tag:theconversation.com,2011:/es/topics/mass-extinctions-9205/articlesMass extinctions – The Conversation2024-02-26T17:19:30Ztag:theconversation.com,2011:article/2243182024-02-26T17:19:30Z2024-02-26T17:19:30ZA Nasa mission that collided with an asteroid didn’t just leave a dent – it reshaped the space rock<figure><img src="https://images.theconversation.com/files/577638/original/file-20240223-18-v91s4p.jpeg?ixlib=rb-1.1.0&rect=0%2C0%2C1917%2C1080&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://images.nasa.gov/details/PIA25329">NASA/Johns Hopkins APL/Steve Gribben</a></span></figcaption></figure><p>A frequent idea in sci-fi and apocalyptic films is that of an asteroid
striking Earth and causing global devastation. While the probabilities of this kind of mass extinction occurring on our planet are incredibly small, they are not zero. </p>
<p>The results of Nasa’s Dart mission to the asteroid Dimorphos <a href="https://www.nature.com/articles/s41550-024-02200-3">have now been published</a>. They contain fascinating details about the composition of this asteroid and whether we can defend Earth against incoming space rocks.</p>
<p><a href="https://science.nasa.gov/mission/dart/">The Double Asteroid Redirection Test (Dart)</a> was a spacecraft mission that launched in November 2021. It was sent to an asteroid called Dimorphos and commanded to collide with it, head on, in September 2022. </p>
<p>Dimorphos posed and poses no threat to Earth in the near future. But the mission was designed to see if deflecting an asteroid away from a collision course with Earth was possible through “kinetic” means – in other words, a direct impact of a human-made object on its surface. </p>
<p>Asteroid missions are never easy. The relatively small size of these objects (compared to planets and moons) means there is no appreciable gravity to enable spacecraft to land and collect a sample. </p>
<p>Space agencies have launched a number of spacecraft to asteroids in recent times. For example, the Japanese space agency’s (Jaxa) <a href="https://www.isas.jaxa.jp/en/missions/spacecraft/current/hayabusa2.html">Hayabusa-2</a> mission reached the asteroid Ryugu in 2018, the same year Nasa’s <a href="https://theconversation.com/five-space-exploration-missions-to-look-%20out-for-in-2023-195839">Osiris-Rex</a> mission rendezvoused with the asteroid Bennu.</p>
<p>The Japanese Hayabusa missions (1 and 2) fired a small projectile at the surface as they approached it. They would then collect the debris as it flew by. </p>
<h2>High-speed collision</h2>
<p>However, the Dart mission was special in that it was not sent to deliver samples of asteroid material to labs on Earth. Instead, it was to fly at high speed into the space rock and be destroyed in the process.</p>
<p>A high-speed collision with an asteroid needs incredible precision. Dart’s target of Dimorphos was actually part of a <a href="https://science.nasa.gov/solar-system/asteroids/didymos/">double asteroid</a> system, known as a binary because the smaller object orbits the larger one. This binary contained both Didymus – the larger of the two objects – and Dimorphos, which behaves effectively as a moon.</p>
<p>The simulations of <a href="https://www.nature.com/articles/s41550-024-02200-3">what has happened to Dimorphos</a> show that while we might expect to see a very large crater on the asteroid from Dart’s impact, it is more likely that it has, in fact, changed the shape of the asteroid instead. </p>
<figure class="align-center ">
<img alt="Dimorphos." src="https://images.theconversation.com/files/577962/original/file-20240226-24-ninx49.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/577962/original/file-20240226-24-ninx49.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/577962/original/file-20240226-24-ninx49.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/577962/original/file-20240226-24-ninx49.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/577962/original/file-20240226-24-ninx49.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/577962/original/file-20240226-24-ninx49.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/577962/original/file-20240226-24-ninx49.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">Dimorphos, as pictured by the Dart spacecraft.</span>
<span class="attribution"><a class="source" href="https://science.nasa.gov/mission/dart/">NASA</a></span>
</figcaption>
</figure>
<h2>Ant hitting two buses</h2>
<p>The collision was of a mass of 580kg hitting an asteroid of roughly 5 billion kg. For comparison, this is equivalent to an ant hitting two buses. But the spacecraft is also travelling around 6 kilometres per second. </p>
<p>The simulation results based on observations of the asteroid Dimorphos have shown that the asteroid now orbits around its larger companion, Didymus, 33 minutes slower than before. Its orbit has gone from 11 hours, 55 minutes to 11 hours, 22 minutes. </p>
<p>The momentum change to the core of Dimorphos is also higher than one would predict from the direct impact, which may seem impossible at first. However, the asteroid is quite weakly constructed, consisting of loose rubble held together by gravity. The impact caused a lot of material to be blown off of Dimorphos. </p>
<p>This material is now travelling in the opposite direction to the impact. This acts <a href="http://www.dynamicscience.com.au/tester/solutions1/war/newton/recoilless.htm">like a recoil</a>, slowing down the asteroid.</p>
<p>Observations of all the <a href="https://www.newscientist.com/article/2340837-photo-shows-10000-km-debris-tail-caused-by-%20dart-asteroid-smash/">highly reflective material that has been shed from Dimorphos</a> allows scientists to estimate how much of it has been lost from the asteroid. Their result is roughly 20 million kilograms – equivalent to about six of the Apollo-era Saturn V rockets fully loaded with fuel. </p>
<p>Combining all the parameters together (mass, speed, angle and amount of material lost) and simulating the impact has allowed the researchers to be fairly confident about the answer. Confident not only regarding the grain size of the material coming from Dimorphos, but also that the asteroid has limited cohesion and the surface must be constantly altered, or reshaped, by minor impacts.</p>
<figure class="align-center ">
<img alt="Artist's impression of Chicxulub asteroid." src="https://images.theconversation.com/files/577961/original/file-20240226-24-p85pi2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/577961/original/file-20240226-24-p85pi2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/577961/original/file-20240226-24-p85pi2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/577961/original/file-20240226-24-p85pi2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/577961/original/file-20240226-24-p85pi2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/577961/original/file-20240226-24-p85pi2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/577961/original/file-20240226-24-p85pi2.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">The dinosaurs were wiped out by a 10km-wide asteroid that hit Earth 66 million years ago.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/planet-earth-big-asteroid-space-potentially-2107872635">Buradaki / Shutterstock</a></span>
</figcaption>
</figure>
<p>But what does this tell us about protecting ourselves from an asteroid impact? Significant recent impacts on Earth have included the <a href="https://blogs.nasa.gov/planetarydefense/2023/02/15/remembering-the-chelyabinsk-impact-10-years-ago-and-looking-to-the-future/">meteor</a> which broke up in the sky over the city of Chelyabinsk, Russia, in 2013, and the infamous <a href="https://earthsky.org/space/what-is-the-tunguska-explosion/">Tunguska
impact</a> over a remote part of Siberia in 1908. </p>
<p>While these were not the kinds of events that are able to cause mass extinctions – like the 10km object that wiped out the dinosaurs when it struck our planet 66 million years ago – the potential for damage and loss of life with smaller objects such as those at Chelyabinsk and Tunguska is very high.</p>
<p>The Dart mission cost US$324 million (£255 million), which is low for a space mission, and with its development phase completed, a similar mission to go and deflect an asteroid heading our way could be launched more cheaply. </p>
<p>The big variable here is how much warning we will have, because a change in orbit of 30 minutes – as was observed when Dart struck Dimorphos – will make little difference if the asteroid is already very close to Earth. However, if we can predict the object path from further out – preferably outside the Solar System – and make small changes, this could be enough to divert the path of an asteroid away from our planet.</p>
<p>We can expect to see more of these missions in the future, not only because of interest in the science surrounding asteroids, but because the ease of removing material from them means that private companies might want to step up their ideas of <a href="https://www.wired.com/story/things-are-looking-up-for-asteroid-mining/">mining these space rocks</a> for precious metals.</p><img src="https://counter.theconversation.com/content/224318/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ian Whittaker does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The mission provided details about how to deflect an asteroid should one threaten Earth in future.Ian Whittaker, Senior Lecturer in Physics, Nottingham Trent UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2125012023-09-19T14:47:51Z2023-09-19T14:47:51ZWhy invasive ants are a silent threat to our ecosystems<figure><img src="https://images.theconversation.com/files/548832/original/file-20230918-27-85srij.jpg?ixlib=rb-1.1.0&rect=0%2C13%2C3113%2C2316&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The yellow crazy ant (Anoplolepis gracilipes) is a notorious invasive ant species.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/yellow-crazy-ant-anoplolepis-gracilipes-1960533274">Lukman_M/Shutterstock</a></span></figcaption></figure><p>Invertebrates are often described by <a href="https://faculty.washington.edu/timbillo/Readings%20and%20documents/ABRIDGED%20READINGS%20for%20PERU/Wilson_1987_Little_things_that_run.pdf">experts</a> as the “little things that run the world”, and ants are certainly one of the top contenders for this role. Ants help ecosystems to function normally and the <a href="https://www.pnas.org/doi/full/10.1073/pnas.2201550119">total weight</a> of all ants on Earth is roughly equivalent to 1.4 billion people, or 33 Empire State Buildings. </p>
<p>Unfortunately, some ants have become invasive species – organisms transported to a new ecosystem that cause damage. These introductions typically happen accidentally by people but can have dire consequences, as my team’s <a href="https://resjournals.onlinelibrary.wiley.com/doi/10.1111/icad.12672">new research</a> shows. </p>
<p>Invasive species are thought to be the <a href="https://link.springer.com/article/10.1007/s10531-018-1595-x">second largest</a> threat to biodiversity after habitat destruction. They are a <a href="https://doi.org/10.1016/j.tree.2005.01.003">leading cause</a> of animal extinctions, potentially leading to species extinction and ecosystem failure. </p>
<p>The International Union for the Conservation of Nature includes <a href="https://portals.iucn.org/library/sites/library/files/documents/2000-126.pdf">five different ant species</a> on its list of 100 of the world’s worst invasive alien species. But while invasive ants have dramatically transformed some of the areas they have been able to invade, other areas appear to be far less affected, or even totally unaffected.</p>
<h2>How bad are invasive ants, really?</h2>
<p>My team’s <a href="https://resjournals.onlinelibrary.wiley.com/doi/10.1111/icad.12672">study</a> draws from research conducted around the world to provide a measure of how bad or good invasive ants are for biodiversity loss. The results show us that invasive ants are every bit as bad as we had assumed.</p>
<p>We extracted data from 46 different research articles that studied how animal communities reacted to invasive ants, and combined the results. We only selected research that was done in relatively “undisturbed” natural environments, free from intensive human activity. </p>
<p>These are areas that invasive ants have dispersed to from more degraded habitats or urban environments. This allows us to more confidently claim that any negative or positive effects on animal communities are because of invasive ants, rather than other invasive species or some form of human disturbance such as agriculture or deforestation.</p>
<p>Our results show that animal communities respond overwhelmingly negatively to invasive ants. We found there were on average 50% fewer individual animals and species in areas invaded by ants, which is a dramatic fall in biodiversity. It is also important to remember these results are averages and, therefore, invasive ants may spell doom for some animal communities above and beyond these numbers.</p>
<figure class="align-center ">
<img alt="A close up of an ant with a large head crawls along a mossy piece of bark." src="https://images.theconversation.com/files/548020/original/file-20230913-19-n2k3ar.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/548020/original/file-20230913-19-n2k3ar.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/548020/original/file-20230913-19-n2k3ar.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/548020/original/file-20230913-19-n2k3ar.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/548020/original/file-20230913-19-n2k3ar.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/548020/original/file-20230913-19-n2k3ar.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/548020/original/file-20230913-19-n2k3ar.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 <em>Pheidole megacephala</em> or big-headed ant.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/macro-image-bigheaded-ant-2215004569">Alen thien/Shutterstock</a></span>
</figcaption>
</figure>
<p>We also found that certain animal types, such as birds, reptiles and beetles, reacted more strongly than others. Native ants were the most strongly affected group. </p>
<p>This makes sense because many native ants will not only be directly attacked by invasive ants but they will also need to compete with them for food and nest sites. This is also bad news because of the general importance of native ants to the wider ecosystem. </p>
<p>Other groups that were badly affected were birds, beetles, butterflies, moths and reptiles. </p>
<p>We also found that the number of individuals in one insect group – bugs such as scale insects, aphids and mealybugs – increased. This group forms “mutualisms” with ants, which is where each species has a net benefit. </p>
<p>These insects are sap-sucking and exude a sugary liquid called “honeydew”, which ants love. Ants will defend these insects from their predators and parasites in return for this sugary secretion, enabling their populations to mutually increase. In some cases, these mutualisms can facilitate invasion – and to disastrous effect. </p>
<h2>How can something so small cause such a big problem?</h2>
<p>Although ants are small relative to how people perceive the world, they are numerous and tend to interact with a wide range of other organisms. This means they may be able to influence the ecosystem from multiple angles of attack. Invasive ants probably actively hunt down other species but competition for food or space is also important. </p>
<p>Ultimately, we need more research that can tease apart how ants are interacting with other species when they invade a location. What do they eat? Who do they compete with for food? Which habitats do they prefer and why? These questions urgently need answers so we can understand, prioritise and optimise how to minimise the negative effects of invasive ants.</p>
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<strong>
Read more:
<a href="https://theconversation.com/why-red-fire-ants-and-yellow-crazy-ants-have-given-themselves-a-green-light-to-invade-australia-208479">Why red fire ants and yellow crazy ants have given themselves a green light to invade Australia</a>
</strong>
</em>
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<p>Overall, our research is worrying. The reduction in animal diversity may have severe consequences for ecosystem functioning and the long-term future of rare species. Although there are crucial considerations to mitigate or reverse these effects, the conservation implications are not straightforward. </p>
<p>Ant eradication regimes are logistically complex and financially expensive, for example, and more than half <a href="https://doi.org/10.1016/j.biocon.2016.03.036">fail</a>. Early detection technology, as well as control measures such as toxic baits, can help conservationists prevent or reverse the effects of invasive ants on our ecosystems.</p>
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<figure class="align-right ">
<img alt="Imagine weekly climate newsletter" src="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.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">
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<p class="fine-print"><em><span>Maximillian Tercel receives funding from Natural Environment Research Council and Durrell Wildlife Conservation Trust.</span></em></p>Invasive ants are a major threat to biodiversity, according to a study.Maximillian Tercel, PhD Candidate in Entomology, Cardiff UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2095932023-08-10T03:24:09Z2023-08-10T03:24:09ZNew evidence suggests the world’s largest known asteroid impact structure is buried deep in southeast Australia<figure><img src="https://images.theconversation.com/files/542059/original/file-20230810-25-7n4kt.png?ixlib=rb-1.1.0&rect=43%2C0%2C2600%2C1005&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Google Maps</span></span></figcaption></figure><p><em>Acknowledgment: I’d like to thank my colleague Tony Yeates, who originated the view of the Deniliquin multi-ring structure as an impact structure – and who was instrumental to this work.</em></p>
<p>In <a href="https://www.sciencedirect.com/science/article/abs/pii/S0040195122002487">recent research</a> published by myself and my colleague Tony Yeates in the journal Tectonophysics, we investigate what we believe – based on many years of experience in asteroid impact research – is the world’s largest known impact structure, buried deep in the earth in southern New South Wales.</p>
<p>The Deniliquin structure, yet to be further tested by drilling, spans up to 520 kilometres in diameter. This exceeds the size of the near-300km-wide <a href="https://en.wikipedia.org/wiki/Vredefort_impact_structure">Vredefort</a> impact structure in South Africa, which to date has been considered the world’s largest.</p>
<h2>Hidden traces of Earth’s early history</h2>
<p>The history of Earth’s bombardment by asteroids is largely concealed. There are a few reasons for this. The first is erosion: the process by which gravity, wind and water slowly wear away land materials through time. </p>
<p>When an asteroid strikes, it creates a crater with an uplifted core. This is similar to how a drop of water splashes upward from a transient crater when you drop a pebble in a pool. </p>
<p>This central uplifted dome is a key characteristic of large impact structures. However, it can erode over thousands to millions of years, making the structure difficult to identify.</p>
<p>Structures can also be buried by sediment through time. Or they might disappear as a result of subduction, wherein tectonic plates can collide and slide below one another into Earth’s mantle layer.</p>
<p>Nonetheless, new geophysical discoveries are unearthing signatures of impact structures formed by asteroids that may have reached tens of kilometres across – heralding a paradigm shift in our understanding of how Earth evolved over eons. These include pioneering discoveries of impact “ejecta”, which are the materials thrown out of a crater during an impact. </p>
<p><a href="https://www.sciencedirect.com/science/article/abs/pii/S1387647317300714">Researchers think</a> the oldest layers of these ejecta, found in sediments in early terrains around the world, might signify the tail end of the Late Heavy Bombardment of Earth. The <a href="https://www.sciencedirect.com/science/article/abs/pii/S1387647317300714">latest evidence</a> suggests Earth and the other planets in the Solar System were subject to intense asteroid bombardments until about 3.2 billion years ago, and sporadically since.</p>
<p>Some large impacts are correlated with mass extinction events. For example, the <a href="https://en.wikipedia.org/wiki/Alvarez_hypothesis">Alvarez hypothesis</a>, named after father and son scientists Luis and Walter Alvarez, explains how non-avian dinosaurs were wiped out as a result of a large asteroid strike some 66 million years ago.</p>
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<em>
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Read more:
<a href="https://theconversation.com/we-found-the-worlds-oldest-asteroid-strike-in-western-australia-it-might-have-triggered-a-global-thaw-130192">We found the world's oldest asteroid strike in Western Australia. It might have triggered a global thaw</a>
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<h2>Uncovering the Deniliquin structure</h2>
<p>The Australian continent and its predecessor continent, <a href="https://en.wikipedia.org/wiki/Gondwana">Gondwana</a>, have been the target of numerous asteroid impacts. These have resulted in at least 38 confirmed and 43 potential impact structures, ranging from relatively small craters to large and completely buried structures.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/541853/original/file-20230809-24-hpgo51.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/541853/original/file-20230809-24-hpgo51.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/541853/original/file-20230809-24-hpgo51.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=516&fit=crop&dpr=1 600w, https://images.theconversation.com/files/541853/original/file-20230809-24-hpgo51.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=516&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/541853/original/file-20230809-24-hpgo51.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=516&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/541853/original/file-20230809-24-hpgo51.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=649&fit=crop&dpr=1 754w, https://images.theconversation.com/files/541853/original/file-20230809-24-hpgo51.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=649&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/541853/original/file-20230809-24-hpgo51.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=649&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">This map shows the distribution of circular structures of uncertain, possible or probable impact origin on the Australian continent and offshore. Green dots represent confirmed impact craters. Red dots represent confirmed impact structures that are more than 100km wide, whereas red dots inside white circles are more than 50km wide. Yellow dots represent likely impact structures.</span>
<span class="attribution"><span class="source">Andrew Glikson and Franco Pirajno</span></span>
</figcaption>
</figure>
<p>As you’ll recall with the pool and pebble analogy, when a large asteroid hits Earth, the underlying crust responds with a transient elastic rebound that produces <a href="https://www.lpi.usra.edu/publications/books/CB-954/CB-954.pdf">a central dome</a>. </p>
<p>Such domes, which can slowly erode and/or become buried through time, may be all that’s preserved from the original impact structure. They represent the deep-seated “root zone” of an impact. Famous examples are found in the Vredefort impact structure and the 170km-wide <a href="https://en.wikipedia.org/wiki/Chicxulub_crater">Chicxulub crater</a> in Mexico. The latter represents the impact that caused the extinction of the dinosaurs.</p>
<p>Between 1995 and 2000, Tony Yeates suggested magnetic patterns beneath the Murray Basin in New South Wales <a href="https://www.aseg.org.au/publications/preview-old">likely represented</a> a massive, buried impact structure. An analysis of the region’s updated geophysical data between 2015 and 2020 confirmed the existence of a 520km diameter structure with a seismically defined dome at its centre.</p>
<p>The Deniliquin structure has all the features that would be expected from a large-scale impact structure. For instance, magnetic readings of the area reveal a symmetrical rippling pattern in the crust around the structure’s core. This was likely produced during the impact as extremely high temperatures created intense magnetic forces.</p>
<p>A central low magnetic zone corresponds to 30km-deep deformation above a seismically defined mantle dome. The top of this dome is about 10km <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015GL065345">shallower than the top</a> of the regional mantle.</p>
<p>Magnetic measurements also show evidence of “radial faults”: fractures that radiate from the centre of a large impact structure. This is further accompanied by small magnetic anomalies which may represent igneous “dikes”, which are sheets of magma injected into fractures in a pre-existing body of rock. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/541855/original/file-20230809-27-qpfxif.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/541855/original/file-20230809-27-qpfxif.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/541855/original/file-20230809-27-qpfxif.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=565&fit=crop&dpr=1 600w, https://images.theconversation.com/files/541855/original/file-20230809-27-qpfxif.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=565&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/541855/original/file-20230809-27-qpfxif.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=565&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/541855/original/file-20230809-27-qpfxif.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=710&fit=crop&dpr=1 754w, https://images.theconversation.com/files/541855/original/file-20230809-27-qpfxif.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=710&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/541855/original/file-20230809-27-qpfxif.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=710&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 ‘total magnetic intensity’ image of the Deniliquin impact structure portrays its 520km-diameter multi-ring pattern, the central core, radial faults and the location of shallow drill holes.</span>
<span class="attribution"><a class="source" href="https://www.sciencedirect.com/science/article/abs/pii/S0040195122002487">Data from Geoscience Australia, published in Glikson and Yeates, 2022</a></span>
</figcaption>
</figure>
<p>Radial faults, and igneous sheets of rocks that form within them, are typical of large impact structures and can be found in the Vredefort structure and the <a href="https://journals.uair.arizona.edu/index.php/maps/article/viewFile/14921/14892">Sudbury impact structure</a> in Canada.</p>
<p>Currently, the bulk of the evidence for the Deniliquin impact is based on geophysical data obtained from the surface. For proof of impact, we’ll need to collect physical evidence of shock, which can only come from drilling deep into the structure.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/these-5-spectacular-impact-craters-on-earth-highlight-our-planets-wild-history-197618">These 5 spectacular impact craters on Earth highlight our planet's wild history</a>
</strong>
</em>
</p>
<hr>
<h2>When did the Deniliquin impact happen?</h2>
<p>The Deniliquin structure was likely located on the eastern part of the Gondwana continent, prior to it splitting off into several continents (including the Australian continent) much later.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/541858/original/file-20230809-21-qpfxif.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/541858/original/file-20230809-21-qpfxif.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/541858/original/file-20230809-21-qpfxif.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=344&fit=crop&dpr=1 600w, https://images.theconversation.com/files/541858/original/file-20230809-21-qpfxif.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=344&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/541858/original/file-20230809-21-qpfxif.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=344&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/541858/original/file-20230809-21-qpfxif.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=432&fit=crop&dpr=1 754w, https://images.theconversation.com/files/541858/original/file-20230809-21-qpfxif.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=432&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/541858/original/file-20230809-21-qpfxif.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=432&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 Deniliquin structure was likely created in eastern Gondwana during the Late Ordovician.</span>
<span class="attribution"><a class="source" href="https://www.nature.com/articles/s41598-022-08941-3#rightslink">Zhen Qiu et al, 2022</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The impact that caused it may have occurred during what’s known as the Late Ordovician mass extinction event. Specifically, I think it may have triggered what’s called the <a href="https://www.britannica.com/science/Ordovician-Silurian-extinction">Hirnantian glaciation stage</a>, which lasted between 445.2 and 443.8 million years ago, and is also defined as the <a href="https://www.sciencedirect.com/science/article/abs/pii/S1342937X23000655">Ordovician-Silurian extinction event</a>. </p>
<p>This huge glaciation and mass extinction event <a href="https://www.britannica.com/science/Ordovician-Silurian-extinction">eliminated</a> about 85% of the planet’s species. It was more than double the scale of the <a href="https://en.wikipedia.org/wiki/Alvarez_hypothesis">Chicxulub impact</a> that killed off the dinosaurs. </p>
<p>It is also possible the Deniliquin structure is older than the Hirnantian event, and may be of an early Cambrian origin (about 514 million years ago). The next step will be to gather samples to determine the structure’s exact age. This will require drilling a deep hole into its magnetic centre and dating the extracted material. </p>
<p>It’s hoped further studies of the Deniliquin impact structure will shed new light on the nature of early <a href="https://www.livescience.com/37584-paleozoic-era.html">Paleozoic</a> Earth.</p><img src="https://counter.theconversation.com/content/209593/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew Glikson 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>Research on the Deniliquin structure points to an asteroid impact that would have been more than double the scale of the one that killed the dinosaurs.Andrew Glikson, Adjunct professor, UNSW SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1968352022-12-20T16:26:16Z2022-12-20T16:26:16ZFive options for restoring global biodiversity after the UN agreement<figure><img src="https://images.theconversation.com/files/502146/original/file-20221220-6047-pj31jb.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C3557%2C2082&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">EDGAR PHOTOSAPIENS / shutterstock</span></span></figcaption></figure><p>To slow and reverse the fastest loss of Earth’s living things since the dinosaurs, almost 200 countries have <a href="https://www.bbc.co.uk/news/science-environment-64019324">signed an agreement</a> in Montreal, Canada, promising to live in harmony with nature by 2050. The <a href="https://www.cbd.int/doc/c/e6d3/cd1d/daf663719a03902a9b116c34/cop-15-l-25-en.pdf">Kunming-Montreal agreement</a> is not legally binding but it will require signatories to report their progress towards meeting targets such as the protection of 30% of Earth’s surface by 2030 and the restoration of degraded habitats.</p>
<p>Not everyone is happy with the settlement, or convinced enough has been promised to avert mass extinctions. Thankfully, research has revealed a lot about the best ways to revive and strengthen biodiversity – the variety of life forms, from microbes to whales, found on Earth. </p>
<p>Here are five suggestions:</p>
<h2>1. Scrap subsidies</h2>
<p>The first thing countries should do is stop paying for the destruction of ecosystems. The Montreal pact calls for reducing incentives for environmentally harmful practices by $US500 billion (£410 billion) each year by 2030.</p>
<p>Research published in 2020 showed that ending fuel and maintenance subsidies would <a href="https://www.frontiersin.org/articles/10.3389/fmars.2020.00523/full">reduce excess fishing</a>. Less fishing means more fish at sea and higher catches for the remaining fleet with less effort. The world’s fisheries could cut emissions and become more profitable.</p>
<p>Scrapping policies which subsidise overexploitation in all sorts of industries – fisheries, agriculture, forestry, and of course, fossil fuels – are in many cases the lowest fruit to be picked in order to save biodiversity.</p>
<h2>2. Protect the high seas</h2>
<p>Almost half of the surface of the Earth is outside national jurisdiction. The high seas belong to no one. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/502153/original/file-20221220-22-q8azuu.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/502153/original/file-20221220-22-q8azuu.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/502153/original/file-20221220-22-q8azuu.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/502153/original/file-20221220-22-q8azuu.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/502153/original/file-20221220-22-q8azuu.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/502153/original/file-20221220-22-q8azuu.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/502153/original/file-20221220-22-q8azuu.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/502153/original/file-20221220-22-q8azuu.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=377&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Most of the world’s oceans are owned by no one. (light blue = exclusive economic zones; dark blue = high seas)</span>
<span class="attribution"><span class="source">B1mbo / wiki (data: VLIZ)</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>In the twilight zone of the ocean, between 200 and 1,000 metres down, fish and krill migrate upwards to feed at night and downwards to digest and rest during the day. This is the ocean’s biological pump, which draws carbon from near the ocean’s surface to its depths, storing it far from the atmosphere and so reducing climate change.</p>
<p>The total mass of fish living in the open ocean is much greater than in overfished coastal seas. Though not exploited to any large extent yet, the high seas and the remote ocean around the Antarctic need <a href="https://www.nature.com/articles/d41586-018-07183-6">binding international agreements</a> to protect them and the important planetary function they serve, which ultimately benefits all life by helping maintain a stable climate.</p>
<h2>3. Ban clear-cutting and bottom trawling</h2>
<p>Certain methods of extracting natural resources, such as clear-cutting forests (chopping down all the trees) and bottom trawling (tugging a big fishing net close to the seafloor) devastate biodiversity and should be phased out. </p>
<p>Clear-cutting removes large quantities of living matter that will not be replenished before the forest has regenerated, which may take hundreds of years, particularly for forests in Earth’s higher latitudes. Many species which are adapted to live in fully grown forests are subsequently doomed by clear-cutting.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/502152/original/file-20221220-6053-8riogv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Aerial shot of rainforest and deforested land" src="https://images.theconversation.com/files/502152/original/file-20221220-6053-8riogv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/502152/original/file-20221220-6053-8riogv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/502152/original/file-20221220-6053-8riogv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/502152/original/file-20221220-6053-8riogv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/502152/original/file-20221220-6053-8riogv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/502152/original/file-20221220-6053-8riogv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/502152/original/file-20221220-6053-8riogv.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"></a>
<figcaption>
<span class="caption">Bad for biodiversity.</span>
<span class="attribution"><span class="source">Richard Whitcombe / shutterstock</span></span>
</figcaption>
</figure>
<p>Bottom trawling catches fish and shellfish indiscriminately, disturbing or even eradicating animals which live on the seafloor, such as certain types of coral and oysters. It also throws plumes of sediment into the water above, <a href="https://www.nature.com/articles/s41586-021-03371-z">emitting greenhouse gases</a> which had been locked away. Seafloors that have been trawled continuously for a long time may appear to be devoid of life, or trivialised with fewer species and less complex ecosystems.</p>
<h2>4. Empower indigenous land defenders</h2>
<p>Indigenous people are the vanguard of many of the best-preserved ecosystems in the world. Their struggle to protect their land and waters and traditional ways of using ecosystems and biodiversity for livelihoods are often the primary reason such important environments still exist. </p>
<p>Such examples are found around the world, for example <a href="https://www.science.org/doi/full/10.1126/sciadv.abn2927">more primates are found on indigenous land</a> than in surrounding areas.</p>
