Were it not for the outbreak of the war and the suspension of the measurement program, it is quite possible he would never have re-engaged the hypothesis of continental displacements at all. He had pinned all his hopes on telegraphic time signal measurements, expecting them to yield rates for the westward drift of North America of about 4 meters (13 feet) per year. This figure was close to the existing but inexact lunar measurements available in 1915, but it is 200 times greater than estimates current at the beginning of the twenty-first century; modern spreading rates are in the range of a few centimeters per year. Thus, no motions within two orders of magnitude of his prediction would have been detected in 1915 and 1916, and Wegener would have witnessed the (apparent) empirical disconfirmation of his hypothesis. He would then perhaps have concentrated for the rest of his professional life on working in the realm of atmospheric physics and pursuing polar meteorology. Had that been the case, he would be known today only to meteorologists interested in surfaces of discontinuity and the theory of precipitation, as well as to historians of Arctic exploration.
In returning to the question of continental displacements, Wegener was aware that geologists had found his hypothesis not so much wrong as repugnant. Why should this have been? He had found geodesists and geophysicists willing to consider the idea seriously, but not, other than Emanuel Kayser (the only geologist he seems to have known personally), the geologists. He needed a geological informant who could help him out of his impasse. Fortunately for Wegener, Emanuel Kayser had recently brought to Marburg, as his protégé, a young geologist named Hans Cloos (1885–1951). Cloos had taken his degree at the University of Freiburg in 1910 and had spent the past few years abroad. He had worked for two years in Java, looking for oil on behalf of the American Petroleum Company.55 Traveling to and from Indonesia, he had been through the Suez Canal and to the Red Sea. He had also circumnavigated Africa and spent some time in German South-West Africa (today Namibia).56
Cloos had not intended to begin an academic career; he was an exploration geologist and traveler stranded by the war in Marburg, awaiting military assignment. Cloos remembered his first encounter with Wegener. He said that Wegener had just “shown up” at his office one day and announced to him that he needed a guide to the geological literature, someone who would be willing to provide geological information and concepts for him. Cloos remembered being struck by his pleasant countenance and especially by his piercing gray-blue eyes. Wegener then sketched for him an “extraordinarily strange train of thought concerning the structure of the earth” and said that, as a physicist, he needed help in exploring it. Cloos took an instant liking to Wegener and said that he found Wegener likable and his ideas strange in about equal measure.57
This initial encounter was the beginning of an intense two-month intellectual relationship, lasting throughout the rest of January, February, and early March 1915; it was also the beginning of a friendship.58 Wegener was grateful for Cloos’s guidance through the complexities of the geological literature, but the heart of their collaboration was the stimulating daily argument and conversation. It was here that Wegener learned for the first time how geologists thought.59 Cloos experienced their interchanges as a spirited exchange of views, in which he would raise geological objections to various aspects of Wegener’s theory, and Wegener would respond with physical arguments. Cloos was sympathetic, although not convinced—a stance he would remain in for more than twenty years. Meanwhile, he saw that Wegener’s principal achievement, already evident in the first version of the theory, was that he had “placed on a solid scientific foundation an easily comprehended, sensationally provocative intellectual construct.”60
Cloos, in his debates with Wegener, provided the latter with valuable information about how geologists would view the various aspects of the hypothesis, outlining problems more evident to a geologist than to a geophysicist. Many parts of the resulting short book, the “first edition” of Die Entstehung der Kontinente und Ozeane, show the direct influence of Cloos’s travels and field experience: the problem of the Red Sea, the need to address the folded mountain chains encircling the Pacific, and especially the question of the island arcs arrayed like festoons from the Kurile Islands south through Japan, the Philippines, and Indonesia. The latter were very fresh in Cloos’s mind and experience, close on his return from the Dutch East Indies.
A few overarching generalizations can guide a closer examination of the book that resulted from this intense collaboration. Perhaps most striking is the extent to which Wegener’s morphological descriptions of continents and oceans remained two-dimensional. This must sound self-contradictory. The hypothesis was, after all, one of floating continental blocks in a viscous fluid substratum; a number of diagrams in both the 1912 and 1915 versions are schematic cross sections of Earth’s interior. Yet in this new version of the idea, Wegener’s principal concern was to explain the various surface elements (relief and structure alike) as a consequence of lateral displacement of continental blocks, via coastline matching where it was evident, and via explanation of the lack of such matching where it could not be seen. There was no detailed concern (other than the existence of mountains) with the morphology of continental surfaces or their undersides.
Equally worthy of note is the way in which Wegener reorganized his materials in the 1915 version. In 1912 Wegener had divided up his presentation in terms of the disciplinary source of his arguments: “geophysical arguments” and “geological arguments,” the latter including discussions of paleontology. In 1915 the twelve chapters of this short (ninety-eight-page) book were focused on specific geological and geophysical questions tied to specific regions of Earth. That is to say, Wegener was shifting his argument into a format (with the help of Cloos) that would be intuitively easier for geologists to grasp. Moreover, in service of this same aim, the terseness of the 1912 version was abandoned in favor of a more colloquial and patient (if still spirited) advocacy.
