A new study by geobiologists at Virginia Tech traces the cause of the first known mass extinction of animals to a decrease in global oxygen availability, which led to the loss of most animals present at the end of the Ediacaran period about 550 million years ago & shows this earliest mass extinction of about 80 percent of animals in this interval. “This involved the loss of many different animal species, but those whose body plans and behavior indicate they relied on significant amounts of oxygen seem to have been hit particularly hard,” Evans said. “This suggests that the extinction event was environmentally driven, like all other mass extinctions in the geological record.”
Evans’ work was published Monday 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 of the University of California Riverside’s Department of Earth and Planetary Sciences, where Evans received his master’s degree and Ph.D.
“Environmental changes such as global warming and deoxygenation can lead to massive animal extinctions and profound ecosystem disruption and reorganization,” said Xiao, who is an associate member of the Global Change Center, part of Virginia Tech’s Fralin Life. Scientific Institute. “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 impact of current environmental changes on the biosphere.”
What exactly caused the decline in global oxygen? That is still up for debate. “The short answer to how it happened is we don’t really know,” Evans said. “It could be any number and combination of volcanic eruptions, tectonic plate movement, asteroid impact, etc., but what we’re seeing is that the animals that are going extinct seem to be responding to reduced global oxygen availability.”
Evans and Xiao’s study is more relevant than one might think. In an unrelated study, Virginia Tech scientists recently found that anoxia, the loss of oxygen availability, is affecting the world’s fresh waters. Cause? Warming waters caused by climate change and excessive runoff of pollutants from land use. Water warming reduces the ability of fresh water to hold oxygen, while the breakdown of nutrients in runoff by freshwater microbes absorbs oxygen.
“Our study shows that, like all other mass extinctions in Earth’s past, this new, first mass animal extinction was caused by major climate change – another in a long list of cautionary tales that demonstrate the dangers of our current climate crisis for animals. life,” said Evans, who is a member of the Agouron Institute Geobiology.
Some perspective: The Ediacaran period lasted roughly 96 million years, marked on both sides 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 geologic 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 years), the Triassic-Jurassic extinction (200 million years ago) and the Cretaceous-Paleogene extinction (65 million years ago).
“Mass extinctions are well known as significant steps in the evolutionary trajectory of life on this planet,” Evans and team wrote in the study. Whatever the inciting cause of the mass extinction, it resulted in several fundamental 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 a significant impact on patterns of diversity during the more than 570 million years of animal history on this planet,” the authors wrote. .
Fossil prints in the 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 occur so early in the evolutionary history of animals that in many cases they appear to be experimenting with different ways of building large, sometimes mobile, multicellular bodies,” Evans said. “There are many ways to recreate what they looked like, but the implication is that before this extinction, the fossils we find often don’t fit into the way we classify animals today. Basically, this extinction may have helped pave the way for the evolution of animals as we know.”
The study, like many other recent publications, was based on the COVID-19 pandemic. Because Evans, Xiao and their team couldn’t get access to the field, they decided to put together a global database based mostly on published records to test diversity change ideas. “Others have suggested that there might have been an extinction around this time, but there was a lot of speculation. So we decided to pull together everything we could to test those 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.
