How The Earth Maintains Life

By EUGENE LINDEN

One of the greatest benefits of the Apollo space program was the image in the rearview mirror as the astronauts rocketed to the moon. It was the first time earthlings could see their home as a whole, and NASA's pictures said with stunning force what neither words nor theories could adequately convey: life has radically transformed this numinous sphere. The heart-stopping beauty of the earth set against the dark void of space earned inventor-scientist James Lovelock the first adherents to a theory that appears to reconcile science and religion in the study of life on earth. Lovelock's idea, named the Gaia hypothesis after the ancient earth goddess of the Greeks, is that the planet is alive and functions as a superorganism in which living things interact with geophysical and chemical processes to maintain conditions suitable for life.

Lovelock was not the first to argue that earth functions like a giant organism; Scottish geologist James Hutton made the same point in 1785. But Lovelock's formulation is compelling because science now has the tools to explore some of the vast interactions that govern global systems. Although Lovelock first articulated his hypothesis in the early 1970s, in collaboration with microbiologist Lynn Margulis, it has only recently begun to have significant impact on the scientific world. Initially, Gaia was only embraced by New Age types who responded to a holistic view of nature that blurred the distinction between life and death.

Lovelock and Margulis have modified the theory over the years to address scientists' criticism that Gaia implied that the earth acted with a sense of purpose. In its newest form, Gaia has inspired a flood of research into the interaction between living systems and the atmosphere, earth and oceans. At the first major scientific conference on Gaia, sponsored by the American Geophysical Union in 1988, the austere group of scientists ended their meeting by giving Lovelock an exuberant standing ovation.

Scientists have begun to regard Gaia more seriously because the world has forced them to do so. If they are to understand such pressing environmental problems as the greenhouse effect or the consequences of mass extinctions, they will have to overcome their reluctance to look beyond their own specialties: nature does not necessarily respect the arbitrary boundaries established for scientific disciplines. By focusing on entire systems, Gaia provides a framework through which marine biologists, geochemists and geophysicists can integrate their work.

According to the Gaia hypothesis, earth's atmosphere would be unstable for life if it were not regulated by the biosphere, the envelope of life surrounding earth. Oxygen levels have remained at roughly 21% of the atmosphere for 200 million years, Lovelock asserts, whereas they should have fluctuated wildly, according to some geochemical models of the atmosphere. Were oxygen levels to rise above 25%, spontaneous fires would break out; if they dropped below 15%, many higher life-forms would suffocate. Climatologist Tyler Volk of New York University argues that life controls earth's temperature as well. In a study recently published in the British journal Nature, he and colleague David Schwartzman asserted that, without the cooling effects of living things, earth would be 80 degrees F warmer.

Lovelock originally thought that some purposeful design organized living things to stabilize the atmosphere and climate. Now he and Margulis believe this regulation is achieved through the simple mechanism of feedback. For instance, in a hypothetical scenario, Lovelock shows that a planet covered simply by light- and dark-colored daisies could control the sun's heat. In this self-regulating model, dark daisies would absorb sunlight and warm the planet, until it became too warm for the dark daisies and instead favored the proliferation of light-reflecting daisies. That would have the effect of cooling the planet until the cycle reversed itself again.

Scientists have yet to uncover the actual mechanisms by which life processes regulate earth's climate and atmosphere. Lovelock maintains that this makes it all the more imperative that man halt the mass extinctions threatened by the destruction of tropical forests, because he does not know what creatures are essential to his own survival. At the American Geophysical Union conference on Gaia, Lovelock argued that diversity makes earth both stable and habitable: "You cannot have a sparse planet any more than you can have half an animal."

Gaia's critics have by no means been silenced. Some dispute the degree to which life-forms stabilize the atmosphere and temper the climate. Others contend that the emergence of oxygen in earth's atmosphere contradicts Gaia because it made the air poisonous for anaerobic creatures of primordial times. Evolutionary scholar Richard Dawkins argues that earth cannot be considered an organism because it does not reproduce. Gaian proponents respond that the increase of oxygen in the atmosphere was slow enough to allow the mix of life- forms to adjust, and physician-author Lewis Thomas answers Dawkins by coyly suggesting that, through space exploration, mankind may be acting as an inadvertent disseminator of earth's spore.

Its critics notwithstanding, Gaia seems to be gaining in influence among both scientists and theologians. To some, Gaia's appeal is that it promises to end the long estrangement of Western science and religion. Even if the biosphere regulates the planet by feedback, Gaia still integrates living things and inanimate forces into a unified system, allowing both science and religion to look at life as something more than a mere accident. Says James Parks Morton, dean of New York City's St. John the Divine Episcopal Cathedral and a leading religious advocate of Gaia's: "The very nature of this hypothesis shows that we are now at a new moment when scientific and religious inquiry is directed to the same reality and discussed in a common language."