These were earlier called the blue-green algae. As s very successful group on primitive earth, they could carry out photosynthesis and the oxygen released during the process changed the earth’s atmosphere and gradually the level of oxygen increased in the earth’s atmosphere.

Difference between Bacteria and Cyanobacteria

Bacteria Cyanobacteria
Smaller cells Comparatively larger cells
May have flagella Do not have flagella
Anoxygenic Oxygenic