One of the most significant events in Earth’s history has been the oxygenation of its atmosphere 2.45–2.32 billion years ago. This accumulation of molecular oxygen in Earth’s atmosphere was so significant that it is now commonly known as the Great Oxidation Event (GOE). The long-reaching effects of the GOE were literally world-changing; the compositions of the atmosphere and hydrosphere were altered, and through various redox reactions (where atoms have their oxidation state changed), the nature of the continents and global climate changed too. However, and perhaps from an anthropocentric viewpoint, the most important effect would be upon the biosphere: the GOE paved the way for the evolution of aerobic (oxygen respiring) organisms, including our earliest ancestors.

It is possible to track the GOE through geochemical traces left in the rock record. However, one thing we're still uncertain about is whether or not this event represents either a sharp increase in oxygen production or a reduction in oxygen sinks - the jury is still out on that one. With this level of ambiguity over the dynamics of the GOE, it may be a little surprising to know that there has been a long-standing consensus on how the oxygen was actually produced: photosynthetic organisms called cyanobacteria (blue-green algae, so named after the pigment they produce).

In this episode we discuss with Dr. Bettina Schirrmeister (University of Bristol) about the evolution of cyanobacteria and the role they played in the GOE.