WEGENER, ALFRED LOTHAR

(b. Berlin, Germany, 1 November 1880;

d. West Greenland, November 1930), atmospheric physics, geophysics. For the original article on Wegener see DSB, vol. 14.

Alfred Wegener was selected for inclusion in the first edition of the Dictionary of Scientific Biography because of the renewed interest in the early 1970s in his theory of continental displacements. It is therefore not surprising that the entry by Keith Bullen characterized Wegener as a scientist with a strong interest in geology and geophysics and passed over his considerable career in meteorology and atmospheric physics. Yet it was precisely this work in atmospheric physics that prepared Wegener to develop a slender intuition concerning the outlines of continents on a map of the Atlantic Ocean into a well-argued geophysical theory of continental displacements.

Early Training. Wegener was born and raised in Berlin and lived there until the completion of his PhD in 1905. He began his graduate career in physics and mathematics and attended Planck’s lectures in thermodynamics and thermochemistry. Wegener adopted Planck’s phenomenological approach, his indifference to hypothetical causal mechanisms, and his concentration on the bulk properties of matter—temperature, pressure, mass, and volume. Wegener heeded Planck’s injunction to think of good theory simply as that mode of treating phenomena that corresponded to the state of empirical research at the moment.

These physical and mathematical studies were pursued in the context of a PhD in astronomy. Berlin astronomy leaned strongly toward planetary astronomy and particularly toward the use of astronomical data to study the Earth. One of Wegener’s instructors had been a leading observer in a program to measure the amount and direction of that slight oscillation of the Earth’s axis of rotation later known as Chandler Wobble. Another instructor concentrated on demonstrating the reality of latitude displacements, and those displacements of the Earth’s axis commonly called pole wander.

After 1903 Wegener began to pursue studies in meteorology with Wilhelm von Bezold, including atmospheric thermodynamics. Bezold, then near the end of his career, spoke of the wonderful new opportunities in atmospheric physics for aspiring scientists and Wegener resolved to pursue atmospheric physics as a career.

In the year following his degree, Wegener worked at the German Aeronautical Observatory at Lindenberg, sending up kites and balloons to study the structure and properties of the atmosphere at altitudes up to five kilometers. He had a minor role in confirming the existence of the stratosphere and with his brother set a world record for time aloft in a balloon—fifty-two hours. From 1906 to 1908, he took part in a Danish expedition to Northeast Greenland. There he conducted a full program of atmospheric investigations with kites and balloons and gained many other necessary skills for polar life and travel, including experience in driving sled dogs.

In 1909 he began his university career at the Physical Institute in Marburg, where he pursued a systematic study of surfaces of discontinuity in the atmosphere: characteristic global levels at which sudden sharp temperature and pressure differences appeared both in cloud layers and in clear air. He wrote to a colleague that his interest in surfaces of discontinuity had the character of an obsession. Between 1909 and 1912, Wegener published almost forty scientific papers, many of which were devoted to this topic. He collected these into a textbook entitled Thermodynamik der Atmosphäre, published in 1911 and in print until it was replaced by his own Physik der Atmosphäre, edited posthumously by Wegener’s brother Kurt in 1935. Wegener’s 1911 textbook contained, among many other

novelties, a full theory of atmospheric discontinuities, including a hypothetical geocoronium layer (later identified as the ionosphere) and a novel theory of the formation of precipitation in cold clouds that continued to be generally accepted under the name of the Wegener-Bergeron theory.

Path Toward Continental Drift. It was at this time, 1910 to 1911, that Wegener had the first intuitions that led to the theory of continental displacements. Returning from the Christmas holidays in late 1910 to his office at the Physical Institute in Marburg, he was invited by his officemate to peruse a new edition of Richard Andree’s Allgemeine Handatlas. This was among the first atlases in Germany to show pictures of the Atlantic continental margins of South America and Africa with the bathymetry data from the Challenger Expedition. Wegener noticed immediately that the outlines of the continents at sea level were repeated at the two-hundred meter depth contour. This meant (to him) that the matching of the east coast of South America and the west coast of Africa was not an artifact of sea level, but something that reflected the structure of the planet as a whole.

Louis Pasteur remarked in an 1854 lecture that “in the field of observation, chance favors only the prepared mind.” What is of interest in this story of Wegener noting the parallelism of the coastlines, observed many times before him, is the way his mind was prepared to see this geophysically significant datum from the standpoint of his work on surfaces of discontinuity in the atmosphere. He immediately hypothesized that the continental surfaces were one earth layer, and the ocean floor was another layer beneath them. By Wegener’s own account, this intuition lay dormant until later in the year 1911, when he came upon a summary of paleontological correlations between Africa and South America of species that could not themselves have crossed an abyssal ocean.

