What Evidence Did Alfred Wegener Use to Develop His Theory of Continental Drift

Alfred Wegener (1880-1930)

"Scientists still practice non appear to sympathise sufficiently that all world sciences must contribute show toward unveiling the state of our planet in earlier times, and that the truth of the thing can but be reached by combing all this evidence. . . It is only past combing the information furnished by all the world sciences that we can hope to determine 'truth' hither, that is to say, to discover the pic that sets out all the known facts in the best organization and that therefore has the highest degree of probability. Further, we have to be prepared always for the possibility that each new discovery, no matter what scientific discipline furnishes it, may change the conclusions we depict."
Alfred Wegener. The Origins of Continents and Oceans (4th edition)

Some truly revolutionary scientific theories may accept years or decades to win general acceptance among scientists. This is certainly truthful of plate tectonics, one of the most of import and far-ranging geological theories of all time; when first proposed, it was ridiculed, but steadily accumulating evidence finally prompted its acceptance, with immense consequences for geology, geophysics, oceanography, and paleontology. And the homo who first proposed this theory was a vivid interdisciplinary scientist, Alfred Wegener.

Born on November i, 1880, Alfred Lothar Wegener earned a Ph.D in astronomy from the Academy of Berlin in 1904. Nevertheless, he had always been interested in geophysics, and as well became fascinated with the developing fields of meteorology and climatology. During his life, Wegener made several key contributions to meteorology: he pioneered the use of balloons to track air circulation, and wrote a textbook that became standard throughout Germany. In 1906 Wegener joined an trek to Greenland to study polar air apportionment. Returning, he accepted a post every bit tutor at the University of Marburg, taking time to visit Greenland again in 1912-1913. (The to a higher place photograph of Wegener was taken during this trek). In 1914 he was drafted into the High german ground forces, but was released from gainsay duty after existence wounded, and served out the state of war in the Ground forces weather forecasting service. Subsequently the state of war, Wegener returned to Marburg, but became frustrated with the obstacles to advocacy placed in his way; in 1924 he accepted a specially created professorship in meteorology and geophysics at the University of Graz, in Austria. Wegener made what was to exist his concluding expedition to Greenland in 1930. While returning from a rescue expedition that brought food to a party of his colleagues camped in the eye of the Greenland icecap, he died, a twenty-four hour period or 2 later on his fiftieth birthday.

While at Marburg, in the autumn of 1911, Wegener was browsing in the university library when he came across a scientific paper that listed fossils of identical plants and animals constitute on opposite sides of the Atlantic. Intrigued by this information, Wegener began to await for, and find, more cases of similar organisms separated by great oceans. Orthodox scientific discipline at the time explained such cases by postulating that state bridges, now sunken, had once connected far-flung continents. Only Wegener noticed the close fit between the coastlines of Africa and Southward America. Might the similarities among organisms exist due, not to land bridges, but to the continents having been joined together at one time? As he afterward wrote: "A confidence of the fundamental soundness of the idea took root in my mind."

Such an insight, to exist accepted, would require large amounts of supporting bear witness. Wegener establish that large-scale geological features on separated continents ofttimes matched very closely when the continents were brought together. For example, the Appalachian mountains of eastern Northward America matched with the Scottish Highlands, and the distinctive rock strata of the Karroo organisation of South Africa were identical to those of the Santa Catarina system in Brazil. Wegener likewise found that the fossils found in a certain identify often indicated a climate utterly different from the climate of today: for example, fossils of tropical plants, such every bit ferns and cycads, are plant today on the Arctic island of Spitsbergen. All of these facts supported Wegener's theory of "continental drift." In 1915 the first edition of The Origin of Continents and Oceans, a book outlining Wegener'southward theory, was published; expanded editions were published in 1920, 1922, and 1929. Most 300 meg years ago, claimed Wegener, the continents had formed a single mass, called Pangaea (from the Greek for "all the Earth"). Pangaea had rifted, or divide, and its pieces had been moving away from each other ever since. Wegener was not the starting time to suggest that the continents had once been connected, but he was the beginning to present extensive evidence from several fields.

