tag:theconversation.com,2011:/fr/topics/origins-of-life-9478/articlesOrigins of Life – The Conversation2023-11-14T19:06:34Ztag:theconversation.com,2011:article/2168432023-11-14T19:06:34Z2023-11-14T19:06:34ZDid this chemical reaction create the building blocks of life on Earth?<figure><img src="https://images.theconversation.com/files/559203/original/file-20231114-21-xy4zlm.jpg?ixlib=rb-1.1.0&rect=53%2C0%2C6000%2C3997&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/molecular-model-messenger-ribonucleic-acid-mrna-2202150169">Shutterstock</a></span></figcaption></figure><p>How did life begin? How did chemical reactions on the early Earth create complex, self-replicating structures that developed into living things as we know them?</p>
<p>According to one school of thought, before the current era of DNA-based life, there was a kind of molecule called RNA (or ribonucleic acid). RNA – which is still a crucial component of life today – can replicate itself and catalyse other chemical reactions.</p>
<p>But RNA molecules themselves are made from smaller components called ribonucleotides. How would these building blocks have formed on the early Earth, and then combined into RNA?</p>
<p>Chemists like me are trying to recreate the chain of reactions required to form RNA at the dawn of life, but it’s a challenging task. We know whatever chemical reaction created ribonucleotides must have been able to happen in the messy, complicated environment found on our planet billions of years ago.</p>
<p>I have been studying whether “autocatalytic” reactions may have played a part. These are reactions that produce chemicals that encourage the same reaction to happen again, which means they can sustain themselves in a wide range of circumstances. </p>
<p>In <a href="https://pubs.rsc.org/en/content/articlelanding/2023/SC/D3SC03185C">our latest work</a>, my colleagues and I have integrated autocatalysis into a well-known chemical pathway for producing the ribonucleotide building blocks, which could have plausibly happened with the simple molecules and complex conditions found on the early Earth.</p>
<h2>The formose reaction</h2>
<p>Autocatalytic reactions play crucial roles in biology, from regulating our heartbeats to forming patterns on seashells. In fact, the replication of life itself, where one cell takes in nutrients and energy from the environment to produce two cells, is a particularly complicated example of autocatalysis.</p>
<p>A chemical reaction called the formose reaction, first discovered in 1861, is one of the best examples of an autocatalytic reaction that could have happened on the early Earth.</p>
<figure class="align-right ">
<img alt="An old black and white photograph of a bald, bearded man wearing an old-fashioned coat." src="https://images.theconversation.com/files/559204/original/file-20231114-27-xbwbu9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/559204/original/file-20231114-27-xbwbu9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=951&fit=crop&dpr=1 600w, https://images.theconversation.com/files/559204/original/file-20231114-27-xbwbu9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=951&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/559204/original/file-20231114-27-xbwbu9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=951&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/559204/original/file-20231114-27-xbwbu9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1196&fit=crop&dpr=1 754w, https://images.theconversation.com/files/559204/original/file-20231114-27-xbwbu9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1196&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/559204/original/file-20231114-27-xbwbu9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1196&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">The formose reaction was discovered by Russian chemist Alexander Butlerov in 1861.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Alexander_Butlerov#/media/File:Butlerov,_A._M._1828-1886.jpg">Wikimedia</a></span>
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<p>In essence, the formose reaction starts with one molecule of a simple compound called glycolaldehyde (made of hydrogen, carbon and oxygen) and ends with two. The mechanism relies on a constant supply of another simple compound called formaldehyde. </p>
<p>A reaction between glycolaldehyde and formaldehyde makes a bigger molecule, splitting off fragments that feed back into the reaction and keep it going. However, once the formaldehyde runs out, the reaction stops, and the products start to degrade from complex sugar molecules into tar.</p>
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<p>The formose reaction shares some common ingredients with a well-known chemical pathway to make ribonucleotides, known as the Powner–Sutherland pathway. However, until now no one has tried to connect the two – with good reason.</p>
<p>The formose reaction is notorious for being “unselective”. This means it produces a lot of useless molecules alongside the actual products you want.</p>
<h2>An autocatalytic twist in the pathway to ribonucleotides</h2>
<p>In our study, we tried adding another simple molecule called cyanamide to the formose reaction. This makes it possible for some of the molecules made during the reaction to be “siphoned off” to produce ribonucleotides.</p>
<p>The reaction still does not produce a large quantity of ribonucleotide building blocks. However, the ones it does produce are more stable and less likely to degrade.</p>
<p>What’s interesting about our study is the integration of the formose reaction and ribonucleotide production. Previous investigations have studied each separately, which reflects how chemists usually think about making molecules.</p>
<figure class="align-center ">
<img alt="A photo showing a drop of blue liquid about to fall from a pipette into one of several empty test tubes." src="https://images.theconversation.com/files/559206/original/file-20231114-26-ceqaiv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/559206/original/file-20231114-26-ceqaiv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/559206/original/file-20231114-26-ceqaiv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/559206/original/file-20231114-26-ceqaiv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/559206/original/file-20231114-26-ceqaiv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/559206/original/file-20231114-26-ceqaiv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/559206/original/file-20231114-26-ceqaiv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Chemistry often focuses on clean, efficient and productive reactions, rather than messy combinations.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/science-laboratory-test-tubes-equipment-1898590327">Shutterstock</a></span>
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<p>Generally speaking, chemists tend to avoid complexity so as to maximise the quantity and purity of a product. However, this reductionist approach can prevent us from investigating dynamic interactions between different chemical pathways.</p>
<p>These interactions, which happen everywhere in the real world outside the lab, are arguably the bridge between chemistry and biology. </p>
<h2>Industrial applications</h2>
<p>Autocatalysis also has industrial applications. When you add cyanamide to the formose reaction, another of the products is a compound called 2-aminooxazole, which is used in chemistry research and the production of many pharmaceuticals.</p>
<p>Conventional 2-aminooxazole production often uses cyanamide and glycolaldehyde, the latter of which is expensive. If it can be made using the formose reaction, only a small amount of glycolaldehyde will be needed to kickstart the reaction, cutting costs.</p>
<p>Our lab is currently optimising this procedure in the hope we can manipulate the autocatalytic reaction to make common chemical reactions cheaper and more efficient, and their pharmaceutical products more accessible. Maybe it won’t be as big a deal as the creation of life itself, but we think it could still be worthwhile.</p>
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Read more:
<a href="https://theconversation.com/weve-been-wrong-about-the-origins-of-life-for-90-years-63744">We've been wrong about the origins of life for 90 years</a>
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<img src="https://counter.theconversation.com/content/216843/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Quoc Phuong Tran 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>Scientists have known about the ‘formose reaction’ for 160 years. New research shows how it could have played a key role in the creation of life.Quoc Phuong Tran, PhD Candidate in Prebiotic Chemistry, UNSW SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2166392023-11-09T19:09:59Z2023-11-09T19:09:59ZA new theory linking evolution and physics has scientists baffled – but is it solving a problem that doesn’t exist?<figure><img src="https://images.theconversation.com/files/558544/original/file-20231109-17-qp5bsl.jpg?ixlib=rb-1.1.0&rect=10%2C42%2C7130%2C4710&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/leafless-tree-with-water-droplets-TYnHpsuAkBg">Tim Johnson / Unsplash</a></span></figcaption></figure><p>In October, a paper titled “<a href="https://www.nature.com/articles/s41586-023-06600-9">Assembly theory explains and quantifies selection and evolution</a>” appeared in the top science journal Nature. The authors – a team led by Lee Cronin at the University of Glasgow and Sara Walker at Arizona State University – claim their theory is an “interface between physics and biology” which explains how complex biological forms can evolve.</p>
<p>The paper provoked strong responses. On the one hand were headlines like “<a href="https://www.sciencealert.com/assembly-theory-bold-new-theory-of-everything-could-unite-physics-and-evolution">Bold New ‘Theory of Everything’ Could Unite Physics And Evolution</a>”.</p>
<p>On the other were reactions from scientists. One evolutionary biologist <a href="https://twitter.com/baym/status/1710815658890432679">tweeted</a> “after multiple reads I still have absolutely no idea what [this paper] is doing”. Another <a href="https://twitter.com/Irishpalaeo/status/1712450672476512424">said</a> “I read the paper and I feel more confused […] I think reading that paper has made me forget my own name.”</p>
<p>As a biologist who studies evolution, I felt I had to read the paper myself. Was assembly theory really the radical new paradigm its authors suggested? Or was it the “<a href="https://twitter.com/AdamRutherford/status/1711160807453569404">abject wankwaffle</a>” its critics decried?</p>
<h2>Hackle-raising claims</h2>
<p>When I sat down to read the paper, the very first sentence of the abstract had my hackles up: </p>
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<p>Scientists have grappled with reconciling biological evolution with the immutable laws of the Universe defined by physics.</p>
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<p>I had no idea we scientists grappled with this. No biologist I know has a problem with the laws of physics or sees any problem with reconciling them with evolution. </p>
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Read more:
<a href="https://theconversation.com/life-modern-physics-cant-explain-it-but-our-new-theory-which-says-time-is-fundamental-might-203129">Life: modern physics can't explain it – but our new theory, which says time is fundamental, might</a>
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<p>The abstract goes on to note that the laws of physics do not predict “life’s origin, evolution and the development of human culture and technology”, and claims we need a “new approach” to understand “how diverse, open-ended forms can emerge from physics without an inherent design blueprint”.</p>
