The build-up of oxygen in the Earth’s atmosphere may have been delayed by the upwelling of iron into the surface ocean from large submarine volcanic eruptions, according to research published online in Nature Geoscience. This contributed to the several-hundred-million-year delay between the evolution of oxygen-producing photosynthesis and the oxygenation of the Earth’s atmosphere about 2.4 billion years ago.

In the lead-up to the Great Oxidation Event, oxygen was primarily produced by cyanobacteria living in the sunlit surface ocean. Elizabeth Swanner, Andreas Kappler and colleagues used laboratory experiments to show that under oxygen-free conditions, certain forms of iron inhibit growth and oxygen production by modern cyanobacteria, which are thought to be representative of ancient microbes. Submarine volcanic activity was common before the Great Oxidation Event, and would have delivered large amounts of iron to the oceans. The authors propose that the periodic intrusion of this volcanic iron into the surface waters would have temporarily limited the production of oxygen in the water column by weakening oxygen-producing microbes. However, it is not clear from this research if iron affected Archaean cyanobacteria in a similar way to their modern counterparts.