Argon-lead isotopic correlation in samples from lunar maria: Records from the ancient lunar regolith

²⁰⁷Pb/²⁰⁶Pb of “low temperature sited” (LTS) lead as reported by Silver (1975) increases with⁴⁰Ar/³⁶Ar of trapped argon in thirteen samples from lunar maria. This strongly supports an earlier conclusion by (1972) that large (⁴⁰Ar/³⁶Ar)_T ratios represent ancient regolith records, and provides a rough (⁴⁰Ar/³⁶Ar)_T timescale.The erasure of (⁴⁰Ar/³⁶Ar)_T records in surface soils by the excavation of deep-seated, “fresh” bedrock and by erosion of particle surfaces via ion sputtering must have been counteracted by conserving processes in the regolith. Two such processes are relatively well understood: agglutinate formation and the excavation and comminution of soil breccias which have preserved an ancient (⁴⁰Ar/³⁶Ar)_T record. The frequency distribution of (⁴⁰Ar/³⁶Ar)_T in 82 “soils” from all Apollo missions suggests a third process, which requires that sizeable “pockets” of ancient regolith materials including soils have survived deep turnover for billions of years.Large-scale mobility of LTS lead throughout all of the regolith does not appear to occur.Inert gas ions with sufficient energy for trapping may have reached the lunar surface more than 3 b.y. ago.The Apollo 11 microbreccias appear to have been formed more than 3 b.y. ago from regoliththen extant on the surface.