The Paleoproterozoic (IPA: , also spelled Palaeoproterozoic) is the first of the three sub-divisions (eras) of the Proterozoic occurring between 2500 Ma and 1600 Ma (million years ago). This is when the continents first stabilized. This is also when Cyanobacteria evolved, a type of bacteria which uses the biochemical process of photosynthesis to produce energy and oxygen.