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September 11, 2007
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Report: dinos took repeat pounding before final exit
Oct. 26, 2006
Courtesy National Science Foundation
and World Science staff
Growing evidence,
paleontologists say, shows that the dinosaurs and their contemporaries were not wiped out by one meteor impact, as is commonly assumed. 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)
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.
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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Growing evidence shows that the dinosaurs and their contemporaries were not wiped out by one meteor impact, as is commonly assumed, according to paleontologists. Gerta Keller of Princeton University in Princeton, N.J., and colleagues announced that new studies indicate multiple meteor impacts, massive volcanism in India and climate changes conspired to finish off the dinosaurs about 65 million years ago. Many scientists have linked the dieoff to a meteor-induced crater on Mexico’s Yucatan Peninsula, called the Chicxulub impact. But that impact may have been the lesser and earlier of a series of meteor impacts and volcanic eruptions 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, said Keller, 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 believed come from space, Keller believes. That layer is believed to mark the impact that finally ended the Age of Reptiles. “The Chicxulub impact alone could not have caused the mass extinction,” said Keller, “because this impact predates the mass extinction.” But where is the other crater? “I wish I knew,” said Keller. She presented her findings this week at the annual meeting of the Geological Society of America in Philadelphia.