Finally, the decision to reorganize the materials into geologically comprehensible sections and topical divisions led to a good deal of repetition, in which the same geological and geophysical arguments ended up under different chapter headings, some being repeated as many as four or five times. The book reads as if it had been written not so much as a single extended argument but as a series of essays addressing specific problems and concerns within the ambit of the hypothesis. This seems to be a residue of the way that Wegener and Cloos went at their discussions: “What about island arcs?” “What about the Red Sea?” “What about the question of New Guinea and Australia?”
Let us now turn to some of the details of Wegener’s argument, emphasizing the things that were new in 1915. Immediately, the first chapter announced in its title a modified stance: “The Displacement Theory as Mediator [Vermittelung] between the Doctrine of Sunken Land Bridges, and the Doctrine of Permanent Oceans.”61 Wegener now placed his argument within the history of geology, rather than outside it, by noting that the dispute over continuities of flora and fauna on opposite sides of the deep ocean went back to Charles Lyell. Rather than criticizing the contraction theory (the theory of Sueß) directly, he invoked paleontologist Emil Böse (1868–1927)—who worked both in Europe and in North America—to declare that while the contraction theory was no longer fully accepted (as adequate), no theory had come forward to take its place and explain everything that it had explained.62
Wegener no longer spoke of sunken continents, but of sunken land bridges, alerted by Cloos that this was a more acceptable formulation. Addressing the difficulties faced by both the contraction theory and the theory of the permanence of oceans, he now acknowledged rhetorically the radical character of his proposed hypothesis: “These difficulties [with the two theories] will disappear completely if one will allow oneself to take but a single momentous step: if one accepts this that the continental platforms can undergo lateral displacements across the face of the earth.”63
In the second chapter, Wegener took up the subject of isostasy and the flotation
of the continents. Most of the documentation was the same as in 1912, as were most of the references, but more prominently featured were the arguments of Joseph Lukashevich (1863–1928). Lukashevich had published in 1911, in St. Petersburg, a small book entitled Sur le méchanisme de l’écorce terrrestre et l’origine des continents. Wegener had adopted in 1912 both Lukashevich’s explanation and diagrammatic representation of floating continents and his formulation that on planetary bodies of a certain size “the molar forces prevail over the molecular forces.”64 Wegener changed that formulation slightly here, to say that for geological structures of a certain size mass forces (gravity) would prevail over molecular forces (solidity); for large dimensions Earth was plastic, whereas at small dimensions it was stably solid.65 This was perhaps an unfortunate choice of words. Plasticity implies the tendency of the material to suffer permanent deformation. That is not really an issue where isostasy is concerned: the issue is the displacement of the viscous substratum of the Sima by large blocks of Sal which float on it, according to their differences in specific gravity. Indeed, the entire explanation of isostasy here was dense and difficult to follow even if one knows the material, which his audience probably did not.
As if sensing he needed to make another attempt to explain these difficult concepts, in the third chapter, “Salic Continents and Simatic Ocean Floors,” Wegener undertook to discuss the mineralogical differentiation of salic (crust) continents and simatic (mantle) ocean floors. Here he reintroduced (from 1912) as evidence of this differentiation the bimodal elevation of Earth’s surface, the flotation of continental blocks, the difference in specific gravity of continental platforms and ocean floors, the evidence for this gravitational difference measured at continental margins, and most of the other arguments from the 1912 paper—including every single one of the cross-sectional illustrations in the earlier publication. In retrospect, it seems that it would have made more logical sense for this chapter (on material differentiation based on density differences) to have come before the consideration of continental flotation presented in the preceding chapter.
Wegener approached the same material yet again in the fourth chapter, entitled “Plasticity of the Sal and Viscosity of the Sima.” In 1912 Wegener had argued that because of the difference in the melt temperature of Sal and that of Sima, at a depth of some tens of kilometers, the Sal, with its higher melting point, would still be solid, whereas the Sima would already have lost its rigidity (Riegheit) and would be indefinitely deformable. In the 1915 version, Wegener no longer speaks of the lessened rigidity of the Sima, but of its greater viscosity (Zähflussigkeit) and tendency to flow. Conversely, in discussing the continents as plastic, he is indicating that as the continents move through the Sima, they are capable of accumulating deformation (fold mountains on the leading margins), while the Sima, though more dense than the Sal, is already at a temperature where its fluidity prevents it from maintaining its deformation: it simply flows.
It had taken Wegener four chapters to work his way through the geophysical material: flotation, gravitational differentiation based on density, and differential deformation and flow as a consequence of differences in melting points at depth. Attempting to reconfigure this material in a way that might prove convincing to geologists had turned out to be very difficult for him; understanding it would be a daunting problem for geologists as well. Other than a few textbook writers and theorists working at the highest level of generality, geologists in 1915 rarely thought on a continental scale. They were rarely interested in what went on deep within Earth. In 1915 only about one-eighth of the continental surfaces had been geologically mapped, and almost all of the workaday effort of geologists was involved in extending this work. Moreover, Eduard Sueß had declared in the final volume of his great synthesis that he did not even believe in isostasy; for those who nevertheless “believed in it,” the American version of isostasy differed from the British, and both of these differed in important respects from French and German work on the same subject. The ease that Wegener had in understanding and in making up his mind was confronted here by a daunting blend (in his geological audience) of ignorance, agnosticism, and indifference to physical theory.
