Life is not just a force for good, it is a force for its own good. Life has a way of managing things in favour of more life. And in the course of doing so, life manages a whole planet. It makes an atmosphere to breathe, and water to drink, and food to eat and then it recycles its own detritus. It hijacks sunlight and passes it around to the next user in digestible, shrink-wrapped form. Having done that, it disposes of itself, directly as nutrient for some other creature, or indirectly as a strata of phosphate or a layer of chalk or fossil limestone, or as energy to burn 1bn years later.
Earlier this month, Austrian scientists detected bacteria, living comfortably in high clouds, reproducing themselves and - some think - serving the world by playing rainmaker, acting as "seeds" around which water vapour could become raindrops.
But this heavenly host of living things surprised no one. Life has been turning up in improbable places for years. People who drilled a mile deep into the basalt of the ocean floor found tiny microbes living on a diet of warmth and rock. Submarine explorers have found huge colonies of strange creatures basking in a kind of chemical cornucopia at the bottom of the ocean's depths, far from any sunlight. Microbes have been found in acid flows, in lakes of soda, down the vents of volcanoes and on the underside of the polar ice, organising the planet for the rest of creation.
Might things have got a little hot when carbon dioxide levels built up dangerously at the dawn of the Eocene, 55m years ago? Fear not. The rapid response team was on hand. An Anglo-American team of scientists reported on Thursday that plankton bloomed, the oceans became a garden and greedily mopped up the excess carbon, cooling the greenhouse world to acceptable levels. Not for the first time, nor the last, the biosphere had risen to the challenge, and adjusted itself.
It is more than 30 years since James Lovelock, a freelance chemist with a background in medical research and a gift for devising sensitive detectors, worked for Nasa on the Mars exploration programme. While doing so, he began to form the idea of the biosphere as a self-regulating entity, of life and the planet as a kind of sensitive organism, not sensitive to any particular form of life, just to the principle of life. He called it the Gaia hypothesis. The novelist William Golding, a friend and neighbour, suggested the name. Gaia was the Earth goddess, the Greeks' Mother Nature.
Touchingly, Lovelock reports in his latest book that he originally thought Golding had suggested calling it the Gyre hypothesis, after the gyres or vortexes that drive ocean and atmospheric circulation. The idea of Gaia caught the imagination of people everywhere. Gaia is a kind of metaphor for a very subtle lesson in the physiology of a planet. But Gaia became a reality, too, for the Greens, particularly those inclined to mysticism. Lovelock doesn't mind. He finds things to marvel at in Gaia, too. "Some very distinguished scientist, I have forgotten his name, told me when I was quite young that the one thing you have got to keep right through your life or right up to your dotage is a sense of childlike wonder and once it goes, stop doing science," he says.
He is fond of individual Greens, but he doesn't have much patience for some Green thinking, and in particular the Green attitude to nuclear power. Never mind the British government's little local difficulty with fuel prices, fossil fuels are literally beginning to cost the earth and meanwhile the Green campaigners are rejecting at least one easy answer to the great problem of how to power an economy without shutting down the biosphere with polluting greenhouse gases.
This answer, Lovelock says, is ecologically clean and tidy and has a very bad press. It is nuclear power. "I can envisage somewhere about 2050, when the greenhouse really begins to bite, when people will start looking back and saying: whose fault was all this? And they will settle on the Greens and say: 'if those damn people hadn't stopped us building nuclear power stations we wouldn't be in this mess'. And I think it is true. The real dangers to humanity and the ecosystems of the earth from nuclear power are almost negligible. You get things like Chernobyl but what happens? Thirty-odd brave firemen died who needn't have died but its general effect on the world population is almost negligible.
"What has it done to wild life? All around Chernobyl, where people are not allowed to go because the ground is too radioactive, well, the wildlife doesn't care about radiation. It has come flooding in. It is one of the richest ecosystems in the region. And then they say: what shall we do with nuclear waste?" Lovelock has an answer for that, too. Stick it in some precious wilderness, he says. If you wanted to preserve the biodiversity of rainforest, drop pockets of nuclear waste into it to keep the developers out. The lifespans of the wild things might be shortened a bit, but the animals wouldn't know, or care. Natural selection would take care of the mutations. Life would go on.
