By the seventeenth of January Wegener had a manuscript of fifty pages, and by the twenty-ninth he had put it through so much revision that he could barely read the first twenty-five pages.5 A month later, on 24 February, he wrote to Köppen that he had sent off the final draft of his article on continental displacements (now sixty-nine typed pages long) to Paul Langhans (1867–1952), the editor of Petermanns Geographische Mitteilungen, the leading journal of geography, and the clearinghouse within the German-speaking world for everything to do with exploration. Wegener’s entrée to this journal was dual: the journal welcomed highly speculative and theoretical work on major issues in geography (the origin of continents was certainly such), and Wegener was well known as a polar traveler—his prospective 1912 expedition with Koch to Greenland had already been announced in Petermanns Mitteilungen. Wegener sent another copy of the completed manuscript to Emanuel Kayser, who promised publication of an abridged and geologically oriented version of the hypothesis, in Geologische Rundschau.6
The extremely rapid pace of Wegener’s research, presentation, and publication raises an interesting question: How did a thirty-one-year-old atmospheric physicist, who had only known for a few weeks that most geologists believed that Brazil and Africa were once connected, end up producing, in slightly over two months, a seventy-page manuscript that collated an enormous range of geological, paleontological, and geophysical evidence into an entirely novel argument about the origin of continents and oceans?
The answer lies, to a certain extent, in a pattern of scientific publication that no longer exists. If Wegener had tried to piece together his argument from individual geological, paleontological, and geophysical journal articles, his labor would have lasted not a few weeks but many years. However, the pattern of publication in the Germany of his day, along with the corresponding attitude toward new theory, came to his aid. In his world, though no longer in ours, senior scientists felt both the right and the obligation to spend the latter part of their careers producing works that integrated enormous quantities of existing material into coherent syntheses. Wegener was able to avail himself of a series of significant, often multivolume synthetic treatises in geology, oceanography, and geophysics, all published within a year or two of his own attempt to write about continents and oceans.
Without these books his initial formulation of his hypothesis would have been an impossible task. Wegener’s initial papers on continents and oceans and all of his subsequent publications on continental displacements were made possible by such syntheses. His initial seventy-page paper was, therefore, a higher-order synthesis and distillation of work already highly organized and integrated by senior scientists for whom it was the work of decades. When we say that Wegener “discovered” or “invented” the modern theory of continental displacements, it is appropriate to recognize that though the germ of the conception was his own, the evidentiary foundation consisted in predigested syntheses of many thousands of individual journal articles written by many hundreds of scientists in the course of the previous half century, brought together by a few leading figures in geology, geophysics, and oceanography, all at the end of their careers and very near the end of their lives.
The work that, above all, made Wegener’s hypothesis possible may be found in the following very short list of very long books. The first, and probably the most important for the Copernican part of Wegener’s effort, was Das Antliz der Erde (The Face of the Earth) by the Austrian geologist Eduard Sueß (1831–1914). This multivolume work took Sueß twenty-one years to complete (1883–1904).7 A second important work, which helped Wegener frame his approach to the question of continents and oceans, was the Handbuch der Ozeanographie (Handbook of oceanography) by Otto Krümmel (1854–1912), in two large volumes (1907, 1911).8 In matters of intercontinental correlation of flora and fauna, Wegener relied quite heavily on Die Entwicklung der Kontinente und Ihrer Lebewelt (The evolutionary development of the continents and their life-forms), published in 1907 by Theodor Arldt (1878–1960).9 A fourth significant and in every respect indispensable work was Physik der Erde (Physics of the Earth) by Maurycy Rudzki (1862–1916), in a 1911 German translation of the 1909 Polish original (Fizika ziemi).10 Finally, as a kind of universal handbook for the study of the intercontinental correlation of sedimentary rocks, the mineralogy of the continents, and data on earthquakes and other dislocating motions of the crust, there was Lehrbuch der allgemeinen Geologie (Textbook of general geology) by Emanuel Kayser (1845–1927), particularly the third (1909) edition of this massive, two-volume, frequently updated work.11
We should learn something about each of these, to get a sense of what they provided Wegener. The work of Edward Sueß is nearly unique in the history of geology, a science that certainly has had an abundance of towering and comprehensive thinkers. Sent to prison for his participation in the Revolution of 1848, Sueß was barred from university admission and academic employment but began a career as a field geologist in the Alps, taking a job at the central Paleontological Museum in Vienna. Twenty-four years later, having risen to the directorship of that museum, he published a highly influential short book, Die Entstehung der Alpen (1875), in which he proposed to interpret the folding of the Alps neither as transverse compression nor as uplift but as the overthrust of the entire mountain system to the north by a one-sided push from the south. His qualitative interpretation of the dynamic cause of this movement was the unequal radial contraction of the cooling Earth.12
Sueß represents, as well as serves as a convenient benchmark for, the assimilation of stratigraphical and paleontological work into a dynamic history of the motions of Earth’s crust. The thematic introduction of this approach to geology in 1875 was followed thirteen years later by the first volume of his massive treatise The Face of the Earth, which in its German original eventually filled three large volumes and more than 2,000 pages. This was not an introductory text for students but a mature summary of geology written by a senior professional for his senior professional colleagues and peers.
