Summary
We know from the geological record that the concentration of oxygen in the atmosphere is naturally regulated: Too much oxygen would have led to global destruction of forests by fire, but too little and any fire would have been unsustainable. But what is the mechanism of oxygen regulation? In their Perspective, Kump and Mackenzie discuss results presented in the same issue by Van Cappellen et al. (p. 493) suggesting that microbes in marine sediments play a crucial role in controlling oxygen levels.
