Did a massive volcanic eruption in India kill off the dinosaurs?

There's a solid consensus among scientists about what happened to the dinosaurs 66 million years ago: A mountain-size 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 Yucatan Peninsula.

But there has long been an alternate theory, espoused by a rump caucus of researchers who think they've never been given a fair hearing. 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, according to a paper published online Thursday 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 one million years.

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

"Both are potentially really important," Schoene said. "I don't know if we can say the extinction would have or would not have happened without both of them."

One obvious scenario: Climate change caused by the eruptions could have stressed the biosphere and set the conditions for a greater die-off when the asteroid smashed the planet.

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