H2-rich fluids from serpentinization: geochemical and biotic implications. Proc Natl Acad Sci U S A

Department of Geophysics, Stanford University, Stanford, CA 94305, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 09/2004; 101(35):12818-23. DOI: 10.1073/pnas.0405289101
Source: PubMed


Metamorphic hydration and oxidation of ultramafic rocks produces serpentinites, composed of serpentine group minerals and varying amounts of brucite, magnetite, and/or FeNi alloys. These minerals buffer metamorphic fluids to extremely reducing conditions that are capable of producing hydrogen gas. Awaruite, FeNi3, forms early in this process when the serpentinite minerals are Fe-rich. Olivine with the current mantle Fe/Mg ratio was oxidized during serpentinization after the Moon-forming impact. This process formed some of the ferric iron in the Earth's mantle. For the rest of Earth's history, serpentinites covered only a small fraction of the Earth's surface but were an important prebiotic and biotic environment. Extant methanogens react H2 with CO2 to form methane. This is a likely habitable environment on large silicate planets. The catalytic properties of FeNi3 allow complex organic compounds to form within serpentinite and, when mixed with atmospherically produced complex organic matter and waters that circulated through basalts, constitutes an attractive prebiotic substrate. Conversely, inorganic catalysis of methane by FeNi3 competes with nascent and extant life.

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    • "In addition to acting as a reducing agent to produce simple organic compounds by FTT in prebiotic synthesis processes , H 2 along with other reduced organic species can also be utilized as the major source of energy for chemoautotrophic microbes (Apps and Van de Kamp, 1993; Sleep et al., 2004; Russell et al., 2010). That energy source allows the development of modern biological communities in the otherwise inhabitable and non-photosynthetic deep subsurface , including subseafloor hydrothermal vents (Jannasch and Mottl, 1985; Nealson et al., 2005; Fry et al., 2008; Parkes et al., 2011), seafloor sediments and oceanic crust (Wellsbury et al., 1997; Fisk et al., 1998; Roussel et al., 2008), continental sediments (Chandler et al., 1997; Onstott et al., 1999), and aquifers in igneous rocks (Pedersen and Ekendahl, 1990; Stevens and McKinley, 1995; Pedersen, 1997). "
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    • "Olivine is also a common phase in many meteorites, and serpentine is the dominant hydroxyl-bearing mineral in CM carbonaceous chondrites (Calas 2013). That the process of serpentinization (and chloritization) is accompanied by conditions of extremely low f O2 has been noted by many authors (Frost 1985; Sleep et al. 2004; Evans et al. 2013; McCollom and Seewald 2013). This conclusion is based not only upon the widespread occurrence of native metals in serpentines, but also on the occurrence of H 2 gas in springs draining areas of active serpentinization (Barnes et al. 1972; McCollom and Seewald 2013; Schrenk et al. 2013). "
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