Earth and the Environment

What are some theories for the extinctions that took place at the end of the Cretaceous period?

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Theories for the extinctions include one or a mixture of the following: drastic cooling of the globe, retreat of the seas, breakup of the continents (see continental drift ), biological disease, reversals of the earth's magnetic field, or a change in atmospheric carbon dioxide and oxygen. Another popular theory was introduced in 1980 by Luis Alvarez and colleagues at the Univ. of California. Alvarez proposed that the earth was struck by an asteroid or comet about 6 mi (10 km) in diameter around 65 million years ago.

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