Strontium-Rubidium Age of an Iron Meteorite

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Science  31 Dec 1965:
Vol. 150, Issue 3705, pp. 1814-1818
DOI: 10.1126/science.150.3705.1814


The isotopic compositions and concentrations of rubidium and strontium were determined in silicate nodules contained in Weekeroo Station meteorite, a brecciated coarse octahedrite. The strontium had a Sr87:Sr86 range from 0.729 to 0.768, showing considerable enrichment in Sr87 in coinparison with achondrites. Data for six samples of nodules lie on a straight line on the Sr-Rb evolution diagram, with an initial Sr87:Sr86 ratio of 0.696 to 0.702; the slope is 0.0674, corresponding to an age of 4.7 x 109 years for λ = 1.39 x 10-11 year-1. These data agree with the previously assigned ages for the formation of stony meteorites and the earth; they support the conclusion that the major period of chemical and physical differentiation in the solar system occurred in a narrow interval at about this time. This result disagrees with the Ar40-K40 ages of 5 to 13 x 109 years determined from other iron meteorites. A wide variety of isotopic-age investigations now seem experimentally feasible on iron meteorites that contain silicates.