Alfred Wegener
Page 76
Wegener also enlisted Karl Andrée, who had depended heavily, in his highly critical 1917 review of Wegener’s book, on the opinions of Carl Diener. Wegener could use Andrée as a test case to see whether correcting Diener’s misunderstandings could make a convert of a skeptic, and in any case he could have a sound critique by Andrée from the standpoint of paleontology. Finally, throughout the first half of 1920, Wegener corresponded with Hans Cloos, who had just settled into a professorship at the University of Breslau. Wegener depended on Cloos to send him any further notices concerning the first edition of the book, and he hoped to count on his support when the new edition appeared.69
Unlike the first edition then, this manuscript would be read through before publication by a geologist, two paleontologists (one for animals and one for plants), a zoologist, a geophysicist, and a climatologist. Under such circumstances, it would be much more difficult for his critics to claim that he had made factual errors, as had happened with Semper, Diener, and Soergel. Now, with his empirical evidence fortified and supported by recognized experts, Wegener could force his critics to admit that many of his supposed “mistakes” were actually differences of expert opinion, with well-respected scientists supporting Wegener’s views on these issues. Wegener was learning that in such debates, it was not just what was said but who was saying it that mattered.
Wegener said that this new edition of his book was so different from the first that it should actually be considered a new book. The papers that Wegener had written in 1912 were reports of a novel hypothesis, with special attention to the problems that it solved, or might solve, and a conjugation of several lines of evidence that rendered it plausible. The short book that he published in 1915 amplified some of the arguments and evidence for which there was no room in a journal article, but once again it contained fundamentally no new insight. The book on which he embarked in 1919 and 1920 came into a very different environment from all his previous work on this topic. His hypothesis was now established in the literature as something worth defending; even more importantly, it was something worth attacking.
Not only had the environment of his theoretical ideas changed, but his reputation and role had also undergone a transformation. He was no longer an unknown instructor in physics and astronomy in a small university in the far southwest of Germany, but a senior scientist at the German Marine Observatory. Whatever the controversial character of his work on continents and oceans, he was a recognized authority on the thermodynamics of the atmosphere, and his work on tornadoes and waterspouts had had an effect he had not imagined: it gave him a large international following among forecast meteorologists, not as a theoretician but as a reliable synthesizer of difficult data sets. Not all of these things, of course, would be available for comment or even inspection to his opponents or his supporters in the realm of continents and oceans, but they were available to him, and his self-confidence had undergone considerable revolution.
The new edition would be a different argument, addressed to a different audience. For one thing, Wegener’s hypothesis was already of interest to the large public in Germany which read popular scientific magazines. As early as 1916, the geodesist Andreas Galle (1858–1943), an expert on variations in Earth’s axis, had written an appreciative article about the attempt (begun by Albrecht in 1914) to measure the separation of Europe and North America in the Deutsche Revue, “Are Europe and North American Moving Apart?,” and treated the matter as an intriguing and serious idea under active investigation by experts.70
By 1919, discussions of Wegener’s ideas written for popular audiences were increasingly common. Edgar Dacqué, still Wegener’s strongest supporter, wrote a short popular book entitled Geographie der Vorwelt (Geography of the prehistoric world) which fully incorporated Wegener’s ideas about the displacement of the pole and continents as essential for a correct understanding of Earth’s past. Heinrich Schmitthenner (1887–1957), reviewing the book for Geographische Zeitschrift, noted that “not every reader will be as willing as the author [Dacqué] to follow Wegener in his brilliant explorations of the dark sea of hypotheses,” but that Dacqué had indeed made a good case that the “permanence problem” could be solved by adopting Wegener’s ideas.71
Wegener’s publisher, Vieweg, wanted to move the book in the second edition from the Sammlung Vieweg (Vieweg Series) to the Sammlung Wissenschaft (Science Series), itself a statement that the book was no longer a speculative suggestion but a serious working hypothesis under active consideration; this was a significant boost. The editor of the Science Series, Eilhard Wiedemann (1852–1928), was a physicist who specialized in thermodynamics and optics, as well as an editor of the distinguished journal Annalen der Physik, where Wegener had just published, in 1918, his detailed mathematical treatment of mirages.72
Ordinarily the move from a popular to a technical series would have meant that Wegener should have made his argument deeper and more technical, but it was evident from the response to the first edition that the argument was already too technical for many readers. Therefore, he chose not to deepen the argument but to reorganize it in order to make it clearer. This was a delicate matter, as he was both responding to critics and attempting to gain new supporters. The book had to answer criticisms raised of the first edition, but it could not be defensive or entirely reactive; it had to move forward.
