Homogeneous accretion of the Earth in the inner Solar System

Original Abstract

Meteorites are classified as either non-carbonaceous- (NC) or carbonaceous (CC), representing bodies that likely formed in the inner- or outer solar system, respectively. Despite its location in the inner solar system, the Earth is thought to contain either minor- (~6 %) or substantial amounts (~40 %) of outer solar system material. However, because neither interpretation leverages variations among multiple isotopic systems simultaneously, Earth's provenance remains equivocal. Here, we examine variations in 10 nucleosynthetic isotope anomalies among planetary- and meteorite parent bodies to show that the linear extension of an array defined by NC bodies in any two isotopic anomalies always intersects the observed isotopic composition of the bulk silicate Earth to within 1 standard deviation. The Earth therefore formed exclusively from inner solar system material whose composition did not vary over the course of accretion and was, on average, unlike that of any chondrite. Extension of the NC array yields isotopic compositions for Mercury and Venus that are more extreme than for Earth, implying a spatial or temporal gradient during the formation of the terrestrial planets.