the internal structure of the Earth.</span>
<span class="attribution"><a class="source" href="https://www.usgs.gov/media/images/earth-cross-section">USGS</a></span>
</figcaption>
</figure>
<p>Both ideas, however, are not without their problems. Firstly, the main part of the tectonic plate, <a href="https://education.nationalgeographic.org/resource/lithosphere/">known as the lithosphere</a>, is incredibly strong and stable. This makes it difficult for fractures to penetrate, enabling magmas to flush through. </p>
<p>In addition, many kimberlites don’t display the chemical “flavours” we’d expect to find in rocks derived from mantle plumes.</p>
<p>In contrast, kimberlite formation is thought to involve exceedingly low degrees of mantle rock melting, often less than 1%. So, another mechanism is needed. Our study offers a possible resolution to this longstanding conundrum.</p>
<p>We deployed statistical analysis, including machine learning – an application of artificial intelligence (AI) – to forensically examine the link between continental breakup and kimberlite volcanism. The results of our global study showed the eruptions of most kimberlite volcanoes occurred 20 to 30 million years after the tectonic breakup of Earth’s continents. </p>
<p>Furthermore, our regional study targeting the three continents where most kimberlites are found – Africa, South America and North America – supported this finding. It also added a major clue: kimberlite eruptions tend to gradually migrate from the continental edges to the interiors over time at a rate that is uniform across the continents.</p>
<p>This begs the question: what geological process could explain these patterns?
To address this question, we employed multiple computer models to capture the complex behaviour of continents as they experience stretching, alongside the convective movements within the underlying mantle.</p>
<h2>Domino effect</h2>
<p>We propose that a domino effect can explain how breakup of the continents eventually leads to formation of kimberlite magma. During <a href="https://egusphere.copernicus.org/preprints/2022/egusphere-2022-139/">rifting</a>, a small region of the continental root – areas of thick rock located under some continents – is disrupted and sinks into the underlying mantle. </p>
<p>Here, we get sinking of colder material and upwelling of hot mantle, causing a process called <a href="https://www.sciencedirect.com/science/article/abs/pii/S0012821X98000892">edge-driven convection</a>. Our models show that this convection triggers a chain of similar flow patterns that migrate beneath the nearby continent. </p>
<p>Our models show that while sweeping along the continental root, these disruptive flows remove a substantial amount of rock, tens of kilometres thick, from the base of the continental plate. </p>
<p>Various other results from our computer models then advance to show that this process can bring together the necessary ingredients in the right amounts to trigger just enough melting to generate gas-rich kimberlites. Once formed, and with great buoyancy provided by carbon dioxide and water, the magma can rise rapidly to the surface carrying its precious cargo. </p>
<figure class="align-center ">
<img alt="Eruption on western vent in Halema‘uma‘u crater, at the summit of Kīlauea." src="https://images.theconversation.com/files/539520/original/file-20230726-19-y5r0d0.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/539520/original/file-20230726-19-y5r0d0.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/539520/original/file-20230726-19-y5r0d0.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/539520/original/file-20230726-19-y5r0d0.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/539520/original/file-20230726-19-y5r0d0.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/539520/original/file-20230726-19-y5r0d0.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/539520/original/file-20230726-19-y5r0d0.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">It hasn’t been clear how the molten rock carrying diamonds got to the surface from deep within the Earth.</span>
<span class="attribution"><a class="source" href="https://www.usgs.gov/media/images/close-view-west-vent-halemaumau-kilauea-october-5-2021">N. Deligne / USGS</a></span>
</figcaption>
</figure>
<h2>Finding new diamond deposits</h2>
<p>This model doesn’t contradict the spatial association between kimberlites and mantle plumes. On the contrary, the breakup of tectonic plates may or may not result from the warming, thinning and weakening of the plate caused by plumes. </p>
<p>However, our research clearly shows that the spatial, time-based and chemical patterns observed in most kimberlite-rich regions can’t be adequately explained solely by the presence of plumes.</p>
<p>The processes triggering the eruptions that bring diamonds to the surface appear to be highly systematic. They start on the edges of continents and migrate towards the interior at a relatively uniform rate.</p>
<p>This information could be used to identify the possible locations and timings of past volcanic eruptions tied to this process, offering insights that could enable the discovery of diamond deposits and other rare elements needed for the green energy transition. </p>
<p>If we are to look for new deposits, it’s worth bearing in mind that there are currently efforts by campaign groups to try to eliminate from world markets those diamonds that are <a href="https://fpi.ec.europa.eu/what-we-do/kimberley-process-fight-against-conflict-diamonds_en">used to fund wars</a> (conflict diamonds) or those coming from mines with poor conditions for workers.</p>
<p>Diamonds may or may not be forever, but our work shows that new ones have been repeatedly created over long periods in the history of our planet.</p><img src="https://counter.theconversation.com/content/210421/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Thomas Gernon receives funding from the WoodNext Foundation and the Natural Environment Research Council (NERC). </span></em></p>Scientists were not previously certain how the precious stones arrived at the Earth’s surface.Thomas Gernon, Associate Professor in Earth Science, University of SouthamptonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2030212023-04-17T12:43:33Z2023-04-17T12:43:33ZWill the Earth last forever?<figure><img src="https://images.theconversation.com/files/519862/original/file-20230406-26-bwayd8.jpg?ixlib=rb-1.1.0&rect=7%2C0%2C2329%2C1670&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">'Earthrise,' a photo of the Earth taken by Apollo 8 astronaut Bill Anders, Dec. 4, 1968.</span> <span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Overview_effect#/media/File:NASA-Apollo8-Dec24-Earthrise-b.jpg">NASA/Bill Anders via Wikipedia</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Will the Earth last forever? – Solomon, age 5, California</strong></p>
</blockquote>
<hr>
<p>Everything that has a beginning has an end. But the Earth will last for a very long time, and its end will come billions of years after anyone who is alive here now is gone. </p>
<p>Before we talk about the future of our planet, let’s review its history and when life appeared on it. The history of human beings is very, very short compared with that of Earth.</p>
<h2>4 billion years old</h2>
<p>Our planet formed from a giant cloud of gas and dust in space, which is called a nebula, <a href="https://theconversation.com/curious-kids-how-do-scientists-work-out-how-old-the-earth-is-90391">about 4.6 billion years ago</a>. The first continent might have formed on its surface as early as <a href="https://www.nationalgeographic.com/science/article/140224-oldest-crust-australia-zircon-science">4.4 billion years ago</a>. </p>
<p>The atmosphere of the early Earth <a href="https://beta.nsf.gov/news/without-oxygen-earths-early-microbes-relied">did not contain oxygen</a>, so it would have been toxic to human beings if they had been present then. It was very different from Earth’s atmosphere today, which is about 21% oxygen. Many life forms, including humans, need oxygen to live. </p>
<p>Where did that oxygen come from? Scientists believe that atmospheric oxygen started to rise <a href="https://theconversation.com/billions-of-years-ago-the-rise-of-oxygen-in-earths-atmosphere-caused-a-worldwide-deep-freeze-139722">about 2.4 billion years ago</a> in a shift they call the Great Oxidation Event. </p>
<p>Tiny microorganisms had already existed on Earth’s surface for a while. Some of them developed the ability to <a href="https://asm.org/Articles/2022/February/The-Great-Oxidation-Event-How-Cyanobacteria-Change">produce energy from sunlight</a>, the way plants do today. As they did it, they released oxygen. It built up in the atmosphere and made it possible for more complex life forms to evolve. </p>
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<figcaption><span class="caption">Cyanobacteria, also known as blue-green algae, were the first organisms that produced oxygen on Earth. Today you can find them all around – even in a pond in New York City’s Central Park.</span></figcaption>
</figure>
<p>This took a long time. The first animals, which may have been sea sponges, probably appeared <a href="https://www.science.org/content/article/earth-s-first-animals-may-have-been-sea-sponges">about 660 million years ago</a>. Depending how we define humans,
humans emerged in Africa about 200,000 years to 2 million years ago, and <a href="https://www.history.com/news/humans-evolution-neanderthals-denisovans">spread out everywhere from there</a>. </p>
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<figcaption><span class="caption">Humans have only been present on Earth for a tiny fraction of our planet’s history.</span></figcaption>
</figure>
<h2>Billions more to go</h2>
<p>Now, as we think about the future of the Earth, we know there are two essential factors that humans need to live here. </p>
<p>First, the Sun provides <a href="https://education.nationalgeographic.org/resource/power-sun/">most of the energy</a> that living things on Earth need to survive. Plants use sunlight to grow and to produce oxygen. Animals, including humans, rely directly or indirectly on plants for food and oxygen. </p>
<p>The other thing that makes the Earth habitable for life is that our planet’s surface keeps moving and shifting. This ever-changing surface environment produces weather patterns and chemical changes in the oceans and on the continents that have <a href="https://www.quantamagazine.org/why-earths-cracked-crust-may-be-essential-for-life-20180607/">enabled life to evolve on Earth</a>. </p>
<p>The movement of the <a href="https://oceanservice.noaa.gov/facts/tectonics.html">giant pieces of Earth’s outer layer</a>, which are called plates, is driven by heat in the interior of the Earth. This source will keep the Earth’s interior hot <a href="https://theconversation.com/how-has-the-inside-of-the-earth-stayed-as-hot-as-the-suns-surface-for-billions-of-years-193277">for billions of years</a>. </p>
<p>So, what will change? Scientists estimate that the Sun will keep shining for another <a href="https://theconversation.com/the-sun-wont-die-for-5-billion-years-so-why-do-humans-have-only-1-billion-years-left-on-earth-37379">5 billion years</a>. But it will gradually get brighter and brighter, and warm the Earth more and more. </p>
<p>This warming is so slow that we wouldn’t even notice it. In about 1 billion years, our planet will be too hot to maintain oceans on its surface to support life. That’s a really long time away: an average human lifetime is <a href="https://worldpopulationreview.com/country-rankings/life-expectancy-by-country">about 73 years</a>, so a billion is more than 13 million human lifetimes. </p>
<p>Long after that – about 5 billion years from now – our Sun will expand into an even bigger star that astronomers call a “red giant,” which eventually will engulf the Earth. Just as our planet existed for over 4 billion years before humans appeared, it will last for another 4 billion to 5 billion years, long after it becomes uninhabitable for humans.</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/203021/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Shichun Huang does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The Earth isn’t permanent, but it was here for four billion years before humans arrived and should be here for several billion more.Shichun Huang, Associate Professor of Earth and Planetary Sciences, University of TennesseeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2002582023-02-21T19:04:05Z2023-02-21T19:04:05ZIn a new study, we’ve observed clues that distinguish the very deepest part of Earth’s core<figure><img src="https://images.theconversation.com/files/511009/original/file-20230220-2192-e5uwge.png?ixlib=rb-1.1.0&rect=263%2C17%2C3544%2C1952&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Rost9/Shutterstock</span></span></figcaption></figure><p>Not so long ago, Earth’s interior was thought to be made up of four layers: the crust, mantle, (liquid) outer core and (solid) inner core.</p>
<p>In a new study <a href="https://doi.org/10.1038/s41467-023-36074-2">published today in Nature Communications</a>, we provide further evidence for the existence of an “innermost inner core” – a distinct internal metallic ball embedded in the inner core like the most petite Russian nesting doll. </p>
<p>Studying Earth’s centre is not just a topic of academic curiosity, but something that sheds light on the very evolution of life on our planet’s surface. </p>
<p>This is because the inner core grows outwards by solidifying materials from the liquid outer core. As these materials solidify, heat is released and causes upward movement in the liquid layer – what’s known as a convection current. In turn, this convection generates our planet’s geomagnetic field.</p>
<p>The magnetic field protects life on Earth from <a href="https://climate.nasa.gov/news/3105/earths-magnetosphere-protecting-our-planet-from-harmful-space-energy/">harmful cosmic radiation</a>. Without the shield it provides, life on Earth would not be possible in the form we know today. </p>
<p>So, understanding the evolutionary history of our planet’s inner core and its connection with the geomagnetic field is relevant to understanding the timeline of life’s evolution on Earth’s surface.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/what-makes-one-earth-like-planet-more-habitable-than-another-33479">What makes one Earth-like planet more habitable than another?</a>
</strong>
</em>
</p>
<hr>
<h2>Studying the insides of the planet</h2>
<p>Like radiologists imaging a patient’s internal organs, seismologists use seismic waves from large earthquakes to study the deep interior of Earth. Earthquakes are our sources, and seismometers recording ground motions or vibrations that move through Earth are our receivers.</p>
<p>However, unlike medical imaging, we do not have the luxury of having sources and receivers equally distributed around the body. Large earthquakes useful for our probes are confined near tectonic margins, such as <a href="https://theconversation.com/five-active-volcanoes-on-my-asia-pacific-ring-of-fire-watch-list-right-now-90618">the Ring of Fire</a> surrounding the Pacific. Meanwhile, seismometers mainly exist on land. </p>
<p>Furthermore, the inner core, which is <a href="http://onlinelibrary.wiley.com/doi/10.1111/j.1365-246X.1995.tb03540.x/abstract">one-fifth of Earth’s radius</a>, accounts for less than 1% of Earth’s volume. To target this relatively small volume in the planet’s centre, seismometers often need to be positioned on the opposite side of the globe, the so-called antipode of an earthquake.</p>
<p>But that’s unlikely in practice because the antipodes of active earthquake zones are often in the ocean, where seismometers are expensive to install. </p>
<p>With the limited data we do have from such antipode measurements, an internal metallic ball within the inner core – the innermost inner core – <a href="http://www.pnas.org/content/99/22/14026">was hypothesised</a> about 20 years ago, with an estimated radius of about 300km.</p>
<p>Several <a href="http://www.sciencedirect.com/science/article/pii/S0031920118302395">lines of evidence</a> have confirmed its <a href="https://www.science.org/doi/10.1126/science.1078159">existence</a>, including <a href="https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020JB020545">recent</a> <a href="https://onlinelibrary.wiley.com/doi/abs/10.1029/2021JB023540">studies</a> from our research group. </p>
<h2>Bouncing seismic waves</h2>
<p>Now, for the first time, we report observations of seismic waves originating from powerful earthquakes travelling back and forth from one side of the globe to the other up to five times like a ricochet. These new observations are exciting because they provide new probes from different angles of the centremost part of our planet. </p>
<p>A critical advantage of our study was getting data from dense continental-scale networks (consisting of several hundred seismometers) installed around some of the largest quakes.</p>
<p>It differs from previous studies because it uses seismic waves that bounce multiple times within Earth, along its diameter and through its centre. By capturing them, we obtain an unparalleled sampling of the innermost inner core.</p>
<h2>A ball in the centre</h2>
<p>The potential difference between the innermost metallic ball and the outer shell of the inner core is not in its chemical composition, like with some other Earth layers. Both are likely made of an iron-nickel alloy with small amounts of lighter chemical elements.</p>
<p>Additionally, the transition from the innermost (solid) ball to the outer shell of the inner core (also solid) seems gradual rather than sharp. That is why we can’t observe it via direct reflections of seismic waves from it. This differs from previous studies documenting sharp boundaries between the other layers inside Earth – from crust to mantle, for example.</p>
<p>So, what precisely did we observe that gives us clues about this innermost inner core?</p>
<p>The observed difference is in anisotropy – a material’s property to let (or propagate) seismic waves faster or slower through it depending on the direction in which they travel.</p>
<p>Different speeds could be caused by different arrangements of iron atoms at high temperatures and pressures, or by the arrangements of atoms when crystals grow.</p>
<p>There is <a href="https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020JB020545">strong evidence</a> that the outer shell of the inner core is anisotropic. The slowest direction of seismic waves is in the equatorial plane (and the fastest is parallel to Earth’s spin axis).</p>
<p>By contrast, in the innermost part of the inner core – as our study of the ricochet waves shows – the slowest direction of propagation forms an oblique angle with the equatorial plane. This is critical, and this is why we can say we’ve detected “distinct” anisotropy in the innermost inner core. </p>
<p>Excitingly, while shallow structures within Earth’s crust and upper mantle are being mapped in incredible detail, we are still at the discovery stage regarding its deepest structures.</p>
<p>However, the image of Earth’s deep interior is getting sharper with the expansion of the dense continental networks, advanced data analysing techniques, and computational capacities.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/just-add-mantle-water-new-research-cracks-the-mystery-of-how-the-first-continents-formed-156845">Just add (mantle) water: new research cracks the mystery of how the first continents formed</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/200258/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Hrvoje Tkalčić receives funding from The Australian Research Council. </span></em></p><p class="fine-print"><em><span>Thanh-Son Pham 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>Earth doesn’t just have an inner core. It also has an innermost inner core, a solid ball within the solid ball in the very middle of the planet.Thanh-Son Pham, Postdoctoral Fellow in Geophysics, Australian National UniversityHrvoje Tkalčić, Professor, Head of Geophysics, Director of Warramunga Array, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1932772023-01-23T13:24:30Z2023-01-23T13:24:30ZHow has the inside of the Earth stayed as hot as the Sun’s surface for billions of years?<figure><img src="https://images.theconversation.com/files/504323/original/file-20230112-43582-jetsqy.jpg?ixlib=rb-1.1.0&rect=0%2C21%2C4685%2C3672&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The slice you see cut out of the Earth reveals its core, depicted here in bright yellow.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/earth-section-royalty-free-image/174700926">fhm/E+ via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>How does the inside of the Earth stay boiling hot for billions of years? Henry, age 11, Somerville, Massachusetts</strong></p>
</blockquote>
<hr>
<p>Our Earth is structured sort of like an onion – it’s one layer after another. </p>
