The Paleoproterozoic (pronounced /ˌpeɪlɪ.oʊˌproʊtərɵˈzoʊ.ɨk/, also spelled Palaeoproterozoic) is the first of the three sub-divisions (eras) of the Proterozoic occurring between 1,600 to 2,500 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.