The first order of business was to provide what the first edition had so conspicuously lacked, namely, a clear, brief, and direct summary of the hypothesis at the very beginning of the book. Wegener wrote such a summary as his first chapter, entitled “Land Bridges, the Permanence of the Oceans, and Isostasy.” It was a reprise of the trajectory of geological theory over the previous fifty years. In a bare twelve pages it moved geological theory in a continuous arc from general satisfaction with the contraction theory (here called the Schrumpfungshypothese—the wrinkling theory) toward the necessity of the displacement hypothesis. It emphasized that the contraction theory, while still popular with some geologists, had been abandoned by most and entirely abandoned by geophysicists, who rejected the idea that it could be the cause of Earth’s surface morphology, and especially not the cause of mountain ranges. The vestigial remnant of the wrinkling theory was the land bridge theory, in which huge sections of formerly continuous continents were supposed to have broken down throughout geological history to create abyssal oceans. However, this vestige, Wegener asserted, was no longer seriously advocated by anyone.73
Wegener updated the context of his hypothesis so that there were only two alternatives: the permanence theory and the theory of continental displacements. The advocates of the permanence theory and of the displacement theory both accepted the same geophysics; their principal differences lay in explaining the distribution of plant and animal remains. The advocates of permanence tried to explain these remains in terms of transgression and regression of the ocean from broad continental margins, such that, given the migration of Earth’s pole of rotation, sometimes broad land bridges were exposed across the Bering Strait, in the North Sea, in the Aegean Sea, in the Bass Strait between Tasmania and Australia, and in many other regions.74
In setting up this opposition, Wegener adopted the framing of the problem offered to him by his supporters, most recently by Irmscher in the fall of 1919. Now his task would be to show the superiority of displacement over permanence by showing the difficulties of the permanence hypothesis. The first of these difficulties would be how the land bridges could have risen to the surface of the ocean in recent geologic history. On an earlier Earth, with shallower oceans, this need not be a problem. In the recent past, with a mean difference between continental surfaces and ocean floors of about 5,000 meters (16,404 feet), “this would seem to be extremely difficult to explain.”75 The second difficulty (of which Wegener was made aware by Dacqué) for the permanence hypothesis was explaining where the water of the ocean went when these land bridges were elevated. This was the inverse of the vexing question of where the water came from in the land brid
ge theory of sunken continents. Both of these processes—the elevation of the bridges and the displacement of the oceans—would involve tremendous disturbances of isostasy, for which the permanence hypothesis gave no account.
In this construction, the displacement hypothesis was no longer a middle ground between other theories; it was “the only way out” of a series of fatal contradictions.76 By accepting this idea of horizontal motion, “we obtain the possibility of reconstructing broad land connections, where today we find deep ocean, and are able to do this without coming into conflict with isostasy and without creating difficulties about the total volume of water on the earth.”77
There remained now the problem of detail: how much did his displacement theory explain? His geological critics hammered this point in their attacks, and even supporters asked for more specific information. Here Wegener sought to finesse the issue: “It is the task of the following sections to show that the displacement theory produces a range of unexpected simplifications, and that it is capable of bringing together the totality of our contemporary knowledge into a single picture. A document as brief as that before you can, naturally, only produce a sketch, and the filling out [of the hypothesis] would require a very great number of painstakingly detailed studies.”78
If Wegener’s book is a sketch, here we can only give a sketch of that sketch, pointing out the principal lines of attack, especially those that differ from his previous versions of his hypothesis. These lines of attack do not appear in different sections of the book but all mixed together. This is nowhere any more apparent than in the first substantive chapter, “The Nature of the Deep Sea Floor.” “The theory of the displacement of continents finds its strongest physical justification,” he claimed, “in a new conception of the nature of the floor of the deep-sea, that one might formulate as a principle: ‘the floors of the deep-sea are not parts of the lithosphere but composed of the heavier material of the barysphere.’”79 The crucial evidence for the correctness of this new view, he wrote, was the existence of a bimodal distribution of elevations of the crust. “In the entire realm of geophysics there is scarcely another example which provides as clear a law as that provided by these elevation statistics.”80
Where, in the previous edition, the difference between the continents and the oceans had rested most strongly on gravity measurements, now he shifted back to morphology. Rudzki, in his 1916 review of the first edition, had suggested that Wegener had overinterpreted the clarity and certainty of gravity measurements. On the other hand, Soergel, in his attack on Wegener in 1917, had concentrated on attacking the bimodal elevation as evidence for displacement. Wegener listened to his supporter, Rudzki, and backed off a bit on gravity measurements; this afforded him the opportunity to respond to Soergel.
Wegener noted that while the bimodal elevation of Earth’s surface had been known for a long time, he had been the first to offer an interpretation or an explanation of it. Soergel, Wegener said, was the only one who seems to have understood this, as well as how crucial a piece of evidence it was for displacement; Soergel had therefore attacked it directly “in his polemic.” He had argued that such a difference could simply be an accidental outfall of a certain range of elevations and depressions; the disturbances of isostasy would be the same. This argument, Wegener replied, was based on a fundamental lack of understanding of statistics. Any accidental distribution of elevations and depressions would produce a “normal curve,” a Gaussian distribution with a single central peak. The only way to get a bimodal distribution was the causal forcing of the situation by some factor other than elevation.81
Wegener pressed forward, citing items of evidence not included in either of his previous versions of the hypothesis. The ocean floor has no mountain ranges, which we know from the explorations of the Challenger Expedition. The ocean floor has only volcanic rocks and a very small class of deep-sea sediments, not the kind of rocks that we find on the continents; we know this from a series of dredging operations. The rocks of the ocean floor are differently magnetized than the rocks of the continents, and seismic waves travel at different speeds through the continental surface and through the ocean floor. This last bit of information he got from his newfound ally Ernst Tams.82
Now the aim and structure of the book begin to come into focus, and its contrast with the previous versions becomes more evident. The material that follows this exemplary treatment of the floor of the deep ocean has four sections, each with a separate but coordinate function, which reveal together Wegener’s new conception of what continental displacements mean for the sciences of Earth, how best to make the case for them, and to whom to make that case.
