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Eos, Transactions American Geophysical Union

Lunar samples, lunar accretion and the early bombardment of the Moon

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Abstract

Recent advances in lunar sample science and planetary accretion theories demand a new look at the bombardment history recorded by the Moon. Among lunar samples there are no impact melts dated older than about 3.9 Ga, yet a heavy bombardment of the Moon from its birth until 3.9 Ga should have produced many melts to be sampled by Apollo, Luna, and the meteorites of lunar origin. The absence of older impact melts cannot be explained by continued isotopic resetting because ejecta blankets are mainly cold and ancient igneous rocks including mare basalts exist. The common 3.85-Ga melt ages cannot be ascribed to a single or even a few basin events (e.g., Imbrium) because the samples show wide differences in chemistry and real, if small, differences in ages; the ages also appear in the lunar meteorites and thus are Moon-wide.

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Ancillary