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Pastimes : Let's Talk About Our Feelings!!! -- Ignore unavailable to you. Want to Upgrade?

To: Grainne who wrote (21470)	5/10/1998 1:48:00 AM
From: LoLoLoLita	Read Replies (2) \| Respond to of 108807

exactly! --------- By Paul Recer The Associated Press W A S H I N G T O N, May 7 - The Earth's orbit causes the planet to encounter more space dust every 100,000 years, and this could cause a cooling that may contribute to climate changes and to periodic extinctions of some life forms. About 30,000 metric tons of space dust, mostly originating from broken-up asteroids, fall into the Earth's atmosphere every year, says Stephen Kortenkamp of the Carnegie Institution of Washington. Particles of the dust reflect sunlight, in effect shading Earth and causing some cooling, said Kortenkamp, who is co-author of a study to be published Friday in the journal Science. Earth's eccentric orbit, which changes slightly from a circle to oval every 100,000 years, can double or triple the amount of dust falling onto the planet, perhaps causing a periodic change in climate, the researchers say. Kortenkamp said this climate change could be enough to start the process leading toward extinctions, such as the disappearance 65 million years ago of the dinosaurs. The researcher said the cooling effect of space dust may have put stress on the dinosaurs and that they were finally killed off by the impact of a large asteroid or comet. "Most people in the field believe there was an impact (that killed the dinosaurs), but there are studies that a gradual extinction began before that," said Kortenkamp. Theory Questioned Other researchers said they believe it unlikely that space dust was a major factor in either extinctions or climate change. If Kortenkamp and his co-author, Stanley Dermott of the University of Florida, are correct, "then we would be faced with extinctions on the order of every 100,000 years," said David Kring of the University of Arizona, an expert on the dinosaur demise. Instead, he said, the geologic history of Earth shows there have been major extinctions at intervals of 100 million years or greater. Kring also noted that the dinosaurs were a highly successful species for 150 million years. "During that time there would have been many cycles of dust increases, but there was no extinction," said Kring. He and Kenneth Farley of the California Institute of Technology also said they doubted that even the greatest amount of dust estimated by Kortenkamp and Dermott would be enough to cause dramatic cooling, such as in an ice age. That amount of dust, Farley said in Science, is "awfully small to do much of anything." Copyright 1998 Associated Press. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.