Cause and Development of an Ice Age

Abstract

The most important single fact about continental glaciation is that, throughout geological time, it has taken place when a major land mass was located close to a pole. North America has undergone perhaps three extensive glaciations: the Pleistocene, roughly the last 10⁶ yr; the Precambrian, approximately 10⁹ yr ago; and the Precambrian, approximately 2 × 10⁹ yr ago. (The oldest of these is subject to some doubt; perhaps the evidence can be interpreted in another way, although a good alternative explanation is not known). At each of these times, North America was located close to a pole; at other times in its history, it was not. The so-called Permian glaciation of North America (about 3 × 10⁸ yr ago) has been based on misinterpreted evidence; no glaciation is indicated, and the continent was actually (based on paleobotanical and paleomagnetic data) close to the equator.