<p>Starting from the top down, there’s the crust, which includes the surface you walk on; then farther down, the mantle, mostly solid rock; then even deeper, the outer core, made of liquid iron; and finally, the inner core, made of solid iron, and with a radius that’s 70% the size of the Moon’s. The deeper you dive, the hotter it gets – parts of the core are as hot as the surface of the Sun.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/504301/original/file-20230112-52283-32zsaz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An illustration that shows the structure of the Earth: its crust, mantle, inner core and outer core." src="https://images.theconversation.com/files/504301/original/file-20230112-52283-32zsaz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/504301/original/file-20230112-52283-32zsaz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=405&fit=crop&dpr=1 600w, https://images.theconversation.com/files/504301/original/file-20230112-52283-32zsaz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=405&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/504301/original/file-20230112-52283-32zsaz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=405&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/504301/original/file-20230112-52283-32zsaz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=509&fit=crop&dpr=1 754w, https://images.theconversation.com/files/504301/original/file-20230112-52283-32zsaz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=509&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/504301/original/file-20230112-52283-32zsaz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=509&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">This illustration depicts the four sections beneath the Earth’s surface.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/the-structure-of-planet-earth-royalty-free-illustration/1256173927">eliflamra/iStock via Getty Images Plus</a></span>
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</figure>
<h2>Journey to the center of the Earth</h2>
<p>As a <a href="https://scholar.google.com/citations?user=DpHUpCwAAAAJ&hl=en&oi=ao">professor of earth and planetary sciences</a>, I study the insides of our world. Just as a doctor can use a technique called <a href="https://blog.radiology.virginia.edu/ultrasound-definition-kids-imaging/">sonography</a> to make pictures of the structures inside your body with ultrasound waves, scientists use a similar technique to image the Earth’s internal structures. But instead of ultrasound, geoscientists use <a href="https://easyscienceforkids.com/seismic-waves/">seismic waves</a> – sound waves produced by earthquakes. </p>
<p>At the Earth’s surface, you see dirt, sand, grass and pavement, of course. <a href="https://www.amnh.org/learn-teach/curriculum-collections/earth-inside-and-out/inge-lehmann-discoverer-of-the-earth-s-inner-core">Seismic vibrations reveal what’s below that</a>: rocks, large and small. This is all part of the crust, which may go down as far as 20 miles (30 kilometers); it floats on top of the layer called the mantle. </p>
<p>The upper part of the mantle typically moves together with the crust. Together, they are called <a href="https://education.nationalgeographic.org/resource/lithosphere">the lithosphere</a>, which is about 60 miles (100 kilometers) thick on average, although it can be thicker at some locations. </p>
<p>The lithosphere is divided into several <a href="https://www.kidsdiscover.com/wp-content/uploads/2012/12/KIDS-DISCOVER-Plate-Tectonics.pdf">large blocks called plates</a>. For example, the Pacific plate is beneath the whole Pacific Ocean, and the North American plate covers most of North America. Plates are kind of like puzzle pieces that fit roughly together and cover the surface of the Earth.</p>
<p>The plates are not static; instead, they move. Sometimes it’s the tiniest fraction of inches over a period of years. Other times, there’s more movement, and it’s more sudden. This sort of movement is what triggers earthquakes and volcanic eruptions. </p>
<p>What’s more, plate movement is a critical, and probably essential, factor driving the evolution of life on Earth, because the moving plates change the environment and <a href="https://theconversation.com/plate-tectonics-may-have-driven-the-evolution-of-life-on-earth-44571">force life to adapt to new conditions</a>. </p>
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<figcaption><span class="caption">You’ll be amazed at all the life happening below your feet.</span></figcaption>
</figure>
<h2>The heat is on</h2>
<p>Plate motion requires a hot mantle. And indeed, as you go deeper into the Earth, the temperature increases. </p>
<p>At the bottom of the plates, around 60 miles (100 kilometers) deep, the temperature is about 2,400 degrees Fahrenheit (1,300 degrees Celsius). </p>
<p>By the time you get to the boundary between the mantle and the outer core, which is 1,800 miles (2,900 kilometers) down, the temperature is nearly 5,000 F (2,700 C). </p>
<p>Then, at the boundary between outer and inner cores, the temperature doubles, to nearly 10,800 F (over 6,000 C). That’s the part that’s <a href="https://www.livescience.com/29054-earth-core-hotter.html">as hot as the surface of the Sun</a>. At that temperature, virtually everything – metals, diamonds, human beings – vaporizes into gas. But because the core is at such high pressure deep within the planet, the iron it’s made up of remains liquid or solid. </p>
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<figcaption><span class="caption">Without plate tectonics, human beings probably would not exist.</span></figcaption>
</figure>
<h2>Collisions in outer space</h2>
<p>Where does all that heat come from? </p>
<p>It is not from the Sun. While it warms us and all the plants and animals on Earth’s surface, sunlight can’t penetrate through miles of the planet’s interior.</p>
<p>Instead, there are two sources. One is the heat that Earth inherited during its formation 4.5 billion years ago. The Earth was made <a href="https://solarsystem.nasa.gov/solar-system/our-solar-system/in-depth/#:%7E">from the solar nebula</a>, a gigantic gaseous cloud, amid endless collisions and mergings between bits of rock and debris <a href="https://www.universetoday.com/35974/planetesimals/">called planetesimals</a>. This process took tens of millions of years.</p>
<p>An enormous amount of heat was produced during those collisions, enough to melt the whole Earth. Although some of that heat was lost in space, the rest of it was locked away inside the Earth, where much of it remains even today. </p>
<p>The other heat source: the decay of radioactive isotopes, distributed everywhere in the Earth. </p>
<p>To understand this, first imagine an element <a href="https://www.ducksters.com/science/chemistry/radiation_and_radioactivity.php">as a family with isotopes as its members</a>. Every atom of a given element has the same number of protons, but different isotope cousins have varying numbers of neutrons. </p>
<p><a href="https://kids.britannica.com/students/article/radioactive-isotope/628328#:%7E">Radioactive isotopes</a> are not stable. They release a steady stream of energy that converts to heat. Potassium-40, thorium-232, uranium-235 and uranium-238 are four of the radioactive isotopes keeping Earth’s interior hot. </p>
<p>Some of those names may sound familiar to you. Uranium-235, for example, is used as a <a href="https://www.eia.gov/energyexplained/nuclear/the-nuclear-fuel-cycle.php#:%7E">fuel in nuclear power plants</a>. Earth is in no danger of running out of these sources of heat: Although most of the <a href="https://www.ducksters.com/science/chemistry/radiation_and_radioactivity.php#:%7E">original uranium-235 and potassium-40 are gone</a>, there’s enough thorium-232 and uranium-238 to last for billions more years. </p>
<p>Along with the hot core and mantle, these energy-releasing isotopes provide the heat to drive the motion of the plates. </p>
<h2>No heat, no plate movement, no life</h2>
<p>Even now, the moving plates keep changing the surface of the Earth, constantly making <a href="https://www.quantamagazine.org/why-earths-cracked-crust-may-be-essential-for-life-20180607/">new lands and new oceans over millions and billions of years</a>. The plates also affect the atmosphere over similarly lengthy time scales. </p>
<p>But without the Earth’s internal heat, the plates would not have been moving. The Earth would have cooled down. Our world would likely have been uninhabitable. You wouldn’t be here.</p>
<p>Think about that, the next time you feel the Earth under your feet.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p><img src="https://counter.theconversation.com/content/193277/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Shichun Huang does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Starting at the surface, you would have to dig nearly 2,000 miles before reaching the Earth’s core. No one could survive that trip – and the 10,000-degree F heat once there would vaporize you anyway.Shichun Huang, Associate Professor of Earth and Planetary Sciences, University of TennesseeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/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/1878522022-07-29T05:21:00Z2022-07-29T05:21:00ZPerfectly imperfect: the discovery of the second-largest pink diamond has left the world in awe. What gives diamonds their colour?<figure><img src="https://images.theconversation.com/files/476639/original/file-20220729-20-vod0jt.jpeg?ixlib=rb-1.1.0&rect=6%2C9%2C2038%2C1352&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Lucapa Diamond Company/EPA</span></span></figcaption></figure><p>Usually when goods are flawed, we expect their value to drop, but it’s the exact opposite for diamonds. Ironically, it is imperfections that impart colour to diamonds – and these “fancy” diamonds are some of the most sought after in the world.</p>
<p>Diamonds are made of carbon atoms organised in compact structures. Clear, perfect diamonds sparkle because light reflects off their internal surfaces. Of course, these diamonds are valuable.</p>
<p>However, when diamonds host impurities, or are subjected to intense pressure, they can develop distinctive colours. Coloured diamonds are extremely prized for their beauty and rarity, and can be several orders of magnitude more expensive than clear diamonds. </p>
<p>So it’s no surprise the world was astonished when the Western Australia-owned Lucapa Diamond Company announced the discovery of the <a href="https://www.abc.net.au/news/2022-07-28/big-pink-diamond-discovered-in-angola-largest-in-300-years/101276078">Lulo Rose</a> this week. The 170-carat rough pink diamond, found in Angola, is the second-largest pink diamond ever discovered. </p>
<h2>Few and far between</h2>
<p>Coloured diamonds represents only 0.01% (one in 10,000) of diamonds mined in the world. Natural yellow and brown are the most common and, as you might expect, are therefore not overly expensive.</p>
<p>However, blue, green, violet, orange, pink and red diamonds are extremely rare and exist in minute quantities. These are truly coveted.</p>
<p>Ultra-rare coloured diamonds have been sold for record-breaking prices. The Pink Star, weighing 59.6 carats (about the size of a strawberry), is the most expensive diamond ever sold, for a staggering A$94.2 million. </p>
<p>It’s worth mentioning the Pink Star originally came from a diamond weighing in at 132.5 carats. More than half of its weight was lost in the process of cutting and polishing the stone – a process that took 20 months.</p>
<p>At 170 carats, it’s quite possible the Lulo Rose, if auctioned, could become the most expensive diamond in history. </p>
<p>The only pink diamond larger than it is the Daria-i-Noor (185 carats), which is the centrepiece of the Iranian crown jewels, and has never been for sale.</p>
<h2>So why are coloured diamonds so scarce?</h2>
<p>Physical and chemical purity yields clear diamonds. So coloured diamonds form as a result of imperfections. But it’s very rare for imperfections to arise in a material that is not only extremely hard, but also chemically simple.</p>
<p>There are three main imperfections that produce coloured diamonds: impurity, damage and distortion. These are imperfections in the structure of the diamond that affect how light passes through the gem – specifically the diffraction and absorption of different wavelengths of light. And this is what leads to the different colours we see. </p>
<p>The main <em>impurities</em> in diamonds comes in the form of very light elements, such nitrogen, boron and hydrogen, which we generally find in abundance in the oceans and atmosphere. These elements can result in specific colours. For example, boron-rich diamonds will be blue, while nitrogen-rich diamonds will be yellow.</p>
<p>Then there are <em>damaged</em> diamonds, wherein the damage happens when a diamond has been sitting adjacent to radioactive elements, such as uranium, thorium or potassium. </p>
<p>Finally, <em>distortion</em> refers to the twisting and bending of a diamond’s crystal lattice under immense pressure. This causes defects a hundred times smaller than the width of a human hair, yet it’s enough to diffract light and bring colour to the gem.</p>
<p>Every coloured diamond has a cocktail of imperfections, which is why no two diamonds are the same. However, they do all have one thing in common: each diamond is rooted in geological history. Diamonds can be billions of years old. In that time, some have travelled from the depths of the planet to its surface, only for us to claim them.</p>
<p>Take yellow and blue diamonds. Light elements such as nitrogen and boron are concentrated in our oceans and atmosphere, but we know diamonds must form within the heart of the planet. So the key here is plate tectonics, and specifically a process called subduction. </p>
<p>Subduction is a geological process by which the oceanic lithosphere (a part of the outer crust) is recycled into Earth’s mantle. This is how light elements manage to get deep into Earth’s interior – eventually becoming part of coloured diamonds. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/476517/original/file-20220728-33778-qu1qi1.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/476517/original/file-20220728-33778-qu1qi1.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=340&fit=crop&dpr=1 600w, https://images.theconversation.com/files/476517/original/file-20220728-33778-qu1qi1.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=340&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/476517/original/file-20220728-33778-qu1qi1.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=340&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/476517/original/file-20220728-33778-qu1qi1.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=427&fit=crop&dpr=1 754w, https://images.theconversation.com/files/476517/original/file-20220728-33778-qu1qi1.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=427&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/476517/original/file-20220728-33778-qu1qi1.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=427&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Diamonds form deep in Earth’s interior.</span>
<span class="attribution"><span class="source">AdobeStock</span></span>
</figcaption>
</figure>
<h2>A unique window into Earth’s interior</h2>
<p>Pink diamonds have their own geological story. Most scientists think carbon on our seabed, when thrust back into Earth’s interior, can not only form diamonds but also be deformed. </p>
<p>When it’s under enormous pressure and considerable temperatures, the way carbon is supposed to be assembled is distorted, and this is what leads to pink diamond formation.</p>
<p>However, if Earth pushes a little too hard, the pink hue quickly turns brown or, as some would call it, “champagne” or “cognac”. Yet there’s still much we don’t know about pink diamonds. For one, why have about 80% of pink diamonds come from a single recently closed mine in Western Australia?</p>
<p>The Argyle mine was once the world’s largest diamond mine, but was <a href="https://www.abc.net.au/news/rural/2020-11-03/wa-argyle-pink-diamond-mine-closure/12840466">shut down</a> in 2020 after becoming economically unviable. Still, this mine is truly unique – not only because of how many pink diamonds it has produced, but because it sits in a geologically intriguing area.</p>
<p>For years, scientists and diamond companies believed diamonds large enough to be mined could be found only in the heart of ancient continents. But the Argyle mine sits at what was once the edge of two continents that collided and stitched together only 1.8 billion years ago. </p>
<p>This might sound like a long time, but in geological terms it’s not. Argyle and its pink diamonds probably hold the answer for pink diamond formation, but finding it will require further examination.</p>
<p>With the mine having closed, and pink diamonds becoming rarer as we speak, one can only hope scientists will soon unravel the mystery of how pink diamonds form. Perhaps, with that knowledge, we may yet find another trove. </p>
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<strong>
Read more:
<a href="https://theconversation.com/we-created-diamonds-in-mere-minutes-without-heat-by-mimicking-the-force-of-an-asteroid-collision-150369">We created diamonds in mere minutes, without heat — by mimicking the force of an asteroid collision</a>
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<img src="https://counter.theconversation.com/content/187852/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Denis Fougerouse receives funding from the Australian Research Council and the Mineral Research Institute of Western Australia. </span></em></p><p class="fine-print"><em><span>Hugo Olierook and Luc Doucet do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Geology experts explain why coloured diamonds are so much rarer than clear ones – and why the newly discovered Lulo Rose might become the most expensive diamond in history.Luc Doucet, Research Fellow at the Earth Dynamics Research Group, member of TIGeR, Curtin UniversityDenis Fougerouse, Research Fellow, School of Earth and Planetary Sciences and The Institute for Geoscience Research (TIGeR), Curtin UniversityHugo Olierook, Research Fellow in Geology, Curtin UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1714082021-11-11T14:41:57Z2021-11-11T14:41:57ZCurious Kids: Why does cold air go down and hot air go up?<figure><img src="https://images.theconversation.com/files/430738/original/file-20211108-9897-12uhqlo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The land surface heats up during the day because of solar radiation coming in from the sun.</span> <span class="attribution"><span class="source">Ed Connor/Shutterstock</span></span></figcaption></figure><p><em>Curious Kids is <a href="https://theconversation.com/africa/topics/curious-kids-36782">a series</a> for children in which we ask experts to answer questions from kids.</em></p>
<p><strong>Does cold air go down because the earth’s core is made out of magma and does hot air go up because it’s cold out in space – and does the circle repeat? (Neo, 10, Boksburg, South Africa)</strong></p>
<p>Thank you, Neo, for this great question! You’ve clearly got a very analytical mind, and would make an excellent <a href="https://academickids.com/encyclopedia/index.php/Atmospheric_physics">atmospheric physicist</a> – that’s a researcher who looks at the physical processes happening in our atmosphere – one day. </p>
<p>The rising of hot air and sinking of cool air is important for almost every aspect of our day to day weather and our long term climate. It affects which way the wind blows and how fast it blows. It also affects whether we are likely to have rain, and the type of rainfall. Over larger areas of the earth, and over longer time periods, it even influences our seasons. So this is a really important question, and one which climatologists like myself work on in many aspects of our jobs.</p>
<p>I want to start by describing what’s happening in the earth’s core, then tell you a little bit about the temperature of space. Once I’ve done that, I’ll explain the real reasons hot air rises and cold air sinks.</p>
<h2>The Earth’s core and outer space</h2>
<p>If you were to cut a slice out of the earth, you would see four clear layers. The crust is the thin outer layer – much like an orange skin. The crust is hard, made up of solid rock. It’s the part of the earth that we walk on. Below that is a thicker layer called the mantle; it’s a <a href="https://coolscienceexperimentshq.com/viscosity-of-a-liquid-experiment/">viscous</a> layer of molten (melted) rock. Below that is the outer core, and right at the centre of the earth the inner core. These are very hot layers of molten rock and metal.</p>
<p>And you are quite right –- the earth’s core is <a href="https://www.nationalgeographic.org/encyclopedia/core/">very, very hot</a>. The inner core, made up of iron, is approximately 6,000°C. Even the upper mantle, just below the crust, has an average temperature of 2,000°C. That’s 100 times hotter than most daytime temperatures during spring in South Africa.</p>
<p>But the temperatures at the top of the crust are controlled far more by the sun than by the temperature of the centre of the earth. We’ll come back to that shortly.</p>
<p>Now, let’s talk about the temperature of space.</p>
<p>The earth is surrounded by an atmosphere – a layer of gases that we breathe in and out, and that control our temperatures by absorbing some of the heat, and reflecting the rest. Beyond the atmosphere is what is called “outer space”.</p>
