Eighty percent of the lava was produced during a single pulse of eruptions, she added.
Coincidental Timing
But prior studies, based on radioactive elements contained in the lava, only showed that the lava flows and the extinctions occurred within about 300,000 years of each other.
So Keller followed a finger of lava across India and down an ancient river valley that channeled it all the way to the Gulf of Bengal, more than 900 miles (1,500 kilometers) from its source.
Some of that lava eventually wound up underwater and slowly accumulated marine sediments containing the fossils of plankton. But none contained species killed off during the K-T extinction, suggesting the flows ended around that time.
The correlation isn't perfect, Keller said. It's always possible that the lava flow ended slightly after the extinction—or even a few tens of thousands of years before—because the geological record isn't complete.
But, she added, "if someone wants to say that this kind of thing has nothing to do with [the] mass extinction—even if it ended 100,000 years earlier—they're out of their mind."
Still Open to Debate
Keller's arguments against Chicxulub as the lone dino-killer have long been contentious, and this one is no exception.
Greg Ravizza, a geochemist at the University of Hawaii who has studied seawater changes related to the Deccan volcanism, argued that Keller is focusing too strongly on when the volcanism ended.
"Keller and co-workers prefer an interpretation that concentrates the bulk of the Deccan volcanism very close to the K-T boundary," he said by email.
But the key question is when the major pulse of Deccan volcanism started, he pointed out.
Furthermore, he said, the lava flows Keller studied weren't even recognized as part of the Deccan volcanism until recently and are geographically isolated from the vast majority of the Deccan Traps.
"Whether or not the upper and lower traps at Rajahmundry [the location studied by Keller] can be claimed to fully represent the two largest and most extensive Deccan volcanic eruptions is still open to debate," Ravizza said.
Meanwhile, Keller's argument that the Deccan Traps eruption forced major climate change may have additional support.
Anne-Lise Chenet is one of the scientists whose radioactive decay studies helped confirm that the Deccan volcanism occurred within a few hundred thousand years of the K-T boundary.
She is also co-author of a study, soon to appear in the Journal of Geophysical Research Letters, that examined the volcanic gases emitted by the flows.
"The amount of sulfur dioxide emitted by each volcanic event ... [leads us] to reconsider the effect of volcanism ... on the climate and environment," she said by email.
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