* This is Part 1 of a two-part installment of “Problematica.” The topic is Thomas Chamberlin’s theory of periodic diastrophism, which also came up when we discussed the origin and consolidation of the term “Cambrian explosion.” The present essay asks how big a deal periodic diastrophism was— was it really the “prevailing idea in [American] geology” prior to plate tectonics, as some contemporary geologists suggested? Well, it’s complicated! The body of this post is followed by two short appendices, which supplement the main text. Problematica is written by Max Dresow…
In 1949, a symposium took place at the annual meeting of the Geological Society of America, jointly sponsored by the Geological Society, the Paleontological Society, and the Society of Vertebrate Paleontology. Called “The Distribution of Evolutionary Explosions in Geologic Time,” it aimed “to examine the foundation in paleontology” of the “diastrophic theory” of Thomas Chamberlin, the preeminent American geologist of the preceding generation.* According to Lloyd Henbest, the diastrophic theory was then “the prevailing idea in historical geology,” its tenets “widely accepted and taught even in their extreme form” (Henbest 1952, 299). Yet there was something strange about this. At the time the symposium was held, Chamberlin had been dead for more than twenty years. It is thus remarkable that his theory retained a leading place in American geology, or at least a prominent enough place to warrant such consideration. Not one to let mere death get in the way of a sterling reputation, Chamberlin continued to bestride his field like a colossus. The symposiasts were assembled to say whether the situation was still tolerable. Ultimately, they decided it was not.
[* I will provide a detailed account of the diastrophic theory— more often known as the theory of periodic diastrophism— below. For now, it is enough to say that it was a theory of large-scale crustal movement that was believed to have major evolutionary consequences.]
Thomas Chamberlin at his desk at the University of Chicago
The first time I read Henbest’s remarks, I was incredulous. Could Chamberlin’s theory really have been that big a deal in 1949? Or was this just a puff of rhetorical gas to get the symposium off the ground? Instinctively, I inclined to the latter position. It’s frankly a bit of a stretch to think that Chamberlin’s ideas had that kind of staying power, especially since they were based on some physical assumptions that were known to be faulty during Chamberlin’s lifetime (Dott 1992). But this judgment, I have to admit, was based on a little more than a hunch.
Then, a while back, I reread George Simpson’s Tempo and Mode in Evolution (1944). Simpson was one of the 1949 symposiasts, and was decidedly cool on the merits of diastrophism as an evolutionary cause. (“Little support is found… for the theory of simultaneous, world-wide physical and biological climaxes at the period and era boundaries.”) This coheres with his reputation as a stalwart (neo-) Darwinian. It is the adaptive churning of populations, not vertical movements of the crust and their effects on physical geography, which power and guide evolutionary change.
Imagine my surprise, then, to encounter the following sentence in Tempo and Mode: “The appearance of new groups, with unrecorded origin-sequences, frequently coincides with climaxes in earth's history— crises of mountain building and land emergence” (Simpson 1944, 112, emphasis added). Admittedly, “[the] coincidence with major climaxes, those between the eras [geological periods], is not as extensive as might be inferred from some texts of historical geology.” (Which ones?) “Nevertheless, there probably is some real coincidence between tectonic episodes and the rise of new taxonomic groups on the mega-evolutionary level, especially as regards terrestrial animals” (113). And when it comes to major extinctions and intercontinental migrations, the coincidences are even more striking.
George Gaylord Simpson and his most famous book, Tempo and Mode in Evolution (1944). Also, like a llama or something
I had Simpson pegged as a critic of Chamberlin— as a no-nonsense Darwinian with little time for grand adventures in geotheory. But in the early 1940s, he was not as skeptical as hindsight would lead you to suppose. It makes you wonder: were Henbest’s remarks on the popularity of periodic diastrophism actually credible? Was I too quick to dismiss the idea that Chamberlin’s influence radiated unabated into the 1940s, at least in the United States? If even Simpson was buying what Chamberlin was selling, who exactly was rejecting it?
I would love to have an answer to these questions, but what I actually have is a caution against assigning too much evidential weight to Simpson’s remarks. I will need to say a bit more before this remark of mine will make sense. But before I do, I owe you a more detailed account of the diastrophic theory itself. (This will take up the remainder of Part 1 of this essay.) Then I will discuss Chamberlin’s immediate influence upon American geology, focusing on the dean of American stratigraphers in the first decades of the twentieth century, E. O. Ulrich. Finally, I will tell you about Chamberlin’s biggest fan among paleontologists: not Simpson, but a person Simpson worked with and admired at the American Museum of Natural History— W. D. Matthew. At which point I will be ready to return to Simpson and my splash of cold water.
