The most common explanation given in textbooks and college classrooms for the failure of continental drift is that it lacked a mechanism. It offered no compelling way to move a continent. Though many geologists, both during the debate about continental drift and afterward, have echoed this claim, it seems an inadequate explanation. Other novel (and sometimes equally strange) observations have achieved widespread acceptance without a clear cause: Gravity, ice ages, quantum mechanics. Even the Alpine thrust sheets that proved the first chink in the armor of contraction theory were widely accepted even though no one could explain how they formed.42 Furthermore, even after Arthur Holmes, a geologist considered to be among the brightest of his generation, developed a model of mantle convection similar to the version now central to the theory of plate tectonics, most geologists did not go back and re-examine the merits of continental drift.43 This suggests that additional factors contributed to its rejection.
In her book The Rejection of Continental Drift, Naomi Oreskes offers a pair of explanations to reconcile American geologists' longstanding opposition to continental drift with their rapid acceptance of plate tectonics in the 1960s. Dismissing arguments that blame the lack of a mechanism or Americans' indifference to theory in the first half of the 1900s, she suggests instead that the underlying cause is epistemic. Wegener's initial presentation of his theory violated certain norms operating in the American geological community. Geologists at this time prized detailed evidence and a careful weighing of alternative hypotheses. Wegener, by contrast, was totally committed to his theory. His zeal may have alienated his American colleagues.44
But Wegener's theory was also caught in a larger tide: the transition of American science from broadly subjective to objective methodologies.45 Spurred by the success of physics in the first years of the twentieth century, previously observation-based fields like geology and biology began to redirect their research into the laboratory. This trend was in full swing in the first half of the 1900s, resulting in a devaluation of old forms of evidence and a corresponding elevation of quantification and measurement. In geology, the change in methods was marked by the waning of field geology and waxing of laboratory studies that used chemical and physical data to place hard constraints on the ages and origins of rocks. Most evidence marshaled by Wegener belonged to the field tradition, allowing his critics to dismiss it as equivocal, incomplete, vague, or, most damning of all, subjective. This perception undermined efforts by geologists like du Toit to use new field evidence to reinforce Wegener's arguments. No matter the extent or quality of the new field evidence, its base nature allowed it to be dismissed outright. By contrast, the geophysical evidence underpinning the plate tectonic revolution of the 1960s was considered novel, numerical, and concrete. Despite the formidable complexity of these data, their perceived certainty shielded them against dismissal and provided a firm foundation upon which to build plate tectonics. The theory of continental drift was perceptive and largely accurate, but could not overcome the diminishing standing of the field tradition from which Wegener made his argument.
Nevertheless, Wegener's theory was pivotal in the development of plate tectonics. Without it, the tectonic revolution could not have succeeded so easily. By the time the key geophysical evidence and arguments for plate tectonics were being published, geologists had had over forty years to consider the practical problems posed by mobile continents and adjust to the oddness of their existence. Many of the issues that troubled Wegener, notably the absence of a mechanism, had already been addressed by geologists studying aspects of continental drift. Finally, the passage of time may have softened scientists' resistance to the unintuitive idea of moving continents. In 1912, Wegener's continents were unforgivably strange; forty years on they could only be less so.
List of Visuals
- The layer of the Earth we live on is broken into a dozen or so rigid slabs (called tectonic plates by geologists) that are moving relative to one another.
United States Geographical Service
- The main types of plate boundaries.
United States Geographical Service (Cross section by José F. Vigil from This Dynamic Planet, a wall map produced jointly by the U.S. Geological Survey, the Smithsonian Institution, and the U.S. Naval Research Laboratory.)
- Distribution of the Glossopteris flora, an important example of a fossil homology.
A.C. Seward, The British Association. Nature, 1771:68 (1903): 556-568
- Isostasy in the Earth's crust. Identical elevation profiles can be explained by differences in (A) the density of the crust, where high elevations occur where rocks are relatively buoyant, or (b) the thickness of the crust, where high elevations are supported by thick roots (like an ice cube).
Graphic by Adam Masur.
- Alfred Wegener in Greenland, 1930 expedition.
Wikipedia: The Free Encyclopedia, Archive of Alfred Wegener Institute
- The locations of certain fossil plants and animals on widely separated continents would form definite patterns if the continents were rejoined.
United States Geographical Service
- Station NIU, Oahu Hawaii, during reobservation of World
Longitude stations. Looking for evidence of continental drift,
but instruments were too crude to measure small earth movements.
C&GS Season's Report Lushene; 2001 National Oceanic & Atmospheric Administration (NOAA). Taken from Proquest's eLibrary.
- Coast and Geodetic Survey Ship PIONEER, in service 1946 - 1966, discovered magnetic striping, the key to plate tectonics.
NOAA Photo Library, Taken from ProQuest's eLibrary.
- Plate motion based on Global Positioning System (GPS) satellite data from NASA JPL. Vectors show direction and magnitude of motion.
Jet Propulsion Laboratory (JPL), NASA
- Bryan Isacks, Jack Oliver, and Lynn R. Sykes,
"Seismology and the New Global Tectonics," Journal of Geophysical
Research 73:18 (1968): 5855-5899.
- Alfred Wegner, The Origin of Continents and Oceans
(Methuen and Co. Ltd., 1924) 13.
- Naomi Oreskes, The Rejection of Continental Drift: Theory
and Method in American Earth Science (Oxford University
Press, 1999) 11. Wegener devotes chapter 4 of his book to fossil
- Wegener 100-101.
- Oreskes 12-14 and 16-17.
- Oreskes 19-20.
- Oreskes 12-14 and 16-17 .
- Oreskes 207-213 and Wegener 17-22.
- Wegener 12-15.
- Oreskes 21-23.
- Oreskes 48-51.
- Oreskes 23.
- Oreskes 23-25.
- Oreskes 37-47.
- Wegener 23-26.
- Wegener 5.
- Wegener 5.
- Wegener 1-4.
- Wegener 160-161.
- Wegener 164-165. Critics of continental drift cited a paradox in Wegener's conception of the ocean floor: How can the ocean floor be weak enough to allow the continents to pass through it yet strong enough to deform the leading edges of the continents? In plate tectonics, plates float on (not through) the mantle substrate.
- Wegener 190-205.
- Wegener 118.
- Anthony Hallam, Great Geological Controversies,
2nd ed. (Oxford University Press, 1989) 147-148.
- Hallam 150.
- Oreskes 292-293.
- Hallam 150 and Oreskes 304-305.
- Wegener 42.
- Hallam 149-150.
- Oreskes 167-177.
- Oreskes 227-236.
- Oreskes 168-170.
- Oreskes 128-193.
- Oreskes 208-219.
- Alexander du Toit, A Geological Comparison of South
America with South Africa (Carnegie Institute of Washington,
- Arthur Holmes, "Radioactivity and Earth Movements," Transactions
of the Geological Society of Glasgow 18 (1931): 559-606.
- Oreskes 268. Hess mentions Holmes's work in his 1961 paper, though he does not cite a specific paper.
- Oreskes 93-99 and 276.
- Harry H. Hess, "A History of Ocean Basins," Petrologic
Studies: A Volume in Honor of A. F. Buddington (Geological
Society of America, 1961): 599-620.
- L. W. Morley and A. Larochelle, "Paleomagnetism as a Means
of Dating Geological Event," Geochronology in Canada
(Royal Society of Canada, 1964) 8: 39-51.
- Hallam 165-166 and Oreskes 265-267.
- F. J. Vine and D. H. Matthews, "Magnetic Anomalies Over
Oceanic Ridges," Nature 201 (1964): 591-592.
- Oreskes 21-23.
- Oreskes 119-120.
- Oreskes, chapter 5.
- Oreskes, chapter 10.