1. Eglinton, G., Scott, P. M., Belsky, T., Burlingame, A. L., and Calvin, M., Science, 145, 263 (1964).
2. Leading references are cited in the following: Urey, H. C., Nature, 193, 1119 (1962). Fitch, F., Schwarcz, H. P., and Anders, E., Nature, 193, 1123 (1962). Briggs, M. H., and Kitto, G. B., Nature, 193, 1126 (1962). Tasch, P., Science, 142, 2156 (1963). Meinschein, W. G., Space Sci. Rev., 2, 653 (1963); Nature, 197, 833 (1963). Briggs, M. H., and Mamikunian, G., Space Sci. Rev., 1, 647 (1962–63). Hayatsu, R., Science, 146, 1291 (1964).
3. (a) Cloud, jun., P. E., Gruner, J. W., and Hagen, H., “Carbonaceous Rocks of the Soudan Iron Formation (Early Precambrian)” (submitted for publication). (b) Personal communication from Prof. P. E. Cloud, jun. We thank Professor Cloud for much helpful information. The age of the Soudan Formation is determined by the isotopic dating of a granitic intrusion.
4. Barghoorn, E. S., and Tyler, S. A., Science, 147, 563 (1965).
5. Eglinton, G., Scott, P. M., Belsky, T., Burlingame, A. L., Richter, W., and Calvin, M. “Occurrence of Isoprenoid Alkanes in a Precambrian Sediment”, Advances in Organic Geochemistry, 2 (Pergamon Press, in preparation); Space Sci. Lab., Univ. Calif., Tech. Rep., Ser. No. 6, issue No. 9 (January 1965).