Wegener undertook a more systematic study of geology, geophysics, paleontology, and oceanography in order to get a sense of the theoretical organization tying together these disparate fields. His rapid traverse through these disciplines in late 1911 taught him two things. The first was that there was massive and incontrovertible evidence— stratigraphical, structural, and paleontological—of former continuity across the Atlantic, and between south hemispheric continents now widely separated by deep oceans. The second was that all the current geophysical explanations of how this former continuity had been broken were impossibly flawed. All were versions of the contraction theory, the nineteenth-century notion that the Earth was continually cooling from an original incandescent state. All versions of the theory implied that the current floors of the ocean were former continental surfaces that had somehow sunk there. Wegener knew this was impossible—the theory of isostasy had established that the continents floated and the discovery of radioactivity indicated that the Earth was not cooling. It occurred to Wegener that the only reasonable explanation, which honored the geological and paleontological evidence of former continuity in the context of some sort of geophysical plausibility, was that the continents had split apart and drifted away from one another. In later 1911 and early 1912 he wrote two papers, both entitled “Die Entstehung der Kontinente” (The origin of continents), defending this position.

Immediately after publishing this hypothesis in 1912 Wegener left for Greenland where he spent the next eighteen months crossing the Greenland ice cap. Most of the scientific work was classical glaciology, though Wegener hoped that the geodesy could support his ideas about continental movement. Upon his return in 1913 he married Else Köppen, daughter of the distinguished climatologist Wladimir Köppen: The latter had already aided him considerably in his meteorological work and would later become his closest collaborator.

Mobilized at the outbreak of World War I (he was a lieutenant and later a captain of infantry) he was wounded twice and remained on convalescent leave through 1915, when he was remobilized into the Army Weather Service. In 1915 he published a book-length extension of his work on continental displacements now entitled Die Entstehung der Kontinente und Ozeane. Near the end of the war he published a catalog of occurrences of tornadoes and water spouts in Europe: This was his reentry into the boundary-layer meteorology which was his principal area of research at this time. Returning to Marburg at the end of the war, he published some interesting simulations on the origins of lunar craters and in 1920 published an extended edition of his book on continental displacements.

As hope evaporated for a professorship at Marburg, Wegener moved his family to Hamburg and merged households with his in-laws. He took up a government job at the German Marine Observatory and directed the geophysical colloquium at the new University of Hamburg.

The period between 1920 and 1924 marked Wegener’s deepest involvement with the theory of continental displacements. A third edition of his book on the subject appeared in 1922 and was translated into English, French, Russian, Italian, Spanish, and Japanese. The theory was widely discussed and seems to have been favored more by geographers and paleoclimatologists than by geologists and geophysicists. It appealed to geologists whose fieldwork took place in the southern hemisphere much more than to those who worked in the northern hemisphere.

In 1924, in combination with his father-in-law, Wegener published a book: Die Klimate der geologischen Vorzeit (Climates of the geological past). The book mapped systematic displacements of the equator and the poles of the Earth by plotting glacial deposits, coal deposits, evaporates, and reef limestones through geologic time. In Wegener’s theory of continental displacement, in contradistinction to modern plate tectonics, the motions of continents were interpreted as the results both of mobility of continental fragments and of true polar wander.

In 1924 Wegener finally obtained a professorship of meteorology and geophysics at the University of Graz in Austria. In these years he was principally concerned with atmospheric optics and acoustics, on which he was the leading expert in the world and on which he wrote a long treatise as part of the encyclopedic Physik der Erde (Geo-physic). He was also the general editor of this text, which appeared in 1928. Notably, he declined to write on the mechanics and thermodynamics of the solid Earth and assigned this section to the young seismologist Beno Gutenberg.

In 1928 Wegener was offered a chance to return to Greenland as the head of his own polar expedition: the first overseas scientific work conducted by Germans since the end of World War I. In 1928 he made a reconnaissance expedition to west Greenland to pick out a landing site and base camp. In 1929 he departed for Greenland with a full shipload of equipment and a team of eager but inexperienced young scientists whom he planned to train as the next generation of German polar scientists. Part of the plan for this expedition was to establish and occupy a base that would overwinter in the middle of the Greenland ice cap, and produce the first complete set of meteorological data from this region. The expedition would also use seismic reflection profiling to determine the extent of the downed flexure of the rock beneath the Greenland ice cap by the weight of the ice itself. Nothing in the expedition plans mentions the theory of continental displacements. Indeed, it was entirely intended to support Wegener’s plan to lead a German expedition to Antarctica in the International Polar Year 1933.

Severe weather and difficulties of supply in the fall of 1929 put the Greenland expedition far behind schedule, and in October Wegener undertook a very dangerous attempt to supply the incomplete base at the center of the ice cap. He left the mid-ice station on his fiftieth birthday, 1 November 1930, planning to return to the west coast base. He died a week later, either of heart failure or of asphyxiation by carbon monoxide from his stove. His body was recovered the following spring. He was found sewn into a sleeping bag next to a cairn marked by his crossed skis. His companion Rasmus Willemsen perished on the return to the coast after marking Wegener’s grave. His body, and Wegener’s final diary which he carried, have never been found. The discovery of Wegener’s body in May 1931 was headline news around the world. In 1931 Leni Riefenstahl starred in an action film entitled SOS Eisberg, which had as its premise an attempt to find Wegener’s lost scientific notes.

