It is traditionally thought that the abundance of breathable oxygen on Earth is simply the result of billions of years of photosynthesis by bacteria, algae and plants, but new research at the University of Leeds is challenging this interpretation.
While photosynthesis does produce huge amounts of O2 on Earth, this oxygen is very quickly consumed by other microbes. The only way to stop this happening, and to allow O2 to build up, is to remove the food source for these microbes by burying dead organisms on the seafloor. This process is known as organic carbon burial, and is known to be very important in letting oxygen accumulate on our planet. However, the controls on the burial process are not well known, and it is usually assumed that the rate of carbon production during photosynthesis is what controls this burial rate.
The team at Leeds built on recent research that shows that a key control on the burial of organic carbon is the ability to protect that carbon from microbes using minerals as a shield. By incorporating this shielding process into a state of the art Earth System Model, they showed that rises in Earth's oxygen levels appear to be strongly linked to the emergence of the continents from the ocean, which is the source for the carbon-protecting minerals through rivers and dust.
The team's research raises important questions for the ability of complex or intelligent life to emerge on 'water world' planets with no continents above sea level, where these minerals would not be available.