A hydrogen-based oxidation mechanism relevant to planetary formation

By Z. Sharp, F. McCubbin, C. Shearer. 2013

143 citations recorded by the source corpus.

Article history: It is now generally accepted that the Moon formed by collision of a Mars-sized impactor with the Earth (Hartmann and Davis, 1975), a process termed "the Giant Impact". The oxygen isotope compositions of both bodies are indistinguishable (Wiechert et al., 2001), a result that would require extensive chemical homogenization. Recent simulations have been developed that predict intimate mixing immediately following the impact (Canup, 2012; ´ Cuk and Stewart, 2012; Pahlevan and Stevenson, 2007), minimizing the oxygen isotope problem. Nevertheless, striking chemical differences remain. We propose that the process of hydrogen degassing and loss to space during magma cooling can explain differences in the water content, oxygen fugacity ( f (O2)), and isotopic composition of Cl and H in the Earth-Moon system. At low f (O2), H2 gas is the stable O-H phase in basalts. The low solubility and rapid diffusivity of H2 explain the presently dry character of most lunar samples. Many of the apparently discrepant observations regarding the hydrous character of the Moon are reconciled by H2 degassing. Early H2 degassing also explains the high f (O2) of Earth's mantle. A loss of only 1/3 'ocean equivalent' water from Earth by hydrodynamic escape of H2 would shift the f (O2 )o f the upper mantle from the very low oxidation state equivalent to the Moon and other primitive differentiated bodies to its present oxidized state (near the fayalite-magnetite-quartz buffer). No other processes, such as late addition of material to Earth or injection of Fe 3+ -rich deep mantle materials to the upper mantle are required to explain the early elevated oxidation state of Earth's upper mantle.

Subfields: Astronomy and Astrophysics, Geophysics

View Paper: https://www.semanticscholar.org/paper/d56f360f0e3f4157f96d80a0ceb84af235fd4247

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Citations in the corpus

Heterogeneous distribution of H2O in the Martian interior: Implications for the abundance of H2O in depleted and enriched mantle sources (2016, background): “…data from Martian meteorites, which are minimally fractionated (Williams et al. 2016), also support the idea that Cl did not degas as anhydrous metal chloride species like those inferred to have degassed from lunar magmas (Sharp et al. 2010, 2013; Shearer et al. 2014; McCubbin et al. 2015b).”
Accretion and differentiation of the terrestrial planets with implications for the compositions of early-formed Solar System bodies and accretion of water (2014, background): “It has been proposed that water that is accreted to the Earth is the main cause of mantle oxidation through the degassing of H2 (Sharp et al., 2013).”
The origin of water in the primitive Moon as revealed by the lunar highlands samples (2014, background): “…degassing of a vapour phase, which is known to be a process that can fractionate H from D isotopes, especially at the low f O2 that prevailed in the lunar interior as the major degassing H-bearing species is H2 (Füri et al., 2014; Sharp et al., 2013; Tartèse and Anand, 2013; Tartèse et al., 2013).”