Human factor seen in faster extinctions

WASHINGTON — Species of plants and animals are becoming extinct at least 1,000 times faster than they did before humans arrived on the scene, and the world is on the brink of a sixth great extinction, according to a new study.

The study looks at past and present rates of extinction, and species now are disappearing from Earth about 10 times faster than biologists had believed, said the study’s lead author, noted biologist Stuart Pimm of Duke University.

“We are on the verge of the sixth extinction,” Pimm said. “Whether we avoid it or not will depend on our actions.”

The work, published Thursday by the journal Science, was hailed as a landmark study by outside experts.

Pimm’s study focused on the rate, not the number, of species disappearing from Earth. It calculated a “death rate” of how many species become extinct each year out of 1 million species.

In 1995, Pimm found that the pre-human rate of extinctions on Earth was about 1. Taking into account new research, Pimm and his colleagues refined that background rate to about 0.1.

Now, that death rate is between 100 and 1,000, he said.

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