For something so close and so obvious, it is sometimes surprising how little we know about the Moon. A paper in this week’s Nature gives us a bit more understanding, by dating one of the oldest Moon rocks we have down here on Earth.

Based on previous samples from ‘up there’ it has been proposed that most Moon volcanism occurred about 3.8-3.9 Gyr. The new paper suggests that there was volcanism on the Moon relatively soon after it formed, sometime around 4.35 Gyr.

Under the admittedly-not-hugely-catchy title ‘Cryptomare magmatism 4.35 Gyr ago recorded in lunar meteorite Kalahari 009’, researchers report the results of “ion microprobe U–Pb dating of phosphates in a lunar meteorite, Kalahari 009, which is classified as a very-low-Ti mare-basalt breccia”. Basically they worked out how old a fragment of the moon a meteorite from there is.

The meteorite probably fell to Earth about 250 years ago, after being chipped off the moon by an asteroid (National Geographic). This new knowledge could help understanding of planetary evolution, says one of the researchers involved.

“We want to understand how the Solar System formed, how the planets formed. The Moon is the only place where you can go to find the first 500 million years of geological history, because these old rocks have been lost on Earth,” Mahesh Anand from the UK’s Open University told the BBC.

Check out Nature’s 2006 Moon Special.

Image: Kalahari 009 / Institut fur Planetologie, Universitaet Muenster.