<p>The complaint that biological evolution seems incompatible with the laws of physics, taken with the use of loaded terms like “design blueprint”, is reminiscent of creationist arguments against evolution. No wonder the blood pressure of evolutionary biologists was spiking.</p>
<p>In the words of <a href="https://www.nature.com/articles/s41586-023-06600-9#comment-6296992737">one Nature commenter</a>: “Why so many creationist tropes in the first few sentences?”</p>
<h2>Biology and physics</h2>
<p>Before I go further, I should note that I may, along with some of scientists quoted above, not fully understand the aim of the paper. But I have problems with what I do understand of it. </p>
<p>First of all, the claim that evolution is at odds with the immutable laws of physics does not seem to be supported. </p>
<p>The paper says “the open-ended generation of novelty does not fit cleanly in the paradigmatic frameworks of either biology or physics”, which doesn’t seem to make much sense. </p>
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<img alt="A microscope photo of fluorescent cells" src="https://images.theconversation.com/files/558547/original/file-20231109-15-kojsc4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/558547/original/file-20231109-15-kojsc4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/558547/original/file-20231109-15-kojsc4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/558547/original/file-20231109-15-kojsc4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/558547/original/file-20231109-15-kojsc4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/558547/original/file-20231109-15-kojsc4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/558547/original/file-20231109-15-kojsc4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Is there a conflict between biology and physics that needs to be explained?</span>
<span class="attribution"><a class="source" href="https://unsplash.com/photos/a-close-up-of-a-cell-phone-case-sIqWYiNLiJU">National Cancer Institute / Unsplash</a></span>
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<p>In the paradigm of biology, we understand there is a variation in biological forms through genetic drift, mutation and selection. Does this <em>need</em> to “fit the paradigm of physics”, as long as it doesn’t break any laws of physics?</p>
<p>Another troubling statement: “To comprehend how diverse, open-ended forms can emerge from physics without an inherent design blueprint, a new approach to understanding and quantifying selection is necessary.” </p>
<p>Is it? One of the tenets of evolutionary theory is that there is no “teleology” – no goal or aimed-for endpoint – in the process. So how could there be a “design blueprint”? Why would its absence need to be explained?</p>
<h2>Putting numbers on the odds of evolution</h2>
<p>So what is assembly theory trying to do? <a href="https://twitter.com/leecronin/status/1711356692720501103">According to Cronin</a>, it “aims to explain selection & evolution before biology”; as such its goal is a theory that unifies inert and living matter and seeks to explain their complexity or otherwise, in the same way.</p>
<p>The paper itself says it is a “framework that does not alter the laws of physics, but redefines the concept of an ‘object’ on which these laws act”. </p>
<blockquote>
<p>[Assembly theory] conceptualizes objects not as point particles, but as entities defined by their possible formation histories. This allows objects to show evidence of selection, within well-defined boundaries of individuals or selected units. </p>
</blockquote>
<p>The “object” in assembly theory is then what “laws of physics” act on. For any object, we can calculate its “assembly index”, a number that measures how complex the object would be to make. </p>
<p>Any object that is both abundant and has a high assembly index is unlikely to have arisen by chance, so it must be a product of evolution and selection. This, in itself, is neither problematic nor new – apart from this calculated “index”.</p>
<p>How do we figure out that assembly index? We count the number of steps it would take to build a molecule, say, or a bodily organ, or a whole organism. The higher the index, the more likely it is to have evolved. </p>
<p>So assembly theory is an attempt to quantify the complexity of something and the likelihood of it having evolved. </p>
<h2>A problem that doesn’t exist?</h2>
<p>Is this useful? It’s hard to say. </p>
<p>For one thing, it implies there is only one pathway to produce a complicated (high assembly index) object such as a biochemical molecule, which is simply not the case.</p>
<p>Also, as <a href="https://twitter.com/professor_dave/status/1710914156612710503">another scientist pointed out</a>: </p>
<blockquote>
<p>it’s obvious that if a molecule is complex and there are lots of copies of it, then it likely emerged from some process of evolution. And most chemists could spot such cases without the need for assembly theory. Although trying to put numbers on it is very neat.</p>
</blockquote>
<p>My own feeling is that this is a poorly written paper, as evidenced by the inability of many biologists to understand what it is trying to do, and much of the negative reaction to the work springs from the hard-to-follow framing and use of phrases that echo creationist talking points. </p>
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Read more:
<a href="https://theconversation.com/physics-has-long-failed-to-explain-life-but-were-testing-a-groundbreaking-new-theory-in-the-lab-215636">Physics has long failed to explain life – but we're testing a groundbreaking new theory in the lab</a>
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<p>As for assembly theory itself, it seems to have been <a href="https://www.quantamagazine.org/a-new-theory-for-the-assembly-of-life-in-the-universe-20230504/">developed</a> in the course of Cronin and Walker’s efforts to find a general way to <a href="https://www.nature.com/articles/s41467-021-23258-x">recognise signs of life on alien planets</a>, and even <a href="https://www.mdpi.com/1099-4300/24/7/884">create artificial life</a>. And perhaps, in those contexts, it may prove useful.</p>
<p>However, as a sweeping new paradigm aiming to unify evolution and physics, assembly theory appears – to me and many others – to be addressing a problem that does not exist.</p><img src="https://counter.theconversation.com/content/216639/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Bill Bateman 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>‘Assembly theory’ aims to explain evolution without biology. Is it a dazzling breakthrough or an attempt to answer questions nobody asked?Bill Bateman, Associate professor, Curtin UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1904962022-09-19T12:21:17Z2022-09-19T12:21:17ZSuper-Earths are bigger, more common and more habitable than Earth itself – and astronomers are discovering more of the billions they think are out there<figure><img src="https://images.theconversation.com/files/484712/original/file-20220914-4859-4nvzdu.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C3892%2C2125&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Astronomers think the most likely place to find life in the galaxy is on super-Earths, like Kepler-69c, seen in this artist's rendering.</span> <span class="attribution"><a class="source" href="http://www.nasa.gov/mission_pages/kepler/multimedia/images/kepler-69c.html">NASA Ames/JPL-CalTech</a></span></figcaption></figure><p>Astronomers now routinely discover <a href="https://exoplanets.nasa.gov/">planets orbiting stars outside of the solar system</a> – they’re called exoplanets. But in summer 2022, teams working on NASA’s <a href="https://www.nasa.gov/tess-transiting-exoplanet-survey-satellite">Transiting Exoplanet Survey Satellite</a> found a few particularly interesting planets orbiting in the habitable zones of their parent stars.</p>
<p>One planet is <a href="https://www.npr.org/2022/09/07/1121465588/new-planet-super-earth-life-nasa">30% larger than Earth</a> and orbits its star in less than three days. The other is <a href="https://exoplanets.nasa.gov/news/1710/discovery-alert-intriguing-new-super-earth-could-get-a-closer-look/">70% larger than the Earth</a> and might host a deep ocean. These two exoplanets are <a href="https://exoplanets.nasa.gov/what-is-an-exoplanet/planet-types/super-earth/">super-Earths</a> – more massive than the Earth but smaller than ice giants like Uranus and Neptune.</p>
<p>I’m a <a href="https://scholar.google.com/citations?user=OrRLRQ4AAAAJ&hl=en">professor of astronomy</a> who studies galactic cores, distant galaxies, <a href="https://www.cambridge.org/core/books/living-cosmos/11D69005D09D25581AE4E6684EC8A3C1">astrobiology</a> and <a href="https://mitpress.mit.edu/9780262047661/worlds-without-end/">exoplanets</a>. I closely follow the search for planets that might host life.</p>
<p>Earth is still the only place in the universe scientists know to be home to life. It would seem logical to focus the search for life on Earth clones – <a href="https://www.space.com/30172-six-most-earth-like-alien-planets.html">planets with properties close to Earth’s</a>. But research has shown that the best chance astronomers have of finding life on another planet is likely to be on a super-Earth similar to the ones found recently.</p>
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<a href="https://images.theconversation.com/files/484702/original/file-20220914-13-irjlj2.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An image showing Earth and Neptune with a middle sized planet in between." src="https://images.theconversation.com/files/484702/original/file-20220914-13-irjlj2.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/484702/original/file-20220914-13-irjlj2.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=277&fit=crop&dpr=1 600w, https://images.theconversation.com/files/484702/original/file-20220914-13-irjlj2.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=277&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/484702/original/file-20220914-13-irjlj2.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=277&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/484702/original/file-20220914-13-irjlj2.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=348&fit=crop&dpr=1 754w, https://images.theconversation.com/files/484702/original/file-20220914-13-irjlj2.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=348&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/484702/original/file-20220914-13-irjlj2.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=348&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">A super-Earth is any rocky planet that is bigger than Earth and smaller than Neptune.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Exoplanet_Comparison_CoRoT-7_b.png#/media/File:Exoplanet_Comparison_CoRoT-7_b.png">Aldaron</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
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<h2>Common and easy to find</h2>
<p>Most super-Earths orbit cool dwarf stars, which are lower in mass and live much longer than the Sun. There are hundreds of cool dwarf stars for every star like the Sun, and scientists have found super-Earths orbiting <a href="http://www.inaf.it/en/inaf-news/billions-of-rocky-planets-in-the-habitable-zones-around-red-dwarfs">40% of cool dwarfs</a> they have looked at. Using that number, astronomers estimate that there are <a href="http://www.inaf.it/en/inaf-news/billions-of-rocky-planets-in-the-habitable-zones-around-red-dwarfs">tens of billions</a> of super-Earths in habitable zones where liquid water can exist in the Milky Way alone. Since all life on Earth uses water, water is thought to be critical for habitability.</p>
