The work shows a great loss of diversity during the Ediacaran period, which lasted between 635 and 540 million years - Archeology & Paleontology News

The work shows a great loss of diversity during the Ediacaran period, which lasted between 635 and 540 million years – Archeology & Paleontology News

A new study by Virginia Tech geobiologists traces the cause of the first known mass extinction of animals to a decline in global oxygen availability, leading to the loss of most of the animals present toward the end of the Ediacaran period around of 550 million. years ago.

Research led by Scott Evans, a postdoctoral researcher in the Department of Geosciences, part of the Virginia Tech School of Sciences, shows this first mass extinction of around 80% of animals during this interval. “This included the loss of many different types of animals, but those whose body plans and behaviors indicate that they relied on significant amounts of oxygen seem to have been particularly affected,” Evans said. “This suggests that the extinction event was environmentally controlled, like all other mass extinctions in the geological record. »

Evans’ work was published on November 7 in the Proceedings of the National Academy of Sciences, a peer-reviewed journal of the National Academy of Sciences. The study was co-authored by Shuhai Xiao, also a professor in the Department of Geosciences, and several researchers led by Mary Droser in the Department of Earth and Planetary Sciences at the University of California, Riverside, where Evans earned her master’s and doctoral degrees.

“Environmental changes, such as global warming and deoxygenation events, can lead to mass animal extinctions and profound ecosystem disruption and reorganization,” said Xiao, an affiliate member of the Global Change Center, part of Virginia Tech Fralin Life. . Institute of Sciences. “This has been shown repeatedly in the study of Earth’s history, including this work on the first documented extinction in the fossil record. Therefore, this study tells us about the long-term impact of current environmental changes on the biosphere. »

What exactly caused the drop in global oxygen? It is still up for debate. “The short answer to how it happened is that we really don’t know,” Evans said. “It could be any number and combination of volcanic eruptions, tectonic plate movements, asteroid impact, etc., but what we see is that the animals that are disappearing appear to be responding to a decrease in global oxygen availability. »

Evans and Xiao’s study is more timely than one might think. In an independent study, Virginia Tech scientists recently found that anoxia, the loss of oxygen availability, affects the world’s freshwater. The cause? Warming of waters caused by climate change and excessive runoff of pollutants from land use. Warming waters decrease the ability of freshwater to hold oxygen, while the degradation of nutrients in runoff by freshwater microbes gobbles up oxygen.

“Our study shows that, as with all other mass extinctions in Earth’s past, this new and first mass extinction of animals was caused by major climate change, yet another in a long line of warning stories showing the dangers of our current climate crisis to animal … life,” said Evans, who is a geobiology fellow at the Agouron Institute.

A bit of perspective: The Ediacaran period spanned about 96 million years, ending on both sides with the end of the Cryogenian period, 635 million years ago, and the beginning of the Cambrian period, 539 million years ago. The extinction event occurs just before a significant break in the geological record, from the Proterozoic eon to the Phanerozoic eon.

There are five known mass extinctions that stand out in animal history, the “big five,” according to Xiao, including the Ordovician-Silurian extinction (440 million years ago), the Late Devonian extinction (370 million years ago), the Permian-Triassic extinction (250 million years ago), the Triassic-Jurassic extinction (200 million years ago), and the Cretaceous-Paleogene extinction (65 million years ago).

“Mass extinctions are well-recognized milestones in the evolutionary trajectory of life on this planet,” Evans and his team wrote in the study. Whatever the cause behind the mass extinction, the result was multiple major changes in environmental conditions. “In particular, we find support for decreased global oxygen availability as the mechanism responsible for this extinction. This suggests that abiotic controls have had significant impacts on diversity patterns throughout the more than 570 million year history of animals on this planet,” the authors wrote. .

Fossil tracks in the rock tell researchers what the creatures that perished during this extinction event might have looked like. And they looked, in Evans’ words, “strange.”

“These organisms occur so early in the evolutionary history of animals that in many cases they appear to be experimenting with different ways of building large, multicellular, and sometimes mobile bodies,” Evans said. “There are many ways to recreate their appearance, but the bottom line is that before this extinction, the fossils we find don’t always correspond perfectly to how we classify animals today. Essentially, this extinction may have helped pave the way. for the evolution of animals as we know them. »

The study, like dozens of other recent publications, grew out of the COVID-19 pandemic. Because Evans, Xiao and their team were unable to access the field, they decided to build a global database based primarily on published records to test insights into the evolution of diversity. “Others suggested there could be an extinction at that time, but there was a lot of speculation. So we decided to put together as much as we could to try and test these ideas. Evans said. Much of the data used in the study was collected by Droser and several UC Riverside graduate students.

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