"I have told the BNFL, or whoever it was, that I would happily take the full output of one of their big power stations. I think the high-level waste is a stainless steel cube of about a metre in size and I would be very happy to have a concrete pit that they would dig - I wouldn't dig it - that they would put it in." He says he would use the waste for two purposes. "One would be home heating. You would get free home heat from it. And the other would be to sterilise the stuff from the supermarket, the chicken and whatnot, full of salmonella. Just drop it down through a hole. I'm not saying this tongue-in-cheek. I am quite serious," he says. "They would be welcome to take pictures of my grandchildren sitting on top of it."
Lovelock regards himself as an eccentric, and a radical, and he enjoys being a member of the awkward squad. The Gaia hypothesis was a huge delight to some, but it was a huge provocation to others. It also plunged Lovelock into a war of metaphors. Most of the battle was with the biologists, who had a different set of metaphors to defend. Some scientists, for example, call the Earth the Goldilocks planet, because Venus, hot enough to melt lead, was too warm and Mars, the frozen desert, was too cold, but Earth was just right for life. So in their view, the planet manages life, not the other way around.
Another group thinks of the fullness and richness of biodiversity as the outcome of "selfish genes", hectically competing to replicate themselves. So for them, life is a battle for tenure rather than an invitation to the dance. And then along came Lovelock, a non-biologist who proposes something disconcerting: that the earth is fit for life because life made it that way. The battle was brisk, because life is the great mystery. There are three great stories that science has to tell: one of these is where the universe came from, one is where life came from and the third is where humans came from. The first and the last are being sorted out right now. Cosmologists think, for instance, that they have the story of creation figured out, except for the first 1,000th of a second. Anthropologists have settled on a consensus that modern humans emerged in Africa about 250,000 years ago, the latest and only survivors in a line of hominids.
But the origin of life is a puzzle. Think of it as a kind of reverse murder mystery. The bringing-to-life happened in a locked room in a strange world 3.4 bn years ago. There is no surviving scene of the not-crime. There are no footprints, no strewn clues. The evidence was destroyed by the very creatures that rose from original experiments in fashioning the living chemistry from non-living chemicals. Whatever conditions made life possible were promptly erased by the action of life itself. The last surviving universal common ancestor went round eliminating all chances of new rivals emerging.
Life came into a planet with an atmosphere of carbon dioxide, and began to alter it, producing as waste a dangerous, reactive gas called oxygen which could ultimately have brought the whole experiment to a halt. So life's - and Gaia's - next step was to favour a balancing set of creatures that consumed oxygen and breathed out carbon dioxide. But once that was done, the original atmosphere was gone, and water and nitrogen cycles were wiping away any evidence that might have been left in the rocks.
Lovelock began thinking of such things three decades ago when he worked on Nasa's search for evidence of life on another planet. He proposed in effect that you could tell that the earth was alive from a million miles away. Its atmospheric chemistry would shout of life. He proposed that the 70s Mars probe instruments could confirm the presence of life on the red planet by detecting an atmosphere of dynamic disequilibrium.
If there had been life on Mars, it would have been a very different planet. The atmosphere of Mars is 98% carbon dioxide and very stable. Venus is 98% carbon dioxide and a very nasty example of a runaway greenhouse effect. The earth no doubt started at 98% carbon dioxide too but today's atmosphere is a mixture of inflammable oxygen and reactive nitrogen with just a touch of carbon dioxide, and something is definitely keeping this explosive mixture primed.
He says Nasa ignored his proposal at the time but the future search for life on planets outside the solar system will be based entirely on Lovelock principles. At some future point, fleets of spacecraft working in exquisite unison will focus on little specks of light reflected from parent stars, looking for the spectral signatures of telltale gases such as oxygen and water vapour and methane.
You couldn't imagine oxygen and methane surviving together for very long in the same atmosphere. So if you spotted these in the gleam from a planet 30 light years away you'd start to wonder. "If there is a lot of methane, oxygen won't rise by accident. So you have to postulate a process on the surface that is producing gigatonnes if not teratonnes of both of those gases all the time and not only that but regulating them, because if you didn't regulate them you would be in danger of making an inflammable atmosphere or something like that. So that then becomes conclusive evidence of life," he says.
