Cyanobacteria are photosynthetic organisms that were believed to exist billions of years ago. It is currently classified under the kingdom Bacteria and got its name from its blue color (cyan).
Cyanobacteria are also known as the blue green algae, blue green bacteria cyanophyta. It can be found in almost every terrestrial and aquatic habitats. Meaning, cyanobacteria can thrive well on the current atmospheric environment of the Earth. The adaptations of cyanobacteria are different from its primitive ancestors. Early forms of cyanobacterium have believed to thrive in an oxygen-free environment.
Cyanobacteria are the only algae colonising new territories including volcanic lavas of recent origin. They can live in a wide range of temperature ranging upto 80 to 85%C. This feature suits well to archaic atmosphere. No other algae can live at this high temperatue. Cyanobacteria is believed to have evolved during Pre-Cambian period in anaerobic atmosphere that contained sulphurated hydrogen, ammonia, hydrogen etc and then in due course of time succeeded to grow in an atmosphere that, contained oxygen. The early atmosphere had no recent composition and there was a time when atmosphere did not contain oxygen. In oxygen-less atmosphere, any present kind of life is impossible but paleontological research permits to believe blue green algae as the earliest plants owing to their capacity of thriving well in sulphurated atmosphere.