ABSTRACT

Corliss eta/. (1981) and Barross and Hoffman (1985) have argued cogently that hot spring sites on the deep sea floor provide the only stable environment in which life could have emerged and become established. Woese eta/. (1990) and Lake (1988) have independently proposed the universal ancestor to have been a hyperthermophile. Schwartzman eta/. (1993) have also emphasised that life could not have had anything but hot beginnings because of the temperature of the early earth. And Shock (1996) has established a theoretical window for the viability of a geochemical metabolism on the mixing of relatively oxidised cool sea water with reduced hydrothermal solutions, between about 80 ·c and 200 ·c. In particular, Shock demonstrates the hypothetical potential of hydrothermal solutions to generate organic polymers from dissolved carbon dioxide on mixing with sea water. The organic metastabilities depend crucially on the initial redox state of the hydrothermal solution. If the hydrothermal solution were in equilibrium with the quartz-fayalitemagnetite (Si02+Fe2Si04+Fe30 4, or QFM) buffer, as in the crust, then organic molecules would be generated. But if the solution equilibrated with the more oxidised pyritepyrrhotite-magnetite (FeS2+FeS+F~04, or PPM) buffer, which happens to approximate the redox state on the outside of the membrane (Russell et a/., 1994), then carbonate would be stable. Thus the conditions envisaged by Shock ( 1996), of a geochemical metabolism in waiting, are realisable at certain putative hot seepage or spring sites.