Mod reconstruction of Pangaea, ca. 255 million years agone -- click to view a much larger version of this map!

Reaction to Wegener's theory was almost uniformly hostile, and often exceptionally harsh and scathing; Dr. Rollin T. Chamberlin of the Academy of Chicago said, "Wegener's hypothesis in general is of the footloose type, in that information technology takes considerable liberty with our globe, and is less bound by restrictions or tied downwardly by awkward, ugly facts than most of its rival theories." Part of the problem was that Wegener had no disarming mechanism for how the continents might movement. Wegener thought that the continents were moving through the earth's crust, similar icebreakers plowing through ice sheets, and that centrifugal and tidal forces were responsible for moving the continents. Opponents of continental drift noted that plowing through oceanic crust would distort continents beyond recognition, and that centrifugal and tidal forces were far too weak to move continents -- one scientist calculated that a tidal force potent plenty to move continents would crusade the Earth to terminate rotating in less than 1 year. Some other problem was that flaws in Wegener'southward original data caused him to make some incorrect and outlandish predictions: he suggested that Northward America and Europe were moving autonomously at over 250 cm per year (about ten times the fastest rates seen today, and nearly a hundred times faster than the measured charge per unit for Northward America and Europe). There were scientists who supported Wegener: the South African geologist Alexander Du Toit supported information technology as an caption for the shut similarity of strata and fossils between Africa and South America, and the Swiss geologist Émile Argand saw continental collisions equally the best caption for the folded and buckled strata that he observed in the Swiss Alps. Wegener'due south theory found more scattered back up after his death, just the majority of geologists continued to believe in static continents and country bridges.

What prompted the revival of continental drift? In big part information technology was increased exploration of the Earth's chaff, notably the bounding main flooring, offset in the 1950s and continuing on to the nowadays day. By the late 1960s, plate tectonics was well supported and accepted by most all geologists. We at present know that Wegener'due south theory was wrong in one major betoken: continents exercise not turn through the body of water floor. Instead, both continents and sea flooring form solid plates, which "float" on the asthenosphere, the underlying stone that is under such tremendous estrus and pressure that it behaves equally an extremely viscous liquid. (Incidentally, this is why the older term "continental drift" is not quite accurate -- both continents and oceanic crust motility.)

Since Wegener'due south twenty-four hours, scientists have mapped and explored the nifty organization of oceanic ridges, the sites of frequent earthquakes, where molten stone rises from below the crust and hardens into new crust. We now know that the further away y'all travel from a ridge, the older the crust is, and the older the sediments on top of the crust are. The clear implication is that the ridges are the sites where plates are moving apart (click on the picture at the left to run into a map of the age of the body of water crust). Where plates collide, great mountain ranges may be pushed up, such as the Himalayas; or if ane plate sinks below another, deep oceanic trenches and bondage of volcanoes are formed. Earthquakes are by far nigh mutual along plate boundaries and rift zones: plotting the location of earthquakes allows seismologists to map plate boundaries and depths (click on the picture at the right to view a map of convulse epicenters). Paleomagnetic data have allowed united states to map past plate movements much more precisely than before. Information technology is even possible to measure the speed of continental plates extremely accurately, using satellite engineering. Withal, Wegener's basic insights remain audio, and the lines of bear witness that he used to back up his theory are nevertheless actively being researched and expanded.

The images of the body of water floor on this folio were provided by the Earth Data Heart A of the National Geophysical Information Heart/ NOAA.

There are a number of splendid World wide web sites dealing with the modern theory of plate tectonics. Hither is a modest sample:

UCMP's own Plate tectonics exhibit.
Plate Tectonics Lesson, from Volcano World

Finally, information technology seems appropriate to mention the Alfred Wegener Institute, the German national research centre for polar and marine inquiry, carrying on Wegener'due south tradition of interdisciplinary earth scientific discipline.