Great Oxidation Event

The Great Oxidation Event, roughly 2.4 billion years ago, was a major shift when Earth's atmosphere saw a significant increase in oxygen. This happened because tiny microorganisms called cyanobacteria started photosynthesizing—using sunlight to produce energy and releasing oxygen as a byproduct. Initially, this oxygen reacted with minerals, but eventually it accumulated in the atmosphere. This change transformed Earth’s environment, making it possible for new life forms to develop and paving the way for complex, multicellular organisms. It was a crucial step in shaping the atmosphere and life as we know it today.