Tuesday, August 10, 2010

The unsolid Earth


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.

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