{"id":8105,"date":"2021-09-29T02:50:01","date_gmt":"2021-09-29T06:50:01","guid":{"rendered":"https:\/\/spaceandplanetarynewswire.com\/?p=8105"},"modified":"2021-09-29T02:50:01","modified_gmt":"2021-09-29T06:50:01","slug":"zeroing-in-on-the-origins-of-earths-single-most-important-evolutionary-innovation","status":"publish","type":"post","link":"https:\/\/spaceandplanetarynewswire.com\/?p=8105","title":{"rendered":"Zeroing in on the Origins of Earth\u2019s \u201cSingle Most Important Evolutionary Innovation\u201d"},"content":{"rendered":"
MIT scientists estimate that oxygenic photosynthesis \u2014 the ability to turn light and water into energy, releasing oxygen\u2014 first evolved on Earth between 3.4 and 2.9 billion years ago. Credits:Image: MIT News, iStockphoto<\/figcaption><\/figure>\n

Some time in Earth\u2019s early history, the planet took a turn toward habitability when a group of enterprising microbes known as cyanobacteria evolved oxygenic photosynthesis \u2014 the ability to turn light and water into energy, releasing oxygen in the process.<\/p>\n

This evolutionary moment made it possible for oxygen to eventually accumulate in the atmosphere and oceans, setting off a domino effect of diversification and shaping the uniquely habitable planet we know today.  <\/p>\n

Now, MIT scientists have a precise estimate for when cyanobacteria, and oxygenic photosynthesis, first originated. Their results<\/a> appear in the Proceedings of the Royal Society B.<\/em><\/p>\n

They developed a new gene-analyzing technique that shows that all the species of cyanobacteria living today can be traced back to a common ancestor that evolved around 2.9 billion years ago. They also found that the ancestors of cyanobacteria branched off from other bacteria around 3.4 billion years ago, with oxygenic photosynthesis likely evolving during the intervening half-billion years, during the Archean Eon.<\/p>\n

Interestingly, this estimate places the appearance of oxygenic photosynthesis at least 400 million years before the Great Oxidation Event, a period in which the Earth\u2019s atmosphere and oceans first experienced a rise in oxygen. This suggests that cyanobacteria may have evolved the ability to produce oxygen early on, but that it took a while for this oxygen to really take hold in the environment.<\/p>\n

\u201cIn evolution, things always start small,\u201d says lead author Greg Fournier, associate professor of geobiology in MIT\u2019s Department of Earth, Atmospheric and Planetary Sciences. \u201cEven though there\u2019s evidence for early oxygenic photosynthesis \u2014 which is the single most important and really amazing evolutionary innovation on Earth \u2014 it still took hundreds of millions of years for it to take off.\u201d<\/p>\n

Fournier\u2019s MIT co-authors include Kelsey Moore, Luiz Thiberio Rangel, Jack Payette, Lily Momper, and Tanja Bosak.<\/p>\n

Slow fuse, or wildfire?<\/strong><\/p>\n

Estimates for the origin of oxygenic photosynthesis vary widely, along with the methods to trace its evolution.<\/p>\n

For instance, scientists can use geochemical tools to look for traces of oxidized elements in ancient rocks. These methods have found hints that oxygen was present as early as 3.5 billion years ago \u2014 a sign that oxygenic photosynthesis may have been the source, although other sources are also possible.<\/p>\n

Researchers have also used molecular clock dating, which uses the genetic sequences of microbes today to trace back changes in genes through evolutionary history. Based on these sequences, researchers then use models to estimate the rate at which genetic changes occur, to trace when groups of organisms first evolved. But molecular clock dating is limited by the quality of ancient fossils, and the chosen rate model, which can produce different age estimates, depending on the rate that is assumed.<\/p>\n

Fournier says different age estimates can imply conflicting evolutionary narratives. For instance, some analyses suggest oxygenic photosynthesis evolved very early on and progressed \u201clike a slow fuse,\u201d while others indicate it appeared much later and then \u201ctook off like wildfire\u201d to trigger the Great Oxidation Event and the accumulation of oxygen in the biosphere.<\/p>\n

