[meteorite-list] Fossils Offer Support for Meteor's Role in Dinosaur Extinction

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Sep 20 11:53:56 2005
Message-ID: <200509201552.j8KFqdu06493_at_zagami.jpl.nasa.gov>

http://www.nytimes.com/2005/09/20/science/space/20mete.html

Fossils Offer Support for Meteor's Role in Dinosaur Extinction
By WILLIAM J. BROAD
New York Times
September 20, 2005

No guns materialized. Even so, the scientists kept a low profile while
digging, eager to avoid security forces from the nearby air base - an
important military site that helped provoke the Cuban missile crisis.
The diggers had no permit and no interest in being asked to explain
their presence.

In the end, they found rare fossils that are shedding new light on what
wiped out the dinosaurs at the end of the Cretaceous period 65 million
years ago.

For more than a decade, the standard view has envisioned a speeding
object from space that crashed into the earth and kicked up enough dust
and rock around the globe to blot out the sun. The smoking gun seemed to
be the discovery beneath the Yucat?n peninsula of Mexico of a
110-mile-wide crater called Chicxulub, after a nearby town.

But lately, doubters have argued that Chicxulub formed 300,000 years
before the mass extinction - too early to have played a role in the
demise of the dinosaurs and hundreds of other plant and animal species
that vanished at the end of the Cretaceous.

The team of scientists zeroed in on Cuba as an ideal place to seek
clues, having heard from Cuban colleagues of a possible trove of fossils
of the right age. The Cuban zone was 600 miles from the Mexican crater.

Now, in the September issue of Geology, the scientists, from Spain, Cuba
and Mexico, report that they have discovered a highly disturbed bed of
fossils that bears numerous signatures of Chicxulub's mayhem. The date
of the disturbance, 65 million years ago, is exactly at the end of the
Cretaceous.

"It's basic" to resolving the debate, Laia Alegret, a team geologist at
the University of Zaragoza in Spain, said in an interview. "But it was
difficult. The site is located opposite a military base. So it's almost
impossible to get a work permit."

The discovery was outside Santa Clara, a city in central Cuba whose
nearby air base drew scrutiny in 1962 when American spy planes spotted
Soviet jets and antiaircraft missiles. It turned out that the base held
Soviet bombers and a half-dozen atom bombs.

"It was definitely a hot spot," said Timothy Naftali, a cold war
historian at the University of Virginia.

Starting around 2000, Dr. Alegret and her European colleagues repeatedly
sought work permits for a nearby hill but always met with stultifying
delays, if not outright rejections. Finally, they slipped into the site
with their Cuban colleagues, going in late 2000, 2002 and 2003. At other
times, the Cubans went in alone.

A rocky outcrop on the hill showed an exposed bed of sedimentary rock
made up of broken bits of minerals and fossils. It was more than 30 feet
thick. The team took 66 samples. Examination with microscopes showed
numerous signs of cosmic violence, including quartz deformed by high
temperatures and pressures, as well as tiny spheres of glass, both
clearly debris from a spectacular fireball.

Microscopic study also revealed the presence of thousands of tiny fossil
creatures, most especially foraminifera. Those one-celled animals have a
bewildering array of minuscule shells. Forams, as they are known, evolve
so fast that geologists, paleontologists and oil companies use their
shifting appearance as reliable guides to geologic dating.

"They told the age of the sediments," Dr. Alegret said. "So we've
definitely confirmed the age of these deposits."

At the end of the Cretaceous, the rocky bed now in Cuba formed on the
ocean bottom at a depth of perhaps 3,300 feet, over a few days or weeks
as tons of debris rained down from the sky and huge waves generated by
the Chicxulub event washed land out to sea.

"It was geologically instantaneous," Dr. Alegret said of the deposit's
formation.

Earth movements over the ages turned that part of the seabed into land.

Dr. Alegret's co-authors include Ignacio Arenillas, Jos? A. Arz, Alfonso
Mel?ndez, Eustoquio Molina and Ana R. Soria of the University of
Zaragoza; Consuelo D?az of the Institute of Geology and Paleontology in
Havana; Jos? M. Grajales-Nishimura of the Mexican Institute of Petroleum
in Mexico City; and Reinaldo Rojas of the National Museum of Natural
History in Havana.

Dr. Alegret said that because of the site's importance, her Cuban
colleagues were talking with the government to have it protected from
rain and erosion. The aim is to save the outcrop for scientific study.
Received on Tue 20 Sep 2005 11:52:38 AM PDT