Geobiologists shed new light on Earth’s first known mass extinction event 550 million years ago
A new study by Virginia Tech geobiologists 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 near the end of the Ediacaran period some 550 million years ago.
Research led by Scott Evans, a postdoctoral researcher in the Department of Geosciences, part of the Virginia Tech College of Science, shows this earliest mass extinction of about 80 percent of animals in this interval. “This involved the loss of many different species of animals, however those whose body plans and behavior show that they relied on significant amounts of oxygen appear to be particularly hard hit,” Evans said. “This suggests that it is extinction event it was environmentally controlled, like all other mass extinctions in the geological record.”
Evans’ paper was published on November 7 in 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 Department of Earth and Planetary Sciences at the University of California Riverside, where Evans earned his master’s and Ph.D.
“Changes in the environment, such as global warming and deoxygenation events, can lead to mass extinctions of animals and profound disruption and reorganization of ecosystems,” said Xiao, who is an associate member of the Global Change Center, part of the Virginia Tech Fralin Life Sciences Institute. “This has been shown repeatedly in studies of Earth history, including and this paper on the first extinction documented in the fossil record. This study therefore informs us about the long-term impact of electricity environmental changes in the biosphere.”
What exactly caused the decline in global oxygen? That 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 movements, asteroid impacts, etc., but what we’re seeing is that animals going extinct seem to be responding to reduced global oxygen availability.”
Evans and Xiao’s study is more timely than one might think. In an unrelated study, Virginia Tech scientists recently found that anoxia, the loss of oxygen availability, affects fresh waters of the world. The cause? Water warming caused by climate change and excessive runoff of pollutants from land use. Warming waters reduce the ability of fresh water to hold oxygen, while the breakdown of nutrients in runoff by freshwater microbes eats up oxygen.
“Our study shows that, like all other mass extinctions in Earth’s past, this new, first animal mass extinction was caused by a large climate change—another in a long list of cautionary tales demonstrating the dangers of our current climate crisis for animal life” said Evans, who is a geobiology fellow at the Agouron Institute.
Some perspective: The Ediacaran period spanned roughly 96 million years, occupied 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 significant break in the geologic record, from the Proterozoic Eon to the Phanerozoic.
There are five known animal 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 million years), the Triassic-Jurassic extinction (200 million years ago) and the Cretaceous-Paleogene extinction (65 million years ago).
“Mass extinctions are well recognized as significant steps in the evolutionary trajectory of life on this planet,” Evans and team wrote in the study. Whatever triggered 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 a significant impact on diversity patterns during the more than 570 million years of animal history on this planet,” the authors wrote. .
Fossil imprints in rocks tell researchers what the creatures that perished in this extinction 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 what they looked like, but the bottom line is that before this extinction, the fossils we find often don’t fit well with the ways we classify animals today. Basically, this extinction may have helped pave the way for the evolution of animals as we know them .”
The study, like a number of other recent publications, arose out of the COVID-19 pandemic. Because Evans, Xiao and their team couldn’t get access to the field, they decided to compile a global database based mostly on published records to test ideas about changing diversity. “Others have suggested that there could be an extinction at this point, but there has been a lot of speculation. So we decided to put together everything we could to try and 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.
Evans, Scott D., Ecological drivers of the first major animal extinction across the Ediacaran White Sea-Nama transition, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2207475119. doi.org/10.1073/pnas.2207475119
Citation: Geobiologists shed new light on Earth’s first known mass extinction event 550 million years ago (2022, November 7) Retrieved November 8, 2022 from https://phys.org/news/2022-11-geobiologists-earth- mass-extinction-event .html
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