The Medea Hypothesis: A response to the Gaia hypothesis

In ancient Greek mythology, Gaia is the earth-mother goddess, the deity that gives life to all others. During the 1960s, British scientist James Lovelock first formulated the Gaia hypothesis, the idea that every living thing on Earth worked in concert to keep conditions at a certain equilibrium, or homeostasis, that was optimum for life.

In other words, organic life was geoengineering, although that geoengineering was unconscious.

One example of this principle: Scientists think life has existed on Earth, a planet that's just over 4.5 billion years old, for some 3.7 billion years. During that time, the sun has grown 30 percent brighter and yet, temperatures have remained relatively stable and within a relatively narrow margin that allows water to exist in liquid form, which is critical to life on Earth.

How have these temperatures been maintained in the face of an ever-stronger Sun? One explanation: Young Earth had more greenhouse gases., but as the sun grew stronger, the amount of these heat-trapping gases in the atmosphere shrank.

That's because life, which is carbon-based, sucked them out of the atmosphere and sequestered them. The end result was a cooling tendency that perfectly balanced out the sun's growing power, canceling out what would have been a runaway warming.

Initially the source of much controversy, the Gaia hypothesis, which Lovelock and others now consider a theory — one step above hypothesis on the "it's-been-proven-scale" — has been extremely influential in earth sciences such as ecology, to say nothing of popular culture.

In the popular imagination, Gaia – the all-nurturing, all-caring mother (earth) goddess – has become something of a cliché in her own right.

But now, Peter Ward, a noted paleontologist at the University of Washington, Seattle, has put forth a compelling counter-hypothesis with an equally prestigious-sounding Greek appellation.

It's called the Medea hypothesis, and the subtitle to Dr. Ward's eponymous new book sums it up: "Is Life on Earth Ultimately Self-Destructive?"

Ward's answer to this question is, as you might guess – yes, that by its very nature, life on Earth will ultimately lead to a premature end to conditions favorable to life on Earth.

In some versions of an ancient Greek myth, Medea, wife of the Argonaut Jason, in a big contrast to mothering Gaia, kills their children out of revenge for Jason becoming enamored of someone else.

Ward's argument, which is antithetical to the Gaia hypothesis: Life will cause its own end long before our sun, which will start expanding into a red giant in about 1 billion years, begins baking the biosphere away.

Most of the book is a systematic and fascinating dismantling of the assumptions underlying Gaia hypothesis. First are Earth's five mass extinctions. Microbes, Ward says, are implicated in all but one of these die-offs, the K-T extinction thought to have been initiated by a meteor strike 65 million years ago.

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