Editing Archean Eon (section)

=== Photosynthesis ===
It is possible that non-photosynthesizing mats were present as early as 4.00 GYA. Originally, they depended on hydrothermal vents for energy and chemical nutrients, but the development of '''photosynthesis''' allowed mats to proliferate outside of these environments by utilizing a more widely available energy source, sunlight (~3.00 GYA). The evolutionary split between bacteria and archaea may also have occurred around this time. 

The earliest photosynthesis may have been powered by '''infrared''' light, using modified versions of pigments whose original function was to detect heat emissions from hydrothermal vents. The development of photosynthetic energy generation enabled the microorganisms first to colonize wider areas around vents and then to use sunlight as an energy source. '''Heterotrophic scavengers''' would have accompanied the photosynthesizers in their migration out of their original hydrothermal neighborhood. 

The evolution of '''purple bacteria''', which do not produce or use oxygen but can tolerate it, enabled mats to colonize areas that locally had relatively high concentrations of oxygen, which was toxic to organisms that were not adapted to it. Microbial mats would have been separated into '''oxidized''' and '''reduced''' layers, and this specialization would have increased their productivity. This would allow for the emergence of cyanobacteria, photosynthesizers who produced oxygen as a byproduct - a group of species that would be responsible for transforming the entire world in the subsequent eon.