Earth’s atmosphere took two billion years to become fully oxygenated

High-resolution isotope data show that a modern-like, oxygen-rich atmosphere was not established until 410 million years ago, supporting a 2-billion-year transitional oxygenation of Earth’s surface. The record also captures a dynamic co-evolution of atmospheric and oceanic reduction–oxidation states, with repeated oxygenation pulses and feedback cycles. Oxygen isotopes in sedimentary sulfate provide details of a stepwise rise in oxygen levels in the atmosphere and oceans.