Extinction

Earth’s biggest extinction event, explained

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The asteroid that killed most of the dinosaurs may be the most well-known extinction event...

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...but it is not the most deadly extinction event.

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Nearly 200 million years before that fateful impact, 95 percent of Earth’s marine life and about 75 percent of land life disappeared within just a few thousand years.

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This turbulent time marked the end of the Permian period and beginning of the Triassic period.

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Debate has raged in the scientific community about whether this extinction is tied to massive amounts of volcanism or to methane released from frozen pockets of deep ocean ice.

Now, evidence from the shells of a humble, clam-like sea creature may have solved the debate.

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In a paper published in Nature Geoscience, scientists reconstruct the sequence of geological and climate events that led to this massive extinction.

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The researchers looked at shells of fossil brachiopods, clam-like animals that lived in the shallow Tethys ocean just before the extinction event.

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Boron isotopes in the shells revealed how acidic the ocean was — a measure directly tied to the concentration of atmospheric carbon dioxide.

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Using that measurement and computer simulations of Earth’s past, the researchers discover that a period of violent volcanism released an enormous amount of carbon dioxide into the atmosphere, which acidified the oceans.

A highly acidic ocean means that shelled animals can’t build their shells.

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The increased carbon dioxide in the atmosphere caused global warming, which led to increased chemical weathering on land.

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Nutrients from weathered rock washed into oceans, where they overloaded ecosystems and led to huge, oxygen-depleted, dead zones — like the one that forms annually in the Gulf of Mexico.

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The combination of a hot globe, acidic oceans, and oxygen-depletion caused nearly all life on Earth to rapidly die out over the next few thousand years.

Now that scientists understand what happened 252 million years ago, they can use those lessons to forecast what might happen in the future.

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Read more science and nature stories here.

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