Introduction to the Cyanobacteria - University of California …
https://ucmp.berkeley.edu/bacteria/cyanointro.html
WEBCyanobacteria are aquatic and photosynthetic, that is, they live in the water, and can manufacture their own food. Because they are bacteria, they are quite small and usually unicellular, though they often grow in colonies large enough to see. They have the distinction of being the oldest known fossils, more than 3.5 billion years old, in fact!
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