<p>The temperature of outer space just outside the earth’s atmosphere is <a href="https://sciencing.com/temperatures-outer-space-around-earth-20254.html">about 10.17°C</a>. Outer space is heated directly by the sun. The areas in the sun are as warm as 120°C, while areas shaded by the earth are as cold as -100°C. Again, you’re right: this is a lot cooler than the earth’s inner core.</p>
<p>It’s correct that the earth’s core is very hot and space is much cooler. But that’s not the reason hot air rises and cool air sinks. </p>
<h2>Thermodynamics</h2>
<p>To come to the real reason, let’s turn to a field of science called <a href="https://www.britannica.com/science/thermodynamics">thermodynamics</a>. This is the branch of physics which studies heat and energy. Thermodynamics allows us to understand exactly what’s happening to individual bubbles of air. Did you know that the air around us is made of millions and millions of tiny air bubbles that sit very closely together?</p>
<p>Heating of the air can occur via conduction or convection – transferring heat to these air bubbles, and sharing it between them. The land surface heats up during the day because of solar radiation coming in from the sun. This incoming solar radiation is absorbed by the earth, warming it up. It is then released from the earth as long wave radiation, and heats up the air above the ground.</p>
<p>Those air bubbles then move around and bump into each other, sharing their heat between themselves.</p>
<p>When the ground heats up an air bubble above it, that air bubble expands – much like our feet swell up when they’re very hot in our shoes. As the air bubble heats up, the weight of that bubble is spread over a bigger area and so it becomes less dense.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/vSXTBnnx4OA?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">This is how density works.</span></figcaption>
</figure>
<p>As these air bubbles become less dense, they rise because they weigh less than what’s next to them. This is the same when you let go of a helium balloon and it floats away: the helium gas in the balloon is less dense than the air in our atmosphere (which is made up of a large amount of much heavier nitrogen). </p>
<p>The opposite happens when air cools down. The air bubbles contract, their weight takes up much less space and so they become more dense, and sink. This can happen if the air particles move away from the source of heat; they might have risen very high, or moved to an area over a cool lake or over some shade.</p>
<p>So, there’s no link between the earth’s core, space’s temperature and the behaviour of cold air versus hot air. But you definitely think like a scientist, Neo, because you are interested in how one thing influences another. Maybe one day you’ll study thermodynamics, too!</p><img src="https://counter.theconversation.com/content/171408/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jennifer Fitchett receives funding from the DSI-NRF Centre of Excellence (GENUS). </span></em></p>This is a really important question, and one which climatologists work on in many aspects of their jobs.Jennifer Fitchett, Associate Professor of Physical Geography, University of the WitwatersrandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1652662021-07-29T14:55:57Z2021-07-29T14:55:57ZEarth’s inner core is growing more on one side than the other – here’s why the planet isn’t tipping<figure><img src="https://images.theconversation.com/files/413581/original/file-20210728-21-1nue266.jpeg?ixlib=rb-1.1.0&rect=6%2C177%2C4386%2C4050&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/argonne/14259873660/">Argonne National Laboratory/flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span></figcaption></figure><p>More than 5,000 kilometres beneath us, Earth’s solid metal inner core wasn’t discovered <a href="https://courses.seas.harvard.edu/climate/eli/Courses/EPS281r/Sources/Inner-Core/Lehmann-1936-extracts+interpretation.pdf">until 1936</a>. Almost a century later, we’re still struggling to answer basic questions about when and how it first formed.</p>
<p>These aren’t easy puzzles to solve. We can’t directly sample the inner core, so the key to unravelling its mysteries lies in collaboration between <a href="https://www.britannica.com/science/seismology">seismologists</a>, who indirectly sample it with seismic waves, <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/geodynamics">geodynamicists</a>, who create models of its dynamics, and <a href="https://booksite.elsevier.com/brochures/geophysics/PDFs/00028.pdf">mineral physicists</a>, who study the behaviour of iron alloys at high pressures and temperatures.</p>
<p>Combining these disciplines, scientists have delivered an important clue about what’s happening miles beneath our feet. In <a href="https://www.nature.com/articles/s41561-021-00761-w">a new study</a>, they reveal how Earth’s inner core is growing faster on one side than the other, which could help explain how old the inner core is, and the intriguing history of Earth’s magnetic field.</p>
<h2>Early Earth</h2>
<p>Earth’s core was formed <a href="https://websites.pmc.ucsc.edu/%7Efnimmo/website/Nimmo_Kleine.pdf">very early</a> in our planet’s 4.5 billion-year history, within the first 200 million years. Gravity pulled the heavier iron to the centre of the young planet, leaving the rocky, silicate minerals to make up <a href="https://theconversation.com/curious-kids-what-is-the-earth-made-of-119192">the mantle and crust</a>. </p>
<p>Earth’s formation captured a lot of heat within the planet. The loss of this heat, and heating by ongoing radioactive decay, have since driven our planet’s evolution. Heat loss in Earth’s interior drives the vigorous flow in the liquid iron outer core, which creates <a href="https://theconversation.com/are-the-earths-magnetic-poles-about-to-swap-places-strange-anomaly-gives-reassuring-clue-142859">Earth’s magnetic field</a>. Meanwhile, cooling within Earth’s deep interior helps power <a href="https://www.nationalgeographic.org/media/plate-tectonics/">plate tectonics</a>, which shape the surface of our planet.</p>
<p>As Earth cooled over time, the temperature at the centre of the planet eventually dropped below the melting point of iron at extreme pressures, and the inner core started to crystallise. Today, the inner core continues to grow at roughly 1mm in radius each year, which equates to the solidification of 8,000 tonnes of molten iron every second. In billions of years, this cooling will eventually lead to the whole <a href="https://theconversation.com/curious-kids-what-would-happen-if-the-earths-core-went-cold-107537">core becoming solid</a>, leaving Earth without its protective magnetic field.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-what-would-happen-if-the-earths-core-went-cold-107537">Curious Kids: what would happen if the Earth's core went cold?</a>
</strong>
</em>
</p>
<hr>
<h2>Core issue</h2>
<p>One might assume that this solidification creates a homogeneous solid sphere, but this isn’t the case. In the 1990s, <a href="https://doi.org/10.1029/96JB03187">scientists</a> realised that the speed of seismic waves travelling through the inner core varied unexpectedly. This suggested that something asymmetrical was happening in the inner core.</p>
<p>Specifically, the eastern and western halves of the inner core showed different seismic wavespeed variations. The eastern part of the inner core is beneath Asia, the Indian Ocean and the western Pacific Ocean, and the west lies under the Americas, the Atlantic Ocean and the eastern Pacific.</p>
<figure class="align-center ">
<img alt="A diagram of the Earth's interior" src="https://images.theconversation.com/files/413736/original/file-20210729-27-hvegx5.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/413736/original/file-20210729-27-hvegx5.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/413736/original/file-20210729-27-hvegx5.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/413736/original/file-20210729-27-hvegx5.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/413736/original/file-20210729-27-hvegx5.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/413736/original/file-20210729-27-hvegx5.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/413736/original/file-20210729-27-hvegx5.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Seismic waves have suggested Earth’s solid iron core is asymmetrical.</span>
<span class="attribution"><span class="source">Sanne Cottaar</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The new study probed this mystery, using new seismic observations combined with geodynamic modelling and estimates of how iron alloys behave at high pressure. They found that the eastern inner core located beneath Indonesia’s Banda Sea is growing faster than the western side beneath Brazil.</p>
<p>You can think of this uneven growth as like trying to make ice cream in a freezer that’s only working on one side: ice crystals form only on the side of the ice cream where the cooling is effective. In the Earth, the uneven growth is caused by the rest of the planet sucking heat more quickly from some parts of the inner core than others.</p>
<p>But unlike the ice cream, the solid inner core is subject to gravitational forces which distribute the new growth evenly through a process of creeping interior flow, which maintains the inner core’s spherical shape. This means that Earth is in no danger of tipping, though this uneven growth does get recorded in the seismic wavespeeds in our planet’s inner core.</p>
<h2>Dating the core</h2>
<p>So does this approach help us understand how old the inner core might be? When the researchers matched their seismic observations with their flow models, they found that it’s likely that the inner core – at the centre of the entire core which formed much earlier – is between 500 million and 1,500 million years old. </p>
<p>The study reports that the younger end of this age range is the better match, although the older end matches <a href="https://theconversation.com/how-we-discovered-that-the-earths-inner-core-is-older-than-previously-thought-48775">an estimate</a> made by measuring changes in the strength of Earth’s magnetic field. Whichever number turns out to be correct, it’s clear that the inner core is a relative youngster, somewhere between a ninth and a third as old as Earth itself.</p>
<p>This new work presents a powerful new model of the inner core. However, a number of physical assumptions the authors made would have to be true for this to be correct. For example, the model only works if the inner core consists of one specific crystalline phase of iron, about which there is some uncertainty.</p>
<p>And does our uneven inner core make the Earth unusual? It turns out that many planetary bodies have two halves which are somehow different to each other. On <a href="https://mars.nasa.gov/mgs/sci/mola/mola-may99.html">Mars</a>, the surface of the northern half is lower-lying while the southern half is more mountainous. The <a href="https://moon.nasa.gov/resources/268/moon-crustal-thickness/">Moon’s</a> near-side crust is chemically different to the far-side one. On <a href="https://solarsystem.nasa.gov/missions/messenger/in-depth/">Mercury</a> and <a href="https://www.nature.com/articles/d41586-018-06095-9">Jupiter</a> it’s not the surface which is uneven but the magnetic field, which doesn’t form a mirror image between north and south. </p>
<p>So while the causes for all of these asymmetries vary, Earth appears to be in good company as a slightly asymmetrical planet in a solar system of lopsided celestial bodies.</p><img src="https://counter.theconversation.com/content/165266/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jessica Irving recieves/has received funding from the UK Space Agency, the National Science Foundation and NASA. </span></em></p><p class="fine-print"><em><span>Sanne Cottaar receives funding from the European Research Council and the National Environmental Research Council. </span></em></p>8,000 tonnes of molten iron solidifies in Earth’s inner core every second – but it’s not distributed equally.Jessica Irving, Senior Lecturer in Geophysics, University of BristolSanne Cottaar, Lecturer in Global Seismology, University of CambridgeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1568992021-03-12T19:00:29Z2021-03-12T19:00:29ZEarth’s early magma oceans detected in 3.7 billion year-old Greenland rocks<figure><img src="https://images.theconversation.com/files/389271/original/file-20210312-13-1o4pbk9.jpg?ixlib=rb-1.1.0&rect=10%2C0%2C7252%2C4845&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">4 billion years ago, the Earth was composed of a series of magma oceans hundreds of kilometres deep.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/realistic-alien-planet-outer-space-3d-1429607681">Larich/Shutterstock</a></span></figcaption></figure><p>Earth hasn’t always been a blue and green oasis of life in an otherwise inhospitable solar system. During our planet’s first 50 million years, around 4.5 billion years ago, its surface was a hellscape of magma oceans, bubbling and belching with heat from Earth’s interior.</p>
<p>The subsequent cooling of the planet from this molten state, and the crystallisation of these magma oceans into solid rock, was <a href="https://www.nature.com/articles/nature06355">a defining stage</a> in the assembly of our planet’s structure, the chemistry of its surface, and the formation of its early atmosphere.</p>
<p>These primeval rocks, containing clues that might explain Earth’s habitability, were assumed to have been lost to the ravages of plate tectonics. But now, <a href="http://dx.doi.org/10.1126/sciadv.abc7394">my team has discovered</a> the chemical remnants of Earth’s magma oceans in 3.7 billion year-old rocks from southern Greenland, revealing a tantalising snapshot of a time when the Earth was almost entirely molten.</p>
<h2>Hell on Earth</h2>
<p>Earth is the product of a chaotic early solar system, which is believed to have featured a number of catastrophic impacts between the Earth and other planetary bodies. The formation of Earth culminated in <a href="https://www.nature.com/articles/35089010">its collision with a Mars-sized impactor planet</a>, which also resulted in the formation of Earth’s moon some 4.5 billion years ago.</p>
<p>These cosmic clashes are thought to have generated enough energy to melt the Earth’s crust and almost all of our planet’s interior (the mantle), creating planetary-scale volumes of molten rock that formed “magma oceans” hundreds of kilometres in depth. Today, in contrast, Earth’s crust is entirely solid, and the mantle is seen as a “plastic solid”: allowing slow, viscous geological movement a far cry from the liquid magma of Earth’s early mantle.</p>
<p>As the Earth recovered and cooled after its chaotic collisions, its deep magma oceans <a href="https://www.sciencedirect.com/science/article/pii/S0012821X19305771">crystallised and solidified</a>, beginning Earth’s journey to the planet we know today. The volcanic gases which bubbled out of Earth’s cooling magma oceans may have been decisive in the formation and composition of our planet’s early atmosphere – which would eventually support life. </p>
<figure class="align-center ">
<img alt="The Earth's layers in a cross-section, showing the core, mantle, and crust" src="https://images.theconversation.com/files/389270/original/file-20210312-20-8ptx8n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/389270/original/file-20210312-20-8ptx8n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/389270/original/file-20210312-20-8ptx8n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/389270/original/file-20210312-20-8ptx8n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/389270/original/file-20210312-20-8ptx8n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=500&fit=crop&dpr=1 754w, https://images.theconversation.com/files/389270/original/file-20210312-20-8ptx8n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=500&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/389270/original/file-20210312-20-8ptx8n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=500&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Earth is now composed of the inner core, the outer core, the lower mantle, the upper mantle, and the crust.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/structure-planet-earth-space-3d-rendering-1614442552">AlexLMX/Shutterstock</a></span>
</figcaption>
</figure>
<h2>Geological search</h2>
<p>Finding geological evidence for the Earth’s former molten state is extremely difficult. This is because magma ocean events are likely to have taken place over 4 billion years ago, and many of the rocks from that period of Earth’s history have since been recycled by plate tectonics. </p>
<p>But while rocks from this period no longer exist, their chemical traces may still be stored in Earth’s depths. Solidified crystals from Earth’s cooling period would have been so dense that they’d have sunk to the base of Earth’s mantle. Scientists even believe that these mineral residues may be stored in isolated zones deep within <a href="https://www.sciencedirect.com/science/article/pii/S0012821X19301797">Earth’s mantle-core boundary</a>.</p>
<p>If they do exist, these ancient crystal graveyards are inaccessible to us – hiding far too deep for us to take direct samples. And if they were to ever rise to the Earth’s surface, the magma ocean crystals would naturally undergo a process of melting and solidifying, leaving only traces of their origins in the volcanic rocks that make it to Earth’s crust.</p>
<h2>Crystal clues</h2>
<p>We knew Greenland would be a good place to search for these traces of Earth’s molten past. Our samples originate from the Isua supracrustal belt in southwestern Greenland, which is a <a href="https://royalsocietypublishing.org/doi/10.1098/rsnr.2009.0004">famous area for geologists</a>. At first glance, Isua’s rocks look just like any modern basalt you’d find on the sea floor. But these rocks some of the oldest in the world, believed to be between 3.7 and 3.8 billion years old. </p>
<p>On analysing Isua’s rocks, we discovered unique iron isotope signatures. These signatures showed that the region of the mantle from which the rocks had formed had been subjected to very high pressure, over 700 kilometres below Earth’s surface. That’s exactly where minerals formed during magma ocean crystallisation would have been located. </p>
<p>But if these rocks did indeed bear traces of crystallised magma ocean, how did they find their way to the Earth’s surface? The answer lies in how the Earth’s interior melts, producing volcanic rocks on the planet’s surface.</p>
<h2>Melting rocks</h2>
<p>When regions of the Earth’s semi-solid mantle heat up and melt, they rise buoyantly towards the Earth’s crust, ultimately producing volcanic rocks when the magma reaches the surface and cools. By studying the chemistry of these rocks on the surface, we can probe the composition of the material that melted to form them.</p>
<p>The isotopic makeup of Isua rocks revealed that their journey to Earth’s surface involved several stages of crystallisation and remelting in the interior of the planet – a kind of distillation process on their way to the surface. But the rocks that emerged, located in present-day Greenland, still retain chemical signatures that connect them to Earth’s magma-covered past. </p>
<p>The results of our work provide some of the first direct geological evidence for the signature of magma ocean crystals in volcanic rocks found on Earth’s surface. Now, we’d like to understand whether other ancient volcanic rocks across the world can tell us more about Earth’s former magma oceans, or whether we’ve instead stumbled upon a geological oddity: more of a one-off clue. </p>
<p>If other volcanoes may have spewed similar geological artefacts, we might also look to modern eruption hotspots such as Hawaii and Iceland for further <a href="https://www.pnas.org/content/117/49/30993.short">isotopic novelties</a> that speak of Earth’s ancient past. It’s possible that more primordial rocks may be found in the future which could help us understand more about the Earth’s violent, magma-covered past.</p><img src="https://counter.theconversation.com/content/156899/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Helen M Williams has received funding from NERC and the ERC. </span></em></p>The rocks provide rare evidence of a time when Earth’s surface was a deep sea of incandescent magma.Helen M Williams, Reader in Geochemistry, University of CambridgeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1436202020-08-12T20:13:03Z2020-08-12T20:13:03ZFrom cave art to climate chaos: how a new carbon dating timeline is changing our view of history<figure><img src="https://images.theconversation.com/files/352428/original/file-20200812-23-cpm0hy.jpg?ixlib=rb-1.1.0&rect=150%2C110%2C6559%2C4355&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>Geological and archaeological records offer important insights into what seems to be an increasingly uncertain future. </p>
<p>The better we understand what conditions Earth has already experienced, the better we can predict (and potentially prevent) future threats. </p>
<p>But to do this effectively, we need an accurate way to date what happened in the past. </p>
