Earth’s composition was modified by collisional erosion

Abstract

The samarium-146 ( 146 Sm)–neodymium-142 ( 142 Nd) short-lived decay system (half-life of 103 million years) is a powerful tracer of the early mantle-crust evolution of planetary bodies. However, an increased 142 Nd/ 144 Nd in modern terrestrial rocks relative to chondrite meteorites has been proposed to be caused by nucleosynthetic anomalies, obscuring early Earth’s differentiation history. We use stepwise dissolution of primitive chondrites to quantify nucleosynthetic contributions on the composition of chondrites. After correction for nucleosynthetic anomalies, Earth and the silicate parts of differentiated planetesimals contain resolved excesses of 142 Nd relative to chondrites. We conclude that only collisional erosion of primordial crusts can explain such compositions. This process associated with planetary accretion must have produced substantial loss of incompatible elements, including long-term heat-producing elements such as uranium, thorium, and potassium.