What do scientists mean when they refer to THE Ice Age?
The phrase "ice age" is often used in the disciplines of paleontology, archeology, ecology, and related fields. But what exactly is meant by this term? Ice ages may be simply defined as periods of exteme cooling, with the most pronounced effects occuring at higher latitudes. The most obvious effect is the "locking up" of great quantities of water in the form of ice. Since there is only a limited amount of free water on the earth at any time, locking up huge amounts of it will have an overall impact on sea levels, effectively lowering them.
Glacial (ice age) and Interglacial (predominately warm) stages in North America:
|Wisconsinan||ice age||75,000 - 10,000|
|Sangamonian||predominantly warm||120,000 - 75,000|
|Illinoisan||ice age||170,000 - 120,000|
|Yarmouthian||predominantly warm||230,000 - 170,000|
|Kansan||ice age||480,000 - 230,000|
|Aftonian||predominantly warm||600,000 - 480,000|
|Nebraskan||ice age||800,000 - 600,000|
|pre-Nebraskan||predominantly warm||1,600,000 - 800,000|
We now know that the cold stages were not uniformly cold, nor were the warmer spans continuously warm. In fact, there is evidence that at least two dozen warm-cold cycles have occurred during the past 1.6 million years, and that some of the changeovers occurred within the period of a century or so. From the standpoint of Quaternary extinctions, it is interesting to note that only the close of the last major glaciation can be correlated with widespread mammal extinctions at high latitudes.