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Serpentinization and the Formation of H2 and CH4 on Celestial Bodies (Planets, Moons, Comets).

Holm NG, Oze C, Mousis O, Waite JH, Guilbert-Lepoutre A - Astrobiology (2015)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: 1 Department of Geological Sciences, Stockholm University , Stockholm, Sweden .

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.

No MeSH data available.


Related in: MedlinePlus

An idealized graphical representation is shown illustrating serpentinization and H2 production with regard to saturation/equilibrium and the activity (a) of H2 (left y axis) versus reaction progress (x axis). The saturation index [the reaction quotient (Q) divided by the equilibrium constant (K)] is shown on the right y axis. Note that the H2 concentration increases (directional arrow) with respect to reaction progress until equilibrium/saturation is achieved (equilibrium arrows). A key point is that H2 production will occur as long as the H2 concentrations are undersaturated (Q/K<1) with respect to equilibrium H2. Arguably, serpentinization systems are dominantly undersaturated with respect to equilibrium H2 (i.e., at disequilibrium).
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f3: An idealized graphical representation is shown illustrating serpentinization and H2 production with regard to saturation/equilibrium and the activity (a) of H2 (left y axis) versus reaction progress (x axis). The saturation index [the reaction quotient (Q) divided by the equilibrium constant (K)] is shown on the right y axis. Note that the H2 concentration increases (directional arrow) with respect to reaction progress until equilibrium/saturation is achieved (equilibrium arrows). A key point is that H2 production will occur as long as the H2 concentrations are undersaturated (Q/K<1) with respect to equilibrium H2. Arguably, serpentinization systems are dominantly undersaturated with respect to equilibrium H2 (i.e., at disequilibrium).

Mentions: Related to mineral composition, the proportion of Fe and Mg in olivine and pyroxene plays a central role with regard to mineral stability and the extent to which H2 may be produced. Generally, Fe-rich primary minerals such as the Fe-rich olivine end-member fayalite (Fe2SiO4) provide a greater opportunity for Fe(II) to oxidize and ultimately form H2. Oze and Sharma (2007) assessed a series of serpentinization reactions focusing on Mg and Fe in olivine to determine the Gibbs free energy of reaction and assess H2 production in context to each reaction. They demonstrated that serpentinization reactions involving mantle olivine (forsteritic olivine), which is Mg-rich with a relatively smaller proportion of Fe, are thermodynamically favorable (defined as ΔGR<0), demonstrating higher yields of H2 (i.e., H2 production) compared to the stoichiometry of the reaction. Conversely, reactions with Fe-rich olivine (<Fo50) are generally thermodynamically unfavorable (defined as ΔGR>0), where H2 yields are less than the stoichiometry of the reaction (i.e., H2 is consumed or not produced). It should be noted that these interpretations are strictly limited to assessing the reaction and not the system with respect to the degree of H2 saturation. An important point is that even a thermodynamically unfavorable serpentinization reaction, such as the Fe-olivine undergoing serpentinization, will have an equilibrium concentration of H2. Serpentinization reactions undersaturated with respect to equilibrium H2 will produce H2 as shown graphically in Fig. 3. Klein et al. (2013) expanded on the thermodynamics of Mg and Fe in a wide variety of minerals that may undergo serpentinization and assessed equilibrium H2 concentrations using a similar methodology as well as affinity calculations, which reiterate that H2-undersaturated systems will produce H2. Despite its utility, thermodynamic/equilibrium modeling of H2 production as shown by Oze and Sharma (2007), Klein et al. (2013), and Sleep et al. (2004) does not address the complexity or time-dependent factors and transitory phases capable of modulating H2 production in real systems well before equilibrium is achieved (i.e., the left side of Fig. 3). In essence, serpentinization and H2 production is a disequilibrium process (as shown and stated in numerous studies) where a wide variety of factors (reaction kinetics, surface reactions, time, fluid flow, etc.) are constantly modifying H2 production and H2 present in related fluids (Schulte et al., 2006).


