Even 5-year-olds, when asked what killed the dinosaurs, would say it was a meteor or something that came from space, says Gregory Ravizza, University of Hawaii-Manoa marine and environmental geologist.

The theory that a single impact from a gigantic space object caused the extinction of more than half of the earth's plant and animal species 65 million years ago has been the general view for 30 to 40 years, said the associate professor of geology and geophysics.

But scientists have continued to ask questions and debate the issue, with some suggesting the extinction was due to multiple impacts or a long series of volcanic eruptions at the Deccan Traps in what is now India, he said.

A paper in a recent Science journal by 41 scientists in 12 countries appears to settle the issue. It summarizes evidence “;which is really compelling and really remarkable that indeed there is one really big impact that coincides with this mass extinction event,”; said Ravizza, one of the participants.

The data—described by Ravizza in an interview and presented in a National Science Foundation teleconference—shows a cataclysmic asteroid crashed into the ocean more than 65 million years ago off the Yucatan Peninsula.

Events 65 million years ago are important today, Ravizza pointed out, because “;they really made clear how releases of huge amounts of energy could have devastating consequences for life on earth.”;

The impact resulted in the Cretaceous-Paleogene (K/P) extinction with “;loss of dinosaurs, all flying reptiles, most marine reptiles and more than half of land plants and insects and hosts of other terrestrial and marine organisms—50 to 70 percent of all species on Earth,”; the scientists said.

Describing the scientific findings in the teleconference, Kirk Johnson of the Denver Museum of Nature & Science said the impact object was about 6 miles in diameter and traveling at 10 times the speed of a rifle bullet.

It struck what is now Chicxulub, Mexico, creating a crater more than 112 miles in diameter and more than 18 miles deep and a hole more than 2 miles deep in the sea floor, he said.

It triggered earthquakes 100 times larger than the recent 8.8-magnitude earthquake in Chile and tsunamis many times larger than the Indian Ocean wave Dec. 26, 2004, the scientists said.

The consequences: worldwide wildfires, acid rain and extended darkness from smoke, dust and iridium that blocked the sun and cooled temperatures. Enormous volumes of rock vaporized and turned into a gas.

Comparing data from 350 clay layer sites at the Cretaceous-Paleogene (or Cretaceous-Tertiary) boundary in soil around the globe, the scientists found high levels of iridium and material that originated from the impact.

Ravizza's Manoa lab analyzes elements such as iridium and osmium that he said are very rare at the earth's surface but rich in most asteroids and meteorites. Looking predominantly at deep-sea sediment records, his team saw a big increase in iridium and osmium consistent with asteroid and meteorite impacts, he said.

Debris from the impact was lifted from the bottom of the sea floor after the event and deposited in faraway regions, he said.

He said the impact object had a chondrite body, which is not surprising since most meteorites are chondritic, “;but from the composition of the material, we have a very good idea it was a particular type of meteorite that is among the more primitive in the solar system.”;

Johnson said the object is believed to have been an asteroid, but a comet cannot be ruled out.

ON THE NET:

» Potentially Hazardous Asteroids
» The Chicxulub Discovery
» UH-Manoa Department of Geology and Geophysics