New research by the University of Exeter explains how oxygen was trapped at such low levels. Professor Tim Lenton and Dr Stuart Daines, of the University of Exeter Geography department, created a computer model to explain how oxygen stabilised at low levels and failed to rise any further, despite oxygen already being produced by early photosynthesis. Their research helps explain why the ‘Great Oxidation Event’, which introduced oxygen into the atmosphere around 2.4 billion years ago, did not generate modern levels of oxygen.