updated 3/6/2006 7:23:03 PM ET 2006-03-07T00:23:03

A geologist who proposed the theory that a comet or asteroid smashed into the Earth and killed off the dinosaurs is the winner of a top research award.

Walter Alvarez, a geologist at the University of California-Berkeley, is the 19th recipient of the nonprofit Desert Research Institute's silver medallion and its $20,000 prize. He was to accept the award on Monday.

Alvarez's nearly two decade-long investigation produced an uncommon scientific drama of personal tenacity and ingenuity, said Stephen G. Wells, president of the institute.

"Until the impact theory was finally proven, Dr. Alvarez and his colleagues were regarded as heretics by the `old guard' in the field of geology," Wells said.

The theory dates to the 1970s in Italy, where Alvarez and his colleagues found high levels of the element iridium, which is extremely rare on Earth, but common in comets and asteroids.

They theorized it must have come from a giant asteroid that sent smoke, dust and iridium into the sky, blocking the sun, lowering the earth's temperature and eventually killing off plants and many species.

Alvarez's theory, first published in the journal Science in 1980, had few supporters until scientists found evidence of a huge impact crater on Mexico's Yucatan Peninsula in 1989. Later studies found evidence of debris from Mexico distributed by tsunamis that went as far as what is now Arkansas.

Alvarez told the story of his discovery in his top-selling nonfiction book in 1997, "T. Rex and the Crater of Doom."

DRI, established in 1959, is a nonprofit, statewide division of the University and Community College System of Nevada with an emphasis on environmental studies.

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