RT Journal Article SR Electronic T1 142Nd Evidence for Early (>4.53 Ga) Global Differentiation of the Silicate Earth JF Science JO Science FD American Association for the Advancement of Science SP 576 OP 581 DO 10.1126/science.1113634 VO 309 IS 5734 A1 Boyet, M. A1 Carlson, R. W. YR 2005 UL http://science.sciencemag.org/content/309/5734/576.abstract AB 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 element–depleted 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.