This study determines the ages of 191 discrete lunar regolith samples from the
Apollo, Luna, and meteorite collections. Model closure ages (for lithified breccias) and
appearance ages (for unconsolidated soils) are calculated using the trapped 40 Ar and 36 Ar
abundances of each sample, determined from published Ar data. Model closure ages of
regolith breccias span *3.9 to 0.01 Ga and appearance ages of soils range from *3.6 to
0.03 Ga; 169 of these ages are published here for the first time, while 22 are recalculated
ages. The regolith breccias with the oldest closure ages originate from the ancient high-
lands and oldest mare surfaces sampled by the Apollo missions. Soils generally have
similar ages to each other, regardless of location and collection depth, with most model
ages \2.0 Ga. Together, the soils and regolith breccias represent a record of regolith
processes over the past 3.9 Ga. The data illustrate that individual landing sites can provide
a diversity of ages, which has implications for planning future missions. Differences in
maturity between older and younger regolith samples may reflect a change in collisional
regimes over time. We note, too, that the closure ages published here are critical data
needed for selecting temporally appropriate regolith samples used to decipher the diversity
of impactors hitting the lunar surface over time and how the Sun has changed in time.

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Available

• Ages of Globally Distributed Lunar Paleoregoliths and Soils from 3.9 Ga to the Present