Growing evidence, paleontologists say, shows that the dinosaurs and their contemporaries were not wiped out by one meteor impact, as is commonly assumed.

Rather, multiple impacts, massive volcanism in India and climate changes conspired to finish off the great reptiles, according to Gerta Keller of Princeton University in Princeton, N.J., and colleagues.

Many scientists have linked the dieoff to a meteor-induced crater on Mexico’s Yucatan Peninsula, called the Chicxulub crater.


Painting of an underwater scene from the Cretaceous period, the late era of the dinosaurs, featuring a long-necked plesiosaur. Plesiosaurs and mosasaurs were the main predators of the Cretaceous seas. A shark is also shown. Plesiosaurs were not dinosaurs but went extinct along with them. (Painting by Vladimir Krb, courtesy North Dakota Geological Survey)

In fact that crash may have been the lesser, and earlier, of a series of events that pounded Earth for more than 500,000 years, according to Keller’s team.

A final, much larger and still unidentified impact 65.5 million years ago seems to have been the last straw, Keller said, exterminating two-thirds of all species in one of Earth’s worst mass extinctions.

It’s that impact—not Chicxulub—that left a famous layer of the element iridium, found in rocks worldwide and thought come from space, Keller argued.

“The Chicxulub impact alone could not have caused the mass extinction,” said Keller, because the impact occurred 300,000 years before the dieoff.

The story that seems to be taking shape, according to Keller, is that Chicxulub, though violent, actually conspired with prolonged, huge eruptions of the Deccan Flood Basalts in India to nudge species towards the brink. A second huge meteor crash finally pushed them over.

The Deccan volcanism released copious greenhouse gases that fueled global warming, she added, so that by the time of Chicxulub, the oceans were 3 to 4 degrees warmer at the bottom. “On land it must have been 7-8 degrees warmer.”

But where is the second crater? “I wish I knew,” said Keller, who presented the findings this week at the annual meeting of the Geological Society of America in Philadelphia.

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