1. Bitz, M. C., and Nagy, B., Proc. US Nat. Acad. Sci., 56, 1323 (1966).
2. Calvin, M., in Chemical Evolution (Oxford University Press, 1969).
3. Schopf, J. S., J. Paleontol, 42, 651 (1968); Meinschein, W. G., Space Science Rev., 2, 480 (1963).
4. Hayes, J. M., Geochim. Cosmochim. Acta, 31, 1395 (1967).
5. Han, J., Simoneit, B. R., Burlingame, A. L., and Calvin, M., Nature, 222, 364 (1969).