hy on Earth do we call our planet Earth? Planet Sea would be a much better name, for it is the water - and the benefits that it has brought - that really distinguishes it from the dry, barren lumps that populate the rest of the solar system. Seventy-two per cent of the Earth's surface is covered by the oceans. All life, including our own ancestors, came from the sea, and no land species could survive without the rain we get from it. And the oceans continue to regulate the climate of our lonely planet, sustaining it as an isolated oasis in the vast black desert of space.

Yet humanity has always exploited the life-giving oceans, treating them as an apparently inexhaustible source of food and a seemingly limitless dump for our wastes. For generation after generation we have managed to get away with it; the immensity of the oceans has been able to tolerate the abuse. But now, as our generation begins to assume responsibility for the health of this misnamed planet, the boundaries have been reached, or crossed. Most of the world's fisheries are at or beyond their limits. And pollution - especially from the carbon dioxide that is the main cause of global warming - now threatens the entire life of the oceans.

The problem seems to be the very thoughtless, self-centred attitude that led us to name the planet after the relatively small part of it on which we live. For it is this mindset that has led to the despoiling of the oceans, and indeed of all the world's life support systems. As a generation, we are going to have to grapple with it if we are to save our seas, and with them the planet itself. It is no easy task, but if we falter we can always look inside ourselves to find a reminder of how much we owe the oceans. For, as the great Rachel Carson - one of the founders of the environmental movement - pointed out, our very blood carries almost exactly the same composition of salts as the seawater from which our ancestors came.