>Exámenes selectividad inglés resueltos C. Madrid
Covered with a mantle that occupies more than two-thirds of its surface, this planet is clearly misnamed Earth. Seen against the blackness of space, it is primarily a world of water. The magic liquid not only gives Earth its distinctive gem-blue colour; it also makes this planet an oasis of life in the sterile void of space.
Some of the other planets -Venus and Mercury, for instance suffer from metal-melting heat. By contrast, Neptune and Pluto are locked in a permanent ice age, with surface temperatures that are near the 459 degrees F of Absolute Zero. But the blue planet, 93 million miles from the sun, is blessed with temperate conditions that, when combined with the unique chemical properties of the water molecule, result in a world where water exists in a liquid state. No other planet in the solar system -as far as scientists have been able to discern -possesses so benign a set of circumstances. Water and the oceans make Earth unique.
As long ago as the 16th century, Leonardo da Vinci realized that "water is the driver of nature". But it is now that mankind is beginning to recognise how fully dependent all life is on the oceans. In interaction with the atmosphere, the oceans help regulate global climate, storing excess heat in the summer and releasing it in winter. They are a source of life-sustaining material and contribute food, minerals and energy, as well as being the roads for commerce and the place where humanity's waste is deposited.
