Age of the Moon: An Isotopic Study of Uranium-Thorium-Lead Systematics of Lunar Samples

Abstract

Concentrations of U, Th, and Pb in Apollo 11 samples studied are low (U. 0.16 to 0.87; Th, 0.53 to 3.4; Pb, 0.29 to 1.7, in ppm) but the extremely radiogenic lead in samples allows radiometric dating. The fine dust and the breccia have a concordant age of 4.66 billion years on the basis of ²⁰⁷Pb/²⁰⁶Pb, ²⁰⁶Pb/²³⁸U, ²⁰⁷Pb/^235U, and²⁰⁸Pb/²³²Th ratios. This age is comparable with the age of meteorites and with the age generally accepted for the earth. Six crystalline and vesicular samples are distinctly younger than the dust and breccia. The ²³⁸U/²³⁵U ratio is the same as that in earth rocks, and ²³⁴U is in radioactive equilibrium with parent ²³⁸U.