Mysteries of glaciation
C. E. P. Brooks, the eminent British geologist, writing in Climate Through the Ages (1949 revised edition) says:
There have been at least four major ice ages: in the early Pro-terozoic, in the late Proterozoic, or Algonkian, in the upper Carboniferous, and in the Pleistocene-Recent period. Of the first two we know little; but that little suggests that they were entirely analogous to the Quaternary. The upper Carboniferous glaciation, on the other hand, was highly abnormal, in that the greatest ice sheets developed in regions which are now not far from the equator.
John Wolbach of Harvard University (paper #6, Shapley’s Climatic Change) expresses substantial agreement with Brooks when he writes that, according to geological evidence, ice sheets in the Pleistocene and Huronian episodes formed most extensively in high and temperate latitudes, while Permian glaciation developed principally in the tropics. He says that the Cambrian or late Proterozoic ice sheets developed not only in temperate zones of North America and Europe, but also in tropical South Africa, in India and in China. He concludes that
the Permian glaciation began in Carboniferous times, with small ice sheets in Australia and South America. In the Permian period, extensive glaciers developed throughout the tropics and south temperate zones. In Africa ample evidence points to glaciers as extensive as those of North America in the Pleistocene. . . . Extensive glaciations also took place in Central India and in regions to the south now submerged by the Indian Ocean.
Glaciation in the Southern Hemisphere
When study of ice ages first began, less consideration was given to glaciation in the southern hemisphere. Earlier writers apparently failed to realize that glaciation was contemporaneous in both hemispheres. That such is true is now generally conceded. R. F. Flint, in his Glacial Geology and the Pleistocene Epoch (p. 453) expresses this view when he says: “the weight of evidence is strongly suggestive that the glacial ages were synchronous throughout the world.” Maurice Gignoux, in Strati-graphic Geology (p. 245), referring to Carboniferous glaciation in the southern hemisphere, says:
The Carboniferous ends with a great glacial development, not confined to mountain valleys, but extending over immense spaces and thus comparable to the Quaternary ice caps of the northern hemisphere.
Evidence indicates that the present ice sheet on the continent of Antarctica was deposited during the Pleistocene, therefore, contemporaneously with deposition of Pleistocene ice sheets in the northern hemisphere.
Many writers, both early and recent, create the impression that glaciation in the southern hemisphere was much less pronounced than in the northern. Evidently, they fail to take into consideration the relative proportions of land and sea in the two hemispheres. In the northern hemisphere the Pleistocene ice sheets in North America and Eurasia extended south to the 50th parallel or even farther, yet probably not more than about 80 percent of all land north of the 50th parallel in the eastern and western hemispheres combined was ice-covered. In the southern hemisphere however, it seems indisputable that literally 100 percent of all land south of the 50th parallel was ice-covered. More than 95 peicent of such land today is still completely blanketed with ice! Also there is unmistakable evidence that the glacial blanket of Antarctica in the past was far thicker than it is now. Hence it certainly is incorrect to believe that glaciation in the southern hemisphere, during the Pleistocene at least, was less severe than it was in the northern hemisphere. Furthermore, no evidence has been discovered to date that Antarctica escaped glaciation during earlier ages when the northern hemisphere was visited by ice sheets.
Enigmas
During more than one hundred years, since 1837, when Louis Agassiz, the famous Swiss naturalist, first made it generally known that the world has experienced glacial episodes, countless scientists have sought in vain to account for the amazing phenomena. In efforts to solve the mystery, many inexplicable enigmas and contradictions are encountered, including the following:
(a) There was no semblance of uniform periodicity in the succession of the episodes
(b) The deposits of ice were localized with little regard to altitude or latitude. They occurred at sea level or at altitudes of only a few hundred feet within 40 degrees or less from the equator. They occurred even within the tropics in some places
(c) They occurred contemporaneously in both the northern and southern hemispheres
(d) It has always been assumed that glaciation eventuated because terrestrial climate grew colder; yet it is the consensus of paleontologists that warm, temperate climates have been the rule throughout geological time, that glacial climates were exceptions to the rule, were of comparatively short duration and were quickly followed again by mild climatic conditions. Decisive evidence that climate degenerated prior to glacier formation has not been discovered
(e) It has likewise always been assumed that the ice sheets accumulated slowly after climate had gradually deteriorated; yet there is definite evidence that the ice appeared with catastrophic suddenness, substituting frigid climatic conditions and inflicting wholesale destruction upon temperate-type fauna and flora existing under benign conditions even within both polar circles and at the very time the ice appeared.
In any attempt to fathom the mystery of ice ages, it should be borne in mind that all glacial periods, certainly from the Cambrian up through the Pleistocene, occurred long after Earth’s crust had formed and cooled and after conditions on Earth had become substantially the same as they are today. Surface configuration, continents and ocean basins were essentially the same then as they are now. Obviously, climatic conditions, air and water to sustain life were very similar. This is definitely proved by the plant and animal life we know existed at the respective periods. The regular, the normal, the ordinary condition throughout the greater part of geological time has been one of mild and comparatively uniform climate extending to and even within both polar circles.
Basic Premises of Theories
Many theories have been advanced to account for glacial episodes. Volumes would be necessary to explain the theories in detail. Suffice it to merely mention their basic factors which, according to the various hypotheses, caused ice ages to eventuate: