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122-475: Continental drift is the theory , originating in the early 20th century, that Earth's continents move or drift relative to each other over geologic time. The theory of continental drift has since been validated and incorporated into the science of plate tectonics , which studies the movement of the continents as they ride on plates of the Earth's lithosphere . The speculation that continents might have "drifted"

244-545: A fjord by the clergyman of Upernavik , who just happened to be visiting a remote congregation at the time. Later in 1913, after his return Wegener married Else Köppen, the daughter of his former teacher and mentor, the meteorologist Wladimir Köppen . The young pair lived in Marburg , where Wegener resumed his university lectureship. There his two older daughters were born, Hilde (1914–1936) and Sophie ("Käte", 1918–2012). Their third daughter Hanna Charlotte ("Lotte", 1920–1989)

366-721: A hypothesis . If a new theory better explains and predicts a phenomenon than an old theory (i.e., it has more explanatory power ), we are justified in believing that the newer theory describes reality more correctly. This is called an intertheoretic reduction because the terms of the old theory can be reduced to the terms of the new one. For instance, our historical understanding about sound , light and heat have been reduced to wave compressions and rarefactions , electromagnetic waves , and molecular kinetic energy , respectively. These terms, which are identified with each other, are called intertheoretic identities. When an old and new theory are parallel in this way, we can conclude that

488-518: A knowledge transfer where there is a task of translating research knowledge to be application in practice, and ensuring that practitioners are made aware of it. Academics have been criticized for not attempting to transfer the knowledge they produce to practitioners. Another framing supposes that theory and knowledge seek to understand different problems and model the world in different words (using different ontologies and epistemologies ). Another framing says that research does not produce theory that

610-407: A chapter on continental drift, proposing that Earth's mantle contained convection cells which dissipated radioactive heat and moved the crust at the surface. Holmes's proposal resolved the phase disequilibrium objection (the underlying fluid was kept from solidifying by radioactive heating from the core). However, scientific communication in the 1930s and 1940s was inhibited by World War II , and

732-735: A few months: after being wounded twice he was declared unfit for active service and assigned to the army weather service. This activity required him to travel constantly between various weather stations in Germany, on the Balkans , on the Western Front and in the Baltic region . Nevertheless, he was able in 1915 to complete the first version of his major work, Die Entstehung der Kontinente und Ozeane ("The Origin of Continents and Oceans"). His brother Kurt remarked that Alfred Wegener's motivation

854-419: A first step toward being tested or applied in a concrete situation; theorems are said to be true in the sense that the conclusions of a theorem are logical consequences of the axioms. Theories are abstract and conceptual, and are supported or challenged by observations in the world. They are ' rigorously tentative', meaning that they are proposed as true and expected to satisfy careful examination to account for

976-413: A foundation to gain further scientific knowledge, as well as to accomplish goals such as inventing technology or curing diseases. The United States National Academy of Sciences defines scientific theories as follows: The formal scientific definition of "theory" is quite different from the everyday meaning of the word. It refers to a comprehensive explanation of some aspect of nature that is supported by

1098-435: A given subject matter. There are theories in many and varied fields of study, including the arts and sciences. A formal theory is syntactic in nature and is only meaningful when given a semantic component by applying it to some content (e.g., facts and relationships of the actual historical world as it is unfolding). Theories in various fields of study are often expressed in natural language , but can be constructed in such

1220-751: A large amount of observational evidence in support of continental drift, but the mechanism remained a problem, partly because Wegener's estimate of the velocity of continental motion, 250 cm/year, was too high. (The currently accepted rate for the separation of the Americas from Europe and Africa is about 2.5 cm/year.) While his ideas attracted a few early supporters such as Alexander Du Toit from South Africa, Arthur Holmes in England and Milutin Milanković in Serbia, for whom continental drift theory

1342-588: A map of the world and considers carefully the coasts of the three [continents]." In 1889, Alfred Russel Wallace remarked, "It was formerly a very general belief, even amongst geologists, that the great features of the earth's surface, no less than the smaller ones, were subject to continual mutations, and that during the course of known geological time the continents and great oceans had, again and again, changed places with each other." He quotes Charles Lyell as saying, "Continents, therefore, although permanent for whole geological epochs, shift their positions entirely in

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1464-407: A minority of scientific proponents over the decades, the theory of continental drift was largely rejected for many years, with evidence in its favor considered insufficient. One problem was that a plausible driving force was missing. A second problem was that Wegener's estimate of the speed of continental motion, 250 cm/year (100 in/year), was implausibly high. (The currently accepted rate for

1586-476: A now-discredited Expanding Earth theory . Continental drift without expansion was proposed by Frank Bursley Taylor , who suggested in 1908 (published in 1910) that the continents were moved into their present positions by a process of "continental creep", later proposing a mechanism of increased tidal forces during the Cretaceous dragging the crust towards the equator. He was the first to realize that one of

1708-601: A paper in 1911 which criticised the prevalent hypothesis, that a bridge of land once connected Europe and America, on the grounds that this contradicts isostasy . Wegener's main interest was meteorology, and he wanted to join the Denmark-Greenland expedition scheduled for mid-1912. He presented his continental drift hypothesis on 6 January 1912. He analysed both sides of the Atlantic Ocean for rock type, geological structures and fossils. He noticed that there

1830-487: A particular social institution. Most of the following are scientific theories. Some are not, but rather encompass a body of knowledge or art, such as Music theory and Visual Arts Theories. Alfred Wegener Alfred Lothar Wegener ( / ˈ v eɪ ɡ ən ər / ; German: [ˈʔalfʁeːt ˈveːɡənɐ] ; 1 November 1880 – November 1930) was a German climatologist , geologist , geophysicist , meteorologist , and polar researcher . During his lifetime he

