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Lunar lava 4 billion years old: report

The plains of solidified lava that give the Moon its quirky human-like face as seen from Earth were created more than 4 billion years ago, according to a paper appearing today in the British weekly Nature.

The evidence comes from an unearthly silvery-grey stone that was blasted off from the face of the Moon, perhaps by an impacting asteroid, and was then captured by Earth's gravity, prompting it to fall to ground in Botswana.

In 1999, the 13.5kg remnant of this roving rock was found by near the village of Kuke, in the Kalahari Nature Reserve, and was sold to meteorite hunters.

The lunar heritage of the rock, named Kalahari 009, has been confirmed by a telltale signature of oxygen isotopes and ratio of iron to manganese in two volcanic minerals, olivine and pyroxene.

The nature of these chemicals puts the rock into the category of a mare basalt -- a lava that flowed out smoothly onto the lunar surface before solidifying, forming dark plains that early skywatchers mistakenly took for seas, mare in Latin.

A new analysis of fragments of phosphate in Kalahari 009 puts the rocks at the whopping old age of 4.35 billion years, give or take 150 million years, Nature says.

This implies that mare-type volcanism must have occurred at least as early as this date, just after the first stage of lunar crust formation, say the authors, led by Kentaro Terada of Hiroshima University and Mahesh Anand of Britain's Open University.
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