Scientists Discovered a Surprise 6th Mass Extinction, Which Came Before the Big 5
Researchers have gone back in time to find an extinction event that predates all other known events of their kind.
The extinction event, which occurred during the Ediacaran Period roughly 550 million years ago, likely came from a drop in oxygen levels.
Environmental factors have led the other five main extinction events in Earth’s history.
The Ediacaran Period’s odd animals never got their chance to shine, thanks to a precarious drop in oxygen levels about 550 million years ago that triggered the first-ever extinction event. At least, that’s the latest theory. A recent study has announced the discovery of an extinction event preceding all five of Earth’s other known mass extinction events.
The study, published in November 2022 in the Proceedings of the National Academy of Sciences, merged research from Virginia Tech and the University of California Riverside to reach the conclusion that the Ediacaran Period—which stretched from 635 million to 540 million years ago—saw the extinction of about 80 percent of all animals.
“This included the loss of many different types of animals, however those whose body plans and behaviors indicate that they relied on significant amounts of oxygen seem to have been hit particularly hard,” Scott Evans, lead researcher on the study, says in a news release. “This suggests that the extinction event was environmentally controlled, as are all other mass extinctions in the geologic record.”
Discovering this new mass extinction event adds to the belief that five key extinction events have occurred since the beginning of the Cambrian Period, about 539 million years ago. The “big five” include 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 (220 million years ago), and the Cretaceous-Paleogene Extinction (65 million years ago).
Blaming a mass extinction on a loss of oxygen isn’t new, but the underlying cause of that oxygen drop is still unknown. “The short answer to how this happened is we don’t really know,” Evans says. “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.”
An unrelated Virginia Tech study says that a loss of oxygen availability is currently impacting the world’s fresh waters, part of a climate crisis that has scientists concerned about the next mass extinction event.
“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,” Evans says.
Now that we know we lost 80 percent of animals so many millions of years ago, interest in what those animals could have been like has increased. The clues found in fossil imprints include soft-bodied organisms that Evans calls “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,” Evans says. “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.”
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