Background

Wegener and his Precursors

Reaction to the Hypothesis

Plate Tectonics

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Wegener and his Precursors

Patrick Hurley cited early speculations of continental drift as far back as Francis Bacon in 1620 (Hurley, 1968), but these early ideas were not followed up. In 1912 Alfred Wegener (1880-1930) read a paper before the Geological Association at Frankfurt-am-Main, Germany, in which he described how the continents were once joined together as one supercontinent and then drifted apart to their present positions. In 1915 Wegener wrote a book about the origins of the continents and oceans. The book was translated into English in 1924, (Wegener). In the 19th century the Austrian geologist Eduard Suess (1831-1914) had fitted the continents together to form what he called "Gondwanaland", (Hurley, 1968). Frank Taylor, an American, had published similar ideas in 1910 (Taylor). Earlier, Fisher, a British geologist, had proposed a mechanism to explain why continental coastlines seemed to fit like pieces of a jigsaw puzzle, (Fisher). Fisher was the author of the first textbook in geophysics and the first leading scholar since Humboldt to publish such ideas .

Until his death in 1930 during an expedition to Greenland, Wegener developed and published his ideas on continental drift. He was the first scientist to spend a substantial part of his career to develop an hypothesis to account for geological, climatic, and fossil evidence that the continents were once joined.

Further reading: Plate tectonics: The Rocky History of an Idea. The supercontinent has been renamed Pangea. Gondwanaland is now called Gondwana, one component of the supercontinent Pangea, formed in Permian to Triassic time (200-300 million years ago) by collision of Gondwana with Laurasia. The name "Gondwana" has been preserved in honor of the pioneer scientists who developed the hypothesis, but altered to reflect later discoveries.

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Reaction to the Hypothesis

Reginald Daly was an exception. Professor of Geology at Harvard from 1912 until his retirement in 1942, and president of the Geological Society of America in 1932, Daly had wide international experience. Born in Canada, he studied at Toronto, Heidelberg, Paris, and Harvard Universities. He included the hypothesis of continental drift in his courses and may have been the only teacher in America who read Wegener's works (Oreskes, 1999). Daly was critical of continental drift, but he treated the hypothesis seriously.

Analysis of the journal, Science, shows that during the 40-year period 1923-1963 there was about one article per year containing the words "continental drift", (Graph). This is misleading, because many of these articles were trivial, such as announcements or short book reviews. A cursory review of the articles themselves suggests that a non-trivial article was published in Science once in five years. In effect, Wegener's hypothesis was ignored.

A browse of the Science articles indicates that Wegener's hypothesis was rejected, but not always treated with hostility. For example, Ralph Chaney (1940) firmly rejected the hypothesis based on a study of trees on both sides of the Atlantic Ocean. Chaney concluded that the north-south movement of forests rather than the movement of continents accounted for differences in the fossil record, "We conclude that the evidence of Eocene floras, made up of close relatives of living trees whose climatic requirements are well known, strongly refutes the hypothesis of continental drift during later geologic time. The question of drift at an earlier date in earth history must be answered by reference to the nature and distribution of plant fossils in older rocks, and need not be considered here." (Chaney dated the Eocene to 60 million years ago, an improvement over the date of 20 million years available to Wegener in 1929.) Map

A modern estimate of separation of North America and Europe since the beginning of the Eocene would be less than 1,500 kilometers (900 miles), based on the rate shown in Press and Siever (1998). Chaney's study was not capable of testing Wegener's hypothesis of continental drift because his methodology was too crude to identify the effects of a small differences in either latitude or longitude. Chaney was unaware of this and, by refusing to consider drift at an earlier date, failed to discover the error in Wegener's timing.

Wegener's map of the Eocene shows the two continents nearly in contact (Wegener, 1929; trans. 1966), thus the timespan Wegener used was too short, 20 million years instead of 100 million. Later studies have shown that some parts of Atlantic opened up during the Cretaceous, over 100 million years ago (Stanley, 1992). Other parts of the Atlantic opened earlier and later (Hurley, 1968). Wegener may have overestimated the amount of separation. Wegener's errors in timing and in distance affected his calculation of the rate of separation. The rate he calculated was about 25 times too big, about 600 millimeters (24 inches) per year, instead of 23 millimeters (one inch), (Press and Siever, 1998). Precise measurement now indicates that Europe and North America are separating by about one millimeter in two weeks (Stanley, 1992). This is about the same as the growth rate of fingernails.

"The coup de grace was administered by Bailey Willis and Charles Schuchert in coordinated articles published in the Geological Society of America Bulletin in 1932." (Newman, 1995). These articles explained similarities in fossils on widely separated continents by postulating land bridges between the continents. The land bridges were an alternative to continental drift, but they no longer existed. As Schuchert wrote in his letter to Willis, "Remember, I am not raising these lands—they are primordial—I am only pointing out their existence and seeking among you geomorphologists a way to get rid of them....", (Oreskes, 1999). Both Willis and Schuchert were familiar with Arthur Holmes's theory that heat from radioactivity and convection could drive plate movement. (What we now call plates Willis had called blocks in previous work.) Letters between Willis and Schuchert shows that both were striving to devise an alternative to continental drift. Schuchert was not comfortable with their collaboration, writing "...we live or die together, nicht wahr?". As a paleontologist and historical geologist, Schuchert was an expert in correlating rock strata using fossil evidence found in sedimentary rocks. But where the postulated land bridges once lay there are now islands of granite and basalt, igneous rocks without fossils. There was no evidence that the land bridges had existed and if they had that they had provided links between ancient plant and animal communities. Why Schuchert agreed to combine forces with Willis is not clear (Oreskes, 1999).

Review of the literature shows that some scholars who rejected the hypothesis were using arguments that were not well-founded in the science of their own times, especially aspects of isostacy (Oreskes, 1999; 2001).

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Plate Tectonics

The hypothesis of continental drift was rejected and later accepted in modified form as the theory of plate tectonics. The history of this hypothesis and theory may help illuminate how theory and method interact in science (Oreskes, 1999). Continental drift as Wegener set it out seems to have two components:

1. Sets of observations indicating that:

  • the continents were once joined as one super-continent that split apart

  • the relative positions of continents and oceans are still changing

2. Specific theories that attempt to explain how this rearrangement came about and continues to operate.

The first component of Wegener's hypothesis has been confirmed, except for the rates of movement, which are much less than what Wegener estimated. The second component of the hypothesis has been replaced by the theory of plate tectonics. In effect, Wegener restated what others had suggested before him, adding a timeframe and suggesting a displacement force, neither of which are accepted today.

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