Earth’s biggest extinction event, explained

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.

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

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

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

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.

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

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.