<p>Based on current projections, about a <a href="https://exoplanets.nasa.gov/what-is-an-exoplanet/planet-types/super-earth/">third of all exoplanets</a> are super-Earths, making them the most common type of exoplanet in the Milky Way. The nearest is only <a href="https://exoplanets.nasa.gov/news/1533/discovery-alert-a-new-super-earth-in-the-neighborhood-six-light-years-away/">six light-years away</a> from Earth. You might even say that our solar system is unusual since it does not have a planet with a mass between that of Earth and Neptune.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/484708/original/file-20220914-16744-zlu3u9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing how a planet passing in front of a star can dim the light." src="https://images.theconversation.com/files/484708/original/file-20220914-16744-zlu3u9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/484708/original/file-20220914-16744-zlu3u9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=187&fit=crop&dpr=1 600w, https://images.theconversation.com/files/484708/original/file-20220914-16744-zlu3u9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=187&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/484708/original/file-20220914-16744-zlu3u9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=187&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/484708/original/file-20220914-16744-zlu3u9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=235&fit=crop&dpr=1 754w, https://images.theconversation.com/files/484708/original/file-20220914-16744-zlu3u9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=235&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/484708/original/file-20220914-16744-zlu3u9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=235&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 exoplanets are discovered by looking for how they dim the light coming from their parent stars, so bigger planets are easier to find.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Planetary_transit.svg#/media/File:Planetary_transit.svg">Nikola Smolenski</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Another reason super-Earths are ideal targets in the search for life is that they’re much easier to <a href="https://sci.esa.int/web/exoplanets/-/60655-detection-methods">detect and study</a> than Earth-sized planets. There are two methods astronomers use to detect exoplanets. One looks for the gravitational effect of a planet on its parent star and the other looks for brief dimming of a star’s light as the planet passes in front of it. Both of these detection methods are easier with a bigger planet.</p>
<h2>Super-Earths are super habitable</h2>
<p>Over 300 years ago, German philosopher Gottfried Wilhelm Leibniz argued that Earth was the “<a href="https://www.gutenberg.org/files/17147/17147-h/17147-h.htm">best of all possible worlds</a>.” Leibniz’s argument was meant to address the question of why evil exists, but modern astrobiologists have explored a similar question by asking what makes a planet hospitable to life. It turns out that Earth is not the best of all possible worlds.</p>
<p>Due to Earth’s tectonic activity and changes in the brightness of the Sun, the climate has veered over time from ocean-boiling hot to planetwide, deep-freeze cold. Earth has been uninhabitable for humans and other larger creatures for most of its 4.5-billion-year history. Simulations suggest the long-term <a href="http://dx.doi.org/10.1038/s43247-020-00057-8">habitability of Earth was not inevitable</a>, but was a matter of chance. Humans are literally lucky to be alive.</p>
<p>Researchers have come up with a <a href="https://doi.org/10.1089/ast.2013.1088">list of the attributes</a> that make a planet very conducive to life. Larger planets are more likely to be geologically active, a feature that scientists think would <a href="https://www.geoscienze.unipd.it/influence-plate-tectonics-life-evolution-and-biodiversity-biogeodynamical-modeling">promote biological evolution</a>. So the most habitable planet would have roughly twice the mass of the Earth and be between 20% and 30% larger by volume. It would also have oceans that are shallow enough for light to stimulate life all the way to the seafloor and an average temperature of 77 degrees Fahrenheit (25 degrees Celsius). It would have an atmosphere thicker than the Earth’s that would act as an insulating blanket. Finally, such a planet would orbit a star older than the Sun to give life longer to develop, and it would have a strong magnetic field that <a href="https://www.eurekalert.org/news-releases/939605">protects against cosmic radiation</a>. Scientists think that these attributes combined will make a planet super habitable.</p>
<p>By definition, super-Earths have many of the attributes of a super habitable planet. To date, astronomers have discovered <a href="https://doi.org/10.1089/ast.2019.2161">two dozen super-Earth exoplanets</a> that are, if not the best of all possible worlds, theoretically more habitable than Earth.</p>
<p>Recently, there’s been an exciting addition to the inventory of habitable planets. Astronomers have <a href="https://doi.org/10.48550/arXiv.2009.12377">started discovering exoplanets</a> that have been <a href="https://www.eso.org/public/news/eso2120/">ejected from their star systems</a>, and there could be <a href="https://www.eso.org/public/news/eso2120/">billions of them</a> roaming the Milky Way. If a super-Earth is ejected from its star system and has a dense atmosphere and watery surface, it could <a href="https://universemagazine.com/en/life-on-super-earths-can-exist-for-84-billion-years/">sustain life for tens of billions of years</a>, far longer than life on Earth could persist before the Sun dies.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/484711/original/file-20220914-4859-utbv87.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A watery world in front of a dim star." src="https://images.theconversation.com/files/484711/original/file-20220914-4859-utbv87.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/484711/original/file-20220914-4859-utbv87.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=328&fit=crop&dpr=1 600w, https://images.theconversation.com/files/484711/original/file-20220914-4859-utbv87.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=328&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/484711/original/file-20220914-4859-utbv87.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=328&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/484711/original/file-20220914-4859-utbv87.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=412&fit=crop&dpr=1 754w, https://images.theconversation.com/files/484711/original/file-20220914-4859-utbv87.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=412&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/484711/original/file-20220914-4859-utbv87.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=412&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">One of the newly discovered super-Earths, TOI-1452b, might be covered in a deep ocean and could be conducive to life.</span>
<span class="attribution"><a class="source" href="http://www.exoplanetes.umontreal.ca/an-extrasolar-world-covered-in-water/?lang=en">Benoit Gougeon, Université de Montréal</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Detecting life on super-Earths</h2>
<p>To detect life on distant exoplanets, astronomers will look for biosignatures, <a href="https://theconversation.com/to-search-for-alien-life-astronomers-will-look-for-clues-in-the-atmospheres-of-distant-planets-and-the-james-webb-space-telescope-just-proved-its-possible-to-do-so-184828">byproducts of biology</a> that are detectable in a planet’s atmosphere. </p>
<p>NASA’s James Webb Space Telescope was designed before astronomers had discovered exoplanets, so the telescope is not optimized for exoplanet research. But it is able to do some of this science and is scheduled to <a href="https://webbtelescope.org/contents/news-releases/2022/news-2022-017#section-id-2">target two potentially habitable super-Earths</a> in its first year of operations. Another set of super-Earths with massive oceans discovered in the past few years, as well as the planets discovered this summer, are also <a href="https://doi.org/10.3847/1538-4357/abfd9c">compelling targets for James Webb</a>. </p>
<p>But the best chances for finding signs of life in exoplanet atmospheres will come with the next generation of giant, ground-based telescopes: the <a href="https://elt.eso.org/science/exoplanets/#atmospheres">39-meter Extremely Large Telescope</a>, the <a href="https://www.tmt.org/">Thirty Meter Telescope</a> and the <a href="https://giantmagellan.org/">25.4-meter Giant Magellan Telescope</a>. These telescopes are all under construction and set to start collecting data by the end of the decade.</p>
<p>Astronomers know that the ingredients for life are out there, but habitable does not mean inhabited. Until researchers find evidence of life elsewhere, it’s possible that life on Earth was a unique accident. While there are many reasons why a habitable world <a href="https://doi.org/10.1098%2Frsta.2013.0082">would not have signs of life</a>, if, over the coming years, astronomers look at these super habitable super-Earths and find nothing, humanity may be forced to conclude that the universe is a lonely place.</p>
<p><em>Editor’s Note: The story has been updated to correct the size of the Giant Magellan Telescope.</em></p><img src="https://counter.theconversation.com/content/190496/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Impey receives funding from the National Science Foundation. </span></em></p>Newly discovered super-Earths add to the list of planets around other stars that offer the best chance of finding life. An astronomer explains what makes these super-Earths such excellent candidates.Chris Impey, University Distinguished Professor of Astronomy, University of ArizonaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1464072020-09-20T19:42:37Z2020-09-20T19:42:37ZIf there is life on Venus, how could it have got there? Origin of life experts explain<figure><img src="https://images.theconversation.com/files/358781/original/file-20200918-18-1xkxztj.jpg?ixlib=rb-1.1.0&rect=71%2C35%2C5919%2C3458&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>The <a href="https://theconversation.com/life-on-venus-traces-of-phosphine-may-be-a-sign-of-biological-activity-146093">recent discovery of phosphine</a> in the atmosphere of Venus is exciting, as it may serve as a potential sign of life (among other possible explanations). </p>
<p>The researchers, who <a href="https://www.nature.com/articles/s41550-020-1174-4">published their findings in Nature Astronomy</a>, couldn’t really explain how the phosphine got there. </p>
<p>They explored all conceivable possibilities, including lightning, volcanoes and even delivery by meteorites. But each source they modelled couldn’t produce the amount of phosphine detected.</p>
<p>Most phosphine in Earth’s atmosphere is produced by living microbes. So the possibility of life on Venus producing phosphine can’t be ignored. </p>
<p>But the researchers, led by UK astronomer Jane Greaves, say their discovery “is not robust evidence for life” on Venus. Rather, it’s evidence of “anomalous and unexplained chemistry”, of which biological processes are just one possible origin.</p>
<p>If life were to exist on Venus, how could it have come about? Exploring the origins of life on Earth might shed some light.</p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/life-on-venus-traces-of-phosphine-may-be-a-sign-of-biological-activity-146093">Life on Venus? Traces of phosphine may be a sign of biological activity</a>
