A Critical Appraisal of the Gaia Hyphothesis Seminar

In 1972 James Lovelock made an interesting proposal. Life is not solely a pas­senger on a fortuitously habitable Earth, he suggested. Instead, life is at the controls of the planetary environment, and has been so down through the geo­logical ages, helping to ensure continued habitability over ~3 bil­lion years. In the thirty years or so since he first proposed it, the Gaia hypothesis has variously inspired, infuriated, and intrigued a whole generation of environ­mental scientists. Today it remains controversial. It is widely credited but by no means enjoys unanimous support.

Gaia is an ambitious idea, of awesome scope. But is it correct? In this talk I will examine in turn each of three main lines of reasoning that have been advanced in its support, and compare them to modern evidence. The first line of reasoning is that the Earth environment is especially comfortable and convenient for life. The second is that biological processes have profoundly altered the state of the environment. The third is that the environment has been stable over geological time. After evaluating each line of reasoning I will progress to the plausibility of the Gaia hypothesis as a whole, concluding that it is not supported by the evidence. Instead a competing hypothesis, co-evolution of life and environment, is suggested to be compatible with our modern understanding in a way that Gaia is not. If time allows, alternative possible answers to the puzzle of long-term habitability will be briefly considered.