The Elemental Abundances (with Uncertainties) of the Most Earth-like Planet
Date
2018
Authors
Wang, Haiyang S
Lineweaver, Charles
Ireland, Trevor
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Publisher
Elsevier
Abstract
To first order, the Earth as well as other rocky planets in the Solar System
and rocky exoplanets orbiting other stars, are refractory pieces of the stellar
nebula out of which they formed. To estimate the chemical composition of rocky
exoplanets based on their stellar hosts' elemental abundances, we need a better
understanding of the devolatilization that produced the Earth. To quantify the
chemical relationships between the Earth, the Sun and other bodies in the Solar
System, the elemental abundances of the bulk Earth are required. The key to
comparing Earth's composition with those of other objects is to have a
determination of the bulk composition with an appropriate estimate of
uncertainties. Here we present concordance estimates (with uncertainties) of
the elemental abundances of the bulk Earth, which can be used in such studies.
First we compile, combine and renormalize a large set of heterogeneous
literature values of the primitive mantle (PM) and of the core. We then
integrate standard radial density profiles of the Earth and renormalize them to
the current best estimate for the mass of the Earth. Using estimates of the
uncertainties in i) the density profiles, ii) the core-mantle boundary and iii)
the inner core boundary, we employ standard error propagation to obtain a core
mass fraction of $32.5 \pm 0.3$ wt%. Our bulk Earth abundances are the weighted
sum of our concordance core abundances and concordance PM abundances. Our
concordance estimates for the abundances of Mg, Sn, Br, B, Cd and Be are
significantly lower than previous estimates of the bulk Earth. Our concordance
estimates for the abundances of Na, K, Cl, Zn, Sr, F, Ga, Rb, Nb, Gd, Ta, He,
Ar, and Kr are significantly higher. The uncertainties on our elemental
abundances usefully calibrate the unresolved discrepancies between standard
Earth models under various geochemical and geophysical assumptions.
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Icarus
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Journal article
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Open Access
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