how is the hypothesis of continental drift

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The Continental Drift Theory: Revolutionary and Significant

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Opposition to Continental Drift Theory

Data supporting continental drift theory.

• Wegener's Search for Scientific Truth

Acceptance of Continental Drift Theory

• MLA, Harvard Graduate School of Design

Continental drift was a revolutionary scientific theory developed in the years 1908-1912 by Alfred Wegener (1880-1930), a German meteorologist, climatologist, and geophysicist, that put forth the hypothesis that the continents had all originally been a part of one enormous landmass or supercontinent about 240 million years ago before breaking apart and drifting to their current locations. Based on the work of previous scientists who had theorized about horizontal movement of the continents over the Earth's surface during different periods of geologic time, and based on his own observations drawing from different fields of science, Wegener postulated that about 200 million years ago, a supercontinent that he called Pangaea (which means "all lands" in Greek) began to break up. Over millions of years the pieces separated, first into two smaller supercontinents, Laurasia and Gondwanaland, during the Jurassic period and then by the end of the Cretaceous period into the continents we know today.

Wegener first presented his ideas in 1912 and then published them in 1915 in his controversial book, "The Origins of Continents and Oceans , " which was received with great skepticism and even hostility. He revised and published subsequent editions of his book in 1920,1922, and 1929. The book (Dover translation of the 1929 fourth German edition) is still available today on Amazon and elsewhere.

Wegener's theory, although not completely correct, and by his own admission, incomplete, sought to explain why similar species of animals and plants, fossil remains, and rock formations exist on disparate lands separated by great distances of sea. It was an important and influential step that ultimately led to the development of the theory of plate tectonics , which is how scientists understand the structure, history, and dynamics of the Earth’s crust.

There was much opposition to Wegener's theory for several reasons. For one, he was not an expert in the field of science in which he was making a hypothesis , and for another, his radical theory threatened conventional and accepted ideas of the time. Furthermore, because he was making observations that were multidisciplinary, there were more scientists to find fault with them.

There were also alternative theories to counter Wegener’s continental drift theory. A commonly held theory to explain the presence of fossils on disparate lands was that there was once a network of land bridges connecting the continents that had sunk into the sea as part of a general cooling and contraction of the earth. Wegener, however, refuted this theory maintaining that continents were made of a less dense rock than that of the deep-sea floor and so would have risen to the surface again once the force weighing them down had been lifted. Since this had not occurred, according to Wegener, the only logical alternative was that the continents themselves had been joined and had since drifted apart.

Another theory was that the fossils of temperate species found in the arctic regions were carried there by warm water currents. Scientists debunked these theories, but at the time they helped stall Wegener’s theory from gaining acceptance.

In addition, many of the geologists who were Wegener's contemporaries were contractionists. They believed that the Earth was in the process of cooling and shrinking, an idea they used to explain the formation of mountains, much like wrinkles on a prune. Wegener, though, pointed out that if this were true, mountains would be scattered evenly all over the Earth's surface rather than lined up in narrow bands, usually at the edge of a continent. He also offered a more plausible explanation for mountain ranges. He said they formed when the edge of a drifting continent crumpled and folded — as when India hit Asia and formed the Himalayas.

One of the biggest flaws of Wegener’s continental drift theory was that he did not have a viable explanation for how continental drift could have occurred. He proposed two different mechanisms, but each was weak and could be disproven. One was based on the centrifugal force caused by the rotation of the Earth, and the other was based on the tidal attraction of the sun and the moon.

Though much of what Wegener theorized was correct, the few things that were wrong were held against him and prevented him from seeing his theory accepted by the scientific community during his lifetime. However, what he got right paved the way for plate tectonics theory.

Fossil remains of similar organisms on widely disparate continents support the theories of continental drift and plate tectonics. Similar fossil remains, such as those of the Triassic land reptile Lystrosaurus and the fossil plant Glossopteris , exist in South America, Africa, India, Antarctica, and Australia, which were the continents comprising Gondwanaland, one of the supercontinents that broke off from Pangaea about 200 million years ago. Another fossil type, that of the ancient reptile Mesosaurus , is only found in southern Africa and South America.  Mesosaurus was a freshwater reptile only one meter long that could not have swum the Atlantic Ocean, indicating that there was once a contiguous landmass that provided a habitat for it of freshwater lakes and rivers.

