Homogeneous accretion of the Earth in the inner Solar System.

Meteorites are classified as either non-carbonaceous or carbonaceous, representing bodies that are likely to have 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 ten nucleosynthetic isotope anomalies among planets and meteorite parent bodies to show that the linear extension of an array defined by non-carbonaceous 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 non-carbonaceous 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.