[meteorite-list] Scientists Dig Deeper Into Massive Crater

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:55:49 2004
Message-ID: <200201221653.IAA27640_at_zagami.jpl.nasa.gov>

http://www.bergen.com/morenews/crater22200201227.htm

Scientists dig deeper into massive crater

By ROBERT S. BOYD
Knight Ridder Newspapers
January 22, 2002

WASHINGTON -- Scientists have begun drilling a mile-deep hole into a huge
underground crater that was left by a mountain-sized asteroid or comet that slammed
into Earth 65 million years ago and, according to a widely accepted theory, wiped out
the dinosaurs.

This month, they reached the uppermost layer of broken rocks buried beneath
Mexico's Yucatan Peninsula that were smashed, twisted, and hurled about by the
tremendous force of the collision.

The researchers hope to learn exactly what the space invader did when it penetrated
the Earth's crust in a fiery ball of unimaginable violence. The goal is to better
understand how the impact devastated the global environment, clearing the way for the
rise of mammals, including humans.

"Since we can't go back 65 million years in a time machine, drilling down to the
65-million-year level is the best we can do," said James Powell, the executive
director of the National Physical Science Consortium at the University of Southern
California in Los Angeles.

The ancient catastrophe marked "the transition between the Age of Reptiles and the
Age of Mammals," said David Kring, a planetary scientist at the University of Arizona
in Tucson and a leader of the drilling team from Mexico and the United States.

"Mammals were able to develop because the impact caused a complete change in the
biological landscape of Earth," Kring said in an interview. "Then evolution took
advantage of the change."

The smashed rubble, technically known as breccia, was found 2,800 feet (a half mile)
below ground, about 25 miles southwest of the Yucatan city of Merida. The crater is
called Chicxulub (pronounced cheek-shoo-loob) for the village located over its center.

Kring, a principal investigator in the Chicxulub Scientific Drilling Project, said the drill
would bring up rocky cores about as thick as a baseball bat that would reveal the
complete history of the ancient disaster.

"For the first time, we will be able to see the entire geology of the structure, all the
way down to the bedrock of the continental crust," he said.

Between the breccia and the bedrock, researchers expect to find a thick stony sheet
that was melted by the intense heat of the long ago crash. The volume of the molten
material could have been as much as 24,000 cubic miles, enough to fill Hudson's Bay
or the Gulf of California with lava.

"People have a hard time understanding the scale of this impact," Kring said.

"It moved millions of tons of rock, some of it more than 60 miles. Material 20 miles
beneath the surface was affected by the shock wave. A large part of the Earth's crust
was uplifted and folded by the blast."

Poisonous gases, dust, smoke, and fire from the impact blotted out the sun, lowered
temperatures, and contaminated the air for months or years, killing more than 75
percent of the plant and animal species in existence.

Wary of another such calamity, astronomers have begun a search for all large "Near
Earth Objects" that might be on a collision course with our planet.

For example, they spotted an asteroid the size of three football fields that streaked
within 500,000 miles -- twice the distance to the moon -- on Jan. 7.

If a space rock is detected early enough, scientists hope they will be able to deflect it
with a nuclear-armed missile. Even a slight change of course could be enough for a
far-off object to miss the Earth.

According to Powell, who is not a member of the Chicxulub project, the drilling could
clear up some mysteries, such as whether the space intruder was a comet or an
asteroid.

Asteroids are rocky objects orbiting between Earth and Jupiter. Comets are balls of ice
and frozen gas from beyond Pluto that periodically swoop through the solar system.
Comets are considered more dangerous than asteroids because their enormous speed
multiplies their power.

In addition, Powell said the drillers might find traces of sulfur-rich rocks in the crater,
helping to explain why the atmosphere poisoned so many living creatures.
Received on Tue 22 Jan 2002 11:53:52 AM PST