What was the great oxidation event and why did it happen?

The Great Oxidation Event was a significant increase in oxygen levels in Earth's atmosphere around 2.4 billion years ago. It happened due to the emergence of photosynthetic organisms like cyanobacteria, which released oxygen as a byproduct of photosynthesis. This event led to the oxygenation of Earth's atmosphere, paving the way for the evolution of aerobic organisms.