Study: Decreased Global Oxygen Availability Caused End-Ediacaran Mass Extinction

Mass extinctions are well recognized as significant steps in the evolutionary trajectory of life on Earth. In new research, geobiologists from Virginia Tech and elsewhere documented the end-Ediacaran extinction, the mass extinction that occurred some 550 million years ago, and tested for potential causes. Their results indicate that the event wiped out up to 80% of marine animals and, like younger mass extinctions, was caused by major shifts in environmental conditions.

Diorama of Ediacaran organisms displayed at the Smithsonian Institution. Image credit: Ryan Somma / CC BY-SA 2.0.

“Environmental changes, such as global warming and deoxygenation events, can lead to massive extinction of animals and profound disruption and reorganization of the ecosystem,” said Virginia Tech’s Professor Shuhai Xiao.

“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 drop in global oxygen? That’s still up for debate.

“The short answer to how this happened is we don’t really know,” said Dr. Scott Evans, a postdoctoral researcher at Virginia Tech.

“It could be any number and combination of volcanic eruptions, tectonic plate motion, an asteroid impact, etc., but what we see is that the animals that go extinct seem to be responding to decreased global oxygen availability.”

In an unconnected study, scientists recently found that anoxia, the loss of oxygen availability, is affecting the world’s fresh waters.

The cause? The warming of waters brought on by climate change and excess pollutant runoff from land use.

Warming waters diminish fresh water’s capacity 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, first mass extinction of animals was caused by major climate change — another in a long list of cautionary tales demonstrating the dangers of our current climate crisis for animal life,” Dr. Evans said.

“Particularly, we find support for decreased global oxygen availability as the mechanism responsible for this extinction.”

“This suggests that abiotic controls have had significant impacts on diversity patterns throughout the more than 570 million-year history of animals on this planet.”

“Fossil imprints in rock tell researchers how the creatures that perished in this extinction event would have looked. And they looked ‘weird’.”

“These organisms occur so early in the evolutionary history of animals that in many cases they appear to be experimenting with different ways to build large, sometimes mobile, multicellular bodies.”

“There are lots of ways to recreate how they look, but the take-home is that before this extinction the fossils we find don’t often fit nicely into the ways we classify animals today.”

“Essentially, this extinction may have helped pave the way for the evolution of animals as we know them.”

The study was published on November 7, 2022 in the Proceedings of the National Academy of Sciences.

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Scott D. Evans et al. 2022. Environmental drivers of the first major animal extinction across the Ediacaran White Sea-Nama transition. PNAS 119 (46): e2207475119; doi: 10.1073/pnas.2207475119