First, though, Thomas Chamberlin. Who was this Goliath of American geology, and what exactly was the theory of periodic diastrophism?
From Glacial Geology to Periodic Diastrophism
Thomas Chrowder Chamberlin was born on a moraine, and went on to become America's preeminent glacial geologist. Perhaps this lay behind his penchant for environmental determinism: the notion that the physical environment, in one way or another, shapes the characteristics of the people who live in that environment. Anyway, it is a striking image: the child of a glacial landscape returning in maturity to decipher the palimpsest on which he had trod, innocent of its deeper rhythms.
Thomas Chamberlin as a young man and a terminal moraine from southern Wisconsin
The mature Chamberlin was an imposing figure. Well over six feet tall and “of large frame and carriage,” he towered over most of his contemporaries (R. Chamberlin 1932, 365). In reputation too, Chamberlin had a few equals. Naomi Oreskes has called him “perhaps the single most influential person in the history of American geology,” largely owing to his role as an institution builder (Oreskes 1999, 69). Among his accomplishments, Chamberlin founded The Journal of Geology, organized the Geology department at the new University of Chicago, and even served as the president of the University of Wisconsin at Madison. He also penned one of the most influential articles on the scientific method ever written (“The method of multiple working hypotheses”), and taught and influenced the celebrated historian Frederick Jackson Turner of “frontier thesis” fame (Jacobs 1968).
Chamberlin made his bones, however, as a member of the Wisconsin and later the U.S. Geological Survey. It was here that he “presented early analyses of moraines, drumlins, eskers, and boulder trains” and used these to infer “regional glacial flow patterns, differentiated ice lobes, and… the outermost limits of the last two glacial advances” (Dott 2006, 30). This final point warrants special comment. The Wisconsin Survey under Chamberlin, and later the glacial division of the USGS, led the way in naming and delineating drift sheets corresponding to separate episodes of glacial advance in North America. This was a major achievement. Earlier, in The Great Ice Age (1874), James Geikie had proposed that there had been at least two glacial periods, sandwiching at least one interglacial. (This claim was built on still earlier work, which found evidence of mild interglacial climates in ice age sediments.) But it was Chamberlin who conclusively demonstrated that there had been multiple episodes of glacial advance in North America; something he and his subordinates accomplished by “the discovery and working out of an extended moraine stretching across the whole of the glaciated area and belonging to a system of glacial movements, which differ in many important respects from the earlier ones” (Chamberlin 1883, 272).*
[* This evidence is much stronger than the evidence Geikie had to go on, since “temporary oscillations, or the shifting of subglacial streams, may produce [buried plant remains in glacial sediments— same as a real interglacial]” (Chamberlin 1883, 271).]
“Theoretical Map of Wisconsin During the Second Glacial Epoch,” prepared by T. C. Chamberlin for Geology of Wisconsin: Survey of 1873-1879, Volume 1 (1883), showing the Driftless Area. And an “Ideal Map of North America During the Ice Age” by T. C. Chamberlin, included as Plate XIV in James Geikie’s The Great Ice Age (1894)
This barely scratches the surface, and already it is enough for a single career. But Chamberlin did not stop there. Spurred on by his activities as head of the glacial division of the USGS, he set himself a new task: unraveling the causes of continental glaciation. This was a major question during the nineteenth century and remained a subject of much controversy when Chamberlin took it up in the 1890s, and identified as a probable culprit atmospheric carbon dioxide.
The idea was hardly new. In 1859, the physicist and mountaineer John Tyndall had shown that certain atmospheric gasses are capable of absorbing heat (Dry 2019). At the time it was known that the earth’s temperature is higher than it ought to be based on the supply of incoming solar radiation. Tyndall linked this to heat-trapping gasses like water vapor and carbon dioxide: “Thus the atmosphere admits of the entrance of the solar heat; but checks its exit, and the result is a tendency to accumulate heat at the surface of the planet.” An important result, to be sure. But Tyndall’s goal was not to explain a discrepancy in surface temperature— it was to explain the cause of the great ice age. Without atmospheric water vapor, Tyndall observed, the planet would be “held fast in the iron grip of frost.” Might it then be the case that changes in the composition of atmospheric gasses explain “all the mutations of climate which the researches of geologists reveal”?