1952-493: A penknife without anaesthetic. Twelve of the Greenlanders returned to West camp. On 19 October the remaining three members of the expedition reached Eismitte . Expedition member Johannes Georgi estimated that there were only enough supplies for three at Eismitte , so Wegener and 27 year-old native Greenlander Rasmus Villumsen took two dog sleds and made for West camp. (Georgi later found that he had underestimated

2074-489: A permanent feature of the Earth's surface, rather than them having "changed places" with the continents. Eduard Suess had proposed a supercontinent Gondwana in 1885 and the Tethys Ocean in 1893, assuming a land-bridge between the present continents submerged in the form of a geosyncline , and John Perry had written an 1895 paper proposing that the Earth's interior was fluid, and disagreeing with Lord Kelvin on

2196-477: A position that was both secure and free of administrative duties. He concentrated on physics and the optics of the atmosphere as well as the study of tornadoes . He had studied tornadoes for several years by this point, publishing the first thorough European tornado climatology in 1917. He also posited tornado vortex structures and formative processes . Scientific assessment of his second Greenland expedition (ice measurements, atmospheric optics, etc.) continued to

2318-447: A recursively enumerable set) in which the concept of natural numbers can be expressed, can include all true statements about them. As a result, some domains of knowledge cannot be formalized, accurately and completely, as mathematical theories. (Here, formalizing accurately and completely means that all true propositions—and only true propositions—are derivable within the mathematical system.) This limitation, however, in no way precludes

2440-787: A scientific investigation of the Treysa meteorite . In 1919, Wegener replaced Köppen as head of the Meteorological Department at the German Naval Observatory ( Deutsche Seewarte ) and moved to Hamburg with his wife and their two daughters. In 1921 he was moreover appointed senior lecturer at the new University of Hamburg . From 1919 to 1923 Wegener did pioneering work on reconstructing the climate of past eras (now known as " paleoclimatology "), closely in collaboration with Milutin Milanković , publishing Die Klimate der geologischen Vorzeit ("The Climates of

2562-437: A single textbook. In mathematical logic , a theory has a related but different sense: it is the collection of the theorems that can be deduced from a given set of axioms , given a given set of inference rules . A theory can be either descriptive as in science, or prescriptive ( normative ) as in philosophy. The latter are those whose subject matter consists not of empirical data, but rather of ideas . At least some of

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2684-552: A small set of basic postulates (usually symmetries, like equality of locations in space or in time, or identity of electrons, etc.)—which is capable of producing experimental predictions for a given category of physical systems. One good example is classical electromagnetism , which encompasses results derived from gauge symmetry (sometimes called gauge invariance) in a form of a few equations called Maxwell's equations . The specific mathematical aspects of classical electromagnetic theory are termed "laws of electromagnetism", reflecting

2806-419: A substantial basis for today's model of plate tectonics . Wegener was involved in several expeditions to Greenland to study polar air circulation before the existence of the jet stream was accepted. Expedition participants made many meteorological observations and were the first to overwinter on the inland Greenland ice sheet and the first to bore ice cores on a moving Arctic glacier. Alfred Wegener

2928-481: A technical term in philosophy in Ancient Greek . As an everyday word, theoria , θεωρία , meant "looking at, viewing, beholding", but in more technical contexts it came to refer to contemplative or speculative understandings of natural things , such as those of natural philosophers , as opposed to more practical ways of knowing things, like that of skilled orators or artisans. English-speakers have used

3050-403: A theory of heat as energy replaced it. Also, the theory that phlogiston is a substance released from burning and rusting material was eliminated with the new understanding of the reactivity of oxygen. Theories are distinct from theorems . A theorem is derived deductively from axioms (basic assumptions) according to a formal system of rules, sometimes as an end in itself and sometimes as

3172-404: A theory's content is based on some formal system of logic and on basic axioms . In a deductive theory, any sentence which is a logical consequence of one or more of the axioms is also a sentence of that theory. This is called the received view of theories . In the semantic view of theories , which has largely replaced the received view, theories are viewed as scientific models . A model

3294-496: A vast body of evidence. Many scientific theories are so well established that no new evidence is likely to alter them substantially. For example, no new evidence will demonstrate that the Earth does not orbit around the sun (heliocentric theory), or that living things are not made of cells (cell theory), that matter is not composed of atoms, or that the surface of the Earth is not divided into solid plates that have moved over geological timescales (the theory of plate tectonics) ... One of

3416-419: A way that their general form is identical to a theory as it is expressed in the formal language of mathematical logic . Theories may be expressed mathematically, symbolically, or in common language, but are generally expected to follow principles of rational thought or logic . Theory is constructed of a set of sentences that are thought to be true statements about the subject under consideration. However,

3538-612: A wilderness of ice when the expedition leader and two of his colleagues died on an exploratory trip undertaken with sled dogs . After his return in 1908 and until World War I , Wegener was a lecturer in meteorology, applied astronomy and cosmic physics at the University of Marburg . His students and colleagues in Marburg particularly valued his ability to clearly and understandably explain even complex topics and current research findings without sacrificing precision. His lectures formed

3660-421: Is a logical framework intended to represent reality (a "model of reality"), similar to the way that a map is a graphical model that represents the territory of a city or country. In this approach, theories are a specific category of models that fulfill the necessary criteria. (See Theories as models for further discussion.) In physics the term theory is generally used for a mathematical framework—derived from