<p>Our research, published today in the journal <a href="https://www.cambridge.org/core/journals/radiocarbon/calibrations/intcal-20">Radiocarbon</a>, offers a way to do just that, through an updated method of calibrating the <a href="https://c14.arch.ox.ac.uk/dating.html">radiocarbon timescale</a>.</p>
<h2>An amazing tool for perusing the past</h2>
<p>Radiocarbon dating has revolutionised our understanding of the past. It is nearly 80 years since Nobel Prize-winning US chemist Willard Libby <a href="https://www.nature.com/articles/d41586-019-01895-z">first suggested</a> minute amounts of a radioactive form of carbon are created in the upper atmosphere. </p>
<p>Libby correctly argued this newly formed radiocarbon (or C-14) rapidly converts to carbon dioxide, is taken up by plants during photosynthesis, and from there travels up through the food chain. </p>
<p>When organisms interact with their environment while alive, they have the same proportion of C-14 as their environment. Once they die they stop taking in new carbon.</p>
<p>Their level of C-14 then halves every 5,730 years due to <a href="https://www.esrl.noaa.gov/gmd/ccgg/isotopes/decay.html">radioactive decay</a>. An organism that died yesterday will still have a high level of C-14, whereas one that died <a href="https://www.acs.org/content/acs/en/education/whatischemistry/landmarks/radiocarbon-dating.html">tens of thousands of years ago will not</a>. </p>
<p>By measuring the level of C-14 in a specimen, we can deduce how long ago that organism died. Currently, with <a href="https://www.nature.com/articles/d41586-019-01895-z">this method</a>, we can date remains up to 60,000 years old.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-what-is-radiocarbon-dating-and-how-does-it-work-9690">Explainer: what is radiocarbon dating and how does it work?</a>
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</em>
</p>
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<h2>A seven-year effort</h2>
<p>If the level of C-14 in the atmosphere had always been constant, radiocarbon dating would be straightforward. But it hasn’t.</p>
<p>Changes in the <a href="https://wserv4.esc.cam.ac.uk/pastclimate/?page_id=19">carbon cycle</a>, impinging <a href="https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/cosmic-radiation">cosmic radiation</a>, the <a href="https://www.pnas.org/content/112/31/9542">use of fossil fuels</a> and <a href="https://theconversation.com/anthropocene-began-in-1965-according-to-signs-left-in-the-worlds-loneliest-tree-91993">20th century nuclear testing</a> have all caused large variations over time. Thus, all radiocarbon dates need to be adjusted (or calibrated) to be turned into accurate calendar ages.</p>
<p>Without this adjustment, dates could be out by up to 10-15%. <a href="https://www.cambridge.org/core/journals/radiocarbon/calibrations">This week we report</a> a seven-year international effort to recalculate three radiocarbon calibration curves: </p>
<ul>
<li>IntCal20 (“20” to signify this year) for objects from the northern hemisphere</li>
<li>SHCal20 for samples from the ocean-dominated southern hemisphere</li>
<li>Marine20 for samples from the world’s oceans.</li>
</ul>
<figure class="align-right ">
<img alt="Close-up of bristlecone pine tree rings." src="https://images.theconversation.com/files/352243/original/file-20200811-20-1ciaghc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/352243/original/file-20200811-20-1ciaghc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/352243/original/file-20200811-20-1ciaghc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/352243/original/file-20200811-20-1ciaghc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/352243/original/file-20200811-20-1ciaghc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/352243/original/file-20200811-20-1ciaghc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/352243/original/file-20200811-20-1ciaghc.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">We dated bristlecone pine tree rings from the second millennium BC.</span>
<span class="attribution"><span class="source">P. Brewer/Uni of Arizona</span></span>
</figcaption>
</figure>
<p>We constructed these updated curves by measuring a plethora of materials that record past radiocarbon levels, but which can also be dated by other methods. </p>
<p>Included in the archives are tree rings from ancient logs preserved in wetlands, cave stalagmites, corals from the continental shelf and sediments drilled from lake and ocean beds. </p>
<figure class="align-center ">
<img alt="An ancient New Zealand kauri tree log." src="https://images.theconversation.com/files/351532/original/file-20200806-24-1vpdpwj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/351532/original/file-20200806-24-1vpdpwj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/351532/original/file-20200806-24-1vpdpwj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/351532/original/file-20200806-24-1vpdpwj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/351532/original/file-20200806-24-1vpdpwj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/351532/original/file-20200806-24-1vpdpwj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/351532/original/file-20200806-24-1vpdpwj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Ancient New Zealand kauri (<em>Agathis australis</em>) logs like this example were used to help construct the calibration curves. This tree is about 40,000 years old and was found buried underground.</span>
<span class="attribution"><span class="source">Nelson Parker</span></span>
</figcaption>
</figure>
<p>In total, the new curves are based on almost 15,000 radiocarbon measurements taken from objects up to 60,000 years old.</p>
<p>Advances in radiocarbon measurement using <a href="https://en.wikipedia.org/wiki/Accelerator_mass_spectrometry">accelerator mass spectrometry</a> mean the updated curves can use very small samples, such as single tree rings from just one year’s growth.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/352423/original/file-20200812-20-685xzm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Close-up of an ancient stalagmite." src="https://images.theconversation.com/files/352423/original/file-20200812-20-685xzm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/352423/original/file-20200812-20-685xzm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=177&fit=crop&dpr=1 600w, https://images.theconversation.com/files/352423/original/file-20200812-20-685xzm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=177&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/352423/original/file-20200812-20-685xzm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=177&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/352423/original/file-20200812-20-685xzm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=223&fit=crop&dpr=1 754w, https://images.theconversation.com/files/352423/original/file-20200812-20-685xzm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=223&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/352423/original/file-20200812-20-685xzm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=223&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Stalagmites from inside the Hulu Cave in China were key to estimating the amount of radiocarbon present in objects between 14,000 and 55,000 years old.</span>
<span class="attribution"><span class="source">Hai Cheng</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>Reassessing old beliefs</h2>
<p>The new radiocarbon calibration curves provide previously impossible precision and detail. As a result, they greatly improve our understanding of how Earth has evolved and how these changes impacted its inhabitants.</p>
<p>One example is the rate of environmental change at the end of the most recent ice age. As the world started to warm some 18,000 years ago, vast ice sheets covering Antarctica, North America (including Greenland) and Europe melted – returning huge volumes of fresh water to the oceans.</p>
<p>But the sea level didn’t rise at a consistent rate like the global temperature. Sometimes it was gradual and other times extremely rapid.</p>
<p>A prime location to detect past sea levels is the <a href="https://www.britannica.com/place/Sunda-Shelf">Sunda Shelf</a>, a large platform of land that was once part of continental Southeast Asia.</p>
<p><a href="https://science.sciencemag.org/content/288/5468/1033.full">One study</a> published in 2000 showed mangrove plant remains found on the seabed recorded a catastrophic 16-metre sea level rise over several hundred years (about half a metre each decade). This event, known as <a href="https://www.giss.nasa.gov/research/briefs/gornitz_10/">Meltwater Pulse-1A</a>, flooded the Sunda Shelf. </p>
<p>Our latest work has modified this story considerably. The new calibration curves reveal this extreme phase of sea level rise actually began 14,640 years ago and lasted just 160 years. </p>
<p>This equates to a staggering one-metre rise each decade – a sobering lesson for the future, considering the current much lower <a href="https://www.theguardian.com/environment/2020/may/08/sea-levels-could-rise-more-than-a-metre-by-2100-experts-say">projected changes for the end of this century</a>. </p>
<h2>An extra half a millennium of art</h2>
<p>Going further back in time, we also looked at some of the world’s oldest cave art in France’s <a href="https://archeologie.culture.fr/chauvet/en">Chauvet Cave</a>, first discovered in 1994. </p>
<p>This cave contains hundreds of beautifully preserved paintings. They depict a European menagerie with long-extinct mammoths, cave lions and woolly rhinoceroses, captured in real-life scenes that provide a window into a lost world.</p>
<p>The Chauvet Cave reveals the artistic sophistication of our <a href="http://www.bradshawfoundation.com/chauvet/index.php">early ancestors</a> in phenomenal detail.</p>
<figure class="align-center ">
<img alt="Chauvet cave paintings depicting wild animals including horses." src="https://images.theconversation.com/files/351623/original/file-20200806-20-11fv1gc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/351623/original/file-20200806-20-11fv1gc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=595&fit=crop&dpr=1 600w, https://images.theconversation.com/files/351623/original/file-20200806-20-11fv1gc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=595&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/351623/original/file-20200806-20-11fv1gc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=595&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/351623/original/file-20200806-20-11fv1gc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=747&fit=crop&dpr=1 754w, https://images.theconversation.com/files/351623/original/file-20200806-20-11fv1gc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=747&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/351623/original/file-20200806-20-11fv1gc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=747&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Chauvet Cave contains hundreds of cave paintings created more than 30,000 years ago.</span>
<span class="attribution"><span class="source">Thomas T/flickr</span></span>
</figcaption>
</figure>
<p>With the new IntCal20 curve, our best estimate for the creation of the oldest radiocarbon-dated painting in the cave is now 36,500 years ago. This is almost 450 years older than previously thought.</p>
<p>These are just two of many more examples of the far-reaching impact our latest work will have. </p>
<p>As <a href="https://www.cambridge.org/core/journals/radiocarbon/calibrations">the new calibration curves</a> are used to re-analyse ages of a host of archaeological and geological records, we can expect major shifts in our understanding of the planet’s past – and hopefully, a better forecast into its future. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/is-that-rock-hashtag-really-the-first-evidence-of-neanderthal-art-31238">Is that rock hashtag really the first evidence of Neanderthal art?</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/143620/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Turney receives funding from The Australian Research Council and is a scientific advisor to cleantech graphite company, CarbonScape (<a href="https://www.carbonscape.com">https://www.carbonscape.com</a>).</span></em></p><p class="fine-print"><em><span>Alan Hogg receives funding from the Marsden fund administered by the Royal Society of New Zealand. </span></em></p><p class="fine-print"><em><span>Paula J. Reimer receives funding from the Leverhulme Trust and UK Research and Innovation. </span></em></p><p class="fine-print"><em><span>Tim Heaton receives funding from the Leverhulme Trust via a research fellowship on "Improving the Measurement of Time via Radiocarbon". </span></em></p>The updated methods are providing a clearer picture of how Earth and its inhabitants evolved over the past 60,000 years - and thus, providing new insight into its future.Christian Turney, Professor, Earth Science and Climate Change, UNSW SydneyAlan Hogg, Professor, Director, Carbon Dating Laboratory, University of WaikatoPaula J. Reimer, Chair professor, Queen's University BelfastTim Heaton, Lecturer in Statistics, University of SheffieldLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1428592020-07-20T19:05:55Z2020-07-20T19:05:55ZAre the Earth’s magnetic poles about to swap places? Strange anomaly gives reassuring clue<figure><img src="https://images.theconversation.com/files/347987/original/file-20200716-35-1nbg7fm.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5540%2C3741&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">St Helena, where Earth's magnetic field behaves strangely.</span> <span class="attribution"><span class="source">Umomos/Shutterstock</span></span></figcaption></figure><p>Deep inside the Earth, liquid iron is flowing and generating the Earth’s magnetic field, which protects our atmosphere and satellites against harmful radiation from the Sun. This field changes over time, and also behaves differently in different parts of the world. The field can even change polarity completely, with the magnetic north and south poles switching places. This is called <a href="https://theconversation.com/the-earths-magnetic-field-reverses-more-often-now-we-know-why-96957">a reversal</a> and last happened 780,000 years ago.</p>
<p>Between South America and southern Africa, there is an enigmatic magnetic region called the South Atlantic Anomaly, where the field is a lot weaker than we would expect. Weak and unstable fields are thought to precede magnetic reversals, so some have argued this feature may be evidence that we are <a href="https://www.frontiersin.org/articles/10.3389/feart.2016.00040/full">facing one</a>. </p>
<p>Now our new study, published in the <a href="https://www.pnas.org/cgi/doi/10.1073/pnas.2001217117">Proceedings of the National Academy of Sciences</a>, has uncovered how long the field in the South Atlantic has been acting up – and sheds light on whether it is something to worry about. </p>
<p>Weak magnetic fields make us more prone to magnetic storms that have the potential to knock out electronic infrastructure, including power grids. The magnetic field of the South Atlantic Anomaly is already so weak that it can adversely affect satellites and their technology when they fly past it.
The strange region is thought to be related to a patch of magnetic field that is pointing a different direction to the rest at the top of the planet’s liquid outer core at a depth of 2,889 kilometres within the Earth. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/348476/original/file-20200720-18366-1l7lzae.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/348476/original/file-20200720-18366-1l7lzae.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=334&fit=crop&dpr=1 600w, https://images.theconversation.com/files/348476/original/file-20200720-18366-1l7lzae.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=334&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/348476/original/file-20200720-18366-1l7lzae.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=334&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/348476/original/file-20200720-18366-1l7lzae.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=420&fit=crop&dpr=1 754w, https://images.theconversation.com/files/348476/original/file-20200720-18366-1l7lzae.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=420&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/348476/original/file-20200720-18366-1l7lzae.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=420&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The geomagnetic field at Earth’s surface with the South Atlantic Anomaly shaded in darkest blue and St Helena marked with a star. The black outline shows the limits of a large region of anomalously slow seismic velocity (implying hot mantle) sitting just on top of Earth’s core. Colours range from weak fields (blue) to strong fields (yellow).</span>
<span class="attribution"><span class="source">Richard K. Bono</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>This “<a href="https://science.sciencemag.org/content/312/5775/900">reverse flux patch</a>” itself has grown over the last 250 years. But we don’t know whether it is simply a one off product of the chaotic motions of the outer core fluid or rather the latest in a series of anomalies within this particular region over long time frames. </p>
<p>If it is a non-recurring feature, then its current location is not significant – it could happen anywhere, perhaps randomly. But if this is the case, the question of whether its increasing size and depth could mark the start of a new reversal remains.</p>
<p>If it is the latest in a string of features reoccurring over millions of years, however, then this would make a reversal less likely. But it would require a specific explanation for what was causing the magnetic field to act strangely in this particular place. </p>
<h2>Volcanic rocks</h2>
<p>To find out, we travelled to Saint Helena – an island in the middle of the South Atlantic Ocean. This island, where Napoleon was exiled to and eventually died in 1821, is made of volcanic rocks. These originate from two separate volcanoes and were erupted from between eight million and 11.5 million years ago. </p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/347981/original/file-20200716-29-gkblfw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/347981/original/file-20200716-29-gkblfw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=795&fit=crop&dpr=1 600w, https://images.theconversation.com/files/347981/original/file-20200716-29-gkblfw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=795&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/347981/original/file-20200716-29-gkblfw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=795&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/347981/original/file-20200716-29-gkblfw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=999&fit=crop&dpr=1 754w, https://images.theconversation.com/files/347981/original/file-20200716-29-gkblfw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=999&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/347981/original/file-20200716-29-gkblfw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=999&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Lead author Yael Engbers is drilling a core on Saint Helena.</span>
<span class="attribution"><span class="source">Andy Biggin</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>When volcanic rocks cool down, small grains of iron-oxide in them get magnetised and therefore save the direction and strength of the Earth’s magnetic field at that time and place. We collected some of those rocks and brought them back to our lab in Liverpool, where we carried out experiments to find out what the magnetic field was like at the time of eruption. </p>
<p>Our results showed us that the field at Saint Helena had very different directions throughout the time of eruption, suggesting that the field in this region was much less stable than in other places. It therefore challenges the idea that the abnormality has only been around for a few centuries. Instead, the whole region has likely been unstable on a timescale of millions of years. This implies the current situation is not as rare as some scientists had assumed, making it less likely that it represents the start of a reversal.</p>
<h2>A window into Earth’s interior</h2>
<p>So what could explain the odd magnetic region? The liquid outer core that is generating it moves (by <a href="https://www.bbc.co.uk/bitesize/guides/zttrd2p/revision/2">convection</a>) at such high speeds that changes can occur on very short, human timescales. The outer core interacts with a layer called the mantle on top of it, which moves far slower. That means the mantle is unlikely to have changed very much in the last ten million years. </p>
<figure class="align-center ">
