Plate tectonics: How Alfred Wegener reimagined the Earth

And Wegener was not the first to notice the amazingly good fit of the coasts of South America and Africa.

On January 6, 1912, during the Geological Association’s annual conference in Frankfurt, Germany, one man stood alone against the establishment. On that day, Alfred Wegener, then 31 years old, presented a theory challenging long-held beliefs about the origins of the Earth’s seas and continents. For, he proposed the idea that the location of the continents on the Earth’s crust might shift during the course of the planet’s history, contradicting the idea that the continents are fixed in place.

The bulk of the scientific community, including the president of the esteemed American Philosophical Society, first dismissed Wegener’s idea as “complete nonsense.” Like Darwin, Wegener challenged the prevailing worldview of his day and was met with hostility, derision, and even violence for his efforts. The bulk of Wegener’s contemporaries disregarded his hypothesis as the ramblings of an “incompetent career switcher” in the earth sciences, and most did not even bother to read his papers. The thought that the solid crust of the Earth might shift about was seen as ridiculous since it went against all that had been accepted as true and given up until that point.

Alfred Wegener doubted the conventional wisdom.

It took almost half a century for further surveys and research to vindicate Wegener and validate his idea. He is now widely regarded as the “father of plate tectonics,” or the theory that first proposed the existence of such features. However, Wegener might also be considered the Copernicus of earth sciences in hindsight, given that he transformed our understanding of the planet and put up with much criticism and hostility as a result.

The pioneering arctic scientist, Alfred Wegener, unfortunately, did not survive to witness the success of his idea. His recuperation came almost 30 years after his death in the Greenland ice deserts in November 1930. But what was so ground-breaking about the concept of “wandering continents”? Why did the scientific community fight so hard against these obvious answers for so long?

The situation at the time of Wegener

At the turn of the twentieth century, the concept of stability still dominated the prevalent view of the Earth. For a long time, many experts believed that the separation of the Earth’s surface into ocean basins and continents was a permanent feature of the planet. According to their theory, the Earth’s heated interior had to cool, causing the planet to contract before any changes could occur. However, some attributed these and other occurrences to the sporadic rising and falling of different regions of the Earth’s crust.

Why do the continents of Africa and South America fit together so perfectly?

None of these explanations, however, have been able to account for the myriad of discrepancies between the many observations and results being made by geoscientists. Some of them were things that previous explorers had already seen, such as how perfectly the contours of South America and Africa, and other continents and islands, fit together. Some landmasses and continents had strikingly similar fauna and vegetation.

Wegener was not the first to notice the amazingly good fit of the coasts of South America and Africa.

The concept of “land bridges” is an effort by biogeographers to provide an explanation for this phenomenon. This means that various plant and animal species should have been able to migrate to and from different continents at different points in history, depending on how broad the land bridges between them were. The modern-day separation of the continents was precipitated by the destruction of these bridges. Climate shifts and conflicting data on the ocean floor’s underlying structure were not explained by this theory, however.

Earthquakes as herd animals

Seismology, a relatively new scientific field, has posed another mystery that has yet to be answered. Seismic waves captured on tape demonstrated that earthquake activity was not uniformly distributed but rather clustered in certain areas. These zones of seismicity, which resembled belts, encircled the globe and followed the peripheries of the continents. Exactly what may have happened to cause this buildup, if it were to occur?

Hugo Benioff, a geologist at the California Institute of Technology, reported that faults and fault surfaces in maritime areas and on the peripheries of continents had signs of being “abnormal.” Seismic studies also showed that the mantle must be mostly solid, dispelling the notion that the Earth’s crust floats on a molten substance.

A young German scientist named Alfred Wegener broke into this muddled scene; he was well-known in his field as a meteorologist and polar researcher, but might be called a “lateral entrant” in the geosciences.

Wegener presents his theory of continental shift

Strangely, Alfred Wegener’s inspiration for plate tectonics came from the land bridge idea, which he subsequently rejected with such vehemence. In 1910, Wegener was working as a professor in meteorology and astronomy at the little University of Marberg when he stumbled across a collection of books and articles on land bridges in the university library. They gave a thorough account of the fossils discovered on both sides of the Atlantic that were taken to demonstrate the reality of a land bridge between South America and Africa.