3782-526: Is a statement that can be derived from those axioms by application of these rules of inference. Theories used in applications are abstractions of observed phenomena and the resulting theorems provide solutions to real-world problems. Obvious examples include arithmetic (abstracting concepts of number), geometry (concepts of space), and probability (concepts of randomness and likelihood). Gödel's incompleteness theorem shows that no consistent, recursively enumerable theory (that is, one whose theorems form

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3904-490: Is relevant to practice. In the context of management, Van de Van and Johnson propose a form of engaged scholarship where scholars examine problems that occur in practice, in an interdisciplinary fashion, producing results that create both new practical results as well as new theoretical models, but targeting theoretical results shared in an academic fashion. They use a metaphor of "arbitrage" of ideas between disciplines, distinguishing it from collaboration. In science,

4026-709: Is under the theory. Sometimes two theories have exactly the same explanatory power because they make the same predictions. A pair of such theories is called indistinguishable or observationally equivalent , and the choice between them reduces to convenience or philosophical preference. The form of theories is studied formally in mathematical logic, especially in model theory . When theories are studied in mathematics, they are usually expressed in some formal language and their statements are closed under application of certain procedures called rules of inference . A special case of this, an axiomatic theory, consists of axioms (or axiom schemata) and rules of inference. A theorem

4148-544: The Aeronautisches Observatorium Lindenberg  [ de ] near Beeskow . He worked there with his brother Kurt , who was likewise a scientist with an interest in meteorology and polar research. The two pioneered the use of weather balloons to track air masses. On a balloon ascent undertaken to carry out meteorological investigations and to test a celestial navigation method using a particular type of quadrant ("Libellenquadrant"),

4270-581: The Greek language . In the book From Religion to Philosophy , Francis Cornford suggests that the Orphics used the word theoria to mean "passionate sympathetic contemplation". Pythagoras changed the word to mean "the passionless contemplation of rational, unchanging truth" of mathematical knowledge, because he considered this intellectual pursuit the way to reach the highest plane of existence. Pythagoras emphasized subduing emotions and bodily desires to help

4392-598: The Mid-Atlantic Ridge , arguing with this that the floor of the Atlantic Ocean was undergoing extension just like Reykjanes. Bernauer thought this extension had drifted the continents only 100–200 km (60–120 mi) apart, the approximate width of the volcanic zone in Iceland . David Attenborough , who attended university in the second half of the 1940s, recounted an incident illustrating its lack of acceptance then: "I once asked one of my lecturers why he

4514-561: The 1930s to the late 1950s, works by Vening-Meinesz , Holmes, Umbgrove , and numerous others outlined concepts that were close or nearly identical to modern plate tectonics theory. In particular, the English geologist Arthur Holmes proposed in 1920 that plate junctions might lie beneath the sea , and in 1928 that convection currents within the mantle might be the driving force. Holmes's views were particularly influential: in his bestselling textbook, Principles of Physical Geology, he included

4636-653: The 20th century. With the advent of the Global Positioning System (GPS) in 1993, it became possible to measure continental drift directly. The Alfred Wegener Institute for Polar and Marine Research in Bremerhaven , Germany, was established in 1980 on Wegener's centenary. It awards the Wegener Medal in his name. The crater Wegener on the Moon and the crater Wegener on Mars, as well as

4758-722: The Asian continent in the Permian period, but failing to account for glaciation in India, Australia and South Africa. Hans Stille and Leopold Kober opposed the idea of continental drift and worked on a "fixist" geosyncline model with Earth contraction playing a key role in the formation of orogens . Other geologists who opposed continental drift were Bailey Willis , Charles Schuchert , Rollin Chamberlin, Walther Bucher and Walther Penck . In 1939 an international geological conference

4880-463: The Earth's mantle contained convection cells which dissipated heat produced by radioactive decay and moved the crust at the surface. His Principles of Physical Geology , ending with a chapter on continental drift, was published in 1944. Geological maps of the time showed huge land bridges spanning the Atlantic and Indian oceans to account for the similarities of fauna and flora and the divisions of

5002-605: The Geological Past") together with his father-in-law, Wladimir Köppen, in 1924. In 1922 the third, fully revised edition of "The Origin of Continents and Oceans" appeared, and discussion began on his theory of continental drift, first in the German language area and later internationally. Withering criticism was the response of most experts. In 1924 Wegener was appointed to a professorship in meteorology and geophysics in Graz ,

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5124-541: The German Geological Society on 6 January 1912. He proposed that the continents had once formed a single landmass, called Pangaea , before breaking apart and drifting to their present locations. Wegener was the first to use the phrase "continental drift" (1912, 1915) ( German : "die Verschiebung der Kontinente" ) and to publish the hypothesis that the continents had somehow "drifted" apart. Although he presented much evidence for continental drift, he

5246-466: The Pleistocene, and during each period of ice accumulation the sea-level sank about 250 feet [75 m]. Wegener was in the audience for this lecture, but made no attempt to defend his work, possibly because of an inadequate command of the English language. In 1943, George Gaylord Simpson wrote a strong critique of the theory (as well as the rival theory of sunken land bridges) and gave evidence for

5368-560: The South Pacific. The modern theory of plate tectonics , refining Wegener, explains that there are two kinds of crust of different composition: continental crust and oceanic crust , both floating above a much deeper " plastic " mantle. Continental crust is inherently lighter. Oceanic crust is created at spreading centers , and this, along with subduction , drives the system of plates in a chaotic manner, resulting in continuous orogeny and areas of isostatic imbalance. Evidence for

5490-563: The Wegener brothers set a new record for a continuous balloon flight, remaining aloft 52.5 hours from 5–7 April 1906. His observations during his time at the Observatorium made a significant contribution to the field of atmospheric physics . In that same year 1906, Wegener participated in the first of his four Greenland expeditions, later regarding this experience as marking a decisive turning point in his life. The Denmark expedition

