Earth system science is shorthand for the recognition that El Niño, climate change and the calamitous 2004 tsunami are all very complex events. El Niño is a natural cyclic blister of hot water in the Pacific that ruins the anchovy harvest off the coast of Peru. It also disturbs weather patterns to trigger floods on the western coasts of the Americas, stoke droughts and forest fires in Indonesia, and blight harvests in Africa. Human complicity in dangerous climate change is now well-established.

The Boxing Day tsunami that killed 250,000 people in the Indian Ocean began with an arbitrary, unpredictable event – a submarine earthquake – but it claimed so many victims because natural mangrove forests and coral reefs that might have absorbed some of the shock had been destroyed, to make way for ports, tourist resorts and fish farms. That much is obvious, but earth system science goes deeper. It is based on recognition that, collectively, the planet’s living creatures – microbes, plants, nematodes, arthropods and vertebrates – both exploit and unconsciously manipulate oceans, atmosphere and rocks in ways that have kept conditions hospitable to life for more than three billion years.

Air is a mix of oxygen and nitrogen, continuously replenished by green growth, and maintained at steady levels. Carbon dioxide released by volcanoes is absorbed by plants and consumed by animals and ultimately turned back into chalk or coal or other stone, in an intricate cycle that sustains all life. Last year Carnegie Institution scientists calculated that two-thirds of the 4,300 known minerals in the Earth’s crust had been fashioned or catalysed directly or indirectly by living things. Earth is not habitable because divine providence or freak conditions furnish the ideal home; it is habitable because life maintains the air-conditioning system, regulates the thermostat and keeps the water running. It is a shock to be reminded that this idea of the biosphere as a responsive organism that regulates its own environment is new, and just 20 years ago was hotly contested within science.

The British scientist James Lovelock proposed what is now the Gaia theory in the 1970s, and defended it against derision from evolutionary biologists throughout the 1980s. Gaia, the ancient Greek earth goddess, provided a focus for a new way of exploring the planet. It made Lovelock – still active in science, and 90 yesterday – a hero not just to the public but also to his fellow scientists. The Gaia theory has gone from heresy to near-orthodoxy in less than four decades and now informs a series of international research programmes. Not bad going, but the exploration has barely begun.