First life on earth: Oxygen

http://en.wikipedia.org/wiki/Origin_of_life#The_oxygen_holocaust

Yes, it's true. Not all anaerobes did produce oxygen, but ones that could use photosynthesis eventually did (cyanobacteria). That would make sense, since we need plants and phytoplankton to produce our oxygen, and in order for their to be plants and phytoplankton in the first place, the first organisms must have started out anaerobic.

Yes. Cyanobacteria, formally called blue-green algae, were responsible for originally oxygenating the atmosphere. I wonder if they were true anaerobes since they gave off oxygen and anaerobes cannot tolerate free oxygen.

At any rate, cyanobacteria still exist. Most are marine or freshwarter unicellular species, but we have a terrestrial macrospecies in Texas. It lies on the ground in the full sun and is dormant most of the time, but after a rain it looks like a piece of seaweed. Cyanobactteria not only use photosynthesis, but are able to fix atmospheric nitrogen. Thus they are as independent a species as exists, needing only water, air, sunlight, and a little dust for minerals.

Are you sure it was blue-green algae? "Algae" is the Latin word for seaweed. Bacteria are not seaweed. Bacteria are protists and seaweed are multi-cellular. I can see that you got "blue-green" from "cyano", which is probably from greek. I think there were forms that were both aerobic and anaerobic, in that they were able to survive regardless of the presence of oxygen (I forget the term for that). Even anaerobes live today; they live in areas where there is little oxygen, such as places with high pressure or thick mud. I think some species of fungus are also able to adjust nitrogen levels. They do this for plants in a symbiotic relationship by living off of their roots.

They were called blue-green algae, even though they are prokaryotes and in the Kingdom Monera—in the 5 kingdom system along with other bacteria. Some books persist in referring to them with the old name. Protists are the protozoa and algae. Some people include the multicellular algae in Protista and some call them plants.

The terrestrial cyanobacteria I referred to is pretty neat stuff. It's actually filamentous but clings together in a colony with some kind of gel. I've seen pieces several inches in diameter.