5612-418: The adjoining stripes reversed polarity. The best explanation was the "conveyor belt" or Vine–Matthews–Morley hypothesis . New magma from deep within the Earth rises easily through these weak zones and eventually erupts along the crest of the ridges to create new oceanic crust. The new crust is magnetized by the Earth's magnetic field, which undergoes occasional reversals . Formation of new crust then displaces

5734-819: The age of the Earth. Apart from the earlier speculations mentioned above, the idea that the American continents had once formed a single landmass with Eurasia and Africa was postulated by several scientists before Alfred Wegener 's 1912 paper. Although Wegener's theory was formed independently and was more complete than those of his predecessors, Wegener later credited a number of past authors with similar ideas: Franklin Coxworthy (between 1848 and 1890), Roberto Mantovani (between 1889 and 1909), William Henry Pickering (1907) and Frank Bursley Taylor (1908). The similarity of southern continent geological formations had led Roberto Mantovani to conjecture in 1889 and 1909 that all

5856-564: The aims are different. Theoretical contemplation considers things humans do not move or change, such as nature , so it has no human aim apart from itself and the knowledge it helps create. On the other hand, praxis involves thinking, but always with an aim to desired actions, whereby humans cause change or movement themselves for their own ends. Any human movement that involves no conscious choice and thinking could not be an example of praxis or doing. Theories are analytical tools for understanding , explaining , and making predictions about

5978-481: The astronomical precession . Wegener also speculated about sea-floor spreading and the role of the mid-ocean ridges , stating that "the Mid-Atlantic Ridge ... zone in which the floor of the Atlantic, as it keeps spreading, is continuously tearing open and making space for fresh, relatively fluid and hot sima [rising] from depth." However, he did not pursue these ideas in his later works. In 1915, in

6100-414: The axioms of that field. Some commonly known examples include set theory and number theory ; however literary theory , critical theory , and music theory are also of the same form. One form of philosophical theory is a metatheory or meta-theory . A metatheory is a theory whose subject matter is some other theory or set of theories. In other words, it is a theory about theories. Statements made in

6222-710: The basis of what was to become a standard textbook in meteorology, first written In 1909/1910: Thermodynamik der Atmosphäre (Thermodynamics of the Atmosphere), in which he incorporated many of the results of the Greenland expedition. On 6 January 1912 he presented his first proposal of continental drift in a lecture to the Geologische Vereinigung (Geological Association) at the Senckenberg Museum , Frankfurt am Main . Later in 1912 he made

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6344-619: The best in his class. Wegener studied physics , meteorology and astronomy at the Friedrich Wilhelm University in Berlin, completing two external semesters at Heidelberg and Innsbruck . His teachers included Wilhelm Förster for astronomy and Max Planck for thermodynamics. From 1902 to 1903 during his studies he was an assistant at the Urania astronomical observatory. He completed his doctoral dissertation on

6466-575: The case for the theory in a long, three-part article and a shorter summary. Plans for a new Greenland expedition grew out of Wegener and Johan Peter Koch 's frustration with the disorganisation and meager scientific results of the Danmark expedition . The new Danish Expedition to Queen Louise Land would involve only four men, take place in 1912–1913, and have Koch for leader. After a stopover in Iceland to purchase and test ponies as pack animals,

6588-436: The construction of mathematical theories that formalize large bodies of scientific knowledge. A theory is underdetermined (also called indeterminacy of data to theory ) if a rival, inconsistent theory is at least as consistent with the evidence. Underdetermination is an epistemological issue about the relation of evidence to conclusions. A theory that lacks supporting evidence is generally, more properly, referred to as

6710-548: The continent of North America had its surface near tide-level, part above and part below it (p.196); and this will probably be proved to be the condition in Primordial time of the other continents also. And, if the outlines of the continents were marked out, it follows that the outlines of the oceans were no less so". Dana was enormously influential in America—his Manual of Mineralogy is still in print in revised form—and

6832-434: The continents had once been joined into a supercontinent ; Wegener noted the similarity of Mantovani's and his own maps of the former positions of the southern continents. In Mantovani's conjecture, this continent broke due to volcanic activity caused by thermal expansion , and the new continents drifted away from each other because of further expansion of the rip-zones, where the oceans now lie. This led Mantovani to propose

6954-401: The continents once fitting together not at the current shore line, but 200 m below this , at the level of the continental shelves , where they match well. Part of the reason Wegener's ideas were not initially accepted was the misapprehension that he was suggesting the continents had fit along the current coastline. Charles Schuchert commented: During this vast time [of the split of Pangea]

7076-603: The country had previously been in the Southern hemisphere as predicted by Wegener. By 1959, the theory had enough supporting data that minds were starting to change, particularly in the United Kingdom where, in 1964, the Royal Society held a symposium on the subject. The 1960s saw several relevant developments in geology, notably the discoveries of seafloor spreading and Wadati–Benioff zones , and this led to

7198-539: The course of ages." and claims that the first to throw doubt on this was James Dwight Dana in 1849. In his Manual of Geology (1863), Dana wrote, "The continents and oceans had their general outline or form defined in earliest time. This has been proved with regard to North America from the position and distribution of the first beds of the Lower Silurian , – those of the Potsdam epoch . The facts indicate that

7320-451: The discipline of medicine: medical theory involves trying to understand the causes and nature of health and sickness, while the practical side of medicine is trying to make people healthy. These two things are related but can be independent, because it is possible to research health and sickness without curing specific patients, and it is possible to cure a patient without knowing how the cure worked. The English word theory derives from

