The geological changes in the distribution of land and water being inadequate to explain the shifting of the poles, the problem is thrown back once more into the domain of astronomy. But before we ask, "What forces in the solar system could have displaced the terrestrial axis?" we shall discuss a theory that has for over three decades occupied the minds of geologists, climatologists, and evolutionists - the theory of the shifting continents. Instead of the poles shifting, according to Wegener's theory the continents drift and pass one after the other through the southern and northern polar regions. In August 1950 the British Association for the Advancement of Science devoted the sessions of its annual convention to debate on the question: Is the theory of the continental drift (slide) right or
wrong? There were many defenders of the theory and as many opponents. The theory was then put to a vote. The result was an even division between "yea" and "nay." The chairman was entitled to cast the deciding vote but abstained. Only through the fortuitous circumstance that the presiding officer was a conscientious - or undecided - person was the sanctification of continental drift averted.
The theory of drifting continents, debated since the 1920s, has its starting point in the "similarity of the shapes of the coastlines of Brazil and Africa." 1 This similarity (or, better, complementation) plus some
early faunal and floral affinities suggested to Professor Alfred Wegener of Graz in Styria that in an early geological age these two continents, South America and Africa, were one land mass. But since animal and vegetable affinities could also be found in other parts of the world, Wegener conjectured that all continents and islands were once a single land mass that in various epochs divided and drifted apart. Those who do not subscribe to the theory of continental drift continue to explain the affinity of plants and animals by "land bridges" or former land connections between continents and also between continents and islands.
In order that continents might move, it is claimed that there must be a basic difference between the composition of the earth's crust that is exposed in land masses and that which exists on the bottom of the ocean. The theory of drifting continents is grounded on the "increasingly well-proven doctrine of isostasy or the flotation of the crust of the earth" on plastic magma. A new nomenclature was
introduced. The land masses or the outer crust are called sial, an abbreviation of silicon and aluminum, two of the elements predominant in the composition of terrestrial rocks. The substratum is called sima, an abbreviation of silicon and magnesium, there being a "good reason for believing that the rocks forming the substratum [bottom] of the ocean bed are more basic in composition and contain a large proportion of magnesia [magnesium oxide]." 2 It is also assumed that the sima underlies the sial of the
continents and, possessing the plastic properties of sealing wax, permits the continents to drift.
Besides accounting for the correspondence between the coastal features of eastern South America and western Africa and between those of other continents, and certain affinities in the animal and plant kingdoms, the theory of drift tries to account for several geological phenomena, all in need of explanation: (1) the cause of the ice ages; (2) the distribution of coal beds; and (3) the formation of mountains. According to Wegener, mountainous crests rose, in the movement of the land, on the
forward side of the floating continents; meeting some resistance in its motion on elastic sima, the sial formed elevations. Thus, when South America moved away from Africa, an elevation was raised on the side turned to the Pacific Ocean, the Andes.
If, from the beginning, there was but one land mass, there could have been only one ocean, too, and, according to Wegener, the only ocean was the Pacific. The Atlantic is a later formation, and its bottom cannot be of sima, like that of the Pacific, but is built of stretched sial. Sufficient proof of the difference in composition of the substrata of the Atlantic and the Pacific has not yet been adduced.
The occurrence in an early glacial period of ice cover in lands now in tropical and subtropical regions is explained by the supposition that these lands were once in the Antarctic. However, their extent is so great that if all of them were joined around the South Pole, many parts that have signs of the Ice Age would still be too remote from the pole. The theory assumes, therefore, that these lands occupied in succession the position of the Antarctic continent today, each in its turn passing through a glacial period; the signs of glaciation in Africa, India, Australia, and South America are accounted for by the successive sliding of these continents through the southern polar region. A similar explanation is offered for the origin of the Ice Age in the Northern Hemisphere, at a much more recent date, when the land masses of North America and Europe wandered close to the North Pole. The North Pole is charted on various points on the globe - in the Pacific, in the Canadian arctic archipelago, in Greenland, in Spitsbergen - all in succession during the Pleistocene, or recent Ice Age.
The coal beds in northern countries, among them Alaska and Spitsbergen, are dated by Wegener from the time when these lands occupied tropical or subtropical belts, on their passage from the Southern Hemisphere to the Northern.
If a theory can explain the origin of mountains, the cause of the ice ages, the coal beds in higher latitudes, and certain common characteristics of the fauna and flora of continents separated by oceans, then the correspondence in the contours of the Brazilian and West African coasts truly served as a clue to the solution of major problems in geology and climatology. However, there are facts that strongly challenge this hypothesis.
The minute difference between the gravitational pulls to which the crust is subjected in higher latitudes and closer to the equator was offered by Wegener as the motive force in the drift of continents. But Harold Jeffreys, a British cosmologist, computed that this force is one hundred billion times too weak to produce the effect "There is therefore not the slightest reason to believe that bodily displacements of continents through the lithosphere [the crust] are possible." 3 Even assuming that this motive force was
sufficient, why did the lands of Europe, Siberia, and North America first move away from the original common land mass toward the equator and then retreat from the equator?
In search of another moving force, A. L. du Toft, a South African scientist, offered a variation of Wegener's theory, namely, a "concept of an earth in which the periodic, though variable, softening of the sub-crust through radioactive heating enables the skin to creep differentially over the core with consequent wrinkling." 4
As for the mountains, not all of them are situated as long ridges parallel to the seacoast. And no compelling evidence has been brought to support the contention that ice ages were consecutive in various parts of the Southern Hemisphere and, in much more recent times, in various parts of the Northern Hemisphere. Furthermore, how explain signs of the recent Ice Age in the Southern
Hemisphere? In Patagonia, New Zealand, and other places in the Southern Hemisphere, signs of recent glaciation are found. It is also certain that the chilling of the Ice Age was simultaneous all over the world.
Coal is found not only in arctic lands but also in Antarctica.
Did, then, this continent travel there from the tropics? And what was the motive force?
If the theory is correct, the motion of the continents should be observable at present; yet, though Wegener claimed, on the basis of certain reports, that Greenland and an island near its western coast still move, repeated observations and triangulations do not support this claim. Wegener perished on an
expedition to Greenland in 1930.
The assumption that ocean floors and continents are eternally different in structure is in contradiction to a great number of observations, though the land surface has been better explored than the bottom of the sea. The idea of a basic difference between the rocks of the ocean bottom and those of the continents is disproved wherever the fossiliferous contents of the land and of the ocean bed are examined. Marine expeditions have failed to find at various places on the ocean bottom the thick layers of sediment that should have been present if the sea had been covering the areas for untold centuries. On the other hand, sediments thousands and even tens of thousands of feet thick have been found on continents. Not only were large stretches of land in North America and Europe and Asia covered by the sea at various times in the past - and some well-investigated localities, like the gypsum beds of Paris, show repeated returns of the waters - but even the largest and highest mountain chains - the Alps, the Andes, the Himalayas - at some time were under the sea. Since the ocean once covered a vast expanse of land, it may at present occupy the place of former land.
The land masses of today do not change their latitudes; the motive force claimed is insufficient by far. Coal beds in Antarctica and recent glaciation in temperate latitudes of the Southern Hemisphere all conspire to invalidate the theory of wandering continents.
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1 A. Wegener: The Origin of Continents and Oceans (1924), p 1.
2 John W. Evans: president of the Geological Society, in Introduction to Wegener: The Origin of Continents and Oceans. 3 H. Jeffreys: The Earth, Its Origin, History and Physical Constitution (2nd ed.; 1929), p. 304.
4 A. L. du Toft: Our Wandering Continents (1937), p. 3. _________________________________