How did photosynthetic plants alter the atmosphere eventually leading to increased diversity in the biosphere?

Photosynthetic plants significantly altered the Earth's atmosphere by producing oxygen as a byproduct of photosynthesis. This increase in atmospheric oxygen, known as the Great Oxygenation Event, allowed for the development of aerobic respiration, which is more efficient than anaerobic processes. As oxygen levels rose, it enabled the evolution of diverse life forms, including complex multicellular organisms. This shift in atmospheric composition ultimately laid the foundation for the rich biodiversity we see today.