¹Francis Nimmo, ²Thorsten Kleine, ³Alessandro Morbidelli, ⁴David Nesvorny
Earth and Planetary Science Letters 648, 119112 Link to Article [https://doi.org/10.1016/j.epsl.2024.119112]
¹Dept. Earth & Planetary Sciences, University of California Santa Cruz, Santa Cruz CA 95064, United States
²Max Planck Institute for Solar System Research, Gottingen 37077, Germany
³College de France, Paris Cedex 05 75 231, France
⁴Dept. Space Studies, Southwest Research Institute, Boulder CO 80302, United States
Copyright: Elsevier

The nucleosynthetic isotope signatures of meteorites and the bulk silicate Earth (BSE) indicate that Earth consists of a mixture of “carbonaceous” (CC) and “non-carbonaceous” (NC) materials. We show that the fraction of CC material recorded in the isotopic composition of the BSE varies for different elements, and depends on the element’s tendency to partition into metal and its volatility. The observed behavior indicates that the majority of material accreted to the Earth was NC-dominated, but that CC-dominated material enriched in moderately volatile elements by a factor of ∼10 was delivered during the last ∼2–10% of Earth’s accretion. The late delivery of CC material to Earth contrasts with dynamical evidence for the early implantation of CC objects into the inner solar system during the growth and migration of the giant planets. This, together with the NC-dominated nature of both Earth’s late veneer and bulk Mars, suggests that material scattered inwards had the bulk of its mass concentrated in a few, large CC embryos rather than in smaller planetesimals. We propose that Earth accreted a few of these CC embryos while Mars did not, and that at least one of the CC embryos impacted Earth relatively late (when accretion was 90–98% complete). This scenario is consistent with the subsequent Moon-forming impact of a large NC body, as long as this impact did not re-homogenize the entire Earth’s mantle.