The first pulse of the Late Ordovician Extinction has been attributed to the Late Ordovician Glaciation. Although there was a longer cooling trend in Middle and Lower Ordovician, the most severe and abrupt period of glaciation occurred in the Hirnantian stage, which was bracketed by both pulses of the extinction. The rapid continental glaciation was centered on Gondwana, which was located at the South Pole in the Late Ordovician. The Hirnantian glaciation is considered one of the most severe ice age of the Paleozoic, which previously maintained the relatively warm climate conditions of a greenhouse earth.