It has long been assumed that oxygen-producing cyanobacteria were responsible for the appearance of oxygen in the earth's atmosphere. If that theory is correct, then how is it possible that they appeared at least 200 million years before the oxygen?
Until about 2.5 billion years ago, the levels of oxygen in the earth's atmosphere were very limited, then they started to rise. It has long been assumed that oxygen-producing cyanobacteria were responsible for the oxygen in the atmosphere. However, there is evidence that cyanobacteria were already present at least 200 million years before the oxygen levels started to rise significantly. This demands an explanation.
Mark Barley and Lee Kump published an article in Nature because they think that they have found a plausible explanation: the earth's tectonic evolution. They believe that about 2.5 billion years ago, the earth's crust underwent massive changes and started to stabilize and that as a result, the number of submarine volcanoes started to diminish in favour of more land-based volcanoes.
Land-based volcanoes spew out enormous amounts of gases. These gases are incredibly hot, but most do not react as well with oxygen as the cooler gases from submarine volcanoes. Therefore, the submarine volcanoes acted as oxygen traps until their numbers started to dwindle, setting the stage for a significant rise of atmospheric oxygen.
Until this change, most of the oxygen produced by the cyanobacteria was simply taken up by the submarine volcanoes.
My first guess would have been that it simply took a very long time before there were enough photosynthesizing organisms to produce measurable amounts of oxygen, but science isn't based on private hunches, and this theory seems to be plausible. It is now up to other scientists to confirm or disprove this theory.