The main source of oxygen in the atmosphere is oxygenic photosynthesis, and its first appearance is sometimes referred to as the oxygen catastrophe. Geological evidence suggests that oxygenic photosynthesis, such as that in cyanobacteria, became important during the Paleoproterozoic era around 2 billion years ago. Modern photosynthesis in plants and most photosynthetic prokaryotes is oxygenic. Oxygenic photosynthesis uses water as an electron donor, which is oxidized to molecular oxygen (O2) in the photosynthetic reaction center. 3.4 billion years ago first photosynthetic bacteria evolved. They absorbed near-infrared rather than visible light and produced sulfur or sulfite compounds rather than oxygen. Their pigments (possibly bacteriochlorophylls) were predecessors to chlorophyll.
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Answer: Cyanobacteria
The main source of oxygen in the atmosphere is oxygenic photosynthesis, and its first appearance is sometimes referred to as the oxygen catastrophe. Geological evidence suggests that oxygenic photosynthesis, such as that in cyanobacteria, became important during the Paleoproterozoic era around 2 billion years ago. Modern photosynthesis in plants and most photosynthetic prokaryotes is oxygenic. Oxygenic photosynthesis uses water as an electron donor, which is oxidized to molecular oxygen (O2) in the photosynthetic reaction center. 3.4 billion years ago first photosynthetic bacteria evolved. They absorbed near-infrared rather than visible light and produced sulfur or sulfite compounds rather than oxygen. Their pigments (possibly bacteriochlorophylls) were predecessors to chlorophyll.