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Opinion
Faye Flam

Earth Has Seen CO2 Spike Before. It Didn’t End Well.

It’s unclear exactly what happened 252 million years ago as the planet warmed, but 90 percent of species went extinct.

Humans might avoid their fate. Especially if an asteroid helps out.

Humans might avoid their fate. Especially if an asteroid helps out.

Photographer: Dan Kitwood/Getty Images

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Corrected

Asteroid impacts used to be science popularizers’ favorite existential threat, but space rocks have been displaced by atmospheric carbon. This is not just fashion but the result of a new reading of our planet’s past.

In the 1990s, scientists thought asteroid impacts had triggered five mass extinctions, including the extinction of the dinosaurs 65 million years ago. Now, they’ve come to realize that the other four of the Earth’s mega-disasters probably came from within — triggered by belches of carbon into the atmosphere and oceans.