Earth may experience 7th mass extinction, not 6th

Earth is currently in the midst of a mass extinction, losing thousands of species each year. New research suggests that environmental changes caused the first such event in recorded history, which happened millions of years earlier than scientists previously thought.

Most dinosaurs died out 66 million years ago at the end of the Cretaceous. Prior to this, the majority of creatures on Earth had been extinct between the Permian and Triassic periods, around 252 million years ago.

Thanks to the efforts of researchers at UC Riverside and Virginia Tech, a similar extinction is now known to have occurred 550 million years ago, during the Ediacaran Period. This discovery is documented in an article in the Proceedings of the National Academy of Sciences.

Although it is unclear whether this represents a true “mass extinction”, the percentage of organisms lost is similar to these other events, including the current one.

Researchers believe environmental changes are responsible for the loss of around 80% of all Ediacaran creatures, which were the planet’s first complex, multicellular life forms.

“Geological records show that the world’s oceans lost a lot of oxygen during this time, and the few species that survived had bodies adapted to low-oxygen environments,” said UCR paleoecologist and co-author Chenyi Tu. author of the study.

Unlike later events, this one was more difficult to document because the creatures that perished were soft-bodied and did not preserve well in the fossil record.

“We suspected such an event, but to prove it, we had to assemble a massive database of evidence,” said Rachel Surprenant, UCR paleoecologist and co-author of the study. The team documented the environment, size, diet, ability to move, and habits of nearly every known Ediacaran animal.

With this project, researchers sought to refute the charge that the major loss of animal life at the end of the Ediacaran period was anything other than an extinction. Some previously thought that the event could be explained by the failure to collect the right data or by a change in animal behavior, such as the arrival of predators.

“We can see the spatial distribution of animals over time, so we know they didn’t just move elsewhere or get eaten – they died,” Chenyi said. “We showed a real decrease in the abundance of the organisms.”

They also tracked the creatures’ surface-to-volume ratios, a metric that suggests falling oxygen levels were to blame for the deaths. “If an organism has a higher ratio, it can get more nutrients, and the bodies of animals that lived in the next era were adapted that way,” said UCR paleoecologist Heather McCandless, co-author of the study.

This project came from a graduate class led by UCR paleoecologist Mary Droser and her former graduate student, now at Virginia Tech, Scott Evans. For the next lesson, students will investigate the origin of these animals rather than their extinction.

Ediacaran creatures would be considered strange by today’s standards. Many animals could move, but they looked like nothing alive today. Among them were Obama crowneda disc-shaped creature named after the former president, and Attenborites janeaea tiny grape-like ovoid named after English naturalist Sir David Attenborough.

“These animals were the first evolutionary experiment on Earth, but they only lasted about 10 million years. Not long at all, evolutionarily speaking,” Droser said.

While it is unclear why oxygen levels declined so precipitously at the end of the era, it is clear that environmental changes can destabilize and destroy life on Earth at any time. Such changes have led to all mass extinctions, including the current one.

“There is a strong correlation between the success of organisms and, to quote Carl Sagan, our ‘pale blue dot,'” said Phillip Boan, a UC Riverside geologist and co-author of the study.

“Nothing is safe from extinction. We can see the impact of climate change on ecosystems and should note the devastating effects as we plan for the future,” Boan said.

(Cover image: dottedhippo/iStock/Getty)