Support for the lunar cataclysm hypothesis from lunar impact melt ages, Science 290

Lunar meteorites represent a more random sampling of lunar material than the Apollo or Luna collections and, as such, lunar meteorite impact melt ages are the most important data in nearly 30 years with which to reexamine the lunar cataclysm hypothesis. Within the lunar meteorite breccias MAC 88105, QUE 93069, DaG 262, and DaG 400, seven to nine different impact events are represented with 40Ar-39Ar ages between 2.76 and 3.92 billion years ago (Ga). The lack of impact melt older than 3.92 Ga supports the concept of a short, intense period of bombardment in the Earth-moon system at;3.9 Ga. This was an anomalous spike of impact activity on the otherwise declining impact-frequency curve. In the early 1970s, 40Ar-39Ar and U-Pb iso-topic analyses of Apollo 15, 16, and 17 high-land rocks (1, 2) revealed surprising, wide-spread isotopic disturbances at 3.9 3 109 years ago (Ga). Argon and lead losses (an