We came from the sea, and we would be nothing without it. Without the sea, no clouds, no rain, no rivers, no life. Seven-tenths of the world's surface is sea. We play at its edges, we put down nets and feed from it, we send cargo across its ruffling surface. And yet it remains the wildest, strangest and least-known part of the planet: a puzzle. Science knows more about the surface of the moon than it does about the ocean floor (somewhere between ten million and a hundred million unclassified species live there; science has still to find out). We do not quite know how the sea works. Is it rising? Warming? How much pollution can it take? How many of its island states will disappear?The sea is the natural arena for adventure, mystery and catastrophe (the Odyssey, Moby-Dick, the Titanic, El Niño). But air has replaced water as the transporting element of the twentieth century, and the sea has been retreating in the imaginations of the West.For too long we have turned out backs to it.