Evidence for the movement of continents on tectonic plates is now extensive. Similar plant and animalfossilsare found around the shores of different continents, suggesting that they were once joined. The fossils ofMesosaurus, a freshwater reptile rather like a small crocodile, found both inBrazilandSouth Africa, are one example; another is the discovery of fossils of the landreptileLystrosaurusinrocksof the same age at locations inAfrica,India, andAntarctica.[37]There is also living evidencethe same animals being found on two continents. Someearthwormfamilies (e.g. Ocnerodrilidae, Acanthodrilidae, Octochaetidae) are found in South America and Africa, for instance.The complementary arrangement of the facing sides of South America and Africa is obvious, but is a temporary coincidence. In millions of years,slab pullandridge-push, and other forces oftectonophysics, will further separate and rotate those two continents. It was this temporary feature which inspired Wegener to study what he defined as continental drift, although he did not live to see his hypothesis generally accepted.Widespread distribution ofPermo-Carboniferousglacial sediments in South America, Africa, Madagascar, Arabia, India, Antarctica and Australia was one of the major pieces of evidence for the theory of continental drift. The continuity of glaciers, inferred from orientedglacial striationsand deposits calledtillites, suggested the existence of the supercontinent ofGondwana, which became a central element of the concept of continental drift. Striations indicated glacial flow away from the equator and toward the poles, based on continents' current positions and orientations, and supported the idea that the southern continents had previously been in dramatically different locations, as well as being contiguous with each other.[14]Works cited[edit]Continental drift was a theory that explained how continents shift position on Earth's surface. Set forth in 1912 by Alfred Wegener, a geophysicist and meteorologist, continental drift also explained why look-alike animal and plant fossils, and similar rock formations, are found on different continents.Wegener thought all the continents were once joined together in an "Urkontinent" before breaking up and drifting to their current positions. But geologists soundly denounced Wegener's theory of continental drift after he published the details in a 1915 book called "The Origin of Continents and Oceans." Part of the opposition was because Wegener didn't have a good model to explain how the continents moved apart.Though most of Wegener's observations about fossils and rocks were correct, he was outlandishly wrong on a couple of key points. For instance, Wegener thought thecontinentsmight have plowed through the ocean crust like icebreakers smashing through ice.There's an irony that the key objection to continent drift was that there is no mechanism, and plate tectonics was accepted without a mechanism," to move the continents, said Henry Frankel, an emeritus professor at the University of Missouri-Kansas City and author of the four volume "The Continental Drift Controversy" (Cambridge University Press, 2012).Although Wegener's "continental drift" theory was discarded, it did introduce the idea of moving continents to geoscience. And decades later, scientists would confirm some of Wegener's ideas, such as the past existence of a supercontinent joining all the world's landmasses as one.Pangaeawas a supercontinent that formed roughly 300 million years ago, and was responsible for the fossil and rock clues that led Wegener to his theory. [Have There Always Been Continents?]The incredible shrinking plantWhen Wegener proposed continental drift, many geologists were contractionists. They thought Earth's incredible mountains were created because our planet was cooling and shrinking since its formation, Frankel said. And to account for the identical fossils discovered on continents such as South America and Africa, scientists invoked ancient land bridges, now vanished beneath the sea.Researchers argued over the land bridges right up until the plate tectonics theory was developed, Frankel said. For instance, as geophysicists began to realize that continental rocks were too light to sink down to the ocean floor, prominent paleontologists instead suggested that the similarities between fossils had been overestimated, Frankel said.Plate tectonicsis the widely accepted theory that Earth's crust is fractured into rigid, moving plates. In the 1950s and 1960s, scientists discovered the plate edges through magnetic surveys of the ocean floor and through the seismic listening networks built to monitor nuclear testing. Alternating patterns of magnetic anomalies on the ocean floor indicatedseafloor spreading, where new plate material is born. Magnetic minerals aligned in ancient rocks on continents also showed that the continents have shifted relative to one another.Evidence for continental driftA map of the continents inspired Wegener's quest to explain Earth's geologic history. Trained as a meteorologist, he was intrigued by the interlocking fit of Africa's and South America's shorelines. Wegener then assembled an impressive amount of evidence to show that Earth's continents were once connected in a single supercontinent.Wegener knew that fossil plants and animals such asmesosaurs, a freshwater reptile found only South America and Africa during the Permian period, could be found on many continents. He also matched up rocks on either side of the Atlantic Ocean like puzzle pieces. For example, the Appalachian Mountains (United States) and Caledonian Mountains (Scotland) fit together, as do the Karroo strata in South Africa and Santa Catarina rocks in Brazil.Despite his incredible evidence for continental drift, Wegener never lived to see his theory gain wider acceptance. He died in 1930 at age 50 of a probable heart attack while on a scientific expedition in Greenland.Additional resources The Wegener Diaries: A virtual exhibition on Alfred Wegener's expeditions to Greenland between 1906 and 1931. Plate tectonics animations: Watch the continents drift to their present positions, provided by the U.S Geological Survey. Ancient Blind Snakes Hitched Ride on Drifting Continents

