[meteorite-list] Mass-Extinction Controversy Flares Again

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:10:06 2004
Message-ID: <200304101624.JAA29346_at_zagami.jpl.nasa.gov>

http://www.nature.com/nsu/030407/030407-7.html

Mass-extinction controversy flares again

Core from asteroid crater fuels debate on what wiped out the
dinosaurs.

Rex Dalton
Nature Science Update
10 April 2003

A claim that the asteroid that struck Mexico 65 million years
ago did not cause the mass extinction that wiped out
dinosaurs triggered heated debate at a meeting this week.

The announcement is based on preliminary analysis of the
first core drilled into the 185-kilometre Chicxulub
asteroid crater near the Yucatan Peninsula. Gerta
Keller of Princeton University in New Haven, Connecticut,
says that she has found microfossils there hinting that
abundant plankton survived for at least 300,000 years after
the impact.

Many believe that the impact shrouded the Earth in dust and debris,
shutting down plant photosynthesis and leading to the rapid demise
of most creatures, from marine microorganisms to dinosaurs.

But Keller reckons that the signs of life in the crater core are "the
smoking gun" that the asteroid didn't cause the widespread die-out,
properly called the Cretaceous-Tertiary (K-T) boundary. What's
more, a lack of evidence of compaction in the core hints that the
impact crater was much smaller than was thought, says Keller's
colleague Wolfgang Stinnesbeck at the University of Karlsruhe,
Germany.

So the group subscribes instead to the idea that a series of asteroid
impacts brought about the K-T boundary.

Jan Smit, a geologist at Vrije University in Amsterdam who is also
studying the crater's sediments, disagrees. He counters that what
Keller's team labels 'fossils' are simply spheres of crystal. Plus he
cites seismology studies that support a major asteroid having created
the Chicxulub crater.

These divergent views were aired at a joint conference of the
European Geophysical Society, the American Geophysical Union and
the European Union of Geosciences in Nice, France. Listeners were
shocked and stunned that two groups could disagree so much.

But the story of the K-T boundary has been long been controversial.
It was first suggested about 25 years ago that a life-obliterating
asteroid plunged into the Earth to trigger the extinction.

Now dozens of scientists around the world are analysing the results
of the first drill of the crater, completed in February 2002, to glean
new data on the events of 65 million years ago. Other drills are
planned, including one closer to the centre of the impact point, to
provide further fuel for debate.

Rex Dalton is the West Coast Correspondent of the journal Nature.
Received on Thu 10 Apr 2003 12:24:36 PM PDT