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Developments in Brief : Theory on Dinosaurs' Demise Finds Support

May 10, 1987|Compiled from Times staff and wire service reports

A team of government geologists has found new evidence to support the controversial theory that some gigantic object crashed into Earth 65 million years ago and wiped out dinosaurs and many other forms of life.

The scientists, from the U.S. Geological Survey in Denver, said they found quartz grains bearing telltale evidence of shock from a tremendous impact at five sites in Europe, one in New Zealand and one from a drill core sample in the bottom of the Pacific Ocean. Similar quartz grains also have been found in Montana and in the Soviet Union.

All the shocked quartz grains came from deposits that originated at the end of the Cretaceous Period 65 million years ago--about the time when dinosaurs and some other species disappeared.

Nobel laureate Luis Alvarez of the Lawrence Berkeley Laboratory and his son Walter, a University of California, Berkeley, geology professor, proposed seven years ago that the mass extinction was caused by the impact of an asteroid or comet that kicked up a global dust cloud that blocked out sunlight for months. The lack of sunlight would have suppressed photosynthetic processes by which plants grow, thus eliminating food supplies for many creatures.

"The Alvarez hypothesis of an Earth-girdling dust cloud of ejecta from the impact of a large extraterrestrial body is strongly supported" by the quartz findings, Bruce Bohor and several associates wrote in the current issue of the journal Science.

The report said the impact that deformed the quartz was powerful enough to spew dust worldwide.

The Alvarez theory originally was based on the discovery of a jump in the element iridium in sediments formed at the end of the Cretaceous Period. Iridium is 1,000 times more abundant in extraterrestrial material than on Earth.

Other evidence in support of the theory was a 1985 report of a worldwide layer of soot in the 65-million-year-old sediments, indicating that some huge impact triggered continent-sized wildfires. But some scientists doubt the theory, saying that there is not enough evidence in the fossil record to indicate that mass extinctions occurred abruptly.

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