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Researchers at Virginia Tech have uncovered new evidence that suggests the earliest known mass extinction on Earth was caused by a drop in oxygen levels some 550 million years ago.

This marks the sixth, and oldest recognized mass extinction event on the planet.

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According to the study and LiveScience.com, about 80% of life on Earth disappeared at the height of the Ediacaran period, when Earth was filled with slug-like creatures and the ancestors of jellyfish.

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A study by researchers at Virginia Tech suggests that the missing fossils of these lifeforms reflect this phenomenon.

“Previous work, by myself and others, had shown diversity changes in these oldest animal communities, collectively known as the Ediacaran biota,” Scott Evans, a postdoctoral researcher at Virginia Tech, said Thursday. “To quantify those changes in diversity and to test the hypothesized causes of such change, we generated a database of every record of Ediacaran fossil occurrences from around the world.”

Evans said the study took about a year and consisted mostly of a literature review.

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But that literature, he said, built on the work of previous decades to help understand early animals.

Until this study, scientists had accepted five mass extinctions on record.

The Ordovician–Silurian extinction occurred 440 million years ago; The Devonian extinction occurred 365 million years ago; The Permian–Triassic extinction occurred 250 million years ago; The Triassic–Jurassic extinction occurred 210 million years ago; And the Cretaceous–Tertiary extinction occurred 65 million years ago.

Clam digger Scott Lavers, above, in this Friday, Sept. 4, 2020, file photo in Freeport, Maine, takes his canoe on his way to work on a mudflat exposed by the receding tide.  Warm waters and invasive species are threatening the way of life for many in the country's seafood industry.

This discovery places it 110 million years before the earliest known extinction.

Of the 20% of life forms that survived, the scientists found that they all had a high surface area, which helps the animals survive.

“I think the most important thing is that we now have a record going back 550 million years, which shows that animals responded to changing environmental conditions, which often resulted in extinction events,” Evans said. “Even though the causes and responses of animals to today’s environmental change may be different, the fact that such change has occurred repeatedly in the past has been shown to be significant enough to lead to major extinction events.” That’s what action we must take. Halt the course of our current human-driven climate change.”