No. 58: Jul-Aug 1988
"An increased ratio of 12 C to 13 C, an indicator of the principal carbon-fixing reaction of photosynthesis, is found in sedimentary organic matter dating back to almost four thousand million years ago -- a sign of prolific microbial life not long after the Earth's formation. Partial biological control of the terrestrial carbon cycle must have been established very early and was in full operation when the oldest sediments were formed."
(Schidlowski, Manfred; "A 3,800-MillionYear Isotopic Record of Life from Carbon in Sedimentary Rocks," Nature, 333: 313, 1988.)
Comment. Photosynthesis is not a simple biological process. To discover that it and life forms using it developed so quickly on the primitive earth is surprising. Did this complexity and "biological control" arise so quickly: (1) by chance; (2) by inoculation from extraterrestrial sources (See Astronomy above.); (3) by act of God; or (4) by Gaia in nascent form? (Note that Gaian overtones emanate from the "Biological control" phrase above.)