These parallels piqued Wegener’s interest, and he began to scour additional sources for proof of connections between the two continents. A short time later, the aspiring meteorologist gushed to his future better half in a letter: “Doesn’t the east coast of South America fit exactly into the west coast of Africa as if they had once been part of a whole? This is a thought I must pursue…”

Which is just what Wegener accomplished. The more he looked into it, however, the more he realized that the accepted wisdom must be mistaken. After all, he wrote to his future father-in-law, the renowned climatologist Wladimir Köppen: “If the history of the earth suddenly suggests an entirely new and meaningful interpretation, why should we hesitate to jettison the old views?” To the public eye for the first time in two weeks, he presented a completely different perspective.

Epiphany scandal

The bombshell was dropped on the general assembly of the Geological Association in Frankfurt, Germany, on January 6, 1912, when Wegener presented his hypothesis of drifting continents and expanding oceans, rejecting the prevailing notion of land bridges. The essence of his concept was that the large-scale form of the Earth’s surface, or more accurately, the distribution of continents and seas, would continually change because the continents were moving.

discovery of plate tectonics

It was obvious to Wegener that the very different compositions of ocean bottoms and continental plateaus rendered the long-term sinking of land links highly improbable. Because of the decreased density of the land masses, it would have been necessary for the bridges to repeatedly rise to the surface, like a cork on water. In contrast, fossils and geological features unequivocally demonstrated an older relationship between the continents, implying that the continents must have moved.

“…rather of the superficial kind”

In a clear and unanimous vote, scientists everywhere rejected this ground-breaking proposal. The president of the American Philosophical Society called it “utter nonsense,” and Rollin Chamberlin, a geologist at the University of Chicago, declared: “Wegener’s hypothesis is of the rather superficial kind. He takes some liberties with our globe without being tied down by tiresome facts.”

Rejection and criticism

How come practically everyone was so strongly against Wegener and his theory? It not only helped him explain the remarkable biogeographical parallels across continents, but it also provided a much-needed explanation for the creation of mountains in the heart of continents like the Urals and the Himalayas.

According to Wegener’s theory, the Ural Mountains are all that remains from a long-ago continental collision, whereas the Himalayas are the product of a much more recent collision and are hence more tectonically active. A fuss was raised when Wegener first proposed this concept, but now it seems obvious and catchy.

Lacking a believable mechanism

This uproar of opposition was all the more surprising given that the concept of moving continents wasn’t exactly novel. As early as 1596, Dutch cartographer Abraham Ortelius proposed that the Americas had been torn away from Europe and Africa by “earthquakes and floods,” writing that “The traces of these cracks are revealed when one looks at a map of the world and compares the coasts of the three continents.”

What, then, was so scandalous about Wegener’s theory? Although Wegener’s hypothesis provided a logical explanation for a wide variety of occurrences in the history of the planet, it was plagued by the fact that it rested on clay. Wegener was unable to identify any forces or processes at the time that could have adequately explained the continents’ movement. Despite being well aware of this flaw, Wegener remained unconcerned about the basic soundness of his theories.

What if plate motion was driven by tides?

According to Wegener, the lighter continents “plowed” through the thicker material much as icebergs do through thin-pack ice because they floated on top of it. Wegener identified changes in centrifugal force and tides as the drivers for this movement, but these forces are too small to have such profound impacts.

The rotation of the Earth would stop in less than a year, according to the calculations of one scientist at the time, who found that a tidal force powerful enough to shift whole continents would do just that. Many people disagreed with Wegener’s theory because they thought his plan to plow the Earth’s continents through the oceanic crust would have permanently disfigured them.

Calculation errors in migration speed

The time limit Wegener proposed for migration was also a flaw in his hypothesis. By using incorrect data, he calculated that North America and Europe were moving apart at a rate of around 100 inches (250 centimeters) per year, which is almost ten times the fastest plate movement currently known and over one hundred times the real migration pace of both plates.

But what Wegener presented to geoscientists in lectures and in his 1915 book, The Origin of Continents and Oceans, was a visionary and ground-breaking proposal despite the inadequacies in portions of his theory. A minority of scientists agreed with Wegener and started looking for proof of continental movement, even though the majority of experts dismissed his theories as ridiculous.

Wegener receives support

Alexander du Toit, a geologist from South Africa, was an early proponent of Alfred Wegener’s ideas. In 1923, prompted by Wegener’s writings, a scientist crossed the Atlantic to South America to examine geological structures there and draw comparisons to those in South Africa. Because of all the ways in which they were the same, he became a firm believer in a continental uprising. Not only did he outline the fundamentals of continental drift in his 1937 book, “Our Wandering Continents,” but also discussed the potential triggers for plate tectonics.

