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Glass supports theory on dinosaur extinction

Atomic dating of bits of melted glass discovered in Haiti supports the theory that the dinosaurs were wiped out by a catastrophic change of climate resulting from an asteroid's collision with the Earth 64-million years ago, scientists say. In a study to be published today in the journal Science, researchers report they have established that tektites, small droplets of glass formed when a asteroid or comet smashes into the Earth, were created at the same time as the mass extinction of the dinosaurs.

Glen Izett of the U.S. Geological Survey said Thursday that the tektites were found in Haiti at the same geologic level of two other materials that are thought to originate from asteroid or comet impacts. The other materials are iridium, an element rare on Earth but common in asteroids, and shocked quartz grains, bits of rock that bear scars from a violent impact.

By dating the tektites, he said, the age of the iridium and shocked quartz deposits also could be dated.

"We dated 23 of these little critters and they turn out to be 64- to 65-million years old," said Izett. Fossil records have established that this was the period in which the dinosaurs died out.

Another expert, Eugene Shoemaker of the U.S. Geological Survey office in Tucson, Ariz., said the tektite study is "a very important indication of a large impact. This is a valuable addition to our knowledge supporting the theory."

A theory first proposed by Luis Alvarez of the University of California suggests that a very large asteroid striking the Earth at a high rate of speed would have exploded vast amounts of dust and debris into the atmosphere. This could have cause a global climate change that the dinosaurs could not tolerate.

The Alvarez theory is based on the fact that there is a worldwide geologic layer of iridium deposited about the same time that fossil records show extinction of the dinosaurs and many other animal species.

Now, said Izett, his work puts a precise date on tektites, another proof of a massive impact of an object from space.

Researchers have identified two sites as the possible impact points for major asteroids or comets 64- to 65-million years ago. One is on the Yucatan Peninsula of Mexico and the other is near Manson, Iowa.

Still other scientists have suggested sites in the Soviet Union and elsewhere.