Saturday, August 13, 2022

Botswana rocks reveal Moon’s geological history

Lunar volcanoes spewed out lava that eventually solidified into the dark plains that early skywatchers mistook for a face. The plains of solidified lava that give the moon its quirky human-like face were created more than 4 billion years ago, a new study says. 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.

An international team of researchers published their study this week in the journal Nature.

In 1999, local people near the village of Kuke, in the grasslands of the
Kalahari Nature Reserve, found the 13.5 kilogram remnant of this roving rock.

They then sold it to meteorite hunters.
Scientists have since confirmed that the rock, named Kalahari 009, came from the moon. They found the telltale signature of oxygen isotopes plus the 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. This is 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, the study says. This suggests 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 Dr Kentaro Terada of Hiroshima University in Japan and Dr Mahesh Anand of the UK’s Open University.

Mare volcanism overlapped with a later stage of volcanism, evidence of which was found in rocks picked up by the Apollo missions.

The ‘man in the moon’ comprises eyes made of the Mare Imbrium and Mare Serenitatis, a nose consisting of Sinus Aestuum, while the Mare Nubium and Mare Cognitum provide its mouth. These and other mare account for nearly a sixth of the lunar surface, mostly on the side visible from earth.


Read this week's paper