<img alt="Picture of the Earth's inner structure." src="https://images.theconversation.com/files/348381/original/file-20200720-37-1ko1mab.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/348381/original/file-20200720-37-1ko1mab.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=371&fit=crop&dpr=1 600w, https://images.theconversation.com/files/348381/original/file-20200720-37-1ko1mab.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=371&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/348381/original/file-20200720-37-1ko1mab.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=371&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/348381/original/file-20200720-37-1ko1mab.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=466&fit=crop&dpr=1 754w, https://images.theconversation.com/files/348381/original/file-20200720-37-1ko1mab.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=466&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/348381/original/file-20200720-37-1ko1mab.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=466&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Earth’s inner structure.</span>
<span class="attribution"><span class="source">wikipedia</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>From <a href="https://www.bgs.ac.uk/discoveringGeology/hazards/earthquakes/seismicWaves.html">seismic waves</a> passing through the Earth, we have some insight into the structure of the mantle. Underneath Africa there is a <a href="https://www.nature.com/articles/ngeo2733">large feature</a> in the lowermost mantle where the waves move extra slow through the Earth – meaning there’s most likely an unusually warm region of the lowermost mantle. This possibly causes a different interaction with the outer core at that specific location, which could <a href="https://www.nature.com/articles/ncomms8865">explain</a> the strange behaviour of the magnetic field in the South Atlantic. </p>
<p>Another aspect of the inside of the Earth is the inner core, which is a solid ball the size of Pluto beneath the outer core. This solid feature is slowly growing, but not at the same rate everywhere. There is a possibility that it is growing faster on one side, causing a flow inside the outer core that is reaching the outer boundary with the rocky mantle just under the <a href="https://www.nature.com/articles/nature12574?proof=true">Atlantic hemisphere</a>. This may be causing irregular behaviour of the magnetic field on the long timescales we found on Saint Helena.</p>
<p>Although there are still many questions about the exact cause of the irregular behaviour in the South Atlantic, this study shows us that it has been around for millions of years and is most likely a result of geophysical interactions in the Earth’s mysterious interior.</p><img src="https://counter.theconversation.com/content/142859/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Yael Annemiek Engbers receives funding from The Leverhulme Trust.</span></em></p><p class="fine-print"><em><span>Andrew Biggin receives funding from The Leverhulme Trust and the Natural Environment Research Council.</span></em></p>The Earth’s magnetic field is a lot weaker than we would expect around the island of St Helena.Yael Annemiek Engbers, PhD candidate, University of LiverpoolAndrew Biggin, Professor of Palaeomagnetism, University of LiverpoolLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1427522020-07-20T11:52:47Z2020-07-20T11:52:47ZEarth’s magnetic field may change faster than we thought – new research<figure><img src="https://images.theconversation.com/files/348116/original/file-20200717-33-1cc38wb.jpg?ixlib=rb-1.1.0&rect=47%2C61%2C4475%2C2420&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">It's long been a mystery how fast the Earth's magnetic field changes.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/abstract-earth-magnetic-fields-250125172">Andrey VP/Shutterstock</a></span></figcaption></figure><p>The Earth’s magnetic field, generated 3,000km below our feet in the liquid iron core, is crucially important to life on our planet. It extends out into space, wrapping us in an electromagnetic blanket that shields the atmosphere and satellites from solar radiation.</p>
<p>Yet the magnetic field is <a href="https://theconversation.com/the-earths-magnetic-north-pole-is-shifting-rapidly-so-what-will-happen-to-the-northern-lights-117237">constantly changing</a> in both its strength and direction and has undergone some dramatic shifts in the past. This includes <a href="https://theconversation.com/why-the-earths-magnetic-poles-could-be-about-to-swap-places-and-how-it-would-affect-us-71910">enigmatic reversals of the magnetic poles</a>, with the south pole becoming the north pole and vice versa. </p>
<p>A long-standing question has been how fast the field can change. Our new study, <a href="https://www.nature.com/articles/s41467-020-16888-0">published in Nature Communications</a>, has uncovered some answers.</p>
<p>Rapid changes of the magnetic field are of great interest because they represent the most extreme behaviour of the ocean of molten iron in the liquid core. By tying the observed changes to core processes, we can learn important information about an otherwise inaccessible region of our planet. </p>
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Read more:
<a href="https://theconversation.com/why-the-earths-magnetic-poles-could-be-about-to-swap-places-and-how-it-would-affect-us-71910">Why the Earth's magnetic poles could be about to swap places – and how it would affect us</a>
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<p>Historically, the fastest changes in Earth’s magnetic field have been <a href="https://theconversation.com/the-earths-magnetic-field-reverses-more-often-now-we-know-why-96957">associated with reversals</a>, which occur at irregular intervals a few times every million years. But we discovered field changes that are much faster and more recent than any of the data associated with actual reversals. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=328&fit=crop&dpr=1 600w, https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=328&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=328&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=412&fit=crop&dpr=1 754w, https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=412&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=412&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Magnetic reversal.</span>
<span class="attribution"><span class="source">NASA.</span></span>
</figcaption>
</figure>
<p>Nowadays satellites help monitor changes in the field in both space and time, complemented by navigational records and ground-based observatories. This information reveals that changes in the modern field are rather ponderous, around a tenth of a degree per year. But, while we know that the field has existed <a href="https://science.sciencemag.org/content/327/5970/1238.abstract?casa_token=QREHDyVnFUUAAAAA:tHfGEiP4L3NrRO-TnbT73JpMhjiNdZXqZDMAuW6RyhdJO9NMBMVdJUBSl6dpvBvasC-uNGzTaGuEYJA">for at least 3.5 billion years</a>, we don’t know much about its behaviour prior to 400 years ago. </p>
<p>To track the ancient field, scientists analyse the magnetism recorded by sediments, lava flows and human-made artefacts. That’s because these materials contain microscopic magnetic grains that record the signature of Earth’s field at the time they cooled (for lavas) or were added to the landmass (for sediments). Sediment records from central Italy around the time of the last polarity reversal almost 800,000 years ago <a href="https://academic.oup.com/gji/article/199/2/1110/618671">suggest relatively rapid field changes</a> reaching one degree per year.</p>
<p>Such measurements, however, are extremely challenging, with results <a href="https://academic.oup.com/gji/article-abstract/213/3/1744/4944226?redirectedFrom=fulltext">still being debated</a>. For example, there are uncertainties in the process by which sediments acquire their magnetism. </p>
<h2>Improved measurements</h2>
<p>Our research takes a different approach by using computer models based on the physics of the field generation process. This is combined with a recently published reconstruction of global variations in Earth’s magnetic field spanning the last 100,000 years, based on a compilation of measurements from sediments, lavas and artefacts. </p>
<p>This shows that changes in the direction of Earth’s magnetic field reached rates that are up to ten degrees per year – ten times larger than the fastest currently reported variations. </p>
<p>The fastest observed changes in the geomagnetic field direction occurred around 39,000 years ago. This shift was associated with a locally weak field in a confined region just off the west coast of central America. The event followed the global “<a href="https://www.sciencedirect.com/science/article/abs/pii/S0012821X12003421">Laschamp excursion</a>” – a “failed reversal” of the Earth’s magnetic field around 41,000 years ago in which the magnetic poles briefly moved far from the geographic poles before returning. </p>
<p>The fastest changes appear to be associated with local weakening of the magnetic field. Our model suggests this is caused by movement of patches of intense magnetic field across the surface of the liquid core. These patches are more prevalent at lower latitudes, suggesting that future searches for rapid changes in direction should focus on these areas.</p>
<h2>The impact on society</h2>
<p>Changes in the magnetic field, such as reversals, probably don’t pose a threat to life. Humans did manage to live through the dramatic Laschamp excursion. Today, the threat is mainly down to our reliance on electronic infrastructure. Space weather events such as geomagnetic storms, arising from the interaction between the magnetic field and incoming solar radiation, could disrupt satellite communications, GPS and power grids. </p>
<figure class="align-center ">
<img alt="Picture of a satellite orbiting Earth." src="https://images.theconversation.com/files/348119/original/file-20200717-19-6qkfuv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/348119/original/file-20200717-19-6qkfuv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/348119/original/file-20200717-19-6qkfuv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/348119/original/file-20200717-19-6qkfuv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/348119/original/file-20200717-19-6qkfuv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/348119/original/file-20200717-19-6qkfuv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/348119/original/file-20200717-19-6qkfuv.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">Satellites are at risk from space weather.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/space-satellite-orbiting-earth-elements-this-363654452">Andrey Armyagov/Shutterstock</a></span>
</figcaption>
</figure>
<p>This is troubling – the economic cost of a collapse of the US power grid due to a space-weather event <a href="https://www.swpc.noaa.gov/content/space-weather-faq-frequently-asked-questions">has been estimated at</a> around one trillion dollars. The threat is serious enough for space weather to appear as a <a href="https://www.gov.uk/government/collections/national-risk-register-of-civil-emergencies">high priority</a> on the UK national risk register. </p>
<p>Space weather events tend to be more prevalent in regions where the magnetic field is weak – something we know can happen when the field is changing rapidly. Unfortunately, computer simulations suggest that directional changes arise after the field strength begins to weaken, meaning we cannot predict dips in field strength by just monitoring the field direction. Future work using more advanced simulations can shed more light on this issue. </p>
<p>Is another rapid change in the magnetic field on its way? This is very hard to answer. The fastest changes are also the rarest events: for example, the changes identified around the Laschamp excursion are over two times faster than any other changes occurring over the last 100,000 years. </p>
<p>This makes it difficult for scientists to predict rapid changes – they are “black swan events” that come as a surprise and have a big impact. One possible route forward is to use physics-based models of how the field behaves as part of the forecast. </p>
<p>We still have a lot to learn about the “speed limit” of Earth’s magnetic field. Rapid changes have not yet been directly observed during a polarity reversal, but they should be expected since the field is thought to become globally weak at these times.</p><img src="https://counter.theconversation.com/content/142752/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christopher Davies receives funding from NERC. </span></em></p>Changes in the Earth’s magnetic field pose a great risk to electronic infrastructure.Christopher Davies, Associate professor, University of LeedsLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1191922019-09-10T11:35:15Z2019-09-10T11:35:15ZCurious Kids: What is the Earth made of?<figure><img src="https://images.theconversation.com/files/291130/original/file-20190905-175682-190kaxm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The view of our planet from aboard the International Space Station.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/content/earth-3">Expedition 43/NASA</a></span></figcaption></figure><p><em>Curious Kids is <a href="https://theconversation.com/africa/topics/curious-kids-36782">a series</a> for children in which we ask experts to answer questions from kids.</em></p>
<p><strong>What is the Earth made of? (Zamo, 3, Nairobi)</strong></p>
<p>The Earth started out as a ball of very, very hot liquid. This liquid was mostly made of two elements called oxygen and silica.</p>
<p>But there were small amounts of other elements too. In fact, it was a mixture of almost every element in existence. This all happened around 4.6 billion years ago – that’s a really long time, so long that we can’t even imagine it.</p>
<p>Over time, Earth began to cool down. The heavier elements, like iron and nickel, sank into the centre of the planet (the core). And it’s hot: the Earth’s core is as hot as the surface of the sun, so hot that we wouldn’t be able to go near it, let alone touch it. But you don’t have to worry about getting too close. Wherever you are, whether in Kenya, China or Brazil, the core is around 1800 miles below your feet. This means we will never be able to visit it. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/291135/original/file-20190905-175705-1h25hp8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/291135/original/file-20190905-175705-1h25hp8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/291135/original/file-20190905-175705-1h25hp8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=618&fit=crop&dpr=1 600w, https://images.theconversation.com/files/291135/original/file-20190905-175705-1h25hp8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=618&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/291135/original/file-20190905-175705-1h25hp8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=618&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/291135/original/file-20190905-175705-1h25hp8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=777&fit=crop&dpr=1 754w, https://images.theconversation.com/files/291135/original/file-20190905-175705-1h25hp8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=777&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/291135/original/file-20190905-175705-1h25hp8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=777&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 stuff the Earth is made of makes it a giant magnet, so we can use things like compasses.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>Even though we can’t actually go to the Earth’s core, we know some things about it. We know, for example, that the core is full of iron, because Earth acts like a giant magnet, drawing some elements to it. This magnetic core is very useful: it means we can use a compass to find our way, like sailors in the ocean. </p>
<h2>The Earth’s crust</h2>
<p>Early on in Earth’s history, minerals began to form. Lighter minerals floated up toward the surface and formed a thin crust of rock around the outside of the planet (which we now live on top of). If Earth was the size of a plum, the rocky crust would be a bit like the thin purple skin. If we want to see below the surface, we can drill down into the crust for thousands of meters. </p>
<p>The crust is mostly made of minerals such as quartz, feldspar and mica. These are the shiny crystals in granite rocks, which you can see in the southwest of Kenya. Over long periods of time these minerals break down into small pieces and are carried around by winds, currents and waves to form soft sediments like sand. Look out for sediments when you are by a river, a lake or a beach.</p>
<p>The crust is made up of huge blocks of rock that move around the Earth’s surface very slowly – as slowly as your fingernails grow. The movement of these plates over millions of years causes continents to split apart and smash together. Right now, East Africa is <a href="https://theconversation.com/africa-is-splitting-in-two-here-is-why-94056">splitting into two pieces</a> along the Great Rift Valley and one day in the distant future, the rift may be flooded by the sea. </p>
<p>In between the core and the crust is a hot, squishy body of rock called the mantle. The mantle is mostly made of a mineral called olivine, which is a beautiful shade of green. The hot mantle has currents that flow like treacle. These slow currents push the plates of rock around at the surface. </p>
<h2>The “blue planet”</h2>
<p>But what makes Earth really special is the part above the crust. Our planet is nicknamed the “blue planet” because it is <a href="https://www.usgs.gov/special-topic/water-science-school/science/how-much-water-there-earth?qt-science_center_objects=0#qt-science_center_objects">covered with water</a>. Can you imagine a planet with no seas, no rivers, and no rain? It would be a very sad place, because there would be no animals or plants. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/_38JDGnr0vA?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">There’s a reason Earth is called “the blue planet”</span></figcaption>
</figure>
<p>Above the water and the land is a thick layer of gas called the atmosphere. Our atmosphere protects us from the sun’s powerful rays, and it is full of oxygen – the gas we all need to breathe. </p>
<p>Of all the planets in the solar system, there’s a reason we call Earth home. It’s made of just the right stuff. It’s not too small, or too big, or too hot or too cold. It’s just right.</p>
<p><em>Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to africa-curiouskids@theconversation.com. Please tell us your name, age, and which city you live in. We won’t be able to answer every question but we will do our best.</em></p><img src="https://counter.theconversation.com/content/119192/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Rosalie Tostevin 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>Of all the planets in the solar system, there’s a reason we call Earth home. It’s made of just the right stuff. It’s not too small, or too big, or too hot or too cold. It’s just right.Rosalie Tostevin, Lecturer, University of Cape TownLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1213312019-08-19T15:53:50Z2019-08-19T15:53:50ZFossil fuel extraction could be contributing to climate change by heating Earth from within<figure><img src="https://images.theconversation.com/files/288341/original/file-20190816-192250-1tq71mt.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C3456%2C2167&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/oil-well-plant-against-sunset-265381037?src=lYOnombRvXsP-w4FDQNcww-1-26">Robert Lucian Crusitu/Shutterstock</a></span></figcaption></figure><p>Almost all <a href="https://www.theguardian.com/science/2019/jul/24/scientific-consensus-on-humans-causing-global-warming-passes-99">scientists agree</a> that burning fossil fuels is contributing to climate change. But agreement is less clear cut on how exactly it’s influencing rising global temperatures.</p>
<p>The world is now 1°C warmer than it was in pre-industrial times. Is this solely down to emissions of greenhouse gasses such as CO₂? Meteorologist Hubert Lamb, regarded as the father of modern climatology, <a href="https://notalotofpeopleknowthat.wordpress.com/2014/05/16/hh-lambclimate-present-past-futurein-reviewpart-iii/">argued that</a> CO₂ levels alone couldn’t account for all of the global warming that’s been observed.</p>
<p>His attention turned instead to the role of thermal emissions. Burning fossil fuels doesn’t just produce greenhouse gases, it also generates a lot of heat, which leaks out to the atmosphere. Nuclear tests and volcanic eruptions are some examples of other large heat sources.</p>
<p>Back in 2009, two scientists in Sweden argued that thermal emissions were <a href="https://doi.org/10.1504/IJGW.2009.027100">more important than CO₂</a> for raising global temperatures. A few years later, two Chinese scientists suggested that heat from the earth’s interior could be <a href="https://doi.org/10.1080/10962247.2012.739501">contributing to rising temperatures</a>. They argued that fossil fuels such as coal, oil and gas in layers and crevices beneath the Earth’s surface act as an insulating blanket, trapping heat from the planet’s interior. As these deposits have been emptied by fossil fuel extraction, more of that heat could be reaching the surface.</p>
<p>This idea is similar to how fat tissue under the skin <a href="https://www.ncbi.nlm.nih.gov/pubmed/23472299">prevents body heat from being lost</a> to the surrounding air.
