Electrons, life and the evolution of Earth's oxygen cycle

摘要: The biogeochemical cycles of H, C, N, O and S are coupled via biologically catalysed electron transfer (redox) reactions. metabolic processes responsible for maintaining these evolved over the first ca 2.3 Ga Earth's history in prokaryotes and, through a sequence events, led to production oxygen photobiologically oxidation water. However, geochemical evidence suggests that there was delay several hundred million years before accumulated atmosphere related changes burial efficiency organic matter fundamental alterations nitrogen cycle. In latter case, presence free molecular allowed ammonium be oxidized nitrate subsequently denitrified. interaction between particular negative feedback, which increased decreased fixed inorganic oceans. This is supported by isotopic analyses sedimentary rocks from Late Archaean, continues present. once sufficient allow nitrification out-compete denitrification, new stable ‘market’ emerged oxygenic photosynthesis aerobic respiration ultimately spread endosymbiotic events massive lateral gene eukaryotic host cells, allowing evolution complex (i.e. animal) life forms. resulting network transfers gas composition far thermodynamic equilibrium it an emergent property), yet relatively on geological time scales. early coevolution N cycles, non-equilibrium gaseous by-products can used as guide search terrestrial planets outside our Solar System.