Wegener was now more than a third of the way through the book and had yet to address a new question or say anything much that was not already in the version of 1912. Only in chapter 5, “Mountain Ranges, Island Arcs, and Deep-Sea Trenches,” do we see new perspectives and new material, and here (probably more than anywhere else in the book) we see the influence of Hans Cloos. Just back from the Dutch East Indies (Indonesia), Cloos had much to say about the complex relations of the mountain ranges along the coast of Asia and the associated convex archipelagos running parallel to the coast, with deep-sea trenches on their outer sides.
The mountains of Asia were of great interest to European geologists but had barely been reconnoitered. One of the most absorbing parts of Edward Sueß’s compendium and treatise had been his stirring descriptions of the complex folding of these huge and often sinuous ranges. The American geologist Bailey Willis (1857–1949) had undertaken an extensive reconnaissance in China in 1903–1904, reporting (in English) for the first time on such great ranges as the T’ien Shan.66 These observations supplemented those of the great German geographer Ferdinand von Richthofen (1833–1905), who had been active in China, as well as in Java, Burma, and Japan, in the later 1860s and early 1870s, and who had developed a theory of these coastal ranges in China and of the associated island arcs.
Using Cloos’s knowledge of the region, Wegener was emboldened to pose a novel hypothesis for these unusual structural elements, in the context of his general picture of continental displacements. It was well known that the coastal mountains of Asia exhibit compressional folding parallel to the coast, and that these compressional folds also appear to have been compressed in their long (north-south) axes, as if subsequently the folding had rotated 90° from its original direction. Wegener proposed that the folded mountain ranges of the coast dated from the time (in the Tertiary) when Asia had been moving toward the Pacific. Subsequently, the continental motion had shifted, this time pushing Asia from north to south, and subjecting the existing mountain ranges to a pressure that forced them into sinuous arcs. When the direction of displacement changed again, with the Asian continent moving once more to the west, the outermost components of the ranges had detached themselves. Wegener used the analogy of what happens when you squeeze a deck of playing cards between the thumb and forefinger: as the pressure increases, eventually the outermost card will fly away, forming a convex bulge.
There were, of course, as many unexplained as explained elements in this construction. Wegener had no idea why the inner, continent-facing concave sides of these archipelagoes should be ringed with volcanoes, while their outer sides were composed of steeply tilted Tertiary sediments, except as a logical consequence of tensional rifting; the Tertiary sediments on the Pacific side of the islands would bespeak their continental origins. As for the ocean deeps parallel to the outer side of the islands, Wegener had no explanation or even conjecture. That he mentioned these structures at all was due to Cloos: the young geologist reaffirmed and strengthened Wegener’s own instinct that if you can see a problem that your theory cannot explain, it is much better for you to mention it than not mention it, that is, not wait for an opponent to point it out.67
When we turn to the next chapter, “The Mechanics of Displacement,” it becomes clear that everything to this point has been a “backstory” to prepare the reader to consider the large-scale regularities of the displacement theory. It was an uphill struggle to have proceeded in this way, to have to teach his audience the basic conceptual vocabulary and physical foundation for his hypothesis in addition to the hypothesis itself. Now the laborious work of didactic presentation of physical concepts could give way to the broad sweep of how the entire process would work, if it were true of the world.
Wegener noted with rueful humor that the one aspect of his theory that crit
ics had found impossible to oppose was the direct connection between the lateral compression of Earth’s crust and the origin of mountain ranges. No other question dominated thinking about Earth’s crust more than the question of mountain ranges; their undeniably compressive structure had been the greatest argument in favor of the theory of a contracting Earth, a theory that Wegener characterized at every opportunity as physically impossible.
Of all the mountain ranges on Earth, the most intensely studied by European geologists were those in their own backyard, the component ranges of the great Alpine system running east to west across the middle of Europe. Their manifold complexities had absorbed the ingenuity and analytical energy of European geologists for 150 years by the time of Wegener’s writing. It was therefore a monument of good sense, as well as a great tribute to the sagacity of Hans Cloos, that Wegener brought up the question of the Alps, only to announce that “on account of their great complexity, it would not be possible to go into the [Alpine] question further in this context.”68 Rather, he urged, it is a much better test of the theory to see what happens in the simpler case: what happens when the Indian peninsula was compressed against Asia, producing the Himalayas, or the smaller case of Spain colliding with Europe and producing the Spanish Pyrenees. This was, of course, the physicist’s approach: pattern first, anomalies and difficulties later. Abstract from the particular phenomena to find the underlying rule. The first apparent rule was that, in general, peninsulas (e.g., Baja California, Spain, Arabia, and the southern half of Greenland) are more compressed than the rest of the continental blocks from which they have become separated.69
Alfred Wegener Page 62