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<h2>The ingredients for life (as we know it)</h2>
<p>Understanding how life formed on Earth not only helps us understand our own origins, but could also provide insight into the key ingredients needed for life, as we know it, to form. </p>
<p>The details around the origins of life on Earth are still shrouded in mystery, with <a href="https://www.scientificamerican.com/article/lifes-origins-by-land-or-sea-debate-gets-hot/">multiple competing scientific theories</a>. But most theories include a common set of environmental conditions considered vital for life. These are: </p>
<p><strong>Liquid water</strong></p>
<p>Water is needed to dissolve the molecules needed for life, to facilitate their chemical reactions. Although other solvents (such as methane) have been suggested to potentially support life, water is most likely. This is because it <a href="http://sitn.hms.harvard.edu/uncategorized/2019/biological-roles-of-water-why-is-water-necessary-for-life/">can dissolve a huge range of different molecules</a> and is found throughout the universe.</p>
<p><strong>Mild temperatures</strong> </p>
<p>Temperatures higher than 122°C destroy most complex organic molecules. This would make it almost impossible for carbon-based life to form in very hot environment. </p>
<p><strong>A process to concentrate molecules</strong> </p>
<p>As the origin of life would have required a large amount of organic molecules, a process to concentrate organics from the diluted surrounding environment would be required – either through absorption onto mineral surfaces, evaporation or floating on top of water in oily slicks. </p>
<p><strong>A complex natural environment</strong></p>
<p>For life to have originated, there would have had to be a complex natural environment wherein a diverse range of conditions (temperature, pH and salt concentrations) could create chemical complexity. Life itself is incredibly complex, so even the most primitive versions would need a complex environment to originate.</p>
<p><strong>Trace metals</strong></p>
<p>A range of trace metals, amassed through water-rock interactions, would be needed to promote the formation of organic molecules.</p>
<p>So if these are the conditions required for life, what does that tell us about the likelihood of life forming on Venus? </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/358787/original/file-20200918-14-6vka30.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Photo of Venus" src="https://images.theconversation.com/files/358787/original/file-20200918-14-6vka30.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/358787/original/file-20200918-14-6vka30.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=615&fit=crop&dpr=1 600w, https://images.theconversation.com/files/358787/original/file-20200918-14-6vka30.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=615&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/358787/original/file-20200918-14-6vka30.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=615&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/358787/original/file-20200918-14-6vka30.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=773&fit=crop&dpr=1 754w, https://images.theconversation.com/files/358787/original/file-20200918-14-6vka30.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=773&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/358787/original/file-20200918-14-6vka30.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=773&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Venus has 90 times the atmospheric pressure of Earth.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<h2>It’s unlikely today …</h2>
<p>The possibility of life as we know it forming on the surface of present-day Venus is incredibly low. An average surface temperature above 400°C means the surface can’t possibly have liquid water and this heat would also destroy most organic molecules. </p>
<p>Venus’s milder upper atmosphere, however, has temperatures low enough for water droplets to form and thus could potentially be suitable for the formation of life. </p>
<p>That said, this environment has its own limitations, such as clouds of sulfuric acid which would destroy any organic molecules not protected by a cell. For example, on Earth, molecules such as DNA are rapidly destroyed by acidic conditions, although some <a href="https://sciencing.com/types-bacteria-living-acidic-ph-9296.html">bacteria can survive</a> in extremely acidic environments.</p>
<p>Also, the constant falling of water droplets from Venus’s atmosphere down to its extremely hot surface would destroy any unprotected organic molecules in the droplets. </p>
<p>Beyond this, with no surfaces or mineral grains in the Venusian atmosphere on which organic molecules could concentrate, any chemical building blocks for life would be scattered through a diluted atmosphere – making it incredibly difficult for life to form. </p>
<h2>… but possibly less unlikely in the past</h2>
<p>Bearing all this in mind, if atmospheric phosphine is indeed a sign of life on Venus, there are three main explanations for how it could have formed. </p>
<p>Life may have formed on the planet’s surface when its conditions were very different to now. </p>
<p>Modelling suggests the surface of early Venus was very similar to early Earth, with lakes (or even oceans) of water and <a href="https://www.nasa.gov/feature/goddard/2016/nasa-climate-modeling-suggests-venus-may-have-been-habitable">mild conditions</a>. This was before a runaway greenhouse effect turned the planet into the hellscape it is today.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/358782/original/file-20200918-16-1s8z2gp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Computer generated surface view of Eistla Regio region on Venus." src="https://images.theconversation.com/files/358782/original/file-20200918-16-1s8z2gp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/358782/original/file-20200918-16-1s8z2gp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=467&fit=crop&dpr=1 600w, https://images.theconversation.com/files/358782/original/file-20200918-16-1s8z2gp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=467&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/358782/original/file-20200918-16-1s8z2gp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=467&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/358782/original/file-20200918-16-1s8z2gp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=587&fit=crop&dpr=1 754w, https://images.theconversation.com/files/358782/original/file-20200918-16-1s8z2gp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=587&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/358782/original/file-20200918-16-1s8z2gp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=587&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 is a computer-generated picture of the Eistla Regio region on Venus’s surface.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>If life formed back then, it might have adapted to spread into the clouds. Then, when intense climate change boiled the oceans away – killing all surface-based life – microbes in the clouds would have become the last outpost for life on Venus.</p>
<p>Another possibility is that life in Venus’s atmosphere (if there is any) came from Earth. </p>
<p>The planets of our inner solar system have been documented to exchange materials in the past. When meteorites crash into a planet, they can send that planet’s rocks hurtling into space where they occasionally intersect with the orbits of other planets.</p>
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<strong>
Read more:
<a href="https://theconversation.com/meteorites-from-mars-contain-clues-about-the-red-planets-geology-130104">Meteorites from Mars contain clues about the red planet's geology</a>
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<p>If this happened between Earth and Venus at some point, the rocks from Earth may have contained microbial life that could have adapted to Venus’s highly acidic clouds (similar to Earth’s acid-resistant bacteria).</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/358784/original/file-20200918-16-7blw0k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Rendered image of meteorite hitting Earth." src="https://images.theconversation.com/files/358784/original/file-20200918-16-7blw0k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/358784/original/file-20200918-16-7blw0k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=384&fit=crop&dpr=1 600w, https://images.theconversation.com/files/358784/original/file-20200918-16-7blw0k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=384&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/358784/original/file-20200918-16-7blw0k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=384&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/358784/original/file-20200918-16-7blw0k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=483&fit=crop&dpr=1 754w, https://images.theconversation.com/files/358784/original/file-20200918-16-7blw0k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=483&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/358784/original/file-20200918-16-7blw0k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=483&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">If rocks from Earth containing microbial life entered Venus’s orbit in the past, this life may have adapted to Venus’s atmospheric conditions.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>A truly alien explanation</h2>
<p>The third explanation to consider is that a truly alien form of life (life as we <em>don’t</em> know it) could have formed on Venus’s 400°C surface and survives there to this day. </p>
<p>Such a foreign life probably wouldn’t be carbon-based, as nearly all complex carbon molecules break down at extreme temperatures. </p>
<p>Although carbon-based life produces phosphine on Earth, it’s impossible to say <em>only</em> carbon-based life can produce phosphine. Therefore, even if totally alien life exists on Venus, it may produce molecules that are still recognisable as a potential sign of life. </p>
<p>It’s only through further missions and research that we can find out whether there is, or was, life on Venus. As prominent scientist Carl Sagan <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3114207/#:%7E:text=non%2Dlocal%20perception-,Introduction,et%20al.%2C%201999">once said</a>: “extraordinary claims require extraordinary evidence”. </p>
<p>Luckily, two of the <a href="https://www.nasa.gov/press-release/nasa-selects-four-possible-missions-to-study-the-secrets-of-the-solar-system">four finalist proposals</a> for NASA’s next round of funding for planetary exploration are focused on Venus.</p>
<p>These include VERITAS, an orbiter proposed to map the surface of Venus, and DAVINCI+, proposed to drop through the planet’s skies and sample different atmospheric layers on the way down.</p><img src="https://counter.theconversation.com/content/146407/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Luke Steller receives funding from a Research Training Program scholarship provided by the Australian government. </span></em></p><p class="fine-print"><em><span>Martin Van Kranendonk receives funding from the Australian Research Council and BHP. </span></em></p>Considering what we know about the key ingredients for life’s formation on Earth, here are three explanations for how this process may have occurred on our sister planet.Luke Steller, PhD Student, UNSW SydneyMartin Van Kranendonk, Professor and Head of School, UNSW SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1265682019-12-16T14:50:11Z2019-12-16T14:50:11ZSpotting alien life – how ‘microfossils’ can fool scientists<figure><img src="https://images.theconversation.com/files/307125/original/file-20191216-124022-8tpis0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Mircobe-like features in a meteorite – later shown to probably be non-biological.</span> <span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Allan_Hills_84001#/media/File:ALH84001_structures.jpg">NASA</a></span></figcaption></figure><p>Earth’s oldest fossils may be <a href="https://theconversation.com/how-we-discovered-the-worlds-oldest-fossils-73802">billions of years old</a> – although such claims are highly controversial. These kinds of discoveries usually start with finding what appear to be preserved outlines of microscopic lifeforms that look similar to microbe fossils found in much younger rocks. The rewards for exploring truly ancient life are high, because as well as providing a glimpse at some of the earliest life on Earth, these microfossils can also act as a model for what evidence we might find for life on other planets such as Mars. </p>
