Introduction & Approach: The closure age of a regolith breccia represents the point in time in which regolith components are sealed off from the solar wind (i.e., buried) and additional lithologic contributions; this can be used as a temporal guide to lunar surface processes such as the bombardment history [e.g., 1]. Those closure ages can be calculated from trapped 40Ar/36Ar using a newly calibrated system [2, after 3]. Thus far, the ages of eighteen Apollo 16  and twenty-five Apollo 15 regolith breccias  have been determined using the new calibration. In this report, we expand that work to include the closure ages of regolith breccias from the remaining Apollo missions and existing lunar meteorites.
Results: We calculated the closure ages of twenty-two Apollo regolith breccias (11, 12, 14, and 17 missions) and thirteen lunar meteorites using 40Ar and 36Ar data in the literature. This augments the existing dataset of [2 & 4] to produce a total of seventy-eight sample closure ages. Six of those ages have negative values, which is an artifact of the calibration’s sensitivity to low ratios of trapped 40Ar/36Ar (i.e., in the very youngest samples) and are not considered further here. The remaining samples have credible closure ages from 3.9 to 0.1 Ga. The oldest samples (i.e., closure ages ≥ 3.4 Ga ) were collected from the ancient highlands (i.e., Apollo 16) and the oldest mare surface seen during the Apollo Program (Apollo 14; 4.2-3.9 Ga ). In contrast, most of the more recent closure ages (≤ 2.0 Ga) were collected from younger mare surfaces (Apollo 11, 12, 15, 17; ≤ 3.9 Ga ). The average temporal interval between individual sample closure ages is ~0.07 Ga, while the smallest and largest interval sizes are <0.01 and ~0.6 Ga, respectively.
Discussion: These results indicate regolith samples obtained from highland sites, like that at Apollo 16, can provide information about the processes shaping the Moon ~4 to 3.4 Ga. The work of  implies regolith breccias from those regions can contribute additional information about the impactors hitting the Earth-Moon system at that time. Likewise, an assessment of impactors striking the Moon throughout younger periods can be derived from regolith samples that were successively closed between 3.4 Ga and the present day. Collectively, the data indicate regolith breccias can provide a fairly complete record of surface processes over the past 4 Ga. Additional samples, either recovered as lunar meteorites or by human and robotic sample return missions, can substantially enhance that record by filling in the remaining temporal gaps and providing complementary records from a geographically diverse set of sites.
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