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

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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 207 Pb/ 206 Pb, 206 Pb/ 238 U, 207 Pb/ 235 U, and 208 Pb/ 232 Th 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 238 U/ 235 U ratio is the same as that in earth rocks, and 234 U is in radioactive equilibrium with parent 238 U.