The Great Oxidation Event

The Great Oxidation Event, around 2.4 billion years ago, was a major shift in Earth's atmosphere when photosynthetic microorganisms began producing large amounts of oxygen as a metabolic byproduct. Before this, Earth's atmosphere had very little oxygen, making it inhospitable for many life forms. As oxygen released by these microbes accumulated in the atmosphere, it dramatically changed the environment, allowing new forms of life to develop and eventually enabling complex multicellular organisms. This event is considered a pivotal turning point that shaped the future of life on Earth.