To investigate this theory in the Earth’s crust, we looked at the figures for global fossil fuel production alongside data for temperature changes on the land and sea surface. <a href="http://www.journaljsrr.com/index.php/JSRR/article/view/30117">Our research</a> suggests that it is possible that temperatures may be rising faster in places where fossil fuels are being extracted from the ground. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/288340/original/file-20190816-192219-56hfu4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/288340/original/file-20190816-192219-56hfu4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/288340/original/file-20190816-192219-56hfu4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/288340/original/file-20190816-192219-56hfu4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/288340/original/file-20190816-192219-56hfu4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/288340/original/file-20190816-192219-56hfu4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/288340/original/file-20190816-192219-56hfu4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">When underground reservoirs of fossil fuels are drained, their role as an insulating blanket between the heat of the Earth’s core and the surface is lost.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-vector/flat-industrial-drilling-rig-oil-field-488551216?src=ZhXxKoA5OfFbABzviMHJEw-1-75">Sentavio/Shutterstock</a></span>
</figcaption>
</figure>
<h2>Rising heat</h2>
<p>Between 2007 and 2017, 45.5 billion tonnes of oil and 36.3 billion cubic metres of natural gas were <a href="https://www.bp.com/content/dam/bp/business-sites/en/global/corporate/pdfs/energy-economics/statistical-review/bp-stats-review-2018-full-report.pdf">removed from the Earth’s crust</a>. When oil and gas is extracted, the voids fill with water, which is a less effective insulator. This means more heat from the Earth’s interior can be conducted to the surface, causing the land and the ocean to warm.</p>
<p>We looked at warming trends in oil and gas producing regions across the world. These places, which included Saudi Arabia, the Arabian Gulf, Gulf of Mexico, the North Sea and Alaska, reported high rates of warming – between <a href="http://www.journaljsrr.com/index.php/JSRR/article/view/30117">three and six times higher than the average rate worldwide</a>.</p>
<p>One of the fastest rates of warming has been observed in the Arctic, where temperatures have <a href="https://doi.org/10.1175/JCLI-D-16-0408.1">risen by 0.6°C every decade</a> since 1978. In Antarctica, however, the increase <a href="https://doi.org/10.1175/JCLI-D-16-0408.1">is just 0.1°C</a>, despite <a href="https://www.esrl.noaa.gov/gmd/dv/ftpdata.html">similar levels of atmospheric CO₂</a> in both polar regions.</p>
<p>One reason for the difference may be that fossil fuels are extracted in the Arctic, but not in the Antarctic. From 2007, <a href="https://science.sciencemag.org/content/324/5931/1175.abstract">more than 400 oil and gas fields</a> have been developed north of the Arctic circle, while in Antarctica, <a href="https://www.asoc.org/component/content/article/9-blog/1184-the-antarctic-oil-myth">fossil fuel extraction is banned</a>. </p>
<p>An <a href="https://www.sciencedirect.com/science/article/pii/S0375650516300657">earlier study</a> found evidence for a similar pattern in the north east of England, where a long history of coal mining has dramatically changed the land’s subsurface. So much so that in the former coalfields around Gateshead and Newcastle, a “heat island” effect was detected below and beneath the ground. This meant the atmosphere above the conurbation was about 2°C warmer than the surrounding area, while the ground beneath Gateshead was found to be up to 4.5°C warmer. </p>
<p>Groundwater that discharged from a mine water pumping station was also found to be unusually warm, in part due to heating from the Earth’s interior. The researchers concluded that this effect could be expected in former coalfields across Britain. </p>
<p>Could higher rates of warming in these places be caused by the Earth losing its internal “heat shield”? The idea that some regions have a protective layer below the ground, stopping heat from the Earth’s interior rising to the surface, isn’t as strange as it may sound. After all, the ozone layer in Earth’s atmosphere protects against ultraviolet radiation, but it was <a href="https://doi.org/10.3137/ao.460101">only discovered in the 19th century</a>. Astounding new findings about the Earth system emerge all the time. </p>
<p>If a similar heat-trapping shield exists in the Earth’s crust, much must be done to reinforce it. Carbon emissions that are captured from industry and energy generation could be stored in the crevices left by extracted fossil fuels, re-insulating the sub-surface and helping to slow the thermal emissions that could be amplifying global warming.</p>
<p>Scientists have said for some time that any hope of halting catastrophic climate change rests on leaving <a href="https://theconversation.com/retire-all-existing-and-planned-fossil-fuel-power-plants-to-limit-warming-to-1-5-c-119607">fossil fuels in the ground</a>. Our preliminary findings could give that warning new urgency. Underground reserves of oil have existed for far longer than humans have exploited them – we know worryingly little about the consequences of emptying them.</p>
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<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=140&fit=crop&dpr=1 600w, https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=140&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=140&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=176&fit=crop&dpr=1 754w, https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=176&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=176&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/imagine-newsletter-researchers-think-of-a-world-with-climate-action-113443?utm_source=TCUK&utm_medium=linkback&utm_campaign=TCUKengagement&utm_content=Imagineheader1121331">Click here to subscribe to our climate action newsletter. Climate change is inevitable. Our response to it isn’t.</a></em></p><img src="https://counter.theconversation.com/content/121331/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Adel Sharif receives funding from the Royal Society, EPSRC and BBSRC and is a founding member of Modern Water plc. </span></em></p><p class="fine-print"><em><span>Rizwan Nawaz 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>Fossil fuels are heating the atmosphere – but the fact that we’re burning them may not be the only reason.Rizwan Nawaz, Researcher in Climate and Water, University of LeedsAdel Sharif, Professor of Water and Process Engineering, University of SurreyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1193952019-07-10T03:45:24Z2019-07-10T03:45:24ZEarth’s core has been leaking for billions of years<p>Earth’s magnetic field protects and makes our planet habitable by stopping harmful high-energy particles from space, including from the Sun. The source of this magnetic field is the core at the centre of our planet.</p>
<p>But the core is very difficult to study, partly because it starts at a depth of about 2,900 kilometres, making it too deep to sample and directly investigate.</p>
<p>Yet we are part of a research team that found a way to get information about Earth’s core, with details published recently in <a href="https://www.geochemicalperspectivesletters.org/article1917" title="182W evidence for core-mantle interaction in the source of mantle plumes">Geochemical Perspective Letters</a>.</p>
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Read more:
<a href="https://theconversation.com/we-made-a-moving-tectonic-map-of-the-game-of-thrones-landscape-117393">We made a moving tectonic map of the Game of Thrones landscape</a>
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<h2>It’s hot down there</h2>
<p>The core is the hottest part of our planet with the outer core reaching temperatures of more than 5,000°C. This has to affect the overlying mantle and it is estimated that 50% of volcanic heat comes from the core. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/283241/original/file-20190709-44437-lazrcy.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/283241/original/file-20190709-44437-lazrcy.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/283241/original/file-20190709-44437-lazrcy.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=552&fit=crop&dpr=1 600w, https://images.theconversation.com/files/283241/original/file-20190709-44437-lazrcy.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=552&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/283241/original/file-20190709-44437-lazrcy.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=552&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/283241/original/file-20190709-44437-lazrcy.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=694&fit=crop&dpr=1 754w, https://images.theconversation.com/files/283241/original/file-20190709-44437-lazrcy.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=694&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/283241/original/file-20190709-44437-lazrcy.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=694&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 layers of the Earth from the outer crust to the inner core.</span>
<span class="attribution"><span class="source">Shutterstock/VRVector</span></span>
</figcaption>
</figure>
<p>Volcanic activity is the planet’s main cooling mechanism. Certain volcanism, such as that which is still forming volcanic islands of Hawaii and Iceland, might be linked to the core by mantle plumes that transfer heat from the core to Earth’s surface.</p>
<p>Yet whether there is any exchange of physical material between the core and the mantle has been a subject of debate for decades. </p>
<p>Our findings suggest some core material does transfer into the base of these mantle plumes, and the core has been leaking this material for the past 2.5 billion years. </p>
<p>We discovered this by looking at very small variations in the ratio of isotopes of the element tungsten (isotopes are basically versions of the same element that just contain different numbers of neutrons).</p>
<p>To study Earth’s core, we need to search for chemical tracers of core material in volcanic rocks derived from the deep mantle.</p>
<p>We know the core has a very distinct chemistry, dominated by iron and nickel together with elements such as tungsten, platinum and gold that dissolve in iron-nickel alloy. Therefore, the metal alloy-loving elements are a good choice to investigate for traces of the core.</p>
<h2>The search for tungsten isotopes</h2>
<p><a href="http://www.rsc.org/periodic-table/element/74/tungsten">Tungsten</a> (chemical symbol W) as the base element has 74 protons. Tungsten has several isotopes, including <sup>182</sup>W (with 108 neutrons) and <sup>184</sup>W (with 110 neutrons).</p>
<p>These isotopes of tungsten have potential to be the most conclusive tracers of core material, because the mantle is expected to have much higher <sup>182</sup>W/<sup>184</sup>W ratios than the core. </p>
<p>This is because of another element, <a href="http://www.rsc.org/periodic-table/element/72/hafnium">Hafnium</a> (Hf), which does not dissolve in iron-nickel alloy and is enriched in the mantle, and had a now-extinct isotope (<sup>182</sup>Hf) that decayed to <sup>182</sup>W. This gives the mantle extra <sup>182</sup>W relative to the tungsten in the core. </p>
<p>But the analysis required to detect variations in tungsten isotopes is incredibly challenging, as we are looking at variations in the <sup>182</sup>W/<sup>184</sup>W ratio in parts per million and the concentration of tungsten in rocks is as low as tens of parts per billion. Fewer than five laboratories in the world can do this type of analysis.</p>
<h2>Evidence of a leak</h2>
<p>Our study shows a substantial change in the <sup>182</sup>W/<sup>184</sup>W ratio of the mantle over Earth’s lifetime. Earth’s oldest rocks have significantly higher <sup>182</sup>W/<sup>184</sup>W than than most rocks of the modern-day Earth.</p>
<p>The change in the <sup>182</sup>W/<sup>184</sup>W ratio of the mantle indicates that tungsten from the core has been leaking into the mantle for a long time.</p>
<p>Interestingly, in Earth’s oldest volcanic rocks, over a time frame of 1.8 billion years there is no significant change in the mantle’s tungsten isotopes. This indicates that from 4.3 billion to 2.7 billion years ago, little or no material from the core was transferred into the upper mantle.</p>
<p>But in the subsequent 2.5 billion years, the tungsten isotope composition of the mantle has significantly changed. We infer that a change in <a href="https://www.britannica.com/science/plate-tectonics">plate tectonics</a>, towards the end of the <a href="https://www.britannica.com/science/Archean-Eon">Archean Eon</a> from about 2.6 billion years ago triggered large enough convective currents in the mantle to change the tungsten isotopes of all modern rocks.</p>
<h2>Why the leak?</h2>
<p>If mantle plumes are ascending from the core-mantle boundary to the surface, it follows that material from Earth’s surface must also descend into the deep mantle. </p>
<p>Subduction, the term used for rocks from Earth’s surface descending into the mantle, takes oxygen-rich material from the surface into the deep mantle as an integral component of plate tectonics.</p>
<p>Experiments show that increase in oxygen concentration at the core-mantle boundary could cause tungsten to separate out of the core and into the mantle. </p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/the-pulse-of-a-volcano-can-be-used-to-help-predict-its-next-eruption-117005">The 'pulse' of a volcano can be used to help predict its next eruption</a>
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<p>Alternatively, inner core solidification would also increase the oxygen concentration of the outer core. In this case, our new results could tell us something about the evolution of the core, including the origin of Earth’s magnetic field.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/283373/original/file-20190709-44497-lulo62.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/283373/original/file-20190709-44497-lulo62.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=519&fit=crop&dpr=1 600w, https://images.theconversation.com/files/283373/original/file-20190709-44497-lulo62.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=519&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/283373/original/file-20190709-44497-lulo62.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=519&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/283373/original/file-20190709-44497-lulo62.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=653&fit=crop&dpr=1 754w, https://images.theconversation.com/files/283373/original/file-20190709-44497-lulo62.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=653&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/283373/original/file-20190709-44497-lulo62.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=653&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Cartoon showing the differences in tungsten isotope ratios between the Earth’s core and mantle, and how the Earth’s core might be leaking material into the mantle plumes.</span>
<span class="attribution"><span class="source">Credit: Neil Bennett</span></span>
</figcaption>
</figure>
<p>Earth’s core started as entirely liquid metal and has been cooling and partially solidifying over time. The magnetic field is generated by the spin of the inner solid core. The time of inner core crystallisation is one of the most difficult questions to answer in Earth and planetary sciences.</p>
<p>Our study gives us a tracer that can be used to investigate core-mantle interaction and the change in the internal dynamics of our planet, and which can boost our understanding of how and when the magnetic field was turned on.</p><img src="https://counter.theconversation.com/content/119395/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Hanika Rizo receives funding from NSERC Discovery Grant (Canada) and the Early Researcher Award from the Ontario Government (Canada). </span></em></p><p class="fine-print"><em><span>Denis Andrault a reçu des financements de UCA, CNRS, ClerVolc.</span></em></p><p class="fine-print"><em><span>David Murphy 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 findings suggest the core has been leaking for the past 2.5 billion years, and that could help scientists understand how the core was formed.Hanika Rizo, Assistant Professor, Carleton UniversityDavid Murphy, Lecturer in Geoscience, Queensland University of TechnologyDenis Andrault, Professor, Université Clermont Auvergne (UCA)Licensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1075372018-12-03T13:47:43Z2018-12-03T13:47:43ZCurious Kids: what would happen if the Earth’s core went cold?<figure><img src="https://images.theconversation.com/files/248129/original/file-20181130-194922-1cuh3u0.jpg?ixlib=rb-1.1.0&rect=0%2C603%2C6324%2C3921&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">It's core to life on Earth. </span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/earth-core-structure-elements-this-3d-284818022?src=1ZzZMfmpZ3QaYnwVT_p8Kw-1-19">Shutterstock.</a></span></figcaption></figure><p><em><a href="https://theconversation.com/au/topics/curious-kids-36782">Curious Kids</a> is a series for children of all ages, where The Conversation asks experts to answer questions from kids. All questions are welcome: find out how to enter at the bottom of this article.</em> </p>
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<blockquote>
<p><strong>What would happen if the Earth’s core was no longer molten hot? – Amelia, age 13, Devon, UK</strong></p>
</blockquote>
<p>Thanks Amelia, that’s a very good question! The Earth’s core is cooling down very slowly over time. One day, when the core has completely cooled and become solid, it will have a huge impact on the whole planet. Scientists think that when that happens, Earth might be <a href="https://www.nap.edu/read/13117/chapter/9#145">a bit like Mars</a>, with a very thin atmosphere and no more volcanoes or earthquakes. Then it would be very difficult for life to survive – but that won’t be a problem for several billions of years.</p>
<p>Right now, the Earth’s core is not entirely molten. The inner core is a sphere of solid iron, while the outer core is made of molten iron thousands of kilometres thick.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/248388/original/file-20181203-194925-f62hpa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/248388/original/file-20181203-194925-f62hpa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/248388/original/file-20181203-194925-f62hpa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=420&fit=crop&dpr=1 600w, https://images.theconversation.com/files/248388/original/file-20181203-194925-f62hpa.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=420&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/248388/original/file-20181203-194925-f62hpa.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=420&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/248388/original/file-20181203-194925-f62hpa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=528&fit=crop&dpr=1 754w, https://images.theconversation.com/files/248388/original/file-20181203-194925-f62hpa.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=528&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/248388/original/file-20181203-194925-f62hpa.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=528&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">What’s inside the Earth.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/rendering-3d-inner-structure-earth-scientific-785502640">Shutterstock.</a></span>
</figcaption>
</figure>
<p>Scientists know this because the shock waves made by earthquakes can be recorded on the other side of the Earth – and we would not expect to see them there if the inner core was also molten. </p>
<p>The whole core was molten back when the Earth was first formed, about 4.5 billion years ago. Since then, the Earth has gradually been cooling down, losing its heat to space. As it cooled, the solid inner core formed, and it’s been growing in size ever since.</p>
<p>But this process is very slow: the inner core only grows about one millimetre a year, because the Earth has a rocky mantle in between its hot core and its cold surface, which stops it from cooling down too quickly – just like your coat keeps you warm in winter.</p>
<p>The slow cooling of our planet causes the molten iron in the outer core to flow and swirl fast as heat is transported to the mantle, and this gives Earth its magnetic field. The magnetic field is like a magnet that acts at a distance, and even though we cannot see it with our eyes, it does lots of important jobs on our planet. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/248400/original/file-20181203-194928-1fqu1uo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/248400/original/file-20181203-194928-1fqu1uo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=487&fit=crop&dpr=1 600w, https://images.theconversation.com/files/248400/original/file-20181203-194928-1fqu1uo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=487&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/248400/original/file-20181203-194928-1fqu1uo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=487&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/248400/original/file-20181203-194928-1fqu1uo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=613&fit=crop&dpr=1 754w, https://images.theconversation.com/files/248400/original/file-20181203-194928-1fqu1uo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=613&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/248400/original/file-20181203-194928-1fqu1uo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=613&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Earth’s magnetic field in action.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/planet-earths-magnetic-field-against-suns-121554235?src=VhATHN7Mq5WHCGldkfS6Lg-1-12">Shutterstock.</a></span>
</figcaption>
</figure>
<p>The Earth’s magnetic field protects life on the Earth’s surface from harmful particles coming from the sun. It also keeps the planet’s atmosphere in place and helps animals to find their way around.</p>
<p>The heat escaping from the core also makes material move around in different layers of our planet – from the rocky mantle to the rigid plates on the surface, where you and I live. </p>
<p>This movement can cause the plates on the surface to rub together, which creates earthquakes and volcanoes. That’s why living in places where two plates meet – such as Nepal or Japan – can be very dangerous. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/248130/original/file-20181130-194935-1385qhc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/248130/original/file-20181130-194935-1385qhc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/248130/original/file-20181130-194935-1385qhc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/248130/original/file-20181130-194935-1385qhc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/248130/original/file-20181130-194935-1385qhc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/248130/original/file-20181130-194935-1385qhc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/248130/original/file-20181130-194935-1385qhc.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">An active volcano in Guatemala.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/lava-going-down-volcano-fuego-antigua-787922728?src=47_cfahON1xdhefOhg0j1g-1-0">Shutterstock.</a></span>
</figcaption>
</figure>
<p>When the molten outer core cools and becomes solid, a very long time in the future, the Earth’s magnetic field will disappear. </p>
<p>When that happens, compasses will stop pointing north, birds will not know where to fly when they migrate, and the Earth’s atmosphere will disappear. This will make life on Earth very difficult for human beings and other life forms. </p>
<p>When the Earth has cooled completely, the movement in the mantle will also stop eventually. Then, the plates on the surface will no longer move and there will be fewer earthquakes and volcanic eruptions. </p>
<p>You might think that this would be good for people – especially those living in places like Tokyo – but volcanic eruptions also produce fertile soil for farming, and gases that make up the air that we breathe. </p>
<p>After all this, Earth could look a bit like Mars. On the surface of Mars, scientists have seen features that are related to volcanoes and moving plates. But they are not moving any more, and there is no magnetic field and only a thin atmosphere left. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/LKLITDmm4NA?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
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<p>We do not know whether the core of Mars is still molten or not, but <a href="https://theconversation.com/mars-insight-here-is-whats-next-after-the-tricky-landing-107749">a robot called InSight</a> recently landed on Mars that will help us to find out! </p>
<p>But for now, you don’t have to worry about the Earth’s core losing all its heat and becoming solid, because the mantle is wrapped around the core, keeping it nice and warm. </p>
<hr>
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<span class="attribution"><a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<li><p><em><a href="https://theconversation.com/curious-kids-what-existed-before-the-big-bang-did-something-have-to-be-there-to-go-boom-103742?utm_source=TCUK&utm_medium=linkback&utm_campaign=TCUKengagement&utm_content=CuriousKidsUK">What existed before the Big Bang? – Ethan, age ten, Sydney, Australia</a></em></p></li>
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<li><p><em><a href="https://theconversation.com/curious-kids-how-do-moths-eat-our-clothes-105978?utm_source=TCUK&utm_medium=linkback&utm_campaign=TCUKengagement&utm_content=CuriousKidsUK">How do moths eat our clothes? – Albie, age five, Australia</a></em></p></li>
