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Research Articles142Nd Evidence for Early (>4.53 Ga) Global Differentiation of the Silicate Earth
New high-precision samarium-neodymium isotopic data for chondritic meteorites show that their 142Nd/144Nd ratio is 20 parts per million lower than that of most terrestrial rocks. This difference indicates that most (70 to 95%) of Earth's mantle is compositionally similar to the incompatible elementdepleted source of mid-ocean ridge basalts, possibly as a result of a global differentiation 4.53 billion years ago (Ga), within 30 million years of Earth's formation. The complementary enriched reservoir has never been sampled and is probably located at the base of the mantle. These data influence models of Earth's compositional structure and require revision of the timing of global differentiation on Earth's Moon and Mars. Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, N.W., Washington, DC 20015, USA. Include this information when citing this paper. * To whom correspondence should be addressed. E-mail: boyet{at}dtm.ciw.edu
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Science. ISSN 0036-8075 (print), 1095-9203 (online)