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The first mass extinction event was from a lack of oxygen, researchers find

Everett Eaton, The Virginian-Pilot on

Published in Science & Technology News

Scientists have speculated for years that the world is coming up on its sixth mass extinction, when a majority of the Earth’s creatures become extinct. But a couple of Virginia Tech researchers are studying what happened in the first extinction in hopes of avoiding another.

A new study led by Scott Evans, a postdoctoral researcher, and co-author Shuhai Xiao, a paleobiologist, showed that 80% of animals and organisms that died off 550 million years ago did so because of a drop in the amount of oxygen in waterways.

Some animals need more oxygen to survive, and the animals hit hardest were those that required more and were less mobile — they couldn’t get to areas with greater oxygen supplies. Larger animals that could take deeper breaths were more likely to live.

“This suggests that the extinction event was environmentally controlled, as are all other mass extinctions in the geologic record,” Evans said in a news release.

A mass extinction occurs when at least 75% of species are destroyed. The Earth has had five. The last one, about 65 million years ago, wiped out most dinosaurs. Scientists still debate the causes of the extinctions but the reasons range from asteroids colliding with the Earth to volcanic activity. Both can also cause temperature shifts that deplete oxygen levels as waters warm.

Climate change has increased average water temperatures and threatens already vulnerable species, said Joe Wood, senior scientist at the Chesapeake Bay Foundation.

Similar to the first extinction, animals that do not move or move very little are the most vulnerable. Today only about 30% of the 82 species of mussels in Virginia are considered stable. Six species are considered threatened or endangered.

 

Though animal and plant life were different then, we can still learn about the consequences of environmental changes, Xiao said. The research project began about four years ago and includes data compiled from more than 200 locations around the globe. Researchers created a database that combined information about changing life diversity from that time period.

More animals and organisms now have the physical ability to relocate and this adaptation was an important step in their evolution.

“Essentially, this extinction may have helped pave the way for the evolution of animals as we know them,” Evans said in the release.

The study was published this month in the Proceedings of the National Academy of Sciences.

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