<h2>5. No more production targets</h2>
<p>Many management practices will have to change, since they are based on unrealistic assumptions. Fisheries, for instance, target a maximum sustainable yield (MSY), a concept developed in the mid 20th century which means taking the largest catch from a fish stock without diminishing the stock in the future. Something similar is also used in forestry, though it involves more economic considerations.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/502151/original/file-20221220-12-i0dd8o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Fishing boat with lots of seagulls" src="https://images.theconversation.com/files/502151/original/file-20221220-12-i0dd8o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/502151/original/file-20221220-12-i0dd8o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/502151/original/file-20221220-12-i0dd8o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/502151/original/file-20221220-12-i0dd8o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/502151/original/file-20221220-12-i0dd8o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/502151/original/file-20221220-12-i0dd8o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/502151/original/file-20221220-12-i0dd8o.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">Fishing for herring near Norway.</span>
<span class="attribution"><span class="source">Alessandro De Maddalena / shutterstock</span></span>
</figcaption>
</figure>
<p>These models were <a href="https://cpb-us-e1.wpmucdn.com/sites.ucsc.edu/dist/9/678/files/2018/09/Larkin-1977.-Transactions-American-Fish-Soc_An-Epitaph-for-the-Concept-of-Maximum-Sustained-Yield-1rnsupk.pdf">heavily criticised</a> in the subsequent decades for oversimplifying how nature works. For instance species often contain several local populations which live separately and reproduce only with each other, yet some of these “substocks” could still become overfished if just one production target was applied for all of them. However, the idea of a maximum sustainable yield has come back into fashion this century as a means to curtail overfishing.</p>
<p>Herring is a good example here. The species forms <a href="https://elifesciences.org/articles/61076">many different substocks</a> across the North Atlantic, yet one maximum yield was adopted over vast areas. In the Baltic Sea for instance, Swedish fishing rights were given to the largest shipowners as a part of a neoliberal economic policy to achieve a more effective fishing fleet. Local stocks of herring are now declining, and with them local adaptations (genetic diversity) could eventually disappear. </p>
<p>Heading for more robust strategies than elusive optimal targets for extracting the most fish or trees while maintaining the stock or the forest may lead to a more resilient pathway regarding biodiversity and climate mitigation. It could involve lower fishing quotas, but also change from industrial fishing to more local fishing with smaller fishing vessels. </p>
<hr>
<figure class="align-right ">
<img alt="Imagine weekly climate newsletter" src="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.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">
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<p class="fine-print"><em><span>Henrik Svedäng does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The UN biodiversity summit COP15 in Montreal is over. Here’s what should happen next.Henrik Svedäng, Researcher, Marine Ecology, Stockholm UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1923172022-10-11T23:02:18Z2022-10-11T23:02:18ZNASA successfully shifted an asteroid’s orbit – DART spacecraft crashed into and moved Dimorphos<figure><img src="https://images.theconversation.com/files/489270/original/file-20221011-20-moap5a.png?ixlib=rb-1.1.0&rect=0%2C368%2C813%2C610&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Double Asteroid Redirection Test successfully changed the orbit of the small moonlet Dimorphos. </span> <span class="attribution"><a class="source" href="https://www.nasa.gov/feature/dart-s-final-images-prior-to-impact">NASA/Johns Hopkins APL</a></span></figcaption></figure><p><em><a href="https://www.nasa.gov/press-release/nasa-s-dart-mission-hits-asteroid-in-first-ever-planetary-defense-test">NASA recently crashed a spacecraft into an asteroid</a> in an attempt to push the rocky traveler off its trajectory. The Double Asteroid Redirection Test – or DART – was meant to test one potential strategy for preventing an asteroid from colliding with Earth. The collision occurred on Sept. 27, 2022, and on Oct. 11, 2022, NASA announced that the mission had <a href="https://www.nasa.gov/press-release/nasa-confirms-dart-mission-impact-changed-asteroid-s-motion-in-space">successfully changed the orbit of the asteroid Dimorphos</a>. David Barnhart is a <a href="https://scholar.google.com/citations?user=lYrFzm4AAAAJ&hl=en&oi=ao">professor of astronautics</a> at the University of Southern California and director of the Space Engineering Research Center there. He watched NASA’s live stream of the successful mission and explains what happened.</em></p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/N-OvnVdZP_8?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">This video, sped up 10 times the actual speed, shows a series of images taken one second apart by the DART spacecraft as it approached Didymos and the smaller Dimorphos before colliding with Dimorphos. The last few images are shown in real speed.</span></figcaption>
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<h2>1. What do the images from DART show?</h2>
<p><a href="https://www.nasa.gov/feature/dart-s-final-images-prior-to-impact">The first images</a>, taken by a camera aboard DART, show the double asteroid system of Didymos – about 2,500 feet (780 meters) in diameter – being orbited by the smaller asteroid Dimorphos, which is about 525 feet (160 meters) long. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/486692/original/file-20220927-22-sxps6q.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A gray, oblong, rocky object floating against the black backdrop of space." src="https://images.theconversation.com/files/486692/original/file-20220927-22-sxps6q.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/486692/original/file-20220927-22-sxps6q.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/486692/original/file-20220927-22-sxps6q.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/486692/original/file-20220927-22-sxps6q.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/486692/original/file-20220927-22-sxps6q.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/486692/original/file-20220927-22-sxps6q.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/486692/original/file-20220927-22-sxps6q.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"></a>
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<span class="caption">This image of the moonlet Dimorphos was taken 11 seconds before the DART spacecraft crashed into the asteroid.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/feature/dart-s-final-images-prior-to-impact">NASA/Johns Hopkins APL</a></span>
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<p>As the targeting algorithm on DART locked onto Dimorphos, the craft adjusted its flight and began heading toward the smaller of the two asteroids. The image taken at 11 seconds before impact and 42 miles (68 kilometers) from Dimorphos shows the asteroid centered in the <a href="https://dart.jhuapl.edu/Mission/Impactor-Spacecraft.php">camera’s field of view</a>. This meant the targeting algorithm was fairly accurate and the craft would collide right at the center of Dimorphos.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/486696/original/file-20220927-20-9p5qi4.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A gray rocky suface from above." src="https://images.theconversation.com/files/486696/original/file-20220927-20-9p5qi4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/486696/original/file-20220927-20-9p5qi4.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/486696/original/file-20220927-20-9p5qi4.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/486696/original/file-20220927-20-9p5qi4.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/486696/original/file-20220927-20-9p5qi4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/486696/original/file-20220927-20-9p5qi4.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/486696/original/file-20220927-20-9p5qi4.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"></a>
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<span class="caption">This photo shows the textured and rock-strewn surface of Dimorphos and was taken two seconds before DART crashed into the surface.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/feature/dart-s-final-images-prior-to-impact">NASA/Johns Hopkins APL</a></span>
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<p>The second-to-last image, taken two seconds before impact, shows the rocky surface of Dimorphos, including small shadows. These shadows are interesting because they suggest that the camera aboard the DART spacecraft was seeing Dimorphos directly on but the Sun was at an angle relative to the camera. They imply the DART spacecraft was centered on its trajectory to impact Dimorphos at the moment, but it’s also possible the asteroid was slowly rotating relative to the camera.</p>
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<a href="https://images.theconversation.com/files/486695/original/file-20220927-20-k9qypk.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A slice of a photo of a gray, rocky surface with the rest of image black." src="https://images.theconversation.com/files/486695/original/file-20220927-20-k9qypk.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/486695/original/file-20220927-20-k9qypk.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=602&fit=crop&dpr=1 600w, https://images.theconversation.com/files/486695/original/file-20220927-20-k9qypk.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=602&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/486695/original/file-20220927-20-k9qypk.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=602&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/486695/original/file-20220927-20-k9qypk.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=756&fit=crop&dpr=1 754w, https://images.theconversation.com/files/486695/original/file-20220927-20-k9qypk.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=756&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/486695/original/file-20220927-20-k9qypk.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=756&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 final image from DART, taken one second before impact, was not able to fully transmit back to Earth.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/feature/dart-s-final-images-prior-to-impact">NASA/Johns Hopkins APL</a></span>
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<p>The final photo, taken one second before impact, only shows the top slice of an image, but this is incredibly exciting. The fact that NASA received only part of the image suggests that the shutter took the picture but DART, <a href="https://www.nasa.gov/press-release/nasa-s-dart-mission-hits-asteroid-in-first-ever-planetary-defense-test">traveling at around 14,000 mph</a> (22,500 kph), was unable to transmit the complete image before impact.</p>
<h2>2. What was supposed to happen?</h2>
<p>The point of the DART mission was to test whether it is possible to <a href="https://theconversation.com/nasa-is-crashing-a-spacecraft-into-an-asteroid-to-test-a-plan-that-could-one-day-save-earth-from-catastrophe-190888">deflect an asteroid with a kinetic impact</a> – by crashing something into it. NASA used the analogy of a golf cart hitting the side of an Egyptian pyramid to convey the relative difference in size between tiny DART and Dimorphos, the smaller of the two asteroids. Prior to the test, Dimorphos orbited Didymos in just under 12 hours. NASA expects the impact to <a href="https://www.nasa.gov/press-release/nasa-s-dart-mission-hits-asteroid-in-first-ever-planetary-defense-test">shorten Dimorphos’ orbit by about 1%</a>. Though small, if done far enough away from Earth, a nudge like this could potentially deflect a future asteroid headed toward Earth just enough to prevent an impact.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/489267/original/file-20221011-21-yzocsl.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Three images of bright blue point of light with expanding clouds of debris." src="https://images.theconversation.com/files/489267/original/file-20221011-21-yzocsl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/489267/original/file-20221011-21-yzocsl.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=200&fit=crop&dpr=1 600w, https://images.theconversation.com/files/489267/original/file-20221011-21-yzocsl.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=200&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/489267/original/file-20221011-21-yzocsl.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=200&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/489267/original/file-20221011-21-yzocsl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=251&fit=crop&dpr=1 754w, https://images.theconversation.com/files/489267/original/file-20221011-21-yzocsl.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=251&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/489267/original/file-20221011-21-yzocsl.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=251&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">These images, taken by the Hubble Space Telescope over the course of a few hours, show the cloud of debris coming from the Didymos system after DART crashed into Dimorphos.</span>
<span class="attribution"><a class="source" href="https://hubblesite.org/contents/media/images/2022/047/01GE2B5TF1HQQT5MPPQ9JY750E?news=true">NASA, ESA, Jian-Yang Li (PSI), Alyssa Pagan (STScI)</a></span>
</figcaption>
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<h2>3. Did it work?</h2>
<p>The last bits of data that came from the DART spacecraft right before impact showed that it was on course. The fact that the images stopped transmitting after the target point was reached was the first sign of success. </p>
<p>Fifteen days before the impact, DART released a <a href="https://www.asi.it/en/planets-stars-universe/solar-system-and-beyond/liciacube/">small satellite with a camera</a> that was designed to document the entire impact. The small satellite has been <a href="https://gizmodo.com/liciacube-images-dart-asteroid-impact-1849585958">sending photos of the impact</a> back to Earth during early October 2022. A number of Earth-based telescopes as well as some satellites in orbit, including Hubble and James Webb, were watching Didymos at the time of the impact as well.</p>
<p>Using data from these telescopes taken at the time of impact as well as over the following weeks, the DART team at NASA has been able to calculate just how much the impact deflected the orbit of Dimorphos. Before DART, it took 11 hours and 55 minutes for the smaller moonlet to orbit the larger asteroid Didymos. The energy from the impact <a href="https://www.nasa.gov/press-release/nasa-confirms-dart-mission-impact-changed-asteroid-s-motion-in-space">shortened Dimorphos’s orbit by 32 minutes</a> – showing the impact to be more than 25 times more effective than NASA’s conservative goal of 72 seconds.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/486701/original/file-20220927-16-aprxc2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Infographic showing the effect of DART's impact on the orbit of Dimorphos." src="https://images.theconversation.com/files/486701/original/file-20220927-16-aprxc2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/486701/original/file-20220927-16-aprxc2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=351&fit=crop&dpr=1 600w, https://images.theconversation.com/files/486701/original/file-20220927-16-aprxc2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=351&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/486701/original/file-20220927-16-aprxc2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=351&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/486701/original/file-20220927-16-aprxc2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=441&fit=crop&dpr=1 754w, https://images.theconversation.com/files/486701/original/file-20220927-16-aprxc2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=441&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/486701/original/file-20220927-16-aprxc2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=441&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 force from DART’s impact should slightly shift the orbit of Dimorphos around Didymos.</span>
<span class="attribution"><a class="source" href="https://dart.jhuapl.edu/Gallery/media/graphics/lg/DART-infographic_v4.jpg">NASA/Johns Hopkins APL</a></span>
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<h2>4. What does the test mean for planetary defense?</h2>
<p>I believe this test was a great proof-of-concept for many technologies that the U.S. government has invested in over the years. And importantly, it proves that it is possible to send a craft to intercept with a minuscule target millions of miles away from Earth and change its orbit. DART has been a great success. </p>
<p>Over the course of the next months and years, researchers will learn just how efficient the impact was – and most importantly, whether this type of kinetic impact can actually move a celestial object ever so slightly at a great enough distance to prevent a future asteroid from threatening Earth.</p>
<p><em>This is an updated version of a <a href="https://theconversation.com/nasa-crashed-a-spacecraft-into-an-asteroid-photos-show-the-last-moments-of-the-successful-dart-mission-191402">story</a> first published on Sept. 27, 2022.</em></p><img src="https://counter.theconversation.com/content/192317/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Barnhart 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 Double Asteroid Redirection Test successfully showed that it is possible to crash a spacecraft into a small asteroid and change its orbit. This technique could save Earth from asteroids in the future.David Barnhart, Professor of Astronautics, University of Southern CaliforniaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1887592022-08-17T18:09:09Z2022-08-17T18:09:09ZMystery crater potentially caused by relative of dinosaur-killing asteroid<figure><img src="https://images.theconversation.com/files/479175/original/file-20220815-5636-q34zaf.png?ixlib=rb-1.1.0&rect=0%2C0%2C1856%2C1099&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Kevin Gill/Flickr</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>The ocean floor is famously less explored than the surface of Mars. And when our team of scientists recently mapped the seabed, and ancient sediments beneath, we discovered what looks like an asteroid impact crater. </p>
<p>Intriguingly, the crater, named “Nadir” after the nearby volcano Nadir Seamount, is of the same age as the Chicxulub impact <a href="https://theconversation.com/dinosaur-killing-asteroid-struck-at-worst-angle-to-cause-maximum-damage-new-research-139394">caused by a huge asteroid</a> at the end of the Cretaceous period, around 66 million years ago, which wiped out the dinosaurs and many other species. </p>
<p>The finding, <a href="http://www.science.org/doi/10.1126/sciadv.abn3096">published in Science Advances</a>, raises the question of whether the crater might be related to Chicxulub in some way. If confirmed, it would also be of huge general scientific interest as it would be one of a very small number of known marine asteroid impacts and so give unique new insights into what happens during such a collision.</p>
<p>The crater was identified using “<a href="https://www.ucl.ac.uk/EarthSci/people/lidunka/GEOL2014/Geophysics4%20-%20Seismic%20waves/reflection%20seismology%202.pdf">seismic reflection</a>” as part of a wider project to reconstruct the tectonic separation of South America from Africa back in the Cretaceous period. Seismic reflection works in a similar manner to ultrasound data, sending pressure waves through the ocean and its floor and detecting the energy that is reflected back. This data allows geophysicists and geologists to reconstruct the architecture of the rocks and sediments. </p>
<p>Scrolling through this data at the end of 2020, we came across a highly unusual feature. Among the flat, layered sediments of the <a href="https://www.britannica.com/place/Guinea-Highlands">Guinea Plateau</a>, west of Africa, was what appeared to be a large crater, a little under 10km wide and several hundred metres deep, buried below several hundred metres of sediment. </p>
<p>Many of its features are consistent with an impact origin, including the scale of the crater, the ratio of height to width and the height of the crater rim. The presence of chaotic deposits outside of the crater floor also look like “ejecta” – material expelled from the crater immediately following a collision. </p>
<figure class="align-center ">
<img alt="A graph showing how the crater may have formed." src="https://images.theconversation.com/files/479174/original/file-20220815-10505-73f28m.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/479174/original/file-20220815-10505-73f28m.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=391&fit=crop&dpr=1 600w, https://images.theconversation.com/files/479174/original/file-20220815-10505-73f28m.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=391&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/479174/original/file-20220815-10505-73f28m.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=391&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/479174/original/file-20220815-10505-73f28m.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=492&fit=crop&dpr=1 754w, https://images.theconversation.com/files/479174/original/file-20220815-10505-73f28m.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=492&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/479174/original/file-20220815-10505-73f28m.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=492&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">How the crater may have formed.</span>
</figcaption>
</figure>
<p>We did consider other possible processes that could have formed such a crater, such as the collapse of a submarine volcano or a pillar (or diapir) of salt below the seabed. An explosive release of gas from below the surface could also be a cause. But none of these possibilities are consistent with the local geology or the geometry of the crater.</p>
<h2>Earthquakes, airblast, fireball and tsunamis</h2>
<p>After identifying and characterising the crater, we built computer models of an impact event to see if we could replicate the crater and characterise the asteroid and its impact. </p>
<p>The simulation that best fits the crater shape is for an asteroid 400 metres in diameter hitting an ocean that was 800 metres deep. The consequences of an impact in the ocean at such water depths are dramatic. It would result in an 800-metre thick water column, as well as the asteroid and a substantial volume of sediment being instantly vapourised – with a large fireball visible hundreds of kilometres away. </p>
<p>Shock waves from the impact would be equivalent to a magnitude 6.5 or 7 earthquake, which would likely trigger underwater landslides around the region. A train of tsunami waves would form.</p>
<p>The air blast from the explosion would be larger than anything heard on Earth in recorded history. The energy released would be approximately a thousand times larger than that from the <a href="https://theconversation.com/tonga-eruption-we-are-watching-for-ripples-of-it-in-space-175132">recent Tonga eruption</a>. It is also possible that the pressure waves in the atmosphere would further amplify the tsunami waves far away from the crater. </p>
<h2>Chicxulub relative?</h2>
<p>One of the most intriguing aspects of this crater is that it is the same age as the giant Chicxulub event, give or take one million years, at the boundary between the Cretaceous and Paleogene periods 66 million years ago. Again, if this really is an impact crater, might there be some relationship between them?</p>
<p>We have three ideas as to their possible relationship. The first is that they might have formed from the break-up of a parent asteroid, with the larger fragment resulting in the Chicxulub event and a smaller fragment (the “little sister”) forming the Nadir crater. If so, the damaging effects of the Chicxulub impact could have been added to by the Nadir impact, exacerbating the severity of the mass extinction event.</p>
<p>The break-up event could have formed by an earlier near-collision, when the asteroid or comet passed close enough to Earth to experience gravitational forces strong enough to pull it apart. The actual collision could then have occurred on a subsequent orbit. </p>
<p>Although, this is less likely for a rocky asteroid, this pull-apart is exactly what happened to the <a href="https://solarsystem.nasa.gov/asteroids-comets-and-meteors/comets/p-shoemaker-levy-9/in-depth/">Shoemaker-Levy 9 comet</a> that collided with Jupiter back in 1994, where multiple comet fragments collided with the planet over the course of several days.</p>
<p>Another possibility is that Nadir was part of a longer lived “impact cluster”, formed by a collision in the asteroid belt earlier in solar system history. This is known as the “little cousin” hypothesis. </p>
<p>This collision may have sent a shower of asteroids into the inner solar system, which may have collided with the Earth and other inner planets over a more extended time period, perhaps a million years or more. We have a precedent for such an event back in the Ordovician period – over 400 million years ago – when there were <a href="https://www.nature.com/articles/srep06724#:%7E:text=Approximately%20470%20million%20years%20ago,fragments%20into%20Earth%20crossing%20orbits.">numerous impact events</a> in a short period of time. </p>
<figure class="align-center ">
<img alt="Seismic map of the Nadir crater." src="https://images.theconversation.com/files/479173/original/file-20220815-21-dga3vg.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/479173/original/file-20220815-21-dga3vg.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=288&fit=crop&dpr=1 600w, https://images.theconversation.com/files/479173/original/file-20220815-21-dga3vg.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=288&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/479173/original/file-20220815-21-dga3vg.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=288&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/479173/original/file-20220815-21-dga3vg.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=362&fit=crop&dpr=1 754w, https://images.theconversation.com/files/479173/original/file-20220815-21-dga3vg.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=362&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/479173/original/file-20220815-21-dga3vg.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=362&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Nadir crater.</span>
</figcaption>
</figure>
<p>Finally, of course, this may just be a coincidence. We do expect a collision of a Nadir-sized asteroid every 700,000 years or so. For now, however, we cannot definitively state that the Nadir crater was formed by an asteroid impact until we physically recover samples from the crater floor, and identify minerals that can only be formed by extreme shock pressures. To that end, we have recently submitted a proposal to drill the crater through the International Ocean Discovery Program. </p>
<p>As with the main impact crater hypothesis, we can only test the little sister and little cousin hypotheses by accurately dating the crater using these samples, as well as by looking for other candidate craters of a similar age.</p>
<p>Perhaps more importantly, could such an event happen in the near future? It is unlikely, but the size of the asteroid that we model is very similar to the <a href="https://theconversation.com/nasa-spacecraft-gets-up-close-with-an-asteroid-that-could-one-day-collide-with-earth-108027">Bennu asteroid currently in near-Earth orbit</a>. This asteroid is considered to be one of the two most hazardous objects in the solar system, with a one-in-1,750 chance of collision with Earth in the next couple of centuries.</p><img src="https://counter.theconversation.com/content/188759/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Uisdean Nicholson receives funding from the Natural Environment Research Council (NERC).</span></em></p><p class="fine-print"><em><span>Sean Gulick has received funding from the US National Science Foundation and NASA for his research into Chicxulub.</span></em></p><p class="fine-print"><em><span>Veronica Bray does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The dinosaurs were possibly annihilated by two asteroids.Uisdean Nicholson, Associate Professor of Geoscience, Heriot-Watt UniversitySean Gulick, Research Professor of Geoscience, The University of Texas at AustinVeronica Bray, Research Scientist, Lunar & Planetary Laboratory, University of ArizonaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1748282022-01-19T16:30:46Z2022-01-19T16:30:46ZPlesiosaurs, pliosaurs, hybodonts: looking back at three prehistoric predators of the Jurassic seas<figure><img src="https://images.theconversation.com/files/441539/original/file-20220119-17-1evl26h.jpg?ixlib=rb-1.1.0&rect=17%2C0%2C5973%2C3375&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Liopleurodon was a pliosaur of the Jurassic period.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/3d-rendered-illustration-liopleurodon-1181537293">SciePro/Shutterstock</a></span></figcaption></figure><p>The fossilised remains of a gigantic ichthyosaur, colloquially known as a “sea dragon”, were <a href="https://www.theguardian.com/science/2022/jan/10/huge-sea-dragon-named-one-of-uks-greatest-fossil-finds">recently uncovered</a> at the Rutland Water Nature Reserve in the UK. Measuring at least ten metres in length and with a skull weighing roughly one tonne, it’s the largest, most complete ichthyosaur of its kind found to date in Britain.</p>
<p>The skeleton was discovered by Joe Davis of the Leicestershire and Rutland Wildlife Trust in February 2021. It was carefully excavated in August and September 2021 by a team of palaeontologists assembled from around the UK (including myself), led by ichthyosaur expert Dr Dean Lomax and palaeontological conservator Nigel Larkin. </p>
<p>Based on analysis of microscopic fossils from the surrounding sediment, we were able to ascertain that the Rutland ichthyosaur is roughly 181.5 to 182 million years old. The creature’s anatomy suggests it most likely belongs to the species <em>Temnodontosaurus trigonodon</em>. This would make it the first occurrence of this ichthyosaur species in the UK.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/441499/original/file-20220119-17-2dzeh3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/441499/original/file-20220119-17-2dzeh3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=290&fit=crop&dpr=1 600w, https://images.theconversation.com/files/441499/original/file-20220119-17-2dzeh3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=290&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/441499/original/file-20220119-17-2dzeh3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=290&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/441499/original/file-20220119-17-2dzeh3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=365&fit=crop&dpr=1 754w, https://images.theconversation.com/files/441499/original/file-20220119-17-2dzeh3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=365&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/441499/original/file-20220119-17-2dzeh3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=365&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A reconstruction of the Rutland ichthyosaur <em>Temnodontosaurus trigonodon</em>.</span>
<span class="attribution"><span class="source">Bob Nicholls</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>It’s a common misconception that ichthyosaurs were “swimming dinosaurs”. But they were actually a group of <a href="https://evolution-outreach.biomedcentral.com/articles/10.1007/s12052-009-0139-y">marine reptiles</a> which lived during the Mesozoic era (between 66 and 252 million years ago). As <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0194742">successful major predators</a>, they were fundamental to Mesozoic marine ecosystems.</p>
<p>The number of ichthyosaur species peaked during the Triassic period (between 250 and 201 million years ago) and especially the Jurassic period (201 to 145 million years ago). But these were not the only predators patrolling the prehistoric seas. Let’s dive in and take a look back at three other extinct sea creatures that dominated the Jurassic oceans.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/a-medical-scan-reveals-the-secrets-of-new-zealands-extinct-marine-reptiles-almost-150-years-after-the-fossils-discovery-164484">A medical scan reveals the secrets of New Zealand's extinct marine reptiles, almost 150 years after the fossils' discovery</a>
</strong>
</em>
</p>
<hr>
<h2>Plesiosaurs</h2>
<p>Plesiosaurs (meaning “near to lizard”) were a group of large, long-necked <a href="https://www.jstor.org/stable/4096890">marine reptiles</a> that belong to the order Plesiosauria. These animals appeared in the <a href="https://www.science.org/doi/10.1126/sciadv.1701144">Late Triassic period</a> and became especially prevalent during the Jurassic period. They thrived until their disappearance in the <a href="https://evolution-outreach.biomedcentral.com/articles/10.1007/s12052-009-0139-y">Cretaceous–Paleogene extinction event</a>, roughly 66 million years ago. Plesiosaurs existed in oceans across the world: in European seas and around the Pacific Ocean, including Australia, North America and Asia. </p>
<p>Plesiosaurs <a href="https://plesiosauria.com/pdf/smith&dyke_2008.pdf">ranged in length</a> from less than 2 metres to more than 17 metres. Some species had incredibly <a href="https://www.jstor.org/stable/3595510">long necks</a>, almost twice as long as the rest of their body. </p>
<p>Plesiosaurs had a broad, flat body, short tail, and four long fins which made this animal a strong swimmer. They also had a small head – but they were filled with sharp, pointed teeth to facilitate their carnivorous diet of fish and ancient squid-like molluscs. Like ichthyosaurs, plesiosaurs gave birth to <a href="https://www.science.org/doi/10.1126/science.1205689">live young</a>. The first almost-complete skeleton of <em>Plesiosaurus</em> was discovered in 1823 at Lyme Regis, Dorset in the UK by pioneering palaeontologist <a href="https://www.cambridge.org/core/journals/british-journal-for-the-history-of-science/article/mary-anning-17991847-of-lyme-the-greatest-fossilist-the-world-ever-knew/58D173F8F79721068E7007FADE70F727">Mary Anning</a>. </p>
<figure class="align-center ">
<img alt="3D rendering of a plesiosaur." src="https://images.theconversation.com/files/441537/original/file-20220119-10207-1sdvk8v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/441537/original/file-20220119-10207-1sdvk8v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=412&fit=crop&dpr=1 600w, https://images.theconversation.com/files/441537/original/file-20220119-10207-1sdvk8v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=412&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/441537/original/file-20220119-10207-1sdvk8v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=412&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/441537/original/file-20220119-10207-1sdvk8v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=518&fit=crop&dpr=1 754w, https://images.theconversation.com/files/441537/original/file-20220119-10207-1sdvk8v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=518&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/441537/original/file-20220119-10207-1sdvk8v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=518&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The <em>Plesiosaurus</em> lived during the Jurassic period.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/plesiosaurus-jurassic-era-3d-illustration-1137225629">Warpaint/Shutterstock</a></span>
</figcaption>
</figure>
<h2>Pliosaurs</h2>
<p>Pliosaurs (meaning “more lizard”) are another group of Jurassic marine reptiles which belong to the order Plesiosauria. But unlike their long-necked plesiosaur cousins, these animals had <a href="https://www.jstor.org/stable/3595510">short necks</a> with a large, elongated head similar to crocodiles. Pliosaurs ranged from around four to ten metres in length, but could be <a href="https://pubmed.ncbi.nlm.nih.gov/18523747/">up to 15 metres</a>. Pliosaurs also had two pairs of powerful paddles and a relatively short tail. </p>
<p>During certain parts of the Jurassic period, they were the top predators of the ocean. The creature’s powerful jaws contained sharp, conical teeth which they used to feed on fish, sharks, ichthyosaurs and other Plesiosauria.</p>
<p>This genus is represented by four species (<em>R. cramptoni, R. propinquus, R. thorntoni</em> and <em>R. zetlandicus</em>) and all currently known specimens have been discovered in Yorkshire and Northamptonshire in the UK. Like plesiosaurs, pliosaurs became extinct in the Cretaceous–Paleogene extinction event 66 million years ago.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/dinosaur-embryo-discovery-rare-fossil-suggests-dinosaurs-had-similar-pre-hatching-posture-to-modern-birds-174040">Dinosaur embryo discovery: rare fossil suggests dinosaurs had similar pre-hatching posture to modern birds</a>
