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The Chicxulub Crater Dig
By
Pasadena Bureau Chief
posted: 07:00 am ET
18 December 2000
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"Chicxulub Dig" SAN FRANCISCO Plans to drill deep into the Chicxulub crater in Mexico next summer will allow scientists to further characterize how an asteroid impact 65 million years ago killed 75 percent of all living species, including the dinosaurs.An asteroid, perhaps as large as 9 miles (15 kilometers) across, slammed into the Earth to create the 120-mile (200-kilometer) diameter crater. The crater is well preserved, but lies buried under hundreds of feet (meters) of sediments where it straddles the coast of Mexicos Yucatan peninsula. The violence of the impact extended deep into Earths crust. "Even at 35 kilometers (22 miles), were seeing the effects of this impact," said Gail Christeson, of the University of Texas Institute for Geophysics, who was part of a scientific panel that presented on Sunday the latest Chicxulub research results during the fall meeting of the American Geophysical Union. 
This three-dimensional map of local gravity and magnetic field variations shows a multiringed structure called Chicxulub named after a village located near its center. The ancient impact kicked up incredible amounts of dust into Earths atmosphere at the time, chilling global temperatures and precipitating what many suspect was a nuclear winter-type scenario.The force of the impact sent some debris so high above the atmosphere, only to undergo the heating of reentry, that portions found in present-day Belize resemble meteorites, said Kevin Pope, of Geo Eco Arc Research. The impacts effect was also global: The fossil record from the layers that immediately follow the event shows a near-total absence of life. Bad air Now, new evidence suggests that it was not only sunlight-blocking dust that prompted the global crisis, but atmospheric chemistry as well. For the high temperatures and pressures associated with the asteroid impact vaporized carbonate- and sulfate-rich rocks at the site, pumping vast amounts of carbon dioxide and sulfur into the atmosphere. "It dumps most of its energy around the impact site itself, so you have to think of how it distributed its effect around the Earth," Virgil Sharpton, a University of Alaska geologist, said of the culprit asteroid. "Its more efficient death through chemistry."
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