Wegener and his CriticsSince his ideas challenged scientists in geology, geophysics, zoogeography and paleontology, it demonstrates the reactions of different communities of scientists. These reactions eventually shut down serious discussion of the concept. The geologist Barry Willis summed it up best:further discussion of it merely incumbers the literature and befogs the mind of fellow students.The students' minds would not be befogged. The world had to wait until the 1960's for a wide discussion of the Continental Drift Theory to be restarted.Why the extreme reaction? Wegener did not even present Continental Drift as a proven theory. He knew he would need more support to convince others. His immediate goal was to have the concept openly discussed. These modest goals did not spare him. His work crossed disciplines. The authorities in the various disciplines attacked him as an amateur that did not fully grasp their own subject. More importantly however, was that even the possibility of Continental Drift was a huge threat to the authorities in each of the disciplines.Radical viewpoints threaten the authorities in a discipline. Authorities are expert in thecurrentview of their discipline. A radical view could even force experts to start over again. One of Alfred Wegener's critics, the geologist R. Thomas Chamberlain, suggested just that :"If we are to believe in Wegener's hypothesis we must forget everything which has been learned in the past 70 years and start all over again."He was right.Continental Drift Theory:Building the CaseIn spite of all the criticism, Wegener was able to keep Continental Drift part of the discussion until his death. He knew that any argument based simply on the jigsaw fit of the continents could easily be explained away. To strengthen his case he drew from the fields of geology, geography, biology and paleontology. Wegener questioned why coal deposits, commonly associated with tropical climates, would be found near the North Pole and why the plains of Africa would show evidence of glaciation. Wegener also presented examples where fossils of exactly the same prehistoric species were distributed where you would expect them to be if there had been Continental Drift (e.g. one species occurred in western Africa and South America, and another in Antartica, India and central Africa)[_1_]. The graphic below shows the striking distribution of fossils on the different continents.

Wegener used an Alexander duToit graphic to demonstrate the uncanny match of geology between eastern South America and western Africa.

Continental Drift Theory:The Fatal FlawThe picture painted of Alfred Wegener's contemporaries might not be fair. One would expect scientists to resist ideas that challenged their life's work. It doesn't explain all of the criticism. There were alternatives. To explain the unusual distribution of fossils in the Southern Hemisphere some scientists proposed there may once have been a network of land bridges between the different continents. To explain the existence of fossils of temperate species being found in arctic regions, the existence of warm water currents was proposed. Modern scientists would look at these explanations as even less credible than those proposed by Wegener, but they did help to preserve the steady state theory.New theories often have rough edges. Wegener did not have an explanation for how continental drift could have occurred. He proposed two different mechanisms for this drift. One was based on the centrifugal force caused by the rotation of the earth and another a 'tidal argument' based on the tidal attraction of the sun and the moon. These explanations could easily be proven inadequate. They opened Wegener to ridicule because they were orders of magnitude too weak. Wegener really did not believe that he had the explanation for the mechanism, but that this should not stop discussion of a hypothesis. Wegener's contemporaries disagreed. A major conference was held by the American Association of Petroleum Geologists in 1926 that was critical of the theory. Alfred Wegener died a few years later. With his death, the Continental Drift Theory was quietly swept under the rug. The existing theories of continent formation were allowed to survive, with little challenge until the 1960's.Wegener and DarwinThe main problem with Wegener's hypothesis of Continental Drift was the lack of a mechanism. He did not have an explanation for how the continents moved. Did this justify the strong reactions to his work? Charles Darwin was missing a mechanism for the inheritance of beneficial traits when he published theOrigin of Speciesin 1859. Darwin had amassed a huge amount of evidence that supported some type of adaptive process that contributed to the evolution of new species. He argued that with the natural variations that occur in populations, any trait that is beneficial would make that individual more likely to survive and pass on the trait to the next generation. If enough of theseselectionsoccured on different beneficial traits you could end up with completely new species. But he did not have a mechanism for how the traits could be preserved over the succeeding generations. The dominant theory of inheritance at the time was that the traits of the parents