How might cyanobacteria have contributed to the evolution of animals?

Cyanobacteria were the first organisms to produce oxygen from water and carbon dioxide. When the oxygen levels increased, an ozone layer developed, which blocked excess ultraviolet light from reaching the land. This made it possible for organisms to move onto land without being killed by UV light. Additionally, the oxygen created an atmosphere that permitted aerobic organisms to evolve, and aerobic organisms were the majority of those that ended up colonizing the land.