1. Arrhenius, G.: 1981,Adv. Space Res. 1 37.
2. Chang, S., DesMarais, D., Mack, R., Miller, S. L., and Strathearn, G. E.: 1983, in J. W. Schopf (ed.),Earth's Earliest Biosphere, Princeton University Press, p. 53.
3. Claoue-Long, J. C., Thirlwall, M. F., and Nesbitt, R. W.: 1984,Nature 307 697.
4. Craig, H. and Lupton, J. E.: 1981, inThe Sea, Vol. 7, The Oceanic Lithosphere, John Wiley and Sons, p. 391.
5. DesMarais, D. J.: 1985, in E. T. Sundquist and W. S. Broecker (eds.),The Carbon Cycle and Atmospheric CO 2 , American Geophysical Union, Washington, D.C., p. 602.