“Variation of temperature caused by a given variation of carbonic acid,” from Svante Arrhenius’s now-celebrated 1896 paper— a major inspiration for Chamberlin’s thinking about “climatic changes”
Chamberlin took up the suggestion around the same time Svante Arrhenius presented his now-famous model of the effects of carbon dioxide on surface temperature. (Arrhenius, too, was seeking an explanation for the ice ages.) For Chamberlin, the key was found in the linked system of oceans and atmosphere:
Cold water absorbs more carbon dioxide than warm water. As the atmosphere becomes impoverished [in carbon dioxide] and the temperature declines, the capacity of the ocean to take up carbon dioxide in solution increases. Instead, therefore, of resupplying the atmosphere in the stress of its impoverishment, the ocean withholds its carbon dioxide to a certain extent, and possibly even turns robber itself by greater absorption… So also, with increased cold the process of organic decay becomes less active, a greater part of the vegetal and animal matter remains undecomposed, and its carbon is thereby locked up, and hence the loss of carbon dioxide through the organic cycle is increased. The impoverishment of the atmosphere is thus hastened and the epoch of cold is precipitated. (Chamberlin 1897, 682)
In modern parlance, what Chamberlin was describing is positive feedback (“the rich become richer”…). But he was not describing a dynamic that was bound to wax indefinitely. Eventually, countervailing forces would come into play, shaping the entire dynamic into a great cycle:
With the spread of glaciation the main crystalline areas, whose alteration is the chief source of depletion, become covered and frozen, and the abstraction of carbon dioxide by rock alteration is checked. The supply continuing the same, by hypothesis, reenrichment begins, and when it has sufficiently advanced warmth returns. With returning warmth, the ocean gives up its carbon dioxide more freely, the accumulated organic products decay and add their contribution of carbonic acid, and the reenrichment is accelerated and interglacial mildness hastened. (Chamberlin 1897, 682)
So here we have a mechanism for a “rhythmic oscillation” of continental glaciation and “interglacial mildness.” When the atmosphere becomes impoverished in carbon dioxide, temperature drops, increasing the capacity of the oceans to absorb carbon dioxide, until “the abstraction of carbon dioxide by rock alteration is checked [by glacial advance],” throwing the engine into reverse. But what gets the whole thing started?
The answer, for Chamberlin, was “a great epoch of general uplift”— that is, an upward movement of the land or diastrophic event (Chamberlin 1897, 678). With the onset of such an event “there would begin an era of relatively rapid atmosphere [sic] exhaustion [of carbon dioxide], which would proceed continuously during [the] elevated stage.” (This is because Chamberlin regarded carbon dioxide as a major agent in the disintegration of crystalline rock, whose weathering draws down carbon dioxide from the atmosphere.) So, basically, it is the production of topographic relief, and the subsequent weathering of exposed rocks, that kick-start intervals of cooling.*
[* Chamberlin’s model of climatic change involved one more ingenious component. Today, “deep-sea circulation is actuated dominantly by polar agencies”; and because of this, “cold waters creep slowly along the depths from the polar seas equator-ward, where they gradually rise to the surface and return on more superficial routes” (Chamberlin 1906, 368). Yet it would not take a great revolution in surface conditions to “flip the switch” and reverse the current. This led Chamberlin to speculate that the switch was probably flipped many times in the past, with domination by polar agencies aiding the spread of glaciers and domination by equatorial agencies aiding the spread of warmth.]
Chamberlin’s 1897 paper in The Journal of Geology
Chamberlin published this model in 1897, the culmination of nearly three decades of work in glacial geology. To a less ambitious scientist it might have been a crowning achievement, the sensible culmination of a career spent amid the bucolic landscapes of the American Midwest. Yet Chamberlin’s ambitions were at this time expanding to embrace larger stretches of space and time. Much larger. Chamberlin the glacial geologist was becoming Chamberlin the planetary scientist, or even Chamberlin the “cosmogonist” (Fleming 2000). It was this expansion that saw the emergence of periodic diastrophism as something more than an explanation of continental glaciation— indeed, as a key part of a comprehensive geotheory.