In 1929, shortly before his departure for Greenland, Wegener published a fourth and, according to him, final edition of his work on the origin of continents and oceans. Unlike the previous three editions, it is not a work of advocacy, but a catalog of contributions to a growing field of research, which, as Wegener noted, was now so large that one person could no longer master it. In response to his many critics who lamented the lack of a mechanism for continental drift, Wegener proposed six candidate mechanisms, and noted laconically that one or more of them might be the case. His studied indifference to plausible but untestable mechanisms persisted to end of his life.

Wegener’s collected works would fill many volumes, most of them connected not with continental displacement or paleoclimatology, but with atmospheric optics, atmospheric acoustics, and atmospheric layering and thermodynamics. Contrary to the notion that he was an outsider and a maverick, he was an extremely influential and well-connected scientist throughout his career. Wegener was known at home and abroad for his work on the complex layering and thermodynamic behavior of the troposphere. This work was the source of his inspiration concerning displacement of continents and put his work squarely in the mainstream of German geophysical speculation during his lifetime. That Germany’s principal scientific institution for polar and marine research should be named the Alfred Wegener Institute is an accurate reflection of his scientific interest and accomplishments.

SUPPLEMENTARY BIBLIOGRAPHY

Wegener’s manuscripts and papers were lost and/or destroyed in 1945. A few hundred surviving letters are in the Deutsches Museum in Munich. Photographs and slim documentary resources are also available in the Heimatsmuseum, Neuruppin, and the Wegener Gedankstätte in Zechlinerhütte bei Reinsberg— both in Germany. Abundant material pertaining to his Greenland work resides in the Dansk Polarcenter in Copenhagen. Scant additional resources lie in the university archives of Graz, Austria, and Marburg and Hamburg, Germany. A complete and annotated checklist of Wegener’s papers and letters became available in 1998 through the labors of Ulrich Wutzke: “Alfred Wegener. Kommentiertes Verzeichnis der schriftlichen Dokumente seines Lebens und Wirkens,” Berichte zur Polarforschung 288 (1998). This supersedes the list (still useful) in Hans Benndorf, “Verzeichnis der Veröffentlichungen von Alfred Wegener,” Gerlands Beiträge zur Geophysik 31 (1931).

WORKS BY WEGENER

“Drachen- und Fesselballonaufsteige ausgeführt auf der Danmark-Expedition 1906–1908.” Meddelelser om Grønland XLII, no. 1 (1909): 5–75.

Thermodynamik der Atmosphäre. Leipzig: J. A. Barth, 1911. “Die Entstehung der Kontinente.” Petermann’s Mittleilungen 58 (1912): 185–195, 253–256, 305–309.

Wind-und Wasserhosen in Europa, Sammlung Wissenschaft Bd. 60. Braunschweig, Germany: Friedrich Vieweg & Son, 1917. Die Entstehung der Mondkrater. Braunschweig, Germany: Friedrich Vieweg & Son, 1921.

Die Entstehung der Kontinente und Ozeane. 3rd (completely revised) ed. Braunschweig, Germany: Friedrich Vieweg & Sohn, 1922.

Köppen, Wladimir, and Alfred Wegener. Die Klimate der geologischen Vorzeit. Berlin: Gebrüder Bornträger, 1924.

OTHER SOURCES

Wegener, Else. Alfred Wegener: Tagebücher, Briefe, Erinnerungen. Wiesbaden, Germany: F. A. Brockhaus, 1960.

Wutzke, Ulrich. Durch die weiβe Wüste: Leben und Leistungen des Grönlandforschers und Entdeckers der Kontinentaldrift Alfred Wegener, Edition Petermann. Gotha, Germany: Justus Perthes Verlag, 1997.

Mott T. Greene

Wegener, Alfred (1880-1930)

German meteorologist

Alfred Wegener was primarily a meteorologist who became much more famous for proposing the idea of continental drift. Decades after his death, the theory of continental drift that he had proposed in 1912 became the well-established foundation for the plate tectonics revolution in the earth sciences. Wegener heard mostly ridicule of his continental drift idea during his lifetime, but in the 1960s, oceanic data convinced scientists that continents do indeed move. Wegener was an eminent meteorologist in his time, but he was appointed professor late in his professional career, and died during one of his scientific trips to Greenland.

Wegener was born in Berlin, Germany to Richard, a minister and director of an orphanage, and Anna Wegener. From an early age, he hoped to explore Greenland, and he walked, hiked, and skated in order to build up his endurance for such a trip. He studied at the universities in Heidelberg, Innsbruck, and Berlin, receiving a doctorate in astronomy from the latter in 1905. Wegener's thesis involved conversion of a thirteenth-century set of astronomical tables into decimal notation; thereafter he abandoned astronomy in favor of meteorology . He carried out experiments with kites and balloons, fascinated with the new science of weather . In 1906, he and his brother Kurt set a world record in an international balloon contest by flying for 52 hours straight.

