How did cyanobacteria change Earths early atmosphere?

Cyanobacteria played a crucial role in transforming Earth's early atmosphere through the process of photosynthesis. By converting carbon dioxide and water into oxygen and glucose, they significantly increased the levels of oxygen in the atmosphere around 2.4 billion years ago, in an event known as the Great Oxygenation Event. This rise in atmospheric oxygen allowed for the evolution of aerobic organisms and drastically altered the planet's chemistry and climate, paving the way for complex life forms to emerge.