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FOR 600 million years, continents have broken up and drifted across the
globe, weird and wonderful creatures have come and gone, but the Earth has
maintained a calm equilibrium. This does not mean that the processes maintaining
the status quo are static—far from it. Just take a look at the changes
happening all around us. A biting winter wind carries particles from nearby rock
or soil. A muddy river carries sediment towards the sea and waves crashing on a
beach grind pebbles to sand, or slowly eat away at cliffs each year. And on the
larger scale, volcanoes spew…