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Humans Will Not Live to See the Planet Rebound

Homo Sapiens Will Die Out Before Earth Can Recover From Mass Species Extinction, Study Finds

By Robert Sanders, Public Affairs
Posted March 15, 2000

The Earth needs, on average, about 10 million years to recover from a mass extinction of the planet's species, far longer than most scientists thought, according to a new study by scientists at Berkeley, and Duke University.

Moreover, the recovery time is the same whether the global die-off involves the loss of most life on Earth or wipes out far fewer species.

This unexpected finding has major implications for the Earth's fate as human activity threatens species around the globe.

"People have argued that we only have to worry about human-caused extinctions if we do something that causes the loss of 80 or 90 percent of species on the planet," said Berkeley environmental scientist James Kirchner. "Our analysis shows that even if the human impact is much smaller than that -- 20 or 30 or even 50 percent of species -- it's still going to take 10 million years for the Earth to recover. That is well past the expected life span of the human species, or even of the genus Homo."

"Extinctions caused by humans don't have to be large to have an effect that reverberates in the ecosystem for tens of millions of years," said paleontologist Anne Weil, a former doctoral student at Berkeley and now a research associate at Duke.

During the past half billion years, life on Earth has blossomed and crashed many times -- some die-offs the result of geologic cataclysm, but most of unknown cause.

Paleontologists have known that the Earth needed a long time to recover from large extinctions. The debate was over the smaller, background extinctions that pepper the fossil record, in which 10 to 20 percent of species died out.

"The presumption has been that while big extinctions require a long recovery, the biosphere should bounce right back after smaller extinctions," Kirchner said.

One critical reason for wanting an answer to this question is that human activity now is eliminating many species each year in what some see as a major, human-caused extinction event.

"We don't know what our current level of extinction is, but some biologists estimate that eliminating 90 percent of tropical rain forests would lead to the extinction of half the species on Earth," Kirchner.

Weil and Kirchner compared the rate of extinction of fossil marine organisms with the rate of evolution or "origination" over the past 530 million years. They found an average of 10 million years between an extinction and a subsequent flourishing of life.

When they eliminated the five mass extinctions from that period, including the extinction 65 million years ago when the dinosaurs died out, the smaller background extinctions also averaged a 10 million-year recovery period.

Weil said that the long recovery period is perhaps not surprising. "Extinction is a double whammy. You not only take out the ecological niche as you take out the species, but you take away the evolutionary potential for radiation, too," Weil said. "Diversification takes a long time to ramp up."

Kirchner notes that their sobering findings don't necessarily imply a stark fate for the Earth.

"It is not preordained that high levels of human-caused extinction have to happen," Kirchner said. "Our future depends on what we choose to do on a national and international level, as a society."

"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."



March 15-21, 2000 (Volume 28, Number 25)
Copyright 2000, The Regents of the University of California.
Produced and maintained by the
Office of Public Affairs at UC Berkeley.
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