An especially important publication in this connection bore the title, “The ulterior basis of time divisions and the classification of geologic history.” In it, Chamberlin declared “[the] most vital problem [facing] the general geologist” to be “the question of whether the earth’s history is naturally divided into periodic phases of world-wide prevalence, or whether it is but an aggregation of local events dependent upon local conditions uncontrolled by overmastering agencies” (Chamberlin 1898, 449). The former position was close to the one advocated by the great Viennese geologist Eduard Suess. The latter resembled that of Charles Lyell. Anyway, Chamberlin’s purpose was to suggest that the history of the earth was measured out in rhythmic pulses: episodes of diastrophic disturbance followed by base-leveling and sedimentary deposition. This, he suggested, was the ultimate basis of stratigraphic correlation, and the reason the major divisions of the geological column were able to be correlated the world over.
Chamberlin had reason to be enthusiastic about the idea. The problem of finding an ultimate basis for correlation— or what came to the same thing, a natural classification of strata based on global events or processes— was a pressing one in late nineteenth century geology. Several international congresses had mostly failed to standardize stratigraphic nomenclature, resulting in a situation that, according to one observer, “confounds the mind, creates disgust for such studies, and threatens us with irremediable confusion” (Ellenberger 1978, 22). There was also widespread disagreement about the placement of stratigraphic boundaries, especially for the ancient rocks of the Paleozoic systems. A proposal like Chamberlin’s promised to address both problems at a stroke, supplying what a follower of Chamberlin would call “a true [natural] basis for intercontinental correlation of not only the grander cycles [systems] but also of their subordinate stages” (Ulrich 1911, 399). By carving the stratigraphic record at its joints, it would at once permit secure long-distance correlation and provide a basis for a “true classification of geologic time” (Ulrich 1911, 290).
Several coupled claims underlay Chamberlin’s grand proposal. The first was that the earth’s crust accumulates great stresses under gravitational contraction, which are periodically relieved in grand movements that distribute the stress far and wide. These are the diastrophic events that mark the boundaries of the largest divisions of geological time, the geological periods (e.g., Triassic, Jurassic, Cretaceous). The major part of the movements consist in the sinking of ocean bottoms, causing the seas to withdraw from the land and sedimentary deposition to largely cease. But there is uplift as well, which conspires with falling ocean bottoms to increase the amount of rock exposed to the air. At which point, erosion begins the work of “cutting down” the surface to base-level, consuming carbon dioxide, stimulating climate change, and driving a pulse of evolution that differentiates the life forms of one period from those of the previous one. This, in conjunction with a (worldwide) gap in sedimentation produced by the diastrophic movement, sharply delineates successive geological periods, with the unconformity marking a “natural” boundary.
“Diagram illustrating the supposed elements of a general deformative movement,” from Chamberlin and Salisbury (1904). What’s pictured here are the results of the collapse of the crust via contraction (from the S shell to the S’ shell), including the deepening of the ocean basins, the upheaval of the continental masses, and the formation of folded mountains by lateral thrusting. The thrusting is pictured by means of lines connecting the S and S’ shells, like the line connecting point a to point a’, which shows the margin of the oceanic crust. In the figure this marginal oceanic crust is thrust onto the continent (or at any rate the continental shelves) in a great lateral movement, to which the continental crust responds by folding.
All this was ultimately down to diastrophism. As Chamberlin wrote in an influential paper of 1909:
I think we must soon come to see that the great deformations [of the earth’s crust] are deep-seated body adjustments, actuated by energies, and involving masses, compared to which the elements of denudation [erosion] and deposition are essentially trivial... It seems clear that diastrophism is fundamental to deposition, and is a condition prerequisite to epicontinental and circum-continental stratigraphy. (Chamberlin, 1909, 693)
In order for geologists to confidently correlate sediments the world over, it was necessary to assume a diastrophic control on sedimentary accumulation. Assume it, though, and the great secret of the sedimentary record would be revealed. The entire record, superficially a jumble, would “assume a rhythmical periodicity susceptible of significant and rational nomenclature.” And to Chamberlin would go the spoils for placing the practice of stratigraphy on firm, theoretical grounds.
It was a grand vision— not entirely original, large parts of it having been lifted from Suess, but stamped with the signature of a powerful thinker. Yet in 1898, when it was launched upon the world, it was more inspiration than induction, more hypothesis than theory. Tossed and buffeted by the waves of scientific opinion, it remained to be seen just what its impact would be. That is the subject of Part 2 of this essay (for which a link will be placed here when it’s available).
Appendix 1: More on Correlation
Above I sketched Chamberlin’s views on correlation in just a few brushstrokes. Now I want to fill in some of the details I left out for the sake of brevity. First, though, a word on correlation itself.
