The Rise of Oxygen in Earth's Early Ocean and Atmosphere

The rapid increase of carbon dioxide in Earth’s modern atmosphere is a matter of major concern. But for the atmosphere of roughly 2.5 billion years ago, interest centers on a different gas: free oxygen spawned by early photosynthesis. The initial increase of O2 in the atmosphere, its delayed build-up in the ocean, its increase to near-modern levels in the sea and air two billion years later, and its cause-and-effect relationship with life are among the most compelling stories in Earth’s history.