Serpentinization and the Formation of H₂and CH₄on Celestial Bodies (Planets, Moons, Comets)

Abstract

Serpentinization involves the hydrolysis and transformation of primary ferromagnesian minerals such as olivine ((Mg,Fe)2SiO4) and pyroxenes ((Mg,Fe)SiO3) to produce H2-rich fluids and a variety of secondary minerals over a wide range of environmental conditions. The continual and elevated production of H2 is capable of reducing carbon, thus initiating an inorganic pathway to produce organic compounds. The production of H2 and H2-dependent CH4 in serpentinization systems has received significant interdisciplinary interest, especially with regard to the abiotic synthesis of organic compounds and the origins and maintenance of life in Earth's lithosphere and elsewhere in the Universe. Here, serpentinization with an emphasis on the formation of H2 and CH4 are reviewed within the context of the mineralogy, temperature/pressure, and fluid/gas chemistry present in planetary environments. Whether deep in Earth's interior or in Kuiper Belt Objects in space, serpentinization is a feasible process to invoke as a means of producing astrobiologically indispensable H2 capable of reducing carbon to organic compounds. Key Words: Serpentinization—Fischer-Tropsch-type synthesis—Hydrogen formation—Methane formation—Ultramafic rocks. Astrobiology 15, 587–600.

Isotope record of mineralogical changes in a spectrum of aqueously altered CM chondrites

“…H 2 release by serpentinization is not limited by low abundances of precursor materials, unlike the previously mentioned Fe oxidation process. The production of H 2 during serpenitization is dependent on many factors, including the Fe/Mg ratio of the precursor silicates, the thermodynamic conditions of the reaction, the efficiency of H 2 removal and the fluid flow rate among others (Holm et al, 2015). The initial Fe/Mg ratio of matrix silicates is important, since it determines how much H 2 will be produced accordingly (Oze and Sharma, 2007):…”

“…However, a caveat here is that, thermodynamically speaking, serpenitization of Fe-rich olivine is not a favourable reaction (at <Fo 50 and variable P-T conditions, olivine is consumed rather than produced) and when reaction 3 reaches equilibrium H 2 will be consumed again in a backward reaction to form anhydrous silicates (Oze and Sharma, 2007). Hence, in order to have a significant H 2 production, abundant Fe-rich silicates and efficient removal of the gas are required (Holm et al, 2015). The least altered CR3 and CO3 chondrites show high modal abundances of Fe-rich amorphous silicates (CR: <15 vol%, Howard et al, 2011;CO: 23-37 vol%, Howard et al, 2014), indicating that the initial conditions for H 2 production by serpentinization would have been optimal.…”

Climate engineering by mimicking natural dust climate control: the iron salt aerosol method

“…Because of the enormous carbonate absorption capacity of the oceanic crust, it has been proposed to use it as a storage of CO 2 (Kelemen and Matter, 2008). As the igneous crust rock aquifer generates H 2 during its contact with ocean water parts of the carbonate precipitation, carbonate is reduced in part to organic and/or graphitic C, depending on the reaction temperatures by biotic or abiotic reduction (Galvez et al, 2013;Holm et al, 2015;Malvoisin et al, 2012;Rumble, 2014;.…”

Post-Main Sequence Evolution of Icy Minor Planets: Implications for Water Retention and White Dwarf Pollution

“…The even more significant contribution of serpentinization is that it alters the rock on the molecular level, embedding water onto its structure (Malamud & Prialnik 2013). In recent years modeling serpentinization reactions inside icy bodies has attracted a lot of attention (Malamud & Prialnik 2013;Holm et al 2015;Malamud & Prialnik 2015;Neveu et al 2015;Travis & Schubert 2015;Malamud & Prialnik 2016), and in the specific case of investigating WD planetary systems, it could be especially important. As noted by Farihi et al (2013), bodies that have sublimated away all their free water can still retain much of the initial water fraction inside hydrated, chemically evolved rocks, subjected to much higher temperatures.…”