[meteorite-list] New Geophysical Data Link Yucatan Crater To Mass Extinction Of Dinosaurs

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:37:35 2004
Message-ID: <200012180117.RAA01396_at_zagami.jpl.nasa.gov>

Office of Public Affairs
University of Texas-Austin
P O Box Z
Austin, Texas 78713-7509
(512) 471-3151 FAX (512) 471-5812

Contact:
Mary Lenz, Office of Public Affairs

December 15, 2000

UT Austin scientist reports results from study of Yucatan crater linked
to mass extinctions of dinosaurs

AUSTIN, Texas -- Scientists at The University of Texas at Austin Sunday
(Dec. 17) will present a report offering new geophysical clues to a
cataclysmic event that may have killed off the dinosaurs.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 Longhornbased out of Port
Aransas.

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.

During the AGU meeting, Christeson will be a panelist at a press conference
organized by AGU on large impact events.

For more information, contact Dr. Katherine Ellins at UT Austin's Institute
for Geophysics at (512) 232-3251 or click on "research" and "OBS" at the
Website: www.ig.utexas.edu

For information from the American Geophysical Union meeting in San
Francisco, contact Harvey Leifert at the AGU press room at (415)
905-1007, or e-mail: hleifert_at_agu.org
Received on Sun 17 Dec 2000 08:17:10 PM PST