London: A return mission to the moon offers the best hope of understanding life on the earth and discovering whether alien life lurks in distant corners of the universe, according to a British scientist.

Ian Crawford, a planetary scientist at University College London, called for the first crewed missions to our nearest celestial neighbour in more than three decades. At a meeting of the U.K.'s Astrobiology Society, he was set to outline how clues to the existence of life in the solar system and beyond may be locked in rocks and debris that crashed on to the moon and were preserved on the sterile surface.

"There's a perception that when it comes to the moon, we've been there, done that. But the Apollo missions landed more than 30 years ago and didn't really scrape the surface, either literally or figuratively," he said. "The moon has been orbiting the earth ever since the two formed, and since then it's been there as a silent witness to everything that's happened in the earth's entire history."

It is the moon's lack of life, atmosphere and geological activity, such as volcanoes or shifting continental plates, that makes it such a good place to look for signs of life.

In the early years of the solar system, meteorites and comets crashed into planets, sending vast clumps of rock into space. Some of the rocks crashed into active planets such as the earth, but eroded away. Those that landed on the moon are likely to be preserved, holding inside them evidence about fledgling life forms or the environments they lived in.

"The earth is about 4.5 billion years old, but the earliest fossils we've found date back to around 3.5 billion years. The problem is we don't have rocks much older than that because they've eroded away, so we don't know if life on the earth began earlier," he said.

The Bush administration plans to return to the moon to reinvigorate the U.S. space agency, NASA, but the plans foresee the creation of a moon base to be used primarily as a staging post ahead of a crewed mission to Mars.

© Guardian Newspapers Limited 2004

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