Answer:
Early cyanobacteria in stromatolites are thought to be responsible for increasing the amount of oxygen in the primeval Earth's atmosphere through their continuing photosynthesis. They were the first known organisms to photosynthesize and produce free oxygen.
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6CO2 + 6H2O --> C6H12O6 + 6O2
carbon dioxide + water --> glucose + oxygen
The arrow indicates sunlight (energy).
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