<p>But how do we know these really are fossils and not some other non-organic geological feature? In 1996, Nasa scientists claimed micro-structures in a meteorite could be the <a href="https://www.space.com/33690-allen-hills-mars-meteorite-alien-life-20-years.html">remains of extraterrestrial life</a>, but further investigation suggested the structures didn’t have biological origins after all.</p>
<p><a href="https://royalsocietypublishing.org/doi/10.1098/rspb.2019.2410">A recent study</a>, published in Royal Society B, has further examined this question by demonstrating how it is possible for some microfossil-like objects to form without any actual microbes. This study may lead to doubts about specific fossils. But ultimately it will help scientists focus their attention on the strongest and most likely case studies for the earliest evidence of life – on this planet or others.</p>
<p>Microbes don’t have easily fossilised hard parts like the bones or teeth of animals. Sometimes a geologist <a href="https://science.sciencemag.org/content/147/3658/563">may be lucky</a> and stumble across glassy silica deposits complete with entombed and immaculately preserved multi-billion-year-old microorganisms.</p>
<p>More commonly, we find some feature that at first glance could be a microfossil of a billion-year-old microscopic lifeform. But on closer inspection, we realise it is perhaps just be a “pseudofossil”, like a speck of microbe-shaped dirt or a lookalike mineral that grew in a crack in the rock. Just because it looks like a microbe doesn’t actually mean it’s a microbe.</p>
<p>To distinguish pseudofossils from real microfossils, geologists and astrobiologists look at the shape, structure and chemical composition of specimens. To know what we are looking for, we can compare these features to those from <a href="https://doi.org/10.1111/gbi.12292">modern fossilised microbes</a> in environments such as alkaline lakes, or from <a href="https://doi.org/10.1073/pnas.1405338111">uncontroversial well-preserved examples</a> from the older rock record. We can also conduct experiments to try to make microfossil-like objects without microbes and compare the results with purported ancient microfossil examples.</p>
<p>Sometimes microfossils are preserved as hair-like tubular filaments of organic carbon. Sometimes the organic carbon has long since disappeared and a microorganism-shaped hole in the rock is all that remains. And sometimes filaments of iron oxide have taken the shape of the organism. This last category includes some recent high-profile finds, including <a href="https://theconversation.com/how-we-discovered-the-worlds-oldest-fossils-73802">those from</a> 4-billion-year-old rocks in Canada.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/307124/original/file-20191216-124027-1uwzw3r.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/307124/original/file-20191216-124027-1uwzw3r.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=454&fit=crop&dpr=1 600w, https://images.theconversation.com/files/307124/original/file-20191216-124027-1uwzw3r.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=454&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/307124/original/file-20191216-124027-1uwzw3r.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=454&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/307124/original/file-20191216-124027-1uwzw3r.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=570&fit=crop&dpr=1 754w, https://images.theconversation.com/files/307124/original/file-20191216-124027-1uwzw3r.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=570&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/307124/original/file-20191216-124027-1uwzw3r.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=570&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">‘Chemical gardening’ can produce mineral features similar to those claimed to be microfossils.</span>
<span class="attribution"><a class="source" href="https://royalsocietypublishing.org/doi/10.1098/rspb.2019.2410">Sean McMahon/Royal Society</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The new study shows that not all hollow tubular filaments made of iron oxide are biogenic microfossils. In an experimental process known as “chemical gardening”, researcher Sean McMahon created a pocket of acidic fluid enclosed within a membrane, sat in a highly alkaline carbonate or silicate solution. </p>
<p>As the outer solution flowed into the pocket, it would grow and eventually rupture, ejecting a jet of the internal fluid that is then rapidly enclosed by a new, tube-like membrane. This process ultimately created complex arrangements of hollow tubular filaments that can superficially resemble shapes of microbial lifeforms.</p>
<h2>Looking like a microbe isn’t enough</h2>
<p>This study is another reminder that extraordinary claims, such as finding Earth’s oldest fossils or life on Mars, must be supported by extraordinary evidence. Finding a microfossil-like shape is no longer enough without <a href="https://api.research-repository.uwa.edu.au/portalfiles/portal/16165129/SP448_1709_1..pdf">supporting evidence</a> that might include three-dimensional high-resolution microscopy, chemical analysis and a thorough consideration of the context and alternatives. </p>
<p>In his paper, McMahon indeed contends that the reported 4-billion-year-old iron oxide filaments are more likely to be the result of fluids chemically reacting with the ancient seafloor than Earth’s oldest fossil lifeforms. </p>
<p>But this research also doesn’t write off the possibility of true ancient iron oxide microfossils or their use as a model for evidence for life on other planets. It is notable that while the chemical experiments reproduced some microfossil-like shapes, they didn’t reproduce other shapes we could use to help identify microscopic life, such as septate (partitioned) filaments with cell walls.</p>
<p>Ultimately, finding the answers to these fundamental questions of when and where life existed requires a long journey, and we still don’t know if we are nearly there yet.</p><img src="https://counter.theconversation.com/content/126568/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alexander Brasier does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>New research shows how rock features that look like fossilised microbes can form without life.Alexander Brasier, Senior Lecturer in Geology, University of AberdeenLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/945512018-05-28T21:49:46Z2018-05-28T21:49:46ZViruses can cause global pandemics, but where did the first virus come from?<p>Viruses such as <a href="https://www.cdc.gov/vhf/ebola/outbreaks/2014-west-africa/index.html">Ebola</a>, <a href="https://www.cdc.gov/flu/pandemic-resources/basics/past-pandemics.html">influenza</a> and <a href="https://www.theglobeandmail.com/news/world/zika-crisis-brazil/article36142168/">Zika</a> make headlines. They grab our attention with their potential to cause widespread disease and death. </p>
<p>But where did these viruses first come from?</p>
<p>Unlike bacteria, viruses aren’t living organisms — they can’t reproduce on their own. Instead, they hijack cells to multiply, spread and cause disease. </p>
<p>But what if it wasn’t always this way? </p>
<p>Scientists studying a so-called giant virus called a Tupanvirus (named for the South American Guarani God of Thunder) found that it, unlike the viruses we encounter today, had an almost complete machinery to take care of itself. </p>
<p>This recent discovery has refuelled the debate over the origin of viruses. </p>
<h2>Frozen viruses</h2>
<p>There is no physical fossil record of viruses like there is for the dinosaurs. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/220347/original/file-20180524-51095-174r2em.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/220347/original/file-20180524-51095-174r2em.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=586&fit=crop&dpr=1 600w, https://images.theconversation.com/files/220347/original/file-20180524-51095-174r2em.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=586&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/220347/original/file-20180524-51095-174r2em.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=586&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/220347/original/file-20180524-51095-174r2em.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=736&fit=crop&dpr=1 754w, https://images.theconversation.com/files/220347/original/file-20180524-51095-174r2em.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=736&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/220347/original/file-20180524-51095-174r2em.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=736&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Beautiful, but deadly. A colourized scanning electron micrograph magnified 20,000 times of Ebola virus particles (green) from a chronically infected African Green Monkey kidney cell (blue).</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Ebola_Virus_-_Electron_Micrograph.tiff">(BernbaumJG/Wikimedia Commons)</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>One way scientists detect viruses, and study their origins, is to look for their <a href="https://www.nature.com/scitable/definition/virus-308">genetic material</a> — molecules of DNA or RNA — in animal tissues and soil. </p>
<p>Even though the movies might have you believe otherwise, viral genetic material has never been detected in fossilized plant leaves or in insects trapped in amber. </p>
<p>However, some ancient viruses have been <a href="http://www.pnas.org/content/111/11/4274">detected in permafrost</a> in Siberia, and there are hopes of discovering more as <a href="https://www.independent.co.uk/news/science/global-warming-ancient-viruses-expose-dormant-thousands-fortitude-years-scientists-warn-a7719201.html">global warming continues</a> to thaw ground that has been frozen for thousands of years. Until then, we remain limited in our ability to precisely reconstruct the origin of viruses. </p>
<h2>Virus evolution</h2>
<p>Viruses are microscopic organisms that require a <a href="https://theconversation.com/explainer-what-is-a-virus-22902">living cell, often called a host, to multiply</a>. They largely consist of genetic material (either DNA or RNA) <a href="https://www.ncbi.nlm.nih.gov/books/NBK8174/">wrapped in a protein coat</a>. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/220351/original/file-20180524-117628-1pysmqe.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/220351/original/file-20180524-117628-1pysmqe.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/220351/original/file-20180524-117628-1pysmqe.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/220351/original/file-20180524-117628-1pysmqe.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/220351/original/file-20180524-117628-1pysmqe.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/220351/original/file-20180524-117628-1pysmqe.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/220351/original/file-20180524-117628-1pysmqe.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">An illustration of the hepatitis C virus.</span>
