20000311

Earth needs 10 m years to recover from extinction

SAN FRANCISCO: It takes the Earth about 10 million years to recover from the mass extinction of plant or animal species -- far longer than previously thought, two scientists reported on Thursday.

And it takes the environment just as long to recover from the extinction of even a few species, small events which nevertheless rip holes in the biosphere that are impossible ever to fully repair.

"When you lose a species, that exact species is never coming back. You can't recreate an animal extinction is final that way," paleontologist Anne Weil, a research associate in the Department of Biological Anthropology and Anatomy at Duke University, said .

"What we were looking for is the point at which entire ecosystems recover. The baseline is an average of 10 million years."

The study by Weil and James Kirchner, an environmental scientist at the University of California-Berkeley, comes amid predictions that as much as half of all the Earth's species could vanish over the next 50 to 100 years.

Kirchner said the study results, published in the current issue of Nature, underlined the fact that humanity itself would be extinct before anything resembling any of the vanishing species is ever seen again on Earth.

"If we deplete Earth's biological diversity, we will leave a biologically impoverished planet, not only for our children and our children's children, but for all the children of our species that there will ever be," he said.

The two scientists arrived at their findings by comparing the extinction rate of fossil marine organisms with their rate of evolution, or "origination," over 530 million years.

Looking at some five major extinction events, like the one that killed the dinosaurs 65 million years ago, as well as smaller die-offs, they concluded that the "lag" between extinction and revival of biodiversity was much longer than had previously been believed, and was remarkably consistent.

"This is a very exciting finding. What we found is a previously unrecognized pattern in the fossil record," Weil said. "The lag is evidence of an evolutionary dymanic which wasn't suspected before, and which we don't yet fully understand."

Kirchner stressed that their sobering findings do not necessarily mean that the multitude of plants and animals currently endangered by human activity are necessarily doomed for ever.

"It's cause for concern, and it's a cause for caution, but its not a cause for depression," Kirchner said. "It is not preordained. Whether it happens depends on the choices we make. We can chose not to let it happen."

But he added that the speed with which fragile environments are being overrun meant the choice would have to be made soon. Many species, in fact, are disappearing from the Earth before human scientists can even catalogue them, he said.

"It has been likened to burning down the library when you don't know how many books are there, let alone what's written in them," he said.-Reuters