7442-543: The effects of continental motion would be the formation of mountains, attributing the formation of the Himalayas to the collision between the Indian subcontinent with Asia. Wegener said that of all those theories, Taylor's had the most similarities to his own. For a time in the mid-20th century, the theory of continental drift was referred to as the "Taylor-Wegener hypothesis". Alfred Wegener first presented his hypothesis to

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7564-400: The elementary theorems of a philosophical theory are statements whose truth cannot necessarily be scientifically tested through empirical observation . A field of study is sometimes named a "theory" because its basis is some initial set of assumptions describing the field's approach to the subject. These assumptions are the elementary theorems of the particular theory, and can be thought of as

7686-562: The end of the 1920s. In November 1926 Wegener presented his continental drift theory at a symposium of the American Association of Petroleum Geologists in New York City, again earning rejection from everyone but the chairman. Three years later the fourth and final expanded edition of "The Origin of Continents and Oceans" appeared. In April–October 1929, Wegener embarked on his third expedition to Greenland, which laid

7808-438: The existence of the supercontinent of Gondwana , 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 that were contiguous with one another. Theory In modern science,

7930-469: The expedition arrived in Danmarkshavn. Even before the trip to the inland ice began the expedition was almost annihilated by a calving glacier . Koch broke his leg when he fell into a glacier crevasse and spent months recovering in a sickbed. Wegener and Koch were the first to winter on the inland ice in northeast Greenland. Inside their hut they drilled to a depth of 25 m with an auger. In summer 1913

8052-498: The expedition's leadership in July, according to the prearranged plan for such an eventuality. Wegener first thought of this idea by noticing that the different large landmasses of the Earth almost fit together like a jigsaw puzzle. The continental shelf of the Americas fits closely to Africa and Europe. Antarctica, Australia, India and Madagascar fit next to the tip of Southern Africa. But Wegener only published his idea after reading

8174-475: The expedition's success, as the German government had contributed $ 120,000 ($ 1.5 million in 2007 dollars). Success depended on enough provisions being transferred from West camp to Eismitte ("mid-ice", also known as Central Station) for two men to winter there, and this was a factor in the decision that led to his death. Owing to a late thaw, the expedition was six weeks behind schedule and, as summer ended,

8296-507: The first edition of his book, Die Entstehung der Kontinente und Ozeane , written in German, Wegener drew together evidence from various fields to advance the theory that there had once been a giant continent, which he named " Urkontinent " (German for "primal continent", analogous to the Greek " Pangaea ", meaning "All-Lands" or "All-Earth"). Expanded editions during the 1920s presented further evidence. (The first English edition

8418-400: The future, but to visit specialist areas that have so far forgotten to write above their gate: "Oh holy Saint Florian, spare this house, set others on fire!" (Max Semper, 1917) Nevertheless, the eminent Swiss geologist Émile Argand advocated Wegener's theory in his inaugural address to the 1922 International Geological Congress. The one American edition of Wegener's work, published in 1925,

8540-595: The groundwork for the German Greenland Expedition which he was planning to lead in 1930–1931. Wegener's last Greenland expedition was in 1930. The 14 participants under his leadership were to establish three permanent stations from which the thickness of the Greenland ice sheet could be measured and year-round Arctic weather observations made. They would travel on the ice cap using two innovative, propeller-driven snowmobiles , in addition to ponies and dog sleds. Wegener felt personally responsible for

8662-455: The idea that similarities of flora and fauna between the continents could best be explained by these being fixed land masses which over time were connected and disconnected by periodic flooding, a theory known as permanentism . Alexander du Toit wrote a rejoinder to this the following year. Alfred Wegener has been mischaracterised as a lone genius whose theory of continental drift met widespread rejection until well after his death. In fact,

8784-443: The intellect function at the higher plane of theory. Thus, it was Pythagoras who gave the word theory the specific meaning that led to the classical and modern concept of a distinction between theory (as uninvolved, neutral thinking) and practice. Aristotle's terminology, as already mentioned, contrasts theory with praxis or practice, and this contrast exists till today. For Aristotle, both practice and theory involve thinking, but

8906-650: The level of consistent and reproducible evidence that supports them. Within electromagnetic theory generally, there are numerous hypotheses about how electromagnetism applies to specific situations. Many of these hypotheses are already considered adequately tested, with new ones always in the making and perhaps untested. Certain tests may be infeasible or technically difficult. As a result, theories may make predictions that have not been confirmed or proven incorrect. These predictions may be described informally as "theoretical". They can be tested later, and if they are incorrect, this may lead to revision, invalidation, or rejection of

9028-521: The magnetized crust apart, akin to a conveyor belt – hence the name. Without workable alternatives to explain the stripes, geophysicists were forced to conclude that Holmes had been right: ocean rifts were sites of perpetual orogeny at the boundaries of convection cells. By 1967, barely two decades after discovery of the mid-oceanic rifts, and a decade after discovery of the striping, plate tectonics had become axiomatic to modern geophysics. In addition, Marie Tharp , in collaboration with Bruce Heezen , who

9150-558: The main tenets of the theory gained widespread acceptance by European researchers already in the 1920s, and the debates were mostly about specific details. However, the theory took longer to be accepted in North America. In the early 1950s, the new science of paleomagnetism pioneered at the University of Cambridge by S. K. Runcorn and at Imperial College by P.M.S. Blackett was soon producing data in favour of Wegener's theory. By early 1953 samples taken from India showed that