Wegener found evidence of tropical plant fossils and coal deposits in the frigid arctic near the North Pole, as well as evidence of glaciation on the plains of Africa, suggesting a different configuration and placement of the continents than their present one.

Wegener observed that the continents and their rock strata fit together like pieces of a jigsaw puzzle, particularly the east coast of South America and the west coast of Africa, specifically the Karoo strata in South Africa and Santa Catarina rocks in Brazil. South America and Africa were not the only continents with similar geology , though. Wegener discovered that the Appalachian Mountains of the eastern United States, for instance, were geologically related to the Caledonian Mountains of Scotland. 

Wegener's Search for Scientific Truth

According to Wegener, scientists still did not appear to understand sufficiently that all earth sciences must contribute evidence toward unveiling the state of our planet in earlier times, and that the truth of the matter could only be reached by combing all this evidence. Only by combing the information furnished by all the earth sciences would there be hope to determine "truth," that is to say, to find the picture that sets out all the known facts in the best arrangement and that therefore has the highest degree of probability. Further, Wegener believed that scientists always need to be prepared for a possibility that a new discovery, no matter what science furnishes it, may modify the conclusions we draw.

Wegener had faith in his theory and persisted in using an interdisciplinary approach, drawing on the fields of geology, geography, biology, and paleontology, believing that to be the way to strengthen his case and to keep up the discussion about his theory. His book, "The Origins of Continents and Oceans , " also helped when it was published in multiple languages in 1922, which brought it worldwide and ongoing attention within the scientific community. When Wegener gained new information, he added to or revised his theory, and published new editions. He kept the discussion of the plausibility of the continental drift theory going until his untimely death in 1930 during a meteorologic expedition in Greenland.

The story of the continental drift theory and its contribution to scientific truth is a fascinating example of how the scientific process works and how scientific theory evolves. Science is based on hypothesis, theory, testing, and interpretation of data, but the interpretation can be skewed by the perspective of the scientist and his or her own field of specialty, or denial of facts altogether. As with any new theory or discovery, there are those who will resist it and those who embrace it. But through Wegener’s persistence, perseverance, and open-mindedness to the contributions of others, the theory of continental drift evolved into the widely accepted theory today of plate tectonics. With any great discovery it is through the sifting of data and facts contributed by multiple scientific sources, and ongoing refinements of the theory, that scientific truth emerges.

When Wegener died, discussion of continental drift died with him for a while. It was resurrected, however, with the study of seismology and further exploration of the ocean floors in the 1950s and 1960s that showed mid-ocean ridges, evidence in the seafloor of the Earth's changing magnetic field, and proof of seafloor spreading and mantle convection, leading to the theory of plate tectonics. This was the mechanism that was missing in Wegener's original theory of continental drift. By the late 1960s, plate tectonics was commonly accepted by geologists as accurate.

But the discovery of seafloor spreading disproved a part of Wegener's theory, because it wasn't just the continents that were moving through static oceans, as he had originally thought, but rather entire tectonic plates, consisting of the continents, ocean floors, and parts of the upper mantle. In a process similar to that of a conveyor belt, hot rock rises from the mid-ocean ridges and then sinks down as it cools and becomes denser, creating convection currents that cause movement of the tectonic plates.

The theories of continental drift and plate tectonics are the foundation of modern geology. Scientists believe that there were several supercontinents like Pangaea that formed and broke apart over the course of Earth's 4.5-billion year lifespan. Scientists also now recognize that Earth is constantly changing and that even today, the continents are still moving and changing. For example, the Himalayas, formed by the collision of the Indian plate and the Eurasian plate is still growing, because plate tectonics is still pushing the Indian plate into the Eurasian plate. We may even be heading toward the creation of another supercontinent in 75-80 million years due to the continued movement of tectonic plates.

But scientists are also realizing that plate tectonics does not work merely as a mechanical process but as a complex feedback system, with even things such as climate affecting the movement of the plates, creating yet another quiet revolution in the theory of plate tectonics variable in our understanding of our complex planet.

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ENCYCLOPEDIC ENTRY

Continental drift.