Sueß, in his massive synthesis, was deliberately moving beyond the conception of “uniformitarianism” proposed by the great British geologist Charles Lyell (1797–1875), whose book Principles of Geology was Darwin’s constant companion on his voyage on the Beagle. Lyell’s doctrine was an argument against the catastrophism (cataclysmic upheavals, collapses, floods, fires, etc.) of earlier versions of Earth history, arguing instead that all the phenomena of geology have been and are produced at the same rate and in the same way that we see them today: “the present is the key to the past.” Sueß aimed, in contrast, to enlarge the meaning of “uniform” change to include some phenomena not currently visible, having in mind the tremendous dislocations evident in Alpine mountain systems. The Face of the Earth was an attempt to turn geologists away from a too great fascination with miniscule causes (the raindrop hollowing out the stone, the coral polyp building up the reef) and to turn their faces toward the very large dislocations caused by the episodic collapse of large sections of Earth’s crust, the subsequent massive overthrust in great mountain belts, and the creation of ocean basins by the downfaulting and subsidence of great blocks of former continental crust.
Sueß was a brilliant writer. The Face of the Earth differs from other theoretical treatises because it is not a series of didactic statements or principles that are then evidenced by examples, but quite the reverse: a spellbinding narrative of the genesis and structure of the great forms of Earth’s crust seen from an aerial vantage point, imagined as they might be viewed by a visitor from space. Those of us accustomed to seeing pictures of Earth taken by astronauts returning from the Moon can hardly imagine the effect of Sueß’s visualization and powers of description on successive generations of geologists into the twentieth century. In its sheer beauty and the rapid pace of its dynamic prose, it is without doubt the most excitingly written book in the history of geology.
No one has ever claimed that Sueß was not devoted to the theory of a contracting Earth, but it is pe
rhaps not often enough emphasized that The Face of the Earth was designed as an integrated defense of the contraction hypothesis over against Charles Lyell’s notion of oscillating continents. Lyell’s vision of the majestic, slow rising and sinking of the continental platforms through geologic time dominated thinking in the English-speaking world well into the mid-twentieth century. Sueß, however, succeeded in converting a very large plurality of the rest of the world’s geologists to his views, and it is important to recognize the extent of this success if we are to understand the crisis within the world geological community when Sueß’s central conception of Earth contraction began to be challenged at the beginning of the twentieth century by increasingly sophisticated work in geophysics. Edward Sueß’s The Face of the Earth would play Ptolemy to Wegener’s Copernican conception of continental displacements. Everything in Sueß’s work is driven by subsidence, by sinking, and it was precisely this subsidence, as the universal motor of geological dynamics, that would be the theory’s eventual downfall.13
If Edward Sueß’s The Face of the Earth would provide the structure against which Wegener could push back, Otto Krümmel’s Handbook of Oceanography not only was an invaluable source of information about the physical characteristics of the oceans but also provided a great deal of information about the topography of the ocean floors. Krümmel was a great follower and admirer of Sueß, and he wanted to treat the ocean floors as submarine dynamical geological regions, dynamic Earth surfaces that happened to be covered with water. Of course, if one believed that ocean floors were former continental surfaces, then their submarine topography should reflect their former life above the surface of the water. Krümmel used the same scheme to differentiate different kinds of ocean floor which Sueß had used to discriminate different kinds of continental surfaces.
Krümmel’s book contained an extensive section on physical oceanography, with a discussion of waves, tides, currents, and ocean circulation, and a great deal of information about layering and surfaces of discontinuity in the ocean. There was an extended and highly sophisticated discussion, based on research up through the first decade of the twentieth century, on the behavior of water masses, those coherent bodies of water with a salinity (chemical composition) that demarcated them from the ocean in general. Such density and salinity differences caused these water masses to sink a certain distance and then travel through the ocean; these were used by oceanographers to track global ocean circulation. Wegener was once again reminded, by this approach to the topic, of the very strong analogies between the atmosphere and the ocean.
