life on earth given 500 million years

Two US scientists have warned in a book that the end of the world has started but it will take 500 million years for life to disappear from earth.

In The Life and Death Of Planet Earth, Donald Brownlee and Peter Ward describe the way earth will eventually self-destruct and say this should encourage man to take better care of the planet.

They said that when compared to a 24 hour clock, the planet is currently at 4:30am after about 4.5 billion years of existence.

At 5:00am, the University of Washington professors write, animal and vegetable life will end after one billion years on earth.

By 8:00am, the oceans will have vaporised and at midday, after 12 billion years, the earth will have been absorbed by the Sun.

By that time, the Sun will have become huge, destroyed any sign of the human presence and dispersed atoms and molecules across space.

"The disappearance of our planet is still 7.5 billion years away, but people really should consider the fate of our world and have a realistic understanding of where we are going," said Mr Brownlee.

"We live in a fabulous place at a fabulous time. It's a healthy thing for people to realize what a treasure this is in space and time, and fully appreciate and protect their environment as much as possible."

Mr Brownlee and Mr Ward said that the possibility of man moving to another planet in that time is remote.

Even if a planet could be found it would be virtually impossible to get there.

But they said it might be possible to send DNA samples on intergalactic space ships in the future in a move like throwing a message in a bottle out to sea.

At the rate at which the Sun is growing and becoming hotter, it is certain to absorb Mercury and Venus, the two planets closer to the Sun.

And even if the earth were to escape the star's expansion, it would still make life on earth impossible.

And the human race's time will come long before the end of the planet.

Rising temperatures will force all living creatures to seek refuge in the sea, the scientists wrote, and those that can adapt will survive for a while.

But eventually even the oceans will become too hot to support life.

The earth's slow death, which has already seen the extinction of dinosaurs, will hand the same fate to elephants, trees, glaciers, oceans and eventually to the last living cells.

"The last life may look much like the first life - a single-celled bacterium, survivor and descendant of all that came before," the authors wrote.

Mr Ward said the predictions are based on what the scientists know already about life on earth and the existence of other stars and planets.

Mr Ward is a palaeontologist and Mr Brownlee an astrophysicist.

In a previous book, entitled Rare Earth they said that life in its most basic form was once quite common across the universe but that it was able to develop on earth because of a rare combination of factors.

Have we got time to pack?