As you may or may not know but the cyanobacteria microbes roughly 3 billion years ago started to produce oxygen, the molecule that allows for oxygenic photosynthesis and aerobic respiration.
Cyanobacteria are phototrophic organisms, which means they contain pigments that absorb light to be used as an energy source. This energy is used to excite electrons which is a form of energy conservation used to drive atp synthesis.
More specific to cyanobacteria they perform oxygenic photosynthesis, which O2 is expelled thus adding to the concentrations of Oxygen for aerobic respirers like us to use for our metabolic functions.
The earth several billion years ago was an anoxic environment which means there was no Oxygen to be used for respiration. Cyanobacteria were critical in the evolution of life as they were the first to produce Oxygen.