That year, Wegener also fulfilled his dream of going to Greenland. Wegener was chosen as official meteorologist for a Danish expedition to northeastern Greenland from 1906 to 1908. It was the first of four trips to Greenland he would take. In 1912, he returned to Greenland with an expedition to study glaciology and climatology; this trip was the longest crossing of the ice cap ever made on foot.

In 1908, Wegener accepted a job teaching meteorology at the University of Marburg. His lectures were very popular with students for their clarity and frankness. He admitted disliking mathematical details, yet in 1911 he published a textbook on the thermodynamics of the atmosphere, which included in embryonic form the modern theory on the origins of precipitation . The following year Wegener married Else Köppen, the daughter of the "Grand Old Man of Meteorology" in Germany, Wladimir Köppen. During World War I Wegener served as a junior military officer and was wounded twice. After the war he succeeded his father-in-law as director of the meteorological research department of the Marine Observatory near Hamburg. There he conducted experiments to reproduce lunar craters by hurling projectiles at various ground substances, demonstrating that the craters were probably of impact, rather than volcanic, origin. He also continued to analyze the data from Greenland, observe meteorological phenomena, and develop his earlier ideas on the origin of the continents and the oceans .

Wegener had first thought of the idea of continental drift in late 1910 while looking at a world map in an atlas. He noticed that the east coast of South America matched like a puzzle piece with the west coast of Africa , but dismissed the idea of drifting continents as improbable. The next year, however, he came across a list of sources arguing that a land bridge must have connected the two continents at one time, since similar fossils from the same time period appeared in both Africa and Brazil. Wegener immediately began to search out fossil evidence to support the idea of drifting continents. Within a few months he presented his hypothesis in two public forums.

Wegener published an extended account of his idea as Die Entstehung der Kontinente und Ozeane (The origin of continents and oceans) in 1915. The first edition was only 94 pages long, with no index. The second edition, much expanded and revised, attracted attention in Europe . The third edition was translated into English, French, Spanish, Swedish, and Russian in 1924 and was then widely read for the first time. The first English translation correctly referred to the idea of "continental displacement," as Wegener had termed it. The name "continental drift" was coined later.

Wegener's was the first coherent and logical argument for continental drift that was also supported by concrete evidence. He proposed that a huge supercontinent had once existed, which he named Pangaea, meaning "all land." He suggested that Pangaea was surrounded by a supersea, Panthalassa, and that 200 million years ago, in the Mesozoic period, Pangaea began to rift into separate continents that moved away from each other. The Americas drifted westward from Europe and Africa, forming the Atlantic Ocean. India moved east from Africa, and Australia severed its ties with Antarctica and moved towards the equator.

Wegener's hypothesis departed radically from the accepted view of the earth in his day. Other geologists believed that the earth was still cooling and contracting from a molten mass, and that lighter rocks such as granite (termed "sial"), moved towards the surface, underlain by denser rocks such as basalt ("sima"). Mountain ranges, they believed, were produced by the cooling contraction, like wrinkles appearing on a drying fruit. To these scientists, the continents and the ocean basins were initial and set features. It seemed impossible for continents to move through the ocean rocks.

Wegener instead proposed that the lighter sial that made up continents could move horizontally through the oceanic sima; if the continents can rise up vertically, he argued, they must be able to move horizontally as well, as long as sufficient force is provided. Thus the Rocky Mountains and the Andes, on the western edges of the Americas, were formed by the resistance of the sima layer to the continents plowing through them. Island arcs like Japan and the West Indies were fragments left behind in the wake of these giant drifting continents.

Wegener's strongest argument was the similarities of rocks, animals, and plants on both sides of the Atlantic. He pointed to the fossils of several reptiles and flora that were known only in Africa and South America, and to the fact that the distribution of some living animals was hard to explain unless the continents had once been connected. Scientists had previously explained these in terms of a land bridge that had once connected the continents and then sunk into the ocean. Wegener argued that this was impossible; if a bridge was made of sial, it could not simply sink and disappear.

However, Wegener couldn't find an adequate mechanism to explain continental drift. He suggested two mechanisms, which were later disproved. One was Pohlflucht, or "flight from the poles," to explain why continents seemed to drift towards the equator. Pohlflucht, also known as the Eötvös force, came from the fact that the Earth is an oblate spheroid, slightly flattened at the poles and bulging at the equator. Second, Wegener had to explain the westward movement of the Americas; he suggested that some kind of tidal force must be doing the work.

Wegener's hypothesis was received with ridicule. For decades, other geologists scoffed at the idea of drifting continents. Some scientists supported him, but there was not enough geological evidence to prove beyond a doubt that he was essentially right. Wegener's first critic was his father-inlaw, Köppen, who apparently wanted Wegener to stay in meteorology and not wander into unknown areas like geophysics. At the first lecture in Frankfurt in 1912, some geologists were apparently indignant at the very notion of continental drift. The initial reaction was mixed at best, and hostile at worst. In 1922, when The Origin of Continents and Oceans first appeared in English, it was blasted in a critical review and at a scientific meeting. Subsequently, continental drift provoked a huge international debate, with scientists ranging themselves on both sides.