Serpentinization and the Formation of H2 and CH4 on Celestial Bodies (Planets, Moons, Comets).

Holm NG, Oze C, Mousis O, Waite JH, Guilbert-Lepoutre A - Astrobiology (2015)

An idealized graphical representation is shown illustrating serpentinization and H2 production with regard to saturation/equilibrium and the activity (a) of H2 (left y axis) versus reaction progress (x axis). The saturation index [the reaction quotient (Q) divided by the equilibrium constant (K)] is shown on the right y axis. Note that the H2 concentration increases (directional arrow) with respect to reaction progress until equilibrium/saturation is achieved (equilibrium arrows). A key point is that H2 production will occur as long as the H2 concentrations are undersaturated (Q/K<1) with respect to equilibrium H2. Arguably, serpentinization systems are dominantly undersaturated with respect to equilibrium H2 (i.e., at disequilibrium).
© Copyright Policy - open-access
Related In: Results  -  Collection

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f3: An idealized graphical representation is shown illustrating serpentinization and H2 production with regard to saturation/equilibrium and the activity (a) of H2 (left y axis) versus reaction progress (x axis). The saturation index [the reaction quotient (Q) divided by the equilibrium constant (K)] is shown on the right y axis. Note that the H2 concentration increases (directional arrow) with respect to reaction progress until equilibrium/saturation is achieved (equilibrium arrows). A key point is that H2 production will occur as long as the H2 concentrations are undersaturated (Q/K<1) with respect to equilibrium H2. Arguably, serpentinization systems are dominantly undersaturated with respect to equilibrium H2 (i.e., at disequilibrium).
Mentions: Related to mineral composition, the proportion of Fe and Mg in olivine and pyroxene plays a central role with regard to mineral stability and the extent to which H2 may be produced. Generally, Fe-rich primary minerals such as the Fe-rich olivine end-member fayalite (Fe2SiO4) provide a greater opportunity for Fe(II) to oxidize and ultimately form H2. Oze and Sharma (2007) assessed a series of serpentinization reactions focusing on Mg and Fe in olivine to determine the Gibbs free energy of reaction and assess H2 production in context to each reaction. They demonstrated that serpentinization reactions involving mantle olivine (forsteritic olivine), which is Mg-rich with a relatively smaller proportion of Fe, are thermodynamically favorable (defined as ΔGR<0), demonstrating higher yields of H2 (i.e., H2 production) compared to the stoichiometry of the reaction. Conversely, reactions with Fe-rich olivine (<Fo50) are generally thermodynamically unfavorable (defined as ΔGR>0), where H2 yields are less than the stoichiometry of the reaction (i.e., H2 is consumed or not produced). It should be noted that these interpretations are strictly limited to assessing the reaction and not the system with respect to the degree of H2 saturation. An important point is that even a thermodynamically unfavorable serpentinization reaction, such as the Fe-olivine undergoing serpentinization, will have an equilibrium concentration of H2. Serpentinization reactions undersaturated with respect to equilibrium H2 will produce H2 as shown graphically in Fig. 3. Klein et al. (2013) expanded on the thermodynamics of Mg and Fe in a wide variety of minerals that may undergo serpentinization and assessed equilibrium H2 concentrations using a similar methodology as well as affinity calculations, which reiterate that H2-undersaturated systems will produce H2. Despite its utility, thermodynamic/equilibrium modeling of H2 production as shown by Oze and Sharma (2007), Klein et al. (2013), and Sleep et al. (2004) does not address the complexity or time-dependent factors and transitory phases capable of modulating H2 production in real systems well before equilibrium is achieved (i.e., the left side of Fig. 3). In essence, serpentinization and H2 production is a disequilibrium process (as shown and stated in numerous studies) where a wide variety of factors (reaction kinetics, surface reactions, time, fluid flow, etc.) are constantly modifying H2 production and H2 present in related fluids (Schulte et al., 2006).

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: 1 Department of Geological Sciences, Stockholm University , Stockholm, Sweden .

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.

No MeSH data available.


Related in: MedlinePlus