9272-441: The men at Eismitte sent a message that they had insufficient fuel and so would return on 20 October. On 24 September, although the route markers were by now largely buried under snow, Wegener set out with thirteen Greenlanders and his meteorologist Fritz Loewe to supply the camp by dog sled. During the journey, the temperature reached −60 °C (−76 °F) and Loewe's toes became so frostbitten they had to be amputated with

9394-446: The metatheory about the theory are called metatheorems . A political theory is an ethical theory about the law and government. Often the term "political theory" refers to a general view, or specific ethic, political belief or attitude, thought about politics. In social science, jurisprudence is the philosophical theory of law. Contemporary philosophy of law addresses problems internal to law and legal systems, and problems of law as

9516-436: The most reliable, rigorous, and comprehensive form of scientific knowledge, in contrast to more common uses of the word "theory" that imply that something is unproven or speculative (which in formal terms is better characterized by the word hypothesis ). Scientific theories are distinguished from hypotheses, which are individual empirically testable conjectures , and from scientific laws , which are descriptive accounts of

9638-551: The most useful properties of scientific theories is that they can be used to make predictions about natural events or phenomena that have not yet been observed. From the American Association for the Advancement of Science : A scientific theory is a well-substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experiment. Such fact-supported theories are not "guesses" but reliable accounts of

9760-474: The movement of continents on tectonic plates is now extensive. Similar plant and animal fossils are found around the shores of different continents, suggesting that they were once joined. The fossils of Mesosaurus , a freshwater reptile rather like a small crocodile, found both in Brazil and South Africa , are one example; another is the discovery of fossils of the land reptile Lystrosaurus in rocks of

9882-411: The new one describes the same reality, only more completely. When a new theory uses new terms that do not reduce to terms of an older theory, but rather replace them because they misrepresent reality, it is called an intertheoretic elimination. For instance, the obsolete scientific theory that put forward an understanding of heat transfer in terms of the movement of caloric fluid was eliminated when

10004-477: The ocean floor using devices developed during World War II to detect submarines. Over the next decade, it became increasingly clear that the magnetization patterns were not anomalies, as had been originally supposed. In a series of papers published between 1959 and 1963, Heezen, Dietz, Hess, Mason, Vine, Matthews, and Morley collectively realized that the magnetization of the ocean floor formed extensive, zebra-like patterns: one stripe would exhibit normal polarity and

10126-670: The organizer of the conference, was also a fixist who together with Troll held the view that excepting the Pacific Ocean continents were not radically different from oceans in their behaviour. The mobilist theory of Émile Argand for the Alpine orogeny was criticized by Kurt Leuchs. The few drifters and mobilists at the conference appealed to biogeography (Kirsch, Wittmann), paleoclimatology ( Wegener, K ), paleontology (Gerth) and geodetic measurements (Wegener, K). F. Bernauer correctly equated Reykjanes in south-west Iceland with

10248-400: The possibility of faulty inference or incorrect observation. Sometimes theories are incorrect, meaning that an explicit set of observations contradicts some fundamental objection or application of the theory, but more often theories are corrected to conform to new observations, by restricting the class of phenomena the theory applies to or changing the assertions made. An example of the former is

10370-409: The rapid resurrection of the continental drift hypothesis in the form of its direct descendant, the theory of plate tectonics . Maps of the geomorphology of the ocean floors created by Marie Tharp in cooperation with Bruce Heezen were an important contribution to the paradigm shift that was starting. Wegener was then recognised as the founding father of one of the major scientific revolutions of

10492-517: The real world. The theory of biological evolution is more than "just a theory." It is as factual an explanation of the universe as the atomic theory of matter or the germ theory of disease. Our understanding of gravity is still a work in progress. But the phenomenon of gravity, like evolution, is an accepted fact. The term theory is not appropriate for describing scientific models or untested, but intricate hypotheses. The logical positivists thought of scientific theories as deductive theories —that

10614-432: The restriction of classical mechanics to phenomena involving macroscopic length scales and particle speeds much lower than the speed of light. Theory is often distinguished from practice or praxis. The question of whether theoretical models of work are relevant to work itself is of interest to scholars of professions such as medicine, engineering, law, and management. The gap between theory and practice has been framed as

10736-651: The same age at locations in Africa , India , and Antarctica . There is also living evidence, with the same animals being found on two continents. Some earthworm families (such as Ocnerodrilidae, Acanthodrilidae, Octochaetidae) are found in South America and Africa. The complementary arrangement of the facing sides of South America and Africa is an obvious and temporary coincidence. In millions of years, slab pull , ridge-push , and other forces of tectonophysics will further separate and rotate those two continents. It

10858-454: The sea waves have been continuously pounding against Africa and Brazil and in many places rivers have been bringing into the ocean great amounts of eroded material, yet everywhere the geographic shore lines are said to have remained practically unchanged! It apparently makes no difference to Wegener how hard or how soft are the rocks of these shore lines, what are their geological structures that might aid or retard land or marine erosion, how often

10980-399: The sediments was chemically and physically different from continental crust. As oceanographers continued to bathymeter the ocean basins, a system of mid-oceanic ridges was detected. An important conclusion was that along this system, new ocean floor was being created, which led to the concept of the " Great Global Rift ". Meanwhile, scientists began recognizing odd magnetic variations across

11102-413: The separation of the Americas from Europe and Africa is about 2.5 cm/year (1 in/year).) Furthermore, Wegener was treated less seriously because he was not a geologist. Even today, the details of the forces propelling the plates are poorly understood. The English geologist Arthur Holmes championed the theory of continental drift at a time when it was deeply unfashionable. He proposed in 1931 that

