How did early life help create the ozone layer?

Early life on Earth, particularly the emergence of photosynthetic organisms like cyanobacteria around 2.4 billion years ago, played a crucial role in creating the ozone layer. These organisms produced oxygen as a byproduct of photosynthesis, which gradually accumulated in the atmosphere. This increase in oxygen led to the formation of ozone (O₃) in the stratosphere when oxygen molecules (O₂) were split by ultraviolet (UV) radiation and recombined. The ozone layer subsequently provided a protective shield against harmful UV radiation, enabling life to thrive on land.