Detractors had plenty of ammunition. It was soon shown that Pohlflucht and tidal forces were about one millionth as powerful as they needed to be to move continents. The paleontological evidence was thought to be inconclusive. In 1928, at a meeting of fourteen eminent geologists, seven opposed it, five supported it without reservation, and two supported it with reservations. From then until after World War II, the subject was put on the back burner of scientific debate. In the only major variant on the theory, South African geologist Alex du Toit, a vigorous defender of continental drift, proposed in 1937 that instead of Pangaea there were two super-continents , Laurasia in the northern hemisphere and Gondwanaland in the south.

Many eminent geologists, such as Sir Harold Jeffreys in England and, later, American paleontologist George Gaylord Simpson, were vehement critics of Wegener and his continental drift theory . Science historians consider it likely that the prestige of the critics often carried too much weight in the argument over the theory itself. Wegener himself often complained about the narrow-mindedness of geophysicists who could not accept new ideas. In 1926 Wegener was finally given a professorship in meteorology and geophysics at the University of Graz. Four years later he sailed from Copenhagen to Greenland as leader of a major expedition. On November 1 of that year, he and others in the party celebrated his fiftieth birthday at a camp in the center of the Greenland ice cap. Wegener headed for the west coast that day, and apparently died of heart failure. His body was later found about halfway between the two camps.

After World War II, and several decades after Wegener's disappearance, other geologists began to uncover clues that eventually led to the plate tectonics revolution. The development of paleomagnetism in the early 1950s demonstrated that rocks in different continents appeared to have different directions of magnetization, as if continents had drifted apart from each other. In addition, oceanographers began to map the ocean floor to learn about its origin. They learned that the ocean floor was not a fixed glob of sima at all. In 1960, American geologist Harry Hammond Hess proposed the theory of seafloor spreading: that the ocean floor is constantly being created at underwater ridges in the middle of the oceans, spreading outward, and being consumed in trenches underneath the continents. By the mid 1960s, new data on magnetic anomalies in the Pacific Ocean revealed that seafloor spreading did indeed occur. Here was the mechanism by which Wegener's continents could drift: The ocean floor was constantly regenerating itself. By the end of the 1960s, continental drift had begun to be accepted by the entire earth science community. It had taken half a century, but Wegener's hypothesis became the foundation for a revolution among geologists and a cornerstone for modern views of Earth's history.

See also Convergent plate boundary; Divergent plate boundary

WEGENER, ALFRED LOTHAR

(b. Berlin, Germany, 1 November 1880; d. Greenland, November 1930), meteorology, geophysics.

Wegener was the son of Richard and Anna Wegener; his father, a doctor of theology, was director of an orphanage. Wegener started his schooling at the Kollnisches Gymnasium in Berlin, studied at the universities of Heidelberg and Innsbruck, and presented a thesis on astronomy at Berlin in 1905. He had meanwhile become interested in meteorology and geology, and a desire to learn at first hand about polar air masses led him to join a Danish expedition to northeastern Greenland in 1906-1908. It was the first of four Greenland expeditions in which he participated. and the exploration of that territory remained one of his dominant interests.

From 1908 to 1912 Wegener was a lecturer in meteorology at the Physical Institute in Marburg. His lectures, noted for their vividness, frankness, and open-mindedness, showed an ability and taste for seizing on broad issues in complicated topics as well as considerable distaste for mathematical detail. In 1912-1913, with Captain J. P. Koch of Denmark Wegener led his second expedition to Greenland: its emphasis was on glaciology and climatology. From 1914 to 1919 he was mainly a junior military officer. After the war he worked at the meteorological experimental station of the German Marine Observatory at Gross Borstel, near Hamburg. A special professorship in meteorology and geophysics was created for Wegener at the University of Graz in 1924. He went to Greenland as a leader of expeditions in 1929-1930 and 1930-1931. In 1930 he was a member of a party that became lost and suffered severe privations, On 1 November of that year, his fiftieth birthday. he left a base in central Greenland for the west coast and was not seen again.

Wegener’s fame today rests on his work as an originator of the idea of continental drift. He stated that he first toyed with the idea in 1910, on noting the degree of apparent correspondence between the shapes of the coasts of the Atlantic on its west and east sides, particularly those of South America and Africa. At first Wegener regarded the idea of drifting continents as improbable, but his interest was rekindled in 1911, when he accidentally learned that evidence of paleontological similarities on both sides of the Atlantic was being used to support the theory that a “land bridge” had once connected Brazil with Africa.

At this time many geologists supported the view that various portions of ocean floors had intermittently risen and fallen in the process of progressive solidification and contraction of the earth from a molten state. This view included the notion that land bridges connecting continents would appear and disappear. Moreover, it was found difficult to reconcile Darwin’s theory of evolution with the widely acknowledged similarities in former organic life on different continents except through some connection such as land bridges.

