TY - JOUR
T1 - Earth and Mars – Distinct inner solar system products
AU - Yoshizaki, Takashi
AU - McDonough, William F.
N1 - Funding Information:
We thank many our colleagues who have listened to various versions of this project and given feedback, especially Eiji Ohtani, Nick Schmerr, Beda Roskovec, Ondřej Šrámek, Sarah Stewart-Mukhopadhyay, Kevin Righter, and Henri Samuel. We also thank Attilio Rivoldini for helpful comments. We greatly appreciate Hugh O’Neill, Bernard Wood, and an anonymous referee for their constructive reviews, which helped improve the manuscript. We thank the journal editor Astrid Holzheid for editorial efforts. TY acknowledges supports from the Japanese Society for the Promotion of Science (JP18J20708) and GP-EES and DIARE research grants. WFM gratefully acknowledges NSF support (EAR1650365).
Publisher Copyright:
© 2021 Elsevier GmbH
PY - 2021/5
Y1 - 2021/5
N2 - Composition of terrestrial planets records planetary accretion, core–mantle and crust–mantle differentiation, and surface processes. Here we compare the compositional models of Earth and Mars to reveal their characteristics and formation processes. Earth and Mars are equally enriched in refractory elements (1.9 × CI), although Earth is more volatile-depleted and less oxidized than Mars. Their chemical compositions were established by nebular fractionation, with negligible contributions from post-accretionary losses of moderately volatile elements. The degree of planetary volatile element depletion might correlate with the abundances of chondrules in the accreted materials, planetary size, and their accretion timescale, which provides insights into composition and origin of Mercury, Venus, the Moon-forming giant impactor, and the proto-Earth. During its formation before and after the nebular disk's lifetime, the Earth likely accreted more chondrules and less matrix-like materials than Mars and chondritic asteroids, establishing its marked volatile depletion. A giant impact of an oxidized, differentiated Mars-like (i.e., composition and mass) body into a volatile-depleted, reduced proto-Earth produced a Moon-forming debris ring with mostly a proto-Earth's mantle composition. Chalcophile and some siderophile elements in the silicate Earth added by the Mars-like impactor were extracted into the core by a sulfide melt (∼0.5% of the mass of the Earth's mantle). In contrast, the composition of Mars indicates its rapid accretion of lesser amounts of chondrules under nearly uniform oxidizing conditions. Mars’ rapid cooling and early loss of its dynamo likely led to the absence of plate tectonics and surface water, and the present-day low surface heat flux. These similarities and differences between the Earth and Mars made the former habitable and the other inhospitable to uninhabitable.
AB - Composition of terrestrial planets records planetary accretion, core–mantle and crust–mantle differentiation, and surface processes. Here we compare the compositional models of Earth and Mars to reveal their characteristics and formation processes. Earth and Mars are equally enriched in refractory elements (1.9 × CI), although Earth is more volatile-depleted and less oxidized than Mars. Their chemical compositions were established by nebular fractionation, with negligible contributions from post-accretionary losses of moderately volatile elements. The degree of planetary volatile element depletion might correlate with the abundances of chondrules in the accreted materials, planetary size, and their accretion timescale, which provides insights into composition and origin of Mercury, Venus, the Moon-forming giant impactor, and the proto-Earth. During its formation before and after the nebular disk's lifetime, the Earth likely accreted more chondrules and less matrix-like materials than Mars and chondritic asteroids, establishing its marked volatile depletion. A giant impact of an oxidized, differentiated Mars-like (i.e., composition and mass) body into a volatile-depleted, reduced proto-Earth produced a Moon-forming debris ring with mostly a proto-Earth's mantle composition. Chalcophile and some siderophile elements in the silicate Earth added by the Mars-like impactor were extracted into the core by a sulfide melt (∼0.5% of the mass of the Earth's mantle). In contrast, the composition of Mars indicates its rapid accretion of lesser amounts of chondrules under nearly uniform oxidizing conditions. Mars’ rapid cooling and early loss of its dynamo likely led to the absence of plate tectonics and surface water, and the present-day low surface heat flux. These similarities and differences between the Earth and Mars made the former habitable and the other inhospitable to uninhabitable.
KW - Chondrites
KW - Cosmochemistry
KW - Earth
KW - Mars
KW - Solar system
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U2 - 10.1016/j.chemer.2021.125746
DO - 10.1016/j.chemer.2021.125746
M3 - Article
AN - SCOPUS:85115291628
VL - 81
JO - Geochemistry
JF - Geochemistry
SN - 0009-2819
IS - 2
M1 - 125746
ER -