The "terminal lunar cataclysm" hypothesis describes a short period at ~3.9 Ga when the Earth-Moon system experienced an anomalously high bombardment flux, creating 5-20 basins and resurfacing 80% of the Moon. The lunar crater record serves as a proxy for all the other terrestrial planets and the assumed lunar flux underpins dynamical models of solar system evolution, so investigation of this period in lunar impact history is a vital topic. I will discuss my research on this controversial issue that uses microbeam techniques to understand the petrology, chemistry, and age of impact-affected lunar samples.