Highly reducing conditions during Alpine metamorphism of the Malenco peridotite (Sondrio, northern Italy) indicated by mineral paragenesis and H2 in fluid inclusions

“…1). Certainly hydrogen would have been available for hydrogenation as a consequence of the well-established ease of oxidation of mafic rocks by water (Neal and Stanger 1984;Coveney et al 1987;Peretti et al 1992 …”

Section: Initial Conditionsmentioning

confidence: 99%

A hydrothermally precipitated catalytic iron sulphide membrane as a first step toward life

et al. 1994

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We propose that life emerged from growing aggregates of iron sulphide bubbles containing alkaline and highly reduced hydrothermal solution. These bubbles were inflated hydrostatically at sulphidic submarine hot springs sited some distance from oceanic spreading centers four billion years ago. The membrane enclosing the bubbles was precipitated in response to contact between the spring waters and the mildly oxidized, acidic and iron-bearing Hadean ocean water. As the gelatinous sulphide bubbles aged and were inflated beyond their strength they budded, producing contiguous daughter bubbles by the precipitation of new membrane.[FeeS2] +/0 or [Fe4S4 ]2+/+ clusters, possibly bonded by hydrothermal thiolate ligands as proferredoxins, could have catalyzed oxidation of thiolates to disulphides, thereby modifying membrane properties.We envisage the earliest iron sulphide bubbles (proCorrespondence to: M. J. Russell Glossary: Hollow pyrite botryoids: hollow hemispheres of cryptocrystalline pyrite (FeS2) 0.1-1 mm across. Fischer-Tropsch syntheses: the highly exothermic catalytic hydrogenation of CO to hydrocarbons and aliphatic oxygenated compounds using finely divided iron. Greigite (Fe3S4): metastable iron sulphide precipitated from aqueous solution in a gel at 100°C and containing two-thirds of its iron as the high-spin ferric ion. Haber-Bosch process: the exothermic catalytic hydrogenation of nitrogen to yield ammonia. Probotryoid: a hydrostatically inflated colloidal iron monosulphide bubble; precursor to hollow botryoids and the progenitor to protocelts. Proferredoxins: [F%S2] and [F%MS4] clusters (M = Fe, Mo, W, Ni, etc.) ligated by abiogenic thiols and thiolates. Protocell: a cell comprised mainly of abiogenic organics including thiols with subordinate iron sulphides, partly as proferredoxins; growth results from catabolism and osmotic pressure botryoids) first growing by hydrostatic inflation with hydrothermal fluid, but evolving to grow mainly by osmosis (the protocellular stage), driven by (1) catabolism of hydrothermal abiogenic organics trapped on the inner walls of the membrane, catalyzed by the iron sulphide clusters; and (2) cleavage of hydrophobic compounds dissolved in the membrane to hydrophilic moieties which were translocated, by the proton motive force inherent in the acidic Hadean ocean, to the alkaline interior of the protocell. The organics were generated first within the hydrothermal convective system feeding the hot springs operating in the oceanic crust and later in the pyritizing mound developing on the sea floor, as a consequence of the reduction of CO, CO e, and formaldehyde by Fe z+-and se--bearing minerals. We imagine the physicochemical interactions in and on the membrane to have been sufficiently complex to have engendered auto-and cross-catalytic replication. The membrane may have been constructed in such a way that a "successful" parent could have "informed" the daughters of membrane characteristics functional for the then-current level of evolution.

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“…Possibly, serpentinization or deserpentinization of these rocks during retrograde metamorphism controlled the formation of the reducing fluids (e.g. Coveney et al, 1987;Peretti et al, 1992;Orione et al, 2003). Moreover, the volumetric properties of the successive FIA's suggest fluid pressure variations accompanied the introduction of such reducing fluids at temperatures <$200°C.…”

Section: Evolution Of the Redox State And The Composition Of The Carbmentioning

confidence: 98%

Metamorphic fluid flow in the northeastern part of the 3.8–3.7Ga Isua Greenstone Belt (SW Greenland): A re-evalution of fluid inclusion evidence for early Archean seafloor-hydrothermal systems

Heijlen

Appel

Frezzotti

et al. 2006

Geochimica et Cosmochimica Acta

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Highly reducing conditions during Alpine metamorphism of the Malenco peridotite (Sondrio, northern Italy) indicated by mineral paragenesis and H2 in fluid inclusions

Cited by 84 publications

References 25 publications

Iron partitioning and hydrogen generation during serpentinization of abyssal peridotites from 15°N on the Mid-Atlantic Ridge

Iron partitioning and hydrogen generation during serpentinization of abyssal peridotites from 15°N on the Mid-Atlantic Ridge

A hydrothermally precipitated catalytic iron sulphide membrane as a first step toward life

Metamorphic fluid flow in the northeastern part of the 3.8–3.7Ga Isua Greenstone Belt (SW Greenland): A re-evalution of fluid inclusion evidence for early Archean seafloor-hydrothermal systems

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