James Lovelock's Gaia hypothesis about earth's evolution must be reassessed by scientists, argues Nick Petford.

Gaia James Lovelock's provocative theory of the earth is back on the agenda with the publication by Oxford University Press of two new editions of the books that propelled this inventor-scientist into a head-on collision with mainstream science. Their publication offers Lovelock a second chance at convincing the wider scientific community about the importance of his work which may yet turn out to rate with plate tectonics as the most productive planetary science hypothesis this century.

While his first book Gaia: A New Look at Life on Earth was a general introduction, his second book The Ages of Gaia: A Bibliography of our Earth was intended to be more scientifically hard-hitting. Lovelock's credentials as a serious scientist are beyond question a Fellow of the Royal Society of London since 1974, practitioner of gas chromatography and inventor of the electron capture detector. These are not the achievements of a crank, and despite attempts by his severest critics, including Oxford zoologist Richard Dawkins and other hard-line evolutionists to rubbish the Gaia hypothesis, his ideas are attracting growing support, particularly among atmospheric chemists and geophysicists involved in climate modelling.

The publication in 1991 of the thematic set of papers Scientists on Gaia edited by Stephen Schneider and Penelope Boston covering the proceedings of a special session of the American Geophysical Union and a symposia on planetary regulation held by the European Union of Geosciences at Strasbourg this year are further evidence that the scientific community is beginning to take Lovelock's ideas more seriously.

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But what exactly is Gaia? And why do so many scientists still find it hard to come to terms with what is beginning to sound increasingly like a truism? In Lovelock's original definition of Gaia, our planet, its rocks, atmosphere and oceans form a superorganism that has evolved through geological time. In short, the earth is alive. To many scientists, this was nothing short of outrageous. How could anyone possibly take seriously the claim that the earth, a lump of rock spinning in space was alive?

The biological community, with its cosy definitions of what it means to call something living was particularly upset. In its indignation it appears to have missed the point that Lovelock was using the concept of a living earth chiefly as a metaphor. Aware of the unease this has aroused, the new edition of Ages goes out of its way to define "alive" as a system where the overriding characteristics are the ability to be self-regulating and self-sustaining. Even the word Gaia coined for his theory by the novelist William Golding after the Greek earth-goddess, has been removed from the text with Lovelock preferring geophysiology a term applied originally to the earth by the geologist and physician James Hutton in the 18th century If new Gaia is more acceptable, the next step is to test it. And here lies the rub what kind of experiment could be set up to prove such an all encompassing theory? According to Lovelock we need look no further than the world of bacteria to see a complete self-regulatory system in action.

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On a larger scale, self-regulation shows up in the complex feedback loops that exist between the geosphere, hydrosphere and atmosphere. Feedback loops between soil moisture and surface radiation above tropical oceans and land surfaces have been found to play a crucial role in controlling global weather patterns. Complementary to this is the fact that although the sun's luminosity has increased on average by one per cent every 100 million years, the fossil record shows that the planet's temperature has not varied by more than a few degrees. Why should this be so? From a geophysiological perspective, the earth itself provided the necessary self-regulation needed to keep the surface temperature constant and tolerable. This is contrary to conventional wisdom that life adapts passively to environmental change. But the claim is backed up by new research showing that the removal of carbon dioxide from the atmosphere during rock weathering a major factor in controlling the earth's climate occurs at much higher rates in the presence of living things. Such feedback loops between the living and inorganic world lie at the heart of Gaia, and are enshrined in Daisyworld, Lovelock's computer model designed to counteract the argument that Gaia is teleological.

So what can we learn from Gaia/geophysiology? The theory offers a way of uniting the earth and life sciences to provide a new and more productive view of the earth and planets. If plate tectonics had been christened Diana, would it be any less worthy of our respect as a fundamental planetary process? Of course not. And so it is with Gaia.

It is time for science to stop being embarrassed by Gaia and reclaim it from the New Age mystics and environmentalists who have hijacked and romanticised it, and made it their own. Gaia accords human beings no special place or privilege and would function very well without us. The question is could we function without it?

Nick Petford is senior lecturer in the school of geological sciences, Kingston University.

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