Mass extinctions have been proven to be the force that keeps the wheel of evolution turning. Scientists have now found the cause of the first known mass extinction that occurred about 550 million years ago.
Geobiologists at Virginia Tech have found that the earliest-known mass extinction was caused due to the diminishing availability of oxygen, which led to the loss of 80% of the animals that lived during the Ediacaran Period. The Ediacaran Period spanned a period of nearly 96 million years, preceded by the Cryogenian Period 635 million years ago and followed by the Cambrian Period 539 million years ago.
The, published in the Proceedings of the National Academy of Science, stated that although the study doesn’t point to the ultimate driver for the mass extinction, analysis of the data collected by scientists shows that animals who were heavily dependent on oxygen for survival did not fare well.
“Those whose body plans and behaviours indicate that they relied on significant amounts of oxygen seem to have been hit particularly hard,” said Scott Evans, a postdoctoral researcher at Virginia Tech and the lead author of the study, in a
“This suggests that the extinction event was environmentally controlled, as are all other mass extinctions in the geologic record,” he added.
Scientists cannot attribute the drop in the level of oxygen around the globe to a particular event. It could be owing to a number of phenomena including volcanic eruptions, tectonic plate movement, asteroid impact or a combination of any of these.
“What we see is that the animals that go extinct seem to be responding to decreased global oxygen availability,” Mr. Evans said.
“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, a co-author of the study.
Shedding light on the kind of animals that existed during this time, Mr. Evans said they looked “weird,” pointing out that they were so early in the evolutionary process that 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,” he added.
Cautionary tale for climate change
The study comes at a time when freshwater bodies are showing anoxia, or a reduced capacity to hold oxygen, brought on by global warming due to climate change and pollutant runoff.
“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 Mr. Evans.
There are five significant mass extinctions, called the ‘Big Five’, that have shaped the evolution of animals—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 most recent Cretaceous-Paleogene Extinction (65 million years ago).