The oxygen cycle is closely linked with the carbon cycle, since the flow of both is associated with the same phenomena: photosynthesis and breath.
Photosynthesis processes release oxygen into the atmosphere, while breath and combustion consume him.
Part of the stratosphere's O2 is transformed by the action of ultraviolet rays on ozone (O3). This forms a layer that acts as a filter, preventing the penetration of 80% of ultraviolet rays. Constant release of chlorofluorocarbons (CFCs) leads to the destruction of the ozone layer.