Kerr, R.A. December 20, 2013. Mega-Eruptions Drove the Mother of Mass Extinctions.  Science  Vol. 342:1424 

[Excerpts]

After 20 years of trying, researchers have finally convicted massive volcanic eruptions in Siberia as the culprit in the greatest of all mass extinctions, one that destroyed 90% of marine species on the planet.

The key evidence came from geochronologists applying the latest dating techniques to both the basalt from the eruptions and the rock encasing fossils of creatures that went extinct about 252 million years ago.

“I’m excited by the very clean-looking dating,” says paleontologist Paul Olsen of the Lamont-Doherty Earth Observatory in Palisades, New York. “It shows you could in fact have the Siberian eruptions cause the mass extinction.” Now, the question is which of the many possible ways that the volcanism could have wiped out species was actually at work.

Suspicion fell on the Siberian Traps—a vast volcanic landscape—more than 2 decades ago because of its enormous size and its age. In one of the greatest volcanic outbursts in Earth’s history, these eruptions carpeted a Western Europe–sized area of Siberia with several million cubic kilometers of basalt.

The best estimate for the initial eruptions is 252.28 million years, with the beginning of the extinction at 251.941 million years ago and its end at 251.880 million years ago. Uncertainties ranged from 0.031 million to 0.110 million years. That puts the volcanic and extinction events in the proper order and close enough to be cause and effect.

Now, researchers will focus on possible kill mechanisms.

Paleontologist Shuzhong Shen said one suspect should be dropped: sudden global warming caused by carbon dioxide pouring from the traps’ eruptions.

Analyses of temperature-sensitive oxygen isotopes in sediments deposited around the time of the extinction reveal a whopping 8°C to 10°C warming, but the rocks show the warming came just after the extinction, ruling out a role in the die-off.

This suggests that the extinction was “very short, only a few thousand years,” a rapidity that supports other potential kill mechanisms including acid rain from sulfur dioxide emissions.

Injecting 1.5 billion tons of volcanic sulfur dioxide into a computer model of the Permian atmosphere acidified rain across the Northern Hemisphere to pH 2, about that of lemon juice. That would have been disastrous for exposed vegetation and every animal that depended on it.

The volcanism may also have touched off toxic coal fires.

As it erupted, the magma that formed the Siberian Traps is known to have pierced coal deposits with a result of a vast, subterranean, coal-fired inferno that belched metal-bearing ash into the stratosphere, where the toxic debris sifted across the Northern Hemisphere.

Now that geochronologists have refined their dating tools, they hope to test suspicions that volcanism was at work in other mass extinctions. Dates for the huge eruptions at the opening of the Atlantic Ocean 201 million years ago and the mass extinction that cleared the way for the dinosaurs overlap, but their order is yet to be determined (Science, 21 December 2012, p. 1522). And several other possible pairings await.