After examining in some detail the paleontological and geological evidence of correspondences on the two sides of the Atlantic. Wegener concluded that the similarities were indeed sufficiently close to demand an explanation, and he linked them to his earlier thinking on continental drift. In a lecture at Frankfurt in January 1912, Wegener announced his theory that continents had actually moved thousands of miles apart during geological time, offering it as an alternative to the land bridge theory. Provisional accounts of the theory appeared in two short papers written in the same year.

During a long sick leave from, war service (he was wounded twice), Wegener wrote an extended account of his continental drift theory, which appeared as Die Entstehung der Kontinente und Ozeane in 1915. This book was his main work on the subject and incorporated the investigations for which he is now noted. (In the book, Wegener referred to “die Verschiebung der Kontinente,” which was accurately translated in the English edition of 1924 as “continental displacement.” The term “continental drift” was coined later.)

In his detailed elaboration, Wegener postulated that near the end of the Permian period (about 200 million years ago), there existed a single supercontinent, which he called Pangaea. It subsequently split into several pieces that began to move, generally westward and in some cases toward the equator. In broad terms. America moved westward from Eurasia and Africa to form the Atlantic Ocean, with India later drifting away from Africa and Australia moving toward the equator from Antarctica. At the beginning of the Quaternary period (50 million years ago) Greenland started to separate from Norway. Island arcs, for example, the Antilles, Japan, and the Philippines, were envisaged as detached fragments left in the wakes of drifting continents. Mountain formation was associated with compression of the advancing front of a moving continent against the resistance of the ocean floor.

In his effort to supply a mechanical explanation, Wegener set down an argument, based on a meteorological analogy, to the effect that the continents would drift steadily under an “Eötvös force,” He held that such a force could cause a floating body on a rotating planet to drift westward. He interpreted evidence on isostasy as indicating that continents are granitelike bodies that can be regarded as floating on a pliable medium. (Isostasy is connected, inter alia, with the notion of mountain “roots” that are somewhat less dense than the surrounding substrata.) Details of Wegener’s interpretation were incompatible with the theory of land bridges, leaving, he thought, continental displacement as the plausible explanation for evidence of paleontological similarities between separated continents. Wegener also suggested Pohlflucht (flight from the poles) as a possible mechanism.

At first Wegener looked upon his version of continental drift as a working hypothesis that would undergo some modification as new evidence emerged, and he spent much effort in seeking such evidence. His confidence in this theory grew strongly, and the later editions of his book show the evidence he accumulated. His most important new evidence was from his studies of paleoclimatology; as a meteorologist Wegener had become interested in ancient climates and drew inferences bearing on continental drift from his investigations of their varying patterns over geological time.

Wegener also particularly sought to strengthen his case by precise geodetic observations that involved repeated astronomical position-finding methods and measurements of radio time transmissions across oceans over a number of years. His search for geodetic support was one of the main motives for his third and fourth Greenland expeditions: he hoped to establish that Greenland is now drifting westward from Europe. But no significant results emerged.

Wegener was not the first to propose a form of continental drift. The apparent congruence of the western and eastern Atlantic coasts had attracted notice as early as about 1600, and the notion that the Atlantic continents had drifted apart in earlier times had been put forward specifically by A. Snider-Pellegrini in 1858. In 1908 the geologist H. B. Baker had suggested that all the continents had been grouped around Antarctica 200 million years ago, and in 1910 F. B. Taylor had independently proposed a general drift of continents toward the equator. But Wegener went to greater lengths in expounding the theory and in his sustained efforts to establish it, and it is his name that is principally remembered.

From 1919 to 1928 a great international controversy raged over continental drift. Wegener’s arguments on mechanism were shown to be untenable, and the paleontological evidence was held to be inconclusive. In 1928, at a historic gathering of fourteen eminent geologists, five supported the notion of continental drift without reservation and two with reservations, while seven opposed it. From then until after World War II, the theory received comparatively little attention. The most noted early variant of the theory was probably du Toit’s proposal in 1937 that instead of a single primordial continent Pangaea, there were two, Laurasia in the northern hemisphere and Gondwanaland in the southern.

Wegener’s other scientific contributions included work on the dynamics and thermodynamics of the atmosphere, atmospheric refraction and mirages, optical phenomena in clouds, acoustical waves, and the design of geophysical instruments, In his endeavors to test his continental drift theory through geodetic measúrements, he designed an efficient balloon theodolite for tracking balloons sent up from ships to great heights.

A principal early objection to Wegener’s theory was the failure to find an acceptable mechanism. Some time after his death, the idea of convection currents inside the earth’s solid upper mantle was developed and a mechanism based on this idea was suggested. The new proposal envisaged an upper mantle that, although behaving like a solid in response to ordinary stresses, flows like a fluid under stresses that have periods comparable with geological time. According to this theory the flow took the form of convection currents and continents were carried, instead of sliding, on top of a convection cell of the moving mantle material.