Consider a water pot

Scientist Arthur Holmes had hypothesized years before that massive sluggish convection currents deep under the Earth’s core may be responsible for the motion of the continents. Hotter rock masses progressively rise from the depths of the earth, like a pot of boiling water, while cooler rocks gradually sink to the surface. However, Holmes still believed, incorrectly, that hot magma currents were located under the continents, whereas sinking motions occurred in the oceans.

In du Toit’s opinion, the theory of such convection provided a satisfactory explanation for the motor of plate motion. It had the distinct benefit that the continents might ride on the back of the convection currents rather than laboriously plowing through the oceanic crust, as Wegener still recommended.

The worldwide scientific community accepted du Toit’s idea but mostly disregarded it, just as they had Wegener’s. Too many people were unable to let go of their long-held, fixed ideas about the Earth, and there was still not enough proof to overcome those doubts.

It took a while, but plate tectonics eventually won

For decades, geoscientists would continue to be under the “spell” of Wegener’s idea. Despite the land bridge theory’s many flaws, it was widely supported by scholars and scientists until the 1960s. This, however, began to progressively shift as fresh scientific findings became available, most notably from the systematic study of seafloors.

Undersea mountains provide the first clues

The catalyst was the discovery of an extended mountain range in the middle of the Atlantic during routine echo-sounding investigations by the German research vessel Meteor in 1925. The northern to the southwestern parts of Africa was covered by this mid-Atlantic ridge. Later research revealed that these mid-ocean ridges wrap around the planet like the seams of a tennis ball. In the middle of each of these undersea ridges, rift valleys were found in 1953 by American scientists Maurice Ewing and Bruce Heezen, along which earthquakes and volcanism had accumulated. These rifts soon started to be linked to cracks in the Earth’s crust.

San Andreas Fault a transform fault
San Andreas Fault – a transform fault.

These hypotheses were supported by the work of American geologist Harry Hess, who, in light of the recent discoveries, thought back to his own studies from immediately after the Second World War. He had previously discovered a large number of odd mountains with flattened crests that resembled volcanoes and were located close to mid-ocean ridges. He named these mountains “Guyots”. He had come up with the theory that the Earth-spanning network of mid-ocean ridges was nothing more than the location of the formation of new ocean bottoms by the year 1960.

Hot lava would rise to the surface at these places via breaches in the Earth’s crust, pushing the current ocean bottom apart on both sides. The cooled debris gradually descends back into the depths of the deep-sea trenches. This movement may easily piggyback on the continents made of lighter material, much like a conveyor belt. Alternatively, Hess put it this way: “The continents do not plow through the oceanic crust under the action of unknown forces, they passively ride mantle material that comes to the surface at the crest of the ridge and then moves sideways away from it.”

The contribution of magnetism to Wegener’s theory

If this idea could still be supported by more evidence, Wegener’s theory of plate tectonics would have one of its motors. And right away, that data was acquired from an unexpected source. In 1956, Australian scientists started a quest to determine if the poles or the continents were moving relative to one another by monitoring magnetism. The changes they saw in the magnetic fields in various areas amply demonstrated that the continents must have moved at some point in the past, providing another piece of evidence to support Wegener’s theory of plate tectonics.

Hess’ theory and the importance of the mid-ocean ridges were further supported by magnetic field measurements of the ocean bottom, which showed a remarkable phenomenon. The polarization of the rocks varied throughout the mid-ocean ridges, forming a symmetrical stripe pattern on each side. Geophysicists Frederick Vine and Drummond Matthews believed that these remarkable symmetries were a blatant indication that new ocean bottom was forming in the center of these stripes. As it rises and flows to one side, the hot magma gradually cools. Its magnetic field “conserves” the direction that the Earth’s magnetic field was in at the moment of its crystallization throughout the process.

This provided at least a clear hint to many geologists that the Earth’s crust is actually dynamic rather than static. After being proposed by Wegener, the idea of Earth plates started to acquire recognition in the middle of the 1960s. Researchers and organizations who had been hesitant up until this point began to embrace the idea of moving plates.

After almost 50 years, Wegener and his pioneering ideas were eventually acknowledged and vindicated, but the arctic explorer and meteorologist did not survive to see the victory. He had previously passed away in 1930 while on a Greenland trip.

What happens at the plate boundaries?

Different types of interactions

As of today, the earth’s crust is separated into twelve large plates that cover the whole surface of the planet instead of being a single, cohesive structure. Rising and descending magma flows affect them:

Hot magma flows with lower densities ascend higher in the Earth’s mantle. The temperature on the surface of the Earth is much lower than at the core. Due to their larger density, the magma flows cool down there and descend down once again. As du Toit has previously postulated, the “drive” for the movement of the continental plates is these convection currents in the earth’s mantle.

