146Sm decays to 142Nd with a relatively short half-life (∼68 Ma). The142Nd/144Nd of modern terrestrial mantle-derived lavas is 18 ± 5 ppm higher than the chondrite reservoir. The difference in142Nd/144Nd between Earth and chondrites likely owes to Sm/Nd ratios 6% higher in the accessible Earth that arose within the first 30 million years following accretion. In order to constrain the early history of the mantle domains sampled by ocean island basalts (OIB) and mid-ocean ridge basalts (MORB), we present high-precision142Nd/144Nd measurements on 11 different lavas from five hot spots, and one lava each from the Indian and Atlantic ridges. The lavas examined in this study bracket much of the known Sr-Nd-Pb-He isotopic variability the in mantle. These data complement existing high-precision142Nd/144Nd data on MORB and OIB lavas. In agreement with previous studies, we find that MORB and OIB lavas examined for high-precision142Nd/144Nd exhibit ratios that are indistinguishable from the terrestrial standard and are 15–20 ppm higher than the average obtained for ordinary and enstatite chondrites. The uniform, superchondritic 142Nd/144Nd data in OIB and MORB are consistent with derivation from a common, early formed (<30 Ma after accretion) progenitor reservoir with Sm/Nd ∼6% higher than chondrites. If there exists any variability in 142Nd/144Nd in the OIBs and MORBs examined to date, it is too small to be resolved with the precision currently available.