Cyanobacteria were the first photosynthetic organisms. How were they responsible for allowing higher life form?

C. They released oxygen, which first scrubbed the iron from the water (making a precipitate), then entered the atmosphere, where UV-C from the Sun made ozone. Ozone blocked UV-B. As the ozone got thicker, life with DNA could exist near the surface of the ocean and even move onto the land. UV-B damages DNA, making for cancer and mutation.