</strong>
</em>
</p>
<hr>
<h2>Hybodont sharks</h2>
<p><em>Hybodus</em> (meaning “humped tooth”) is an extinct genus of shark which first appears towards the end of the Permian period (260 million years ago). It became highly successful in the shallow Jurassic seas, away from the deep waters that plesiosaurs and pliosaurs inhabited. </p>
<p>This genus possessed streamlined, fusiform bodies (spindle-shaped, elongated and tapering at both ends) which enabled them to move quickly though the water. They also had two fins on their backs which would have helped them steer with precision. These opportunistic predators typically grew to roughly two metres long.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/441516/original/file-20220119-19-cbrdus.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/441516/original/file-20220119-19-cbrdus.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=264&fit=crop&dpr=1 600w, https://images.theconversation.com/files/441516/original/file-20220119-19-cbrdus.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=264&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/441516/original/file-20220119-19-cbrdus.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=264&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/441516/original/file-20220119-19-cbrdus.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=331&fit=crop&dpr=1 754w, https://images.theconversation.com/files/441516/original/file-20220119-19-cbrdus.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=331&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/441516/original/file-20220119-19-cbrdus.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=331&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A <em>Hybodus fraasi</em> fossil from Germany.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Hybodus_fraasi_(fossil).jpg">Wikimedia commons</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p><em>Hybodus</em> consumed a wide variety of prey thanks to their teeth, which were arranged into two groups. At the front were sharp, pointed teeth which were useful for grabbing prey including fish and squid; while the back teeth were rounded and more suited for crushing the shells of crustaceans. </p>
<p>In fact, a specimen of <em>Hybodus</em> belonging to the species <em>H. hauffianus</em> from Holzmaden in Germany was found stuffed with <a href="https://link.springer.com/article/10.1186/s13358-021-00225-z">belemnites</a> (extinct cephalopod molluscs), suggesting that this creature died after overindulging on too many belemnite rostra (shells). </p>
<p>The hybodonts <a href="https://www.sciencedirect.com/science/article/abs/pii/S0031018204004201?via%3Dihub">became extinct</a> towards the end of the Late Cretaceous period, some 66 million years ago. The first fossilised <em>Hybodus</em> teeth were found in the UK around the mid-19th century, but remains including skeletons, isolated teeth and head and fin spines have now been recovered from Asia, Europe, Africa and North America.</p><img src="https://counter.theconversation.com/content/174828/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The excavation of the Rutland ichthyosaur was organised by Dr Dean Lomax (University of Manchester), Nigel Larkin (University of Reading) and Dr Mark Evans (British Antarctic Survey and University of Leicester). The team also included: Dr Emma Nicholls (Horniman Museum and Gardens); Darren Withers, David Savory and Mick Beeson (Peterborough Geological and Palaeontological Group); Emily Swaby (The Open University); Paul de la Salle (The Etches Collection) and Carol Skiggs; Dr Ian Boomer (University of Birmingham); Tom Harvey (University of Leicester); Steven Dey (ThinkSee3D); Phil Rye; and Dawn and Matthew Butler. The excavation could not have taken place without the assistance of the Rutland and Leicestershire Wildlife Trust, Anglian Water and Rutland County Council. </span></em></p>The fossil of a gigantic ichthyosaur was recently discovered in the UK. It wasn’t the only creature lurking in the Jurassic oceans.Emily Swaby, PhD candidate, School of Environment, Earth & Ecosystem Sciences, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1688392021-10-13T19:12:42Z2021-10-13T19:12:42ZHumans are driving animals and plants to the edge. But are we really heading into a mass extinction?<figure><img src="https://images.theconversation.com/files/426080/original/file-20211012-24-aqip4l.jpg?ixlib=rb-1.1.0&rect=53%2C26%2C5937%2C3961&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock/Nick Greaves</span></span></figcaption></figure><p>It is now common to refer to the current biodiversity crisis as the sixth mass extinction. But is this true? Are we in the middle of an event on the same scale as the five ancient mass extinctions Earth has experienced?</p>
<p>Humans are indeed driving animals and plants to extinction. Land clearance, habitat modification and, above all, climate change are all placing biodiversity under stress. </p>
<p>Many species have died out since the arrival of humans and many more are threatened. </p>
<p>But to answer this question fully, we have to look at the rates at which species were going extinct before the appearance of humans and compare it to today’s rate.</p>
<p>Life on Earth has diversified from a single cell more than 3.7 billion years ago to the <a href="https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1001127">estimated 8.7 million species</a> alive today.</p>
<p>But as I describe in my book <a href="https://www.cambridge.org/core/books/extinctions/A4B6AA42F403802A0F9D99F64ECF583E">Extinctions: living and dying in the margin of error</a>, this journey has been a roller coaster ride. There have been times when biodiversity exploded with many new species evolving relatively quickly. Conversely, there have been extremely short intervals of time when biodiversity crashed in a mass extinction. </p>
<p>The scale of biodiversity loss in a mass extinction is extraordinary. In the five mass extinctions on Earth, estimates of species loss range from around 70% at the end of the Cretaceous up to 95% at the end of the Permian, the <a href="https://royalsocietypublishing.org/doi/10.1098/rstb.1994.0045">largest of the mass extinctions</a>. </p>
<figure class="align-center ">
<img alt="The Gubbio section, found in Italy, represents a complete record of the end-of-Cretaceous mass extinction." src="https://images.theconversation.com/files/425820/original/file-20211011-25-auc2tn.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/425820/original/file-20211011-25-auc2tn.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=390&fit=crop&dpr=1 600w, https://images.theconversation.com/files/425820/original/file-20211011-25-auc2tn.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=390&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/425820/original/file-20211011-25-auc2tn.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=390&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/425820/original/file-20211011-25-auc2tn.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=491&fit=crop&dpr=1 754w, https://images.theconversation.com/files/425820/original/file-20211011-25-auc2tn.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=491&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/425820/original/file-20211011-25-auc2tn.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=491&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Gubbio section, found in Italy, represents a complete record of the end-of-Cretaceous mass extinction. The exact instant when about 70% of species went extinct is marked by the cleft running diagonally across the image.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Each of these events resulted in a wave of extinctions washing across all of the planet’s ecosystems. Reefs were wiped out, dinosaurs disappeared, insect species were decimated and plants went through massive upheavals. It took up to a million years for ecosystems to recover from a mass extinction.</p>
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<strong>
Read more:
<a href="https://theconversation.com/ocean-ecosystems-take-two-million-years-to-recover-after-mass-extinction-new-research-124328">Ocean ecosystems take two million years to recover after mass extinction – new research</a>
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<h2>Ancient and modern extinction rates</h2>
<p>Estimating prehuman extinction rates from the somewhat patchy fossil record is fraught. Nevertheless, researchers have <a href="https://www.nature.com/articles/nature09678">managed do it</a>, albeit using only vertebrate fossils. </p>
<p>Their estimate suggests prior to the arrival of humans, vertebrate species were going extinct at the rate of about two per million species lost every year. </p>
<p>In 2015, another research team took this estimate and compared it with <a href="https://pubmed.ncbi.nlm.nih.gov/26601195/">present day vertebrate extinction rates</a>. They found vertebrates are going extinct 53 times faster today than they were before humans arrived.</p>
<p>If the increase in extinction rates recorded in vertebrates is on a similar scale across the planet’s entire biota, humans have triggered a significant rise in the rate of species going extinct. </p>
<p>But is that enough to consider our current biotic crisis a mass extinction?</p>
<figure class="align-center ">
<img alt="Trilobites once filled the world's oceans but died out at the end of the Permian." src="https://images.theconversation.com/files/426088/original/file-20211013-23-1jrxqxl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/426088/original/file-20211013-23-1jrxqxl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/426088/original/file-20211013-23-1jrxqxl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/426088/original/file-20211013-23-1jrxqxl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/426088/original/file-20211013-23-1jrxqxl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/426088/original/file-20211013-23-1jrxqxl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/426088/original/file-20211013-23-1jrxqxl.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">Trilobites were ancient arthropods that filled the world’s oceans from the early Cambrian, some 520 million years ago, until the mass extinction at the end of the Permian, 252 million years ago.</span>
<span class="attribution"><span class="source">Shutterstock/Tami Freed</span></span>
</figcaption>
</figure>
<p>To answer that question, we need to consult the <a href="https://www.iucnredlist.org/">Red List</a> run by the International Union for the Conservation of Nature (<a href="https://www.iucn.org/">ICUN</a>). This list is an attempt to assess the threat of extinction of all known species by assigning each to a category of descending threat: extinct or extinct in the wild, severe threat of extinction, threatened and so on. </p>
<h2>Are we there yet?</h2>
<p>A glance across the Red List confirms that, as with the ancient mass extinctions, today’s species loss affects the entire biosphere. However, the situation changes when we compare the current level of extinction with those from the big five mass extinctions. </p>
<figure class="align-left ">
<img alt="A fossil of a plant that went extinct 550 million years ago." src="https://images.theconversation.com/files/426110/original/file-20211013-17-1vj5w5g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/426110/original/file-20211013-17-1vj5w5g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/426110/original/file-20211013-17-1vj5w5g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/426110/original/file-20211013-17-1vj5w5g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/426110/original/file-20211013-17-1vj5w5g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/426110/original/file-20211013-17-1vj5w5g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/426110/original/file-20211013-17-1vj5w5g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">This fossil (Arborea arborea) is part of the Ediacaran fauna from South Australia which went extinct about 550 million years ago.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>As noted above, the loss of species during the ancient mass extinctions is massive. Data from the Red List suggest we haven’t come close to those. For example, the Red List assigns only 1.46% of mammal species to the extinct or extinct in the wild categories. It considers less than 1% of amphibian species are extinct or extinct in the wild. For insects, it’s 0.65%, bivalves 4% and corals 0%. This level of species loss isn’t close to the losses recorded in the fossil record.</p>
<p>While the rate at which species are going extinct has risen and the entire ecosystem is affected, we have, at the moment at least, only low levels of extinction. </p>
<p>Unfortunately, species extinction levels show only part of the problem. To see the full extent of the crisis, we need to add the species the Red List considers to be under threat of extinction to those already extinct. </p>
<p>When we do, the picture changes. Taken together, the percentage of mammals that are extinct or under threat of extinction rises from 1.46% to 23.48%, amphibian numbers rise to 33.56%, insects to 19.23% and corals to 26.85%. These numbers demonstrate the true scale of the threat facing the planet’s biosphere.</p>
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Read more:
<a href="https://theconversation.com/animals-are-disappearing-from-forests-with-grave-consequences-for-the-fight-against-climate-breakdown-new-research-124746">Animals are disappearing from forests, with grave consequences for the fight against climate breakdown – new research</a>
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<p>I don’t like referring to today’s crisis as a mass extinction because it allows us to focus entirely on extinction levels, and they are low. Others have coined a new term to reflect the fact that although many species are extinct, there are many more threatened with extinction: <a href="https://www.science.org/doi/10.1126/science.1251817">defaunation</a>. </p>
<p>Defaunation better describes the crisis unfolding in the planet’s biosphere. To avoid a slide into a full-blown mass extinction, we must not allow defaunation to continue. We know how to do this: reduce emissions, protect vulnerable ecosystems and regenerate degraded ones.</p><img src="https://counter.theconversation.com/content/168839/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michael Hannah is affiliated with NZ Labour party</span></em></p>While current extinction rates remain lower than during previous mass extinction events, the number of species under threat of dying out is growing, reflecting the true scale of loss.Michael Hannah, Associate Professor, Te Herenga Waka — Victoria University of WellingtonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1636242021-06-30T13:31:25Z2021-06-30T13:31:25ZDinosaurs were already in decline before the asteroid wiped them out – new research<p>Some 66 million years ago, on the Yucatán peninsula in Mexico, a <a href="https://arxiv.org/abs/1403.6391">12 kilometre-wide asteroid</a> crashes to Earth. The impact causes an explosion whose magnitude is hard to imagine today – several billion times more powerful than the atomic bomb dropped on Hiroshima.</p>
<p>Most of the animals on the American continent are killed immediately. The impact also triggers worldwide tsunamis. Tons and tons of dust are ejected into the atmosphere, plunging the planet into darkness. This “nuclear winter” causes the extinction of many plant and animal species.</p>
<p>Among the latter, the most emblematic: the dinosaurs. But how were the dinosaurs faring before this cataclysm? This is the question we try to answer in our new study, the results of which have just been published in the scientific journal <a href="https://doi.org/10.1038/s41467-021-23754-0"><em>Nature Communications</em></a>.</p>
<p>We were interested in six families of dinosaurs, the most representative and the most diversified of the 40 million years that preceded the arrival of the asteroid.</p>
<p>Three of these families were carnivorous: the Tyrannosauridae, the Dromaeosauridae (including the famous velociraptors, made famous by the <em>Jurassic Park</em> movies) and the Troodontidae (small dinosaurs similar to birds). </p>
<p>The other three were herbivores: the Ceratopsidae (represented in particular by the Triceratops), the Hadrosauridae (the richest of all the families in terms of diversity) and the Ankylosauridae (represented in particular by the ankylosaur, a dinosaur covered in bony armour with a club-like tail).</p>
<p>We knew that all these families had survived until the end of the Cretaceous marked by the fall of the asteroid. Our goal was to determine at what rate these families diversified – formed new species – or became extinct.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/408816/original/file-20210629-18-ci9req.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/408816/original/file-20210629-18-ci9req.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/408816/original/file-20210629-18-ci9req.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=315&fit=crop&dpr=1 600w, https://images.theconversation.com/files/408816/original/file-20210629-18-ci9req.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=315&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/408816/original/file-20210629-18-ci9req.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=315&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/408816/original/file-20210629-18-ci9req.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=396&fit=crop&dpr=1 754w, https://images.theconversation.com/files/408816/original/file-20210629-18-ci9req.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=396&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/408816/original/file-20210629-18-ci9req.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=396&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Possible appearance of an Ankylosaurus based on Carpenter 2004 skeletal reconstruction and fossil photographs.</span>
<span class="attribution"><a class="source" href="https://fr.wikipedia.org/wiki/Ankylosaurus#/media/Fichier:Ankylosaurus_dinosaur.png">Mariana Ruiz Villarreal LadyofHats/Wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>For five years, we compiled all the known information on these families in order to try to work out how many of them there were on Earth at a particular time, and which species were in each group. In palaeontology, each fossil is given a unique number for the sake of traceability, which allows us to follow it through the scientific literature over time.</p>
<p>The work was tedious – we inventoried most of the known fossils for these six families, which represented more than 1,600 individuals from around 250 species. It’s not easy to properly categorise each of the species and date them correctly: one researcher might have given a record a certain date and species, and then another might reexamine it and make a different analysis. In these cases, we had to make our own calls – if we had too many doubts, we eliminated the fossil from the study.</p>
<p>Once each fossil was properly categorised, we used a statistical model to estimate the number of species that evolved over time for each family. We were thus able to trace the species that appeared and those that disappeared between 160 and 66 million years ago and estimate, again for each family, the rates of speciation – the evolution of new species – and extinction over time.</p>
<p>To estimate these rates, we had to take several confounding factors into account. The fossil record is biased: it is uneven in time and space, and some types of dinosaur simply do not fossilise as well as others. This is a well-known problem in palaeontology when estimating the dynamics of past diversity.</p>
<p>Sophisticated models can account for uneven preservation over time and between species. In doing so, the fossil record becomes more reliable for estimating the number of species at any given time. But it is important to be cautious, because we are talking about estimates, and these estimates may change if we find more fossils, for example, or new analytical models.</p>
<h2>A steep decline</h2>
<p>Our results show that the number of species was in steep decline from 10 million years before the asteroid strike until the dinosaurs were wiped out. This decline is particularly interesting because it is worldwide, and affects both carnivorous groups such as tyrannosaurs, and herbivorous groups such as triceratops.</p>
<p>Some species declined sharply, like the ankylosaurs and ceratopsians, and only one family out of the six – the troodontids – shows a very small decline, which took place in the last five million years of dinosaurs’ existence.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/409123/original/file-20210630-13-1ds3ugw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/409123/original/file-20210630-13-1ds3ugw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/409123/original/file-20210630-13-1ds3ugw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=349&fit=crop&dpr=1 600w, https://images.theconversation.com/files/409123/original/file-20210630-13-1ds3ugw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=349&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/409123/original/file-20210630-13-1ds3ugw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=349&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/409123/original/file-20210630-13-1ds3ugw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=438&fit=crop&dpr=1 754w, https://images.theconversation.com/files/409123/original/file-20210630-13-1ds3ugw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=438&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/409123/original/file-20210630-13-1ds3ugw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=438&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">a) Dynamics of speciation (blue) and extinction (red) rates through time for the six dinosaur families. b) Diversification rates over time.</span>
<span class="attribution"><span class="source">Fabien Contamine</span></span>
</figcaption>
</figure>
<p>What could have caused this strong decline? One theory is climate change: at that time, the Earth underwent a period of global cooling of 7 to 8°C.</p>
<p>We know that dinosaurs need a warm climate for their metabolism to function properly. As we often hear, they were not ectothermic (cold-blooded) animals like crocodiles or lizards, nor endothermic (warm-blooded), like mammals or birds. They were mesotherms, a metabolic system between reptiles and mammals and needed a warm climate to maintain their temperature and thus perform basic biological functions. This temperature decrease must have had a strong impact on them.</p>
<p>It should be noted that we found a staggered decline between herbivores and carnivores: the grass-eaters declined slightly before the meat-eaters. It’s probable that the decline of herbivores caused the decline of carnivores. This is what we call cascade extinction.</p>
<h2>The knockout blow</h2>
<p>One big question remains: what would have happened if the asteroid had not crashed? Would dinosaurs have gone extinct anyway, due to the decline that had already begun, or could they have rebounded? It’s very difficult to say. Many palaeontologists believe that if the dinosaurs had survived, primates and therefore humans would never have appeared on Earth.</p>
<p>An important fact is that a possible rebound in diversity can be very heterogeneous and group-dependent, so that some groups would have survived and others not. Hadrosaurs, or “duck-billed” dinosaurs, for example, showed some form of resilience to the decline and might have bounced back after.</p>
<p>What we can say is that the ecosystems at the end of the Cretaceous period were under significant pressure due to climatic deterioration and major changes in vegetation, and that the asteroid dealt the final blow. This is often the case in the disappearance of species: first they are in decline and under pressure, then another event intervenes and finishes off a group that may have been on the verge of extinction anyway.</p><img src="https://counter.theconversation.com/content/163624/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Fabien Condamine ne travaille pas, ne conseille pas, ne possède pas de parts, ne reçoit pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'a déclaré aucune autre affiliation que son organisme de recherche.</span></em></p>If the asteroid caused the very sudden end of the dinosaurs, a new study shows that their decline had begun 10 million years earlier.Fabien Condamine, Chercheur au CNRS en Phylogénie et Evolution Moléculaire, Université de MontpellierLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1633092021-06-28T09:37:41Z2021-06-28T09:37:41ZPrehistoric creatures flocked to different latitudes to survive climate change – the same is taking place today<figure><img src="https://images.theconversation.com/files/408173/original/file-20210624-23-167gtr3.png?ixlib=rb-1.1.0&rect=739%2C8%2C1932%2C809&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Dinosaur_park_formation_fauna.png">J.T. Csotonyi/wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Life on Earth is most diverse at the equator. This pattern, where species biodiversity increases as we move through the tropics towards the equator, is seen on land and in the oceans, and has been documented across a broad range of animal and plant groups, from <a href="https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1001775">mammals</a> and <a href="https://www.journals.uchicago.edu/doi/abs/10.1086/519009?casa_token=KISLkv8QEj4AAAAA%3A6-lZhiu31_ooIxOAJNYQZzW-bGT8sF2extvVAtV0abeqi_0-OduN1OU7S_dK6UwghhYgzh6Ux14&journalCode=an">birds</a>, to <a href="https://www.nature.com/articles/s41467-018-04218-4">ants</a> and even <a href="https://www.journals.uchicago.edu/doi/full/10.1086/508635?casa_token=LSurevVXHl4AAAAA%3Aact0lSJMtF8MzBbm1GiJQs2lA6uS1vAWadix6qVxgJ7eJe0ROIKekeHwd_5IvRYLxM6iBpjyQGM">trees</a>.</p>
<p>Despite this pattern being so striking today, the distribution of biodiversity across latitudes – called the <a href="https://www.sciencedirect.com/science/article/pii/B9780128096659098098">latitudinal biodiversity gradient</a> – hasn’t always been like this. Studies looking at the evolution of biodiversity by latitude have shown that during some intervals in Earth’s history, species biodiversity was actually highest at latitudes far from the equator.</p>
<p>Understanding why latitudinal biodiversity has shifted over hundreds of millions of years, often linked to <a href="https://theconversation.com/five-mass-extinctions-and-what-we-can-learn-from-them-about-the-planet-today-79971">mass extinction events</a>, is critical in today’s world, where we’re facing climate change, habitat loss and decreasing biodiversity worldwide. Looking back in geological time reveals an alarming picture of what we’re set to lose if we fail to address increasing global temperatures.</p>
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Read more:
<a href="https://theconversation.com/what-is-a-mass-extinction-and-are-we-in-one-now-122535">What is a 'mass extinction' and are we in one now?</a>
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<p><a href="https://www.annualreviews.org/doi/abs/10.1146/annurev.ecolsys.34.012103.144032?casa_token=AnfHQJDzSNQAAAAA:-m18WiYPzX5IRGE8mTLJVbgP-Hg00Tp0AzU_0mgAbZRjsDqNjgaTjmqXxksJZGFIuqplNbFKTo99">Several different hypotheses</a> have been proposed to explain why high biodiversity clusters around certain latitudes, but climate is often regarded as a key driver, both in the present day and through history as shown by the <a href="https://www.sciencedirect.com/science/article/pii/S0169534713002358">geological record</a>. Climate affects organisms in many ways, including <a href="https://www.jstor.org/stable/2401068?casa_token=kqQ9fnw-n5EAAAAA%3AtpczwQNR_ceMjjm8cRuEWkSHaUic__OhypraifJQ1HZ4jMUe1VRoz3-LJEH1btrdlqV18Q4T9u2g0GeLo2A7d47Gop-gPNF7QHgcT3LXbYoa0fStRhs&seq=1#metadata_info_tab_contents">where they can live</a>, when they <a href="https://www.journals.uchicago.edu/doi/abs/10.1086/285538">reproduce</a>, and even how they control their internal processes such as <a href="https://esajournals.onlinelibrary.wiley.com/doi/abs/10.2307/1940107">temperature regulation</a>.</p>
<p>Modern biodiversity peaks in low-latitude equatorial regions, such as in the tropical rainforests of the Amazon and central Africa. This pattern is more likely to be recorded during “icehouse” times, when ice sheets are present in both poles simultaneously – like today. </p>
<p>During warmer intervals, called “<a href="https://theconversation.com/hothouse-earth-our-planet-has-been-here-before-heres-what-it-looked-like-101413">hothouse</a>” or “greenhouse” Earth states, bimodal peaks have been recorded. This means there were two bands where biodiversity was highest, and these wrapped around the Earth at mid-latitudes, or regions sitting between 25° and 65° north and south of the equator.</p>
<figure class="align-center ">
<img alt="Map of earth showing latitudes" src="https://images.theconversation.com/files/408151/original/file-20210624-15-14qetub.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/408151/original/file-20210624-15-14qetub.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=353&fit=crop&dpr=1 600w, https://images.theconversation.com/files/408151/original/file-20210624-15-14qetub.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=353&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/408151/original/file-20210624-15-14qetub.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=353&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/408151/original/file-20210624-15-14qetub.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=443&fit=crop&dpr=1 754w, https://images.theconversation.com/files/408151/original/file-20210624-15-14qetub.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=443&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/408151/original/file-20210624-15-14qetub.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=443&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Biodiversity was once highest around today’s Mediterranean and southern Africa.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/world-map-latitude-degrees-north-pole-1962211288">chemistrygod/Shutterstock</a></span>
</figcaption>
</figure>
<p>The fossil record provides our best window into Earth’s ancient biodiversity. But estimating patterns of biodiversity from the fossil record has been tricky, because it’s riddled with <a href="https://www.theguardian.com/science/lost-worlds/2012/aug/17/bias-fossil-record">gaps and biases</a> that limit our understanding. </p>
<p>But in the past two decades, <a href="https://www.palaeontologyonline.com/articles/2018/patterns-in-palaeontology-how-do-we-measure-biodiversity-in-the-past/">new analytical techniques</a> have allowed palaeontologists to estimate what prehistoric biodiversity patterns might have looked like, even from data that might appear, superficially at least, a little patchy. These techniques have recently revealed what latitudinal diversity looked like over 200 million years ago, in the aftermath of the most devastating mass extinction events ever recorded.</p>
<h2>Prehistoric habitats</h2>
<p>The <a href="https://www.nationalgeographic.com/science/article/permian-extinction">end-Permian mass extinction</a>, which took place 251 million years ago, resulted in the extinction of <a href="https://www.sciencedirect.com/science/article/pii/S0031018212007018?casa_token=niK9Iax0BI8AAAAA:QQariz_exhQIO4g21fQmdcdep3zm85Cp0bRF20uqZ_A9D1tKoB0MKfEa6Z5Gsosbo13EzALS">over 80% of species</a> on Earth. The extinction event was caused by an <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3252959/">unstable climate</a> after widespread volcanic eruptions. At this time, and for the following 50 million years of the <a href="https://www.nhm.ac.uk/discover/the-triassic-period-the-rise-of-the-dinosaurs.html">Triassic period</a>, the continents were arranged into a single landmass, known as <a href="https://www.britannica.com/place/Pangea">Pangaea</a>.</p>
<p><a href="https://www.sciencedirect.com/science/article/pii/S0031018211002987?casa_token=ZZAy60g_G0wAAAAA:qsksnxx-aqK99FvKPOLT9D2j2DOonMAOojDEXjK6a_wcR67O4i1FFfQ-kwB93vazp9MqaegG">The climate</a> of the period was generally hotter and more arid than the present day, and vast deserts surrounded the equator. Instead of ice sheets, polar regions had temperate climates, like those we find at mid-latitudes today. Life in the oceans, meanwhile, was not only subjected to equatorial sea surface temperatures <a href="https://science.sciencemag.org/content/338/6105/366.abstract?casa_token=WkTNFatVVJ0AAAAA:RSix9UmDSmWYColl3dasvxhMxIXxk5J9DSferDd2RpyVw8auWM6Fay3cQRYdhzsX99Ycfg2OKe4wPg">as high as 40°C</a>, but also falling oxygen levels and ocean acidification.</p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/global-warmings-evil-twin-ocean-acidification-19017">Global warming’s evil twin: ocean acidification</a>
</strong>
</em>
</p>
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<p>The period following the end-Permian mass extinction was one of recovery. A <a href="https://www.pnas.org/content/117/30/17578">recent study</a> found a latitudinal diversity gradient in the oceans similar to today’s was present for much of the Triassic (251–201 million years ago). Immediately following the mass extinction event, however, the researchers found a flat biodiversity gradient. There was no peak in species biodiversity at any latitude, which they attributed to high extinction rates near the equator due to extreme warming and ocean anoxia – when oxygen in ocean water is depleted.</p>
<p>On land, the vertebrates that survived the mass extinction soon developed a <a href="https://royalsocietypublishing.org/doi/abs/10.1098/rspb.2020.1125">bimodal</a> latitudinal biodiversity gradient, with the highest peak occurring in low-latitude regions of the northern hemisphere, but with a second peak in mid-latitude regions of the southern hemisphere. This pattern is likely to have been driven by the extreme climatic conditions on Pangaea, including high temperatures and strongly seasonal rainfall, associated with the formation of a “<a href="https://www.journals.uchicago.edu/doi/abs/10.1086/648217">megamonsoon</a>”.</p>
<p>Later in the <a href="https://theconversation.com/triassic-mass-extinction-may-give-clues-on-how-oceans-will-be-affected-by-climate-change-39655">Triassic</a>, on the approach to yet another <a href="https://www.britannica.com/science/end-Triassic-extinction">mass extinction event</a>, most land vertebrates, including early mammals and early dinosaurs, exhibited <a href="https://onlinelibrary.wiley.com/doi/full/10.1111/pala.12514">high diversity</a> at mid-latitudes, both north and south of the equator. This pattern is similar to that recorded for land vertebrates <a href="https://royalsocietypublishing.org/doi/10.1098/rspb.2017.0231">during the Permian period</a>, just before the mass extinction. </p>
<p>One exception were the <a href="https://www.britannica.com/animal/crurotarsan-reptile">pseudosuchians</a> – the group that consists of <a href="https://www.nature.com/articles/ncomms9438/">crocodilians</a> and their fossil relatives. Interestingly, while the latitudinal biodiversity of other species shifted over the subsequent 200 million years, arriving at the equator in the present day, pseudosuchian biodiversity has remained highest at low latitudes throughout their <a href="https://www.nature.com/articles/ncomms9438">entire evolutionary history</a>. </p>
<p>This is likely due to their physiology, specifically their tolerance of high temperatures. Reptiles are <a href="https://www.thoughtco.com/ectothermic-definition-2291709">ectotherms</a>, or “cold-blooded” organisms, that rely on their external environment to regulate their internal body temperature. Today, crocodiles and other reptiles are restricted to areas of the world with warmer, more stable temperatures, and the same would have been true of their fossil relatives.</p>
<h2>Prehistory repeats?</h2>
<p>These insights into past mass extinction events are critical for understanding how Earth’s current patchwork of biodiverse regions could change. As global temperatures <a href="https://timescavengers.blog/climate-change/co2-past-present-future/">continue to rise</a>, some studies have predicted that species will disperse towards the poles from equatorial regions – but if the pace of change is too rapid, they <a href="https://royalsocietypublishing.org/doi/full/10.1098/rspb.2014.1995">risk going extinct</a>. </p>
<p>Others suggest that global warming might lead to the climate becoming more similar across different latitudes, potentially producing a peak in biodiversity at mid-latitudes. There’s already evidence that marine latitudinal biodiversity has become <a href="https://www.pnas.org/content/118/15/e2015094118.short?casa_token=FCeWYmuriVQAAAAA:dKaWWdlx60uK189AdfRdgeLQafwlAZzvsuhm8bzLQpj6nvoJpKAzH8N38rxwLRvtxlV_g0xqLTT9Fw">increasingly bimodal</a> over the last 50 years. </p>
