When we look at the major mass extinctions on Earth, the first of the Big Five Extinctions is considered to be the Late Ordovician, which took place about 445 million years ago. However, the evidence that animals experienced another mass death around 100 million years ago has been growing in the last few years. About 550 million years ago, a sudden drop in global oxygen availability led to the death of 80 percent of all mammals.
Evidence of its extinction, called the Ediacaran Period, comes from two important fossil records. One of them dates from 560 to 550 million years ago and is known as the White Sea community. The more recent one dates from 550 to 539 million years ago and is called the Nama community. Earlier fossils show 70 genera of large-scale animals, but later fossils show only 14.
It’s possible that this difference was due to sampling or conservation biases between the two communities, but the team found no evidence of this. They found that among these marine animals, those with a larger surface area relative to their volume were more likely to survive. This is seen as an indication that those who can get more oxygen survive.
“Our work shows that this new, first mass extinction of animals, like all other mass extinctions in Earth’s past, was due to massive climate change,” said Scott Evans of Virginia Tech in a statement.
It is unclear what the exact cause of this mass extinction was, and if it really was caused by a depletion of oxygen. Volcanoes, tectonic plates or even a meteor can cause this.
Mass extinctions laid the foundation for the evolution of life on Earth and shaped the types of organisms that survive today.
The study was carried out during the COVID-19 pandemic by creating a database of available records from the period. Fossils of these animals found in ancient rocks show these multicellular creatures as “strange”, as researchers put it.
“These organisms appear so early in the evolutionary history of animals that in most cases they seem to be experimenting with different ways of building large, sometimes mobile, multicellular bodies,” says Evans. “The fossils we found before this extinction don’t quite fit the way we classify animals today. Basically, this extinction may have paved the way for the evolution of animals as we know them.”
The study was published in the journal Proceedings of the National Academy of Science.
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