Heterogeneous accretion of Earth inferred from Mo-Ru isotope systematics. (arXiv:2001.05405v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Hopp_T/0/1/0/all/0/1">Timo Hopp</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Budde_G/0/1/0/all/0/1">Gerrit Budde</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kleine_T/0/1/0/all/0/1">Thorsten Kleine</a>
The Mo and Ru isotopic compositions of meteorites and the bulk silicate Earth
(BSE) hold important clues about the provenance of Earth’s building material.
Prior studies have argued that non-carbonaceous (NC) and carbonaceous (CC)
meteorite groups together define a Mo-Ru ‘cosmic’ correlation, and that the BSE
plots on the extension of this correlation. These observations were taken as
evidence that the final 10-15% of Earth’s accreted material derived from a
homogeneous inner disk reservoir with an enstatite chondrite-like isotopic
composition. Here, using new Mo and Ru isotopic data for previously
uninvestigated meteorite groups, we show that the Mo-Ru correlation only exists
for NC meteorites, and that both the BSE and CC meteorites fall off this Mo-Ru
correlation. These observations indicate that the final stages of Earth’s
accretion were heterogeneous and consisted of a mixture of NC and CC materials.
The Mo-Ru isotope systematics are best accounted for by either an NC heritage
of the late veneer combined with a CC heritage of the Moon-forming giant
impactor, or by mixed NC-CC compositions for both components. The involvement
of CC bodies in the late-stage accretionary assemblage of Earth is consistent
with chemical models for core-mantle differentiation, which argue for the
addition of more oxidized and volatile-rich material toward the end of Earth’s
formation. As such, this study resolves the inconsistencies between homogeneous
accretion models based on prior interpretations of the Mo-Ru systematics of
meteorites and the chemical evidence for heterogeneous accretion of Earth.
The Mo and Ru isotopic compositions of meteorites and the bulk silicate Earth
(BSE) hold important clues about the provenance of Earth’s building material.
Prior studies have argued that non-carbonaceous (NC) and carbonaceous (CC)
meteorite groups together define a Mo-Ru ‘cosmic’ correlation, and that the BSE
plots on the extension of this correlation. These observations were taken as
evidence that the final 10-15% of Earth’s accreted material derived from a
homogeneous inner disk reservoir with an enstatite chondrite-like isotopic
composition. Here, using new Mo and Ru isotopic data for previously
uninvestigated meteorite groups, we show that the Mo-Ru correlation only exists
for NC meteorites, and that both the BSE and CC meteorites fall off this Mo-Ru
correlation. These observations indicate that the final stages of Earth’s
accretion were heterogeneous and consisted of a mixture of NC and CC materials.
The Mo-Ru isotope systematics are best accounted for by either an NC heritage
of the late veneer combined with a CC heritage of the Moon-forming giant
impactor, or by mixed NC-CC compositions for both components. The involvement
of CC bodies in the late-stage accretionary assemblage of Earth is consistent
with chemical models for core-mantle differentiation, which argue for the
addition of more oxidized and volatile-rich material toward the end of Earth’s
formation. As such, this study resolves the inconsistencies between homogeneous
accretion models based on prior interpretations of the Mo-Ru systematics of
meteorites and the chemical evidence for heterogeneous accretion of Earth.
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