<p>With a possible “<a href="https://www.nhm.ac.uk/discover/what-is-mass-extinction-and-are-we-facing-a-sixth-one.html">sixth mass extinction</a>” looming, or even already <a href="https://theconversation.com/earths-sixth-mass-extinction-has-begun-new-study-confirms-43432">taking hold</a>, a <a href="https://science.sciencemag.org/content/355/6325/eaah4787">long-term perspective</a> will be critical for understanding how to sustain Earth’s biodiversity into the future.</p><img src="https://counter.theconversation.com/content/163309/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Emma Dunne receives funding from The Leverhulme Trust. </span></em></p><p class="fine-print"><em><span>Bethany Allen has received funding from the UK Natural Environment Research Council (NERC).</span></em></p>Today, Earth’s biodiversity is highest at the equator – but it hasn’t always been this way.Emma Dunne, Postdoctoral Researcher, School of Geography, Earth and Environmental Sciences, University of BirminghamBethany Allen, PhD Student, School of Earth and Environment, University of LeedsLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1435252021-03-30T17:04:10Z2021-03-30T17:04:10ZHuge volcanic eruption didn’t cause climate change and mass extinction 140 million years ago<figure><img src="https://images.theconversation.com/files/392298/original/file-20210329-19-1skvk5f.jpg?ixlib=rb-1.1.0&rect=35%2C0%2C5955%2C3979&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Paraná basin in Brazil provides evidence that one of the world's largest super-eruptions did not cause a mass extinction.</span> <span class="attribution"><span class="source">(Shutterstock)</span></span></figcaption></figure><p>Mass extinctions are times in Earth’s past when large proportions of life suddenly and catastrophically died. These have occurred periodically over <a href="https://doi.org/10.1146/annurev.earth.33.092203.122654">the past 550 million years</a>. The exact causes of these extinctions are not fully understood, but there appears to be a remarkable coincidence <a href="http://doi.org/10.1130/2014.2505(02)">between mass extinctions and huge volcanic eruptions that form large igneous provinces (LIPs)</a>. </p>
<p>LIPs are <a href="https://doi.org/10.1029/93RG02508">massive volcanoes that produce millions of cubic kilometres of basaltic magma</a> in a <a href="https://doi.org/10.1016/j.epsl.2012.01.015">very short time</a>. They are much bigger in scale than the famous super eruptions — <a href="https://www.usgs.gov/faqs/how-do-giant-eruptions-yellowstone-national-park-region-compare-other-large-historic-eruptions">like the Yellowstone caldera supervolcano</a> — which typically release less than 5,000 cubic kilometres of magma.</p>
<p>The magma from LIPs can release enough gases during eruption, such as carbon dioxide (a greenhouse gas) or sulphur-based compounds, <a href="http://elementsmagazine.org/2019/10/02/deep-carbon-life-cycle-large-igneous-provinces/">to change the climate</a>. This climate change in turn affects the composition of the oceans and quickly leads to <a href="https://doi.org/10.1016/j.epsl.2020.116174">the death of life on Earth</a>. </p>
<p>While huge volcanic eruptions have been linked to mass extinctions on Earth, our research shows that one of the world’s largest known LIPs may have had no effect on climate or caused any extinctions. Before our study, the precise age of the LIP was not really known; with our improved dataset and higher precision analysis, we were able to show that these things did not occur at the same time.</p>
<h2>Not just eruptions</h2>
<p>Research has also suggested that basalt from LIPs, which intrude into the crust, <a href="https://doi.org/10.1016/j.epsl.2008.11.015">can heat up and change — metamorphose — sedimentary rocks that are rich in volatiles</a>, compounds that vaporize readily. This metamorphism can release huge amounts of gases <a href="https://doi.org/10.1130/G25325A.1">such as methane and sulphur dioxide from the sediments</a>, which <a href="https://doi.org/10.1073/pnas.2000095117">also change the climate — leading to mass extinctions</a>.</p>
<p>Both of these mechanisms have been blamed for causing the climate change which resulted in mass extinctions. However, there are also cases of <a href="https://doi.org/10.1130/2014.2505(02)">LIPs that don’t seem to cause mass extinctions and also extinctions that have no apparent LIP</a>. The relationship between these huge LIP volcanic eruptions and mass extinctions may not be as clear as previously thought. Disentangling the exact mechanisms involved has been the focus of <a href="https://doi.org/10.1016/j.palaeo.2016.11.005">numerous</a> <a href="https://doi.org/10.1073/pnas.1709070114">scientific</a> <a href="https://doi.org/10.1016/j.palaeo.2017.03.014">studies</a>.</p>
<p>One extremely important factor to consider is the exact age of the LIP relative to the mass extinction. If the ages of the climate change, associated mass extinction and the LIP do not overlap, then the volcanism is not the cause.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/392329/original/file-20210329-21-1k7uj99.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An artist's rendition of a post-volcanic eruption landscape" src="https://images.theconversation.com/files/392329/original/file-20210329-21-1k7uj99.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/392329/original/file-20210329-21-1k7uj99.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/392329/original/file-20210329-21-1k7uj99.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/392329/original/file-20210329-21-1k7uj99.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/392329/original/file-20210329-21-1k7uj99.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/392329/original/file-20210329-21-1k7uj99.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/392329/original/file-20210329-21-1k7uj99.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"></a>
<figcaption>
<span class="caption">An artist’s rendition of a post-volcanic eruption landscape.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<h2>Brazilian eruption</h2>
<p>To investigate whether one of the world’s largest LIPs caused massive climate change and a mass extinction, our research team generated <a href="https://doi.org/10.1130/G47766.1">highly precise ages for the Paraná-Etendeka LIP in Brazil</a>. We dated the mineral zircon that crystallized within the erupted lava flows using the U-Pb system allowing us to precisely determine the eruption age of the lavas. <a href="https://doi.org/10.1038/ncomms15596">This technique produces precise and accurate ages for LIPs</a>. </p>
<p>Numerous studies had linked this LIP to <a href="https://sp.lyellcollection.org/content/463/1/17?etoc=">a mass extinction event found in the oceans</a>. The first thing we wanted to know was when did this LIP erupt, and for how long. Once we had this information, we could determine if it occurred at exactly the same time as the mass extinction event.</p>
<p>Our study focused on the Paraná Magmatic Province — the South American portion of the LIP in Brazil — which is by far the largest, and produced approximately one million cubic kilometres of magma.</p>
<p>When this LIP erupted, 140 million years ago, South America and Africa were connected and <a href="https://www.sciencedirect.com/science/article/pii/S0040195118303160">were part of the Gondwana supercontinent</a>. This LIP erupted in Brazil and Namibia, when both of these areas were neighbours <a href="https://doi.org/10.1016/j.marpetgeo.2013.10.015">before the opening of the Southern Atlantic Ocean</a>.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-the-earths-last-supercontinent-broke-apart-to-form-the-world-we-have-today-131632">How the Earth's last supercontinent broke apart to form the world we have today</a>
</strong>
</em>
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<p>Many studies have suggested that this LIP caused global climate change which led to a small mass extinction and also a reduction in the oxygen concentration in the oceans. This period is called <a href="https://doi.org/10.1016/j.gloplacha.2015.06.001">the Valanginian event</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/373135/original/file-20201204-19-jkshs9.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A cliff and waterfall surrounded by trees" src="https://images.theconversation.com/files/373135/original/file-20201204-19-jkshs9.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/373135/original/file-20201204-19-jkshs9.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/373135/original/file-20201204-19-jkshs9.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/373135/original/file-20201204-19-jkshs9.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/373135/original/file-20201204-19-jkshs9.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/373135/original/file-20201204-19-jkshs9.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/373135/original/file-20201204-19-jkshs9.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">Volcanic rocks (dacites overlying basalts) from the Paraná LIP related to the opening of the South Atlantic Ocean at Caracol State Park, in Rio Grande do Sul, Brazil.</span>
<span class="attribution"><span class="source">(Ana Carolina Lucchetti)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>No environmental effects</h2>
<p>Our research shows that that the Paraná LIP erupted extremely quickly, around one million years after the mass extinction and so it is unlikely to have been the cause. There is one older part of the Paraná LIP that we did not work on which could have caused the Valanginian event. But most LIPs erupt over a <a href="https://doi.org/10.1038/s41467-017-00083-9">very short period of time</a>, so it is unlikely that the older portion is more than one million years older than the rest of the province. </p>
<p>We also did not work on the <a href="https://doi.org/10.1007/s004450000115">Etendeka part of the province in Namibia</a>. However this part of the province is extremely small in comparison to the South American part, and we expect that it erupted coincidentally with the Paraná, <a href="https://doi.org/10.1016/j.epsl.2015.01.009">although it may have continued to erupt for longer</a> (and therefore may be younger). </p>
<p>Our study of the Paraná LIP proves that the eruption of huge volumes of LIP magma alone may not be enough to cause mass extinctions. The question that remains is why this huge eruption of magma had almost no effect on the climate; our theory is that the lack of volatile-rich sediments around the Paraná LIP meant that no extra volatiles were released due to metamorphism during the positioning, or emplacement, of the LIP. Perhaps the metamorphism of sediments by LIP magmas, and the gas released associated with this, is the main driver of climate change leading to mass extinctions? </p>
<p>Earth’s largest mass extinction event occurred at the <a href="https://doi.org/10.1073/pnas.1317692111">end of the Permian period</a>, <a href="http://doi.org/10.1126/sciadv.1500470">coinciding with the eruption of the Siberian Traps LIP</a>. This LIP intruded large volatile rich sedimentary basins which likely caused <a href="https://doi.org/10.1016/j.palaeo.2017.01.045">the release of massive amounts of volatile compounds</a>. </p>
<p>Our findings for the Paraná LIP also depend on the <a href="https://doi.org/10.1016/j.gloplacha.2015.06.001">age of the Valanginian event</a>. Currently, the age estimation for this event is based on cyclic analysis of ocean sediments, but it is possible that with greater precision, we may find it overlaps with the Paraná LIP. While huge volcanic eruptions have been linked to mass extinctions on Earth, our research shows that one of the world’s largest known LIPs may have had no effect on climate or caused any extinctions. But for now, it seems that the Paraná LIP had almost no environmental effect on our planet.</p><img src="https://counter.theconversation.com/content/143525/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Joshua Davies receives funding from the NSERC discovery program, as well as the Canadian Foundation for Innovation (CFI). </span></em></p><p class="fine-print"><em><span>Brenda C. Rocha received funding from São Paulo Research Foundation (FAPESP) and CAPES Foundation</span></em></p><p class="fine-print"><em><span>Nicolas D. Greber receives funding from Swiss National Science Foundation. </span></em></p>Huge volcanic eruptions were once believed to be the cause of mass extinctions on Earth. However, new research has found that super eruptions did not necessarily result in mass extinctions.Joshua Davies, Professor, Sciences de la Terre et de l'atmosphère, Université du Québec à Montréal (UQAM)Brenda Chung Rocha, Professor, Geosciences, Universidade de São Paulo (USP)Nicolas Greber, Assistant professor, Geochemistry, University of BernLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1562322021-03-02T14:27:24Z2021-03-02T14:27:24ZScientists have found dust from the asteroid that wiped out the dinosaurs inside the crater it left<figure><img src="https://images.theconversation.com/files/387199/original/file-20210302-15-1mk088s.jpg?ixlib=rb-1.1.0&rect=366%2C146%2C6109%2C4589&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A large impact.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/meteor-glowing-enters-earths-atmosphere-elements-297359225">Shutterstock/Vadim Sadovski</a></span></figcaption></figure><p>More than 99% of all organisms that have ever lived on Earth are now extinct. Most of these just died out quietly. However, in Earth’s history there have been five major <a href="https://theconversation.com/five-mass-extinctions-and-what-we-can-learn-from-them-about-the-planet-today-79971">mass extinction</a> events – known as <a href="http://science.sciencemag.org/content/215/4539/1501.abstract">the big five</a> – during which many species became extinct at the same time.</p>
<p>Each of the big five events caused at least a 40% loss of all species on Earth. Yet humans hold a particular grudge against the most recent one, which brought a sudden end to the 160-million-year history of the dinosaurs. This was the Cretaceous-Paleogene extinction and it happened 66 million years ago, wiping out about 75% of all species on Earth at the time. Except sea turtles and crocodiles, no four-legged animals bigger than 25kg survived.</p>
<p>After decades of heated debate, scientists have settled on two leading theories about what caused this extinction. The first possibility is the <a href="https://theconversation.com/dinosaur-killing-asteroid-struck-at-worst-angle-to-cause-maximum-damage-new-research-139394">impact of an asteroid</a> which created the 180km wide Chicxulub impact crater in the modern day Yucatán Peninsula in Mexico. Second, a series of eruptions in a volcanic area known as <a href="https://theconversation.com/more-bad-news-for-dinosaurs-chicxulub-meteorite-impact-triggered-global-volcanic-eruptions-on-the-ocean-floor-91053">Deccan Traps</a> in India.</p>
<p>Last week, an international team of scientists with data from four independent laboratories <a href="https://advances.sciencemag.org/content/7/9/eabe3647">published a study</a> claiming to have ended the debate. They say the 12km-wide asteroid was the one to blame.</p>
<h2>A case closed?</h2>
<p>The study looked at rock samples collected in the crater, which is now under water. They found a layer of terrestrial mud mixed with “space dust” containing the element iridium, which can be found in high concentrations in meteorites but is rare in the Earth’s crust. This layer was four times thicker in the impact crater than in the surrounding area. </p>
<p>The team found a 5cm layer of sediment immediately below the limestone from the earliest Paleogene, the geologic period that began immediately after the extinction. This thin layer of sediment had iridium concentrations of one part per billion, compared to the 0.04 parts per billion in the Earth’s crust. </p>
<figure class="align-center ">
<img alt="A map showing where the Chicxulub crater is, in the Yucatán Peninsula." src="https://images.theconversation.com/files/387187/original/file-20210302-13-1em1hdm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/387187/original/file-20210302-13-1em1hdm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=560&fit=crop&dpr=1 600w, https://images.theconversation.com/files/387187/original/file-20210302-13-1em1hdm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=560&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/387187/original/file-20210302-13-1em1hdm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=560&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/387187/original/file-20210302-13-1em1hdm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=703&fit=crop&dpr=1 754w, https://images.theconversation.com/files/387187/original/file-20210302-13-1em1hdm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=703&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/387187/original/file-20210302-13-1em1hdm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=703&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The impact crater.</span>
<span class="attribution"><a class="source" href="https://www.eurekalert.org/multimedia/pub/257216.php?from=493921">The University of Texas at Austin/Jackson School of Geosciences/ Google Maps</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The asteroid is thought to have hit the planet at about 20km per second, more than 50 times faster than the speed of sound in air. Not only did it destroy the immediate surroundings, but it also sent a cloud of vaporised rock and microscopic dust with high levels of iridium that travelled across the Earth. The global blanket of cloud blocked out sunlight, cooled Earth’s surface for decades by up to 10°C, and triggered a global “impact winter”. The cold and dark regime was followed by large-scale photosynthesis shutdown, disrupted food webs worldwide and the collapse of ecosystems.</p>
<p>Spikes of iridium in dust from this time have been found in <a href="http://science.sciencemag.org/content/327/5970/1214.abstract">over 100 places</a> around the world from America, Asia, Europe, Oceania, all the way to Antarctica. These were first identified in <a href="http://science.sciencemag.org/content/208/4448/1095.abstract">findings from the 1980s</a>. </p>
<p>The early studies did not win a global consensus because the evidence couldn’t link the high iridium concentrations to the Chicxulub crater. But this new study provides this crucial link, and places an important time constraint too. The dust must have deposited within just a few decades – less than 20 years – after the impact. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/five-mass-extinctions-and-what-we-can-learn-from-them-about-the-planet-today-79971">Five mass extinctions – and what we can learn from them about the planet today</a>
</strong>
</em>
</p>
<hr>
<h2>The Armageddon of dinosaurs</h2>
<p>Although the sudden nature of this extinction is backed up by changes in the fossil record, the record of microscopic organisms points towards a long-term shift instead. This is the argument in favour of a volcanic extinction, with a series of eruptions happening over tens of thousands of years.</p>
<p>Massive and prolonged volcanic eruptions have been linked to other volcanism-extinction events – like the Siberian Traps eruptions, which marked the extinction at the <a href="https://doi.org/10.1038/s41467-017-00083-9">end of the Permian</a> period. In the case of the dinosaur extinction event, however, it could not have been caused by volcanism alone. </p>
<figure class="align-center ">
<img alt="A drawing of a T-rex looking at a small flying dinosaur in a forest." src="https://images.theconversation.com/files/387186/original/file-20210302-17-69grd3.jpg?ixlib=rb-1.1.0&rect=40%2C54%2C1816%2C1195&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/387186/original/file-20210302-17-69grd3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/387186/original/file-20210302-17-69grd3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/387186/original/file-20210302-17-69grd3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/387186/original/file-20210302-17-69grd3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=500&fit=crop&dpr=1 754w, https://images.theconversation.com/files/387186/original/file-20210302-17-69grd3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=500&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/387186/original/file-20210302-17-69grd3.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">All non-avian dinosaurs were wiped out 66 million years ago.</span>
<span class="attribution"><a class="source" href="https://media.eurekalert.org/multimedia_prod/pub/media/257217.jpg">Willgard Krause/ Pixabay</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The Deccan Traps released more than ten million cubic kilometres of material and gases, which caused a long term global warming of between 2 and 4°C, <a href="https://pubs.geoscienceworld.org/gsa/geology/article/46/2/147/525172/A-new-high-resolution-chronology-for-the-late">150 to 300 thousand years before the extinction</a>, just before the asteroid blow. </p>
<p>The Deccan Traps eruption lasted several million years, starting long before the asteroid impact. In fact, the main phase of Deccan Traps volcanism, at around 66 million years ago, might have been <a href="http://science.sciencemag.org/content/350/6256/76.abstract">triggered by the Chicxulub</a> impact. </p>
<p>The increase of nutrients into the oceans led to <a href="https://doi.org/10.1016/j.lithos.2004.09.016">planktonic blooms and low oxygen level in the oceans</a>, yet the oceans were not completely oxygen free. Deccan volcanism might have induced biotic stress but not the organisms’ total demise. </p>
<p>Dinosaurs might have their doomsday set in an unfortunate double trouble of an asteroid volcano combo, or a single giant impact. Either way, the large asteroid has played a key role. This new study has found the missing piece of evidence that links the dinosaurs’ extinction to the Chicxulub impact, and that it happened in a geological blink of an eye.</p><img src="https://counter.theconversation.com/content/156232/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Queenie Hoi Shan Chan does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>A new study found iridium, an element found in asteroids, in the rocks of the Chicxulub impact crater.Queenie Hoi Shan Chan, Lecturer in Earth Sciences, Royal Holloway University of LondonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1530912021-01-13T05:00:06Z2021-01-13T05:00:06ZWorried about Earth’s future? Well, the outlook is worse than even scientists can grasp<figure><img src="https://images.theconversation.com/files/378461/original/file-20210113-21-rwemte.jpg?ixlib=rb-1.1.0&rect=0%2C8%2C5568%2C3692&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Daniel Mariuz/AAP</span></span></figcaption></figure><p>Anyone with even a passing interest in the global environment knows all is not well. But just how bad is the situation? Our new paper shows the outlook for life on Earth is more dire than is generally understood. </p>
<p>The research <a href="https://www.frontiersin.org/articles/10.3389/fcosc.2020.615419/full">published today</a> reviews more than 150 studies to produce a stark summary of the state of the natural world. We outline the likely future trends in biodiversity decline, mass extinction, climate disruption and planetary toxification. We clarify the gravity of the human predicament and provide a timely snapshot of the crises that must be addressed now. </p>
<p>The problems, all tied to human consumption and population growth, will almost certainly worsen over coming decades. The damage will be felt for centuries and threatens the survival of all species, including our own.</p>
<p>Our paper was authored by 17 leading scientists, including those from Flinders University, Stanford University and the University of California, Los Angeles. Our message might not be popular, and indeed is frightening. But scientists must be candid and accurate if humanity is to understand the enormity of the challenges we face.</p>
<figure class="align-center ">
<img alt="Girl in breathing mask attached ot plant in container" src="https://images.theconversation.com/files/378462/original/file-20210113-21-1vk2ung.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/378462/original/file-20210113-21-1vk2ung.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/378462/original/file-20210113-21-1vk2ung.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/378462/original/file-20210113-21-1vk2ung.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/378462/original/file-20210113-21-1vk2ung.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/378462/original/file-20210113-21-1vk2ung.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/378462/original/file-20210113-21-1vk2ung.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">Humanity must come to terms with the future we and future generations face.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>Getting to grips with the problem</h2>
<p>First, we reviewed the extent to which experts grasp the scale of the threats to the biosphere and its lifeforms, including humanity. Alarmingly, the research shows future environmental conditions will be far more dangerous than experts currently believe.</p>
<p>This is largely because academics tend to specialise in <a href="https://www.tandfonline.com/doi/abs/10.1080/15487733.2007.11907989">one discipline</a>, which means they’re in many cases unfamiliar with the <a href="https://www.dymocks.com.au/book/fragile-dominion-by-simon-levin-and-simon-a-levin-9780738203195">complex system</a> in which planetary-scale problems — and their potential solutions — exist. </p>
<p>What’s more, positive change can be impeded by governments <a href="https://www.embopress.org/doi/full/10.15252/embr.201643381">rejecting</a> or ignoring scientific advice, and <a href="https://www.nature.com/articles/s41562-020-0884-z">ignorance of human behaviour</a> by both technical experts and policymakers.</p>
<p>More broadly, the human <a href="https://www.nature.com/articles/s41562-020-0884-z">optimism bias</a> – thinking bad things are more likely to befall others than yourself – means many people underestimate the environmental crisis. </p>
<h2>Numbers don’t lie</h2>
<p>Our research also reviewed the current state of the global environment. While the problems are too numerous to cover in full here, they include:</p>
<ul>
<li><p>a <a href="https://www.nature.com/articles/nature25138">halving</a> of vegetation biomass since the agricultural revolution around 11,000 years ago. Overall, humans have altered almost <a href="https://ipbes.net/global-assessment">two-thirds</a> of Earth’s land surface</p></li>
<li><p>about <a href="https://science.sciencemag.org/content/366/6471/eaax3100">1,300 documented</a> <a href="https://www.nature.com/articles/s41559-019-0906-2">species extinctions</a> over the past 500 years, with many more unrecorded. More broadly, population sizes of animal species have declined by more than <a href="https://www.worldwildlife.org/publications/living-planet-report-2020">two-thirds</a> over the last 50 years, suggesting more extinctions are imminent</p></li>
</ul>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/what-is-a-mass-extinction-and-are-we-in-one-now-122535">What is a 'mass extinction' and are we in one now?</a>
</strong>
</em>
</p>
<hr>
<ul>
<li><p>about <a href="https://www.un.org/sustainabledevelopment/blog/2019/05/nature-decline-unprecedented-report/">one million</a> plant and animal species globally threatened with extinction. The combined mass of wild mammals today is less than <a href="https://www.pnas.org/content/115/25/6506">one-quarter</a> the mass before humans started colonising the planet. Insects are also <a href="https://www.annualreviews.org/doi/abs/10.1146/annurev-ento-011019-025151">disappearing rapidly</a> in many regions</p></li>
<li><p>85% of the global wetland area <a href="https://www.publish.csiro.au/mf/mf14173">lost</a> in 300 years, and more than 65% of the oceans <a href="https://www.nature.com/articles/ncomms8615">compromised</a> to some extent by humans</p></li>
<li><p>a halving of live coral cover on reefs in less than <a href="https://www.nature.com/articles/nclimate1674">200 years</a> and a decrease in seagrass extent by <a href="https://science.sciencemag.org/content/366/6471/eaax3100">10% per decade</a> over the last century. <a href="https://www.pnas.org/content/113/48/13785">About 40%</a> of kelp forests have declined in abundance, and the number of large predatory fishes is <a href="https://onlinelibrary.wiley.com/doi/full/10.1046/j.1467-2979.2003.00103.x">fewer than 30%</a> of that a century ago.</p></li>
</ul>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/378178/original/file-20210112-15-1ornvrk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="State of the Earth's environment" src="https://images.theconversation.com/files/378178/original/file-20210112-15-1ornvrk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/378178/original/file-20210112-15-1ornvrk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=521&fit=crop&dpr=1 600w, https://images.theconversation.com/files/378178/original/file-20210112-15-1ornvrk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=521&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/378178/original/file-20210112-15-1ornvrk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=521&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/378178/original/file-20210112-15-1ornvrk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=654&fit=crop&dpr=1 754w, https://images.theconversation.com/files/378178/original/file-20210112-15-1ornvrk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=654&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/378178/original/file-20210112-15-1ornvrk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=654&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Major environmental-change categories expressed as a percentage relative to intact baseline. Red indicates percentage of category damaged, lost or otherwise affected; blue indicates percentage intact, remaining or unaffected.</span>
<span class="attribution"><span class="source">Frontiers in Conservation Science</span></span>
</figcaption>
</figure>
<h2>A bad situation only getting worse</h2>
<p>The human population has reached <a href="https://www.prb.org/2020-world-population-data-sheet/">7.8 billion</a> – double what it was in 1970 – and is set to reach about 10 billion by 2050. More people equals more food insecurity, soil degradation, plastic pollution and biodiversity loss. </p>
<p>High population densities make pandemics more likely. They also drive overcrowding, unemployment, housing shortages and deteriorating infrastructure, and can spark conflicts leading to <a href="https://theconversation.com/by-inciting-capitol-mob-trump-pushes-u-s-closer-to-a-banana-republic-152850">insurrections</a>, terrorism, and war.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/climate-explained-why-we-need-to-focus-on-increased-consumption-as-much-as-population-growth-138602">Climate explained: why we need to focus on increased consumption as much as population growth</a>
</strong>
</em>
</p>
<hr>
<p>Essentially, humans have created an ecological <a href="https://www.investopedia.com/terms/p/ponzischeme.asp">Ponzi scheme</a>. Consumption, as a percentage of Earth’s <a href="https://www.footprintnetwork.org">capacity to regenerate itself</a>, has grown from 73% in 1960 to <a href="https://www.mdpi.com/2079-9276/7/3/58">more than 170% today</a>. </p>
<p>High-consuming countries like Australia, Canada and the US use multiple units of fossil-fuel energy to produce one energy unit of food. Energy consumption will therefore increase in the near future, especially as the global middle class grows.</p>
<p>Then there’s climate change. Humanity has already exceeded global warming of 1°C this century, and will almost assuredly <a href="https://www.ipcc.ch/sr15/chapter/spm/">exceed 1.5 °C</a> between 2030 and 2052. Even if all nations party to the <a href="https://unfccc.int/process-and-meetings/the-paris-agreement/the-paris-agreement">Paris Agreement</a> ratify their commitments, warming would still reach between 2.6°C and 3.1°C by 2100.</p>
<figure class="align-center ">
<img alt="people walking on a crowded street" src="https://images.theconversation.com/files/364900/original/file-20201022-18-iwc4eu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/364900/original/file-20201022-18-iwc4eu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/364900/original/file-20201022-18-iwc4eu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/364900/original/file-20201022-18-iwc4eu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/364900/original/file-20201022-18-iwc4eu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/364900/original/file-20201022-18-iwc4eu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/364900/original/file-20201022-18-iwc4eu.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 human population is set to reach 10 billion by 2050.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>The danger of political impotence</h2>
<p>Our paper found global policymaking falls far short of addressing these existential threats. Securing Earth’s future requires prudent, long-term decisions. However this is impeded by short-term interests, and an economic system that <a href="https://theconversation.com/piketty-challenges-us-to-consider-if-we-need-to-rein-in-wealth-inequality-67552">concentrates wealth among a few individuals</a>.</p>
<p>Right-wing populist leaders with <a href="https://www.nature.com/articles/d41586-018-07236-w">anti-environment agendas</a> are on the rise, and in many countries, environmental protest groups have been labelled “<a href="https://theconversation.com/extinction-rebellion-terror-threat-is-a-wake-up-call-for-how-the-state-treats-environmental-activism-129804">terrorists</a>”. Environmentalism has become weaponised as a political ideology, rather than properly viewed as a universal mode of self-preservation.</p>
<p>Financed <a href="https://theconversation.com/a-brief-history-of-fossil-fuelled-climate-denial-61273">disinformation campaigns</a>, such as those against climate action and <a href="http://alert-conservation.org/issues-research-highlights/2014/11/27/progress-in-the-battle-against-illegal-logging">forest protection</a>, protect short-term profits and claim meaningful environmental action is too costly – while ignoring the broader cost of not acting. By and large, it appears unlikely business investments <a href="https://www.un.org/press/en/2019/ecosoc6972.doc.htm">will shift at sufficient scale</a> to avoid environmental catastrophe.</p>
<h2>Changing course</h2>
<p>Fundamental change is required to avoid this ghastly future. Specifically, we and many others suggest: </p>
<ul>
<li><p><a href="https://theconversation.com/life-in-a-degrowth-economy-and-why-you-might-actually-enjoy-it-32224">abolishing</a> the goal of perpetual economic growth</p></li>
<li><p>revealing the true cost of products and activities by forcing those who damage the environment to pay for its restoration, such as through <a href="https://theconversation.com/carbon-pricing-works-the-largest-ever-study-puts-it-beyond-doubt-142034">carbon pricing</a></p></li>
<li><p>rapidly eliminating fossil fuels</p></li>
<li><p>regulating markets by curtailing monopolisation and limiting undue corporate influence on policy</p></li>
<li><p>reigning in corporate lobbying of political representatives</p></li>
<li><p>educating and <a href="https://www.ted.com/talks/katharine_wilkinson_how_empowering_women_and_girls_can_help_stop_global_warming">empowering women</a> across the globe, including giving them control over family planning.</p></li>
</ul>
<figure class="align-center ">
<img alt="A coal plant" src="https://images.theconversation.com/files/378465/original/file-20210113-15-6b1vqv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/378465/original/file-20210113-15-6b1vqv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/378465/original/file-20210113-15-6b1vqv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/378465/original/file-20210113-15-6b1vqv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/378465/original/file-20210113-15-6b1vqv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/378465/original/file-20210113-15-6b1vqv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/378465/original/file-20210113-15-6b1vqv.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 true cost of environmental damage should be borne by those responsible.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>Don’t look away</h2>
<p>Many organisations and individuals are devoted to achieving these aims. However their messages have not sufficiently penetrated the policy, economic, political and academic realms to make much difference.</p>
<p>Failing to acknowledge the magnitude of problems facing humanity is not just naïve, it’s dangerous. And science has a big role to play here. </p>
<p>Scientists must not sugarcoat the overwhelming challenges ahead. Instead, they should <em>tell it like it is</em>. Anything else is at best misleading, and at worst potentially lethal for the human enterprise.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/mass-extinctions-and-climate-change-why-the-speed-of-rising-greenhouse-gases-matters-56675">Mass extinctions and climate change: why the speed of rising greenhouse gases matters</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/153091/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Corey J. A. Bradshaw receives funding from the Australian Research Council. The Rockefeller Foundation provided funding for elements of this research via a Bellagio Writer's Fellowship to CJAB and PRE.</span></em></p><p class="fine-print"><em><span>Daniel T. Blumstein receives funding from the US National Science Foundation and the Australian Research Council.</span></em></p><p class="fine-print"><em><span>Paul Ehrlich 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>Humanity is destroying Earth’s ability to support complex life. But coming to grips with the magnitude of the problem is hard, even for experts.Corey J. A. Bradshaw, Matthew Flinders Professor of Global Ecology and Models Theme Leader for the ARC Centre of Excellence for Australian Biodiversity and Heritage, Flinders UniversityDaniel T. Blumstein, Professor in the Department of Ecology and Evolutionary Biology and the Institute of the Environment and Sustainability, University of California, Los AngelesPaul Ehrlich, President, Center for Conservation Biology, Bing Professor of Population Studies, Stanford UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1486232020-11-26T19:01:45Z2020-11-26T19:01:45ZCurious Kids: could dinosaurs evolve back into existence?<figure><img src="https://images.theconversation.com/files/371456/original/file-20201126-17-hqh45o.jpg?ixlib=rb-1.1.0&rect=336%2C176%2C5271%2C3354&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><blockquote>
<p><strong>Will there ever be dinosaurs again? — Anonymous</strong></p>
</blockquote>
<p><a href="https://theconversation.com/au/topics/curious-kids-36782"><img src="https://images.theconversation.com/files/291898/original/file-20190911-190031-enlxbk.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=90&fit=crop&dpr=1" width="100%"></a></p>
<p>What an interesting question! Well, technically dinosaurs are still here in the <a href="https://www.science20.com/news_articles/evolving_by_shrinking_how_dinosaurs_became_birds-135809">form of birds</a>. Just like you’re a direct descendant of your grandparents, birds are the only remaining direct descendants of dinosaurs.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/371439/original/file-20201126-29-by0jzz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="_3D T. rex rendering_" src="https://images.theconversation.com/files/371439/original/file-20201126-29-by0jzz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/371439/original/file-20201126-29-by0jzz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/371439/original/file-20201126-29-by0jzz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/371439/original/file-20201126-29-by0jzz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/371439/original/file-20201126-29-by0jzz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/371439/original/file-20201126-29-by0jzz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/371439/original/file-20201126-29-by0jzz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1131&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"><em>Tyrannosaurus rex</em> belonged to a dinosaur group called theropods.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>But I suppose what you’re really asking is whether dinosaurs like <em>Tyrannosaurus</em> or <em>Triceratops</em> could ever exist again. Although that would be fascinating, the answer is almost definitely no. </p>
<p>While there’s only one generation between you and your grandparents – that is, your parents – there are many millions of generations between today’s birds and their ancient dinosaurs ancestors.</p>
<p>This is why today’s birds look, sound and behave so differently to the prehistoric beasts that once roamed Earth.</p>
<h2>Animals evolve to change, but can’t choose how</h2>
<p>To understand this, we have to understand “evolution”. This is a process that explains how every living thing (<a href="https://www.nationalgeographic.com/magazine/2017/04/evolution-genetics-medicine-brain-technology-cyborg/">including humans</a>) <em>evolved</em> from past living things over millions, or even billions, of years. </p>
<p>Different animals evolve their own differences to help them survive in the world. For example, 66 million years ago, birds survived the <a href="https://www.nationalgeographic.com/science/prehistoric-world/dinosaur-extinction/">catastrophic event</a> that killed all other dinosaurs and marked the end of the Mesozoic era.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/371443/original/file-20201126-21-18xjx4p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="3D rendering of _T. rex_ facing off against a _Triceratops_ herd." src="https://images.theconversation.com/files/371443/original/file-20201126-21-18xjx4p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/371443/original/file-20201126-21-18xjx4p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=424&fit=crop&dpr=1 600w, https://images.theconversation.com/files/371443/original/file-20201126-21-18xjx4p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=424&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/371443/original/file-20201126-21-18xjx4p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=424&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/371443/original/file-20201126-21-18xjx4p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=532&fit=crop&dpr=1 754w, https://images.theconversation.com/files/371443/original/file-20201126-21-18xjx4p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=532&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/371443/original/file-20201126-21-18xjx4p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=532&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Fossils suggest face-offs between <em>T. rex</em> and <em>Triceratops</em> were common.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>After this, a blanket of ash wrapped around the world, cooling it and blocking out the sunlight plants need to survive. Plant-eating animals would have struggled to stay alive.</p>
<p>But birds did, perhaps because they were small even then. They likely ate seeds and insects and took shelter in small spaces. And being able to fly would have helped them explore far and wide for food and shelter. </p>
<p>That said, if the conditions that came after the dinosaur extinction event returned today, no modern animal would evolve back into a dinosaur. This is because animals today have a very different evolutionary past to dinosaurs. </p>
<p>They evolved to have features that help them survive in <em>today’s</em> world, rather than a prehistoric one. And these features limit the ways they can evolve in the future.</p>
<h2>Which came first, the chicken or the dinosaur?</h2>
<p>For an animal to be an actual “dinosaur”, it must belong to a group of animals known by scientists as Dinosauria. These all descended from a common ancestor shared by <em>Triceratops</em> and modern birds.</p>
<p>Other than birds, Dinosauria doesn’t include <em>any</em> living creature. So for a dinosaur to re-evolve in the future, it would have to come from a bird.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/XAzGC89n0S4?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">This animation helps paint a picture of how dinosaurs eventually evolved to become birds. (American Museum of Natural History/Youtube)</span></figcaption>
</figure>
<p>Dinosauria’s extinct members included sauropods, stegosaurs, ankylosaurs, ornithopods, ceratopsians and non-bird theropods. Modern birds evolved from a small group of theropods. However, since so much time has passed, this link is limited. </p>
<p>Specifically, birds have a very different collection of “genes”. These are the same built-in “rules” your parents passed down to you that decide, for example, what colour your eyes will be. </p>
<p>The more generations that pass between an ancestor and their descendant, the more different their genes will be.</p>
<h2>Even if it could happen, what would this take?</h2>
<p>Think of how much a bird would need to change to look like <em>Tyrannosaurus rex</em> or <em>Triceratops</em>. A lot.</p>
<p>Dinosaurs had long tails with bones all along them. Birds’ tails are stumpy and have been for more than 100 million years. It’s unlikely this would ever be reversed.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/371444/original/file-20201126-19-1677xfz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A falcon illustration with its skeleton inside visible." src="https://images.theconversation.com/files/371444/original/file-20201126-19-1677xfz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/371444/original/file-20201126-19-1677xfz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/371444/original/file-20201126-19-1677xfz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/371444/original/file-20201126-19-1677xfz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/371444/original/file-20201126-19-1677xfz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/371444/original/file-20201126-19-1677xfz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/371444/original/file-20201126-19-1677xfz.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">While some types of birds have long tail feathers, such as falcons (above) and pheasants, on the inside their tails are short.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>Also, modern birds walk on their back legs only and (in most cases) have <a href="https://www.rspb.org.uk/birds-and-wildlife/natures-home-magazine/birds-and-wildlife-articles/how-do-birds-survive/birds-legs-and-feet/">four toes</a> and three “fingers” in their wings. </p>
<p>Compare that with <em>Triceratops</em>, which walked on all four limbs, had five fingers on its front feet (the inner three of which were weight-bearing) and four toes on its back feet.</p>
<p>It may not be <em>impossible</em> for birds to gain two more fingers to have five like <em>Triceratops</em>; some people with a condition called “polydactyly” have more than five fingers, but this is very rare.</p>
<p>There aren’t really any situations where an extra finger (or one less) would be necessary for a bird’s survival. Thus, there’s little to no chance birds will evolve to change in this way.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/371451/original/file-20201126-19-12qvdc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Diagram showing different types of bird feet" src="https://images.theconversation.com/files/371451/original/file-20201126-19-12qvdc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/371451/original/file-20201126-19-12qvdc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=406&fit=crop&dpr=1 600w, https://images.theconversation.com/files/371451/original/file-20201126-19-12qvdc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=406&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/371451/original/file-20201126-19-12qvdc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=406&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/371451/original/file-20201126-19-12qvdc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=510&fit=crop&dpr=1 754w, https://images.theconversation.com/files/371451/original/file-20201126-19-12qvdc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=510&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/371451/original/file-20201126-19-12qvdc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=510&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Most birds have four toes and three ‘fingers’ in their wings.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>Even if birds did eventually start to walk on all four limbs (legs and wings), they wouldn’t move the same way a <em>Triceratops</em> did because the purpose of a bird’s wings is very different to that of a <em>Triceratops’s</em> legs.</p>
<h2>Dinosaurs are history</h2>
<p>We know from fossil discoveries that <em>Triceratops</em> and <em>Tyrannosaurus</em> had scaly skin covering most of their bodies. Most modern birds have scaly feet, but none are scaly all over.</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/365432/original/file-20201026-13-rp2x88.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/365432/original/file-20201026-13-rp2x88.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=797&fit=crop&dpr=1 600w, https://images.theconversation.com/files/365432/original/file-20201026-13-rp2x88.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=797&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/365432/original/file-20201026-13-rp2x88.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=797&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/365432/original/file-20201026-13-rp2x88.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1002&fit=crop&dpr=1 754w, https://images.theconversation.com/files/365432/original/file-20201026-13-rp2x88.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1002&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/365432/original/file-20201026-13-rp2x88.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1002&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Although <em>Triceratops</em> had a ‘beak’ this was very different to a bird’s beak.</span>
<span class="attribution"><span class="source">Stephen Poropat/American Museum of Natural History</span></span>
</figcaption>
</figure>
<p>It’s hard to imagine what would force any bird to naturally replace its feathers with scales. Birds need feathers to fly, to save energy (by staying warm) and to put on special displays to attract mates.</p>
<p><em>Triceratops</em> did have a “beak” at the front of its mouth, but this evolved completely separately to the beaks of birds and had two extra bones — something no living animal has.</p>
<p>What’s more, behind its beak and jaws, <em>Triceratops</em> had rows of teeth. While some birds such as geese have spiky beaks. No bird in the past 66 million years has ever had teeth. </p>
<p>Considering these huge differences, it’s really unlikely birds will ever evolve to look more like their extinct dinosaur relatives. And no extinct dinosaur will ever come back to life either — except maybe in movies!</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/371470/original/file-20201126-21-x732j9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Geese with open mouths" src="https://images.theconversation.com/files/371470/original/file-20201126-21-x732j9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/371470/original/file-20201126-21-x732j9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/371470/original/file-20201126-21-x732j9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/371470/original/file-20201126-21-x732j9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/371470/original/file-20201126-21-x732j9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/371470/original/file-20201126-21-x732j9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/371470/original/file-20201126-21-x732j9.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">Geese don’t have actual ‘teeth’, but they do have sharp points in their mouth to hold onto slippery things.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure><img src="https://counter.theconversation.com/content/148623/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Stephen Poropat 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>66 million years ago, birds survived the calamity that wiped out all prehistoric dinosaurs. But could birds once again evolve into their long lost ancestors?Stephen Poropat, Postdoctoral Researcher (Palaeontology), Swinburne University of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1501702020-11-17T18:48:48Z2020-11-17T18:48:48ZHow chemical clues from prehistoric microbes rewrote the story of one of Earth’s biggest mass extinctions<figure><img src="https://images.theconversation.com/files/369758/original/file-20201117-19-o78hjw.jpg?ixlib=rb-1.1.0&rect=0%2C17%2C3872%2C2086&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Microbial mats in Shark Bay, Western Australia, similar to those that lived around 200 million years ago.</span> <span class="attribution"><span class="source">Yalimay Jimenez Duarte WA-OIGC, Curtin University</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Chemical clues left behind by humble microbes have rewritten the timeline of one of the biggest mass extinction events in Earth’s history.</p>
<p>The so-called “end-Triassic mass extinction”, thought to have occurred just over 200 million years ago, wiped out swathes of prehistoric creatures both on land and in the oceans. It was prompted by the breakup of the supercontinent Pangea, which triggered massive volcanic activity that flooded the atmosphere with carbon dioxide and acidified the oceans.</p>
<p>But our new research, <a href="https://www.pnas.org/content/early/2020/11/10/1917661117">published in Proceedings of the National Academy of Sciences</a>, suggests these cataclysmic events actually happened later than previously thought.</p>
<p>We made this discovery by examining molecular fossils — trace chemicals derived from microbial “mats” that bathed in prehistoric waters. </p>
<h2>A likely story</h2>
<p>Traditionally, scientists have placed the mass extinction event, and the volcanic upheaval that presaged it, at about <a href="https://www.britannica.com/science/Triassic-Period/Terrestrial-reptiles-and-the-first-mammals">201 million years ago</a>.</p>
<p>They came to this conclusion after studying rocks of that age from the Bristol Channel, UK, which show a distinctive chemical signature. The ratios of different isotopes of carbon within these rocks suggest this was the moment when the global atmosphere changed, as huge amounts of methane were pumped into the skies due to massive volcanic activity covering the central Atlantic, in turn altering the chemical composition of rocks that formed during this time.</p>
<figure class="align-center ">
<img alt="View of St Audrie's Bay, UK" src="https://images.theconversation.com/files/369761/original/file-20201117-15-1vh39ka.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/369761/original/file-20201117-15-1vh39ka.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/369761/original/file-20201117-15-1vh39ka.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/369761/original/file-20201117-15-1vh39ka.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/369761/original/file-20201117-15-1vh39ka.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/369761/original/file-20201117-15-1vh39ka.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/369761/original/file-20201117-15-1vh39ka.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Bristol Channel is home to rock formations that give an insight into prehistoric life (and death) some 200 million years ago.</span>
<span class="attribution"><span class="source">Calum Peter Fox</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>But we made a discovery that challenged this assumption. We found evidence of ancient microbial mats in the same region, at the same time. It was these flourishing communities of microbes that actually created the change in the chemical signature of the rocks, rather than a global volcanic event.</p>
<p>These microbial mats formed as the region’s waters changed from salty seawater to brackish or fresh water, and water levels dropped to puddle-like centimetre depths. This is another reason why scientists mistook this event for a mass extinction — marine creatures disappeared from the local fossil record at this time not because they had all died out, but because it was no longer marine. </p>
<p>Of course, the world’s marine creatures had only earned a relatively brief reprieve. We know the volcanic cataclysm did occur, but just not as long ago as previously assumed. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/elementary-new-theory-on-mass-extinctions-that-wiped-out-life-48806">Elementary new theory on mass extinctions that wiped out life</a>
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</em>
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<h2>Still going strong</h2>
<p>Remarkably, the microbial mats recorded in UK samples are similar to <a href="https://www.frontiersin.org/articles/10.3389/fmicb.2020.560336/full?&utm_source=Email_to_authors_&utm_medium=Email&utm_content=T1_11.5e1_author&utm_campaign=Email_publication&field=&journalName=Frontiers_in_Microbiology&id=560336">living microbial mats in Australia</a>, such as in Western Australia’s Shark Bay. It’s amazing to think similar microbial communities are still living on Australia’s shorelines to this day. </p>
<p>Microbes have also been useful resources in research to learn about several other mass extinction events too, such as the “Great Dying” that marked the end of <a href="https://science.sciencemag.org/content/307/5710/706.abstract">the Permian period</a> roughly 252 million years ago, and the dramatic demise of the dinosaurs in a mass extinction some <a href="https://pubs.geoscienceworld.org/gsa/geology/article/48/4/328/580289/Microbial-life-in-the-nascent-Chicxulub-crater">66 million years ago</a>. </p>
<p>For example, pigments and lipid remains from microbial mats found in the Chicxulub crater in the Gulf of Mexico — formed by the asteroid that wiped out the dinosaurs — show that photosynthetic processes had <a href="https://pubs.geoscienceworld.org/gsa/geology/article/48/4/328/580289/Microbial-life-in-the-nascent-Chicxulub-crater">bounced back within 200,000 years of the impact</a>.</p>
<p>Microbial mats also have helped to <a href="https://www.nature.com/articles/srep02768">preserve</a> an amazing range of fossil evidence from prehistoric animals, including soft tissues, <a href="https://www.nature.com/articles/s41598-017-13873-4">red blood cells</a> and chemical clues to ancient animals’ diets.</p>
<h2>A warning from prehistory</h2>
<p>While we don’t know exactly how much later the global end-Triassic mass extinction event actually occurred, what we can say is that our research sounds a stark warning for potential future mass extinctions on Earth.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/369738/original/file-20201117-21-4x9frb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Schematic diagram of environmental changes" src="https://images.theconversation.com/files/369738/original/file-20201117-21-4x9frb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/369738/original/file-20201117-21-4x9frb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=317&fit=crop&dpr=1 600w, https://images.theconversation.com/files/369738/original/file-20201117-21-4x9frb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=317&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/369738/original/file-20201117-21-4x9frb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=317&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/369738/original/file-20201117-21-4x9frb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=399&fit=crop&dpr=1 754w, https://images.theconversation.com/files/369738/original/file-20201117-21-4x9frb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=399&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/369738/original/file-20201117-21-4x9frb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=399&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Schematic diagram showing the factors driving global ecological change in the modern day and at the end of the Triassic period.</span>
<span class="attribution"><span class="source">Victor Lesh</span></span>
</figcaption>
</figure>
<p>The end of the Triassic Period featured huge environmental shifts, including declines in biodiversity, ocean acidification, reduced oxygen levels, habitat destruction, nutrient shifts and changing sea levels. </p>
<p>Knowing more about these changes will provide crucial information that could help understanding the threats our own ecosystems face today, and potentially help safeguard them for the future.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/triassic-mass-extinction-may-give-clues-on-how-oceans-will-be-affected-by-climate-change-39655">Triassic mass extinction may give clues on how oceans will be affected by climate change</a>
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<img src="https://counter.theconversation.com/content/150170/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Kliti Grice receives funding from ARC. </span></em></p><p class="fine-print"><em><span>Calum Peter Fox receives funding from ARC. </span></em></p>The end-Triassic mass extinction was a cataclysm for the world’s prehistoric species, killed off by volcanoes that altered Earth’s seas and skies. But new research shows it didn’t happen when we thought.Kliti Grice, John Curtin Distinguished Professor of Organic and Isotope Geochemistry, Curtin UniversityCalum Peter Fox, Researcher, Curtin UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1462482020-09-16T18:29:13Z2020-09-16T18:29:13ZNewly discovered mass extinction event triggered the dawn of the dinosaurs<figure><img src="https://images.theconversation.com/files/358163/original/file-20200915-20-15gp9vz.jpg?ixlib=rb-1.1.0&rect=49%2C155%2C1930%2C915&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">D. Bonadonna/ MUSE, Trento</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Huge volcanic eruptions 233 million years ago pumped carbon dioxide, methane and water vapour into the atmosphere. This series of violent explosions, on what we now know as the west coast of Canada, led to massive global warming. Our <a href="https://advances.sciencemag.org/content/advances/6/38/eaba0099.full.pdf">new research</a> has revealed that this was a planet-changing mass extinction event that killed off many of the dominant tetrapods and heralded the dawn of the dinosaurs. </p>
<p>The best known mass extinction happened at the end of the Cretaceous period, 66 million years ago. This is when dinosaurs, <a href="https://theconversation.com/pterosaurs-should-have-been-too-big-to-fly-so-how-did-they-manage-it-60892">pterosaurs</a>, marine reptiles and ammonites all died out. This event was caused primarily by the impact of a giant asteroid that blacked out the light of the sun and caused darkness and freezing, followed by other massive perturbations of the oceans and atmosphere.</p>
<p>Geologists and palaeontologists agree on a roster of five such events, of which the end-Cretaceous mass extinction was the last. So our new discovery of a previously unknown mass extinction might seem unexpected. And yet this event, termed the Carnian Pluvial Episode (CPE), seems to have killed as many species as the giant asteroid did. Ecosystems on land and sea were profoundly changed, as the planet got warmer and drier. </p>
<figure class="align-center ">
<img alt="An erupting volcano." src="https://images.theconversation.com/files/358352/original/file-20200916-14-10ku33l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/358352/original/file-20200916-14-10ku33l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/358352/original/file-20200916-14-10ku33l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/358352/original/file-20200916-14-10ku33l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/358352/original/file-20200916-14-10ku33l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/358352/original/file-20200916-14-10ku33l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/358352/original/file-20200916-14-10ku33l.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">Huge volcanic eruptions changed life on Earth 233 million years ago.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/volcano-erupting-lava-volcan-landscape-tungurahua-90131104">Sutterstock/AmmitJack</a></span>
</figcaption>
</figure>
<p>On land, this triggered profound changes in plants and herbivores. In turn, with the decline of the dominant plant-eating tetrapods, such as rhynchosaurs and dicynodonts, the dinosaurs were given their chance. </p>
<p>The dinosaurs had originated some 15 million years earlier and <a href="https://advances.sciencemag.org/content/advances/6/38/eaba0099.full.pdf">our new study</a> shows that, as a result of the CPE, they expanded rapidly in the subsequent 10 million to 15 million years and became the dominant species in the terrestrial ecosystems. The CPE triggered the “age of the dinosaurs” which lasted for a further 165 million years.</p>
<p>It wasn’t only the dinosaurs that were given a foothold. Many modern tetrapod groups, such as turtles, lizards, crocodiles and mammals date back to this newly discovered time of revolution.</p>
<h2>Following the clues</h2>
<p>This event was first noticed independently back in the 1980s. But it was thought that it was restricted to Europe. First, geologists in Germany, Switzerland and Italy recognised a major turnover among marine faunas about 232 million years ago, termed the Rheingraben event. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/five-mass-extinctions-and-what-we-can-learn-from-them-about-the-planet-today-79971">Five mass extinctions – and what we can learn from them about the planet today</a>
</strong>
</em>
</p>
<hr>
<p><a href="https://www.nature.com/articles/321857a0">Then in 1986</a>, I recognised this independently as a global-scale turnover among tetrapods and ammonites. But at that time, the age dating was much weaker than now and it was impossible to be sure whether these were both the same event.</p>
<p>The jigsaw pieces started falling into place when an episode of about 1 million years of humid climates was recognised throughout the UK and parts of Europe by geologists <a href="https://pubs.geoscienceworld.org/gsa/geology/article/17/3/265/204901?casa_token=W6hhoQX7ZP0AAAAA:Fz17Rarsuqi6pLf3Scv69a4VKPKEVChkHSB4yNFMefAcGMTRIs0nPc4r3jrf9CZhkuq--3g">Mike Simms and Alastair Ruffell</a>. Then geologist <a href="https://environment.leeds.ac.uk/see/staff/1221/dr-jacopo-dal-corso">Jacopo dal Corso</a> spotted a coincidence in timing of the CPE with the peak of <a href="https://www.sciencedirect.com/science/article/pii/S0921818115000296?casa_token=q8kb-2NBaU0AAAAA:swvCyd1pE2P39_hETqmochWBfrYO1iVV3P8Si0cYsUjbJSovjHcAiCxubnnZ4hPeFHfN3F_UAUs">eruptions of the Wrangellia basalts</a>. </p>
<p>Wrangellia is a term geologists give to a narrow tectonic plate that is attached to the west coast of the North American continent, north of Vancouver and Seattle. </p>
<figure class="align-center ">
<img alt="Map highlighting Wrangellia flood basalts" src="https://images.theconversation.com/files/358353/original/file-20200916-20-133i4kh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/358353/original/file-20200916-20-133i4kh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=596&fit=crop&dpr=1 600w, https://images.theconversation.com/files/358353/original/file-20200916-20-133i4kh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=596&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/358353/original/file-20200916-20-133i4kh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=596&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/358353/original/file-20200916-20-133i4kh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=749&fit=crop&dpr=1 754w, https://images.theconversation.com/files/358353/original/file-20200916-20-133i4kh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=749&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/358353/original/file-20200916-20-133i4kh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=749&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Map showing the distribution of Wrangellia flood basalts in Alaska, Yukon and British Columbia.</span>
<span class="attribution"><a class="source" href="https://www.eoas.ubc.ca/research/wrangellia/1wrang.html">University of British Columbia (EOAS)</a></span>
</figcaption>
</figure>
<p>Finally, in a review of the evidence from <a href="https://www.cambridge.org/core/journals/geological-magazine/article/carnian-humid-episode-of-the-late-triassic-a-review">Triassic-aged rocks</a>, the signature of the CPE was detected – not only in Europe, but also in South America, North America, Australia and Asia. This was far from being a Europe-only event. It was global.</p>
<h2>Volcanic eruptions</h2>
<p>The massive Wrangellia eruptions pumped carbon dioxide, methane and water vapour into the atmosphere, leading to global warming and an increase in rainfall worldwide. There were as many as five pulses of eruptions associated with warming peaks from 233 million years ago. The eruptions led to acid rain as the volcanic gases mixed with rainwater to shower the Earth in dilute acid. Shallow oceans also became acidified. </p>
<p>The sharp warming drove plants and animals from the tropics and the acid rain killed plants on land, while <a href="https://theconversation.com/ocean-acidification-is-chemistry-not-conjecture-15497">ocean acidification</a> attacked all marine organisms with carbonate skeletons. This stripped away the surfaces of the oceans and the land. Life may have begun to recover, but when the eruptions ceased, temperatures remained high while the tropical rainfall ceased. This is what caused the subsequent drying of the land on which the dinosaurs flourished.</p>
<p>Most extraordinary was the re-casting of the marine carbonate factory. This is the global mechanism by which calcium carbonate forms great thicknesses of limestones and provides material for organisms like corals and molluscs to build their shells. The CPE marked the start of modern coral reefs, as well as many of the modern groups of plankton, suggesting profound changes in ocean chemistry. </p>
<figure class="align-center ">
<img alt="Timeline illustration of mass extinction events" src="https://images.theconversation.com/files/358349/original/file-20200916-24-sz016q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/358349/original/file-20200916-24-sz016q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=343&fit=crop&dpr=1 600w, https://images.theconversation.com/files/358349/original/file-20200916-24-sz016q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=343&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/358349/original/file-20200916-24-sz016q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=343&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/358349/original/file-20200916-24-sz016q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=431&fit=crop&dpr=1 754w, https://images.theconversation.com/files/358349/original/file-20200916-24-sz016q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=431&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/358349/original/file-20200916-24-sz016q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=431&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A timeline of mass extinction events.</span>
<span class="attribution"><span class="source">D. Bonadonna/MUSE, Trento</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Before the CPE, the main source of carbonate in the oceans came from microbial ecosystems, such as limestone-dominated mud mounds, on continental shelves. But after the CPE, it was driven by coral reefs and plankton, where new groups of micro-organisms, such as <a href="https://ucmp.berkeley.edu/protista/dinoflagellata.html">dinoflagellates</a>, appeared and bloomed. This profound switch in fundamental chemical cycles in the oceans marked the beginning of modern marine ecosystems.</p>
<p>And there are going to be important lessons for how we help our planet recover from climate change. Geologists need to investigate the details of the Wrangellia volcanic activity and understand how these repeated eruptions drove the climate and changed the Earth’s ecosystems. There have been a number of volcanically-induced mass extinctions in the history of the Earth and the physical perturbations, such as global warming, acid rain and ocean acidification, are among the challenges we see today.</p>
<p>Palaeontologists will need to work more closely on the data from marine and continental fossil records. This will help us understand how the crisis played out in terms of the loss of biodiversity, but also to explore how the planet recovered.</p><img src="https://counter.theconversation.com/content/146248/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michael J. Benton receives funding from the Natural Environment Research Council (UK) and the European Research Council.</span></em></p>Our new research has discovered how a series of volcanic eruptions 233 million years ago fundamentally changed life on Earth.Michael J. Benton, Professor of Vertebrate Palaeontology, University of BristolLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1408892020-07-20T13:27:45Z2020-07-20T13:27:45ZWhy some species thrive after catastrophe – rules for making the most of an apocalypse<figure><img src="https://images.theconversation.com/files/347993/original/file-20200716-37-2p3kw7.jpg?ixlib=rb-1.1.0&rect=0%2C438%2C1875%2C1294&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Some species can do well in the face of extreme hardship.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/close-black-lava-green-fern-hawaii-42141481">George Burba/Shutterstock</a></span></figcaption></figure><p>Sixty-six million years ago, an <a href="https://science.sciencemag.org/content/327/5970/1214.abstract?casa_token=rse9tRx1m3EAAAAA:JA0HIX0oWHQsZAy80RHTxsa0jKO8UdvdPbaOLbbHXt5WxYzmu56TDok9A-ua3_bV8RhixQeV5olNZA">asteroid</a> struck the Earth. The world was plunged into darkness, killing the dinosaurs and over 90% of all species alive. Today, every living thing <a href="https://theconversation.com/profiles/nick-longrich-209117/dashboard#">descends from</a> the handful of surviving species. But not all survivors thrived. </p>
<p>Some groups – birds and placental mammals, butterflies and ants, sunflowers, grasses – diversified, taking advantage of the devastation. Some, like crocodiles and turtles, didn’t. And still others, like <a href="https://pubs.geoscienceworld.org/uwyo/rmg/article-abstract/24/special_paper_3/95/87858/Competitive-exclusion-and-taxonomic-displacement?redirectedFrom=PDF">multituberculate mammals</a> and <a href="https://ucmp.berkeley.edu/taxa/verts/archosaurs/choristodera.php">champsosaurus</a>, survived the asteroid but went extinct in the aftermath. </p>
<p>Why the difference? Surprisingly, what separated winners and losers wasn’t how hard extinction hit them. Rather, winners had qualities that made them adaptable and competitive after the extinction: they were fast-growing, mobile, cooperative and clever. </p>
<figure class="align-center ">
<img alt="Shark swimming." src="https://images.theconversation.com/files/343060/original/file-20200621-43196-1ggrr3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/343060/original/file-20200621-43196-1ggrr3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=376&fit=crop&dpr=1 600w, https://images.theconversation.com/files/343060/original/file-20200621-43196-1ggrr3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=376&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/343060/original/file-20200621-43196-1ggrr3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=376&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/343060/original/file-20200621-43196-1ggrr3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=473&fit=crop&dpr=1 754w, https://images.theconversation.com/files/343060/original/file-20200621-43196-1ggrr3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=473&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/343060/original/file-20200621-43196-1ggrr3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=473&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Sharks, great survivors, weren’t great innovators.</span>
<span class="attribution"><span class="source">Wikipedia</span></span>
</figcaption>
</figure>
<p>Some groups were completely eliminated: dinosaurs, <a href="https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.2001663">pterosaurs</a>, <a href="https://www.sciencedirect.com/science/article/pii/S1342937X10001851">plesiosaurs</a> and ammonites. Obviously, they couldn’t take part in a recovery. But among survivors, the groups that won out tended to be those hit hard by extinction. </p>
<p><a href="https://www.researchgate.net/publication/230889811_Major_extinctions_of_land-dwelling_vertebrates_at_the_Cretaceous-Tertiary_boundary_eastern_Montana">Crocodilians, turtles</a> and <a href="https://www.sciencedirect.com/science/article/pii/S0960982218307632">sharks</a> were spared the brunt of the extinction, but aren’t especially diverse now. Meanwhile, groups that dominate today were devastated. Snakes and lizards saw <a href="https://www.pnas.org/content/109/52/21396">over 80% extinction</a>. Mammals were hit harder, suffering 90% extinction. Perhaps <a href="https://www.nature.com/articles/nature15697">three bird species survived</a>, suggesting extinction rates of 99.9% or more. </p>
<p>These groups were winners only in a relative sense – 99.9% extinction is terrible, but beats 100% extinction among tyrannosaurs. But while these animals initially suffered, they thrived when the dust literally settled. Four things gave them an edge.</p>
<h2>Metabolism</h2>
<p>First, winners had high metabolisms. Metabolic rate is how fast biological processes happen – meaning chemical reactions letting organisms grow, move, digest and reproduce. </p>
<figure class="align-center ">
<img alt="Field of sunflowers." src="https://images.theconversation.com/files/344391/original/file-20200628-104504-c6kbcc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/344391/original/file-20200628-104504-c6kbcc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=371&fit=crop&dpr=1 600w, https://images.theconversation.com/files/344391/original/file-20200628-104504-c6kbcc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=371&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/344391/original/file-20200628-104504-c6kbcc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=371&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/344391/original/file-20200628-104504-c6kbcc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=467&fit=crop&dpr=1 754w, https://images.theconversation.com/files/344391/original/file-20200628-104504-c6kbcc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=467&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/344391/original/file-20200628-104504-c6kbcc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=467&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Fast-growing sunflowers complete their lives in a summer.</span>
<span class="attribution"><span class="source">Wikipedia</span></span>
</figcaption>
</figure>
<p>Higher metabolism requires more food. This was initially a liability for warm-blooded birds and mammals during the impact winter, when plants couldn’t photosynthesise food. But afterwards, being able to eat, grow and breed fast let birds and mammals rapidly increase their numbers, compete effectively, and colonise new habitats. Fast-growing flowering plants, especially grasses, flourished at the expense of slower-growing species.</p>
<p>Even within these groups, we see high metabolism providing an edge. Among mammals, placental mammals, with their higher metabolisms, outcompeted <a href="https://www.redalyc.org/pdf/3699/369944274002.pdf">marsupials</a>. Passerines, the most diverse group of birds, also have <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0003261">higher metabolic rates</a> than other birds. </p>
<h2>Mobility</h2>
<p>Second, mobility promotes adaptability. Flight let birds, bats, butterflies and ants colonise new habitats, then diversify. Mammals, being highly mobile, quickly invade new habitats – think <a href="https://www.nationalgeographic.org/article/how-european-rabbits-took-over-australia/">rabbits in Australia</a>, or deer in New Zealand – in a way that turtles don’t. </p>
<figure class="align-center ">
<img alt="Two greylay geese flying above a landscape." src="https://images.theconversation.com/files/343059/original/file-20200621-43205-1lj3n6b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/343059/original/file-20200621-43205-1lj3n6b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=413&fit=crop&dpr=1 600w, https://images.theconversation.com/files/343059/original/file-20200621-43205-1lj3n6b.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=413&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/343059/original/file-20200621-43205-1lj3n6b.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=413&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/343059/original/file-20200621-43205-1lj3n6b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=519&fit=crop&dpr=1 754w, https://images.theconversation.com/files/343059/original/file-20200621-43205-1lj3n6b.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=519&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/343059/original/file-20200621-43205-1lj3n6b.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=519&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Graylag geese in flight.</span>
<span class="attribution"><span class="source">Wikipedia</span></span>
</figcaption>
</figure>
<p>Flowering plants also evolved tricks – fruits, parachutes, burs, floating husks – to let wind, water or animals carry their seeds. It’s harder to displace competitors once they’re established, so being first into a new habitat provides a massive competitive advantage.</p>
<h2>Cooperation</h2>
<p>Third, winners tend to cooperate. Lions and wolves form prides and packs to take down prey and defend territory, elephants and zebras use herds for defence. Birds flock to find food and evade predators. </p>
<p>Ants and mound-building termites assemble vast family groups, outcompeting solitary insects. Birds, mammals and social insects also cooperate with relatives by feeding and <a href="https://theconversation.com/the-origin-and-evolution-of-love-131109">caring for offspring</a>, preserving their genes more efficiently.</p>
<figure class="align-center ">
<img alt="Group of ants holding a leaf." src="https://images.theconversation.com/files/347995/original/file-20200716-31-1cqcza5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/347995/original/file-20200716-31-1cqcza5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/347995/original/file-20200716-31-1cqcza5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/347995/original/file-20200716-31-1cqcza5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/347995/original/file-20200716-31-1cqcza5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/347995/original/file-20200716-31-1cqcza5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/347995/original/file-20200716-31-1cqcza5.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">Ants cooperate.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/ant-action-standing-bridge-unity-teamconcept-1118781845">frank60/Shutterstock</a></span>
</figcaption>
</figure>
<p>Meanwhile, some species cooperate with other species. Leafcutter ants and termites form alliances with fungi, cultivating them in return for food. Flowering plants give away nectar and fruit to animals, which then pollinate flowers and spread their seeds. By cooperating, these species compete more effectively, so cooperative animals like ants, elephants and orcas tend to play bigger roles in the ecosystem than solitary ones like alligators and turtles.</p>
<h2>Intelligence</h2>
<p>But maybe the most remarkable trend is the rise of intelligence. Mammals and birds have the largest brains of any animals. The largest-brained mammals, the <a href="https://www.pnas.org/content/107/37/16216#F2">placentals</a>, have outcompeted marsupials and egg-laying monotremes. The most diverse birds, the passerines and parrots, are the <a href="https://pubmed.ncbi.nlm.nih.gov/15467290/">brainiest</a>. </p>
<p>Among insects, the social insects – ants, bees, termites – have complex behaviours that emerge from interactions of unintelligent individuals. This phenomenon is known as swarm intelligence, and not coincidentally, these insects dominated ecosystems after the asteroid winter. </p>
<figure class="align-center ">
<img alt="A dog wading through the sea on a rocky beach." src="https://images.theconversation.com/files/344395/original/file-20200628-104529-1uxc6cz.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/344395/original/file-20200628-104529-1uxc6cz.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=445&fit=crop&dpr=1 600w, https://images.theconversation.com/files/344395/original/file-20200628-104529-1uxc6cz.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=445&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/344395/original/file-20200628-104529-1uxc6cz.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=445&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/344395/original/file-20200628-104529-1uxc6cz.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=560&fit=crop&dpr=1 754w, https://images.theconversation.com/files/344395/original/file-20200628-104529-1uxc6cz.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=560&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/344395/original/file-20200628-104529-1uxc6cz.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=560&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Polynesian dogs swim readily, and hunt crabs.</span>
<span class="attribution"><span class="source">Nick Longrich</span></span>
</figcaption>
</figure>
<p>But intelligence doesn’t just make animals more competitive. It accelerates adaptation, because the first step in changing your DNA is changing your mind. </p>
<p>For example, before mammals could <a href="https://evolution-outreach.biomedcentral.com/articles/10.1007/s12052-009-0135-2">evolve into whales</a>, they first had to learn to swim and fish, only afterwards could natural selection create flippers and sonar. Before horses could evolve, their omnivorous ancestors switched to a vegan diet, then, natural selection favoured tall-crowned teeth and complex guts to break down tough plants. Behaviour leads; genes follow.</p>
<figure class="align-center ">
<img alt="A humpback whale jumping out of the sea." src="https://images.theconversation.com/files/344396/original/file-20200628-104516-9uctpp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/344396/original/file-20200628-104516-9uctpp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/344396/original/file-20200628-104516-9uctpp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/344396/original/file-20200628-104516-9uctpp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/344396/original/file-20200628-104516-9uctpp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/344396/original/file-20200628-104516-9uctpp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/344396/original/file-20200628-104516-9uctpp.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">Humpback whale.</span>
<span class="attribution"><span class="source">wikipedia</span></span>
</figcaption>
</figure>
<p>The greater an animal’s behavioural flexibility, the more tricks it can learn, and so the greater its adaptive potential. Animals don’t consciously decide their evolutionary futures. But they do choose what to eat, how to forage or where to live. </p>
<p>Whale ancestors didn’t dream of becoming dolphins, but they did dream of catching fish, and they imagined new fishing grounds. Being able to learn from yesterday, process information in dreams tonight, imagine different outcomes tomorrow – learning, memory processing, creativity – increase the number of potential evolutionary futures.</p>
<h2>No accident</h2>
<p>The continents were isolated in the early Cenozoic era just after the asteroid hit. Yet remarkably similar ecosystems dominated by mammals and birds evolved independently in South America, Africa, Australia and the Eurasian-North American supercontinent. That implies these groups’ dominance wasn’t an accident. </p>
<p>What’s striking is that these trends weren’t new – dinosaurs show similar patterns. Dinosaurs of the Cretaceous period had higher growth rates than their ancient Triassic ancestors. They were more mobile, some were fast runners, others – <a href="https://www.pnas.org/content/108/37/15253">birds</a> – flew.</p>
<p>The <a href="https://www.tandfonline.com/doi/pdf/10.1671/0272-4634(2000)020%5B0615%3AFEANTD%5D2.0.CO%3B2">brains of these</a> later dinosaurs were larger than earlier counterparts. <em>T. rex</em> was faster, <a href="https://www.tandfonline.com/doi/pdf/10.1671/0272-4634(2000)020%5B0615%3AFEANTD%5D2.0.CO%3B2">smarter</a> and had a faster <a href="https://www.nature.com/articles/nature02699">metabolism</a> than its forebears. Many – <a href="https://pubs.geoscienceworld.org/sepm/palaios/article-abstract/16/5/482/99813/The-Taphonomy-of-a-Centrosaurus-Ornithischia?redirectedFrom=fulltext">ceratopsians</a>, <a href="https://pubs.geoscienceworld.org/cjes/article-abstract/52/8/642/301101/Hadrosaurid-Edmontosaurus-bonebeds-from-the?redirectedFrom=fulltext">duckbills</a>, <a href="https://www.nature.com/articles/srep35782">avimimids</a> – show herding behaviours unknown from earlier dinosaurs.</p>
<p>During the asteroid winter, the rules briefly changed. Warm-blooded, fast-moving, cooperative, intelligent <a href="https://www.pnas.org/content/108/37/15253">birds</a>, mammals and dinosaurs fared poorly against turtles and alligators. Dinosaurs vanished. Afterwards, these trends reasserted themselves. </p>
<p>Evolution may offer us some lessons here. Be quick. Move to find new opportunities. Work with others. Try new things. But above all, change – adapt. </p>
<p>These are almost always good strategies, but especially when you’re down, trying for a comeback.</p><img src="https://counter.theconversation.com/content/140889/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nicholas R. Longrich 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>When the dinosaurs went extinct, some species took over the world. Adaptability, not survivability, explains why.Nicholas R. Longrich, Senior Lecturer in Evolutionary Biology and Paleontology, University of BathLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1395192020-06-01T10:22:49Z2020-06-01T10:22:49ZPrehistoric climate change damaged the ozone layer and led to a mass extinction<figure><img src="https://images.theconversation.com/files/338387/original/file-20200528-51509-l9s17i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/planet-earth-spectacular-sunset-elements-this-1463607272">muartat/Shutterstock</a></span></figcaption></figure><p>Mass extinctions are very important to how life evolved on Earth. For example, when an asteroid <a href="https://theconversation.com/dinosaur-killing-asteroid-struck-at-worst-angle-to-cause-maximum-damage-new-research-139394">hit the Earth</a> 66 million years ago, the resulting dinosaur extinction led mammals <a href="https://theconversation.com/mass-extinctions-made-life-on-earth-more-diverse-and-might-again-122350">to take their place</a>. </p>
<p>My colleagues and I have <a href="https://advances.sciencemag.org/content/6/22/eaba0768">published new research</a> on the mass extinction that took place 359 million years ago at the boundary between the Devonian and Carboniferous geological periods. There have been many <a href="https://link.springer.com/article/10.1134/S0001437016050015">previous speculations</a> as to the cause of this event, including volcanic eruptions, asteroid impacts, climate change, sea level changes, wildfires and the rise of the first forests. </p>
<p>But we have shown that the extinctions on land at this time may have been caused by a catastrophic thinning of the ozone layer that let in damaging levels of ultra-violet radiation. <a href="https://phys.org/news/2018-02-thinning-ozone-layer-driven-earth.html">Something similar</a> contributed to the mass extinctions at the end of the Permian and Triassic periods, but these events were caused by volcanic eruptions. Our research suggests the Earth has a natural internal process triggered by a warming climate that can destroy the ozone layer, a serious warning for our own period of climate change. </p>
<p>The Late Devonian extinction played a <a href="https://www.pnas.org/content/107/22/10131">significant role</a> in the development of vertebrate life. It included the loss of the dominant group of armoured freshwater fish. The survivors were the sharks and the rather minor group of bony fish that subsequently spread out to dominate our younger oceans. </p>
<p>The event also shaped our own evolution because it led to the extinction of the first four-legged “tetrapods”. These were “fish” whose fins had evolved to become limbs with between six and eight fingers and toes. The first land-dwelling tetrapods with five fingers and toes – our ancestors – don’t appear in the fossil record until after this extinction. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/338380/original/file-20200528-51496-17hrmhk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/338380/original/file-20200528-51496-17hrmhk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=343&fit=crop&dpr=1 600w, https://images.theconversation.com/files/338380/original/file-20200528-51496-17hrmhk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=343&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/338380/original/file-20200528-51496-17hrmhk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=343&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/338380/original/file-20200528-51496-17hrmhk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=431&fit=crop&dpr=1 754w, https://images.theconversation.com/files/338380/original/file-20200528-51496-17hrmhk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=431&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/338380/original/file-20200528-51496-17hrmhk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=431&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Devonian Period saw the first tetrapods emerge.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/devonian-landscape-3d-render-759826384">Nicolas Primola/Shutterstock</a></span>
</figcaption>
</figure>
<p>To find out exactly what caused the Late Devonian extinction, we looked for evidence of what happened in the atmosphere that was captured by fossilised plants from before and after the event. In particular, we looked at the resistant walls of the microscopic remains of pollen and spores, taken from fossils found in East Greenland and released by dissolving the rock samples in acid. </p>
<p>The resistant walls of spores and pollen are there to protect the cell contents from ultra-violet radiation. But there is a brief interval between the creation of a new cell and the formation of its protective wall when it is vulnerable.</p>
<p>The kinds of spores we examined are covered in small spines that are normally identical in length and have perfectly pointed tips. But most of the spines in our samples were malformed in a wild variety of shapes, suggesting the DNA of their cells was damaged by ultra-violet radiation. This suggests that the Earth’s protective ozone shield was down as the spores were formed.</p>
<p>Other spores and pollen had pigmented walls that acted as a protective tan, enabling those plants to survive. But a number of important plant groups quickly became extinct and the forest ecosystem collapsed. Those groups that survived were still disrupted and it took several million years to rebuild, creating quite a different ecosystem in the process. </p>
<p>Our samples came from a very large ancient lake that existed all year round despite being in a very arid part of the world. Such lakes only form when glaciers collapse and the world’s seasonal monsoon is very active due to solar heat, so the global climate must have been in a warming period.</p>
<h2>Extinction mechanism</h2>
<p>Other scientists <a href="https://science.sciencemag.org/content/337/6096/835">have shown</a> that high summer temperatures over continental areas can increase the transport of water vapour high into the atmosphere. This water vapour carries with it organic carbon compounds that include chlorine, which are produced naturally by a wide variety of plants, algae and fungi. Once these compounds are near the ozone layer, they release the chlorine and this breaks down ozone molecules.</p>
<p>This produces a positive feedback loop because a collapsing terrestrial ecosystem will release a flush of nutrients into the oceans, which can cause a rapid increase in algae. So the more the ozone layer is damaged, the more plants die, and the more ozone-damaging compounds are released. Later on, the ozone layer will naturally recover as the climate cools and the algae helps remove carbon dioxide from the atmosphere.</p>
<p>The discovery of this potential new extinction mechanism indicates that a warming climate, such as we have now, has the potential to erode the ozone layer to let in damaging ultra-violet radiation. This has consequences for all life on Earth, both on the land and in shallow waters. </p>
<p>We believe it is as important as recognising that asteroid impacts caused mass extinctions. Once we knew about the consequences of asteroid impacts, there followed an intense collective research effort to <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL073191">assess the threat</a>. We now <a href="https://astronomy.com/news/2018/07/tracking-asteroids">plot the paths</a> of all large extra-terrestrial objects likely to come close to the Earth’s orbit.</p>
<p>Similarly, we now need to focus effort on understanding the links between global warming and the production and atmospheric transport of chlorine-bearing carbon compounds that have the potential to cause similar destruction of our ozone layer.</p>
<p>We now need to make further studies of the rocks with malformed spores to work out the duration of the extinction and the likely rate of temperature change required to push enough ozone-destroying chemicals high into the atmosphere. We also want to do ultra-violet malformation experiments on living fern-like plants which have spiny spores.</p><img src="https://counter.theconversation.com/content/139519/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Marshall receives funding from NERC and National Geographic. He is affiliated with CASP and the Etches Collection as a charitable trustee. </span></em></p>New research on the Late Devonian extinction suggests the ozone layer could be naturally depleted as the temperature rises.John Marshall, Professor of Earth Science, University of SouthamptonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1393942020-05-27T09:12:03Z2020-05-27T09:12:03ZDinosaur-killing asteroid struck at worst angle to cause maximum damage – new research<figure><img src="https://images.theconversation.com/files/337874/original/file-20200527-141303-2dqgdv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/meteor-shower-elements-this-image-furnished-324036791">Vadim Sadovski/Shutterstock</a></span></figcaption></figure><p>Few geological events fascinate as much as the one that happened 66 million years ago. Evidence suggests a huge asteroid <a href="https://theconversation.com/dinosaurs-could-have-avoided-mass-extinction-if-the-killer-asteroid-had-landed-almost-anywhere-else-87109">hit our planet</a>, triggering a chain of events that led to a <a href="https://theconversation.com/catastrophic-failure-of-earths-global-systems-led-to-the-extinction-of-the-dinosaurs-we-may-yet-go-the-same-way-114348">mass extinction</a> in which more than 70% of species on Earth – including the dinosaurs – disappeared. </p>
<p>A <a href="https://www.nature.com/articles/s41467-020-15269-x">new study</a> narrows down the trajectory of this asteroid, which could help us better understand how the impact affected the planet beneath it and how material was dispersed in its aftermath. The research suggests that the angle of impact of this asteroid may have led to the worst possible consequences for Earth’s inhabitants.</p>
<p>The asteroid is long gone – pulverised when it hit Earth – but it left a 200km-wide crater. By looking at the geometry and structure of this crater, it is possible to test asteroid trajectories with computer simulations and see which one is more likely to leave a scar as observed in real life.</p>
<p>The crater is no longer visible, it is buried beneath hundreds of metres of sediment deposited since the impact. But various pieces of evidence pointed geoscientists to the Yucatán Peninsula in Mexico as the site of the crater’s location, and it was named after a local village, Chicxulub. Various datasets have since been collected to allow researchers to appreciate the features of this crater. </p>
<p>In 2016, I joined a joint <a href="https://www.ecord.org/expedition364/">scientific expedition</a> organised by the International Ocean Discovery Program and the International Continental Scientific Drilling Program. We spent two months at sea, drilling samples from the crater in a specific location, its peak ring.</p>
<p>Peak rings are formed during large impact events. The one in the Chicxulub crater consists of a roughly 80km-diameter inner ring of hills, effectively forming a second circle within the crater. Peak rings are more easily observed on other rocky bodies in our solar system, such as the <a href="https://www.lpi.usra.edu/features/102016/schrodinger/">Schrödinger Crater on the Moon</a>. </p>
<p>Our 2016 expedition aimed at understanding how these features form, and what happens to the target rocks during an impact. It is difficult to produce experiments that replicate the high pressures, temperatures and aftermath of asteroid impacts events. That is why researchers use computer simulations.</p>
<p>The samples recovered during the 2016 expedition helped to <a href="https://science.sciencemag.org/content/354/6314/878.abstract">refine models</a> of how the peak ring, and ultimately the Chicxulub crater, was formed. For an asteroid that arrived vertically on the surface, the model suggests the object would have been pulverised within the first minute while making a cavity roughly 30km deep. </p>
<p>During the next two minutes, the bottom of this cavity was thrust up by the resulting forces to to a height of more than 10km. Then during the following two minutes, this uplifted central part of the cavity collapsed outward, forming the peak ring. In fact, the impact was so powerful it even brought up part of the Earth’s mantle, the layer below the surface crust found more than 30km deep underground.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/ankmTU89X_A?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>The new study from researchers at Imperial College London, published in Nature Communications, pushes the modelling even further. By testing different asteroid sizes, speeds and angles of impact – 90° (vertical), 60°, 45° and 30° relative to Earth’s surface – it is possible to simulate which scenario would have left a crater that looks like the real one.</p>
<p>The shape and continuity of Chicxulub’s peak ring suggests that the actual asteroid had an angle of between 60° and 45°. If the peak ring was truncated somewhere (like a horse-shoe), that would suggest a shallower angle, but it does not seem to be the case. The direction of the asteroid is more challenging to estimate. </p>
<p>But by looking at the relative positions of the centres of the crater, the peak ring and the uplift of the mantle mentioned above, it is possible to estimate where the asteroid was coming from. With a vertical impact, the three centres would be expected to match, but they do not. Their offset could indicate that the asteroid was coming from the north-east.</p>
<h2>After the impact</h2>
<p>Regardless of the direction, the actual angle is pretty important to picture what happened after the impact. The estimated range of angles, and especially 60° relative to Earth’s surface, would have led to the most efficient vaporising of the rocks and projection of <a href="https://theconversation.com/did-a-burning-oil-spill-wipe-out-the-dinosaurs-62456">toxic gases and particles</a> evenly in the region and globally. </p>
<p><a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL074879">Other simulations</a> suggest that a 60° to 30° range would have released much more gas and many more projectiles than with a vertical (90°) or a shallow (15°) angle. This suggests that not only did the asteroid fall in a spot more likely to release toxic material, but it also did so very efficiently, leading to the worst-case scenario for our planet – and the dinosaurs.</p>
<p>A <a href="https://pubs.geoscienceworld.org/gsa/geology/article-abstract/24/11/963/187987/Cretaceous-Tertiary-Chicxulub-impact-angle-and-its?redirectedFrom=PDF">previous study</a> suggested that a shallower angle and a different direction would have meant the effect of the impact was more severe in the northern hemisphere. Under the new model with a steeper angle, the ejected material would have been spread more evenly. This might allow researchers in the future to revise the wider record of the impact to better reconstruct the events that happened in its aftermath.</p><img src="https://counter.theconversation.com/content/139394/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Erwan Le Ber affiliated with the International Ocean Discovery Program.</span></em></p>The trajectory of the Chicxulub asteroid led to the most efficient release of gas and projectile rocks – which was disastrous for life on Earth.Erwan Le Ber, Research Associate, International Ocean Discovery Program, University of LeicesterLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1353272020-05-05T18:11:41Z2020-05-05T18:11:41ZWill humans go extinct? For all the existential threats, we’ll likely be here for a very long time<figure><img src="https://images.theconversation.com/files/332634/original/file-20200505-83736-1bjqlmw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/tragedy-victim-human-skull-desert-1179542422">RomanRaD/Shutterstock</a></span></figcaption></figure><p>Will our species go extinct? The short answer is yes. The fossil record shows everything goes extinct, eventually. Almost all species that ever lived, over 99.9%, are extinct. </p>
<p>Some left descendants. Most – plesiosaurs, trilobites, <em>Brontosaurus</em> – didn’t. That’s also true of other human species. Neanderthals, Denisovans, <em>Homo erectus</em> all vanished, leaving just <em><a href="https://theconversation.com/were-other-humans-the-first-victims-of-the-sixth-mass-extinction-126638">Homo sapiens</a></em>. Humans are inevitably heading for extinction. The question isn’t <em>whether</em> we go extinct, but <em>when</em>. </p>
<p>Headlines often suggest this extinction is imminent. The threat of <a href="https://cosmosmagazine.com/space/space-agency-ups-risk-of-asteroid-earth-collision">earth-grazing asteroids</a> is a media favourite. <a href="https://www.theguardian.com/technology/2018/mar/11/elon-musk-colonise-mars-third-world-war">Mars</a> is regularly mooted as a bolt hole. And there is the ongoing menace of the climate emergency.</p>
<p>Humans have vulnerabilities. Large, warm-blooded animals like us don’t handle ecological disruptions well. Small, cold-blooded turtles and snakes can last months without food, so they survived. Big animals with fast metabolisms – tyrannosaurs, or humans – require lots of food, constantly. That leaves them vulnerable to even brief food chain disruptions caused by catastrophes such as <a href="https://science.sciencemag.org/content/340/6135/941">volcanoes</a>, <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2006PA001349">global warming</a>, <a href="https://royalsocietypublishing.org/doi/full/10.1098/rspb.2016.0007">ice ages</a> or the <a href="https://science.sciencemag.org/content/327/5970/1214">impact winter</a> after an asteroid collision.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/327303/original/file-20200411-192985-1fefl5g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/327303/original/file-20200411-192985-1fefl5g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=369&fit=crop&dpr=1 600w, https://images.theconversation.com/files/327303/original/file-20200411-192985-1fefl5g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=369&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/327303/original/file-20200411-192985-1fefl5g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=369&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/327303/original/file-20200411-192985-1fefl5g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=464&fit=crop&dpr=1 754w, https://images.theconversation.com/files/327303/original/file-20200411-192985-1fefl5g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=464&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/327303/original/file-20200411-192985-1fefl5g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=464&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Tyrannosaurus quickly became extinct when impact winter made food scarce.</span>
</figcaption>
</figure>
<p>We’re also long-lived, with long generation times, and few offspring. Slow reproduction makes it hard to recover from population crashes, and slows natural selection, making it difficult to adapt to rapid environmental changes. That doomed mammoths, ground sloths, and <a href="https://science.sciencemag.org/content/292/5523/1888">other megafauna</a>. Big mammals reproduced <a href="https://www.journals.uchicago.edu/doi/abs/10.1086/671995">too slowly</a> to withstand, or adapt, to human overhunting.</p>
<p>So we’re vulnerable, but there are reasons to think humans are resistant to extinction, maybe uniquely so. We’re a deeply strange species – widespread, abundant, supremely adoptable – which all suggest we’ll stick around for a while.</p>
<h2>Everywhere and abundant</h2>
<p>First, we’re everywhere. Geographically widespread organisms fare better during catastrophes such as an <a href="https://science.sciencemag.org/content/268/5209/389">asteroid impact</a>, and <a href="https://www.pnas.org/content/105/Supplement_1/11528">between mass extinction events</a>. Large geographic range means a species doesn’t put all its eggs in one basket. If one habitat is destroyed, it can survive in another.</p>
<p><a href="https://www.iucnredlist.org/species/22823/14871490">Polar bears</a> and <a href="https://www.iucnredlist.org/species/712/121745669">pandas</a>, with small ranges, are endangered. <a href="https://www.iucnredlist.org/species/41688/121229971">Brown bears</a> and red foxes, with huge ranges, aren’t. Humans have the largest geographic range of any mammal, inhabiting all continents, remote oceanic islands, in habitats as diverse as deserts, tundra, and rainforest. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/327302/original/file-20200411-109282-1t4n0pd.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/327302/original/file-20200411-109282-1t4n0pd.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=238&fit=crop&dpr=1 600w, https://images.theconversation.com/files/327302/original/file-20200411-109282-1t4n0pd.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=238&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/327302/original/file-20200411-109282-1t4n0pd.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=238&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/327302/original/file-20200411-109282-1t4n0pd.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=299&fit=crop&dpr=1 754w, https://images.theconversation.com/files/327302/original/file-20200411-109282-1t4n0pd.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=299&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/327302/original/file-20200411-109282-1t4n0pd.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=299&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Humans exist everywhere, making us difficult to eradicate.</span>
<span class="attribution"><span class="source">Wikipedia</span></span>
</figcaption>
</figure>
<p>And we’re not just everywhere, we’re abundant. With 7.8 billion people, we’re among the most common animals on Earth. Human biomass <a href="https://www.pnas.org/content/115/25/6506">exceeds that of all wild mammals</a>. Even assuming a pandemic or nuclear war could eliminate 99% of the population, millions would survive to rebuild.</p>
<p>We’re also generalists. Species that survived the dinosaur-killing asteroid rarely relied on a single food source. They were <a href="https://onlinelibrary.wiley.com/doi/full/10.1111/jeb.12882">omnivorous mammals</a>, or predators such as <a href="https://pubs.geoscienceworld.org/gsa/geology/article-abstract/20/6/556/205786">alligators and snapping turtles</a> that eat anything. Humans eat thousands of animal and plant species. Depending on what’s available, we’re herbivores, piscivores, carnivores, omnivores.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/332624/original/file-20200505-83745-3wcwmy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/332624/original/file-20200505-83745-3wcwmy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/332624/original/file-20200505-83745-3wcwmy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/332624/original/file-20200505-83745-3wcwmy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/332624/original/file-20200505-83745-3wcwmy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/332624/original/file-20200505-83745-3wcwmy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/332624/original/file-20200505-83745-3wcwmy.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">Not picky eaters.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/crocodile-head-closeup-south-africa-1488773522">Alexander Narrina/Shutterstock</a></span>
