abiotic synthesis of organic nutrients was much more difficult than it had been from methane. The evolution of autotrophs' photosynthetic pathways which used the energy in sunlight to at first directly synthesize ATP and later to synthesize carbohydrates from and water meant that life did not go extinct as more and more of the free nutrients were used up. From this point, all life on earth depended on the photosynthetic activity of autotrophs as the base of the food chain. The released by photosynthesis ended the conditions under which abiotic synthesis of organic compounds could occur. The in the atmosphere could quickly oxidize organic compounds and formed the ozone layer which screened out most ultraviolet light. Thus, once living organisms had arisen, they changed their environment in a way that destroyed the conditions from which life had originated. At the same time, the presence of atmospheric and the aerobic respiration it permitted allowed life to flourish as it never had before.
