The bombardment history on the lunar farside revealed by ⁴⁰ Ar/ ³⁹ Ar geochronology of Chang’e-6 impact melt rocks

The reconstruction of the lunar bombardment history is pivotal to understanding the evolution of Earth-Moon system. So far, it heavily depends on geochronological studies of lunar nearside samples but lacks direct sample constraints from the lunar farside. Here, we present 28 single-clast 40 Ar/ 39 Ar ages of impact melt rocks returned by the Chang’e-6 mission. They reveal impact events spanning from ∼4.33 to ∼1.13 billion years (Ga). In particular, three melt clasts date to ∼4.16 Ga, consistent with the recent dating of the Apollo basin, and only two ages fall at 4.0 to 3.7 Ga. The presence of older ages (>4.0 Ga) and lack of predominant age around ∼3.9 Ga suggest that the lunar farside bombardment was not dominated by a cataclysmic spike but by a smooth long-term decline punctuated by later impacts.