11224-498: The shapes of continents on opposite sides of the Atlantic Ocean (most notably, Africa and South America) seem to fit together. W. J. Kious described Ortelius's thoughts in this way: Abraham Ortelius in his work Thesaurus Geographicus ... suggested that the Americas were "torn away from Europe and Africa ... by earthquakes and floods" and went on to say: "The vestiges of the rupture reveal themselves if someone brings forward

11346-416: The snow. Villumsen resumed his journey, but he was never seen again. Six months later, on 12 May 1931, Wegener's skis were discovered. Expedition members built a pyramid-shaped mausoleum in the ice and snow, and Alfred Wegener's body was laid to rest. Wegener had been 50 years of age and a heavy smoker, and it was believed that he had died of heart failure brought on by overexertion . Kurt Wegener took over

11468-448: The speaker did not experience or test before. In science, this same concept is referred to as a hypothesis , and the word "hypothetically" is used both inside and outside of science. In its usage outside of science, the word "theory" is very often contrasted to " practice " (from Greek praxis , πρᾶξις) a Greek term for doing , which is opposed to theory. A "classical example" of the distinction between "theoretical" and "practical" uses

11590-400: The strand lines have been elevated or depressed, and how far peneplanation has gone on during each period of continental stability. Furthermore, sea-level in itself has not been constant, especially during the Pleistocene, when the lands were covered by millions of square miles of ice made from water subtracted out of the oceans. In the equatorial regions, this level fluctuated three times during

11712-442: The subject of applying the astronomical data of Alfonsine tables to contemporary computational methods in 1905 under the supervision of Julius Bauschinger and Wilhelm Förster . Despite becoming a doctor in the field of astronomy, Wegener had always maintained a strong interest in the developing fields of meteorology and climatology and his studies afterwards focused on these disciplines. In 1905 Wegener became an assistant at

11834-399: The supplies, and that Wegener and Villumsen could have overwintered at Eismitte. ) They took no food for the dogs and killed them one by one to feed the rest until they could run only one sled. While Villumsen rode the sled, Wegener had to use skis, but they never reached the camp. Wegener died in his tent around 90 miles from Eismitte and was hastily buried with his skis stuck upright in

11956-440: The team crossed the inland ice, the four expedition participants covering a distance twice as long as Fridtjof Nansen 's southern Greenland crossing in 1888. Only a few kilometres from the western Greenland settlement of Kangersuatsiaq the small team ran out of food while struggling to find their way through difficult glacial break-up terrain. But at the last moment, after the last pony and dog had been eaten, they were picked up at

12078-409: The term "theory" refers to scientific theories , a well-confirmed type of explanation of nature , made in a way consistent with the scientific method , and fulfilling the criteria required by modern science . Such theories are described in such a way that scientific tests should be able to provide empirical support for it, or empirical contradiction (" falsify ") of it. Scientific theories are

12200-416: The term "theory" refers to "a well-substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experiment." Theories must also meet further requirements, such as the ability to make falsifiable predictions with consistent accuracy across a broad area of scientific inquiry, and production of strong evidence in favor of

12322-515: The theory became known as the Permanence theory . This appeared to be confirmed by the exploration of the deep sea beds conducted by the Challenger expedition , 1872–1876, which showed that contrary to expectation, land debris brought down by rivers to the ocean is deposited comparatively close to the shore on what is now known as the continental shelf . This suggested that the oceans were

12444-497: The theory from multiple independent sources ( consilience ). The strength of a scientific theory is related to the diversity of phenomena it can explain, which is measured by its ability to make falsifiable predictions with respect to those phenomena. Theories are improved (or replaced by better theories) as more evidence is gathered, so that accuracy in prediction improves over time; this increased accuracy corresponds to an increase in scientific knowledge. Scientists use theories as

12566-417: The theory still required work to avoid foundering on the orogeny and isostasy objections. Worse, the most viable forms of the theory predicted the existence of convection cell boundaries reaching deep into the Earth, that had yet to be observed. In 1947, a team of scientists led by Maurice Ewing confirmed the existence of a rise in the central Atlantic Ocean, and found that the floor of the seabed beneath

12688-557: The theory. In mathematics, the term theory is used differently than its use in science ─ necessarily so, since mathematics contains no explanations of natural phenomena per se , even though it may help provide insight into natural systems or be inspired by them. In the general sense, a mathematical theory is a branch of mathematics devoted to some specific topics or methods, such as set theory , number theory , group theory , probability theory , game theory , control theory , perturbation theory , etc., such as might be appropriate for

12810-407: The truth of any one of these statements is always relative to the whole theory. Therefore, the same statement may be true with respect to one theory, and not true with respect to another. This is, in ordinary language, where statements such as "He is a terrible person" cannot be judged as true or false without reference to some interpretation of who "He" is and for that matter what a "terrible person"

12932-446: The way nature behaves under certain conditions. Theories guide the enterprise of finding facts rather than of reaching goals, and are neutral concerning alternatives among values. A theory can be a body of knowledge , which may or may not be associated with particular explanatory models . To theorize is to develop this body of knowledge. The word theory or "in theory" is sometimes used outside of science to refer to something which

13054-417: The word theory since at least the late 16th century. Modern uses of the word theory derive from the original definition, but have taken on new shades of meaning, still based on the idea of a theory as a thoughtful and rational explanation of the general nature of things. Although it has more mundane meanings in Greek, the word θεωρία apparently developed special uses early in the recorded history of

13176-407: Was a significant similarity between matching sides of the continents, especially in fossil plants . From 1912, Wegener publicly advocated the existence of "continental drift", arguing that all the continents were once joined in a single landmass and had since drifted apart. He supposed that the mechanisms causing the drift might be the centrifugal force of the Earth's rotation (" Polflucht ") or