The project of correlation involves the matching of sedimentary deposits on the basis of shared features— usually, features taken to be indicative of shared age. It has long been a leading aim of geological research. As Rachel Laudan writes, “[nineteenth century] geologists put most of their energy into determining the succession of formations in the field and then correlating successions in different parts of the world” (Laudan 1987, 141). Likewise, Martin Rudwick describes correlation as “the central problem of stratigraphical geology as geologists sought to expand [the enterprise] from the local towards the programmatically global” (Rudwick 1985, 53). Yet there was a problem at the very core of this project. This was a problem that arose out of the absence of an external standard for checking especially long-distance correlations (Dresow 2021). How could a geologist know that rocks containing similar fossils (say) were really deposited at the same time? Only if the fossils recorded a truly global signal— if faunal composition changed in a coordinated way all over the world— would the transition from one fauna to another represent a moment in geological time. But who could say if this were the case?
More pragmatically, geologists in the 1880s and ‘90s had seen both the rapid multiplication of unit names and the divergence of standards and nomenclatures employed in different areas.* At some point, this chaos would have to be tamed and discordant series made to mesh. But without a reason for favoring one set of names over another— or better, a rational framework for a truly global stratigraphy— the process of integration was likely to be a slog.
[* As Mott Greene (1982) notes, there were more than 700 new unit names introduced in the United States alone between 1886 and 1890, as the first generation of western surveys finished their work. And not all of these were valid. Of the more than 14,000 total unit names then in circulation, more than a third would be abandoned by the middle of the twentieth century.]
Le Palais des Fétes in Strasbourg, site of the First International Geological Congress (1878), where the standardization of classification schemes was a leading issue. Thomas Chamberlin attended and read a paper on the Kettle Moraine
Enter Chamberlin. The great promise of periodic diastrophism was that it might provide this rational framework, carving the stratigraphic record at its natural “joints.” But of course this presupposed that the stratigraphic record has natural joints to carve. And specifically, that it has joints corresponding to globally correlable features. So Chamberlin first asserted that this is the case: that the “physical and vital action” has proceeded not by “heterogeneous impulses” but by “correlated pulsations”— rhythmic oscillations affecting the whole surface of the globe (Chamberlin 1898, 450). There are, he said, three general grounds for holding this view.
The first was the presumption (which he takes to be widespread) that great earth movements affect all quarters of the globe. “Minor stresses” will often find relief in local readjustment, but the “profound stresses” that accumulate in the crust over large stretches of time “cannot be relieved, it is assumed, without generating appreciable stresses in other portions of the globe and leading to general readjustments” (Chamberlin 1898, 450). In a globe in which “all parts owe their positions to the stress and tension of other parts,” this is reasonable, and Chamberlin was confident that downward movements in one part of the globe produce upward movements other parts, with truly global implications.
The second “ground of belief in a fundamental periodicity in terrestrial progress” was “founded on the conviction that the major movements of the earth’s surface have consisted of the sinking of the ocean bottoms and the withdrawal of additional waters into the basins whose capacities were thereby increased” (Chamberlin 1898, 451). Chamberlin observed that most geologists take for granted that “the great movements of the earth’s crust have consisted fundamentally of shrinking” (452). He also observed that most geologists think the earth was once a perfect spheroid. So, because the oceans bottoms are today much closer to the center of the earth than the continental masses, it follows that the dominant process in the evolution of the planet has been the collapse of the ocean basins.
A pair of figures from Chamberlin (1898) illustrating the process of baseleveling. Figure 2 shows the endpoint of the process depicted in Figure 1, where all the “land carried away by erosion” (e) has been built into a continental terrace (d)
Chamberlin then asserted that, as the oceans have fallen, so have the continents risen (if not absolutely, at least relatively). Indeed, he thinks that the downward and upward movements have been coupled, such that a causal connection exists between the deepening of the oceans and the production of elevation. The result of this jostling is sea-level change, as the waters of the ocean withdraw from the continental terraces into the newly foundered ocean basins. (That is, until sediments eroded from the land begin to fill the ocean, causing the seas to rise again.) And all this is recorded in the rocks, which preserve “a homologous series of deposits the world over”— a global signature of the diastrophic “pulse.” Beginning at the bottom of the series, there will be deposits or surfaces corresponding to
(1) the stages of climacteric base-leveling [i.e., the erosion of physical relief to a minimum of elevation] and sea-transgression [highstand, or maximum sea-level; see Fig. 2];
(2) the stages of retreat [sea-level fall] which are the first stages of diastrophic movement after the quiescent period [corresponding to the collapse of ocean basins];
(3) the stages of climacteric diastrophism and of greatest sea-retreat [lowstand, or minimum sea-level; Fig. 1, focusing on line o-o]; and
(4) the stages of early quiescence, progressive degradation, and sea-advance [sea-level rise].
