The oldest records of photosynthesis.
There is diverse, yet controversial fossil evidence for the existence of photosynthesis 3500 million years ago.  Among the most persuasive evidence is the stromatolites described from low grade metasedimentary rocks in Western Australia and South Africa.  Based on the understanding of the paleobiology of stromatolites and using pertinent fossil and Recent analogs, these Early Archean stromatolites suggest that phototrophs evolved by 3500 million years ago.  The evidence allows further interpretation that cyanobacteria were involved.  Besides stromatolites, microbial and chemical fossils are also known from the same rock units.  Some microfossils morphologically resemble cyanobacteria and thus complement the adduced cyanobacterial involvement in stromatolite construction.  If cyanobacteria had evolved by 3500 million years ago, this would indicate that nearly all prokaryotic phyla had already evolved and that prokaryotes diversified rapidly on the early Earth.
Awramik
S M
SM
Department of Geological Sciences, University of California, Santa Barbara 93106, USA.
D001315:Australia; D018407:Bacterial Physiological Phenomena; D005075:Biological Evolution; D000458:Cyanobacteria / Q000502:physiology*; D005580:Fossils; D055593:Geological Phenomena; D005844:Geology; D010163:Paleontology; D010788:Photosynthesis / Q000502:physiology*; D011387:Prokaryotic Cells / Q000502:physiology; D013019:South Africa