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Crocodile Survival Casts Doubt on Dinosaur Big Freeze



Scientist: Crocodile Survival Casts Doubt on Dinosaur Big Freeze
By JANE E. ALLEN

SEATTLE (AP) - The survival of crocodiles 65 million years ago casts doubt on
the theory that a dramatic deep freeze wiped out dinosaurs, a scientist says.

Paul Markwick's presentation at a meeting of the Geological Society of America
on Wednesday added to the debate over whether an asteroid or comet hitting the
Earth killed the dinosaurs by throwing so much debris into the atmosphere that
the temperature plummeted.

"A climate change potent enough to exterminate all dinosaurs would undoubtedly
have a major effect on the climatically sensitive crocodilians, but I don't see
any evidence for that," said Markwick, a graduate student in geophysical science
at the University of Chicago. "The survival of crocs ... says it cannot have
been a major climate change."

Many scientists subscribe to the theory that an asteroid strike at Chicxulub in
Mexico's Yucatan may have led to the demise of the dinosaurs.

Chicxulub is home to a buried crater more than 100 miles wide that could have
been formed by a blast with the explosive power of 100 to 300 megatons of TNT.

The theory holds that the asteroid crash created a huge explosion that cast
enough dust and rock into the atmosphere to block out the sun, turning the Earth
cold and inhospitable to all but the hardiest organisms.

But several scientists at the meeting showed that some types of plants and
animals slipped through. The scientists are searching for explanations as to
just what happened at the border of the Cretaceous and Tertiary periods 65
million years ago.

Scott Wing, a paleobotanist and curator for the Smithsonian Institution in
Washington, said he still accepts the theory that an asteroid or comet
collision cause a deep freeze.

"Just because the impact causes some extinctions doesn't mean it caused all
extinctions," Wing said.