SCIENCE ON THE MOON

The rocks and soil returned by the Apollo 11 crew quickly revealed that not only was Mare Tranquillitatis a basalt plain, it was astonishingly old in comparison to typical terrestrial rocks. 1’he Standing Stones at Calanais happen to be made of gneiss which is among Earth’s oldest rocks at around two to three billion years old. Compare this to 3.6 billion years for the Apollo 11 site. Also of surprise to the geologists was the presence of particles of anorthosite, a mineral rich in aluminium, among the soil samples. Later missions would reveal the importance of this type of rock in decoding the Moon’s history.

Some scientists were none too impressed when Apollo 12 was sent to another mare site merely to prove they could land near a defunct probe. It seemed there was little to distinguish it from the Apollo 11 site but when the samples were returned, its basalts were found to be a half billion years younger, showing that lunar volcanism had been active over an extended period.

Both Apollos 12 and 14, especially the latter, returned samples that came to be described as being KREEPy (K. is the chemical symbol for potassium, P for phosphorus and REE means rare earth elements, and the V makes it an adjective). The importance of KREEP lies in the fact that these elements are not easily incorporated into the crystal lattice of a solidifying rock. Therefore in a large body of magma that is slowly solidifying, the last rock to harden will be rich in KREEP and this clue would become significant as later missions added further evidence to our evolving knowledge of the Moon’s early history.