Even within glacial periods, the climate varied. Animals in northern areas that were not adapted to arctic conditions went extinct or moved south when temperatures dropped and vice versa. They pushed in and out of Africa, in response to those climatic pulses. Based on deep sea cores, we know that by 1. Thus evidence from past flora and fauna supports the more robust craniofaciodental anatomy of species that lived during the early Pleistocene, e.
The northern seas were ice-covered. South of the ice sheets large lakes accumulated because outlets were blocked and the cooler air slowed evaporation. When the Laurentide ice sheet retreated, north central North America was totally covered by Lake Agassiz. Over a hundred basins, now dry or nearly so, were overflowing in the North American west. Lake Bonneville, for example, stood where Great Salt Lake now does.
In Eurasia, large lakes developed as a result of the runoff from the glaciers. Rivers were larger, had a more copious flow, and were braided. African lakes were fuller, apparently from decreased evaporation. Deserts on the other hand were drier and more extensive. Rainfall was lower because of the decrease in oceanic and other evaporation. Over 11 major glacial events have been identified, as well as many minor glacial events.
During a glacial, the glacier experiences minor advances and retreats. These events are defined differently in different regions of the glacial range, which have their own glacial history depending on latitude, terrain and climate. There is a general correspondence between glacials in different regions.
Investigators often interchange the names if the glacial geology of a region is in the process of being defined. However, it is generally incorrect to apply the name of a glacial in one region to another. For most of the 20th century only a few regions had been studied and the names were relatively few. Today the geologists of different nations are taking more of an interest in Pleistocene glaciology.
As a consequence, the number of names is expanding rapidly and will continue to expand. Many of the advances and stadials remain unnamed. Also, the terrestrial evidence for some of them has been erased or obscured by larger ones, but evidence remains from the study of cyclical climate changes.
The glacials in the following tables show historical usages, are a simplification of a much more complex cycle of variation in climate and terrain, and are generally no longer used. These names have been abandoned in favor of numeric data because many of the correlations were found to be either inexact or incorrect and more than four major glacials have been recognized since the historical terminology was established. Corresponding to the terms glacial and interglacial, the terms pluvial and interpluvial are in use Latin: pluvia, rain.
A pluvial is a warmer period of increased rainfall; an interpluvial, of decreased rainfall. Formerly a pluvial was thought to correspond to a glacial in regions not iced, and in some cases it does. Rainfall is cyclical also. Pluvials and interpluvials are widespread.
There is no systematic correspondence of pluvials to glacials, however. Moreover, regional pluvials do not correspond to each other globally. Any coincidence is an accident of regional factors. Only a few of the names for pluvials in restricted regions have been strategraphically defined. Glacial and Quaternary Geology. New York: Wiley, xiv, p. Google Scholar. Sharp, R. Living Ice: Understanding Glaciers and Glaciation.
Cambridge: Cambridge University Press, xii, p. Two elephant genera survive in the Old World, in Africa and India, but all the mammoths and mastodons became extinct. Banner illustration by Mauricio Anton. Fossil Horses The Pleistocene Epoch 1. Painting by Charles R. Knight Charles Knight painted a reconstruction of a tar pit as it might have appeared 40, years ago.
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