</figcaption>
</figure>
<p>But most importantly, we adapt unlike any other species, through learned behaviours — culture - not DNA. We’re animals, <a href="https://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1001342">we’re mammals</a>, but we’re such weird, special mammals. We’re different. </p>
<p>Rather than taking generations to change our genes, humans use intelligence, culture and tools to adapt our behaviour in years or even minutes. Whales took millions of years to evolve flippers, pointy teeth, sonar. In millenia, humans invented fishhooks, boats and fish-finders. Cultural evolution outpaces even viral evolution. Viral genes <a href="https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1002243">evolve in days</a>. It takes a second to ask someone to wash their hands. </p>
<p>Cultural evolution isn’t only faster than genetic evolution, it’s different. In humans, natural selection created an animal capable of intelligent design, one that doesn’t blindly adapt to the environment, but consciously reshapes it to its needs. Horses evolved grinding molars and complex guts to eat plants. People domesticated plants, then cleared forests for crops. Cheetahs evolved speed to pursue their prey. We bred cows and sheep that don’t run. </p>
<p>We’re so uniquely adaptable, we might even survive a mass extinction event. Given a decade of warning before an asteroid strike, humans could probably stockpile enough food to survive years of cold and darkness, saving much or most of the population. Longer-term disruptions, like ice ages, might cause widespread conflicts and population crashes, but civilisations could probably survive. </p>
<p>But this adaptibility sometimes makes us our own worst enemies, too clever for our own good. Changing the world sometimes means changing it for the worse, creating new dangers: nuclear weapons, pollution, overpopulation, climate change, pandemics. So we’ve mitigated these risks with nuclear treaties, <a href="https://www.smithsonianmag.com/science-nature/the-political-history-of-cap-and-trade-34711212/">pollution controls</a>, <a href="https://www.theguardian.com/global-development/2016/mar/08/rise-use-contraception-global-population-growth-family-planning">family planning</a>, <a href="https://www.wsj.com/articles/solar-power-is-beginning-to-eclipse-fossil-fuels-11581964338">cheap solar power</a>, vaccines. We’ve escaped every trap we set for ourselves.</p>
<p>So far.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/327330/original/file-20200412-138728-1ci0d68.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/327330/original/file-20200412-138728-1ci0d68.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=351&fit=crop&dpr=1 600w, https://images.theconversation.com/files/327330/original/file-20200412-138728-1ci0d68.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=351&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/327330/original/file-20200412-138728-1ci0d68.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=351&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/327330/original/file-20200412-138728-1ci0d68.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=441&fit=crop&dpr=1 754w, https://images.theconversation.com/files/327330/original/file-20200412-138728-1ci0d68.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=441&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/327330/original/file-20200412-138728-1ci0d68.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=441&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Pessimistic scenarios could lead to the breakdown of civilisation.</span>
</figcaption>
</figure>
<h2>Interconnected world</h2>
<p>Our global civilisation also invented ways to support each other. People in one part of the world can provide food, money, education,and vaccines to vulnerable people elsewhere. But interconnectivity and interdependence also create vulnerabilities. </p>
<p>International trade, travel and communications link people around the world. So <a href="https://www.amazon.com/Big-Short-Inside-Doomsday-Machine/dp/0393338827/ref=sr_1_3?dchild=1&keywords=the+big+short&qid=1586628329&sr=8-3">financial gambles on Wall Street</a> destroy European economies, violence in one country inspires murderous extremism on the other side of the globe, a virus from a cave in China spreads to threaten the lives and livelihoods of billions.</p>
<p>This suggests a limited optimism. <em>Homo sapiens</em> have already survived over 250,000 years of <a href="https://science.sciencemag.org/content/292/5517/686">ice ages</a>, <a href="https://www.nature.com/articles/nature25967">eruptions</a>, <a href="https://www.amazon.co.uk/Plagues-People-William-McNeill/dp/0385121229">pandemics</a>, and <a href="https://www.amazon.co.uk/Making-Atomic-Bomb-Richard-Rhodes/dp/1471111237/ref=sr_1_1?dchild=1&keywords=the+making+of+the+atomic+bomb&qid=1586620485&s=books&sr=1-1">world wars</a>. We could easily survive another 250,000 years or, longer. </p>
<p>Pessimistic scenarios might see natural or manmade disasters leading to widespread breakdown of social order, even civilisation and the loss of most of the human population – a grim, post-apocalyptic world. Even so, humans would likely survive, scavenging society’s remains, Mad Max-style, perhaps reverting to subsistence farming, even becoming hunter-gatherers.</p>
<p>Survival sets a pretty low bar. The question isn’t so much whether humans survive the next three or three hundred thousand years, but whether we can do more than just survive.</p><img src="https://counter.theconversation.com/content/135327/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nicholas R. Longrich 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>Large numbers, huge ranges, and adaptibility make the human species very difficult to eradicateNicholas R. Longrich, Senior Lecturer in Evolutionary Biology and Paleontology, University of BathLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1326272020-04-29T15:48:10Z2020-04-29T15:48:10ZHow bison, moose and caribou stepped in to do the cleaning work of extinct mammoths<figure><img src="https://images.theconversation.com/files/330714/original/file-20200427-145560-nibdjc.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C3777%2C2050&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Unlike mammoths, bison survived in Alaska at the end of the last ice age.</span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/QvCcqTHlLCE">Hans Veth/Unsplash</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>The extinction of one species can create ripples that transform an ecosystem. That’s particularly true for so-called “ecosystem engineer” species. Beavers are one example – they dam rivers, creating ponds and channels that <a href="https://theconversation.com/beavers-are-set-to-recolonise-the-uk-heres-how-people-and-the-environment-could-benefit-132116">offer refuge for spawning fish and small mammals</a>.</p>
<p>Large herbivores such as <a href="http://thinkelephants.blogspot.com/2012/10/elephants-ecosystems-engineers.html">elephants, horses and reindeer</a> are engineers too – they break down shrubs and trees to create open grasslands, habitats that benefit a wealth of species.</p>
<p>We know that their ancestors – such as the woolly mammoth – shaped the world around them in a similar way, but what happened to those ancient ecosystems when they died out?</p>
<p>Our <a href="https://www.cambridge.org/core/journals/quaternary-research/article/tracking-latequaternary-extinctions-in-interior-alaska-using-megaherbivore-bone-remains-and-dung-fungal-spores/BD3C13789FBB262EDCA8432CBB47067E">new research published in the journal Quaternary Research</a> studied the extinction of mammoth, wild horse and saiga antelope towards the end of the last ice age in interior Alaska, analysing fossilised <a href="https://methodsblog.com/2016/07/19/european-bison/">dung fungal spores</a> recovered from the bottom of lakes and <a href="https://www.nps.gov/articles/aps-17-1-4.htm">ancient bones recovered from buried</a> sediments.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-what-effect-did-the-asteroid-that-wiped-out-the-dinosaurs-have-on-plants-and-trees-132386">Curious Kids: What effect did the asteroid that wiped out the dinosaurs have on plants and trees?</a>
</strong>
</em>
</p>
<hr>
<p>We wanted to know how ancient ecosystems responded to these species dying out so that it might teach us more about mass extinctions today. What we discovered could offer hope for modern ecosystems facing biodiversity loss.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/330716/original/file-20200427-145536-v86bx3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/330716/original/file-20200427-145536-v86bx3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=346&fit=crop&dpr=1 600w, https://images.theconversation.com/files/330716/original/file-20200427-145536-v86bx3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=346&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/330716/original/file-20200427-145536-v86bx3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=346&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/330716/original/file-20200427-145536-v86bx3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=435&fit=crop&dpr=1 754w, https://images.theconversation.com/files/330716/original/file-20200427-145536-v86bx3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=435&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/330716/original/file-20200427-145536-v86bx3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=435&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A museum replica of a woolly mammoth. Mammoths helped maintain open habitats by grazing herbs, trees and bushes.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/dvur-kralove-czech-republic-08132013-big-1024532596">Noska Photo/Shutterstock</a></span>
</figcaption>
</figure>
<h2>How ancient ecosystems coped with extinctions</h2>
<p>The late-Quaternary extinctions occurred towards the end of the last ice age. In North America, they saw the loss of large herbivores and carnivores, whose relatives still roam other continents as elephants, wild horses and tigers. This was a period of rapid climate change and growing pressure from humans.</p>
<p><a href="https://www.researchgate.net/publication/269820457_Late_Quaternary_megafaunal_extinctions_on_the_continents_A_short_review">Previous research showed that 69% of large mammals</a> were lost from North America around this time. Similar losses were seen on other continents, <a href="https://www.discovermagazine.com/planet-earth/dung-fungus-reveal-that-humans-not-climate-change-killed-australias-giant-beasts">including Australia</a>. The diversity of mammal species shrank, but more significant was the <a href="https://doc.rero.ch/record/210391/files/PAL_E4398.pdf">crash in numbers of all mammals</a>, including species that survived the extinction event.</p>
<p><a href="https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.12576">Previous research</a> showed that elsewhere in the Americas, the loss of ecosystem engineers like the woolly mammoth led to an explosion in plant growth, as trees and shrubs were no longer grazed and browsed so intensively. In turn, there were larger and more frequent wildfires.</p>
<p>But in Alaska, our results revealed that other species of wild herbivores, including bison, moose, caribou and musk ox, increased in abundance, making up for the loss of mammoths, saiga antelopes and wild horses.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/330718/original/file-20200427-145499-105esni.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/330718/original/file-20200427-145499-105esni.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=509&fit=crop&dpr=1 600w, https://images.theconversation.com/files/330718/original/file-20200427-145499-105esni.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=509&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/330718/original/file-20200427-145499-105esni.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=509&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/330718/original/file-20200427-145499-105esni.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=639&fit=crop&dpr=1 754w, https://images.theconversation.com/files/330718/original/file-20200427-145499-105esni.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=639&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/330718/original/file-20200427-145499-105esni.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=639&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Saiga antelopes used to roam North America, but they are now only found in scattered pockets of Asia.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Saiga_antelope#/media/File:Saiga_antelope_at_the_Stepnoi_Sanctuary.jpg">Andrey Giljov/Wikipedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>This suggests that as extinctions occurred, other large herbivores were able to fill the gap, partially taking over the lost role of ecosystem engineer. This insight from 13,000 years ago could offer hope for modern conservationists. Substituting an extinct ecosystem engineer with a similar species still living today may work to revive lost ecological processes.</p>
<p>Reintroducing large herbivores in this way is often referred to as “<a href="https://www.esf.edu/efb/parry/Invert_Cons_14_Readings/Seddon_etal_2014.pdf">rewilding</a>”. Today’s landscapes on most continents are <a href="https://www.chrispackham.co.uk/news/what-is-rewilding">empty of large vertebrate animals</a>, largely because of the late Quaternary extinctions we studied. <a href="https://www.researchgate.net/publication/257973653_Rewilding_North_America">One of the key arguments</a> behind rewilding is that bringing some of those species back to landscapes could boost biodiversity more broadly and create more diverse, resilient ecosystems.</p>
<p>But without resurrecting the woolly mammoth, our research indicates it may be possible to bring back some of the ecosystem engineering benefits of extinct species by reintroducing their living relatives or substitute species, ultimately helping surviving plants and animals to thrive.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/could-resurrecting-mammoths-help-stop-arctic-emissions-95956">Could resurrecting mammoths help stop Arctic emissions?</a>
</strong>
</em>
</p>
<hr>
<p>Our work in Alaska shows that the consequences of engineer extinctions are not always overwhelmingly negative. Studying this rare instance when ecosystems coped better with extinctions can help us design more effective conservation measures for megaherbivores today. </p>
<p>A good example of creative thinking in conservation can be found in Columbia. Here, pet hippos that escaped from Pablo Escobar’s private collection have multiplied in the wild and now appear to be recreating processes that were <a href="https://www.theguardian.com/environment/2020/mar/24/pablo-escobars-cocaine-hippos-show-how-invasive-species-can-restore-a-lost-world-aoe">lost thousands of years ago</a> when native megaherbivores died out. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/330721/original/file-20200427-145499-1a33zx6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/330721/original/file-20200427-145499-1a33zx6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/330721/original/file-20200427-145499-1a33zx6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/330721/original/file-20200427-145499-1a33zx6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/330721/original/file-20200427-145499-1a33zx6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/330721/original/file-20200427-145499-1a33zx6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/330721/original/file-20200427-145499-1a33zx6.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">These hippos are technically invasive species in Colombia and are wild descendants of Pablo Escobar’s pets.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/hippopotamus-colombia-1351698167">Perla Sofia/Shutterstock</a></span>
</figcaption>
</figure>
<p>This includes the creation of well trodden hippo paths between wetlands and feeding areas on firmer ground, which help deepen water channels, disperse seeds and fertilise wetlands. Over 13,000 years ago, these processes would have been carried out by the now extinct <a href="https://prehistoric-fauna.com/Macrauchenia-patagonica">giant llama</a>, and semi-aquatic <a href="https://dcpaleo.org/notoungulata/">notoungulata</a>.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/330738/original/file-20200427-145544-1ud4ur2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/330738/original/file-20200427-145544-1ud4ur2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=358&fit=crop&dpr=1 600w, https://images.theconversation.com/files/330738/original/file-20200427-145544-1ud4ur2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=358&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/330738/original/file-20200427-145544-1ud4ur2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=358&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/330738/original/file-20200427-145544-1ud4ur2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=450&fit=crop&dpr=1 754w, https://images.theconversation.com/files/330738/original/file-20200427-145544-1ud4ur2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=450&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/330738/original/file-20200427-145544-1ud4ur2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=450&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Notoungulata were hoofed, sometimes heavy-bodied grazing mammals that inhabited South America from 57 million years to 11,000 years ago.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Notoungulata#/media/File:Toxodon.jpg">ArthurWeasley/Wikipedia</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Although it may seem an eternity since mammoths walked the Earth, our research suggests that some of the effects they had on the world around them can be resurrected without a Jurassic Park-style breakthrough in <a href="https://www.thoughtco.com/the-resurrection-of-extinct-animals-1091999">de-extinction</a>.</p><img src="https://counter.theconversation.com/content/132627/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Maarten van Hardenbroek van Ammerstol receives funding from UKRI/NERC. </span></em></p><p class="fine-print"><em><span>Ambroise Baker does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The historical record is full of surprises – and it could encourage conservationists to think more creatively.Ambroise Baker, Lecturer in Biology, Teesside UniversityMaarten van Hardenbroek van Ammerstol, Lecturer in Physical Geography, Newcastle UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1308692020-04-02T21:35:38Z2020-04-02T21:35:38ZWhile we fixate on coronavirus, Earth is hurtling towards a catastrophe worse than the dinosaur extinction<figure><img src="https://images.theconversation.com/files/324623/original/file-20200401-23086-1fgcm8t.jpg?ixlib=rb-1.1.0&rect=2%2C2%2C1914%2C1195&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Pixabay </span></span></figcaption></figure><p>At several points in the history of our planet, increasing amounts of carbon dioxide in the atmosphere have caused extreme global warming, prompting <a href="https://www.sciencedaily.com/releases/2019/07/190708154057.htm">the majority of species</a> on Earth to die out.</p>
<p>In the past, these events were triggered by a huge <a href="https://www.scientificamerican.com/article/volcanoes-may-have-triggered-the-last-unexplained-mass-extinction/">volcanic eruption</a> or asteroid impact. Now, Earth is heading for another mass extinction – and human activity is to blame.</p>
<p>I am an Earth and Paleo-climate scientist and <a href="https://link.springer.com/search?dc.creator=%22Andrew%20Y.+Glikson%22">have researched</a> the relationships between asteroid impacts, volcanism, climate changes and mass extinctions of species.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/heres-what-the-coronavirus-pandemic-can-teach-us-about-tackling-climate-change-134399">Here's what the coronavirus pandemic can teach us about tackling climate change</a>
</strong>
</em>
</p>
<hr>
<p>My research suggests the current growth rate of carbon dioxide emissions is faster than those which triggered two previous mass extinctions, including the event that wiped out the dinosaurs. </p>
<p>The world’s gaze may be focused on COVID-19 right now. But the risks to nature from human-made global warming – and the imperative to act – remain clear.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/324785/original/file-20200402-23109-tia1km.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/324785/original/file-20200402-23109-tia1km.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=370&fit=crop&dpr=1 600w, https://images.theconversation.com/files/324785/original/file-20200402-23109-tia1km.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=370&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/324785/original/file-20200402-23109-tia1km.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=370&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/324785/original/file-20200402-23109-tia1km.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=465&fit=crop&dpr=1 754w, https://images.theconversation.com/files/324785/original/file-20200402-23109-tia1km.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=465&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/324785/original/file-20200402-23109-tia1km.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=465&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The current rate of CO2 emissions is a major event in the recorded history of Earth.</span>
<span class="attribution"><span class="source">EPA</span></span>
</figcaption>
</figure>
<h2>Past mass extinctions</h2>
<p>Many species can adapt to slow, or even moderate, environmental changes. But Earth’s history shows that extreme shifts in the climate can cause many species to <a href="https://www.abc.net.au/news/2019-11-13/what-is-a-mass-extinction-are-we-in-one-now/11699372">become extinct</a>. </p>
<p>For example, about 66 million years ago an asteroid hit Earth. The subsequent smashed rocks and widespread fires released massive amounts of carbon dioxide over <a href="https://www.pnas.org/content/99/12/7836">about 10,000 years</a>. Global temperatures soared, sea levels rose and oceans became acidic. About <a href="https://www.britannica.com/science/K-T-extinction">80% of species</a>, including the dinosaurs, were wiped out.</p>
<p>And about 55 million years ago, global temperatures spiked again, over <a href="https://www.nature.com/articles/ngeo578;%20https://www.nature.com/articles/ngeo1179;https://www.whoi.edu/fileserver.do?id=136084&pt=2&p=148709">100,000 years or so</a>. The cause of this event, known as the <a href="https://www.britannica.com/science/Paleocene-Eocene-Thermal-Maximum">Paleocene-Eocene Thermal Maximum</a>, is not entirely clear. One theory, known as the <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2010RG000326">“methane burp” hypothesis</a>, posits that a massive volcanic eruption triggered the sudden release of methane from ocean sediments, making oceans more acidic and killing off many species. </p>
<p>So is life on Earth now headed for the same fate?</p>
<h2>Comparing greenhouse gas levels</h2>
<p>Before industrial times began at the end of the 18th century, carbon dioxide in the atmosphere sat at around <a href="https://data.giss.nasa.gov/modelforce/ghgases/">300 parts per million</a>. This means that for every one million molecules of gas in the atmosphere, 300 were carbon dioxide.</p>
<p>In February this year, atmospheric carbon dioxide reached <a href="https://www.esrl.noaa.gov/gmd/ccgg/trends/">414.1 parts per million</a>. Total greenhouse gas level – carbon dioxide, methane and nitrous oxide combined – reached almost <a href="https://www.esrl.noaa.gov/gmd/aggi/">500 parts per million of carbon dioxide-equivalent</a></p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/324842/original/file-20200402-74904-1jce5z4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/324842/original/file-20200402-74904-1jce5z4.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=562&fit=crop&dpr=1 600w, https://images.theconversation.com/files/324842/original/file-20200402-74904-1jce5z4.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=562&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/324842/original/file-20200402-74904-1jce5z4.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=562&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/324842/original/file-20200402-74904-1jce5z4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=706&fit=crop&dpr=1 754w, https://images.theconversation.com/files/324842/original/file-20200402-74904-1jce5z4.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=706&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/324842/original/file-20200402-74904-1jce5z4.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=706&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">Author provided/The Conversation</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Carbon dioxide is now pouring into the atmosphere at a rate of <a href="https://www.esrl.noaa.gov/gmd/ccgg/trends/">two to three parts per million each year</a>. </p>
<p>Using carbon records stored in fossils and organic matter, I have determined that current carbon emissions constitute an extreme event in the recorded history of Earth.</p>
<p><a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.13342">My research</a> has demonstrated that annual carbon dioxide emissions are now faster than after both the asteroid impact that eradicated the dinosaurs (about 0.18 parts per million CO2 per year), and the thermal maximum 55 million years ago (about 0.11 parts per million CO2 per year).</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/193811/original/file-20171108-14193-emn16n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/193811/original/file-20171108-14193-emn16n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=417&fit=crop&dpr=1 600w, https://images.theconversation.com/files/193811/original/file-20171108-14193-emn16n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=417&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/193811/original/file-20171108-14193-emn16n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=417&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/193811/original/file-20171108-14193-emn16n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=524&fit=crop&dpr=1 754w, https://images.theconversation.com/files/193811/original/file-20171108-14193-emn16n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=524&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/193811/original/file-20171108-14193-emn16n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=524&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">An asteroid wiped out the dinosaurs 66 million years ago.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>The next mass extinction has begun</h2>
<p>Current atmospheric concentrations of carbon dioxide are not yet at the levels seen 55 million and 65 million years ago. But the massive influx of carbon dioxide means the climate is changing faster than many plant and animal species <a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.13342">can adapt</a>.</p>
<p><a href="https://www.un.org/sustainabledevelopment/blog/2019/05/nature-decline-unprecedented-report/">A major United Nations report</a> released last year warned around one million animal and plant species were threatened with extinction. Climate change was listed as one of five key drivers. </p>
<p>The report said the distributions of 47% of land-based flightless mammals, and almost 25% of threatened birds, may already have been negatively affected by climate change.</p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-what-effect-did-the-asteroid-that-wiped-out-the-dinosaurs-have-on-plants-and-trees-132386">Curious Kids: What effect did the asteroid that wiped out the dinosaurs have on plants and trees?</a>
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<hr>
<p>Many researchers fear the climate system is approaching a <a href="https://www.pnas.org/content/115/33/8252">tipping point</a> - a threshold beyond which rapid and irreversible changes will occur. This will create a cascade of <a href="https://sites.hks.harvard.edu/sed/docs/hjs_esa_environment_0510.pdf">devastating effects</a>.</p>
<p>There are already signs tipping points have been reached. For example, <a href="https://www.theguardian.com/environment/2018/feb/27/arctic-warming-scientists-alarmed-by-crazy-temperature-rises">rising Arctic temperatures</a> have led to <a href="https://www.jpl.nasa.gov/news/news.php?feature=7616">major ice melt</a>, and weakened the <a href="https://www.globalresearch.ca/melting-ice-sheets-and-weakened-polar-fronts-onset-of-climate-tipping-points/5668981">Arctic jet stream</a> – a powerful band of westerly winds.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/324802/original/file-20200402-23115-hbrt5q.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/324802/original/file-20200402-23115-hbrt5q.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=469&fit=crop&dpr=1 600w, https://images.theconversation.com/files/324802/original/file-20200402-23115-hbrt5q.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=469&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/324802/original/file-20200402-23115-hbrt5q.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=469&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/324802/original/file-20200402-23115-hbrt5q.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=589&fit=crop&dpr=1 754w, https://images.theconversation.com/files/324802/original/file-20200402-23115-hbrt5q.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=589&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/324802/original/file-20200402-23115-hbrt5q.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=589&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A diagram showing the weakening Arctic jet stream, and subsequent movements of warm and cold air.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>This allows north-moving warm air to cross the polar boundary, and cold fronts emanating from the poles to <a href="https://link.springer.com/article/10.1007%2Fs10584-019-02458-x">intrude south into Siberia, Europe and Canada</a>. </p>
<p>A shift in climate zones is also causing the tropics to expand and migrate toward the poles, at a rate of about <a href="https://theconversation.com/the-worlds-tropical-zone-is-expanding-and-australia-should-be-worried-77701">56 to 111 kilometres per decade</a>. The tracks of tropical and extra-tropical cyclones are likewise shifting toward the poles. Australia is highly vulnerable to this shift.</p>
<h2>Uncharted future climate territory</h2>
<p><a href="https://www.nature.com/articles/nature16494">Research</a> released in 2016 showed just what a massive impact humans are having on the planet. It said while the Earth might naturally have entered the next ice age in about 20,000 years’ time, the heating produced by carbon dioxide would result in a period of super-tropical conditions, delaying the next ice age to about 50,000 years from now.</p>
<p>During this period, chaotic <a href="https://www.bloomsbury.com/us/storms-of-my-grandchildren-9781608195022/">high-energy stormy conditions</a> would prevail over much of the Earth. <a href="https://www.springer.com/gp/book/9783319572369">My research suggests</a> humans are likely to survive best in sub-polar regions and sheltered mountain valleys, where cooler conditions would allow flora and fauna to persist. </p>
<p>Earth’s next mass extinction is avoidable – if carbon dioxide emissions are dramatically curbed and we develop and deploy technologies to <a href="http://www.ecosmagazine.com/?act=view_file&file_id=EC147p14.pdf">remove carbon dioxide from the atmosphere</a>. But on the current trajectory, human activity threatens to make large parts of the Earth <a href="https://www.goodreads.com/book/show/41552709-the-uninhabitable-earth">uninhabitable</a> - a planetary tragedy of our own making. </p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/anatomy-of-a-heatwave-how-antarctica-recorded-a-20-75-c-day-last-month-134550">Anatomy of a heatwave: how Antarctica recorded a 20.75°C day last month</a>
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</em>
</p>
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<img src="https://counter.theconversation.com/content/130869/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew Glikson does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The risks to nature from man-made global warming – and the imperative to act – are clear.Andrew Glikson, Earth and paleo-climate scientist, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1321052020-02-20T09:39:34Z2020-02-20T09:39:34ZNew analysis sheds important light on an ancient mass extinction event<figure><img src="https://images.theconversation.com/files/316171/original/file-20200219-10995-4wzvhf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Loskop, one of the two hills at the Permo-Triassic boundary site in the Karoo Basin in South Africa's Free State province.</span> <span class="attribution"><span class="source">Jennifer Botha</span></span></figcaption></figure><p><em>The <a href="https://www.nationalgeographic.com/science/prehistoric-world/permian-extinction/">end-Permian mass extinction</a> is considered to be the most devastating biotic event in the history of life on Earth – it caused dramatic losses in global biodiversity, both in water and on land. About 90% of marine and 70% of terrestrial (land) species went extinct. This event may have been responsible for opening up niche spaces that ushered in the age of the dinosaurs. We know that the end-Permian in the marine realm happened about 251.9 million years ago – but the age and duration of the extinction on land, and whether it coincided with the marine extinctions, is one of the most hotly debated topics in palaeontology.</em> </p>
<p><em><a href="https://www.sciencedirect.com/science/article/pii/S003101821930728X">New research</a> from South Africa’s Free State province may go some way to settling the debate. Dr Jennifer Botha, who led the research team, explained the findings to The Conversation Africa’s Natasha Joseph.</em></p>
<p><strong>What did you find in your research?</strong></p>
<p>The <a href="https://www.sciencedirect.com/science/article/pii/S1464343X05001184">South African Karoo Basin</a> preserves the most complete sequence of the end-Permian extinction on land. In <a href="https://www.sciencedirect.com/science/article/pii/S003101821930728X">our study</a> we examined a site in the country’s Free State province to try and figure out when the end-Permian mass extinction happened. Our findings suggest the answer is a maximum of 251.7 million years ago, with an error margin of about 300 000 years either way; geologically speaking this is quite short and still falls within the 251.9 marine date. This suggests the land extinction event happened at the same time as the marine extinction event.</p>
<p><strong>How did you figure this out?</strong></p>
<p>The Karoo Basin, which includes about two-thirds of South Africa and parts of Lesotho, is the best region in the world for studying the end-Permian extinction on land. This is because of its rich fossil record and relatively complete sedimentological sequence. </p>
<p>Our research involved a comprehensive study of palaeontological, sedimentological, geochemical and detrital zircon data from the Free State site. <a href="https://www.amnh.org/learn-teach/curriculum-collections/earth-inside-and-out/zircon-chronology-dating-the-oldest-material-on-earth">Zircons</a> are crystals found in volcanic ash and their radioisotopes – variants of different chemical elements – can be used to date the sediments in which they are found. Zircons from an ash bed provide the most accurate dates, but detrital zircons, which have been redeposited in the sediments, can also be used when a pristine ash bed is lacking.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/316127/original/file-20200219-10991-mik7di.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/316127/original/file-20200219-10991-mik7di.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=465&fit=crop&dpr=1 600w, https://images.theconversation.com/files/316127/original/file-20200219-10991-mik7di.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=465&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/316127/original/file-20200219-10991-mik7di.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=465&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/316127/original/file-20200219-10991-mik7di.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=585&fit=crop&dpr=1 754w, https://images.theconversation.com/files/316127/original/file-20200219-10991-mik7di.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=585&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/316127/original/file-20200219-10991-mik7di.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=585&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The end-Permian mass extinction in the South African Karoo Basin correlated with the marine extinction at Meishan, China. Radiometric dates:1, marine realm; 2, terrestrial realm.Terrestrial beds in metres, marine beds in centimetres. AZ, Assemblage.
