Earth is currently in the midst of a mass extinction with the loss of thousands of species every year. Recent research shows that environmental changes caused the first events in history, which occurred millions of years earlier than scientists previously realized.
Most of the famous dinosaurs disappeared 66 million years ago at the end of the Cretaceous period. Prior to that, the majority of Earth's creatures died out between the Permian and Triassic periods, roughly 252 million years ago.
Thanks to the efforts of researchers at the University of California, Riverside (UCR) and Virginia Tech, it is now known that a similar extinction occurred 550 million years ago, during the Ediacaran period. The discovery is documented in a paper in the Proceedings of the National Academy of Sciences.
While it's unclear whether this was a true "mass extinction," the percentage of organisms lost is similar to other events, including one currently underway.
Researchers believe that environmental changes were responsible for the disappearance of around 80% of all Ediacaran creatures, the first complex multicellular life forms on the planet.
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"Geological records show that the world's oceans lost a great deal of oxygen during that time, and some of the surviving species had bodies adapted for low oxygen environments," said Chenyi Tu, a UCR paleoecologist, quoted from Scitech Daily.
Unlike later events, these earliest are more difficult to document because the creatures that perished were soft-bodied and not as well preserved in the fossil record.
"We suspect such an event, but to prove it we have to collect a huge database of evidence," said Rachel Surprenant, a UCR paleoecologist.
The team documented nearly all of the known Ediacaran animals' environment, body size, diet, locomotion abilities, and habits.
With this project, researchers seek to disprove accusations that the huge loss of animal life at the end of the Ediacaran period was something other than extinction. Some scientists previously believed that the event could be explained by data that was not collected, or changes in animal behavior, such as the arrival of a predator.
"We can see the spatial distribution of animals over time, so we know they don't just move elsewhere or get eaten, they die. We have shown a marked decrease in the abundance of organisms," said Chenyi.
They also tracked the creature's ratio of surface area to volume, a measurement that points to decreased oxygen levels as a cause of death.
"If an organism has a higher ratio, it can get more nutrients, and the bodies of animals that lived in later eras adapted this way," said UCR paleoecologist Heather McCandless.
This research project stems from a graduate class led by UCR paleoecologist Mary Droser and former graduate student, now at Virginia Tech, Scott Evans. For the next class, students will investigate the origins of these animals, not their extinction.
An Ediacaran creature would be considered grotesque by today's standards. Many animals could move, but they resembled nothing living today. Among them are Obamus coronatus, a disc-shaped creature named after the 44th US President Barack Obama, and the small ovoid raisin-shaped Attenborites janeae named after British naturalist Sir David Attenborough.
"These animals were the first evolutionary experiments on Earth, but they only lasted about 10 million years. Not long, in evolutionary terms," said Droser.
While it's not clear why oxygen levels dropped so drastically at the end of a mass extinction, it's clear that environmental changes could destabilize and destroy life on Earth at any time. These changes have driven 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.
"No one is immune to extinction. We can see the impact of climate change on ecosystems and must pay attention to the deleterious impacts when we plan for the future," said Boan.