How young is volcanism on the Moon

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By Yuri Amelin and Qing-Zhu Yin, Science. 

Excerpt: Analyses of rocks and soils delivered by the Apollo and Luna missions have established that the Moon is ancient, dry, and depleted of volatile elements. Studies also have indicated that early in its history, the Moon was covered with molten rock. This magma ocean eventually cooled and produced a compositionally diverse surface crust (1). How long the Moon produced magma has been an open question. On page 1077 of this issue, Wang et al. (2) report that volcanism on the Moon occurred as recently as 120 million years ago (Ma). This implies that the Moon may still be able to produce magma. ...Determining the time range of lunar volcanism can be expanded by studying volcanic glass beads produced by lava fountains (eruptions) and preserved in lunar regolith (surface rock and debris) (11). These beads, despite sizes of only a few tens of micrometers, can be dated with argon (40Ar/39Ar) and uranium-lead (U-Pb) radioactive isotope decay methods (12, 13).... 

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