Carbonate reefs may have triggered a bout of global cooling



Earth's history shows a steady stream of extreme climatic change, spanning everything from planet-engulfing glaciers to tropical conditions near high latitudes. These large climate shifts are often attributed to permanent changes: the opening of a new waterway, the evolution of photosynthesizing plants, or massive bouts of erosion. Punctuating each long stretch of roughly steady climate are smaller transient shifts in environmental conditions commonly associated with changes in atmospheric carbon dioxide concentration. Yet the initial change in the climate system that led to the shift in carbon dioxide concentration for each period often remains unknown.