Geobiologists shed new light on Earth’s first known mass extinction, 550 million years ago

A new study by Virginia Tech geobiologists traces the cause of the first known mass extinction of animals to decreased global availability of oxygen, which led to the loss of a majority of the animals present by the end of the Ediacaran period, so about 550 million years ago.

The study led by Scott Evans, a postdoctoral researcher in the Department of Geosciences, part of the Virginia Tech College of Science, shows this earliest massive become extinct of about 80 percent of the animals in this interval. “This included the loss of many different types of animals, but those whose body plans and behavior indicate they depended on significant amounts of oxygen appear to have been hit particularly hard,” 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 of the Department of Earth and Planetary Sciences at the University of California Riverside, where Evans received his master’s degree and Ph.D.

“Environmental changes, such as global warming and deoxygenation events, can lead to mass extinctions of animals and profound disruption and reorganization of the ecosystem,” said Xiao, who is an associate member of the Global Change Center, part of the Virginia Tech Fralin Life Sciences Institute. repeatedly in the study of Earth’s history, including this work on the first extinction documented in the fossil record. This study thus informs us about the long-term impact of electricity environmental changes on the biosphere.”

What exactly caused the decline in global oxygen? That is still up for debate. “The short answer to how this happened is that we don’t really know,” Evans said. “It could be any number and combinations of volcanic eruptions, tectonic plate movement, an 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 research is more current than one might think. In an unrelated study, Virginia Tech scientists recently found that anoxia, the loss of oxygen availability, the world’s fresh waters. Cause? Water warming due to climate change and excessive discharge of pollutants from land use. Warming water decreases the ability of freshwater to hold oxygen, while the breakdown of nutrients in the runoff by freshwater microbes swallows oxygen.

“Our study shows that, as with all other mass extinctions in the Earth’s past, this new, first mass extinction of animals was caused by large climate change—another in a long list of cautionary tales highlighting the dangers of our current climate crisis for . demonstrate animals livesaid Evans, a fellow of the Agouron Institute of Geobiology.

Some perspective: The Ediacaran period spanned about 96 million years, booked on either side towards the end of the cryogenic 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), the Triassic-Jurassic Extinction (200 million years ago) and the Cretaceous-Paleogene Extinction (65 million years ago).

“Mass extinctions are widely recognized as important steps in the evolutionary trajectory of life on this planet,” Evans and team wrote in the study. Whatever the instigating cause of the mass extinction, the result was several major shifts 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 a significant impact on diversity patterns throughout the more than 570 million-year history of animals on this planet,” they wrote. the authors. .

Fossil imprints in rock tell researchers what the creatures that perished during 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 seem to be experimenting with different ways of building large, sometimes mobile, multicellular bodies,” Evans said. “There are many ways to mimic what they look like, but the upside is that the fossils we find before this extinction don’t often fit well with the way we classify animals today. Essentially, this extinction may have helped pave the way.” make for the evolution of animals as we know them.”

The study, like dozens of other recent publications, emerged from the COVID-19 pandemic. Unable to access the field, Evans, Xiao and their team decided to build a global database, based primarily on published data, to test ideas about changing diversity. “Others had suggested that there would be an extinction at this point, but there was a lot of speculation. So we decided to put everything together to test those ideas.” said Evans. Much of the data used in the study was collected by Droser and several graduate students from the University of California Riverside.