Describe history of cyanobacteria
chloroplasts originated as cyanobacteria or prochlorobacteria living within other cells
•Fossils of cyanobacteria, 3.5 billion years old, found in Australia.
•3 billion years ago, cyanobacteria produced oxygen as by-product of photosynthesis.
•Oxygen accumulated in atmosphere, becoming substantial 1 billion years ago.
•As oxygen accumulated, other photosynthetic organisms appeared and forms of aerobic respiration developed.
•In last half billion years enough ozone for UV shield and for photosynthetic organisms to survive on land.