sunnuntai 21. kesäkuuta 2009

Maa onkin Medea, ei Gaia ?


(Peter Ward, a University of Washington paleontologist)

The Gaia hypothesis, named for the ancient Greek goddess of Earth, even put forth the idea that our planet behaves as a kind of giant organism, with its complex systems finely tuned to compensate when one system gets out of kilter.

But actually it is the Gaia view that is out of kilter, says Peter Ward, a University of Washington paleontologist who has looked closely at conditions that existed during numerous mass extinction events in Earth's history.

In a new book, he suggests the planet ultimately is inhospitable to life, and that life itself might be the primary reason. Rather than Gaia, he invokes the darker Medea from Greek mythology.

"The Medea hypothesis says life is already shutting down Earth as a habitable planet. Not just the diversity of life, but the actual biomass," Ward said. "Life keeps evolving, and there are unintended, often negative, consequences."

He noted that throughout Earth's history, carbon has been stripped from the atmosphere and stored in trees, rocks, even the oceans. He said those processes will continue until atmospheric carbon dioxide drops to 10 parts per million, a point at which no plants can live. Once plants are gone, within 20 million years the oxygen will plummet to 1 percent of the total atmosphere and life as we know it will end. "Then you've gotten to a point where it will be forever impossible to get diversity of life back. It will be forever impossible to regain an oxygen-rich atmosphere. That's not Gaia. It's the opposite of Gaia," he said.

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