[meteorite-list] Study: Dinosaurs Died Within Hours After Asteroid Hit Earth 65 Million Years Ago

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue May 25 15:02:07 2004
Message-ID: <200405251902.MAA20065_at_zagami.jpl.nasa.gov>

http://www.colorado.edu/news/releases/2004/168.html

Study: Dinosaurs Died Within Hours After Asteroid Hit Earth 65 Million Years Ago
University of Colorado at Boulder
May 24, 2004

According to new research led by a University of Colorado at Boulder
geophysicist, a giant asteroid that hit the coast of Mexico 65 million
years ago probably incinerated all the large dinosaurs that were alive at
the time in only a few hours, and only those organisms already sheltered
in burrows or in water were left alive.

The six-mile-in-diameter asteroid is thought to have hit Chicxulub in the
Yucatan, striking with the energy of 100 million megatons of TNT, said
chief author and Researcher Doug Robertson of the department of
geological sciences and the Cooperative Institute for Research in
Environmental Sciences. The "heat pulse" caused by re-entering ejected
matter would have reached around the globe, igniting fires and burning up
all terrestrial organisms not sheltered in burrows or in water, he said.

A paper on the subject was published by Robertson in the May-June issue
of the Bulletin of the Geological Society of America. Co-authors include
CU-Boulder Professor Owen Toon, University of Wyoming Professors Malcolm
McKenna and Jason Lillegraven and California Academy of Sciences
Researcher Sylvia Hope.

"The kinetic energy of the ejected matter would have dissipated as heat
in the upper atmosphere during re-entry, enough heat to make the normally
blue sky turn red-hot for hours," said Robertson. Scientists have
speculated for more than a decade that the entire surface of the Earth
below would have been baked by the equivalent of a global oven set on
broil.

The evidence of terrestrial ruin is compelling, said Robertson, noting
that tiny spheres of melted rock are found in the Cretaceous-Tertiary, or
KT, boundary around the globe. The spheres in the clay are remnants of
the rocky masses that were vaporized and ejected into sub-orbital
trajectories by the impact.

A nearly worldwide clay layer laced with soot and extra-terrestrial
iridium also records the impact and global firestorm that followed the
impact.

The spheres, the heat pulse and the soot all have been known for some
time, but their implications for survival of organisms on land have not
been explained well, said Robertson. Many scientists have been curious
about how any animal species such as primitive birds, mammals and
amphibians managed to survive the global disaster that killed off all the
existing dinosaurs.

Robertson and colleagues have provided a new hypothesis for the
differential pattern of survival among land vertebrates at the end of the
Cretaceous. They have focused on the question of which groups of
vertebrates were likely to have been sheltered underground or underwater
at the time of the impact.

Their answer closely matches the observed patterns of survival.
Pterosaurs and non-avian dinosaurs had no obvious adaptations for
burrowing or swimming and became extinct. In contrast, the vertebrates
that could burrow in holes or shelter in water -- mammals, birds,
crocodilians, snakes, lizards, turtles and amphibians -- for the most
part survived.

Terrestrial vertebrates that survived also were exposed to the secondary
effects of a radically altered, inhospitable environment. "Future studies
of early Paleocene events on land may be illuminated by this new view of
the KT catastrophe," said Robertson.

Located on the CU-Boulder campus, CIRES is a joint institute of
CU-Boulder and the National Oceanic and Atmospheric Administration.

Contact: Doug Robertson, (303) 492-3694
Owen Toon, (303) 492-1534
Jim Scott, (303) 492-3114
Greg Swenson, (303) 492-3113
Received on Tue 25 May 2004 03:01:56 PM PDT