  Several lines of evidence indicate a non-chondritic composition for Bulk
Earth. If Earth formed from the accretion of chondritic material, its
non-chondritic composition, in particular the super-chondritic 142Nd/144Nd and
low Mg/Fe ratios, might be explained by the collisional erosion of
differentiated planetesimals during its formation. In this work we use an
N-body code, that includes a state-of-the-art collision model, to follow the
formation of protoplanets, similar to proto-Earth, from differentiated
planetesimals (> 100 km) up to isolation mass (> 0.16 M_Earth). Collisions
between differentiated bodies have the potential to change the core-mantle
ratio of the accreted protoplanets. We show that sufficient mantle material can
be stripped from the colliding bodies during runaway and oligarchic growth,
such that the final protoplanets could have Mg/Fe and Si/Fe ratios similar to
that of bulk Earth, but only if Earth is an extreme case and the core is
assumed to contain 10% silicon by mass. This may indicate an important role for
collisional differentiation during the giant impact phase if Earth formed from
chondritic material.

Earth and Planetary Astrophysics;Geophysics