Mysteries of glaciation
CHAPTER ONE
MYSTERIES OF GLACIATION
An Imaginary Aerial Tour
The reader is invited to accompany the author on an imaginary world-wide aerial tour for the purpose of observing phenomenal terrestrial conditions which existed very, very recently, as measured by the geological time clock. We will imagine we are living in the closing millenia of the Pleistocene epoch, perhaps only 25,000 or 30,000 years ago.
One warm summer day we take off from southern Texas in a northeasterly direction on our jet-propelled magic carpet. We have barely gained altitude when, upon reaching the area where the present Mississippi and Ohio rivers converge, we suddenly pass over the margin of a great expanse of solid blue ice which completely obscures hills, plains and lakes of the land beneath us. The ice is certainly at least hundreds and probably thousands of feet thick.
As we continue onward, our amazement grows as the immensity of the ice blanket becomes increasingly apparent. We continue northeasterly over New York State, New England, Nova Scotia, Newfoundland and the Grand Banks, without finding a single break in continuity of the ice sheet. We swing northward over Davis Strait and Greenland, westward over Hudson Bay and Canada to the Pacific Coast, thence north over upper Canada and the Arctic Ocean. After passing over the North Pole and continuing south into Northern Russia, we swing westward and pass over the Scandinavian Peninsula, the Baltic Sea and the British Isles.
We have seen no uncovered land whatsoever, except a tiny patch in southern Wisconsin, some areas in Alaska and Siberia plus here and there a mountain peak protruding above the surface of the ice. Davis Strait, Hudson Bay, the Great Lakes of North America, all the islands off the northern borders of North America, the Baltic and North seas and shoal portions of the North Atlantic and the Arctic Ocean are all unbroken fields of ice. Not a bird, not a beast, not a tree or plant of any kind lives anywhere throughout this unbelievably vast expanse of horribly desolate, deadly silent, bitterly cold ice.
Deciding to continue our explorations, we find areas similarly covered with ice in Europe, Asia, China, even India; also in South America and Africa. There is some ice in Australia, New Zealand and Tasmania. A somewhat enlarged Antarctica is completely ice-covered.
Thus our imaginary tour disclosed a very considerable percentage of Earth’s land surface in both hemispheres buried under immense, deep blankets of solid ice. In North America the ice extended south to latitude 40; in India and Africa to even lower latitudes. Amazingly, even at mid-temperate latitudes the ice covered some areas only a few hundred feet above sea levell All continental platforms were just like they are today except that they were somewhat larger. A great many land areas, now separated by oceanic waters, were then joined. The Chukchi Peninsula of Siberia was connected with the Seward Peninsula of Alaska. The China and Japan seas were dry land. The island chain from Asia to Australia was so much enlarged that the two continents were virtually connected. The British Isles were connected to the European continent. The Baltic and North seas were ice-covered dry land. In all the oceans there were islands and ridges which are now submerged.
We noted large inland lakes in continental basins which are now arid. Between the Rockies and the Sierras of North America a vast lake existed. Large areas of the Russian steppes were under water. A much larger Caspian Sea embraced the Aral Sea. A huge lake existed in the Sahara of Northern Africa. The Black Sea was separated from and much higher than the Mediterranean. The waters of the latter were a hundred fathoms below their present level. Roaring streams, cutting deep furrows into her mountainous shores, were pouring their waters into her basin. An isthmus at Gibraltar joined Europe and Africa.
All oceans were noticeably smaller and shallower than at present. However, it was obvious that they were destined to increase considerably in breadth and depth within a few hundred years because of the tremendous amount of water pouring into them from the melting ice sheets. We saw many signs that terrific floods, caused by tremendous rainfalls, must have recently occurred in areas throughout the world which were not ice-covered.
Solar conditions, lunar and terrestrial relations and motions, axial inclination of the Earth and eccentricity of her orbit appeared to be the same then as they are now. Only a moderate difference in climate was discernible, apparently due solely to the chilling effect of the enormous ice sheets. Rain storms in torrid and temperate latitudes and snows in colder regions were occurring much as they do today. It was apparent that within a few thousand years all the ice would be melted away, except in polar regions and on mountain peaks.
Raging rivers flowing from melting ice fields were making their way to the oceans, down valleys and canyons which the turbulent waters were rapidly eroding. These rivers obviously were adding enormous loads of silt, sand and gravel to ocean floors along continental borders. In other places violent streams were racing down inland mountain slopes, accomplishing erosions and depositing sedimentary strata in inland basins on a greatly magnified scale compared to today.
The foregoing description of conditions which existed on Earth during what geologists call a very recent period, cannot be greatly in error, according to current scientific belief, based upon evidence and careful study by leaders in the field.
Glaciations Occurred Repeatedly
The glaciation we observed took place during the Pleistocene period, which began about one million years ago. There were four fluctuations of increase and decrease of the ice during that epoch as shown by clearly disclosed advances and retreats of the terminal moraines of the ice sheets. It is more or less customary for writers to refer to the Pleistocene period, or epoch, as “The Ice Age,” thereby giving the impression that it was the only geological period in which glaciation occurred.
However, other glaciations, similar to the one we observed on our imaginary excursion, but varying in severity, are known to have occurred time and again at irregular intervals, separated by millions of years. Eleven glacial episodes have been identified with the following periods, beginning with the most ancient: Keewatin, Timiskamian, Huronian, Animikean, Kewee-nawan-Cambrian, Ordovician, Silurian-Devonian, Carboniferous-Permian, Triassic-Jurassic, Eocene, Pleistocene. Naturally, evidence of the extent and effects of the more ancient ones has been largely obliterated by subsequent erosion and tectonic disturbances.