Labeled illustration of cyanobacteria. Cyanobacteria live in water and produce their own food by photosynthesis. They form the oldest fossils, dated at 3.5 billion years old and still remain one of the largest and most important groups of bacteria on earth. They are thought to have had a profound influence on the evolution of life on earth by converting the early reducing atmosphere to an oxidizing one. Detailed here are the: capsule (outer shell, aqua), mucoid sheath (purple lining), thylakoids (light/dark green), slime coat (light area on capsule), cell wall (layers in purple lining), cell membrane, peptidoglycan layer, outer membrane, rubisco (colored pieces in blue boxy shapes), carboxysome (blue boxy shape), nucleoid (bright dotted area), and ribosomes (light green specks).