A new study shows Earth's first known mass extinction occurred 550 million years ago

Virginia Tech geobiologists have recently concluded that the loss of the bulk of the species existing at the end of the Ediacaran Period (nearly 550 million years ago) was caused by a drop in oxygen availability worldwide.

As stated by Virginia Tech, Scott Evans, a postdoctoral researcher in the Department of Geosciences, demonstrates that this period saw the earliest mass extinction of species, which killed off around 80 percent of them.

"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,” Evans said.

“This suggests that the extinction event was environmentally controlled, as are all other mass extinctions in the geologic record.”

The study was published in PNAS on November 7.

“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 Shuhai Xiao, the study's coauthor.

“This has been demonstrated 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 current environmental changes on the biosphere.”

What exactly caused the drop in global oxygen? 

As per Evans, the simple answer is, "We don't know." As he suggests, the animals that go extinct appear to be reacting to a reduction in the amount of oxygen available on a global scale, albeit it might be caused by any number and combination of tectonic plate motion, volcanic eruptions, and asteroid impacts.

“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,” said Evans, who is also an Agouron Institute Geobiology fellow.

5 big mass extinctions in the history

According to Xiao, the "Big Five" are five known mass extinctions in animal history: 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 Triassi Jurassic Extinction (200 million years ago), and the Cretaceous Paleogene Extinct (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.

“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,” the authors wrote.

Study abstract:

The Ediacara Biota—the oldest communities of complex, macroscopic fossils—consists of three temporally distinct assemblages: the Avalon (ca. 575–560 Ma), White Sea (ca. 560–550 Ma), and Nama (ca. 550–539 Ma). Generic diversity varies among assemblages, with a notable decline at the transition from White Sea to Nama. Preservation and sampling biases, biotic replacement, and environmental perturbation have been proposed as potential mechanisms for this drop in diversity. Here, we compile a global database of the Ediacara Biota, specifically targeting taphonomic and paleoecological characters, to test these hypotheses. Major ecological shifts in feeding mode, life habit, and tiering level accompany an increase in generic richness between the Avalon and White Sea assemblages. We find that ∼80% of White Sea taxa are absent from the Nama interval, comparable to loss during Phanerozoic mass extinctions. The paleolatitudes, depositional environments, and preservational modes that characterize the White Sea assemblage are well represented in the Nama, indicating that this decline is not the result of sampling bias. Counter to expectations of the biotic replacement model, there are minimal ecological differences between these two assemblages. However, taxa that disappear exhibit a variety of morphological and behavioral characters consistent with an environmentally driven extinction event. The preferential survival of taxa with high surface area relative to volume may suggest that this was related to reduced global oceanic oxygen availability. Thus, our data support a link between Ediacaran biotic turnover and environmental change, similar to other major mass extinctions in the geologic record.