"The Medea Hypothesis:" a downhill trajectory for life on Earth

When avid science readers browse the shelves for new titles, the books that grab their attention are best described by a single adjective: thought-provoking. And no scientist/author is more provocative in his approach and innovative in his thinking than University of Washington astrobiologist Peter Ward.

Ward's previous books have challenged broadly accepted interpretations. If his conclusions dashed cherished hopes, such as the likelihood of communicating with other intelligent civilizations in "Rare Earth" (co-authored by Donald Brownlee), at least readers had the comfort of knowing that they live on a favored world.

But readers looking for solace will not find it in Ward's latest effort, "The Medea Hypothesis: Is Life on Earth Ultimately Self- Destructive?" (Princeton University Press, 208 pp., $24.95). This time Ward goes after motherhood itself — or at least the central idea of the Gaia ("good mother") hypothesis that has evolved to describe the relationship between life and the planet as a whole.

While acknowledging that the Gaia hypothesis "has proved both vigorous and enormously rich ... [and] has attracted some of the best brains in all of science," Ward argues that when tested, many of its aspects have come up short.

So he develops a counter-hypothesis. His archetype of the anti-Gaia is Medea, wife of the legendary Jason, who killed all of her children in a fit of rage against her husband. Simply stated, the Medea hypothesis claims that instead of enhancing or evolving in concert with Earth for mutual benefit, life is predatory and ultimately self-destructive. Certainly, we humans seem to be testing the limits of the biosphere.

One Gaian interpretation posits that humanity may destroy itself, but the Earth will recover from our destructiveness. Another is that we will learn our lesson in time to save our species, develop a culture of sustainability, and stabilize the world.

But is the central Gaian assumption correct? Does life change the planet in ways that enhance its own survival, or do those changes accelerate life's ultimate decline? To answer that question, Ward, ever the scientist, examines the evidence.

His reading of the geologic record is distinctly Medean. According to his estimates, Earth's total biomass peaked about a billion years ago, even before evolution of complex plants and animals. Likewise, he argues that Earth's diversity peaked early in the age of animals and has been declining ever since.

These declines have been caused by the gradual reduction of carbon dioxide in Earth's atmosphere, which Ward attributes to biologically driven geological processes. (The current increase in CO2 caused by burning of fossil fuels will be but a blip in the long-term history of the planet.)

The inevitable result will be the demise of most plant life and the consequent oxygen starvation of animals. That calamity will come long before solar or geological changes would doom Earth life forever.

In other words, life's natural processes will hasten the depletion of Earth's life-support system.

It sounds bleak, but Ward finds a glimmer of optimism. Human ingenuity can provide a Gaian force to counter a Medean nature. He suggests we can extend Earth's viability by changing it with benevolence aforethought.

"Only engineering will save us now," he concludes. "Time to roll up the sleeves, take out the slide rules, encourage the boffins, and get to work. All of us." If that statement doesn't provoke thoughtful readers, it's hard to imagine what will.

Physicist Fred Bortz's most recent book for young readers is "Astrobiology" in Lerner's middle-grade "Cool Science" series.