The early 1950’s saw the development of the new science of paleomagnetism, which indicated that remnant rock magnetism has preferred directions persisting over large areas of individual continents but varying from continent to continent. The directions are, moreover, generally different from the lines of magnetic force existing at the earth’s surface today. When continental drift, coupled with polar wandering, was invoked to fit the paleo-magnetic evidence, interest in Wegener’s work, with the modification that convection currents provide the driving mechanism for continental drift, was strongly revived.

A great quantity of evidence on characteristics of midocean ridges was later brought to bear. These ridges, now known to exist on the floors of all the main oceans, are characterized by some unusual properties, including: abnormally high heat flow from the earth’s interior, sequences of magnetic and gravity anomalies, thinning of the sediment cover as a ridge is approached, and interesting sequences in ages of ocean-floor material near ridges, giving rise to the notion of “sea-floor spreading.” Many geologists have associated the ridges with the top of rising convection currents, and certain ocean trenches with the locations of descending currents. Other recent evidence has indicated that a layer immediately below continents is much weaker than had previously been supposed.

At the same time, older arguments continue to be maintained and newer arguments to be raised against continental drift. Some distinguished geophysicists assert that the currently proposed mechanism does not stand up to fine analysis. Further questions include the following: Why should the east coastline of South America remain largely undistorted although its postulated westerly drift relative to Africa has involved a sideways global distortion of thousands of miles? How reliable are the assumptions made about the earth’s magnetic field? What is the reason for the comparative recency, as compared with the age of the earth, of the envisaged drift? Ad hoc answers to all these questions have been put forward by protagonists of the theory, yet again their answers have been questioned.

The enthusiasms of a considerable number of earth scientists lead them to assert, sometimes with a religious fervor, that continental drift is now established. It can at least be said that, whether large-scale continental drift in the envisaged sense has occurred or not, and whatever the finer detail may turn out to be, it is now widely recognized that movements and distortions of the earth’s outer layers over geological time must have been substantial. The theory of continental drift also is stimulating many scientists to gather new observations of much value to ideas on the evolution of the earth.

BIBLIOGRAPHY

I. Original Works. The principal publication for which Wegener is now noted is Die Entstehung der Kontinente and Ozeane (Brunswick, 1915; rev. eds., 1920, 1922, and 1929). the 3rd ed. (1922) translated into English, French, Spanish, Swedish, and Russian. A 5th ed., rev. by Kurt Wegener, appeared in 1936. His other publications include Thermodynamik der Atmosphäre (Leipzig, 1911); “Die Enstehung der Kontinente und Ozeane,” in Mitteilungen aus Justus Perthes geographischer Anstalt,58 (1912), 185–195, 253–256. 305–309; Die Klimate der geologischen Vorzeït (Berlin, 1924), written with W. Köppen; “Denkschrift über Inlandeis-Expedition nach Grönland.” in Deutsche Forschung (Berlin), 42 (1928), 181; and Mit Motorboot und Schlitten in Grönland (Leipzig, 1930).

II. Secondary Literature. For a full list of Wegener’s publications, see H. Benndorf, “Alfred Wegener,” in Beiträge zur Geophysik,31 (1931), 337–377. Further details of his life are in Else Wegener, Alfred Wegener (Wiesbaden, 1960); J. Georgi. “Memories of Alfred Wegener,” in Continental Drift, S. K. Runcorn. ed. (London, 1962), 309–324; and K. Wolcken. “Alfred Wegener.” in Meteoros (1955), 379–382. An important contemporaneous review of Wegener’s work on continental drift was published by the American Association of Petrologists in Theory of Continental Drift; a Symposium on the Origin and Movement of Land Masses, Both Inter-continental and Intra-continental, as Proposed by Alfred Wegener, E. De. Golyer, ed. (London, 1928).

K. E. Bullen

Alfred Lothar Wegener

1880-1930

German Meteorologist and Geophysicist

Alfred Lothar Wegener was a meteorologist and geophysicist best known for his theory of continental drift, according to which Earth's continents once formed a single landmass and over time drifted to their present positions. Largely rejected during his lifetime, Wegener's idea of continental motion is now universally accepted, although the details of his work have been superseded by plate tectonics.

Wegener was born in Berlin, Germany, on November 1, 1880, to Richard and Anna Schwarz Wegener. He attended the universities at Heidelberg and Innsbruck and received his doctorate in astronomy from Berlin in 1905. In 1906 he accompanied a Danish expedition to Greenland as their meteorologist. Upon returning Wegener lectured in meteorology at the Physical Institute in Marburg (1908-12). Wegener helped lead a second expedition to Greenland in 1912-13 to study glaciology and climatology. In 1924 a special chair of meteorology and geophysics was created for Wegener at the University of Graz. He again led expeditions to Greenland in 1929-30 and 1930-31. He died during the latter trip while attempting to resupply his party.

