a spiral-shaped fossil from the Helicoprion, a shark that lived in the Permian.
James St. John/Flickr
This fossilized spiraling shark tooth is from the Helicoprion, an unusual shark that lived during the Permian. The tooth whorl was located inside the shark’s lower jaw. The fossil is on display at the Idaho Museum of Natural History.

The largest extinction in Earth’s history marked the end of the Permian period, some 252 million years ago. Long before dinosaurs, our planet was populated with plants and animals that were mostly obliterated after a series of massive volcanic eruptions in Siberia.

Fossils in ancient seafloor rocks display a thriving and diverse marine ecosystem, then a swath of corpses. Some 96 percent of marine species were wiped out during the “Great Dying,” but what’s been debated until now is exactly what made the oceans inhospitable to life — the high acidity of the water, metal and sulfide poisoning, a complete lack of oxygen, or simply higher temperatures.

“This is the first time that we have made a mechanistic prediction about what caused the extinction that can be directly tested with the fossil record, which then allows us to make predictions about the causes of extinction in the future,” said Justin Penn, a UW doctoral student in oceanography, about new research published in Science from the University of Washington and Stanford University.

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