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Amber Holds Clues To Dinosaur Demise

SCIENTISTS trying to unravel the dinosaurs' fate have improved on science fiction.

In the movie ``Jurassic Park,'' biochemists took dinosaur blood from fossil insects embalmed in amber and cloned the great beasts. Experts consider that scenario unlikely. But scientists now are taking fossil air from bubbles preserved in amber and deducing how dinosaurs may have become extinct.

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They may have suffocated. Oxygen concentrations in the fossil air suggest that the dinosaurs evolved during an extended period when Earth's atmosphere was far richer in oxygen than it is today. A decline from a high concentration of 35 percent oxygen to the current 21 percent level may have been more than the evolution of dinosaur metabolism could cope with.

In describing this scenario at the Geological Society of America's annual meeting here, a four-member research team explained it is part of a scheme that ties many aspects of Earth's geological history into a new theory. The team includes geologist Gary P. Landis of the United States Geological Survey in Denver; paleontologists J. Keith Rigby Jr. of the University of Notre Dame and Robert E. Sloan of the University of Minnesota at Minneapolis; and physiologist Rich A. Hengst at Purdue University in West Lafayette, Ind.

Their ideas also give a new perspective to the theory that an asteroid impact wiped out dinosaurs and other species at the end of the Cretaceous period 65 million years ago. They suggest that such an impact was incidental to the main forces behind the dinosaurs' demise.

Dr. Landis reported that the fossil air samples show that, for 2 million to 3 million years before the asteroid hit, atmospheric oxygen concentration was declining.

Landis explained: ``This rapid shift ... put an enormous strain on all plants and animals. Dinosaur respiratory systems just couldn't deal with it.'' He added that his team's research indicates the dinosaurs ``gradually died out over a 10 million year interval preceding the [asteroid] impact, with nearly two-thirds of known species extinct before the hypothesized impact.''

To explain what happened, the four scientists have developed what they call the ``Pele hypothesis,'' named for the Hawiian volcano goddess Pele. It works like this:

Volcanic processes deep within our planet - perhaps near the core - drive a sustained epoch of intense volcanic activity. The eruptions pump massive amounts of carbon dioxide (CO2 ) into the air for hundreds of thousands or millions of years. Plants thrive on the CO2 enrichment. The heat-trapping gas also warms the climate.

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The burgeoning plant growth prevents a runaway greenhouse through photosynthesis. Plants remove the carbon from carbon dioxide and leave oxygen as a byproduct in the air. This raises atmospheric oxygen levels. The volcanism is also accompanied by a rise in sea level as the volcanic processes lift the sea floor. When the volcanism subsides, the scenario reverses. Sea level drops, atmospheric CO2 and oxygen levels fall, and the climate cools.

Dr. Sloan told a press conference that this ``Pele hypothesis'' can be tested by looking at the geological record. So far, he said, it appears to account for many aspects of geological and biological evolution. Dr. Rigby explained that the oxygen-level changes near the end of the Cretaceous fit the theory.

Rigby added that he and his colleagues are presenting the concept to fellow scientists now so that others will help evaluate it. He said he expects it ``to generate controversy in some circles.''