The American enthusiasm for possible life on Mars amuses him. "I think it is all part of the American frontier mentality. This Mars is the ultimate place, we can go there when we have screwed up the earth. We have the technology, we can fix it. The national legend of America is very tied up with Star Trek and if you go to scientific meetings you hear Star Trek metaphors paraded around all the time and to them it no longer is a kind of story, it is reality and there is a great danger in their thinking."
Lovelock is now 81. He and his wife Sandy - his first wife, Helen, the mother of his children, died after a long illness - have completed the 600-miles coastal walk from Poole, Dorset to Minehead , Somerset. He has pursued a long career as a kind of freelance scientist and he says big corporations are not for him, although he is happy to sell them his inventions. He doesn't care for science run by bureaucracies. He lives in an idyllic corner of Devon, on a 35-acre farm, on which he has planted 25,000 trees.
He takes the long view of eco-hazards, he says. He isn't bothered by the menace of industrial chemicals like PCBs or agricultural fertilisers in the way that Greenpeace or Friends of the Earth are. A chemist from the start, he points out that according to a Royal Society of Chemistry survey, chemists live longer than most scientists. The big threat to the planet, he says, is people: there are too many, doing too well economically and burning too much oil.
"It's the people that count and the only message I would have to give is to stop fretting, stop looking for scapegoats, people are to blame for the condition of the earth. It is me, you, all of us that are to blame and if we are going to do anything about it we have to tackle it individually, not expect anybody to take the load off us and do it. If you are a housewife in Balham you are not, probably, doing anywhere near as much to damage the planet as suburbanites and exurbanites living around here, using their cars wholly unnecessarily in huge numbers of journeys and burning far more fuel. The more money you have, the more damage you can do."
His new book is a hymn to science, and to Gaia and to the other makers of his great idea, and to the forces that made him choose to swim upstream, to stay independent, to be free to follow his nose. He grew up with Quaker principles, and became a conscientious objector in the second world war. He spent 20 years at the National Institute for Medical Research at Mill Hill, a lab with 100 scientists and six Nobel prizewinners, and then he started pleasing himself, usually by devising instruments that pleased big business, or Nasa, or the Ministry of Defence.
He built a detector so sensitive it could trace seemingly infinitesimally small concentrations of chlorofluorocarbons in the atmosphere. Famously, he remarked that such low levels could do no harm. He should have written no toxic harm, he says. They were, of course, the chemicals that began to demolish the ozone layer. He thinks the big dangers to the planet are the greenhouse effect and the spread of humanity. Humans, just by their fecundity, and their economic demands, have begun to affect habitat and biodiversity so furiously that it might be that one day Gaia might not be able to step in and adjust the conditions to secure her own reign. The planetary regulator might not regulate so efficiently.
In that sense, biodiversity was a kind of insurance, a spreading of bets to allow life to survive the kind of catastrophes - from outer space, or from volcanoes - that have seriously interrupted evolution at least five times in the last 600m years. Meanwhile, humans could get their comeuppance in some quite mundane but unexpected way.
"Every few hundred years or less, there is a natural geological disaster, like a big volcano. Tambora was the last, in 1815, and the one before that was Laki in 1783. Both of those were followed by two years without any harvest. Now in those days, people survived. There were famines, but people survived. What would happen now?" he asks. He was speaking before the British pickets began their fuel blockade, and before panic-stricken consumers began clearing supermarket shelves. He was speaking long before word began to leak of UK government statement to be made on Monday about research into the possibility of some future collision with a large asteroid, an event which would darken the sky, shake continents, shut down agriculture and certainly clear the supermarket shelves the world over.
He was simply taking, as he has done all his life, the long view. "Two years without a harvest? It would probably bust civilisation. People would survive all right. It really would cut us back, and that is the sort of thing nobody really prepares for. It's not some ecological poison or GM foods or nuclear that is going to get us, it is going to be some perfectly ordinary natural event."