Ages of Gaia

In an interview on Life Beyond Earth

Tell me about James Lovelock’s Ages of Gaia.

Lovelock has written five or six books. I chose his second book, Ages of Gaia. Gaia is the Greek goddess of Mother Earth and Lovelock’s Gaia hypothesis is the idea that life itself stabilises a planet’s environment. He would say that the reason the Earth is habitable is precisely because it is inhabited. It’s an interesting theory but I don’t think you have to have an inhabited planet in order to have a habitable planet.

He came to that view thinking about the faint young sun problem. This is a problem which is near and dear to my heart, because I have worked on it for a long time. We know that the solar system – the Earth and the sun – are about four and a half billion years old, and the sun, we think, was about 30 per cent less bright early in solar system history. This means that if the Earth was no different from how it is today and we have the same atmosphere and the same greenhouse effect, then the Earth would have been frozen over during the first half of its history.

Lovelock was aware of this. CO2, along with water vapour, is our main greenhouse gas so Lovelock suggested that there was more CO2 in the early atmosphere, and then organisms took CO2 out of the atmosphere by using photosynthesis. And that counteracted the increase in solar luminosity. That is really how he came up with the Gaia hypothesis.