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A global drop in oxygen triggered the first mass extinction

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A new study by geobiologists at Virginia Tech attributes the first known mass extinction of animals to declining global oxygen availability.

The research, published in PNAS, refers to the loss of 80 percent of the animals present near the end of the Ediacaran Period around 550 million years ago.

“This included the loss of many different types of animals, however those whose body plans and behaviors indicate they relied on significant amounts of oxygen appear to have been particularly affected,” Scott Evans, a postdoctoral researcher in the Department of Geosciences, said in a statement. and study author. “This suggests that the extinction event was environmentally controlled, like all other mass extinctions in the geological record.”

“Environmental changes, such as global warming and deoxygenation events, can lead to mass animal extinctions and profound ecosystem disruption and reorganization,” said co-author Shuhai Xiao, a professor of geosciences. “This has been shown repeatedly in the study of Earth’s history, including this work on the first documented extinction in the fossil record. This study tells us about the long-term impact of current environmental changes on the biosphere.”

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

In an unrelated study, Virginia Tech scientists recently found that anoxia, the loss of oxygen availability, is affecting the world’s freshwater. The cause? The warming of waters caused by climate change and excess polluting runoff from land use. Warming waters decrease the ability of freshwater to hold oxygen, while the breakdown 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.

The Ediacaran Period spanned approximately 96 million years, bounded on both sides by the end of the Cryogenous 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 as significant steps in the evolutionary trajectory of life on this planet,” Evans and his team wrote in the study. Whatever the instigating cause of the mass extinction, the result was multiple major changes in environmental conditions. “In particular, we find support for declining global oxygen availability as the mechanism responsible for this extinction. This suggests that abiotic controls have had a significant impact on diversity patterns over the more than 570 million years.” history of animals on this planet,” the authors wrote.

Fossil tracks 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 lots of ways to recreate what they look like, but the take-home message is that before this extinction, the fossils we found often didn’t fit well into the ways we classify animals today. Essentially, this extinction may have helped pave the way for the evolution of animals as we know it”.

Europe Press

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