THE Earth is a recycling scheme that has been running for a third of the age of the universe. Microbes and plants endlessly pull carbon, nitrogen and oxygen from the atmosphere and pump them back out in different forms. Water evaporates from the oceans, rains down on the land, pours back to the seas. As it does so it washes away whole mountain ranges-which then rise again from sea-floor sediments when oceans squeeze themselves shut. As oceans reopen new crust is pulled forth from volcanoes; old crust is destroyed as tectonic plates return to the depths from which those volcanoes ultimately draw their fire.

The Earth has finite resources of matter. But thanks to its own internal heat and the light of the sun it has almost unlimited supplies of energy with which to remake itself over a vast range of timescales. Water lasts in the atmosphere for a fortnight or so; carbon dioxide stays in the oceans for thousands of years. Mountains rise and fall over tens of millions of years; oceans open and close at rates even slower than that.

And for some things, in some places, there is a sort of stillness. The argon in the atmosphere just sits […]