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Earth Will Last a Little Longer

The Earth has been granted a reprieve and will probably escape being swallowed up when the Sun dies in about 7.5 billion years. New calculations actually extend the length of time the Earth will be habitable by 200 million years.

In the end, the surface of the planet will become too hot for life to survive. Earth-dwellers will have to find alternative homes in space, says Dr. Robert Smith, of the University of Sussex in the U.K. ?We had better get used to the idea that we shall need to build our own survival capsules -- the planets are simply too far apart for planet-hopping to be a viable solution,? he says. ?Perhaps this is the ultimate justification for developing an International Space Station.?

Solar evolution theory predicts that our star will eventually run out of fuel. When that happens, it will expand to an enormous size, becoming what is known as a red giant. It will then swallow the closest planets, including Mercury and Venus. Until now, astronomers had always thought that the Earth would be swallowed up too.

But Smith thinks those figures are wrong. According to new calculations, the orbit of the Earth will increase slightly beyond the outer atmosphere of the red giant, as its gravitational pull weakens. If this is the case, the Earth will escape destruction, although its surface will be charred. ?The text books will have to be slightly changed because we no longer think that the Earth will be swallowed up by the Sun but it will be frazzled to a cinder,? says Smith.

?Previous calculations suggested that the Earth will be vaporized by being swallowed up by the Sun,? Smith says. ?Our calculations show that the Earth will survive as a body but it will still be lifeless because it will get so hot that nothing will be able to survive on its surface.? He predicts it will be 5.7 billion years before the planet becomes too hot to sustain life. ?One effect of the calculations,? he says, ?is that we may have 200 million years longer than previous people have thought.?

Other scientists are less optimistic. Professor James Kasting, a geoscientist at Pennsylvania State University, believes water on Earth will boil away in about one billion years, ending life on our planet. ?The story for life on Earth is long over by the time the Sun becomes a red giant,? he says. ?The question of what happens 6-7 billion years from now is interesting from an academic point of view but that?s not when life will end.?

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