Earth and Mars -- Distinct Inner Solar System Products


Earth and Mars

Terrestrial planets provide Solar System insights into the evolution of accretion, core-mantle and crust-mantle differentiation, and surface processes. The Earth and Mars have equal enrichment in refractory elements (1.9 × CI), although the Earth is more volatile-depleted and less oxidized than Mars.

Their chemical compositions were established by nebular chemical fractionation, with negligible contributions from post-accretionary losses of moderately volatile elements. During its formation before and after the nebular disk's lifetime, the Earth accreted more chondrules and less matrix than Mars and chondritic asteroids, making it the most volatile-depleted of these bodies.

The volatile-depleted, reduced proto-Earth was struck by an oxidized Mars-like (i.e., composition and mass) body, resulting in a debris ring having mostly a proto-Earth's mantle composition. This event resulted in the emulsification of the impactor, including its core, followed by oxidation and re-equilibration of the post-impact silicate Earth. Later, a sulfide melt (∼0.5% of the mass of the Earth's mantle) was extracted into the core, resulting in further depletion of chalcophile elements in the silicate Earth.

In contrast, Mars accreted under nearly uniform oxidizing conditions before the dissipation of a nebular disk. This rapid growth and small size made Mars less volatile element depleted body as compared to the Earth. 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.

Takashi Yoshizaki, William F. McDonough

Comments: 62 pages, 17 figures, 3 tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Geophysics (physics.geo-ph)
Cite as: arXiv:2006.11051 [astro-ph.EP] (or arXiv:2006.11051v1 [astro-ph.EP] for this version)
Submission history
From: Takashi Yoshizaki
[v1] Fri, 19 Jun 2020 10:08:55 UTC (11,106 KB)
Astrobiology, Astrochemistry

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