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<p class="fine-print"><em><span>Paula Koelemeijer receives funding from the Royal Society and University College Oxford. </span></em></p>The Earth’s core is cooling down, and one day it will be completely solid – when that happens, Earth might look a lot like Mars.Paula Koelemeijer, Royal Society University Research Fellow, UCLLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/866382017-11-08T10:47:41Z2017-11-08T10:47:41ZMysterious ‘geomagnetic spike’ 3,000 years ago challenges our understanding of the Earth’s interior<figure><img src="https://images.theconversation.com/files/193179/original/file-20171103-26426-11y44sy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Earth has a powerful magnetic field.</span> <span class="attribution"><span class="source">NASA</span></span></figcaption></figure><p>The Earth’s magnetic field, generated some 3,000km below our feet in the liquid iron core, threads through the whole planet and far into space – protecting life and satellites from harmful radiation from the sun. But this shielding effect is far from constant, as the field strength varies significantly in both space and time. </p>
<p>Over the last century, the field strength has changed relatively slowly: the biggest change is a 10% fall in the southern Atlantic, which is still a large enough effect to <a href="https://news.spaceweather.com/new-maps-of-the-south-atlantic-anomaly/">cause electronic problems for satellites</a> that have passed through the region. However, <a href="http://www.sciencedirect.com/science/article/pii/S0012821X16300553">new observations</a> and <a href="https://www.nature.com/articles/ncomms15593">modelling</a> suggest that a much greater change strangely occurred around 1000BC in a much smaller region. </p>
<p>This “geomagnetic spike” offers a potentially profound new insight into the dynamics and evolution of Earth’s hidden interior that is now starting to be uncovered. </p>
<p>So what are geomagnetic spikes and what are the prospects and implications of another one coming along? The geomagnetic spike of 1000BC was <a href="https://www.tau.ac.il/sites/tau.ac.il.en/files/media_server/imported/662/files/2013/08/ShaarETAL11_Timna30_EPSL.pdf">first identified</a> from copper slag heaps located in <a href="https://www.wired.com/2010/12/magnetic-copper-slag/">Jordan and Israel</a>. These were dated from organic material within the slag heaps using radiocarbon dating. </p>
<p>Scientists then investigated the copper using sophisticated laboratory techniques to work out what the Earth’s magnetic field was at the time – relying on the fact that when melted iron cools rapidly, it freezes with a signature of the field at that instant. By taking samples from different layers of the slag heap – with slightly different ages and magnetisation – they could also see how the field strength changed with time. They found that the copper slag had recorded Earth’s magnetic field strength rising and then falling by over 100% in only 30 years.</p>
<p>Unexpectedly high field strengths around 1000BC have also been uncovered in <a href="https://www.sciencedirect.com/science/article/pii/S0012821X1200475X">Turkey</a>, <a href="https://www.pnas.org/content/114/1/39.abstract">China</a> and <a href="http://www.geofisica.unam.mx/LatinmagLetters/LL13-03-SP/A/PA07.pdf">Georgia</a> from a variety of sources. Remarkably, the field strength in <a href="https://www.nature.com/articles/ncomms15593">India, Egypt and Cyprus</a> around the same time was completely normal, indicating that the spike was perhaps only 2,000km wide. Such a rapid change over such a small area marks out the geomagnetic spike as one of the most extreme variations of Earth’s magnetic field ever recorded.</p>
<p>The spike seen in Jordan is the result of a much stronger and narrower magnetic feature that was created in Earth’s liquid core. The process that generated the spike is still shrouded in mystery, though it is likely related to the flow of iron within the core, which drags around the magnetic field as it moves (currents produce magnetic fields). The core is heated from below and cooled from above, so the iron within is thought to undergo vigorous turbulent motion, similar to a strongly heated pan of water. One possibility is that the spike was drawn to the surface of Earth’s core <a href="https://www.nature.com/articles/ncomms15593">by a jet of upward moving iron</a>. </p>
<p>After this, the spike may have moved northwest before merging with other magnetic features near the geographic poles. Alternatively, the spike intensity may have waned while it remained under Jordan. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/193739/original/file-20171108-1987-199z3mk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/193739/original/file-20171108-1987-199z3mk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=130&fit=crop&dpr=1 600w, https://images.theconversation.com/files/193739/original/file-20171108-1987-199z3mk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=130&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/193739/original/file-20171108-1987-199z3mk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=130&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/193739/original/file-20171108-1987-199z3mk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=163&fit=crop&dpr=1 754w, https://images.theconversation.com/files/193739/original/file-20171108-1987-199z3mk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=163&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/193739/original/file-20171108-1987-199z3mk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=163&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Figure 1. Strength of Earth’s magnetic field in 2010 (left) and 1000BC (right).</span>
<span class="attribution"><span class="source">Nature comms and https://academic.oup.com/gji/article/197/2/815/617637</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>All of these options suggest that behaviour of the liquid iron at the top of Earth’s core around 1000BC was very different to that seen today. Most of our knowledge of the core derives from roughly the last 200 years, corresponding to the time when direct magnetic field measurements have been available. Prior to discovery of the spike there was no reason to suspect that core flow speeds would be much different in 1000BC to today – indeed, the available models suggest there was little difference.</p>
<p>However, explaining the rapid changes associated with the spike requires flows <a href="https://www.sciencedirect.com/science/article/pii/S0012821X13006547">five to ten times those at present</a>, a large change in a short space of time. Moreover, such a narrow spike requires a similarly localised flow, which contrasts with the global-scale circulations we see today. The prospect that the iron core could flow faster and change more suddenly than previously thought, together with the possibility that even more extreme spike-like events occurred in the past, is challenging some conventional views on the dynamics of Earth’s core. </p>
<h2>Future impact?</h2>
<p>Changes in Earth’s magnetic field are not generally thought to have direct consequences for life, but there are potentially significant societal implications that arise from our reliance on electronic infrastructure. A variety of effects <a href="https://theconversation.com/why-the-earths-magnetic-poles-could-be-about-to-swap-places-and-how-it-would-affect-us-71910">can arise</a> from interactions between Earth’s magnetic field and charged particles reaching Earth from the sun. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/193744/original/file-20171108-27001-1w9t6s5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/193744/original/file-20171108-27001-1w9t6s5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/193744/original/file-20171108-27001-1w9t6s5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/193744/original/file-20171108-27001-1w9t6s5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/193744/original/file-20171108-27001-1w9t6s5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/193744/original/file-20171108-27001-1w9t6s5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/193744/original/file-20171108-27001-1w9t6s5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Aurora during a geomagnetic storm.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>Of particular importance are geomagnetic storms (caused by the solar wind), which are known to cause power outages and disruption to satellite and communications systems. The economic implications of severe storms are estimated to <a href="https://news.agu.org/press-release/extreme-space-weather-induced-electricity-blackouts-could-cost-u-s-more-than-40-billion-daily/?utm_source=CPRE&utm_medium=email&utm_campaign=press%20releases&utm_content=17-03%20space%20weather%20economic%20impacts">run into billions of pounds</a> and their importance is now reflected in the <a href="https://www.gov.uk/government/publications/national-risk-register-of-civil-emergencies-2017-edition">national risk register</a>. </p>
<p>Geomagnetic storms tend to be most prevalent in regions where Earth’s magnetic field is unusually weak. Spikes are regions of unusually strong magnetic field, but a <a href="https://simple.wikipedia.org/wiki/Maxwell%27s_equations">fundamental law of nature</a> means that they must be accompanied by regions of weaker field elsewhere on the globe. The key question is whether the field gets a little bit weaker over a large region or becomes very weak in just a small region. The latter “anti-spike” scenario could be similar to or more extreme than the current south Atlantic weak spot. </p>
<p>Whether there will be more spikes is hard to say. Until very recently, the Jordanian spike was the only such event ever observed. However, there is now <a href="https://www.sciencedirect.com/science/article/pii/S0012821X16300760">tantalising new evidence</a> for another spike-like feature in Texas, also around 1000BC. Our understanding of what spikes should look like, how they change in time, and <a href="https://www.nature.com/articles/ncomms15593">how they relate to the motion</a> of the liquid iron in Earth’s core are also improving rapidly. </p>
<p>Coupled with numerical simulations that model the dynamics of Earth’s core, it may soon be possible to make the first predictions of how often spikes occur and the most likely locations where they could have occurred in the past (and may occur in the future). It could turn out that they are more common than we think.</p><img src="https://counter.theconversation.com/content/86638/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christopher Davies receives funding from NERC (project reference NE/L011328/1). </span></em></p>A strange patch of extremely strong magnetic field occurred over Jordan in 1000BC. Could we be about to face another one?Christopher Davies, NERC Independent Research Fellow/Lecturer in Geophysics, University of LeedsLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/775352017-05-15T12:00:34Z2017-05-15T12:00:34ZA giant lava lamp inside the Earth might be flipping the planet’s magnetic field<figure><img src="https://images.theconversation.com/files/169328/original/file-20170515-6984-1u4gelz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>If you could travel back in time 41,000 years to the last ice age, your compass would point south instead of north. That’s because for a period of a few hundred years, the <a href="https://phys.org/news/2012-10-extremely-reversal-geomagnetic-field-climate.html">Earth’s magnetic field was reversed</a>. Magnetic <a href="https://theconversation.com/why-the-earths-magnetic-poles-could-be-about-to-swap-places-and-how-it-would-affect-us-71910">reversals have happened repeatedly</a> over the planet’s history, sometimes lasting hundreds of thousands of years. We know this from the way it affects the alignment of magnetic minerals, that we can now study on the Earth’s surface.</p>
<p>Several ideas exist to explain why magnetic field reversals happen. <a href="http://www.sciencedirect.com/science/article/pii/S0012821X15000345">One of these</a> just became more plausible. My colleagues and I discovered that regions on top of the Earth’s core could behave like giant lava lamps, with blobs of rock periodically rising and falling deep inside our planet. This could affect its magnetic field and cause it to flip. The way we made this discovery was by studying signals from some of the world’s most destructive earthquakes.</p>
<p>Around 3,000km below our feet – 270 times further down than the deepest part of the ocean – is the start of the Earth’s core, a liquid sphere of mostly molten iron and nickel. At this <a href="https://www.scientificamerican.com/article/the-core-mantle-boundary-2005-07/">boundary between the core</a> and the rocky mantle above, the temperature is almost 4,000°C degrees, similar to that on the surface of a star, with a pressure more than 1.3m times that at the Earth’s surface.</p>
<p>On the mantle side of this boundary, solid rock gradually flows over millions of years, driving the plate tectonics that cause continents to move and change shape. On the core side, fluid, magnetic iron swirls vigorously, creating and sustaining the Earth’s magnetic field that protects the planet from the radiation of space that would otherwise strip away our atmosphere.</p>
<p>Because it is so far underground, the main way we can study the core-mantle boundary is by looking at the seismic signals generated by earthquakes. Using information about the shape and speed of seismic waves, we can work out what the part of the planet they have travelled through to reach us is like. After a particularly large earthquake, the whole planet vibrates like a ringing bell, and measuring these oscillations in different places can tell us how the structure varies within the planet.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/169329/original/file-20170515-7009-kt9j8t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/169329/original/file-20170515-7009-kt9j8t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/169329/original/file-20170515-7009-kt9j8t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/169329/original/file-20170515-7009-kt9j8t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/169329/original/file-20170515-7009-kt9j8t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/169329/original/file-20170515-7009-kt9j8t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/169329/original/file-20170515-7009-kt9j8t.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">New model Earth?</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>In this way, we know there are two large regions at the top of the core where seismic waves travel more slowly than in surrounding areas. Each region is so large that it would be 100 times taller than Mount Everest if it were on the surface of the planet. These regions, termed <a href="http://www.nature.com/ngeo/journal/v9/n7/abs/ngeo2733.html">large-low-velocity-provinces</a> or more often just “blobs”, have a significant impact on the dynamics of the mantle. They also influence how the core cools, which alters the flow in the outer core. </p>
<p>Several particularly destructive earthquakes over recent decades have enabled us to measure a special kind of seismic oscillations that travel along the core-mantle boundary, <a href="http://onlinelibrary.wiley.com/doi/10.1002/grl.50514/full">known as Stoneley modes</a>. <a href="https://www.nature.com/articles/ncomms15241">Our most recent research</a> on these modes shows that the two blobs on top of the core have a lower density compared to the surrounding material. This suggests that material is actively rising up towards the surface, consistent with other geophysical observations. </p>
<h2>New explanation</h2>
<p>These regions might be less dense simply because they are hotter. But an exciting alternative possibility is that the chemical composition of these parts of the mantle cause them to behave like the blobs in a lava lamp. This would mean they heat up and periodically rise towards the surface, before cooling and splashing back down on the core.</p>
<p>Such behaviour would change the way in which heat is extracted from the core’s surface over millions of years. And this <a href="http://www.sciencedirect.com/science/article/pii/S0012821X15000345">could explain</a> why the Earth’s magnetic field sometimes reverses. The fact that the field has changed so many times in the Earth’s history suggests that the internal structure we know today may also have changed.</p>
<p>We know the core is covered with a landscape of mountains and valleys like the Earth’s surface. By using more data from Earth oscillations to study this topography, we will be able to produce more detailed maps of the core that will give us a much better understanding of what is going on deep below our feet.</p><img src="https://counter.theconversation.com/content/77535/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Paula Koelemeijer receives funding from University College, Oxford. </span></em></p>Signals from violent earthquakes are helping reveal the landscape of the planet’s insides.Paula Koelemeijer, Postdoctoral Fellow in Global Seismology, University of OxfordLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/475282017-02-06T04:52:22Z2017-02-06T04:52:22ZDoes an anomaly in the Earth’s magnetic field portend a coming pole reversal?<figure><img src="https://images.theconversation.com/files/155051/original/image-20170131-3248-1n8ah.jpg?ixlib=rb-1.1.0&rect=382%2C12%2C3873%2C2707&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">What's north would become south.</span> <span class="attribution"><a class="source" href="https://spaceflight.nasa.gov/gallery/images/station/crew-23/html/iss023e058455.html">NASA </a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>The Earth is blanketed by a magnetic field. It’s what makes compasses point north, and protects our atmosphere from continual bombardment from space by charged particles such as protons. Without a magnetic field, our atmosphere would slowly be stripped away by harmful radiation, and life would almost certainly not exist as it does today.</p>
<p>You might imagine the magnetic field is a timeless, constant aspect of life on Earth, and to some extent you would be right. But Earth’s magnetic field actually does change. Every so often – on the order of several hundred thousand years or so – the magnetic field has flipped. North has pointed south, and vice versa. And when the field flips it also tends to become very weak.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/154585/original/image-20170127-30413-incc40.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/154585/original/image-20170127-30413-incc40.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=328&fit=crop&dpr=1 600w, https://images.theconversation.com/files/154585/original/image-20170127-30413-incc40.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=328&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/154585/original/image-20170127-30413-incc40.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=328&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/154585/original/image-20170127-30413-incc40.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=412&fit=crop&dpr=1 754w, https://images.theconversation.com/files/154585/original/image-20170127-30413-incc40.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=412&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/154585/original/image-20170127-30413-incc40.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=412&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">On the left, the Earth’s magnetic field we’re used to. On the right, a model of what the magnetic field might be like during a reversal.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:NASA_54559main_comparison1_strip.gif">NASA/Gary Glazmaier</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>What currently has geophysicists like us abuzz is the realization that the strength of Earth’s magnetic field has been decreasing for the last 160 years at an alarming rate. This collapse is centered in a huge expanse of the Southern Hemisphere, extending from Zimbabwe to Chile, known as the South Atlantic Anomaly. The magnetic field strength is so weak there that it’s a hazard for satellites that orbit above the region – the field no longer protects them from <a href="http://scitechdaily.com/new-hubblecast-video-explores-south-atlantic-anomaly/">radiation which interferes</a> with satellite electronics.</p>
<p>And the field is continuing to grow weaker, potentially portending even more dramatic events, including a global reversal of the magnetic poles. Such a major change would affect our navigation systems, as well as the transmission of electricity. The spectacle of the northern lights might appear at different latitudes. And because more radiation would reach Earth’s surface under very low field strengths during a global reversal, it also might affect rates of cancer.</p>
<p>We still don’t fully understand what the extent of these effects would be, adding urgency to our investigation. We’re turning to some perhaps unexpected data sources, including 700-year-old African archaeological records, to puzzle it out.</p>
<h2>Genesis of the geomagnetic field</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/154587/original/image-20170127-30424-1tgdu3e.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/154587/original/image-20170127-30424-1tgdu3e.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/154587/original/image-20170127-30424-1tgdu3e.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=371&fit=crop&dpr=1 600w, https://images.theconversation.com/files/154587/original/image-20170127-30424-1tgdu3e.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=371&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/154587/original/image-20170127-30424-1tgdu3e.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=371&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/154587/original/image-20170127-30424-1tgdu3e.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=466&fit=crop&dpr=1 754w, https://images.theconversation.com/files/154587/original/image-20170127-30424-1tgdu3e.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=466&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/154587/original/image-20170127-30424-1tgdu3e.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=466&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Cutaway image of the Earth’s interior.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Earth_poster.svg">Kelvinsong</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Earth’s magnetic field is created by <a href="http://www.geomag.bgs.ac.uk/education/earthmag.html#_Toc2075563">convecting iron in our planet’s liquid outer core</a>. From the wealth of <a href="https://www.ngdc.noaa.gov/geomag/geomag.shtml">observatory and satellite data</a> that document the magnetic field of recent times, we can model what the field would look like if we had a compass immediately above the Earth’s swirling liquid iron core. </p>
<p>These analyses reveal an astounding feature: There’s a patch of reversed polarity beneath southern Africa at the core-mantle boundary where the liquid iron outer core meets the slightly stiffer part of the Earth’s interior. In this area, the polarity of the field is opposite to the average global magnetic field. If we were able to use a compass deep under southern Africa, we would see that in this unusual patch north actually points south.</p>
<p>This patch is the main culprit creating the South Atlantic Anomaly. In numerical simulations, unusual patches similar to the one beneath southern Africa appear immediately prior to geomagnetic reversals.</p>
<p>The poles have reversed frequently over the history of the planet, but the <a href="http://doi.org/10.1002/ggge.20263">last reversal is in the distant past</a>, some 780,000 years ago. The rapid decay of the recent magnetic field, and its pattern of decay, naturally raises the question of what was happening prior to the last 160 years.</p>
<h2>Archaeomagnetism takes us further back in time</h2>
<p>In archaeomagnetic studies, geophysicists team with archaeologists to learn about the past magnetic field. For example, clay used to make pottery contains small amounts of magnetic minerals, such as magnetite. When the clay is heated to make a pot, its magnetic minerals lose any magnetism they may have held. Upon cooling, the magnetic minerals record the direction and intensity of the magnetic field at that time. If one can determine the age of the pot, or the archaeological site from which it came (using radiocarbon dating, for instance), then an archaeomagnetic history can be recovered. </p>
<p>Using this kind of data, we have a partial history of archaeomagnetism for the Northern Hemisphere. In contrast, the Southern Hemisphere archaeomagnetic record is scant. In particular, there have been virtually no data from southern Africa – and that’s the region, <a href="http://dx.doi.org/10.1016/j.epsl.2011.03.030">along with South America</a>, that might provide the most insight into the history of the reversed core patch creating today’s South Atlantic Anomaly.</p>
<p>But the ancestors of today’s southern Africans, Bantu-speaking metallurgists and farmers who began to migrate into the region between 2,000 and 1,500 years ago, unintentionally left us some clues. <a href="http://doi.org/10.1146/annurev.an.11.100182.001025">These Iron Age people</a> lived in huts built of clay, and stored their grain in hardened clay bins. As the <a href="http://www.sahistory.org.za/article/pre-1500">first agriculturists of the Iron Age of southern Africa</a>, they relied heavily on rainfall. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/154840/original/image-20170130-7693-ejv2dc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/154840/original/image-20170130-7693-ejv2dc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/154840/original/image-20170130-7693-ejv2dc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/154840/original/image-20170130-7693-ejv2dc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/154840/original/image-20170130-7693-ejv2dc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/154840/original/image-20170130-7693-ejv2dc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/154840/original/image-20170130-7693-ejv2dc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/154840/original/image-20170130-7693-ejv2dc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Grain bins of the style used centuries ago.</span>
