Great Oxidation Event

Approximately 2.4 billion years ago, Earth's atmosphere underwent a dramatic transformation known as the Great Oxidation Event (GOE). During this period, oxygen levels rose significantly from near-zero to about 10% of present atmospheric levels. This revolutionary change was primarily driven by photosynthetic cyanobacteria, which had evolved the ability to produce oxygen as a byproduct of photosynthesis. The GOE fundamentally altered Earth's biogeochemical cycles and created new ecological niches. This event had profound consequences for life, triggering a mass extinction of anaerobic organisms while facilitating the eventual emergence of aerobic metabolism and more complex life forms.