The Continental Drift Theory: Revolutionary and Significant

Diagram of the Earth
From an article by Alfred Wegener (1880-1930) on his theory of Continental Drift published in Discovery, London, 1922. Getty Images

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 this 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 during the Jurassic period, called Laurasia and Gondwanaland, 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 his book in subsequent editions 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 also an important and influential step in leading to the modern theory of plate tectonics, which is how scientists understand the earth’s structure, history, and dynamics of the earth’s crust and the movement of continents today.

OPPOSITION TO CONTINENTAL DRIFT THEORY

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 since he maintained 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.” 1

Another theory was that warm water currents carried the fossils of temperate species found in arctic regions. Modern scientists debunked these theories, but at the time they helped stall Wegener’s theory.

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, which 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.

“Wegener also offered a more plausible explanation for mountain ranges….Wegener said they formed when the edge of a drifting continent crumpled and folded - as when India hit Asia and formed the Himalayas.” 2

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. 3

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.

Despite the resistance to his theory, during his lifetime Wegener continued to advocate for it, and there was much about it that was right.

DATA SUPPORTING CONTINENTAL DRIFT 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.4

Wegener also found evidence of tropical plant fossils and coal deposits in the frigid Arctic near the North Pole, and also evidence of glaciation in 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

"Scientists still do 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 can only be reached by combing all this evidence. . . It is only by combing the information furnished by all the earth sciences that we can hope to determine 'truth' here, 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, we have to be prepared always for the possibility that each new discovery, no matter what science furnishes it, may modify the conclusions we draw."

Wegener had faith in his theory and persisted in his 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 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 of his book. He kept the discussion of the plausibility of the Continental Drift Theory going until his untimely death in 1930.

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.

ACCEPTANCE OF CONTINENTAL DRIFT THEORY

When Wegener died, discussion of Continental Drift died with him for awhile. 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 sea floor 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 of continental drift, because it wasn’t just the continents that were moving through static oceans, as Wegener had originally thought, but rather entire tectonic plates, consisting of the continents, ocean floors, and parts of the upper mantle together. 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.

Today, the theories of continental drift and Plate Tectonics are the foundation of modern geology.  Scientists believe that there were several supercontinents like Pangaea that have formed and broken apart over the course of the Earth’s 4.5 billion year lifespan. Scientists also now recognize that the Earth is constantly changing, and that even today, the continents are still moving and changing. For example, the Himalayan mountain range, formed by the collision of India and Asia, is still growing, because continental drift is still pushing India into Asia. We may even be heading towards the creation of another supercontinent in another 75-80 million years due to the continued movement of the continents.

But scientists are also realizing that plate tectonics do 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 because we understand our planet increasingly as a complex system”6 and throwing yet another variable into our understanding of our complex Earth.

REFERENCES

1. Sant, Joseph (2017). Wegener and Continental Drift Theory. Retrieved from http://www.scientus.org/Wegener-Continental-Drift.html on Apr 28, 2017.

2. Excerpts and Readings on Alfred Wegener (1880-1930), http://pangaea.org/wegener.htm   

3. Sant, Joseph (2017). Wegener and Continental Drift Theory. Retrieved from http://www.scientus.org/Wegener-Continental-Drift.html on Apr 28, 2017.

4. Continental Drift, National Geographic, http://www.nationalgeographic.org/encyclopedia/continental-drift/

5. Alfred Wegener (1880-1930), Berkeley Univ., http://www.ucmp.berkeley.edu/history/wegener.html

6. Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences, Flipped from head to toe: 100 years of continental drift theory, Science Daily, January 5, 2012, https://www.sciencedaily.com/releases/2012/01/120104133151.htm

 

RESOURCES AND FURTHER READING

Alfred Wegener (1880-1930), Berkeley Univ., http://www.ucmp.berkeley.edu/history/wegener.html

Bressan, David, Alfred Wegener’s Lost Cause For His Continental Drift Theory, forbes.com, https://www.forbes.com/sites/davidbressan/2017/01/06/alfred-wegeners-lost-cause-for-his-continental-drift-theory/#14859f711149

Conniff, Richard, When Continental Drift Was Considered Pseudoscience, Smithsonian Magazine, June 2012, http://www.smithsonianmag.com/science-nature/when-continental-drift-was-considered-pseudoscience-90353214/

Continental Drift, National Geographic, http://www.nationalgeographic.org/encyclopedia/continental-drift/

Continental Drift: The Evolution of Earth; Continental Drift Theory: Understanding Our Changing Earth, Futurism, https://futurism.com/continental-drift-theory-2/

Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences, Flipped from head to toe: 100 years of continental drift theory, Science Daily, January 5, 2012, https://www.sciencedaily.com/releases/2012/01/120104133151.htm

Sant, Joseph (2017). Wegener and Continental Drift Theory. Retrieved from http://www.scientus.org/Wegener-Continental-Drift.html on Apr 28, 2017.