Gaia Theory

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James Lovelock

February 2003

Regulated planet

Anyone on a spacecraft far outside the solar system looking at Earth with an infrared telescope and spectrometer would see a planet that was unequivocally rich with life. They would detect an atmosphere that, apart from the noble gases, has a composition almost wholly determined by the organisms at the surface. So tightly coupled is life with the atmosphere, that if some catastrophe removed all life from Earth without changing anything else, the atmosphere and surface chemistry would rapidly – in geological terms – move to a state similar to Mars or Venus.

They are dry planets with atmospheres dominated by carbon dioxide and close to the chemical equilibrium state. By contrast, we have a cool, wet planet with an unstable atmosphere that somehow stays constant and always fit for life. The odds against such stability are close to infinity. Science is not concerned with such improbabilities, so we are forced to consider the difficult but more likely alternative – something regulates the atmosphere. What is it?

It has to be something connected with life at the surface because we know that some atmospheric gases (oxygen, methane and nitrous oxide) are almost wholly biological products, while others (nitrogen and carbon dioxide) have been massively changed in abundance by organisms.

Moreover, the climate depends on atmospheric composition and there is evidence that Earth has kept a comfortable climate ever since life began in spite of a 30% increase of solar luminosity. Together, these facts led me to propose in a 1969 paper in the Journal of the American Astronautical Society that the biosphere was regulating the atmosphere in its own interests. When I discussed this idea with my neighbour the novelist William Golding, he suggested that I call it Gaia, the name the ancient Greeks gave to their Earth goddess.

Two years later I started collaborating with the American biologist Lynn Margulis on what we called the Gaia hypothesis. We postulated the biosphere to be an active, adaptive control system, able to maintain Earth in homeostasis.

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