THE discovery that primitive life may have existed on Mars more than three billion years ago is "not enormously surprising", according to the director of the Armagh Observatory, Prof Mark Bailey.
While greeting the NASA discovery with caution, Prof Bailey said it is "great news that some sort of bacterium has been found inside a meteorite".
Prof Bailey said he was not too shocked by the latest revelations because existing evidence that rivers once flowed on Mars means it was not always the cold, arid and inhospitable planet it is today.
According to Prof Bailey, the fact that Mars once had rivers means that its atmosphere was at one stage similar to that existing on Earth in an era when primitive life got a foothold here.
Both Earth and Mars were formed 4,500 million years ago, Prof Bailey explained. For about 500 million years, no life existed on Earth. Then came the "late heavy bombardment" around 4,000 million years ago when asteroids and comets struck the planet. This caused a dramatic rise in the Earth's temperature. Its atmosphere was sterilised and it became an inhospitable place for life.
Yet, as soon as the Earth cooled, some 200 million years later, "life got going", said Prof Bailey. "What that tells us is that life in its most simple form is a robust phenomenon. If you extrapolate that to Mars, if it had an environment in which there was running water, a warmer climate and a thicker atmosphere, then conditions wouldn't have been so different from those you would expect to be sufficient to support life, and therefore it's not very surprising that life would have got going."
The late heavy bombardment which sterilised the Earth's atmosphere also led to the loss of Mars's atmosphere. This is because the Earth is 10 times as massive as Mars and was "better able to hold onto its atmosphere", said Prof Bailey.
"It's not enormously surprising that finally someone found evidence of life on Mars because in the case of the Earth we know that life began extremely early in an extremely inhospitable environment," he said.
The real puzzle, he added, is how the elementary form of life which existed on Earth for so long suddenly, about 500 million years ago, diversified into the whole range of complex plant and animal life forms that now exist.