How did pphotosynthetic bacteria begin to change the earth 3.5 million years ago?

Photosynthetic bacteria, particularly cyanobacteria, began to significantly alter the Earth's atmosphere around 3.5 billion years ago by producing oxygen through the process of photosynthesis. This gradual release of oxygen led to the Great Oxidation Event, transforming the planet's atmosphere and enabling the evolution of aerobic organisms. The increase in atmospheric oxygen also contributed to the formation of the ozone layer, which protects life from harmful ultraviolet radiation. Overall, these changes set the stage for the development of more complex life forms.