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Argon-40/ Argon-39 Dating of Lunar Rock Samples

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Science  30 Jan 1970:
Vol. 167, Issue 3918, pp. 466-468
DOI: 10.1126/science.167.3918.466


Seven crystalline rock samples returned by Apollo 11 have been analyzed in detail by means of the 40Ar--39Ar dating technique. The extent of radiogenic argon loss in these samples ranges from 7 percent to ≥ 48 percent. Potassium-argon ages, corrected for the effects of this loss, cluster relatively closely around the value of 3.7 x 109 years. Most of the vulcanism associated with the formation of the Mare Tranquillitatis presumably occurred around 3.7 x 109 years ago. A major cause of the escape of gas from lunar rock is probably the impact event which ejected the rock from its place of origin to its place of discovery. Upper limits for the times at which these impact events occurred have been estimated.

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