Gaia Theory

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James Lovelock

February 2003

Conventional view

Until quite recently, the conventional wisdom of science was that we were indeed very fortunate to have been born on a planet that by chance circled its star (the Sun) at exactly the right distance to be right for life. Moreover, most scientists believed that life adapts to the material world it finds and that the whole Earth environment including the air, the oceans and the surface rocks were all products of geological forces alone.

We are just beginning to realise how wrong is this view of Earth. I think it happened because we arbitrarily separated biology and geology – we teach the evolution of life and the evolution of Earth as separate subjects in separate buildings in our universities. It may be easier to teach this way but the price is that we lose sight of the whole planet while examining ever more minutely its details. Earth evolves as a single system, and its living organisms and their material environment are closely connected parts of the whole.

Atmospheric clues

My interest in Earth as a whole system began in 1965 when I was part of a Nasa team preparing the instruments for the search for life on Mars. I soon grew disenchanted with the approach of my biologist colleagues who planned instruments that would find the kind of life they knew about on Earth. They showed little concern about the possibility that Martian life might be quite different. I couldn't help wondering whether there might be a more general way to detect life whatever its form.

The great physicist Schrödinger in his book What is Life (1944) proposed that one characteristic of life was its ability to reduce its entropy, or in simpler but less accurate words, bring order from chaos. although it's not easy to understand or measure entropy directly, we can use Schrödinger's idea for recognising planetary life simply by chemically analysing the composition of a planet's atmosphere.

If life existed on a planet it would be obliged to use the atmosphere as a source of raw materials and a place to deposit wastes. Such use would reduce the entropy of the atmosphere and change the chemical composition into something easily recognised as different from the neutral equilibrium atmosphere of a dead planet.

When I compared the atmospheres of Mars and Venus with that of Earth it was immediately apparent that our atmosphere was far from a state of chemical equilibrium and therefore much lower in entropy. Whereas the atmospheres of the other two planets were close to equilibrium, high in entropy, and therefore, according to my ideas, bereft of life. My proposal is now part of Nasa's astrobiology program and they aim to use it in the search for life on extra solar planets.

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