<span class="attribution"><a class="source" href="https://www.cdc.gov/nchhstp/newsroom/2016/hcv-perinatal.html">U.S. Centers for Disease Control and Prevention</a></span>
</figcaption>
</figure>
<p>These DNA and RNA sequences may change over time, accumulating modifications to the genetic code that favour the survival of the virus. Scientists can look at these genetic sequences to estimate how different viruses are related and how they may have evolved. </p>
<p>These studies have shown us that viruses do not have a <a href="https://www.sciencedirect.com/science/article/pii/S0923250809001065">single origin</a>; that is, they did not all arise from one single virus that changed and evolved into all the viruses we know today. Viruses probably have a number of independent origins, almost certainly at different times. </p>
<p>One assumption scientists make when considering the origin of viruses is that <a href="https://www.sciencedirect.com/science/article/pii/S1879625711001374">each co-evolved with its host</a>. For example, the herpes virus that infects humans evolves over time, adapting so that it will continue to retain the ability to infect human cells.</p>
<p>If we consider that all life forms on Earth began <a href="https://www.nature.com/news/how-life-emerged-from-deep-sea-rocks-1.12109">in the ocean</a>, then it’s reasonable to believe that viruses evolved with their hosts in the seas. As these creatures moved onto land and evolved, viruses also evolved and gained the ability to infect terrestrial organisms. </p>
<p><a href="https://www.sciencedaily.com/releases/2018/04/180404133510.htm">Earlier this year, scientists discovered</a> evidence that some viruses may be millions of years old and have been in existence since the first vertebrates existed. But this doesn’t explain the origin of viruses per se.</p>
<h2>Origin stories</h2>
<p><a href="https://genomebiology.biomedcentral.com/articles/10.1186/gb-2006-7-6-110">One theory</a> hypothesizes that viruses arose from circular DNA (also called a plasmid) that can replicate independently and move between cells, transferring genetic information from one organism to another. For example, some <a href="https://www.nytimes.com/2018/04/13/health/drug-resistant-typhoid-epidemic.html">plasmids carry the genes responsible for antibiotic drug resistance</a>. According to this theory, the plasmid escaped from cells and evolved in a way that allowed it to enter another cell to produce viruses.</p>
<p>Another theory suggests that viruses could have evolved from more complex free-living organisms, such as bacteria, or cells. A <a href="https://www.ncbi.nlm.nih.gov/pubmed/29328916#">recent study</a> showed that a protein called ARC that is important for memory in humans can form virus-like particles and transfer RNA between cells. Perhaps similar ancient proteins evolved to move from one organism to another. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/220348/original/file-20180524-51130-4dyg97.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/220348/original/file-20180524-51130-4dyg97.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/220348/original/file-20180524-51130-4dyg97.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/220348/original/file-20180524-51130-4dyg97.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/220348/original/file-20180524-51130-4dyg97.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/220348/original/file-20180524-51130-4dyg97.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/220348/original/file-20180524-51130-4dyg97.jpeg?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 Tupanvirus is a giant virus that can infect protists and amoebas, but are no threat to humans.</span>
</figcaption>
</figure>
<p>And then there was that recent discovery of <a href="https://www.nature.com/articles/s41467-018-03168-1">the giant Tupanvirus in a Brazilian soda lake</a>. Lakes like this are very salty and have a high pH. They may mimic the conditions of aquatic environments on Earth billions of years ago. </p>
<p>Tupanvirus has a more complete set of protein-making machinery than any other known virus. Unlike other viruses, it’s probably not as dependent on the cell it infects to replicate. This discovery has reignited interest in the theory that viruses arose from complex, free-living cells. </p>
<h2>Which came first?</h2>
<p>Both the theories above assume that cells existed before viruses, and that viruses potentially evolved in the presence of cells. </p>
<p>But there is yet another hypothesis that proposes that viruses existed first, even before cells. In a prehistoric world, viruses might have existed as self-sustaining entities, a sort of ancient machine that could probably reproduce its genetic material. Over time, these prehistoric viruses may have formed complex, organized structures that eventually evolved into <a href="https://www.sciencedirect.com/science/article/pii/S016895250500288X?via%3Dihub">cell-like entities</a>. </p>
<p>For the time being, these are only theories. The technology and resources we have today cannot confidently test these theories and identify the most plausible explanation for the origin of viruses.</p>
<p>An alternative — yet seemingly impossible — strategy would be to isolate or identify viruses in their primitive forms on other planets such as Mars. Staying on Earth seems like a more plausible approach. </p>
<p>The ongoing discovery of new viruses, like Tupanvirus or a <a href="http://www.pnas.org/content/111/11/4274">30,000-year-old </a> relative of giant DNA viruses (Pithovirus), may allow us to piece together the puzzle of their origins.</p><img src="https://counter.theconversation.com/content/94551/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Arinjay Banerjee receives funding from Saskatchewan Innovation and Opportunity and the Department of Veterinary Microbiology, University of Saskatchewan. </span></em></p><p class="fine-print"><em><span>Karen Mossman receives funding from the Canadian Institutes for Health Research and the Natural Sciences and Engineering Research Council of Canada. </span></em></p><p class="fine-print"><em><span>Vikram Misra receives funding from the Natural Sciences and Engineering Research Council (NSERC) of Canada through Discovery and CREATE grants. . </span></em></p>Recent discoveries of ancient viruses are helping scientists understand their origins.Arinjay Banerjee, Research Scientist and Principal Investigator, University of SaskatchewanKaren Mossman, Professor of Pathology and Molecular Medicine and Acting Vice President, Research, McMaster UniversityVikram Misra, Professor of Veterinary Microbiology, University of SaskatchewanLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/383132016-10-03T15:49:08Z2016-10-03T15:49:08ZBacterial cell walls, antibiotics and the origins of life<figure><img src="https://images.theconversation.com/files/138675/original/image-20160921-21683-sf7vdc.jpg?ixlib=rb-1.1.0&rect=64%2C47%2C899%2C555&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-205420948/stock-photo-petri-dish-with-bacteria-in-chemical-lab.html?src=bQN-DVdRTv4nmWol3S1AnQ-1-48">Shutterstock</a></span></figcaption></figure><p>Antonie van Leeuwenhoek, the 17th-century Dutch scientist, was the first person to see single-celled organisms through a microscope and describe what he called “animalcules”. Three centuries later we’ve learned a great deal about microorganisms such as bacteria, as a source of deadly diseases, <a href="https://theconversation.com/why-bacteria-could-be-the-answer-to-a-future-without-oil-35443">industrial enzymes</a> and wonderful wines <a href="http://onlinelibrary.wiley.com/doi/10.1002/jib.49/abstract">and beers</a>. We have also learned much about their design. Recent work on some of the most important structures in bacteria and what happens when we interfere with them, has even illuminated how the first lifeforms on Earth may have emerged.</p>
<p>Bacteria are single-celled organisms and the cell wall that surrounds their plasma membrane, is made from a polymer (rather like a mesh) of amino acids and sugars. This wall is a crucial structure for bacterial shape and division, which makes it a good target for antibiotics. Elements of it also trigger powerful immune responses against infections. So studying the cell wall can help us understand how pathogens evade our defences and how key antibiotics such as penicillin work, which might in turn inform us about how antibiotic resistance might arise and help us to keep our best antibiotics safe from overuse. </p>
<h2>Seeing is believing</h2>
<p>About 100 years ago, the invention of <a href="http://labtestsonline.org.uk/understanding/analytes/gram-stain/tab/test/">gram staining</a>, which uses special dyes to stain the cell wall, revealed at least two major classes of bacteria: gram-positive and gram-negative. Both include nasty pathogens, including resistant <em>Staphylococcus aureus</em> (MRSA) and <em>E.coli</em>.</p>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/76599/original/image-20150331-1266-1dad695.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/76599/original/image-20150331-1266-1dad695.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=747&fit=crop&dpr=1 600w, https://images.theconversation.com/files/76599/original/image-20150331-1266-1dad695.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=747&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/76599/original/image-20150331-1266-1dad695.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=747&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/76599/original/image-20150331-1266-1dad695.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=939&fit=crop&dpr=1 754w, https://images.theconversation.com/files/76599/original/image-20150331-1266-1dad695.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=939&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/76599/original/image-20150331-1266-1dad695.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=939&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">TB-causing bacteria.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/niaid/5149398678/in/photolist-8R31PQ-r6Qgk-a2Ltvs-nTpfYq-a2HASi-mWsNFo-a4NU78-dYC4gL-9CjrCJ-9y4sDM-moDLNK-8kGUwp-c9v3mj-9CjrAh-dKAcaM-c9uRwQ-poKGRx-bpxj9Z-56Gvtf-bpzxT4-eF9FGk-9y7kCs-a4RLqW-rdpprZ-92V71R-moEfpC-moDtY2-bxWoYu-56Cmwe-axZxvE-np8B7A-bwHUWH-pWTA41-dYBEXW-jZr1d-rEkWRZ-7NvZ1v-Dj4uW-rErNRx-6449sV-8JYeoi-9djCHD-CzdaJ-Czd9K-Czd8E-eeuc9-56CmMX-56GvKj-56GvJy-56CmH8">NIAID</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>But it is only recently, with advances in microscopic imaging methods, that we now see bacteria as immensely complex bio-machines. The average bacterium, for example, is capable of making about 5,000 different proteins, which form most of the important structures of the cell and carry out the majority of functions. FtsZ, the master regulator of division, forms an amazing <a href="https://www.umass.edu/microbio/chime/pipe/ftsz/present/ftszinvivo.htm">ring structure</a> at the precise centre of the cell, and MreB, which <a href="http://emboj.embopress.org/content/30/24/4856">determines the cylindrical shape of the cell wall</a>, forms arcs running around the edge of the cell. </p>
