| Summary: | This chapter provides a detailed investigation of where, when, and how photosynthesis originated and then evolved in non-eukaryotic organisms. It looks at some of the best accepted geological evidence for the earliest photosynthesis that comes from marine sedimentary deposits in rocks from the Buck Reef Chert in South Africa dated to 3.4 Ga. It also talks about rocks found in the Isua Greenstone Belt in Greenland, dating back from about 3.8 Ga, which harbour geochemical signatures consistent with photosynthesis. The chapter highlights the possibility that anoxygenic photosynthesis had already evolved well before 3 Ga, at a time when the Earth was still a highly anaerobic planet. It covers the two key evolutionary innovations required for the evolution of photosynthesis: first is the evolution of the reaction centre (RC) proteins, and second is a requirement for the evolution of biosynthetic pathways of chlorophylls and related pigments.
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