wereblendedin the offspring. But this would mean that any beneficial trait would be diluted out of the population within a few generations. This is because most of the blending over the next generations would be with individuals that did not have the trait.The lack of a mechanism to preserve traits didn't seem a problem. Within 5 years, Oxford University was teaching Darwin's theory as fact. The Oxford texts stated, "Though evidence might be required to show that natural selection accounts for everything ascribed to it, yet no evidence is required to show that natural selection has always been going on, is going on now, and must ever continue to go on. Recognizing this is ana prioricertainty, let us contemplate it under its two distinct aspects." At Oxford, evolution by natural selection had gone from hypothesis toa prioricertainty in the space of 5 years. Many in the scientific community simply chose to ignore the lack of mechanism. Wegener had no such luck with his own theory.[_2_].The mechanism of inheritance was explained shortly after the Origin of Species was published. It was ignored. In 1865, an obscure Augustinian monk from Moldavia presented a paper to the Natural History Society of Brunn where he discussed the results of experiments on pea plants. The results presented by this monk, Gregor Mendel, pointed to traits being inherited 'whole' (also known as particulate inheritance), and that certain traits (recessive traits) that disappear in one generation can reappear in a following generation (seeMendel and Evolution). This would have gone a long way in plugging at least one hole in the Darwin's theory. Mendel's work was largely ignored until about 1900. Shortly afterward it was incorporated into our modern view of evolution known as the 'modern synthesis'.Darwin's theory had another problem. His theory proposed a gradual evolution through successive generations. The fossil record didn't co-operate. There seemed to be a 'explosion' of different life-forms over a relatively short time span (in geologic terms) in the early Cambrian period. There also didn't seem to be any transitional forms of life preceding these species. This eventually became known as theCambrian Explosion. Darwin himself recognized this as a serious issue with his theory and he discussed it in theOrigin of Species. Darwin explained away the problem as a problem with the fossil record and not with his theory. Over the course of the twentieth century, a much better picture of the fossil record of both the Cambrian and Pre-Cambrian eras was developed. The new discoveries made the problem worse. Much worse. In the early twentieth century, the American paleontologist, Charles Walcott, discovered and excavated the Burgess Shale in British Columbia, Canada. He found 65,000 more specimens of early Cambrian life, many of which were complex multi-celled animals. At the time there still was no evidence of transitional forms in the pre-Cambrian. Only recently have they started discovering isolated examples of moderately complex multi-celled animals from the Pre-Cambrian. This still doesn't explain the step-change in the diversity of life-forms in the Cambrian.Wegener and GalileoWegener also shares much in common with Galileo. Wegener probably had at least as strong a case for Continental Drift in 1929 as Galileo had for the Copernican model in 1633. Galileo's problems over the Copernican Model are usually presented as a conflict with the Church, and not a conflict with other scientists (seeGalileo's Battle for the Heavens). Most discussions do not even mention the main problems associated with the Copernican model. It was a scientific controversy with many parallels to the Continental Drift controversy.Galileo had his own 'tidal argument' ; one that was even more embarassing than Wegener's. Galileo argued that the tides were caused by the sun. How could a great scientist who had spent his youth less than 20 kilometres from the sea be so wrong about tides! He presented an argument for Copernicism based on there only being 1 tide per day and where the tides cycle over the year and not over a month. While it took a noted geologist to show that Wegener's tidal argument was ridiculous, Galileo's tidal argument could be proven wrong by anyone living near the sea.The tidal argument wasn't the only problem with Galileo's defense of Copernicism. Wegener's critics never presented strong arguments that Continental Drift couldn't have happened. They did show that themechanismthat Wegener suggested was driving Continental Drift was inadequate. The scientists of Galileo's day did have scientifically valid reasons to doubt a moving earth. A moving earth required that a phenomenon known asstellar parallax(seeCopernicism and Stellar Parallax) would be observed . No one in Galileo's day or for two centuries after his death was able to observe this phenomenon.Another argument against Copernicism was very simple; the data didn't support it! By the time of the Galileo Affair, there was 80 years of data comparing the performance of Copernican-based tables (Prutenic) and Ptolemaic-based tables (Alphonsine). In 1551, only 8 years after Copernicus's death, the Prutenic tables were developed from the Copernican model to predict the positions of stars and planets. It didn't seem that one was much better than the other. A reasonable conclusion based on this experience is that if the Ptolemaic was wrong, then the Copernican was not right. Today we know these scientists were right to doubt the performance of the Copernican model. Modern statistical analyses shows little difference in performance between the two models[_3_]. It is the Keplerian system of planetary motion that is taught in schools, not the Copernican or the