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Good news is, mass extinctions take centuries ...

| Thursday, March 3, 2011

The Earth has undergone mass extinctions, during which more than 75 percent of existing species disappear, exactly five times in the past 540 million years. If things continue as they are we may be at the beginning of the sixth, a group of biologists and paleontologists suggest in a cautionary paper in Wednesday's edition of the journal Nature.

But they also signal that the threat is at such an early stage, with so many questions yet to be answered, that there's hope for avoiding this outcome.

The projection comes from researchers at the University of California, Berkeley, the University of Sao Paulo in Brazil and the National Evolutionary Synthesis Center in Durham, N.C. They looked at the animals listed as "critically endangered," "endangered" and "threatened" by the International Union for Conservation of Nature.

The IUCN lists 18,351 species on its "Red List of Threatened Species," considered the global standard for the conservation status of animal and plant species. All are at risk based on current and projected habitat loss or destruction because of human encroachment and climate change. Of those, 1,940 are listed as critically endangered, meaning the species' numbers have decreased, or will decrease, by 80% within three generations.

Then they raise the big "ifs."

If those animals were all to go extinct and if the rate of extinction were to continue unabated, amphibian, bird and mammal extinctions would reach "Big Five" magnitude within as little as three centuries to as far out as 2,200 years, they calculate. All of the mass extinctions of the past also transpired over many centuries or longer.

Biologists estimate that within the last 500 years, at least 80 mammal species have gone extinct out of a beginning total of 5,570 known species.That may be only 1.4 percent, but "just because the magnitude is low ... doesn't mean to say that they aren't significant," says co-author Charles Marshall, UC Berkeley professor of integrative biology, in a press release.

The researchers say they based their calculations on fairly conservative estimates of known extinction events from the fossil record, and information about extinct and threatened species today. They acknowledge that these are estimates and highlight the need for more research.

Meanwhile, the U.S. Fish and Wildlife Service yesterday officially declared the eastern cougar extinct, 79 years after the last one was reported in the wild in the United States.

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