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