<p>Many bacteria are “rod” shaped, with two hemispherical caps or “poles”, and they grow by elongating this cylinder shape. To replicate, the cell grows inward, and then they divide – relying on that amazing FtsZ machine - always precisely at the mid-point of the cell. The whole process is incredibly efficient and it’s very rare to find cells that fail to divide properly.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/ejWlaCASKp4?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Replicating Bacillus subtilis.</span></figcaption>
</figure>
<p>The cell wall, which acts as a huge sac-like molecule that covers the whole cell surface, is really important in this growth and division. It’s a tough material but it also has to be capable of being enlarged continuously to enable growth, and then has to be precisely and elaborately moulded to enable cell division.</p>
<p>The invention of the cell wall was a key step in enabling bacteria to spread across the planet in the early phase of life on earth and virtually all modern bacteria have a wall made of more or less the same material. It must have evolved very early and the machinery responsible for making the wall has remained essentially unchanged since then. </p>
<h2>L-form bacteria and the origins of life</h2>
<p>For all the importance of this wall, then, it is a surprise that many bacteria are able to switch almost effortlessly into <a href="http://www.discoverymedicine.com/Gerald-J-Domingue/2010/09/23/demystifying-pleomorphic-forms-in-persistence-and-expression-of-disease-are-they-bacteria-and-is-peptidoglycan-the-solution/">a cell-wall deficient</a> “L-form” state. Not only do they become completely resistant to many antibiotics in this state but they may also be able to pass under the radar screen of our immune systems. </p>
<p>These special bacteria have been implicated in many chronic or persistent diseases but they are difficult to study as they are so fragile and slow growing. We wanted to know much more about their basic biology so <a href="http://www.nature.com/nature/journal/v457/n7231/full/nature07742.html">began working with</a> our favourite lab bacterium, <em>Bacillus subtilis</em>. Although they are difficult to culture, with some technical tricks <a href="https://elife-publishing-cdn.s3.amazonaws.com/04629/elife-04629-v2.pdf">we worked out how to do it</a> – and found that it’s surprisingly easy to generate the switch that turns them from normal bacteria to L-forms.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/KkurYIivp4U?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Special L-form Bacillus subtilis.</span></figcaption>
</figure>
<p>Our first remarkable finding was that these bacteria become completely independent of the normally essential division machinery. Instead, they use a strange and seemingly haphazard process, forming tubes that split into multiple small cells, or blebbing, in which bulges in the membrane extrude and detach to form new cells. This happens because they <a href="http://www.sciencedirect.com/science/article/pii/S0092867413001359">make an excess amount</a> of membrane, which increases their surface area relative to volume. </p>
<p>Understanding the strange behaviour of L-form bacteria might even give us insights into early simpler lifeforms. Many scientists <a href="http://www.the-scientist.com/?articles.view/articleNo/42472/title/On-the-Origins-of-Life/">are trying to work out</a> how life might have evolved and there are plausible ideas for how the early steps may have taken place. After the first chemical building blocks accumulated and <a href="https://en.wikipedia.org/wiki/RNA">RNA</a> developed to store information and act as a catalyst (followed later by DNA and proteins), there needed to be a container of some kind – the creation of the first cells, with replication-enabling enzymes inside – for natural selection to happen. The invention of a structure that replicators could surround themselves with to protect their “goods” would have been a key step in evolution. In modern cells, this structure is the complex plasma membrane supported by the cell wall. </p>
<p>At about the same time that we were uncovering the strange replication mechanism for L-forms, theoretical scientists and biophysicists were pondering how simple membrane sacs could be divided. <a href="http://arxiv.org/pdf/0903.3488.pdf">They showed</a> that all you need to do to a very simple membrane sac is increase its surface area, avoiding any leaks. If the surface area to volume ratio increases, the sacs undergo spontaneous changes in shape and even divide. This test-tube form of division looks remarkably similar to what we discovered the L-forms were doing. So, as it turns out, our work looking at bacteria has revealed a surprisingly simple mechanism for replication that may be a hangover from those used by some of the first cells on the planet.</p><img src="https://counter.theconversation.com/content/38313/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jeff Errington receives funding from the Wellcome Trust and the European Research Council. </span></em></p>Bacteria are single-celled organisms but you’d be fooled to think they weren’t also hugely complex.Jeff Errington, Director of the Centre for Bacterial Cell Biology, Newcastle UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/637442016-08-15T14:40:39Z2016-08-15T14:40:39ZWe’ve been wrong about the origins of life for 90 years<figure><img src="https://images.theconversation.com/files/134105/original/image-20160815-15267-j90ozr.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.flickr.com/photos/noaaphotolib/5014973927/">NOAA Photo Library/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>For nearly nine decades, science’s favorite explanation for the origin of life has been the “primordial soup”. This is the idea that life began from a series of chemical reactions in a warm pond on Earth’s surface, triggered by an external energy source such as lightning strike or ultraviolet (UV) light. But recent research adds weight to an alternative idea, that life arose deep in the ocean within warm, rocky structures called <a href="https://theconversation.com/study-tracing-ancestor-microorganisms-suggests-life-started-in-a-hydrothermal-environment-62924">hydrothermal vents</a>.</p>
<p>A study published last month <a href="http://www.nature.com/articles/nmicrobiol2016116">in Nature Microbiology</a> suggests the last common ancestor of all living cells fed on hydrogen gas in a hot iron-rich environment, much like that within the vents. Advocates of the conventional theory <a href="http://www.nytimes.com/2016/07/26/science/last-universal-ancestor.html?_r=0">have been sceptical</a> that these findings should change our view of the origins of life. But the hydrothermal vent hypothesis, which is often described as <a href="http://news.bbc.co.uk/2/hi/science/nature/2541393.stm">exotic and controversial</a>, explains how living cells evolved the ability to obtain energy, in a way that just wouldn’t have been possible in a primordial soup.</p>
<p>Under the <a href="http://cshperspectives.cshlp.org/content/2/11/a002089.short">conventional theory</a>, life supposedly began when lightning or UV rays caused simple molecules to join together into more complex compounds. This culminated in the creation of information-storing molecules similar to our own DNA, housed within the protective bubbles of primitive cells. Laboratory experiments confirm that trace amounts of molecular building blocks that make up <a href="http://science.sciencemag.org/content/117/3046/528">proteins</a> and <a href="http://www.nature.com/nature/journal/v459/n7244/abs/nature08013.html">information-storing molecules</a> can indeed be created under these conditions. For many, the primordial soup has become the most plausible environment for the origin of first living cells.</p>
<p>But life isn’t just about replicating information stored within DNA. All living things have to reproduce in order to survive, but replicating the DNA, assembling new proteins and building cells from scratch require tremendous amounts of energy. At the core of life are the mechanisms of obtaining energy from the environment, storing and continuously channelling it into cells’ key metabolic reactions.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/134112/original/image-20160815-27213-6i8vuf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/134112/original/image-20160815-27213-6i8vuf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/134112/original/image-20160815-27213-6i8vuf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/134112/original/image-20160815-27213-6i8vuf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/134112/original/image-20160815-27213-6i8vuf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/134112/original/image-20160815-27213-6i8vuf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/134112/original/image-20160815-27213-6i8vuf.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">Did life evolve around deep-sea hydrothermal vents?</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Fauna_on_hydrothermal_vents.jpg">U.S. National Oceanic and Atmospheric Administration/Wikimedia Commons</a></span>
</figcaption>
</figure>
<p>Where this energy comes from and how it gets there can tell us a whole lot about the universal principles governing life’s evolution and origin. Recent studies <a href="http://science.sciencemag.org/content/344/6188/1092">increasingly suggest</a> that the primordial soup was not the right kind of environment to drive the energetics of the first living cells.</p>
<p>It’s classic textbook knowledge that all life on Earth is powered by energy supplied by the sun and captured by plants, or extracted from simple compounds such as hydrogen or methane. Far less known is the fact that all life harnesses this energy in the same and quite peculiar way.</p>
<p>This process works a bit <a href="http://www.nature.com/scitable/topicpage/why-are-cells-powered-by-proton-gradients-14373960">like a hydroelectric dam</a>. Instead of directly powering their core metabolic reactions, cells use energy from food to pump protons (positively charged hydrogen atoms) into a reservoir behind a biological membrane. This creates what is known as a “concentration gradient” with a higher concentration of protons on one side of the membrane than other. The protons then flow back through molecular turbines embedded within the membrane, like water flowing through a dam. This generates high-energy compounds that are then used to power the rest of cell’s activities.</p>
<p>Life could have evolved to exploit any of the countless energy sources available on Earth, from heat or electrical discharges to naturally radioactive ores. Instead, all life forms are driven by proton concentration differences across cells’ membranes. This suggests that the earliest living cells harvested energy in a similar way and that life itself arose in an environment in which proton gradients were <a href="http://onlinelibrary.wiley.com/doi/10.1002/bies.200900131/abstract">the most accessible power source</a>.</p>
<h2>Vent hypothesis</h2>
<p>Recent studies based on sets of genes that were likely to have been present within the first living cells trace the origin of life back to <a href="http://www.sciencedirect.com/science/article/pii/S0005272816303838">deep-sea hydrothermal vents</a>. These are porous geological structures produced by chemical reactions between solid rock and water. Alkaline fluids from the Earth’s crust flow up the vent towards the more acidic ocean water, creating natural proton concentration differences remarkably similar to those powering all living cells.</p>
<p>The studies suggest that in the earliest stages of life’s evolution, chemical reactions in primitive cells were likely driven by these non-biological proton gradients. Cells then later learned how to produce their own gradients and escaped the vents to colonise the rest of the ocean and eventually the planet.</p>