\u201cIn order for us to understand the history of habitability on Earth, it\u2019s important for us to distinguish between these hypotheses,\u201d he says.<\/p>\n

Horizontal genes<\/strong><\/p>\n

To precisely date the origin of cyanobacteria and oxygenic photosynthesis, Fournier and his colleagues paired molecular clock dating with horizontal gene transfer \u2014 an independent method that doesn\u2019t rely entirely on fossils or rate assumptions.<\/p>\n

Normally, an organism inherits a gene \u201cvertically,\u201d when it is passed down from the organism\u2019s parent. In rare instances, a gene can also jump from one species to another, distantly related species. For instance, one cell may eat another, and in the process incorporate some new genes into its genome.<\/p>\n

When such a horizontal gene transfer history is found, it\u2019s clear that the group of organisms that acquired the gene is evolutionarily younger than the group from which the gene originated. Fournier reasoned that such instances could be used to determine the relative ages between certain bacterial groups. The ages for these groups could then be compared with the ages that various molecular clock models predict. The model that comes closest would likely be the most accurate, and could then be used to precisely estimate the age of other bacterial species \u2014 specifically, cyanobacteria.<\/p>\n

Following this reasoning, the team looked for instances of horizontal gene transfer across the genomes of thousands of bacterial species, including cyanobacteria. They also used new cultures of modern cyanobacteria taken by Bosak and Moore, to more precisely use fossil cyanobacteria as calibrations. In the end, they identified 34 clear instances of horizontal gene transfer. They then found that one out of six molecular clock models consistently matched the relative ages identified in the team\u2019s horizontal gene transfer analysis.<\/p>\n

Fournier ran this model to estimate the age of the \u201ccrown\u201d group of cyanobacteria, which encompasses all the species living today and known to exhibit oxygenic photosynthesis. They found that, during the Archean eon, the crown group originated around 2.9 billion years ago, while cyanobacteria as a whole branched off from other bacteria around 3.4 billion years ago. This strongly suggests that oxygenic photosynthesis was already happening 500 million years before the Great Oxidation Event (GOE), and that cyanobacteria were producing oxygen for quite a long time before it accumulated in the atmosphere.<\/p>\n

The analysis also revealed that, shortly before the GOE, around 2.4 billion years ago, cyanobacteria experienced a burst of diversification. This implies that a rapid expansion of cyanobacteria may have tipped the Earth into the GOE and launched oxygen into the atmosphere.<\/p>\n

Fournier plans to apply horizontal gene transfer beyond cyanobacteria to pin down the origins of other elusive species.<\/p>\n

\u201cThis work shows that molecular clocks incorporating horizontal gene transfers (HGTs) promise to reliably provide the ages of groups across the entire tree of life, even for ancient microbes that have left no fossil record \u2026 something that was previously impossible,\u201d Fournier says. <\/p>\n","protected":false},"excerpt":{"rendered":"

Some time in Earth\u2019s early history, the planet took a turn toward habitability when a group of enterprising microbes known as cyanobacteria evolved oxygenic photosynthesis \u2014 the ability to turn light and water into energy, releasing oxygen in the process. This evolutionary moment made it possible for oxygen to eventually accumulate in the atmosphere and…<\/p>\n","protected":false},"author":71,"featured_media":8107,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"ngg_post_thumbnail":0,"fifu_image_url":"https:\/\/news.mit.edu\/sites\/default\/files\/images\/202109\/MIT-First-Photo-01-press.jpg","fifu_image_alt":"Zeroing in on the Origins of Earth\u2019s \u201cSingle Most Important Evolutionary Innovation\u201d","footnotes":""},"categories":[207],"tags":[],"class_list":["post-8105","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-research"],"_links":{"self":[{"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=\/wp\/v2\/posts\/8105","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=\/wp\/v2\/users\/71"}],"replies":[{"embeddable":true,"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=8105"}],"version-history":[{"count":1,"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=\/wp\/v2\/posts\/8105\/revisions"}],"predecessor-version":[{"id":8106,"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=\/wp\/v2\/posts\/8105\/revisions\/8106"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=\/wp\/v2\/media\/8107"}],"wp:attachment":[{"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=8105"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=8105"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=8105"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}