Neodymium Isotope Evidence for a Chondritic Composition of the Moon

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Science  02 Jun 2006:
Vol. 312, Issue 5778, pp. 1369-1372
DOI: 10.1126/science.1126114

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Samarium-neodymium isotope data for six lunar basalts show that the bulk Moon has a 142Nd/144Nd ratio that is indistinguishable from that of chondritic meteorites but is 20 parts per million less than most samples from Earth. The Sm/Nd formation interval of the lunar mantle from these data is Embedded Image million years after the onset of solar system condensation. Because both Earth and the Moon likely formed in the same region of the solar nebula, Earth should also have a chondritic bulk composition. In order to mass balance the Nd budget, these constraints require that a complementary reservoir with a lower 142Nd/144Nd value resides in Earth's mantle.

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