ArticlesAge Measurements

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

Science  30 Jan 1970:
Vol. 167, Issue 3918, pp. 463-466
DOI: 10.1126/science.167.3918.463

Abstract

The 87Rb-87Sr internal isochrons for five rocks yield an age of 3.65 ±0.05 x 109 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 x109 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 x 109 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 131Xe/126Xe ratio. No evidence for 129I 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.