Did volcanic eruption help kill off the dinosaurs?

There's a solid consensus among scientists about what happened to the dinosaurs 66 million years ago: A mountain-sized meteorite crashed into the planet and triggered a mass extinction. The debris from the impact has been found in hundreds of locations around the world. Geologists have also found signs of the giant crater, centered on the tip of Yucatán Peninsula.

But there has long been an alternate theory, espoused by a rump caucus of researchers. They believe the extinction was caused, at least in part, by an extraordinary volcanic eruption in India.

This eruption created the Deccan Traps, a geological formation that covers nearly 200,000 square miles of western India. It was created by a flood of basaltic lava, the kind of eruption seen today on the Big Island in Hawaii. But the eruption that formed the Deccan Traps was unusually prolonged and prodigious. All told, the eruption produced about 1.3 million cubic kilometers of lava, which is about 1.3 million times as much material produced by the 1980 eruption of Mount St. Helens. The eruption pumped enormous, climate-changing quantities of carbon dioxide and sulfur dioxide into the atmosphere.

Now scientists have found a way to date more precisely the Deccan Traps eruption, and the results are a boost, potentially, for the volcano-did-it camp.

The main pulse of the lava flow began about 250,000 years before the mass extinction event, and ended about 500,000 years after, said a paper published online in the journal Science. Thus if the eruption is not a significant factor in the mass extinction, it's a remarkable coincidence. Earlier attempts to date the Deccan Traps, using less precise methods, had a much larger margin of error, on the order of plus-or-minus 1 million years.

The lead author of the paper, Blair Schoene, a professor of geosciences at Princeton, said the results indicate that both the catastrophic impact and the more gradual, but extraordinary, volcanic eruption could have been factors in the end-Cretaceous mass extinction.

"Both are potentially really important," Schoene said.

"I sort of favor the one-two punch idea," Schoene said.

Stronger words come from one of the paper's co-authors, Gerta Keller, another Princeton professor who has been among the most outspoken proponents of the hypothesis that the Deccan Traps caused the mass extinction. Keller has long maintained that the asteroid impact happened earlier than the die-off and couldn't have been the trigger. She has long been viewed as a maverick in the scientific community.

"I think this is a game-changer," she said of the results. She said the new dating strengthens the case for volcanism as the "primary cause" of the mass extinction. "The data is so strong at this point that the momentum is entirely on my side."

The researchers took rock samples in India and scrutinized them for crystals containing uranium and lead. Crystals of zircon form in magma with trace amounts of uranium inside. The uranium gradually decays into lead. Because the rate at which uranium decays is well known, the ratio of uranium and lead isotopes in the crystals serves as a kind of clock, revealing how long it has been since the crystals formed.

The fundamental problem for the hypothesis that volcanism caused the mass extinction is that it doesn't seem to be necessary. The mass extinction, including the demise of the non-avian dinosaurs, was for a long time among the greatest mysteries in science, but few people view it as a mystery anymore.