Since changes of sea-level will be roughly contemporaneous the world over, these deposits can be regarded as essentially equivalent in age. If this is true, Chamberlin concluded, “the arbitrary divisions that now vex our system may be largely eliminated” (Chamberlin 1898, 462).
Chamberlin might have left matters here. But he went on: “[the] third agency which affords some promise of becoming a means for strict correlation of transoceanic events and the division of these events into their natural epochs is an assumed fluctuation in the constitution of the atmosphere” (Chamberlin 1898, 459). Since I’ve already covered this in detail I won’t dwell on it here, other than to say that, for Chamberlin, large-scale diastrophism drove evolution via changes in the amount of carbon dioxide in the atmosphere (producing climate change) and changes in sea-level (producing more or less extensive shallow seas). So, the same process that leaves a physical signal in the rock record will also leave a climatic and a biological one. For Chamberlin, stratigraphy and paleontology were woven together on the loom of diastrophism.
Appendix 2: Chamberlin and Salisbury’s Geology
In the early part of the twentieth century, firmly enshrined at the University of Chicago, Chamberlin joined with his longtime friend and colleague, Rollin Salisbury, to author a textbook. Prior to this, the major American textbook in geology had been James Dwight Dana’s Manual of Geology, first published in 1862, and updated in 1867 and 1895. But in 1900 Dana was dead and his Manual was beginning to creak under the weight of its mid-nineteenth century frame. There was need of a more comprehensive update, and this came in the form of a new work, simply titled Geology, of which the first volume appeared in 1904.
A two-page spread from the chapter on structural geology, with a series of nicely reproduced images
Chamberlin and Salisbury’s Geology began with a statement of purpose: “not merely to set forth the present status of knowledge, but to present it in such a way that the student will be introduced to the methods and spirit of the science, led to a sympathetic interest in its progress, and prepared to receive intelligently, and greet cordially, its future advances” (Chamberlin and Salisbury 1904, iii). The work was originally designed to fill two volumes, the first of which would involve “a consideration of the principles which govern the activity of geological agencies,” and the second “the history of past ages.” But eventually the historical part was divided into two volumes, allowing the complete work to swell to more than 2,000 pages. (Introductory textbooks were not for the faint of heart!)
Not surprisingly, the theme of diastrophism plays throughout Geology. On just the second page of Volume I, Chamberlin and Salisbury identify “[t]hree sets of processes, now in operation on the surface of the lithosphere,” which have “given rise to most of the details of its configuration, and even many of its larger features.” These are diastrophism, vulcanism, and gradation (roughly, erosion and sedimentary deposition). Of these, the most important is diastrophism, which “includes all crustal movements, whether slow or rapid, gentle or violent, slight or extensive.” It receives its most systematic treatment in Chapter 9, which begins:
The body of the earth is subject to an infinite variety of movements, ranging from the almost inconceivably rapid to the almost imperceptibly slow, and from the almost immeasurably minute to the enormously massive. (Chamberlin and Salisbury 1904, 526)
All these movements are diastrophic, but for practical purposes, they can be divided into two categories: the “minute and rapid,” of which the major example is earthquakes, and the “slow and massive.” Included under the heading of “slow and massive movements” are the “great periodic movements,” which comprise mountain-forming movements, plateau-forming movements, and continent-forming movements. These are the “deep-seated body adjustments” of which Chamberlin would speak in 1909, especially the mountain- and plateau-forming movements. (Continent-forming movements were thought to be confined to the early part of earth’s history.) They are the great pacemakers of geological time, the pulse-beat of the solid earth.
