The evolution of oxygenic photosynthesis had profound effects on the biogeochemistry of the planet. The increase in atmospheric oxygen levels brought about alterations to a range of biogeochemical processes involving changes in the availability of a host of elements, including nitrogen, sulfur and many metal ions such as iron and manganese, central to biological activities. Critically for photosynthetic organisms, the increase in oxygen levels in the atmosphere following the evolution of oxygenic photosynthesis and the Great Oxidation Event had consequences for the assimilation of inorganic carbon via the enzyme ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco). Although there are a number of alternative pathways leading to autotrophic CO2 assimilation, 99% of primary productivity on the planet is carried out by processes that involve Rubisco and the Benson–Calvin–Bassham cycle. The accumulation of O2 in the atmosphere also had major repercussions for increasing the energetic yield of the catabolism of photosynthate by allowing oxidative respiration, with a much greater ATP yield than from anaerobic fermentative processes. The interaction of O2 with UVC radiation led to the production of UVC- and UVB-absorbing O3. This also significantly influenced life on Earth and facilitated the colonisation of the upper ocean and terrestrial surface.