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Pastimes : Let's Talk About Our Feelings!!!

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To: The Philosopher who wrote (52045)	8/19/1999 12:19:00 AM
From: Father Terrence	Read Replies (1) of 108807

Mass Extinction Rates Extinction rates have varied considerably over the history of life on earth. Paleontologists distinguish five episodes of "mass extinctions"--relatively short (1 million to 10 million year) periods during which a significant fraction of diversity in a wide range of taxa went extinct. The most significant mass extinction, as the end of the Permian (250 million years ago), may have eliminated 77 to 96 percent of species. Even apart from these mass extinctions, background rates of extinction are not constant. For example, for the past 250 million years, relatively high rates of extinction have occurred nine times--at intervals of approximately 26 to 28 million years. Two of these nine episodes were mass extinctions, one in the late Triassic, 220 million years ago, and one in the late Cretaceous, 65 million years ago. Global biological diversity is now close to its all time high. Floral diversity, for example, reached its highest level ever several tens of thousands of years ago. Similarly, the diversity of marine fauna has risen to a peak in the last few million years. wri.org

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