Metals likely promoted protometabolism in early ocean alkaline hydrothermal systems

Abstract

One of the most plausible scenarios of the origin of life assumes the preceding prebiotic autotrophic metabolism in sulfide-rich hydrothermal vent environments. However, geochemical mechanisms to harness the reductive power provided by hydrothermal systems remain to be elucidated. Here, we show that, under a geoelectrochemical condition realizable in the early ocean hydrothermal systems, several metal sulfides (FeS, Ag2S, CuS, and PbS) undergo hour- to day-scale conversion to the corresponding metals at ≤−0.7 V (versus the standard hydrogen electrode). The electrochemically produced FeS-Fe0 assemblage promoted various reactions including certain steps in the reductive tricarboxylic acid cycle with efficiencies far superior to those due to pure FeS. The threshold potential is readily generated in the H2-rich alkaline hydrothermal systems that were probably ubiquitous on the Hadean seafloor. Thus, widespread metal production and metal-sustained primordial metabolism were likely to occur as a natural consequence of the active hydrothermal processes on the Hadean Earth.

A hydrogen-dependent geochemical analogue of primordial carbon and energy metabolism

“…Proposals for the nature of primordial CO2 fixation and energy conservation at biochemical origins typically posit the participation of external energy sources 50 such as UV light 51 , heat, impact, pressure, electrical currents, or ion gradients 28 to push organic synthesis forward. The reactions reported here require no additional energy source for a protometabolic acetyl-CoA pathway to unfold from H2 and CO2 other than the natural reactivity of two gasses and metal catalysts, indicating that neither membranes, though essential for the emergence of free-living cells 6,52-54 , nor external potentials 19,55 were required for primordial CO2 fixation along an exergonic, H2-dependent, nonenzymatic pathway to C3 products. The energy for the synthesis of compounds capable of phosphorylating ADP via substrate level phosphorylation 6,11,12 -for reactions reported here, and for those of the enzymatically catalysed acetyl-CoA pathwaystems from the exergonic synthesis of biologically relevant organic compounds from H2 and CO2.…”

Thioester synthesis through geoelectrochemical CO2 fixation on Ni sulfides

“…We prepared metal sulfides including NiS by simply mixing an aqueous solution of the corresponding metal chloride and an aqueous solution of sodium sulfide. The obtained sulfides were exposed to a constant electric potential for 7 days in 100 mM NaCl at room temperature (25 ± Figure S8), [16] NiS showed no XRD signal for Ni 0 in the examined potential range (≤-1.0 VSHE) ( Figure 1a). The Ni 0 percentage up to 12% (Figure 1f) is well above the detection limit of XRD ( Figure S10) if the formation of meso-or macroscopic crystalline structure is assumed.…”

“…[15] It was later found that FeS undergoes day-scale electroreduction to Fe 0 . [16] The resultant FeS-Fe 0 assemblage, named FeS_PERM (FeS partially electroreduced to metal), showed exceptional capability of promoting various prebiotically important reactions owing to synergy between surface Fe sites with different oxidation states (Fe 2+ and Fe 0 ). [17,18] In our previous works, [15,16] NiS exhibited neither CO evolution nor Ni 0 formation detectable by X-ray diffraction (XRD) analysis.…”

“…[16] The resultant FeS-Fe 0 assemblage, named FeS_PERM (FeS partially electroreduced to metal), showed exceptional capability of promoting various prebiotically important reactions owing to synergy between surface Fe sites with different oxidation states (Fe 2+ and Fe 0 ). [17,18] In our previous works, [15,16] NiS exhibited neither CO evolution nor Ni 0 formation detectable by X-ray diffraction (XRD) analysis. However, our further investigation presented below found noncrystalline growth of Ni 0 under geochemically feasible potential conditions, with a substantial amount of CO bound on the resultant surface Ni 0 sites.…”

Iron‐Silicate Chemical Garden Morphology and Silicate Reactivity with Alpha‐Keto Acids

“…Chemical gardens have been investigated in a variety of studies as a laboratory or experimental simulation for geological mineral structures such as hydrothermal vent chimneys (Figure 1). [1–7] Such geological structures exist in Earth's oceans and likely also formed on early Earth where they have been suggested as possible settings for the emergence of life [8,9] . Hydrothermal vents and chimneys have also been hypothesized to exist on other ocean worlds in our solar system such as Enceladus, a moon of Saturn [10,11] or Europa, a moon of Jupiter .…”