Dating rocks from the moon
As a result, the absolute ages of lunar craters are primarily determined through isotope geochronology of components of the target rocks that were shocked and heated to the point of melting, and which have since solidified.
However, lunar rocks may have experienced multiple impact events over the course of billions of years of bombardment, potentially complicating attempts to date samples and relate the results to the ages of particular impact structures.
When a meteor strikes another planetary body, the impact produces very large amounts of energy, some of which goes into shock heating and melting the target rocks.
Analayzing this rock with the new laser microprobe 40Ar/39Ar technique, scientists were able to determine the age relationships of three of the distinct generations of impact melt it includes.This allowed the researchers to tweak the technique used for dating rock samples, making it more accurate.In doing so, it pushes back the estimated date of the hypothesized impact that formed the moon by about 60 million years ( /- 20 million years).While the laser microprobe 40Ar/39Ar technique has been applied to a large number of problems in terrestrial geochronology, including studies of texturally complex samples, this is the first time it has been applied to samples from the Apollo archive.The samples analyzed by the ASU team are known as lunar impact melt breccias — mash-ups of glass, rock and crystal fragments that were created by impact events on the moon’s surface.