The Great Oxygenation Event

The Great Oxygenation Event, around 2.5 billion years ago, was a period when photosynthetic microorganisms, like cyanobacteria, began producing large amounts of oxygen as a byproduct of their metabolic processes. This increase in oxygen transformed Earth's atmosphere from an ancient, mostly oxygen-free environment to an oxygen-rich one. This change had profound effects: it enabled the evolution of complex, multicellular life and caused some existing anaerobic organisms to die out, as they couldn't survive in oxygen. The event is a key milestone in Earth's history, shaping the atmosphere and biosphere we know today.