13298-577: Was born in Hamburg . Lotte would in 1938 marry the famous Austrian mountaineer and adventurer Heinrich Harrer , while in 1939, Käte married Siegfried Uiberreither , Austrian Nazi Gauleiter of Styria . As an infantry reserve officer Wegener was immediately called up when the First World War began in 1914. On the war front in Belgium he experienced fierce fighting but his term lasted only

13420-646: Was born in Berlin on 1 November 1880, the youngest of five children, to Richard Wegener and his wife Anna. His father was a theologian and teacher of classical languages at the Joachimsthalschen Gymnasium and Berlinisches Gymnasium zum Grauen Kloster . In 1886 his family purchased a former manor house near Rheinsberg , which they used as a vacation home. Wegener attended school at the Köllnische Gymnasium on Wallstrasse in Berlin, completing his Abitur in 1899, graduating as

13542-729: Was first put forward by Abraham Ortelius in 1596. A pioneer of the modern view of mobilism was the Austrian geologist Otto Ampferer . The concept was independently and more fully developed by Alfred Wegener in his 1915 publication, "The Origin of Continents and Oceans". However, at that time his hypothesis was rejected by many for lack of any motive mechanism. In 1931, the English geologist Arthur Holmes proposed mantle convection for that mechanism. Abraham Ortelius ( Ortelius 1596 ), Theodor Christoph Lilienthal (1756), Alexander von Humboldt (1801 and 1845), Antonio Snider-Pellegrini ( Snider-Pellegrini 1858 ), and others had noted earlier that

13664-489: Was held in Frankfurt . This conference came to be dominated by the fixists, especially as those geologists specializing in tectonics were all fixists except Willem van der Gracht. Criticism of continental drift and mobilism was abundant at the conference not only from tectonicists but also from sedimentological (Nölke), paleontological (Nölke), mechanical (Lehmann) and oceanographic ( Troll , Wüst ) perspectives. Hans Cloos ,

13786-593: Was initially sceptical of Tharp's observations that her maps confirmed continental drift theory, provided essential corroboration, using her skills in cartography and seismographic data, to confirm the theory. Geophysicist Jack Oliver is credited with providing seismologic evidence supporting plate tectonics which encompassed and superseded continental drift with the article "Seismology and the New Global Tectonics", published in 1968, using data collected from seismologic stations, including those he set up in

13908-501: Was led by the Dane Ludvig Mylius-Erichsen and charged with studying the last unknown portion of the northeastern coast of Greenland. During the expedition Wegener constructed the first meteorological station in Greenland near Danmarkshavn , where he launched kites and tethered balloons to make meteorological measurements in an Arctic climatic zone. Here Wegener also made his first acquaintance with death in

14030-411: Was not talking to us about continental drift and I was told, sneeringly, that if I could prove there was a force that could move continents, then he might think about it. The idea was moonshine, I was informed." As late as 1953—just five years before Carey introduced the theory of plate tectonics —the theory of continental drift was rejected by the physicist Scheidegger on the following grounds. From

14152-483: Was primarily known for his achievements in meteorology and as a pioneer of polar research, but today he is most remembered as the originator of continental drift hypothesis by suggesting in 1912 that the continents are slowly drifting around the Earth (German: Kontinentalverschiebung ). His hypothesis was not accepted by mainstream geology until the 1950s, when numerous discoveries such as palaeomagnetism provided strong support for continental drift, and thereby

14274-522: Was published in 1924 as The Origin of Continents and Oceans , a translation of the 1922 third German edition.) The last German edition, published in 1929, revealed the significant observation that shallower oceans were geologically younger. It was not translated into English until 1962. Note prior advocates for various forms of continental dynamics: Abraham Ortelius , Antonio Snider-Pellegrini , Eduard Suess , Roberto Mantovani , Otto Ampferer , and Frank Bursley Taylor . In his work, Wegener presented

14396-503: Was that temporary feature that inspired Wegener to study what he defined as continental drift although he did not live to see his hypothesis generally accepted. The widespread distribution of Permo-Carboniferous glacial 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 oriented glacial striations and deposits called tillites , suggested

14518-415: Was the premise for investigating polar wandering, the hypothesis was initially met with scepticism from geologists, who viewed Wegener as an outsider and were resistant to change. The German geologist Max Semper wrote a critique of the theory, which culminated in this mockery against Wegener: "... so one can only ask for the necessary distance to be maintained and the request to stop honouring geology in

14640-491: Was to "reestablish the connection between geophysics on the one hand and geography and geology on the other, which had become completely ruptured because of the specialized development of these branches of science." Interest in this small publication was however low, also because of wartime chaos. By the end of the war Wegener had published almost 20 additional meteorological and geophysical papers in which he repeatedly embarked for new scientific frontiers. In 1917 he undertook

14762-501: Was unable to provide a convincing explanation for the physical processes which might have caused this drift. He suggested that the continents had been pulled apart by the centrifugal pseudoforce ( Polflucht ) of the Earth's rotation or by a small component of astronomical precession , but calculations showed that the force was not sufficient. The Polflucht hypothesis was also studied by Paul Sophus Epstein in 1920 and found to be implausible. Although now accepted, and even with

14884-494: Was written in "a dogmatic style that often results from German translations". In 1926, at the initiative of Willem van der Gracht, the American Association of Petroleum Geologists organised a symposium on the continental drift hypothesis. The opponents argued, as did the Leipziger geologist Franz Kossmat , that the oceanic crust was too firm for the continents to "simply plough through". From at least 1910, Wegener imagined

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