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AP: Clues to Dinosaurs' Demise Sought

Clues to Dinosaurs' Demise Sought

Filed at 11:09 p.m. ET

SAN FRANCISCO (AP) -- The rock and dust kicked up by
an asteroid impact 65 million years ago were not
enough to kill the dinosaurs, according to researchers
-- but the debris may have sparked a deadly global
chemical reaction in the atmosphere.

New studies show the Chicxulub impact crater on the
coast of Mexico's Yucatan Peninsula is smaller than
once thought, making dinosaur extinction difficult to
explain completely. Researchers presented those
findings Sunday at the American Geophysical Union's
fall meeting.

``If you rely on little pieces of debris actually
clobbering organisms, then you're in trouble,'' said
Virgil ``Buck'' Sharpton of the Geophysical Institute
at the University of Alaska in Fairbanks.

Since 1980, research on the dinosaurs' disappearance
has focused on the 125-mile crater and the
10-mile-wide asteroid believed to have created it.
Dust from the impact was thought to have blocked out
sunlight for years.

Now, however, drilling around the Yucatan crater
indicates the presence of carbonates and sulfate
rocks. The new theory is that these were vaporized by
the asteroid impact, a process that would have
released chemicals that produce sulfur and the
greenhouse gas carbon dioxide.

The sulfur compounds would be especially toxic,
Sharpton said.

``They do nasty things. They form little globules that
persist in the atmosphere for some considerable amount
of time -- decades to a hundred years,'' he said.
``They also mix with water in the atmosphere and
produce sulfuric acid.''

So besides old theories about a nuclear winter-type
global cooling, researchers believe the giant
oxygen-breathing reptiles also may have choked on
carbon dioxide and suffered showers of caustic acid.

``How do you initiate the global crisis? It had to be
atmospheric chemistry of some sort,'' Sharpton said.
``That's the only way you can transport the effect
globally of something that dumps the majority of its
energy into a single spot on the Earth's surface.''

Rock and dust alone from Chicxulub probably would not
have been sufficient to snuff out life on the other
side of the globe, Sharpton said -- even a small
pocket of life would have repopulated the planet.

To test the theories further, Sharpton and colleagues
plan to drill 1.5 miles into the crater and retrieve
samples of the rock present in what was a shallow sea
when the asteroid hit. The project, located 50 miles
south of Merida will not begin before June.

Studies of Chicxulub have more value than explaining
the dinosaur extinction, said Gail Christeson of the
University of Texas Institute for Geophysics in

``We're interested not just because it's the point of
impact but because of what we can learn about other
asteroid impact craters,'' she said.

Scientists hope to learn what might happen if a future
asteroid or comet crashes into Earth.

Other studies presented at the AGU meeting compare
Chicxulub with the much older Sudbury crater near
Ontario. By comparing different levels of melted rock
at the bottom of both craters, researchers are more
confident that Sudbury was formed by a high-velocity
comet and Chicxulub by a slower-moving asteroid.

Comets are chunks of dirty ice; asteroids are giant

Such large impacts are estimated to occur only once
every 350 million years. That makes such craters --
especially well-preserved ones such as Chicxulub --
difficult to find on Earth.

``We've got an opportunity, a unique opportunity on
the face of the Earth, to study a crater in three
dimensions that has been preserved almost in pristine
shape,'' Sharpton said. ``And that's really what we
want to do.''


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"Catapultam habeo. Nisi Pecuniam omnen mihi dabis ad capul tuum saxum immane 


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