The idea of continental drift occurred to Wegener in 1910 when he noted the correspondence between the Atlantic shores of Africa and South America. He initially dismissed the idea as improbable. His interest was rekindled in 1911 when he learned paleontological evidence was being used to argue that a land bridge once connected Africa with Brazil.

Wegener became convinced the paleontological and geological similarities required explanation and presented a provisional account of his continental drift theory in 1912. An extended version appeared in 1915 under the title Die Entstehung der Kontinente und Ozeane ("The Origins of the Continents and Oceans") which was not widely read until the third edition appeared in 1924. Wegener was not the first to conceive of continental drift, but his account was the most fully developed and supported by extensive evidence.

Wegener proposed the existence of a supercontinent, which he named Pangaea, surrounded by a supersea, Panthalassa. He believed Pangaea began to split and move apart about 200 hundred million years ago. His strongest supports for the theory were the rocks and the flora and fauna on both sides of the Atlantic. Also, geodetic measurements indicated that Greenland was moving away from Europe. Finally, the separation of Earth's crust into a lighter granite floating on a heavier basalt suggested the possibility of continental horizontal transport.

The most serious problem for Wegener's theory was the lack of suitable mechanism. It was difficult to imagine a force strong enough to displace the continents through the solid mantle and oceanic crust. Wegener suggested two mechanisms that were later shown to be only one millionth as powerful as required. By 1928 Wegener's theory had been generally discounted.

Arthur Holmes suggested a viable driving mechanism in 1929. He argued that radioactive heating created convective currents within Earth's mantle, resulting in an internal zone of slippage. The motions thus generated were small but sufficient to account for the displacement of continental landmasses. Holmes' work drew little attention due to the disrepute of continental drift theory.

The discovery of mid-oceanic ridges after World War II renewed interest in Wegener's theory. Paleomagnetic studies in the early 1950s indicated that rocks have magnetic orientations that vary from continent to continent—consistent with continental drift. Wegener's work gained further support in the 1960s with the acceptance of sea-floor spreading and the discovery of subduction zones. Holmes's driving mechanism was then revived and is still widely accepted.

It was eventually recognized that Earth's crust is composed of plates moving relative to each other. Today, plate tectonics is the principal theory of the genesis, structure, and dynamics of Earth's continents.

STEPHEN D. NORTON

Alfred Lothar Wegener

The German meteorologist, Arctic explorer, and geophysicist Alfred Lothar Wegener (1880-1930) is remembered for his theory of continental drift.

Alfred Wegener son of an Evangelical preacher, was born in Berlin on Nov. 1, 1880. He attended university at Heidelberg, Innsbruck, and Berlin. He became interested in arctic climatology and joined the 1906-1908 Danish expedition to Greenland as meteorologist. He returned there in 1912-1913 and, wintering on a high glacier, completed studies begun on his first visit.

In 1908 Wegener settled at Marburg, lecturing there with enviable clarity on meteorology and astronomy. The next years were perhaps his most fruitful: he wrote up his Greenland material; produced his Thermodynamik der Atmosphäre (1911), a standard textbook which ran through several editions; and conceived his idea of continental drift. He saw active service in World War I.

Wegener was a scientific civil servant at the Meteorological Department of the Deutsche Seewarte in Hamburg (1919-1924) and professor of meteorology and geophysics at the University of Graz (1924-1930). There he drew together aspects of subjects hitherto considered disparate while planning for a two-winter expedition to Greenland, scheduled to begin in 1930. He made a preliminary visit in 1929. Early in November 1930, in attempting to cross Greenland from an ice-cap camp to the Kamarujuk base on the west coast, he lost his life.

Most of Wegener's life was spent in conventional meteorology, and his contributions both there and in polar exploration have been recognized. But Wegener is most widely remembered for his theory of continental drift. In 1910 he was struck by the congruity of the east and west Atlantic shorelines. This, coupled with his fortuitous reading of evidence indicative of a land bridge from Brazil to Africa, led him to examine the geologic and paleoclimatologic evidence for his rapidly burgeoning continental drift theory. He suggested that until Mesozoic times the light material of the earth's crust formed one continental block floating on the dense core, that relative movement has since occurred, and that the geographic poles have wandered. These views he published in 1912 and expanded into book form as Die Entstehung der Kontinente und Ozeane (1915; The Origins of Continents and Oceans, 1924). The theory first received adverse criticism and then interested discussion. Many objections were overcome in later editions of the work, but in seeking a mechanism for the movements, Wegener failed. Thus the theory was long discounted. Recent work based on new information has led to a general acceptance of the concept.

Further Reading

Wegener's biography by his daughter, Else Wegener, Alfred Wegener (1960), is in German. S.K. Runcorn, ed., Continental Drift (1962), includes a memoir on Wegener. Background on Wegener is in Johannes Georgi, Mid Ice: The Story of the Wegener Expedition to Greenland (trans. 1934).

Additional Sources

Schwarzbach, Martin, Alfred Wegener, the father of continental drift, Madison, Wis.: Science Tech, 1986. □