<span class="attribution"><span class="source">John Tarduno</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>The communities often responded to times of drought with rituals of cleansing that involved burning mud granaries. This somewhat tragic series of events for these people was ultimately a boon many hundreds of years later for archaeomagnetism. Just as in the case of the firing and cooling of a pot, the clay in these structures recorded Earth’s magnetic field as they cooled. Because the floors of these ancient huts and grain bins can sometimes be found intact, we can sample them to obtain a record of both the direction and strength of their contemporary magnetic field. Each floor is a small magnetic observatory, with its compass frozen in time immediately after burning.</p>
<p><a href="http://dx.doi.org/10.1038/ncomms8865">With our colleagues, we’ve focused our sampling</a> on Iron Age village sites that dot the Limpopo River Valley, bordered today by Zimbabwe to the north, Botswana to the west and South Africa to the south.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/154841/original/image-20170130-7693-1w1eu3f.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/154841/original/image-20170130-7693-1w1eu3f.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/154841/original/image-20170130-7693-1w1eu3f.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=196&fit=crop&dpr=1 600w, https://images.theconversation.com/files/154841/original/image-20170130-7693-1w1eu3f.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=196&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/154841/original/image-20170130-7693-1w1eu3f.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=196&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/154841/original/image-20170130-7693-1w1eu3f.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=246&fit=crop&dpr=1 754w, https://images.theconversation.com/files/154841/original/image-20170130-7693-1w1eu3f.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=246&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/154841/original/image-20170130-7693-1w1eu3f.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=246&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">What’s happening deep within the Earth, beneath the Limpopo River Valley?</span>
<span class="attribution"><span class="source">John Tarduno</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Magnetic field in flux</h2>
<p>Sampling at Limpopo River Valley locations has yielded the first archaeomagnetic history for southern Africa between A.D. 1000 and 1600. What we found reveals a period in the past, near A.D. 1300, when the field in that area was decreasing as rapidly as it is today. Then the intensity increased, albeit at a much slower rate.</p>
<p>The occurrence of two intervals of rapid field decay – one 700 years ago and one today – suggests a recurrent phenomenon. Could the reversed flux patch presently under South Africa have happened regularly, further back in time than our records have shown? If so, why would it occur again in this location?</p>
<p>Over the last decade, researchers have accumulated <a href="http://dx.doi.org/10.1016/j.epsl.2005.01.037">images from the analyses of earthquakes’ seismic waves</a>. As seismic shear waves move through the Earth’s layers, the speed with which they travel is an indication of the density of the layer. Now we know that a large area of slow seismic shear waves characterizes the core mantle boundary beneath southern Africa.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/157392/original/image-20170218-10195-1qexrl5.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/157392/original/image-20170218-10195-1qexrl5.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/157392/original/image-20170218-10195-1qexrl5.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=364&fit=crop&dpr=1 600w, https://images.theconversation.com/files/157392/original/image-20170218-10195-1qexrl5.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=364&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/157392/original/image-20170218-10195-1qexrl5.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=364&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/157392/original/image-20170218-10195-1qexrl5.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=457&fit=crop&dpr=1 754w, https://images.theconversation.com/files/157392/original/image-20170218-10195-1qexrl5.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=457&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/157392/original/image-20170218-10195-1qexrl5.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=457&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Location of the South Atlantic Anomaly.</span>
<span class="attribution"><span class="source">Michael Osadicw/John Tarduno</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>This particular region underneath southern Africa has the somewhat wordy title of the African Large Low Shear Velocity Province. While many wince at the descriptive but jargon-rich name, it is a profound feature that must be tens of millions of years old. While thousands of kilometers across, its boundaries are sharp. Interestingly, the reversed core flux patch is nearly coincident with its eastern edge.</p>
<p>The fact that the present-day reversed core patch and the edge of the African Large Low Shear Velocity Province are physically so close got us thinking. We’ve come up with a <a href="http://dx.doi.org/10.1038/ncomms8865">model linking the two phenomena</a>. We suggest that the unusual African mantle changes the flow of iron in the core underneath, which in turn changes the way the magnetic field behaves at the edge of the seismic province, and leads to the reversed flux patches. </p>
<p>We speculate that these reversed core patches grow rapidly and then wane more slowly. Occasionally one patch may grow large enough to dominate the magnetic field of the Southern Hemisphere – and the poles reverse.</p>
<p>The conventional idea of reversals is that they can start anywhere in the core. Our conceptual model suggests there may be special places at the core-mantle boundary that promote reversals. We do not yet know if the current field is going to reverse in the next few thousand years, or simply continue to <a href="https://doi.org/10.3389/feart.2015.00061">weaken over the next couple of centuries</a>.</p>
<p>But the clues provided by the ancestors of modern-day southern Africans will undoubtedly help us to further develop our proposed mechanism for reversals. If correct, pole reversals may be “Out of Africa.”</p>
<hr>
<p><em>This story was updated to correct the units used in the last figure; magnetic field strength is depicted in tens of nanoTesla.</em></p><img src="https://counter.theconversation.com/content/47528/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Tarduno receives funding from the US National Science Foundation. </span></em></p><p class="fine-print"><em><span>Vincent Hare receives funding from the US National Science Foundation and !Khure Africa, a dual South Africa/France collaborative Earth System programme. </span></em></p>Are we headed to a magnetic reversal and all the global disruption that would bring? Enter archaeomagnetism. A look at the archaeological record in southern Africa provides some clues.John Tarduno, Professor of Geophysics, University of RochesterVincent Hare, Postdoctoral Associate in Earth and Environmental Sciences, University of RochesterLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/487752015-10-08T21:45:25Z2015-10-08T21:45:25ZHow we discovered that the Earth’s inner core is older than previously thought<figure><img src="https://images.theconversation.com/files/97803/original/image-20151008-9685-zyr3l.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Dating the Earth's enigmatic inner core: a Pluto-sized ball of iron that is super hot and frozen at the same time. </span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Earth_poster.svg">Kelvinsong/wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>According to recent estimates, the Earth’s solid inner core started forming between half a billion and one billion years ago. However, our <a href="http://www.nature.com/nature/journal/v526/n7572/full/nature15523.html">new measurements</a> of ancient rocks as they cool from magma have indicated that it may actually have started forming more than half a billion years earlier.</p>
<p>While this is still relatively late in the Earth’s four-and-a-half billion year history, the implication is that the Earth’s deep interior may not have been as hot in the deep past as some have argued. That means the core is transferring heat to the surface more slowly than previously thought, and is less likely to play a big role in shaping the Earth’s surface through tectonic movements and volcanoes.</p>
<p>Just after the Earth formed from collisions in a huge cloud of material that also formed the Sun, it was molten. This was because of the heat generated by the formation process and the fact that it constantly collided with other bodies. But after a while, as the bombardment slowed, the outer layer cooled to form a solid crust. </p>
<p>The Earth’s <a href="http://www.bbc.co.uk/schools/gcsebitesize/geography/natural_hazards/tectonic_plates_rev1.shtml">inner core</a> is, today, a Pluto-sized ball of solid iron at the centre of our planet surrounded by an outer core of molten iron alloyed to some, as yet unknown, lighter element. Despite the Earth being hottest at its centre (about 6,000°C), liquid iron freezes into a solid because of the very high pressures there. As the Earth continues to cool down, the inner core grows at a rate of about 1mm per year by this freezing process. </p>
<p>Knowing the point in time at which the Earth’s centre cooled down sufficiently to first freeze iron gives us a fundamental reference point for the entire <a href="http://www.bbc.co.uk/programmes/b05s3gyv">thermal history</a> of the planet.</p>
<p>The <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magearth.html">magnetic field of the Earth</a> is generated by the movement of electrically conducting molten iron in the outer core. This movement is generated by light elements released at the inner core boundary as it grows. Therefore, the time when iron was first frozen also represents a point in time when the outer core received a strong additional source of power. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/97810/original/image-20151008-9659-1ywcarw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/97810/original/image-20151008-9659-1ywcarw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/97810/original/image-20151008-9659-1ywcarw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/97810/original/image-20151008-9659-1ywcarw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/97810/original/image-20151008-9659-1ywcarw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/97810/original/image-20151008-9659-1ywcarw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/97810/original/image-20151008-9659-1ywcarw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Earth’s magnetic field.</span>
<span class="attribution"><a class="source" href="https://creativecommons.org/licenses/by/2.0/">NASA/Flicr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>It is the signature of this boost of the magnetic field – the largest long-term increase in its entire history – that we think we have observed in the magnetic records recovered from igneous rocks formed at this time. Magnetic particles in these rocks “lock-in” the properties of the Earth’s magnetic field at the time and place that they cool down from magma. </p>
<p>The signal can then be recovered in the laboratory by measuring how the magnetisation of the rock changes as it progressively heated up in a controlled magnetic field. Hunting for this signature is <a href="http://onlinelibrary.wiley.com/doi/10.1111/j.1365-246X.1992.tb04640.x/abstract;jsessionid=20774B15E9F544E5879DF9B23E2D3563.f03t01">not a new idea</a> but has only just become viable – a combination of having increased amounts of measurement data available and new approaches to analysing them. </p>
<p>The Earth has maintained a magnetic field for most of its history through a “dynamo” process. This is similar in principle to a wind-up radio or a bicycle-powered light bulb in that mechanical energy is converted to electromagnetic energy. Before the inner core first started to solidify, this “geodynamo” is thought to have been powered by another entirely different and inefficient “<a href="http://www.bbc.co.uk/schools/gcsebitesize/science/aqa_pre_2011/energy/heatrev1.shtml">thermal convection</a>” process. </p>
<p>Once iron started to freeze out of the liquid at the base of the core, the remainder became less dense, providing an additional source of buoyancy and leading to much more efficient <a href="http://www.geomagnetism.org/?p=404">“compositional convection”</a>. Our results suggest that this efficiency saving happened earlier in the Earth’s history than previously thought, meaning that the magnetic field would have been sustained for longer with less energy overall. Since the energy is mostly thermal, this implies that the core as a whole is likely cooler than it would have been if the inner part formed later. </p>
<h2>Heat and plate tectonics</h2>
<p>A cooler core implies lower heat flow across the core-mantle boundary. This is important for all of Earth sciences because it could be one of the drivers for making tectonic plates move and is also a source of <a href="http://serc.carleton.edu/sp/erese/mantle-plumes.html">plume</a> volcanism at the Earth’s surface. We know that these processes are a <a href="http://www.geology.sdsu.edu/how_volcanoes_work/Volcano_tectonic.html">result of mantle convection</a> produced, ultimately, by the flow of heat out of the planet at a rate that we can measure rather precisely. What we still do not know is how much of this heat lost at the Earth’s surface is from the mantle and how much is from the core. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/97813/original/image-20151008-9675-1li0p9p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/97813/original/image-20151008-9675-1li0p9p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=368&fit=crop&dpr=1 600w, https://images.theconversation.com/files/97813/original/image-20151008-9675-1li0p9p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=368&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/97813/original/image-20151008-9675-1li0p9p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=368&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/97813/original/image-20151008-9675-1li0p9p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=462&fit=crop&dpr=1 754w, https://images.theconversation.com/files/97813/original/image-20151008-9675-1li0p9p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=462&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/97813/original/image-20151008-9675-1li0p9p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=462&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Mantle convection - the process that drives plate tectonics.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Mantle_convection#/media/File:Oceanic_spreading.svg">Surachit/wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Heating from the core is thought to produce plumes welling up from just above the core-mantle boundary, which might help drive the flow within the mantle. The suggestion from our findings is that the core contribution to the surface heat flow is lower than implied from other studies and that <a href="http://geology.about.com/library/bl/blnutshell_subduction.htm">subduction in the ocean</a>, when one tectonic plate goes under another down into the mantle, are much more important in driving mantle convention than the heat rising from the core.</p>
<p>The debate about the age of the inner core and the resulting thermal evolution of the Earth is not yet over. More palaeomagnetic data are needed to confirm that the sharp increase in magnetic field strength that we have observed is really the largest in the planet’s history. Furthermore, modelling needs to verify whether some other event could have created the magnetic strengthening at this time.</p>
<p>Nevertheless, as things stand, theory and observation combine to indicate that the Earth was two-thirds of its present age before it started growing an inner core – meaning earth scientists may have to revise their understanding of the planet’s history.</p><img src="https://counter.theconversation.com/content/48775/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew John Biggin receives funding from the Royal Society and has previously been funded by the Natural Environment Research Council. He is a fellow of the Royal Astronomical Society and a member of the American Geophysical Union.</span></em></p>The Earth’s inner core is more than half a billion years older than previously thought, shows a study. The results could help us better understand the processes that shape the planet’s surface.Andrew Biggin, Lecturer in Geophysics, University of LiverpoolLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/393302015-03-25T19:13:46Z2015-03-25T19:13:46ZNewly discovered layer in Earth’s mantle can affect surface dwellers too<figure><img src="https://images.theconversation.com/files/75996/original/image-20150325-14532-15qn5fr.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">No Earths were harmed in the making of this image</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/argonne/14259873660/">Johan Swanepoel/Shutterstock</a></span></figcaption></figure><p>Sinking tectonic plates get jammed in a newly discovered layer of the Earth’s mantle – and could be causing earthquakes on the surface.</p>
<p>It was previously thought that Earth’s <a href="http://www.britannica.com/EBchecked/topic/349935/lower-mantle">lower mantle</a>, which begins at a depth of around 700 km and forms the major part of the mantle, is fairly uniform and varies only gradually as it goes deeper.</p>
<p>However, our new <a href="http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2393.html">study</a> points towards a layer in the mantle characterised by a strong increase in viscosity – a finding which has strong implications for our understanding of what’s going on deep down below our feet.</p>
<h2>The deep unknown</h2>
<p>The Earth’s mantle is the largest shell inside our planet. Ranging from about 50 km to 3000 km depth, it links the hot liquid <a href="http://education.nationalgeographic.com.au/education/encyclopedia/core/?ar_a=1">outer core</a> – with temperatures higher than 5,000K – to the Earth’s surface. </p>
<p>The movement of materials within the Earth’s mantle is thought to drive <a href="http://science.nationalgeographic.com/science/earth/the-dynamic-earth/plate-tectonics-article/">plate tectonic movements</a> on the surface, ultimately leading to earthquakes and volcanoes. The mantle is also the Earth’s largest reservoir for many elements stored in mantle minerals. Throughout Earth’s history, substantial amounts of material have been exchanged between the deep mantle and the surface and atmosphere, affecting both the life and climate above ground.</p>
<p>Because mankind is incapable of directly probing the lower mantle – the <a href="http://www.slate.com/blogs/atlas_obscura/2014/05/08/kola_superdeep_borehole_is_the_world_s_deepest_hole.html">deepest man-made hole</a> is only around 12 km deep – many details of the global material recycling process are poorly understood. </p>
<p>We do know, however, that the main way materials are transferred from the Earth’s surface and atmosphere back into the deep mantle occurs when one tectonic plate <a href="http://www.livescience.com/43220-subduction-zone-definition.html">slides under another</a> and is pushed down below another into the mantle.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/75976/original/image-20150325-14515-gt7xes.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/75976/original/image-20150325-14515-gt7xes.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=444&fit=crop&dpr=1 600w, https://images.theconversation.com/files/75976/original/image-20150325-14515-gt7xes.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=444&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/75976/original/image-20150325-14515-gt7xes.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=444&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/75976/original/image-20150325-14515-gt7xes.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=558&fit=crop&dpr=1 754w, https://images.theconversation.com/files/75976/original/image-20150325-14515-gt7xes.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=558&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/75976/original/image-20150325-14515-gt7xes.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=558&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A strong increase in the viscosity leads to a stiff layer which catches sinking slabs.</span>
<span class="attribution"><span class="source">Hauke Marquardt</span></span>
</figcaption>
</figure>
<h2>A trap for sinking plates</h2>
<p>So far most researchers assumed that these sinking plates either stall at the boundary between the upper and lower mantle at a depth of around 700 km or sink all the way through the lower mantle to the core-mantle boundary 3,000 km down. </p>
<p>But our new <a href="http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2393.html">research</a>, published in the latest online issue of Nature Geoscience, shows that many of these sinking slabs may in fact be trapped above a previously undiscovered impermeable layer of rock within the lower mantle.</p>
<p>We found that enormous pressures in the lower mantle, which range from 25 GPa (gigapascal) to 135 GPa, can lead to surprising behaviour of matter. To picture just how high this pressure is, balancing the Eiffel Tower in your hand would create pressures on the order of 10 GPa. These pressures lead to the formation of a stiff layer in the Earth’s mantle. Sinking plates may become trapped on top of this layer, which reaches its maximum stiffness at a depth below 1,500km.</p>
<h2>Under pressure</h2>
<p>We formed this conclusion after performing laboratory experiments on ferropericlase, a magnesium/iron oxide that is thought to be one of the main constituents of the Earth’s lower mantle. We compressed the ferropericlase to pressures of almost 100 GPa in a <a href="http://www.hpdo.com/intro.html">diamond-anvil cell</a>, a high-pressure device which compresses a tiny sample the size of a human hair between the tips of two minuscule brilliant-cut diamonds. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/75982/original/image-20150325-14500-itiy2z.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/75982/original/image-20150325-14500-itiy2z.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=639&fit=crop&dpr=1 600w, https://images.theconversation.com/files/75982/original/image-20150325-14500-itiy2z.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=639&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/75982/original/image-20150325-14500-itiy2z.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=639&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/75982/original/image-20150325-14500-itiy2z.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=803&fit=crop&dpr=1 754w, https://images.theconversation.com/files/75982/original/image-20150325-14500-itiy2z.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=803&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/75982/original/image-20150325-14500-itiy2z.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=803&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A diamond-anvil cell compresses a tiny sample under high pressure between two minuscule diamonds.</span>
<span class="attribution"><span class="source">Image via Hauke Marquardt</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>While under compression, the ferropericlase was probed with high-energy x-rays to investigate how it deforms under these high pressures. We found that the ability of the material to resist irreversible deformation increased by over three times under high pressures.</p>
<p>These results were used to model the change of viscosity with depth in Earth’s lower mantle. While previous estimates have indicated only gradual variations of viscosity with depth, we found a dramatic increase of viscosity throughout the upper 900 km of the lower mantle. </p>
<p>Such a strong increase in viscosity can stop the descent of slabs and, in doing so, strongly affect the deep Earth material cycle. These new findings are supported by <a href="http://royalsocietypublishing.org/content/roypta/360/1800/2475.full.pdf">3-D imaging observations</a> based on the analysis of seismic wave speeds travelling through the Earth that also indicate that the slabs stop sinking before they reach a depth of 1500 km.</p>
<h2>Surface effects</h2>
<p>If true, the existence of this stiff layer in the Earth’s mantle has wide-ranging implications for our understanding of the deep Earth material cycle. It could limit material mixing between the upper and lower parts of the lower mantle, meaning mantle regions with previously different geochemical signatures stay isolated in separate patches instead of mixing over geologic time. </p>
<p>What’s more, a stiff mid-mantle layer could also put stress on slabs much closer to the Earth’s surface, potentially acting as a trigger of deep earthquakes.</p>
<p>We are really just at the beginning of a deeper understanding of the inner workings of our planet, many of which ultimately affect our life on its surface.</p><img src="https://counter.theconversation.com/content/39330/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Hauke Marquardt receives funding from the German Science Foundation DFG.</span></em></p>The discovery of a thickly viscous layer which traps sinking plates below Earth’s surface has wide implications, not least as a cause of earthquakes.Hauke Marquardt, Researcher in Mineral Physics, Bayreuth UniversityLicensed as Creative Commons – attribution, no derivatives.