We propose that the precipitation of a gelatinous iron‐sulphide membrane is the necessary first step towards life. Membrane vesicles were inflated with alkaline, sulphide‐bearing hydrothermal (<200°C) solution and grew on a submarine sulphide mound in acid iron‐bearing Hadean seawater. Once a critical size had been reached (0.1–1 mm) vesicles would have budded contiguous self‐similar daughters. We assume that the membrane was rendered insulating by the adsorption and/or oxidative precipitation of organic and organosulphur compounds. As a consequence of the naturally induced proton‐motive (chemiosmotic) force, and the activity of the iron monosulphide redox catalysts within the membrane, organic compounds would have accumulated within the vesicle. Osmotically driven growth therefore became more significant with time. The geochemical environment envisaged as responsible for this first step towards life is consistent with that widely accepted for the
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