Zone; Fm, Formation; Mbr, Member.</span>
<span class="attribution"><span class="source">Author supplied</span></span>
</figcaption>
</figure>
<p>We collected fossils from the site to pinpoint the palaeontologically-defined extinction. We also studied the sediments, which allowed us to see how and when the climate changed during the extinction. This also helped us to pinpoint the event. </p>
<p>We then collected carbonate nodules (lumps of rock containing carbonate) from paleosols at the site – these are ancient soils. Analysing the isotopes from these palaeosols showed us they were similar to palaeosols found at other terrestrial and marine sites dating back to the Permian and Triassic periods. The <a href="https://www.nationalgeographic.com/science/prehistoric-world/triassic/">Triassic Period</a> immediately followed the Permian Period. </p>
<p>All of our analysis suggests that there was a mass extinction event at the time of the end-Permian, on land – and more importantly that it happened at the same time as the marine end-Permian extinction.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/316172/original/file-20200219-11017-8xgxou.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/316172/original/file-20200219-11017-8xgxou.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=285&fit=crop&dpr=1 600w, https://images.theconversation.com/files/316172/original/file-20200219-11017-8xgxou.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=285&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/316172/original/file-20200219-11017-8xgxou.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=285&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/316172/original/file-20200219-11017-8xgxou.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=359&fit=crop&dpr=1 754w, https://images.theconversation.com/files/316172/original/file-20200219-11017-8xgxou.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=359&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/316172/original/file-20200219-11017-8xgxou.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=359&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The therocephalian therapsid, Scaloposaurus constrictus, a mammalian forerunner, forms part of the Early Triassic recovery fauna following the end-Permian mass extinction.</span>
<span class="attribution"><span class="source">Author supplied</span></span>
</figcaption>
</figure>
<p>Our findings have global ramifications. They do not support previous arguments that propose the end-Permian extinction occurred later on land compared to the sea. Instead, they suggest these events happened at the same time.</p>
<p><strong>Why is this sort of dating important? What is the value in knowing how long ago something happened?</strong></p>
<p>Being able to connect the land and marine extinctions to a single event shows just how catastrophic the end-Permian mass extinction was. </p>
<p>This type of research has applications to understanding the current mass extinction in what has been called the <a href="https://www.theguardian.com/environment/2017/jul/10/earths-sixth-mass-extinction-event-already-underway-scientists-warn">sixth mass extinction</a>. That’s because any information gleaned from past mass extinctions can give us insight into how and why organisms are going extinct today. We can also, as <a href="https://theconversation.com/how-looking-250-million-years-into-the-past-could-save-modern-species-60338">I’ve written before</a>, use information from the past to predict which species might survive and which may be more sensitive to extinction.</p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/how-looking-250-million-years-into-the-past-could-save-modern-species-60338">How looking 250 million years into the past could save modern species</a>
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<img src="https://counter.theconversation.com/content/132105/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jennifer Botha was funded by the National Research Foundation (GUN 98819), the DST-NRF Centre of Excellence in Palaeosciences (CoE-Pal) and the Palaeontological Scientific Trust (PAST).</span></em></p>The analysis suggests that there was a mass extinction event at the time of the end-Permian, on land - and that it happened at the same time as the marine end-Permian extinction.Jennifer Botha, Specialist Museum Scientist and Head of Department (National Museum, Bloemfontein) and Research Affiliate, University of the Free StateLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1278032019-12-03T18:36:08Z2019-12-03T18:36:08ZDid people or climate kill off the megafauna? Actually, it was both<figure><img src="https://images.theconversation.com/files/304383/original/file-20191129-45248-1sspxz7.jpg?ixlib=rb-1.1.0&rect=4%2C9%2C1497%2C1116&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">When freshwater dried up, so did many megafauna species.</span> <span class="attribution"><a class="source" href="https://epicaustralia.org.au">Centre of Excellence for Australian Biodiversity and Heritage</a>, <span class="license">Author provided</span></span></figcaption></figure><p>Earth is now firmly in the grips of its sixth “mass extinction event”, and it’s mainly <a href="https://theconversation.com/radical-overhaul-needed-to-halt-earths-sixth-great-extinction-event-68221">our fault</a>. But the modern era is definitely not the first time humans have been implicated in the extinction of a wide range of species.</p>
<p>In fact, starting about 60,000 years ago, many of the world’s largest animals disappeared forever. These “<a href="https://australianmuseum.net.au/learn/australia-over-time/megafauna/">megafauna</a>” were first lost in <a href="http://sahultime.monash.edu.au/explore.html">Sahul</a>, the supercontinent formed by Australia and New Guinea during periods of low sea level. </p>
<p>The causes of these extinctions have been debated for decades. Possible culprits include <a href="https://theconversation.com/climate-change-wiped-out-australias-megafauna-13966">climate change</a>, <a href="https://theconversation.com/new-analysis-finds-no-evidence-that-climate-wiped-out-australias-megafauna-53821">hunting or habitat modification by the ancestors of Aboriginal people</a>, or a <a href="https://royalsocietypublishing.org/doi/10.1098/rspb.2015.2399">combination of the two</a>.</p>
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<strong>
Read more:
<a href="https://theconversation.com/what-is-a-mass-extinction-and-are-we-in-one-now-122535">What is a 'mass extinction' and are we in one now?</a>
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<p>The main way to investigate this question is to build timelines of major events: when species went extinct, when people arrived, and when the climate changed. This approach relies on using <a href="https://theconversation.com/new-analysis-finds-no-evidence-that-climate-wiped-out-australias-megafauna-53821">dated fossils from extinct species</a> to estimate when they went extinct, and archaeological evidence to determine <a href="https://theconversation.com/an-incredible-journey-the-first-people-to-arrive-in-australia-came-in-large-numbers-and-on-purpose-114074">when people arrived</a>. </p>
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Read more:
<a href="https://theconversation.com/an-incredible-journey-the-first-people-to-arrive-in-australia-came-in-large-numbers-and-on-purpose-114074">An incredible journey: the first people to arrive in Australia came in large numbers, and on purpose</a>
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</p>
<hr>
<p>Comparing these timelines allows us to deduce the likely windows of coexistence between megafauna and people.</p>
<p>We can also compare this window of coexistence to long-term models of climate variation, to see whether the extinctions coincided with or shortly followed abrupt climate shifts.</p>
<h2>Data drought</h2>
<p>One problem with this approach is the scarcity of reliable data due to the extreme rarity of a dead animal being fossilised, and the low probability of archaeological evidence being preserved in Australia’s harsh conditions.</p>
<p>This means many studies are restricted to making conclusions regarding drivers of extinction at the scale of single palaeontological sites or of specific archaeological sites. </p>
<p>Alternatively, timelines can be constructed by including evidence across large spatial scales, such as over the <a href="https://theconversation.com/new-analysis-finds-no-evidence-that-climate-wiped-out-australias-megafauna-53821">entire continent of Australia</a>. </p>
<p>Unfortunately, this “lumping” of the available evidence across many different sites disregards the variation in the relative contribution of different extinction drivers across the landscape.</p>
<h2>Mapping extinction</h2>
<p>In our <a href="https://www.nature.com/articles/s41467-019-13277-0">research published in Nature Communications</a>, we developed advanced mathematical tools to map the regional patterns of the timing of megafauna disappearances and the arrival of Aboriginal ancestors across south-eastern Australia. </p>
<p>Based on these new maps, we can now work out where humans and megafauna coexisted, and where they did not. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/304225/original/file-20191128-178078-mo80fk.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/304225/original/file-20191128-178078-mo80fk.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/304225/original/file-20191128-178078-mo80fk.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=653&fit=crop&dpr=1 600w, https://images.theconversation.com/files/304225/original/file-20191128-178078-mo80fk.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=653&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/304225/original/file-20191128-178078-mo80fk.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=653&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/304225/original/file-20191128-178078-mo80fk.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=821&fit=crop&dpr=1 754w, https://images.theconversation.com/files/304225/original/file-20191128-178078-mo80fk.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=821&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/304225/original/file-20191128-178078-mo80fk.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=821&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Areas of coexistence and non-coexistence between humans and megafauna.</span>
<span class="attribution"><span class="source">F. Saltré</span></span>
</figcaption>
</figure>
<p>It turns out humans coexisted with the megafauna over about 80% of south-eastern Sahul for up to 15,000 years, depending on the region in question. </p>
<p>In other regions such as Tasmania, there was no such coexistence. This rules out humans as a likely driver of megafauna extinction in those areas. </p>
<p>We then aligned these windows of coexistence and non-coexistence in each part of the landscape with several environmental measures derived from climate simulations over the past 120,000 years. This gave us an idea about which factors best explained the timing of megafauna extinction in each part of the landscape. </p>
<p>Despite a major effect on extinctions in areas where megafauna and people did not coexist, there was nothing at all to explain the timing of megafauna extinctions in places where megafauna and people coexisted. </p>
<p>This surprising result suggested that we had missed something important in our analyses.</p>
<h2>Connecting the dots</h2>
<p>The major flaw in our approach was to analyse each location independently of its surroundings. Our initial model had failed to take account of the fact that an extinction in one place can affect an extinction in another location nearby. </p>
<p>Once we changed our model to incorporate these effects, the real picture finally emerged. We found that megafauna extinctions in areas were they coexisted with humans were most likely caused by a combination of human pressure and access to water.</p>
<p>In the other 20% of the landscape, where humans and megafauna did not coexist, we found that extinctions likely occurred because of a lack of plants, driven by increasingly dry conditions. This doomed many plant-eating megafauna species to extinction. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/304380/original/file-20191129-45296-yb8dhl.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/304380/original/file-20191129-45296-yb8dhl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/304380/original/file-20191129-45296-yb8dhl.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/304380/original/file-20191129-45296-yb8dhl.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/304380/original/file-20191129-45296-yb8dhl.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/304380/original/file-20191129-45296-yb8dhl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=425&fit=crop&dpr=1 754w, https://images.theconversation.com/files/304380/original/file-20191129-45296-yb8dhl.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=425&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/304380/original/file-20191129-45296-yb8dhl.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=425&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Relative importance (in %) of variables best describing the timing (first row) and the directional gradient (second row) of megafauna extinction in areas of non-coexistence (first column) and coexistence (second column) of people and megafauna.</span>
<span class="attribution"><span class="source">F. Saltré</span></span>
</figcaption>
</figure>
<h2>Space is key</h2>
<p>This is the first evidence that tens of thousands of years ago, the combination of humans and climate change was already making species more likely to disappear. Yet this pattern was invisible if we ignored the interconnectedness of the various regions involved. </p>
<p>This might be just the beginning we need for a new, more nuanced treatment of environmental change in the deep past in other regions of the world.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/11-000-scientists-warn-climate-change-isnt-just-about-temperature-126261">11,000 scientists warn: climate change isn't just about temperature</a>
</strong>
</em>
</p>
<hr>
<p>More importantly, our results reinforce <a href="https://theconversation.com/11-000-scientists-warn-climate-change-isnt-just-about-temperature-126261">scientists’ stark warning</a> about the immediate future of our planet’s plants and wildlife. Given rising human pressures on the natural world, coupled with an unprecedented pace of global warming, modern species are facing similar ravages.</p><img src="https://counter.theconversation.com/content/127803/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Corey J. A. Bradshaw receives funding from the Australian Research Council.</span></em></p><p class="fine-print"><em><span>Frédérik Saltré and Katharina J. Peters 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>A drying climate and the arrival of people together finished off Australia’s megafauna.Frédérik Saltré, Research Fellow in Ecology & Associate Investigator for the ARC Centre of Excellence for Australian Biodiversity and Heritage, Flinders UniversityCorey J. A. Bradshaw, Matthew Flinders Fellow in Global Ecology and Models Theme Leader for the ARC Centre of Excellence for Australian Biodiversity and Heritage, Flinders UniversityKatharina J. Peters, Postdoctoral Fellow, Flinders UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1266382019-11-21T15:33:10Z2019-11-21T15:33:10ZWere other humans the first victims of the sixth mass extinction?<figure><img src="https://images.theconversation.com/files/302005/original/file-20191115-66945-1ccxz9v.jpg?ixlib=rb-1.1.0&rect=5%2C291%2C830%2C485&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A Neanderthal skull shows head trauma, evidence of ancient violence</span> <span class="attribution"><a class="source" href="http://humanorigins.si.edu/evidence/human-fossils/fossils/saint-c%C3%A9saire">Smithsonian National Museum of Natural History</a></span></figcaption></figure><p>Nine human species walked the Earth 300,000 years ago. Now there is just one. The Neanderthals, <em>Homo neanderthalensis</em>, were <a href="https://theconversation.com/why-the-neanderthals-may-have-been-more-sophisticated-hunters-than-we-thought-new-study-98870">stocky hunters</a> adapted to Europe’s cold steppes. The related <a href="https://theconversation.com/fresh-clues-to-the-life-and-times-of-the-denisovans-a-little-known-ancient-group-of-humans-110504">Denisovans</a> inhabited Asia, while the more primitive <a href="https://theconversation.com/a-snapshot-of-our-mysterious-ancestor-homo-erectus-101122"><em>Homo erectus</em></a> lived in Indonesia, and <a href="https://www.nature.com/articles/108371a0.pdf"><em>Homo rhodesiensis</em></a> in central Africa. </p>
<p>Several short, small-brained species survived alongside them: <a href="https://theconversation.com/homo-naledi-fossil-discovery-a-triumph-for-open-access-and-education-47726"><em>Homo naledi</em></a> in South Africa, <a href="https://theconversation.com/how-much-evidence-is-enough-to-declare-a-new-species-of-human-from-a-philippines-cave-site-115139"><em>Homo luzonensis</em></a> in the Philippines, <a href="https://theconversation.com/fast-evolution-explains-the-tiny-stature-of-extinct-hobbit-from-flores-island-124747"><em>Homo floresiensis</em></a> (“hobbits”) in Indonesia, and the mysterious <a href="https://theconversation.com/bone-suggests-red-deer-cave-people-a-mysterious-species-of-human-52437">Red Deer Cave People</a> in China. Given how quickly we’re discovering new species, more are likely waiting to be found.</p>
<p>By 10,000 years ago, they were all gone. The disappearance of these other species resembles a mass extinction. But there’s no obvious environmental catastrophe – volcanic eruptions, climate change, asteroid impact – driving it. Instead, the extinctions’ timing suggests they were caused by the spread of a new species, evolving <a href="https://science.sciencemag.org/content/358/6363/652.abstract">260,000-350,000 years ago</a> in <a href="https://www.nature.com/articles/s41586-019-1714-1">Southern Africa</a>: <em>Homo sapiens</em>. </p>
<p>The spread of modern humans out of Africa has caused a <a href="https://www.theguardian.com/environment/2017/jul/10/earths-sixth-mass-extinction-event-already-underway-scientists-warn">sixth mass extinction</a>, a greater than 40,000-year event extending from the disappearance of Ice Age mammals to the destruction of rainforests by civilisation today. But were other humans the first casualties? </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/302000/original/file-20191115-66925-p0qco1.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/302000/original/file-20191115-66925-p0qco1.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/302000/original/file-20191115-66925-p0qco1.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/302000/original/file-20191115-66925-p0qco1.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/302000/original/file-20191115-66925-p0qco1.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/302000/original/file-20191115-66925-p0qco1.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=500&fit=crop&dpr=1 754w, https://images.theconversation.com/files/302000/original/file-20191115-66925-p0qco1.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=500&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/302000/original/file-20191115-66925-p0qco1.png?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"></a>
<figcaption>
<span class="caption">Human evolution.</span>
<span class="attribution"><span class="source">Nick Longrich</span></span>
</figcaption>
</figure>
<p>We are a uniquely dangerous species. We hunted <a href="https://www.amazon.com/Quaternary-Extinctions-Prehistoric-Paul-Martin/dp/0816511004/ref=sr_1_3?keywords=prehistoric+extinctions+martin&qid=1573645985&sr=8-3">wooly mammoths, ground sloths</a> and <a href="https://science.sciencemag.org/content/287/5461/2250.full?_ga=2.156387641.382776719.1573642705-28080894.1573476299">moas</a> to extinction. We destroyed plains and forests for farming, modifying over <a href="https://www.geosociety.org/gsatoday/archive/22/12/article/i1052-5173-22-12-4.htm">half the planet’s land area</a>. We altered the planet’s climate. But we are most dangerous to other human populations, because we compete for resources and land.</p>
<p>History is full of examples of people warring, displacing and wiping out other groups over territory, from Rome’s destruction of Carthage, to the American conquest of the West and the British colonisation of Australia. There have also been recent genocides and ethnic cleansing in <a href="https://theconversation.com/remembering-srebrenica-more-than-20-years-on-99122">Bosnia</a>, Rwanda, <a href="https://theconversation.com/islamic-states-genocidal-crimes-demand-justice-how-can-it-be-done-97646">Iraq</a>, Darfur and <a href="https://theconversation.com/rohingya-crisis-this-is-what-genocide-looks-like-83924">Myanmar</a>. Like language or tool use, a capacity for and tendency to engage in genocide is arguably an intrinsic, <a href="https://www.amazon.com/Third-Chimpanzee-Evolution-Future-Animal/dp/0060845503/ref=sr_1_1?keywords=the+third+chimpanzee&qid=1573645399&sr=8-1">instinctive part of human nature</a>. There’s little reason to think that early <em>Homo sapiens</em> were less territorial, less violent, less intolerant – less human.</p>
<p>Optimists have painted early hunter-gatherers as peaceful, <a href="https://theconversation.com/explainer-the-myth-of-the-noble-savage-55316">noble savages</a>, and have argued that our culture, not our nature, creates violence. But field studies, historical accounts, and archaeology <a href="https://www.amazon.com/Constant-Battles-Why-We-Fight/dp/0312310900/ref=sr_1_1?keywords=constant+battles&qid=1573829278&sr=8-1">all show</a> that war in <a href="https://www.amazon.com/War-Before-Civilization-Peaceful-Savage/dp/0195119126">primitive cultures was intense, pervasive and lethal</a>. Neolithic weapons such as clubs, spears, axes and bows, combined with guerrilla tactics like raids and ambushes, were devastatingly effective. Violence was the leading cause of death among men in these societies, and wars saw higher casualty levels per person than World Wars I and II. </p>
<p>Old bones and artefacts show this violence is ancient. The 9,000-year-old Kennewick Man, from North America, has a spear point embedded in his pelvis. The 10,000-year-old <a href="https://www.nature.com/articles/nature16477">Nataruk site</a> in Kenya documents the brutal massacre of at least 27 men, women, and children. </p>
<p>It’s unlikely that the other human species were much more peaceful. The existence of <a href="https://www.nature.com/articles/nature13727">cooperative violence in male chimps</a> suggests that war predates the evolution of humans. Neanderthal skeletons show <a href="https://www.nature.com/articles/s41586-018-0696-8">patterns</a> of <a href="https://www.pnas.org/content/99/9/6444.short">trauma</a> consistent with warfare. But sophisticated weapons likely gave <em>Homo sapiens</em> a military <a href="http://www.paleoanthro.org/media/journal/content/PA20100100.pdf">advantage</a>. The arsenal of early <em>Homo sapiens</em> probably included <a href="https://www.sciencedirect.com/science/article/pii/S030544030500230X">projectile weapons</a> like javelins and <a href="http://digitallibrary.amnh.org/bitstream/handle/2246/2613/N2403.pdf?sequence=1">spear-throwers</a>, throwing sticks and <a href="https://www.nature.com/articles/nature16477">clubs</a>.</p>
<p>Complex tools and culture would also have helped us efficiently harvest a wider range of animals and plants, feeding larger tribes, and giving our species a strategic advantage in numbers.</p>
<h2>The ultimate weapon</h2>
<p>But cave <a href="https://theconversation.com/borneo-cave-discovery-is-the-worlds-oldest-rock-art-in-southeast-asia-106252?fbclid=IwAR38kVzZ5Pa1zSZH7ZGWz1jFwJBRt_m035lvW-H6coqc8evaHWD1Ba6HisI">paintings</a>, <a href="https://www.nature.com/articles/nature07995">carvings</a>, and <a href="https://www.nature.com/articles/nature08169">musical instruments</a> hint at something far more dangerous: a sophisticated capacity for abstract thought and communication. The ability to cooperate, plan, <a href="https://www.amazon.com/War-Carl-von-Clausewitz-ebook/dp/B005R9EB68/ref=sr_1_1?keywords=clausewitz+on+war&qid=1573644303&s=digital-text&sr=1-1">strategise</a>, <a href="http://www.gutenberg.org/ebooks/1232">manipulate</a> and <a href="https://www.amazon.com/Art-War-Sun-Tzu-ebook/dp/B07YRX3MBM/ref=sr_1_2?keywords=sun+tzu+giles&qid=1573644250&s=digital-text&sr=1-2">deceive</a> may have been our ultimate weapon.</p>
<p>The incompleteness of the fossil record makes it hard to test these ideas. But in Europe, the only place with a relatively complete archaeological record, fossils show that within <a href="https://www.nature.com/articles/nature13621">a few thousand years</a> of our arrival , Neanderthals vanished. Traces of <a href="https://science.sciencemag.org/content/328/5979/710/tab-pdf">Neanderthal DNA in some Eurasian people</a> prove we didn’t just replace them after they went extinct. We met, and we mated.</p>
<p>Elsewhere, DNA tells of other encounters with archaic humans. East Asian, Polynesian and Australian groups have <a href="https://www.nature.com/articles/nature09710">DNA</a> from <a href="https://www.cell.com/cell/fulltext/S0092-8674(19)30218-1">Denisovans</a>. DNA from <a href="https://www.nature.com/articles/ng.3621#ref23">another species</a>, possibly <em>Homo erectus</em>, occurs in many Asian people. African genomes <a href="https://www.pnas.org/content/108/37/15123">show traces of DNA</a> from yet another <a href="https://www.sciencedirect.com/science/article/pii/S0092867412008318">archaic species</a>. The fact that we interbred with these other species proves that they disappeared only after encountering us. </p>
<p>But why would our ancestors wipe out their relatives, causing a mass extinction – or, perhaps more accurately, a mass genocide?</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/301300/original/file-20191112-178506-5fhhk2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/301300/original/file-20191112-178506-5fhhk2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=639&fit=crop&dpr=1 600w, https://images.theconversation.com/files/301300/original/file-20191112-178506-5fhhk2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=639&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/301300/original/file-20191112-178506-5fhhk2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=639&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/301300/original/file-20191112-178506-5fhhk2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=803&fit=crop&dpr=1 754w, https://images.theconversation.com/files/301300/original/file-20191112-178506-5fhhk2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=803&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/301300/original/file-20191112-178506-5fhhk2.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">13,000-year-old spear points from Colorado.</span>
<span class="attribution"><span class="source">Chip Clark, Smithsonian Institution</span></span>
</figcaption>
</figure>
<p>The answer lies in <a href="https://www.amazon.com/Constant-Battles-Why-We-Fight/dp/0312310900/ref=sr_1_1?keywords=constant+battles&qid=1573829278&sr=8-1">population growth</a>. Humans reproduce exponentially, like all species. Unchecked, we historically <a href="http://www.gutenberg.org/ebooks/4239">doubled our numbers every 25 years</a>. And once humans became cooperative hunters, we had no predators. Without predation controlling our numbers, and little family planning beyond <a href="http://www.gutenberg.org/ebooks/4239">delayed marriage</a> and <a href="https://www.annualreviews.org/doi/pdf/10.1146/annurev.es.06.110175.000543">infanticide</a>, populations grew to exploit the available resources.</p>
<p>Further growth, or food shortages caused by drought, harsh winters or overharvesting resources <a href="https://www.amazon.com/Constant-Battles-Why-We-Fight/dp/0312310900/ref=sr_1_1?keywords=constant+battles&qid=1573829278&sr=8-1">would inevitably lead tribes into conflict</a> over food and foraging territory. Warfare became a check on population growth, perhaps the most important one.</p>
<p>Our elimination of other species probably wasn’t a planned, coordinated effort of the sort practised by civilisations, but a war of attrition. The end result, however, was just as final. Raid by raid, ambush by ambush, valley by valley, modern humans would have worn down their enemies and taken their land. </p>
<p>Yet the extinction of Neanderthals, at least, took a long time – thousands of years. This was partly because early <em>Homo sapiens</em> lacked the advantages of later conquering civilisations: <a href="https://www.amazon.com/Third-Chimpanzee-Evolution-Future-Animal/dp/0060845503/ref=sr_1_1?keywords=the+third+chimpanzee&qid=1573645399&sr=8-1">large numbers, supported by farming</a>, and <a href="https://www.amazon.com/Plagues-Peoples-William-McNeill-ebook/dp/B0047747QK/ref=sr_1_1?keywords=plagues+and+peoples&qid=1573645434&sr=8-1">epidemic diseases like smallpox, flu, and measles</a> that <a href="https://theconversation.com/european-colonisation-of-the-americas-killed-10-of-world-population-and-caused-global-cooling-110549">devastated their opponents</a>. But while Neanderthals lost the war, to hold on so long they must have fought and won many battles against us, suggesting a level of intelligence close to our own.</p>
<p>Today we look up at the stars and wonder if we’re <a href="https://theconversation.com/evolution-tells-us-we-might-be-the-only-intelligent-life-in-the-universe-124706">alone in the universe</a>. In <a href="https://www.amazon.com/Hobbit-Lord-Rings-Fellowship-Towers/dp/0345538374/ref=sr_1_2?keywords=the+lord+of+the+rings&qid=1573645527&sr=8-2">fantasy</a> and <a href="https://www.imdb.com/title/tt0060028/">science fiction</a>, we wonder what it might be like to meet other intelligent species, like us, but not us. It’s profoundly sad to think that we once did, and now, because of it, they’re gone.</p><img src="https://counter.theconversation.com/content/126638/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nicholas R. Longrich 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>300,000 years ago, there were lots of different species of human. Now it’s only us – and we’re probably the reason why.Nicholas R. Longrich, Senior Lecturer, Paleontology and Evolutionary Biology, University of BathLicensed as Creative Commons – attribution, no derivatives.