Ptolemaic. Galileo knew of Kepler's model and had never accepted it during his lifetime.Winners, Losers, Insiders, OutsidersWhy was one theory above was quickly accepted, another quickly dismissed, and the other a cause of controversy amongst scientists. Analysis from a strictly scientific basis won't help. All of the theories had strengths and weaknesses. We might have to look beyond the world of ideas to the world of people, events and things.Darwin, was the ultimate insider in English scientific circles. His grandfather, Erasmus, was an early student of evolution and his half-cousin, Francis Galton, was a noted statistician who was considered the father of eugenics. Being part of the Wedgewood-Darwin clan meant having no worries about money and established connections in the scientific world. When evolution by natural selection was under attack, Darwin could enlist the efforts of a Who's Who of mid-nineteenth century English science. The most famous of the early defenses of Darwinism was not by Darwin himself but by the famous biologist, Thomas Huxley and the social philosopher, Herbert Spencer. Darwin's ideas were adopted by supporters of laissez-faire capitalism. "Survival of the fittest" gave an ethical dimension to the no-holds barred capitalism of the late nineteenth century. Andrew Carnegie, the fabulously rich robber baron, used elements of evolution by natural selection to justify his own ruthless business practices.Alfred Wegener wasn't an insider. He had to earn all his allies. His few allies (duToit and Holmes) were no match for his many skeptics. His place of birth may have played a role. Anti-German bias was very strong in the 1910's and 1920's in English-speaking countries. This resulted in German-based names for cities, streets, foods and animal breeds being changed to names that were more 'patriotic'. Being German wasn't Wegener's only problem; the arguments he used to support his hypothesis crossed into disciplines that were not his specialty. He was trained as an astronomer and worked as a meterologist. He was considered an outsider for a reason.The early history of the Copernican model is an example of the effect of outside forces. The publication of Copernicus'de Revolutionibusdrew very little criticism from the Catholic countries. The most serious early criticisms came from the Protestant countries in Europe. The Vatican's interest in the publication had begun 10 years earlier, after a series of lectures given to Pope Clement VII on Copernicus's work. Any doubt of the church's support for Copernicus' work ended with the actual publication. The original publication included a copy of the letter from the Vatican urging him to share his work, a dedication to the pope, and a thank you to a bishop who was an important supporter of his work. The involvement of the church may have muted criticism from academics in the Catholic countries of Europe and encouraged criticism in the Protestant countries. The reverse happened after Galileo's trial in 1633. Galileo was tried for not obeying an order from 1616 to not teach the Copernican theory as true but only as a hypothesis. He was placed under house arrest in his villa in the Tuscan hills just outside Florence (seeGalileo's Battle for the Heavens).Science:A Question of FaithScience depends on facts. It also depends on reason. But fact and reason alone cannot explain how science works. The examples chosen all had some compelling support and serious shortcomings. Part of the answer may lie in the sociology of groups. Another part lies in simple faith: faith that future scientists will address a theory's shortcomings. Darwin needed an explanation for the Cambrian Explosion and a mechanism for the preservation of traits (seeMendel and Darwin) . Wegener needed a mechanism for Continental Drift. Galileo needed an explanation for the lack of stellar parallax and the poor performance of his model (seeGalileo's Battle for the Heavens) . It is not only the community that requires faith. The champions of these new theories require faith in their ideas, even when facts contradict their hypotheses. In each case above, there were facts which when combined with the current assumptions of the time clearly contradicted their hypotheses. None of these scientists let those facts get in the way. Paul Feyerabend, a modern philosopher of science, presents a similar view, where he argues that science is sometimes required to work "against the facts". His key example was how the heliocentric system made less sense than a geocentric system during Galileo's time. One irony missed by discussions of science and religion is how much both depend on faith.

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1. Jordan, R.G, Florida Atlantic University,The Newton Project, http://courses.science.... ,This page provides a good summary of Wegeners problems with the noted scientists of his time. It also details some of the arguments he used to support his hypothesis...back

2. Spencer, Herbert, Williams and Norgate,The Principles of Biology, ,The textbook mentioned 'natural selection' no less than 25 times. Herbert Spencer, the author, had been an important defender of Darwin when Origin of Species was first published. Principles of Biology was the biology text at University of Oxford between 1864 and 1867...back

3. Babb, Stanley E.,, Isis, Sept. 1977,Accuracy of Planetary Theories, Particularly for Mars,, , pp. 426-34In this article Stanley Babb compares the predictions of the Copernican and Ptolemaic models against the actual planetary positions using computer-based statistical analysis. The results did not show much difference between the two systems, but the earth-centred system (the Ptolemaic) did perform better for planets such as Mars...backS