Effects of the thermal gradient. Adapting the reactor setup (Figure ), we screened the effect of temperature on both chambers. With both chambers at 75˚C, formic and acetic acid were observed in appreciable quantities (Table , entry 1), whereas when both chambers were cooled to 6˚C, none was detected (Table , entry 2). Under a temperature-gradient scenario similar to Hadean vent models, the yields for formic acid and acetic acid (Table , entry 3) nearly matched the allhot tests. Coupled with the all hot (slightly higher organic formation) and all cold (no products detected) tests, the temperature gradient results suggest that higher temperatures on the vent side increase the rate of H2 oxidation (the reaction cannot proceed with a 'cold' vent side). The ocean side can be either 'hot' or 'cold', and still produce significant short chain carboxylic acids. Perhaps the thermodynamic effect of temperature reduction on the ocean side is countered by kinetic advantage of increased concentrations of CO2 at colder temperatures.