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Published January 30, 1970 | public
Journal Article

Ages, Irradiation History, and Chemical Composition of Lunar Rocks from the Sea of Tranquillity


The ^(87)Rb-^(87)Sr internal isochrons for five rocks yield an age of 3.65±0.05 × 10^9 years which presumably dates the formation of the Sea of Tranquillity. Potassium-argon ages are consistent with this result. The soil has a model age of 4.5 × 10^9 years, which is best regarded as the time of initial differentiation of the lunar crust. A peculiar rock fragment from the soil gave a model age of 4.44 × 10^9 years. Relative abundances of alkalis do not suggest differential volatilization. The irradiation history of lunar rocks is inferred from isotopic measurements of gadolinium, vanadium, and cosmogenic rare gases. Spallation xenon spectra exhibit a high and variable 1^(31)Xe/^(126)Xe ratio. No evidence for ^(129)I was found. The isotopic composition of solar-wind xenon is distinct from that of the atmosphere and of the average for carbonaceous chondrites, but the krypton composition appears similar to average carbonaceous chondrite krypton.

Additional Information

© 1970 American Association for the Advancement of Science. We thank our fellow inmates Pai Young and Uwe Derksen for the sophisticated skill and knowledge they have brought to this study, without which this work would not have been accomplished. We also acknowledge the unstinting efforts of J. Brown, H. L. Derksen, L. llay, and T. Wen. This work was supported by NASA contract 64049.

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August 23, 2023
October 23, 2023