<P> The Great Oxygenation Event , the beginning of which is commonly known in scientific media as the Great Oxidation Event ( GOE , also called the Oxygen Catastrophe , Oxygen Crisis , Oxygen Holocaust , Oxygen Revolution , or Great Oxidation ) was the biologically induced appearance of dioxygen ( O ) in Earth 's atmosphere . Geological , isotopic , and chemical evidence suggest that this major environmental change happened around 2.45 billion years ago ( 2.45 Ga ) , during the Siderian period , at the beginning of the Proterozoic eon . The causes of the event are not clear . The current geochemical and biomarker evidence for the development of oxygenic photosynthesis before the Great Oxidation Event has been mostly inconclusive . </P>
when did earth 's atmosphere change due to living organisms
around 2.45 billion years ago ( 2.45 Ga ) , during the Siderian period , at the beginning of the Proterozoic eon