Homogeneous accretion of the Earth in the inner Solar System

TL;DR

This study demonstrates that Earth's composition resulted solely from inner solar system material, showing no significant contribution from outer solar system bodies during its formation.

Contribution

It provides isotopic evidence that Earth's accretion was homogeneous and exclusively from inner solar system material, challenging previous mixed-origin hypotheses.

Findings

Earth's isotopic composition aligns with inner solar system material only.

Mercury and Venus show more extreme isotopic compositions, indicating gradients during planet formation.

Earth's formation involved homogeneous accretion without outer solar system material.

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.