Gone from this edition is the sense that Wegener, working alone, had come up with a Copernican rewriting of the history of Earth as a counterpoint to Edward Sueß’s “Ptolemy.” In fact, gone is the idea that continental displacements are something that belongs to the realm of geology, or that the scientists that need to be convinced of their reality are geologists. Wegener’s new view is that he, as a geophysicist (his new self-description), is uniting the findings of geophysics with the findings of geography. His aim is to give a comprehensive explanation of the history of the large-scale morphology of the surface of Earth and therefore also an explanation of the distribution of life-forms.
This new description of his profession and the reasons for his book is certainly worth a few moments of reflection. At the end of the opening chapter, Wegener acknowledged that others before him had seen the parallelism of the coastlines and had spoken of the link between the displacement of the continents and the creation of mountain ranges. Yet, he said, “as a geophysicist [italics added] I came across these works naturally for the first time only through my examination of the geological literature as I worked out the details of the theory.”83 This is a different picture of the relationship of geology and geophysics than we have seen previously; Wegener now expects his readers to understand that these fields of investigation are so separate that no one who worked in one field might reasonably be expected to master the contents of the literature of the other without undertaking a detailed study for some reason. In this new view of things, he was in 1920—and had been in 1911–1912—a geophysicist.
Yet what of his attempt to unify the structure and bulk physical properties of Earth’s landmasses, oceans, and atmosphere on the one hand with the details of topography and animal and plant geography on the other? Certainly these seem farther afield from one another than the relationship between geophysics and geology. Of course, one could account for this odd conjugation through his collaboration with Köppen. Wegener had first become acquainted with Köppen as a meteorologist when in 1906 he attempted to borrow or buy some of Köppen’s “Hamburg Style” kites to take to Greenland. It was only as their relationship matured that he came to appreciate that his father-in-law’s fame stemmed principally from his work as a climatologist, as the inventor of a system of climate classification based on the geography of plants. Köppen’s system of latitude zones became the basis of their collaborative work on the migration of Earth’s pole of rotation through time. Indeed, Köppen seems to have been won over to Wegener’s ideas in 1919–1920 as the “Ariadne’s thread through the labyrinth of paleoclimatology” (der rote Faden im Labyrinth der Paläoklimatologie).84
Earlier (in chap. 9) we approached Wegener’s initial intuition of continental displacements by suggesting that in addition to finding out how Wegener may have “discovered” continental displacements, we should perhaps be interested in how “continental displacements had discovered him.” We suggested that his training and circumstances prepared him not just to have an intuition but also to develop it into a mature theory. Now, as we move from an examination of the formulation of Wegener’s hypothesis in 1911–1912 to its extensive modification in 1919–1920, we may ask not only what Wegener did to revise his hypothesis but also in what ways his changed milieu and audience helped to revise his hypothesis for him.
Consider the following. Wegen
er had published several articles between 1906 and 1912 in Gerlands Beiträge zur Geophysik. Georg Gerland (1833–1919), a geographer, had founded this journal with the express intent of reforming geography scientifically. For him, this had meant a fourfold limitation of geography to geophysics, plant geography, animal geography, and sociology. Such an endeavor had no immediate antecedents in geography in Germany, since he was directing geographers to the phenomena of geophysics (the physical interactions of land, water, and air), where they had made little contribution.85
Gerland’s founding editorial in the first issue had argued that (logically) the study of the forms of relief on Earth’s surface should begin with an explanation of the continents, but that after a half century of work in geophysics there was still no explanation of why there should be continents at all. Gerland wanted to push geography toward consideration of high-level generalizations, and he thought of geography as the senior science in which the results of the geophysical sciences—meteorology, seismology, volcanology, terrestrial magnetism, geodesy, and hydrology—all served to help understand Earth. This universal science of geography had the final aim (for Gerland) of understanding how all these processes, interacting in a realm of land, water, and air, produced habitat for plants, animals, and human beings.86
Not just Gerland but his student Alfred Hettner (1859–1941), who founded Geographische Zeitschrift, remained interested in questions of high generality. Many of the leaders of German geography in this era committed themselves to a study of the origins of the largest landforms—both continents and oceans. This was true of Ferdinand von Richthofen (1833–1905) and Albrecht Penck (1858–1945), who succeeded him at the Institut für Meereskunde (Oceanographic Institute) in Berlin. Penck, like Köppen, was a climatologist and deeply committed to a physical understanding of the origin of ice ages.