More Evidence for Large K-T Asteroid

Tektite glass found in northeast Mexico chemically resemblessamples from the proposed asteroid impact crater recently discoveredby University of Arizona researcher Alan R. Hildebrand and his colleagues near Chicxulub, Yucatan, as well residues found at a site in Haiti, according to a team of researchers from UC Davis, UC Berkeley and University of Arizona. Taken together, the samples provide significant geochemical evidence for the popular but controversial theory that a large asteroid hit the earth 65 million years ago, causing abrupt climatic changes and the extinctions of many organisms, including dinosaurs, says UC Davis geology professor Stanley V. Margolis, who has analyzed the chemical composition of the glass tektites from the Mexican site. According to the hypothesis initially proposed by Walter Alvarez and coworkers at UC Berkeley, the K-T asteroid -- which derives its nickname from its apparent arrival at the boundary between the Cretaceous and Tertiary eras in Earth's history -- would have slammed into the Yucatan peninsula at the Chicxulub site, melted the terrestrial rock and thrown the molten particles up into the air. As they cooled, the particles rained down as tiny dense glass tektites. Sixty-five million years ago, the Mimbral, Mexico, site would have been an equivalent distance from the crater as the previously described Haiti site. Chemical analysis of the samples also are not consistent with the competing notion that volcanoes were the source of the glass tektites, Margolis says. Margolis, Alvarez and their colleagues will present three papers addressing various aspects of this discovery at the 1991 Geological Society of America annual meeting in San Diego, 9 a.m., Thursday, Oct. 24. Reporters who want more detailed background information on the story may join the researchers at a news conference at noon, Wednesday, Oct. 23, at the San Diego Convention Center in Room 5A. EMBARGOED until 9 a.m., Thursday, October 24.

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Andy Fell, Research news (emphasis: biological and physical sciences, and engineering), 530-752-4533,