[meteorite-list] The K-T Impact Extinctions: Dust Didn't Do It

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:55:50 2004
Message-ID: <200201240055.QAA19841_at_zagami.jpl.nasa.gov>

http://www.geosociety.org/pubntrst/pr/02-04.htm

Geological Society of America
Boulder, Colorado

Contact information:
Kevin O. Pope
Geo Eco Arc Research
16305 St. Mary's Church Road
Aquasco, MD 20608
Phone: 301-888-1048
E-mail: kpope_at_starband.net
(NB: Dr. Pope will be out of town from January 27 to February 9, 2002.)

Ann Cairns
Director - Communications and Marketing
acairns_at_geosociety.org, 303-357-1056

FOR IMMEDIATE RELEASE: January 23, 2002

GSA Release No. 02-04

The K-T Impact Extinctions: Dust Didn't Do It
By Kara LeBeau, GSA Staff Writer

Scientists basically agree that an asteroid struck the Earth some 65
million years ago and its impact created the Chicxulub crater in Yucatan,
Mexico. More controversial is the link between this impact and a major
mass extinction of species that happened at the geological (K-T) boundary
marked by the impact.

But what mechanism did the impact trigger to cause mass extinction? The
conventional theory is that impact dust obscured the sun, shutting down
photosynthesis and snuffing out life. Kevin Pope from Geo Eco Arc
Research shows in the February issue of GEOLOGY that the assumptions
behind this theory are amiss, and therefore damage estimates from future
asteroid impacts are also amiss.

This latter point became a recent issue when a large asteroid passed
near the Earth on January 7 and news reports exaggerated its potential
impact effects.

"Based on the old, inaccurate dust numbers, which erroneously suggested
that a medium-sized asteroid (1-2 km in diameter) could cause global
climate change and famine, scientists calculated that one's chance of
getting killed by an asteroid impact were about the same as dying in a
plane crash," Pope said. "My new impact dust estimates indicate that
death by an asteroid is far less likely and that such medium-sized
asteroid impacts would not have catastrophic global effects. But of
course the regional effects would still be devastating."

To truly understand the influence of impact dust, scientists need to
find a way to directly measure the amount of small dust particles
in such places as the K-T boundary. In the meantime, Pope studied
patterns of coarse dust particles to create a model that showed
how the small dust particles were dispersed. Incorporating these
geological observations with new theoretical work, Pope asserts that
very few of the particles are of the size that it would take to shut
down photosynthesis for any significant length of time and therefore
the original K-T impact extinction hypothesis is not valid. He
believes it may have been sulfate aerosols produced from impacted
rocks and soot from global fires that could have shut down
photosynthesis and caused global cooling.

"The original studies of the clay layer found at the K-T boundary
assumed much or all of this layer was derived from fine impact dust,"
he said. "More recent studies of this layer have shown this not
to be the case. Furthermore, earlier estimates were based on
extrapolations of data from surface atomic bomb blasts, which had
about 100 million times less energy than the Chicxulub impact.
Extrapolation over eight orders of magnitude is risky business."

Pope was involved in the "discovery" of the Chicxulub crater in 1989-
1990 when he worked at the NASA Ames Research Center. (Oil geologists
had discovered the crater and reported the finding in 1981, but it
was basically ignored.) He was using satellite images to map water
resources in the Yucatan with Adriana Ocampo and Charles Duller when
they found the semi-circular ring of sink holes. They thought the
crater might be the K-T impact site and published their hypothesis
in the May 1991 issue of NATURE.
Received on Wed 23 Jan 2002 07:55:30 PM PST