ABOUT four billion years ago, during a time called the late heavy bombardment, Earth, Mars and the moon were flinging rocks into space at a tremendous rate.
Now astrobiologists are keen to track down terrestrial meteorites that may have survived on the moon, in the hope of finding within them biomarkers to reveal information about the origins of life on Earth.
Recent research by University of NSW astronomer and associate professor Jeremy Bailey, Ian Crawford of London's Birbeck College and others has cleared up a crucial question. Some of the rocks may well have survived the journey and the crash landing.
If found, they may yield information that cannot be gleaned from the rocks on Earth. "The problem with the study of life on Earth is that the further back you go in time, the harder it is to find rocks, because Earth is continually recycling its crust through the process of plate tectonics," Bailey explains.
That makes most of Earth's crust too young for his purposes because the oldest rocks suitable for study are about 3.5billion years old. Given the Earth is estimated to be about 4.5 billion years old, there is a billion-year gap. And it is the crucial billion years, the period that holds the secrets of the origins of life.
Hence the importance of the late heavy bombardment, from 3.8 billion to 4.5 billion years ago, which is when most of the craters on the moon are believed to have been formed.
"While the moon has no atmosphere to slow them down, gravity is much weaker so (meteorites) don't hit so hard," Bailey says.
The team's computer modelling revealed how an object would deform at the moment of impact on the surface and whether it would survive or melt.
"In some cases, depending on velocity and angle of impact, they can survive. Now we want to try more, different kinds of rocks and see which ones survive best."
Ultimately it may be possible to conduct searches on the moon via the NASA space program, but more immediate hope is offered by the recent missions mounted by Japan, China and India. "They are talking about moon landing as well as orbiting it."
Still, locating terrestrial meteorites is no easy task. "Even if this stuff is sitting on the moon, it will be like finding a needle in a haystack."