How have photosynthetic bacteria changed the composition of the atmosphere?

Photosynthetic bacteria, particularly cyanobacteria, played a pivotal role in shaping Earth's atmosphere by producing oxygen through photosynthesis. This process, known as the Great Oxygenation Event, occurred around 2.4 billion years ago and led to a significant increase in atmospheric oxygen levels. The rise of oxygen allowed for the development of aerobic life forms and changed the chemical composition of the atmosphere, making it more conducive to the evolution of complex organisms. This transformation laid the groundwork for the diverse ecosystems we see today.