Continental drift describes one of the earliest ways geologists thought continents moved over time. Today, the theory of continental drift has been replaced by the science of plate tectonics.

Earth Science, Geology, Geography, Physical Geography

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Continental drift describes one of the earliest ways geologists thought continents moved over time. Today, the theory of continental drift has been replaced by the science of plate tectonics .

The theory of continental drift is most associated with the scientist Alfred Wegener . In the early 20th century, Wegener published a paper explaining his theory that the continental landmasses were “drifting” across the Earth, sometimes plowing through oceans and into each other. He called this movement continental drift.

Wegener was convinced that all of Earth’s continents were once part of an enormous , single landmass called Pangaea.

Wegener, trained as an astronomer , used biology , botany , and geology describe Pangaea and continental drift. For example, fossils of the ancient reptile mesosaurus are only found in southern Africa and South America. Mesosaurus, a freshwater reptile only one meter (3.3 feet) long, could not have swum the Atlantic Ocean. The presence of mesosaurus suggests a single habitat with many lakes and rivers.

Wegener also studied plant fossils from the frigid Arctic archipelago of Svalbard, Norway. These plants were not the hardy specimens adapted to survive in the Arctic climate . These fossils were of tropical plants, which are adapted to a much warmer, more humid environment. The presence of these fossils suggests Svalbard once had a tropical climate .

Finally, Wegener studied the stratigraphy of different rocks and mountain ranges . The east coast of South America and the west coast of Africa seem to fit together like pieces of a jigsaw puzzle , and Wegener discovered their rock layers “fit” just as clearly. South America and Africa were not the only continents with similar geology. Wegener discovered that the Appalachian Mountains of the eastern United States, for instance, were geologically related to the Caledonian Mountains of Scotland.

Pangaea existed about 240 million years ago. By about 200 million years ago, this supercontinent began breaking up. Over millions of years, Pangaea separated into pieces that moved away from one another. These pieces slowly assumed their positions as the continent we recognize today.

Today, scientists think that several supercontinents like Pangaea have formed and broken up over the course of the Earth’s lifespan. These include Pannotia, which formed about 600 million years ago, and Rodinia, which existed more than a billion years ago.

Tectonic Activity

Scientists did not accept Wegener’s theory of continental drift. One of the elements lacking in the theory was the mechanism for how it works—why did the continents drift and what patterns did they follow? Wegener suggested that perhaps the rotation of the Earth caused the continents to shift towards and apart from each other. (It doesn't.)

Today, we know that the continents rest on massive slabs of rock called tectonic plates . The plates are always moving and interacting in a process called plate tectonics.

The continents are still moving today. Some of the most dynamic sites of tectonic activity are seafloor spreading zones and giant rift valleys .

In the process of seafloor spreading, molten rock rises from within the Earth and adds new seafloor ( oceanic crust ) to the edges of the old. Seafloor spreading is most dynamic along giant underwater mountain ranges known as mid-ocean ridges . As the seafloor grows wider, the continents on opposite sides of the ridge move away from each other. The North American and Eurasian tectonic plates, for example, are separated by the Mid-Atlantic Ridge . The two continents are moving away from each other at the rate of about 2.5 centimeters (1 inch) per year.

Rift valleys are sites where a continental landmass is ripping itself apart. Africa, for example, will eventually split along the Great Rift Valley system . What is now a single continent will emerge as two—one on the African plate and the other on the smaller Somali plate. The new Somali continent will be mostly oceanic, with the Horn of Africa and Madagascar its largest landmasses.

The processes of seafloor spreading, rift valley formation, and subduction (where heavier tectonic plates sink beneath lighter ones) were not well-established until the 1960s. These processes were the main geologic forces behind what Wegener recognized as continental drift.

Colliding Skyward The collision of the Indian subcontinent and Asian continent created the Himalayan mountain range, home to the world's highest mountain peaks, including 30 that exceed 7300 meters (24,000 feet). Because continental drift is still pushing India into Asia, the Himalayas are still growing.

Urkontinent Alfred Wegener’s original name for his proposed, ancient continent was “Urkontinent”— ur meaning “first or original,” and kontinent meaning “continent” in Wegener’s native language, German. A more popular name for this huge ancient landmass is Pangaea, which means “all lands” in Greek.

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Last Updated

October 19, 2023

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