This column is provided as a public service by the Geophysical Institute, University of Alaska Fairbanks, in cooperation with the UAF research community. Ned Rozell is a science writer at the institute.

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SAN FRANCISCO—Sixty-five million years ago, dinosaurs disappeared from Earth. Sixty-five million years ago, an object larger than this city of San Francisco crashed into our planet. Coincidence? Maybe not.

Two of the thousands of scientists here at the annual meeting of the American Geophysical Union will soon drill a test core into the Chicxulub crater to find out more about the greatest catastrophe Earth has ever experienced.

Chicxulub impact crater is more than 200 kilometers in diameter, a mammoth divot in Earth caused by a meteorite, probably a comet. Located on the Yucatan Peninsula in Mexico, the crater is the thumbprint of a random event so unsettling that it may have wiped out thousands of species, including dinosaurs.

Finding out how a meteorite can destroy most of the life on Earth is the mutual goal of Buck Sharpton, with the Geophysical Institute of the University of Alaska Fairbanks, and Luis Marin, with Mexican National University. The two researchers met at a point halfway between their homes this week at the AGU conference in San Francisco. Here, they presented plans to drill a two-kilometer hole into the crater, a project they’ll begin in the spring of 2000.

Sixty-five million years ago, a meteorite traveling about 50 kilometers per second tore a hole through Earth’s atmosphere. The object, a rough sphere about 15 kilometers in diameter, hit the planet with a force millions of times more powerful than a nuclear bomb. The shock created a giant crater and turned the meteorite to dust, which is now found in soils all over the world.

Scientists think the impact may have caused a double whammy that killed the dinosaurs. Sulfur particles from gypsum rock evaporated by the impact could have clogged the atmosphere, the 30-mile shell of gases surrounding Earth. The floating particles could have blocked sunlight, causing a “nuclear winter” that cooled down the planet and decimated plants for a few years. Plant-eating animals died. They were followed by meat-eaters. Sulfur particles falling into the ocean also may have turned water as acidic as battery acid, dooming most of the creatures in the sea. When the atmosphere was finally cleared of the sulfur after a couple of years, immense amounts of carbon dioxide released from vaporized limestone may have then caused a greenhouse effect, trapping heat from the sun and causing a warming that may have killed anything that survived the effects of the sulfur.

Sharpton and Marin hope to tap the secrets of Chicxulub impact crater by drilling a hole and pulling up a continuous core of material. The core will tell them what type of rock was vaporized during the impact, which will help them determine the feasibility of the nuclear-winter and greenhouse-effect scenarios. The core might hold the clues to one of the greatest mysteries of science: what killed the dinosaurs, and how did they die?

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