Paleoclimatology is the attempt to reconstruct ancient climates and their causes.nLike all reconstructions, they are based on specific assumptions that are worthy of reconsideration.
Glaciation: ice sheets wide-spread over separate continents or localized on part of a supercontinent.

Wegener looked at evidence for glaciation around the world, especially where the average person doesn't think of it as existing, in the Southern hemisphere. He came to believe that climatic events that could affect a large part of a super-continent like Pangaea would nevertheless--from a global perspective--seem relatively small and localized when compared to the same events distributed over continents separated by oceans. Advancing and retreating ice sheet s would be examples of such events.

To see what he meant, look at the image of the globe below. It shows current relationships among continents. The darkened areas (blobs) in the southern regions all around the globe show areas that appear to have been covered with ice sheets an estimated 250 million years ago, during the Permian Period at the end of the Paleozoic era. How could one or several ice sheets cover so much, so separated ground? Wegener suggested that perhaps they didn't.

Areas of Permian glaciation

To follow Wegener's thinking, imagine pulling those southern-most areas towards one central point at the center of the very bottom. Pulling them together creates one Pangaea-like mass. It has an Antarctic-like area as part of it, covering what are now those darkened areas.

Southernmost Permian Glaciation

So, Wegener also drew the conclusion that in the late Paleozoic Era (Permian Period), just before the presumed break-up of the super-continent Pangaea, glaciation spread out from the Antarctic area of the super-continent. It left traces (those darkened areas) on those parts of Pangaea that later separated out to become Northern Australia, southern Africa, India and a strip of South America. (Of course, Wegener actually reasoned from glaciation evidence in those areas back to the centralized mass that became called Pangaea) It is commonly recognized that during the Paleozoic Era (570 to 225 million years ago) North America was much nearer the equator.

It's possible that the existence of a large mass like Pangaea allowed free circulation of warm equatorial waters to the poles, making the development of a truly massive ice sheet impossible.

But what about evidences of Pleistocene glaciation? Specialists recognize roughly 20 cycles of glaciation during roughly 2 million years.



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