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Filling in cosmic holes.

A recent scientific finding has given credence to a theory, debated for over a decade, about the mass extinction of dinosaurs. Evidence of the occurrence of a cosmic catastrophe--sometime between the Cretaceous and Tertiary periods some sixty-five million years ago--began to mount in 1980 when geologists at the University of Berkeley in California discovered large amounts of the rare metal iridium, an element more common in outer space than on our planet. Subsequently, they found "shocked" quartz grains, caused only by episodes of intense stress, followed by the unearthing of ancient soot deposits, an indication of large scale burning.

Slowly a theory took hold about a huge meteorite crashing into Earth, screening out the sun with air borne debris and igniting worldwide forest fires. But there was a missing link. Where was the impact crater, exactly the right age and big enough, to provoke such devastation? Finally the crater has been identified--deep under the Yucatan Penninsula's northern coastline--and precisely dated.

"It looks to me like this is the smoking gun," said geologist Walter Alvarez, who along with his father Luis and two others is the theory's original proponent. But the gun has long stopped smoking. And visitors will have a hard time finding the crater, now dubbed Chicxulub (A Mayan word for "devil's tail") in honor of the nearby town, buried as it is under 65 million years of ensuing sedimentary deposits.

Although not all scientists agree that an extraplanetary event ended the dinosaurs' earthly reign, the Chicxulub meteorite has a lot going for it as the leading candidate. The crater is 110 miles wide, a size hole easily dug by a meteorite six miles across hitting Earth in a blast equal to 10,000 times the strength of the world's entire nuclear arsenal simultaneously detonated.

The crater also overlies a bed of limestone, which when struck would have vaporized into carbon dioxide, leading first to a rapid temperature drop followed by greenhouse effect warming. And its location in this Hemisphere explains why the beasts gathered so densely--perhaps to eat and drink from suddenly scarce food and water sources--before dying in the "dinosaur graveyards" of the western United States.

So even though there is nothing of Chicxulub to see with the naked eye, many dinosaur lovers might still want to make the pilgrimage to the Yucatan just for the thrill of walking in the oversize footstep of the extraterrestrial assassin of their beloved, cold-blooded friends.
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Title Annotation:Americas !Ojo!; dinosaur extinction theory
Author:Werner, Lou
Publication:Americas (English Edition)
Date:Sep 1, 1992
Previous Article:Life's art through the ages.
Next Article:A collision of worlds at the MET.

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