Cyanobacteria, also called cyanophytes and incorrectly referred to as “blue-green algae,” are a phylum of photosynthetic, Gram-negative bacteria. They appear in the fossil record 3.5 billion years ago, during the Paleoarchean Era, and are currently found in nearly every water-bearing environment from oceans and lakes to temporarily-moistened desert rocks. They were the first oxygen-producing organisms to evolve on Earth.
