The 1950s was a wonderful time. I worked for the National Institute for Medical Research in north London for 20 years, and in those days Britain led the world. But, though I loved my job, I felt that I had tramlines going down to the grave, and I couldn’t stand it.

Then out of the blue came a letter from Nasa, asking me to help design instruments for the first lunar and Mars missions. It was so exciting, it was like getting a love letter. In 1961 Nasa’s main science lab, the Jet Propulsion Laboratory [JPL] in California, consisted of a few shacks on a hillside, but it was a young lab, with enthusiastic staff.

I’ve always liked to crisscross scientific boundaries, and one day I wandered in among the space biologists. They had designed automated pathology labs to land on Mars and take scoops of earth. Having trained in bacteriology, I wanted to know how they knew anything they found would grow in our atmosphere.

Eventually I was given an ultimatum: “How would you look for life on Mars?” By Friday I had the answer: we should analyse the atmosphere around Mars. If there is life on the planet, it will use the atmosphere as a source of raw materials and a depository for waste products.

By 1965 I was working on various contracts in my lab at home in Wiltshire, while still commuting to the States. One afternoon in September that year I was working with the astronomer Carl Sagan in the space-science division of JPL when another astronomer, Lou Caplan, came in carrying armfuls of data from the Pic du Midi observatory in France. These contained a complete analysis of the Martian and Venusian atmospheres, and we saw for the first time that both planets had atmospheres dominated by carbon dioxide. Then my mind flipped and I thought: “By comparison, Earth’s atmosphere is incredible. It consists of oxygen mixed with methane, which, combined in different proportions, would explode. Looked at as a whole, our atmosphere is a combustible mixture.”

It came to me in a flash of enlightenment — that for the atmosphere to persist and keep stable, something must be regulating it. And if most of the gases came from living organisms, life at the surface must be doing the regulating.

All this burst out of my mouth at once, and Carl said: “I don’t believe life can possibly regulate the atmosphere… ” Then he added: “But it could explain the ‘cool-sun problem’.” Astronomers have always known that the sun was far cooler when life on Earth began. By now my heart was pounding and I said: “My God! The Earth is regulating the climate as well as atmospheric composition!”

A neighbour of mine, the writer Bill Golding, later suggested that I name my theory Gaia, after the Greek goddess of the Earth. I was consumed with Gaia from then, and the gathering together of numerous apparently unconnected facts has shaped my life ever since.

Gaia theory is really a new theory of evolution, and I was aware that it was contrary to everything that had gone before. The biologists and geologists attacked it violently. Only the climatologists were positive about it.

But it was by no means a miserable period, because everywhere I looked, from zoology to biology, I found things to back up my theory. The rules of Gaia are very simple: any species that fouls its environment lessens the chance of its progeny flourishing and will become extinct. My great sadness was I didn’t realise the significance of Gaia earlier. But I don’t know whether it would have made a difference, because during the 1960s we were fixated with the cold war.

Gaia, the point when the Earth started to regulate the atmosphere to sustain life, is now around 4 billion years old. In human terms she’s about 80, so we’re pretty sure she has at most a billion years to go. Nothing in science is certain, but I believe we’ve pushed Gaia beyond the point where self-regulation’s possible. We’ve added half-a-million-million tons of carbon dioxide to our atmosphere and, despite warnings, we carry on destroying the Earth while worrying about trivial risks, from power lines to pesticides.

The Earth is already on course for a new hot state, about 8C warmer than it is now. It will mean a world largely denuded of life. Like Gaia, were she sentient, I know my time is shortening. I have no belief in the hereafter, but it’s comforting to think I will merge with the chemistry of this living planet. Gaia will repair herself, but slowly. Over the course of 200,000 years the atmosphere will adjust and climb back down, and what life remains will migrate from the poles and start again — as it has many times before .

The Revenge of Gaia by James Lovelock is published by Penguin, price £16.99