- AUSTIN, Texas - Scientists
at The University of Texas at Austin Sunday presented a report offering
new geophysical clues to a cataclysmic event that may have killed off the
dinosaurs.
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- This report on Mexico's Chicxulub crater will be presented
by Dr. Gail Christeson, a research associate at UT Austin's Institute for
Geophysics (UTIG), at the fall meeting of the American Geophysical Union
in San Francisco. UT Austin's involvement in the project was sponsored
by the National Science Foundation.
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- The Chicxulub structure was formed 65 million years ago
when a large celestial body -- a comet or an asteroid -- slammed into the
Yucatan Peninsula with a force that makes a nuclear blast seem like a firecracker.
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- The impact produced fires, acid rain and tsunami-like
destructive waves. The collision gouged a crater nearly eight miles deep
and sent 12,000 cubic miles of rock, dirt and debris spinning into the
earth's atmosphere. The material blocked the sun, causing extreme changes
in the Earth's climate, which many scientists believe resulted in mass
extinctions.
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- The collision marked the abrupt end of the Cretaceous
period in geologic time and the start of the Tertiary period. And many
scientists currently believe that the event wiped out 80 percent of all
living species in the ocean. It also may have destroyed many terrestrial
species, including the dinosaurs.
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- Christeson and UTIG senior research scientists, including
Dr. Richard T. Buffler and Dr. Yosio Nakamura, worked with an international
team of scientists to survey the Chicxulub crater, which remains as an
unusual circular feature buried beneath 1,000 meters of sediments under
the northern Yucatan Peninsula and the Gulf of Mexico. Co-authors on Christeson's
presentation are Jo Morgan and Mike Warner from Imperial College in London,
and Colin Zelt from Rice University in Houston.
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- The aim of the researchers was to determine the Chicxulub
crater's actual size and to characterize its internal structure. Such details
should make it easier for scientists to understand how the crash actually
could have caused mass extinctions. It should also allow them to assess
the present-day risk posed by the thousands of comets and asteroids that
cross earth's orbit.
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- The team collected seismic reflection, refraction, gravity
and magnetic data over the crater. This research has provided the first
direct evidence of a crater with the multi-ring basin shape that is typical
of the largest impact craters on the moon and Venus.
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- The impact was so enormous it changed the shape of the
earth's crust -- 22 miles below the surface of the planet. The Chicxulub
crater is the first location where deformation at the base of the crust
has been found in a terrestrial impact crater.
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- The scientific team concluded that the Chicxulub crater
is about 125 miles in diameter, and that 12,000 cubic miles of debris was
blasted out of the earth by the impact. The impact carved out a cavity
about 7.5 miles below sea level. Mount Everest, in comparison, is 5.5 miles
high. Prior to this research, the size and morphology of the Chicxulub
crater had been in dispute, with estimates of its diameter ranging between
180 and 300 kilometers.
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- Such a large discrepancy in size translates to a factor
of ten differences in the energy of the impact with quite different consequences
for the Earth's environment. The energy released by the impact that blew
out the Chicxulub crater was equivalent to about 100 million megatons,
many orders of magnitude greater than the nuclear explosion at Hiroshima,
a 15-kiloton blast.
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- To collect the seismic data in the Gulf of Mexico, the
scientists deployed an array of Ocean Bottom Seismograph (OBS), instruments
which had been developed at UT Austin's Institute for Geophysics for undersea
projects such as this one. The OBS instruments were deployed from the UT
Austin Marine Science Institute vessel RV Longhorn based out of Port Aransas.
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- Additional analysis of the OBS data revealed that a region
at the center of the crater about 22 miles in diameter has been uplifted
by about 11 miles as a result of the impact and removal of overlying material.
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- During the AGU meeting, Christeson will be a panelist
at a press conference organized by AGU on large impact events.
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- For more information, click on "research" and
"OBS" at the Website: http://www.ig.utexas.edu
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- Note: This story has been adapted from a news release
issued by University Of Texas, Austin for journalists and other members
of the public. If you wish to quote from any part of this story, please
credit University Of Texas, Austin as the original source. You may also
wish to include the following link in any citation: http://www.sciencedaily.com/releases/2000/12/001225061758.htm
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