A GLOBAL LUNAR IMPACT BOMBARDMENT ~800 MA AGO RECORDED IN LUNAR IMPACT GLASSES

Standard lunar crater chronology systems assume there has been little change in the impact flux over the past three billion years. We investigate geochemically-distinct lunar impact glasses (“exotic” impact glasses) and in this presentation, provide some insight to the lunar impact history, particularly in the most recent one billion years. Although a sampling bias may have influenced the observed age distribution of lunar impact glasses, glass spherules and fragments that are geochemically distinct from the regolith in which they were collected appear to reflect a potential impact record for large cratering events. These so-called "exotic" glass populations show a higher concentration of ages between 700 and 900 Ma; that range of ages overlaps the formation of Copernicus Crater at ~800 Ma. We have identified “exotic” lunar impact glasses that were not produced by local, small impacts and are geochemically distinct from the Apollo 12 ropy glasses. In this study, we investigate a possible geochemical link between the exotic impact glass population and the Copernicus Crater region. Whether or not the lunar impact rate spiked at ~800 Ma, we examine the provenances of those “exotic” glass spherules.