It is worth quoting at length Chamberlin and Salisbury’s remarks under the heading “Fundamental conceptions [of diastrophism]”:
The existence of any land at all is dependent on the inequalities of the surface and of the density of the lithosphere, for if it were perfectly spheroidal and equidense, the hydrosphere would cover it completely to a depth of about two miles. Not only are inequalities necessary to the existence of land, but these inequalities must be renewed from time to time, or the land area would soon, geologically speaking, be covered by the sea. The renewal has been made again and again in geological history by movements that have increased the inequalities in the surface of the lithosphere. With each such movement, apparently, the oceans have withdrawn more completely within the basins, and the continents have stood forth more broadly and relatively higher, until again worn down. This renewal of inequalities appears to have been, in its great features, a periodic movement, recurring at long intervals. In the intervening times, the sea has crept out over the lower parts of the continents, moving on steadily and slowly toward their complete submersion, which would inevitably have been attained if no interruption had checked and reversed the process. These are the great movements of the earth, and in them lies, we believe, the soul of geologic history and the basis for its grand divisions… At the same time, there have been numerous minor surface movements in almost constant progress. (Chamberlin and Salisbury 1904, 539)
How many students read this passage can only be guessed at, but given that the book went through two editions and was later abridged as A College Text-book of Geology (and other similar titles), the number is likely very large.*
[* These abridgements were in print for twenty years, from 1909 to 1929. The second and final edition of Geology was published in 1907.]
The “great nebula in Andromeda,” which, Chamberlin and Salisbury observe, “has sometimes been suspected to be in reality a stellar system outside our own,” but which they regard as a great cloud of planetesimal bodies. It was the infall of these cold planetesimal bodies that Chamberlin held to be responsible for the origin of planets and their growth by accretion
The other thing to mention about Chamberlin and Salisbury’s Geology is the prominent place it gives to the planetesimal hypothesis. This began as an origin story for the earth to contrast with the ailing nebular hypothesis and grew into an organizing framework large enough to encompass even periodic diastrophism. Against the nebular hypothesis, Chamberlin argued that the sun and planets did not coalesce out of a spinning gaseous nebula, first forming a series of rings around a central body, and later a series of planets around a star. Instead, the photo-planetary material was ejected from the sun early in its history, perhaps in virtue of a close encounter with another stellar body. Anyway, by the time the material that would form that planets began to coalesce, it was cold, not hot; and while the planet would later heat up due to gravitational shrinkage, it would remain throughout a solid rocky mass, not (e.g.) a solid rind wrapping a hot fluid interior (Chamberlin and Moulton 1909).
So much for the origin of the earth. But the planetesimal hypothesis also sought to account for the planet’s growth, and by this means the origin of its major features. (Think of things like the differentiation between ocean basins and continents, and the placement of mountain chains.) It’s all too much to get into, but some of the more striking features of the account can be put into a list (following Dott 1992). These include:
the early and permanent differentiation of oceanic and continental regions, each with wedge-like cross sections extending to the earth’s center (in early versions— later the wedges were held to be shallower);
the gravitational “lightening” of the continents by the preferential removal of more basic constituents through weathering;
the sinking of denser sea-floor wedges, which periodically force continental wedges upward;
the gradual accumulation of stresses among wedges that are relieved quickly and periodically; and
the concentration of lateral movements at continental margins, causing the crustal folding and faulting seen in mountain chains.
“Diagram intended to illustrate the evolution of the ocean basins under the planetesimal hypothesis” (original caption title). The Roman numerals around the bottom indicate times, with ‘I’ being the earliest and ‘III’ the latest. In Chamberlin and Salisbury’s words, “I represents an early stage in the evolution of the hydrosphere when it was largely subterranean, being held in the porous zone and only appearing at the surface in the volcanic pits developed by explosive vulcanism of the supposed lunar type.” Notice the continent gradually rising at C’ and C”, and the ocean basins deepening and becoming interconnected at B’ and B”.
The whole business is far removed from the work that made Chamberlin’s name: a detailed study of Wisconsin’s glacial landscape, including the Kettle Moraine. But for Chamberlin it all hung together; the flow of giant glaciers, the jostling of crustal wedges, the crumpling of mountains along great arcs, and the very nativity of the solid earth. It was a dizzying climax for a man who had begun his career as a high school science teacher in south-central Wisconsin. And yet it had followed an intelligible trajectory. From Beloit to the world.
References
Arrhenius, S. 1896. On the influence of carbonic acid in the air upon the temperature of the ground. Philosophical Magazine and Journal of Science 41:237–276.
Chamberlin, T. C. 1883. Geology of Wisconsin: (1883) pt. I. General geology. Wisconsin. Geological Survey.
Chamberlin, T. C. 1897. The method of multiple working hypotheses. Journal of Geology 5:837–848.
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