science

In the first few hours after a giant asteroid crashed into the coast of Mexico nearly 65 million years ago, the Earth's atmosphere became so hot that it quickly incinerated any unprotected life on land, according to a new report by a team of American geophysicists and geologists.

The report, which appears in the May-June issue of the Bulletin of the Geological Society of America, contradicts the widely accepted theory that the dinosaurs died out over a period of months or years after the asteroid impact at Chicxulub, Mexico.

"We think the nuclear winter was still important, but we think a lot of life died immediately," said Doug Robertson, the University of Colorado at Boulder geophysicist who led the research team. "The heat from the impact would have reduced the biomass on continents to a fine ash."

Using estimates based on existing research, the five researchers calculated that the energy released by the asteroid strike was equivalent to that in 100 million megatons of TNT. The force of the impact would have thrown debris high into the air, much of it burning up while still in the atmosphere, the report said. This, in turn, would have turned the Earth into a giant broiler oven.

Any organisms that were not in the ocean or burrowed underground would have died within "minutes to hours," according to the report.

"The types of organisms that were sheltered are almost an exact match of what we know made it through, like turtles, crocodiles and even birds," said Robertson.

Robertson's team supported its findings with data culled from drilling samples and natural outcrops around the world, which have revealed a layer of clay thought to be deposited from the fallout of the asteroid impact. In addition to containing soot and extraterrestrial iridium -- the existence of which supports the general asteroid theory -- the clay holds tiny spheres of melted rock, most likely deposited by the firestorm after the impact.