<p>While proponents of the primordial soup theory argue that electrostatic discharges or the Sun’s <a href="http://www.sciencemag.org/news/2015/03/researchers-may-have-solved-origin-life-conundrum">ultraviolet radiation drove</a> life’s first chemical reactions, modern life is not powered by any of these volatile energy sources. Instead, at the core of life’s energy production are ion gradients across biological membranes. Nothing even remotely similar could have emerged within the warm ponds of primeval broth on Earth’s surface. In these environments, chemical compounds and charged particles tend to get evenly diluted instead of forming gradients or non-equilibrium states that are so <a href="http://rstb.royalsocietypublishing.org/content/368/1622/20120254.short">central to life</a>.</p>
<p>Deep-sea hydrothermal vents represent <a href="http://jgs.geoscienceworld.org/content/154/3/377">the only known environment</a> that could have created complex organic molecules with the same kind of energy-harnessing machinery as modern cells. Seeking the origins of life in the primordial soup made sense when little was known about the universal principles of life’s energetics. But as our knowledge expands, it is time to embrace alternative hypotheses that recognise the importance of the energy flux driving the first biochemical reactions. These theories seamlessly bridge the gap between the energetics of living cells and non-living molecules.</p><img src="https://counter.theconversation.com/content/63744/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Arunas L Radzvilavicius receives funding from The Engineering and Physical Sciences Research Council (EPSRC). </span></em></p>New research suggests the “primordial soup” theory can’t explain how living cells evolved to harness energy.Arunas L. Radzvilavicius, UCLLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/235122014-03-19T04:07:29Z2014-03-19T04:07:29ZCan bleach help solve the origin of life in the primordial soup?<figure><img src="https://images.theconversation.com/files/44271/original/f3k7tp49-1395201740.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C1024%2C680&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Hydrogen peroxide – widely used in hair bleach – may also hold the key to life on early Earth.</span> <span class="attribution"><a class="source" href="http://www.flickr.com/photos/brandobean/3601125287/sizes/l/">Brandon Milner Photography/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span></figcaption></figure><p>A chemical found in hair bleach may help answer questions about the origins of life and explain why new life does not emerge on modern Earth.</p>
<p>Hydrogen peroxide may have helped transform RNA (<a href="https://theconversation.com/explainer-what-is-rna-15169">ribonucleic acid</a>) into one of the building blocks of life, we found in a <a href="http://arxiv.org/abs/1402.3875">study</a> published today in <a href="http://dx.doi.org/10.1098/rsif.2013.1052">Journal of the Royal Society Interface</a>. </p>
<p>More than 3.6 billion years ago there were no living cells and no proteins in the primordial soup on earth.</p>
<p>The <a href="http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1989/altman-article.html">RNA world</a> hypothesis holds that cell-free <a href="http://online.liebertpub.com/doi/abs/10.1089/ast.2012.0868">communities grew</a> in rock pores around hydrothermal vents and replicated and evolved, <em>before</em> the evolution of DNA and cell membranes.</p>
<p>But cell-free RNA replication requires thermal cycling – heating to separate the base-paired double strands and a cooling phase to <a href="http://www.biology-online.org/dictionary/Anneal">anneal</a> complementary strands into newly replicated double helices.</p>
<p>This fact is often overlooked in hypotheses about the origin of life, although the polymerase chain reaction (<a href="https://www.genome.gov/10000207">PCR</a>) method routinely used to amplify DNA in the lab uses artificially imposed thermal cycling.</p>
<p>So what mechanism may have provided spontaneous, self-sustained thermal cycling on the ancient earth?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/42713/original/pfgffcpm-1393552533.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2550%2C1114&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/42713/original/pfgffcpm-1393552533.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2550%2C1114&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/42713/original/pfgffcpm-1393552533.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=262&fit=crop&dpr=1 600w, https://images.theconversation.com/files/42713/original/pfgffcpm-1393552533.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=262&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/42713/original/pfgffcpm-1393552533.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=262&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/42713/original/pfgffcpm-1393552533.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=329&fit=crop&dpr=1 754w, https://images.theconversation.com/files/42713/original/pfgffcpm-1393552533.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=329&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/42713/original/pfgffcpm-1393552533.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=329&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Primordial soup in a can – what about a new recipe for life?</span>
<span class="attribution"><a class="source" href="http://www.mbio.ncsu.edu/jwb/soup.html">James W Brown</a></span>
</figcaption>
</figure>
<h2>The breakthrough</h2>
<p>Our study brought together interdisciplinary researchers at the Australian National University and Leeds University, UK. </p>
<p>Bringing insights gained from applied mathematics and chemical engineering to bear on a problem that has been tackled by chemists and molecular biologists, we described and tested a previously unrecognised mechanism for driving a replicating molecular system on the pre-biotic earth.</p>
<p><a href="http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.108.238104">Researchers had suggested</a> earlier that thermal cycling may have been provided by convective oscillations in millimetre-sized rock pores.</p>
<p>We proposed that thermal cycling in the primordial soup may have been provided by a natural thermochemical oscillator, driven by spontaneous, <a href="http://chemistry.about.com/cs/generalchemistry/a/aa051903a.htm">exothermic</a> (heat producing) reactions of <a href="http://www.wisegeek.org/what-is-hydrogen-peroxide.htm">hydrogen peroxide</a>.</p>
<p>A thermochemical oscillator is an exothermally reacting chemical system that gives a periodic temperature response. They have been studied experimentally since <a href="http://dx.doi.org/10.1002/aic.690150611">1969</a>.</p>
<p>Hydrogen peroxide is a simple molecule with the chemical formula H₂O₂. It is made and used in vast quantities in the polymer industry and has some domestic uses in hair bleach and antiseptics, but it also occurs in small quantities naturally on the Earth and in the biosphere. </p>
<p>Oscillatory thermoconversion is typical of highly energetic, thermally sensitive, liquids such as hydrogen peroxide. </p>
<p>Such liquids have high specific heat capacity so their intermolecular bonds can absorb much of the heat of reaction. But when the bonds cannot absorb any more heat the temperature spikes to a maximum, then declines to a minimum, and the cycle begins again.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/43453/original/cb7wf4hs-1394424844.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/43453/original/cb7wf4hs-1394424844.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=328&fit=crop&dpr=1 600w, https://images.theconversation.com/files/43453/original/cb7wf4hs-1394424844.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=328&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/43453/original/cb7wf4hs-1394424844.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=328&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/43453/original/cb7wf4hs-1394424844.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=413&fit=crop&dpr=1 754w, https://images.theconversation.com/files/43453/original/cb7wf4hs-1394424844.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=413&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/43453/original/cb7wf4hs-1394424844.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=413&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">This is what the hydrogen peroxide thermochemical oscillations look like. The upper plot shows the temperature response, in the lower plot we can see that the hydrogen peroxide concentration oscillates out of phase with the temperature</span>
</figcaption>
</figure>
<p>The hydrogen peroxide oscillator turns out to have just the right period – around 90 seconds – to drive the replication of small RNAs. If the period is too long the RNAs decay faster than replication can increase them. If the period is too short the strands do not separate completely and replication fails.</p>
<h2>Replication, amplification and evolution</h2>
<p>We set up detailed computational simulations and found that the hydrogen peroxide oscillator can indeed drive rapid RNA replication and amplification.</p>
<p>But there’s more. In the presence of RNA template strands the oscillatory system can become quasi-periodic, and the thermal oscillations can take on more complex forms – biperiodic, for example.</p>
<p>This may lend additional, powerful capabilities to a molecular replicating system. A biperiodic temperature response is capable of replicating two different RNA species, and nature may well have done exactly that in the primordial rock pores.</p>
<p>How might complementary RNA strands have been produced in the pre-biotic primordial soup? Well, it has been shown that long <a href="http://www.ask.com/question/what-is-a-polynucleotide">polynucleotides</a> can be synthesised on mineral surfaces. We proposed a surface-promoted scheme, which itself may be driven by the hydrogen peroxide oscillator.</p>
<p>A truly living system must evolve, as well as replicate. Now, RNA is not totally stable in the presence of hydrogen peroxide. This is good, because it allows for some infidelity in replication.</p>
<p>In other words, we also have evolution! RNA that is modified by the action of hydrogen peroxide in such a way that confers resilience to hydrogen peroxide damage would, of course, be selected for. We have natural selection, too!</p>
<h2>Other worlds</h2>
<p>Experiments have indicated that hydrogen peroxide was present on the early Earth, and may easily have occurred in high enough concentrations to undergo oscillatory thermoconversion in hydrothermal rock pores.</p>
<p>Hydrogen peroxide is known also to occur abundantly on Jupiter’s moon Europa, and is believed to have occurred formerly on Mars, which suggests that these planetary bodies may have evolved their own RNA worlds!</p>
<p>Our results also may provide an answer to the (previously unanswerable) question of why life does not emerge from non-living precursors on the modern earth. We do not find spontaneously self-replicating and evolving RNA communities around modern hydrothermal vents.</p>
<p>The answer? Quite simply there are no longer the amounts of hydrogen peroxide in those environments that were there in the good old days!</p><img src="https://counter.theconversation.com/content/23512/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Rowena Ball receives funding from the Australian Research Council.</span></em></p>A chemical found in hair bleach may help answer questions about the origins of life and explain why new life does not emerge on modern Earth. Hydrogen peroxide may have helped transform RNA (ribonucleic…Rowena Ball, ARC Future Fellow, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.