Religions > Atheism > Seismic images show dinosaur-killing meteor made bigger splash
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Religions > Atheism |
| User: |
"johac" |
| Date: |
24 Jan 2008 12:54:39 AM |
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Seismic images show dinosaur-killing meteor made bigger splash |
The K-T bib bang may have been bigger than previously thought. Of
course, the Deccan Traps volcanism might have had something to do with
it too.
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University of Texas at Austin
Seismic images show dinosaur-killing meteor made bigger splash
AUSTIN, TexasThe most detailed three-dimensional seismic images yet of
the Chicxulub crater, a mostly submerged and buried impact crater on the
Mexico coast, may modify a theory explaining the extinction of 70
percent of life on Earth 65 million years ago.
The Chicxulub crater was formed when an asteroid struck on the coast of
the Yucatan Peninsula. Most scientists agree the impact played a major
role in the ³KT Extinction Event² that caused the extinction of most
life on Earth, including the dinosaurs.
According to Sean Gulick, a research scientist at the Institute for
Geophysics at The University of Texas at Austinıs Jackson School of
Geosciences and principal investigator for the project, the new images
reveal the asteroid landed in deeper water than previously assumed and
therefore released about 6.5 times more water vapor into the atmosphere.
The impact site also contained sulfur-rich sediments called evaporites,
which would have reacted with water vapor to produce sulfate aerosols.
According to Gulick, an increase in the atmospheric concentration of the
compounds could have made the impact deadlier in two ways: by altering
climate (sulfate aerosols in the upper atmosphere can have a cooling
effect) and by generating acid rain (water vapor can help to flush the
lower atmosphere of sulfate aerosols, causing acid rain). Earlier
studies had suggested both effects might result from the impact, but to
a lesser degree.
³The greater amount of water vapor and consequent potential increase in
sulfate aerosols needs to be taken into account for models of extinction
mechanisms,² says Gulick.
The results appear in the February 2008 print edition of the journal
Nature Geosciences.
An increase in acid rain might help explain why reef and surface
dwelling ocean creatures were affected along with large vertebrates on
land and in the sea. As it fell on the water, acid rain could have
turned the oceans more acidic. There is some evidence that marine
organisms more resistant to a range of pH survived while those more
sensitive did not.
Gulick says the mass extinction event was probably not caused by just
one mechanism, but rather a combination of environmental changes acting
on different time scales, in different locations. For example, many
large land animals might have been baked to death within hours or days
of the impact as ejected material fell from the sky, heating the
atmosphere and setting off firestorms. More gradual changes in climate
and acidity might have had a larger impact in the oceans.
Gulick and collaborators originally set out to learn more about the
trajectory of the asteroid. They had hoped the craterıs structure in the
subsurface would hold a tell-tale signature. Instead, the structure
seemed to be most strongly shaped by the pre-impact conditions of the
target site.
³We discovered that the shallow structure of the crater was determined
much more by what the impact site was like before impact than by the
trajectory of the impactor,² says Gulick.
If scientists can determine the trajectory, it will tell them where to
look for the biggest environmental consequences of impact, because most
of the hazardous, shock-heated and fast-moving material would have been
thrown out of the crater downrange from the impact.
Researchers at Imperial College in London are already using computer
models to search for possible signatures in impact craters that could
indicate trajectory regardless of the initial surface conditions at the
impact site.
³As someone who simulates impact events using computers, this work
provides valuable new constraints on both the pre-impact target
structure and the final geometry of the cratered crust at Chicxulub,²
says Gareth Collins, a research fellow at Imperial College.
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http://www.eurekalert.org/pub_releases/2008-01/uota-sis012308.php
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John #1782
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