Research ArticleGEOCHEMISTRY

Metals likely promoted protometabolism in early ocean alkaline hydrothermal systems

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Science Advances  19 Jun 2019:
Vol. 5, no. 6, eaav7848
DOI: 10.1126/sciadv.aav7848
  • Fig. 1 Geoelectrochemical metal production in the early ocean alkaline hydrothermal systems.

    (A) At the vent-seawater interface, metal sulfides precipitated through mixing between the ancient seawater rich in metal cations (for example, Fe2+) and the alkaline hydrothermal fluid containing HS were exposed to a negative electric potential and were electroreduced to the corresponding metals (for example, Fe0) with the reactivity depending on the potential and the nature of sulfides. (B to E) X-ray diffraction (XRD) patterns of FeS, Ag2S, CuS, and PbS before and after the electrolysis, respectively. The small peaks noted by asterisks (*) in (B) represent NaCl signals. The XRD data for the other sulfides are presented in fig. S3. The potential/pH diagrams of the relevant metal-sulfide systems are shown in the left columns. The colors represent the thermodynamically predicted stability regions of metals (red) and sulfides (green, orange, and blue refer to the sulfides with the metal/sulfur ratio of 1, >1, and <1, respectively) in the aqueous condition examined in the present study.

  • Fig. 2 Summary of the electroreduction behaviors of metal sulfides under a simulated early ocean condition.

    (A) A circle located at a potential and a metal indicates that a detectable amount of the metal was generated during the 7-day electrolysis with the potential. Analogously, crosses show that no metal production was observed in our experiment. The color of the cross denotes the dominant sulfide stoichiometry seen after the 7-day electrolysis (see Fig. 1 legend for the color convention). The numbers indicate the duration in hours of experiments required by the complete sulfide-to-metal conversions. (B) A redox calculation for 1 mmol kg−1 H2 [H2(aq) → 2H+ + 2e] as a function of temperature and pH indicates a geoelectrochemically feasible potential range of 0 to −1.1 V versus SHE.

  • Fig. 3 Nonenzymatic reactions in the presence of as-prepared FeS (blue) and the FeS electrochemically reduced at −0.7 V (versus SHE) for 7 days (FeS_PERM) (red).

    The yields were calculated relative to the initial amounts of starting materials of respective reactions. A full dataset for the identified and quantified products are presented in fig. S9 and tabulated in table S1 together with the results under the following conditions: with H2 gas, with FeCl2, with pure Fe0, and without reductant. The right diagram shows the reactions examined in the present study (a to g) and those demonstrated previously by simulating hydrothermal vent environments on the early Earth [CO2 → CO in (6) and CO → C2 and C3 compounds in (7, 9)].

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/6/eaav7848/DC1

    Fig. S1. A schematic of the electrochemical cell.

    Fig. S2. XRD patterns of FeS electrolyzed at −1.0 V versus SHE for different durations.

    Fig. S3. XRD patterns of metal sulfides before and after the 7-day electrolysis.

    Fig. S4. Total charges build up during the electrolysis.

    Fig. S5. Calibration curves for organic acids by the LC-electric conductivity detector system.

    Fig. S6. Calibration curves for NO3 and NO2 by the LC-electric conductivity detector system.

    Fig. S7. Calibration curves for amino acids and ammonia by the LC-fluorescence detector system.

    Fig. S8. Calibration curves for H2, CO, CH4, and C2H6 by the GC-BID detector system.

    Fig. S9. Nonenzymatic reactions in the presence of pure H2 gas, FeCl2, FeS, FeS_PERM, and Fe0 and those examined in the absence of reductant.

    Fig. S10. Analytical results of fumarate (5 mM, 1.5 ml) incubated with the FeS_PERM (100 mg) at 80°C for 2 days.

    Fig. S11. Reductive amination of four keto acids promoted by the FeS_PERM in one serum bottle.

    Fig. S12. XRD patterns of CuS electrolyzed at −0.8 and −1.0 V (versus SHE) for short durations.

    Fig. S13. XRD patterns of pure Fe0 used in the present study.

    Fig. S14. GC chromatograms of the gas headspaces of serum bottles measured after the reduction experiments of organic/inorganic compounds.

    Table S1. Summary of the reduction experiments of organic/inorganic compounds.

    Table S2. Amounts of H2, CO, CH4, and C2H6 in the serum bottles (30 ml) after the reduction experiments of organic/inorganic compounds.

    Table S3. Thermodynamic data for sulfide minerals.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. A schematic of the electrochemical cell.
    • Fig. S2. XRD patterns of FeS electrolyzed at −1.0 V versus SHE for different durations.
    • Fig. S3. XRD patterns of metal sulfides before and after the 7-day electrolysis.
    • Fig. S4. Total charges build up during the electrolysis.
    • Fig. S5. Calibration curves for organic acids by the LC-electric conductivity detector system.
    • Fig. S6. Calibration curves for NO3 and NO2 by the LC-electric conductivity detector system.
    • Fig. S7. Calibration curves for amino acids and ammonia by the LC-fluorescence detector system.
    • Fig. S8. Calibration curves for H2, CO, CH4, and C2H6 by the GC-BID detector system.
    • Fig. S9. Nonenzymatic reactions in the presence of pure H2 gas, FeCl2, FeS, FeS_PERM, and Fe0 and those examined in the absence of reductant.
    • Fig. S10. Analytical results of fumarate (5 mM, 1.5 ml) incubated with the FeS_PERM (100 mg) at 80°C for 2 days.
    • Fig. S11. Reductive amination of four keto acids promoted by the FeS_PERM in one serum bottle.
    • Fig. S12. XRD patterns of CuS electrolyzed at −0.8 and −1.0 V (versus SHE) for short durations.
    • Fig. S13. XRD patterns of pure Fe0 used in the present study.
    • Fig. S14. GC chromatograms of the gas headspaces of serum bottles measured after the reduction experiments of organic/inorganic compounds.
    • Table S1. Summary of the reduction experiments of organic/inorganic compounds.
    • Table S2. Amounts of H2, CO, CH4, and C2H6 in the serum bottles (30 ml) after the reduction experiments of organic/inorganic compounds.
    • Table S3. Thermodynamic data for sulfide minerals.

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