HYDROTHERMAL AND OCEANIC PH CONDITIONS OF POSSIBLE RELEVANCE TO THE ORIGIN OF LIFE

Because of the continuous focusing of thermal and chemical energy, anc ient submarine hot springs are contenders as sites for the origin of l ife. But it is generally assumed that these would be of the acid and h igh-temperature 'black smoker' variety (Corliss et al., 1981). In fact today the greater part of the ocean circulates through off-ridge spri ngs where it issues after modification at temperatures of around 40-de grees-C or so but with the potential to reach 200-degrees-C. Such offr idge or ridge-flank springs remind us that there are other candidate s ites for the origin of life. Although there is no firm indication of t he pH of these off-ridge springs we have argued that the solutions are likely to be alkaline rather than acid. We test the feasibility of th is idea using EQ geochemical water-rock interaction modelling codes (W olery 1983) and find that for a range of possible initial chemistries of Hadean seawater, the pH of issuing solutions at around 200-degrees- C is around one or more units alkaline. Such pH values hold for intera ction with both basaltic and komatiitic crust. The robustness of this result suggests to us that alkaline submarine springs of moderate temp erature, carrying many hundreds of ppm HS- to the ocean basins, are al so serious contenders as sites for the origin of life, particularly as Hadean seawater was probably slightly acid, with a dissolved iron con centration approaching 100 ppm. On mixing of these solutions, supersat uration, especially of iron sulphide, would lead to the precipitation of colloidal gels. In our view iron sulphide was the likely substance of, or contributor to, the first vesicle membranes which led to life, as the supply of organic molecules would have been limited in the Hade an. Such a membrane would have had catalytic properties, expansivity, and would have maintained the natural chemiosmotic gradient, a consequ ence of the acid ocean and the alkaline interior to the vesicles.