impact theory

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A proposal, published in 1984 by Walter Alvarez and five colleagues, that the mass extinction of various groups of organisms that occured at the end of the Cretaceous (q.v.) resulted from the collision of the earth with an asteroid or comet. Rocks at the Cretaceous-Tertiary boundary have high iridium concentrations, and this iridium is postulated to have arisen from the pulverized asteroid.

Subjects: Genetics and Genomics.

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