2,500 million years ago tectonic activity on Earth caused a huge increase in the amount of oxygen in the atmosphere, according to some geochemicals from the National University of Australia. At that time, all the continents of the Earth joined together, and collisions of tectonic plates caused the ascent of the terrestrial surface and the formation of mountains. According to these scientists, the erosion of these mountains caused nutrient-rich sediments to reach the sea and contributed to the growth of the oxygen-producing cyanobacteria that lived in the sea.