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.
Highlights
Serpentinization of ultramafic rocks occurring in midocean ridges, forearc systems, and terrestrial ophiolites on Earth is a geochemical and water-dependent process that results in a variety of gas and fluid species
Molecular hydrogen (H2) is the most influential and relevant species in the abiotic synthesis of organic compounds produced as a consequence of serpentinization due to its ability to reduce carbon (i.e., CO, CO2, HCO3À, CO23 À ) and produce methane (CH4) and a wide variety of other organic compounds
Fischer-Tropsch-type processes are critical for H2 to react with carbon sources to advance the synthesis of organic compounds
Summary
Serpentinization of ultramafic rocks occurring in midocean ridges, forearc systems, and terrestrial ophiolites (i.e., obducted/accretionary oceanic crust) on Earth is a geochemical and water-dependent process that results in a variety of gas and fluid species. 2007; Seyfried et al, 2007; Milliken and Rivkin, 2009; Shock and Canovas, 2010; Zolotov, 2014), it is evident that H2 production and the concurrent formation of CH4 is not a straightforward process, especially when environmental factors, secondary mineral formation, fluid chemistry, mineral chemistry (including rates of Mg-Fe diffusion), fluid flow, carbonate saturation, and time-dependent kinetic processes are considered (e.g., Bach et al, 2006; Evans, 2010; Evans et al, 2013) Regardless of these complicating factors, serpentinization is a common alteration process on Earth and a major pathway for producing H2 and CH4 over a wide range of geological, environmental, and laboratory conditions, potentially contributing to the origins and early evolution of life (Schrenk et al, 2013). We put forth that serpentinization is, in a true sense, a universal process that leads to the formation of molecular hydrogen and related CH4 in a wide variety of environments
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