There are other ways of looking at extinctions that contradict this idea

There are other ways of looking at extinctions that contradict this idea

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There are other ways of looking at extinctions that contradict this idea. Extinction rates in the Phanerozoic show a pattern of decrease in background extinction rate (see figure below; "background" means excluding the five big peaks). Does this mean that species are becoming more adapted because they are more resistant to extinction? The jury is still out (i.e., we don't know). Moreover, some data sets show rates of extinction that vary dramatically over absolute time, suggesting that extinction rates arenot constant over time but vary widely. Compare figure 22.13, page 633. Once question is how much variation one
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Unformatted text preview: tolerates before saying that extinction rates are not approximately linear. One interesting observation about extinction patterns is that a periodicity has been documented in one data set. The cycle appears to be 26 million years . See figure 23.7, page 652. Explanations for periodicity have been varied: Companion death star (Planet X out beyond Pluto) cycling past earth every 26 million years which hurls asteroids at earth killing many taxa. Needless to say, some of these ideas made astronomers HOWL with LAUGHTER....
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This note was uploaded on 11/06/2011 for the course BIO BSC1010 taught by Professor Gwenhauner during the Fall '10 term at Broward College.

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