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Assertion: Sixth extinction presently in progress different from the previous episode. Reason: Difference is in the rate; current species extinction rates are estimated to be 100 to 1000 times faster than in the pre-human times.
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The assertion is "Sixth extinction presently in progress different from the previous episode." The reason is "Difference is in the rate; current species extinction rates are estimated to be 100 to 1000 times faster than in the pre-human times." Show more…
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Many biologists think the current rate of species extinction indicates that a sixth mass extinction is underway. Life has endured numerous mass extinctions and has always bounced back. How might the impact of human activities make this sixth mass extinction different from previous mass extinctions?
The number of species has increased through time, although not at a constant rate. Five major extinction events have substantially, although briefly, reduced the number of species. Diversity rebounds, but the recovery is not rapid, and the groups making up that diversity are not the same as those that existed before the extinction event. Unfortunately, humans are causing a sixth mass extinction event. In what ways is the current mass extinction event different from those that have occurred in the past?
Extinction is the ultimate fate of all species. The most extreme of these are called mass extinctions. Extinctions occurring at normal rates are referred to as background extinctions. Studies in marine organisms have documented a secular decline in global background origination and extinction rates through the Phanerozoic. Look again at Figure $18.28 .$ What do the spikes in the figure signify? How far is the alteration in solar luminosity responsible for decline in rate of extinction? Does the rate of background extinction vary from clade to clade?
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