Study shows Earth’s first known mass extinction event 550 million years ago

ANI |
UPDATED: 09 November 2022 04:20 IST

Washington [US]Nov 9 (ANI): A new study by geobiologists at Virginia Tech traces the cause of the first known mass extinction of animals to reduced global availability of oxygen, leading to the loss of the majority of animals present near the end of the Ediacaran period about 550 million years ago .
Research led by Scott Evans, a postdoctoral researcher in the Department of Geosciences, part of the Virginia Tech College of Sciences, points to this early mass extinction of about 80 percent of animals during this time. “This involved the loss of many different types of animals, but those whose body patterns and behaviors indicate that they relied on significant amounts of oxygen appear to have been particularly hard hit,” Evans said. “This suggests that the extinction event was environmentally controlled, like all other mass extinctions in the geological record.”
Evans’ work was published Nov. 7 in the Proceedings of the National Academy of Sciences, a peer-reviewed journal of the National Academy of Sciences. The study was authored by Shuhai Xiao, also a professor in the Department of Geosciences, and several researchers led by Mary Droser from the Department of Earth and Planetary Sciences at the University of California Riverside, where Evans earned his master’s and Ph.D.
“Environmental changes such as global warming and deoxygenation events can lead to mass extinction of animals and profound ecosystem disruption and reorganization,” said Xiao, who is a member of the Global Change Center, part of Virginia Tech Fralin Life. Institute of Sciences. “This has been demonstrated repeatedly in the study of Earth history, including this work on the first extinction documented in the fossil record. This study thus informs us about the long-term effects of current environmental changes in the biosphere.”
What exactly caused the global oxygen drop? This is still up for debate. “The short answer to how this happened is we don’t really know,” Evans said. “It could be any number and combination of volcanic eruptions, tectonic plate movement, asteroid impacts, etc., but what we’re seeing is that the animals that are going extinct seem to be responding to the reduced global availability of oxygen.”
Evans and Xiao’s study is more timely than one might imagine. In an unrelated study, Virginia Tech scientists recently found that anoxia, the loss of oxygen availability, is affecting the world’s fresh waters. The cause? The warming of waters caused by climate change and excessive runoff of pollutants from land use. Warming waters reduce the ability of freshwater to hold oxygen, while the breakdown of nutrients in runoff by freshwater microbes eats up oxygen.

“Our study shows that, as with all other mass extinctions in Earth’s past, this new, first-ever animal mass extinction was caused by major climate change — another in a long list of cautionary tales demonstrating the dangers of the current climate crisis for animal life,” said Evans, who is an Aguron Institute Geobiology Fellow.
Some perspective: The Ediacaran Period lasted about 96 million years, bounded on either side by the end of the Cryogenian Period — 635 million years ago — and the beginning of the Cambrian Period — 539 million years ago. The extinction event comes just before a major break in the geological record, from the Proterozoic to the Phanerozoic.
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-Triad 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 as important steps in the evolutionary trajectory of life on this planet,” Evans and his team wrote in the study. Whatever the cause of the mass extinction, the result was multiple major changes in environmental conditions. “In particular, we find support for reduced global oxygen availability as the mechanism responsible for this extinction. This suggests that abiotic controls have had significant effects on patterns of diversity throughout the history of animals on this planet for more than 570 million years “, the authors wrote. .
Fossils in rock tell researchers what the creatures that perished in this extinction event would have looked like. And they looked, in Evans’ words, “weird.”
“These organisms appear so early in the evolutionary history of animals that in many cases they seem to be experimenting with different ways to build large, sometimes mobile, multicellular bodies,” Evans said. “There are many ways to recreate their appearance, but the good thing is that before this extinction the fossils we find don’t often match the ways we classify animals today. In fact, this extinction may have helped pave the way for the evolution of animals as we know them”.
The study, like many other recent publications, arose out of the COVID-19 pandemic. Because Evans, Xiao and their team couldn’t access the field, they decided to create a global database based mostly on published records to test ideas about changing diversity. “Others had suggested that there might be an extinction at this time, but there was a lot of speculation. So we decided to gather everything we could to try and test these ideas.” Evans said. Much of the data used in the study was collected by Droser and several graduate students at the University of California Riverside. (A I)