At the very beginning of the first volume of his work, Krümmel had given an interesting and extended discussion of the various ways in which one might decide on a classificatory scheme for the world’s oceans. He reviewed six different possible ways to organize his material. Oceans could be classified by their location and arrangement, by their size, by their form, by their chemical composition and contents, by their dynamic behavior in motion, or, last of all, by their origins, their Entstehung.14 “Of all the classifications of the objects of the dry surface of Earth,” he wrote, “it is the genetic classification [Entstehung], based on the origin of the forms, which ranks highest. For who explores the intrinsic organization and modes of generation of different forms, encounters, as Alfred Hettner says, the real nature of things.”15
It was Krümmel who convinced Wegener that his approach to continents and oceans should be framed in terms of their origins, rather than some of the other categorical approaches. These other approaches were available, of course, and particularly attractive to Wegener was the approach through consideration of chemical differentiation of Earth. In Sueß’s account, Earth was seen to be composed of three concentric shells of different density and of different chemical composition. The outermost shell, as well as the thinnest, Sueß had called “Sal,” to indicate that its principal constituents were silica and aluminum. The name “Sal” was confusing, because this is the Latin word for “salt,” and the term was soon adapted to “Sial.” For the mantle of Earth, the shell below the silica and aluminum crust, Sueß used the acronym “Sima,” an indication that its principal constituents were now silica and magnesium. Finally, there was the metallic core, composed of “Nife,” nickel and iron. Wegener knew he could trust the latter aspect of the conceptual scheme because Sueß had derived it from calculations of Earth’s density by Wiechert, at Göttingen.16
The chemical differentiation of discrete Earth shells, so attractive to Wegener, would be an important piece of supporting data. The main line of attack, however, would be through the origin of the major forms of Earth’s surface. It was clear to Wegener that even though Krümmel was correct (that the best approach to such questions was that of “origins”), nevertheless Krümmel’s own view of the origins of oceans was as fundamentally mistaken as Sueß’s view of the origins and histories of the continents. Krümmel had adopted wholesale Sueß’s version of the contraction theory and applied it to the oceans, in detail. Wegener knew that this answer was wrong and that he was in a position to correct it.
Nearly as valuable as either of these two sources was the comparative treatment of the development of life-forms on the continents throughout geological history provided by Thedor Arldt, in his Evolutionary Development of the Continents and Their Life Forms. Arldt was working in a discipline well known today, but it was sufficiently novel in 1907 that in the opening pages of his 730-page treatise he felt compelled to define for his audience the word “Paleogeography.” Arldt’s methodology was interesting and comprehensive. He had read and assimilated the work of most of the major paleontologists and paleogeographers of his day, but rather than using a few “index fossils” to map connections between continents, he produced statistical summaries of identical species on continents now separated by deep oceans (such as South America and Africa). He did this for each different period of geologic time and expressed his results in terms of percentages of species shared at any given time and the likelihood of an actual connection.17
As helpful as Arldt’s statistical summaries of species’ abundance may have been, Wegener did not have to read all 730 pages to get the point. The “business end” of this remarkable book was the ensemble of twenty-three global Mercator maps inserted as sequential plates tipped in at the end of the text. These displayed, in multicolored format, the conclusions laboriously arrived at by Arldt in reading every existing account of the distribution of mammals, of reptiles, and of amphibians and the Dipnoi (freshwater lungfishes, species that Arldt found particularly decisive for establishing continental connections). There were also maps of mountain ranges of Earth, showing continuations of the mountains of Scandinavia in Labrador, of the mountains of Europe (especially the Alps) in the Appalachians of the United States, and of the mountains of North Africa in the geology of the northernmost part of South America. Following these were maps of former continental surfaces superimposed on the geographic distribution of the current continents, for the Cambrian, Silurian, Devonian, Carboniferous, Triassic, Jurassic, Cretaceous, early Tertiary, and later Tertiary periods, and finally the glacial age. These paleogeographic reconstructions were derived from already-existing maps that Arldt had found in the literature, which seemed to him to best represent the percentage distributions of fossil species he had calculated on his own.18
Theodor Arldt’s map of the “Diffusion of the Reptilia” (including dinosaurs). Note the main migration routes “across the Atlantic,” indicating matching fossil species on both sets of continents (Europe–America and Africa–South America). This and many similar charts in Arldt’s book made a persuasive argument for a former continuity of continents now separated by abyssal oceans. From Theodor Arldt, Die Entwicklung der Kontinente und ihrer Lebewelt (1907), in Handbuch der Palaeogeographie, 2 vols. (Leipzig: Gebrüder Borntraeger, 1919–1922), 1647.
From Wegener’s standpoint, these maps painted an overwhelmingly convincing picture of former geological and, more importantly, paleontological continuitie
s throughout all of Earth history since the Cambrian. This continuity, particularly notable across the North Atlantic and South Atlantic continents, began to attenuate just where Keilhack had said it would: somewhat restricted connections in the Cretaceous, further reduced in the early Tertiary, completely broken in the later Tertiary except for a small land bridge between Greenland and Europe through Iceland, and finally pinched off toward the end of the Quaternary glacial age, or, as Arldt termed it, the “Diluvialzeit.”19
All of this was empirically reconfirmed and reinforced by Kayser’s geological textbook, with its particular attention to intercontinental correlation of stratigraphical sequences and fossil species, in which the material presented by Arldt in a series of maps found a more comprehensive tabular presentation.20 The message that Wegener got from these geological and paleontological works was that, within the German-speaking world at least, and to some extent the French-speaking world as well, there was nearly universal consensus on the existence of great paleocontinents of some sort, even if the reconstructions varied. Geological orthodoxy seems to have been that, through much of geological history, there was at least some connection across the Atlantic in both the Northern and Southern Hemispheres. Subsequently, for whatever reason (accounts varied from geologist to geologist), this had been progressively attenuated and disrupted in the Tertiary and finally severed within the past few hundred thousand years.
Alfred Wegener Page 46
