The Proterozoic, which lasted even longer than the Archean Era, saw the atmosphere changes from reducing to oxygenated, driving the original anaerobic inhabitants of the Earth into a few restricted anoxic refuges and enabling the rise of aerobic life (both prokaryote and the more complex eukaryotic cell, which requires the high octane boost that oxygen enables.) Stromatolites (colonial cyanobacteria), which had appeared during the Archean, were common. The modern regime of continental drift began, and saw the formation of supercontinent of Rodinia, and several extensive ice ages. Late in the Proterozoic a runaway icehouse effect meant that the preceding warm conditions were replaced by a "snowball" with ice several kilometers deep covering the globe. Warming conditions saw the short-lived Edicarian biota and finally the appearance of first metazoa.