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Mass extinction? Man may still have time to catalog Earth's species.

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The stakes are high, many researchers say. Human population growth and activities – from altering landscapes and oceans to altering climate – are widely seen as the drivers behind the current mass-extinction event, the planet’s sixth.

"We are the asteroid," says Michael Novacek, provost and curator at the American Museum of Natural History in New York, referring to the event widely held to have triggered the demise of the dinosaurs 65 million years ago.

"This may be the most important century in our evolutionary history, where the environment is really transformed to a level where the nature of life on Earth is redefined," says Dr. Novacek, who was not part of the team performing the new analysis.

Getting a handle on the full range of nonbacterial species the planet hosts is important for a number of reasons, researchers say. A full listing of what lives where would provide important information for maintaining the health of ecosystems on which humans rely for food, clean water, and other so-called ecosystem services. And undiscovered species could represent new sources of compounds for pharmaceuticals or appear as novel structures human engineers could mimic for lighter, stronger materials.

At its broadest, the widespread loss of biodiversity before anyone has a chance to take the full measure of what's out there makes it difficult to fully grasp the ecological consequences of its loss.

Novacek and others say they are a bit surprised at the relatively low number of nonbacterial species the team estimates as living on the planet – about half the 10 million that others estimate as realistic. And the trio's estimate for a global extinction rate – less than 1 percent per decade – is far below the worst-case scenario of 5 percent per decade some have estimated.

Still, Costello and colleagues acknowledge that if extinction rates are on the high side, say 5 percent per decade, half the 5 million nonbacterial species he and his colleagues estimate as currently inhabiting Earth will have vanished within 150 years.

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