Tectonic plates slam against, sink under, or move past one another. Characteristic forms of plate boundaries occur depending on the sorts of plates and the directions in which the plates move relative to one another.

Subduction: The heavier plate gives way

Subduction zones are created when two oceanic plates collide or when an oceanic plate subducts under a continental plate. The process involves one piece of oceanic crust being pushed beneath and pushed downward into the depths of the ocean. Crustal materials, in their downward journey, encounter hotter regions at greater depths. Approximately 1,800 and 2,700 degrees Fahrenheit (1,000 and 1,500 degrees Celsius) can be found at a depth of 60 miles (100 kilometers), causing the rocks to melt.

Volcanic mountains arise on the non-submerging plate as a consequence of oceanic plate collisions with continental plates. The Andes, for instance, were formed when the oceanic Nazca plate dipped under the South American plate. In contrast, the islands of Japan and the Philippines were created when two oceanic plates clashed. Trenches on the ocean floor may reach incredible depths when they form in front of a subduction zone. One such example is the Mariana Trench, which was created when the Philippine and Pacific plates collided.

Collision: folding, lifting and thrusting

High mountains, like the Alps or the Himalayas, may arise when two continental plates meet. The remaining piece of oceanic crust that was formerly located between them is forced downward into the depths first. Then, the crusts of the two continents press against one another. They are both light and equally buoyant, so they don’t sink too far. Overthrusting and folding, two of the many tectonic processes, result.

Beginning about 60 million years ago, as the Indian Plate advanced toward Eurasia and met around 40 million years ago, the Himalayas started to take shape. This resulted in the displacement of rocks over two massive fault surfaces. With India’s continued northward expansion at a rate of five millimeters each year, the Himalayas are constantly expanding to meet it.

Transform disturbance: gliding with small and large obstacles

However, collisions between Earth’s crustal plates are not usually 90 degrees. Frequently, they will attempt to sidestep one another. There are no prominent landforms, such as towering mountains or deep sea trenches, or explosive volcanic activity, anywhere near these so-called transform faults. However, these plate boundaries provide significant difficulties at depth because they do not glide past one another easily. The rock keeps getting stuck, building up stress deep down.

The stress is then released as an earthquake when the rock breaks apart. The San Andreas Fault in California is one of these regions known for its high seismic risk. Over there, the Pacific Plate is sliding over the North American Plate. The rate of movement is around 0.40 inches (1 centimeter) per year.

Birth of new crust in the middle of the seas

In addition to being common on land, transform faults are common at mid-ocean ridges, another key location for plate tectonics. Magma rises from the Earth’s mantle at them, following cracks in the lithosphere to the surface. It is at these locations that the crust cracks and the plates are pushed apart. Magma flows into the spreading zone, where it cools and hardens as a new oceanic crust. Giant undersea mountains can be seen rising from the bottom of these new crust formation zones.

As the Earth’s crust is constantly being renewed, oceans like the Atlantic have been able to keep growing in size throughout the planet’s history. The Mid-Atlantic and East Pacific ridges’ crusts are still drifting apart at a rate of 0.80 inches and 4.7 inches (2 and 12 centimeters) per year, respectively.

The revolutions in the theory of tectonics

The widespread adoption of plate tectonics was a watershed moment in the development of geosciences and their understanding of the planet. Many compare it to past paradigm shifts, such as Charles Darwin’s theory of evolution and Albert Einstein’s theory of relativity.

While this is happening, the traditional understanding of tectonics as the movement and collision of unyielding plates is falling apart once again. Recent studies depict plate tectonics as a self-regulating system of interactions in which all subsystems of planet Earth participate. It’s not a machine; it’s a series of intricate feedback loops.

Climate determines mountain form

A good climatic example would be one in which high mountains have a significant role in shaping the local weather. This new understanding of how climate influences tectonics is itself revolutionary. In the case of the Andes, for instance, the collision of the Nazca plate with South America is responsible for their formation. Sediment from the South Andes Mountains is carried by the humid environment to the Pacific Ocean. This rock is deposited on the South American crust by the Nazca Plate as it moves westward.

Alternatively, the Nazca Plate rasps the continental crust in the northern and central Andes, where sediment cannot build up due to the region’s dry environment. It is this process, with its dramatically increased friction, that ultimately transmits a force that causes the Andean plateau to expand in both height and breadth. This, in turn, decreases erosion by increasing the rain shadow on the western side of the Andes. The Andes, for example, have only existed for about 45 million years, but the subduction of the Nazca plate under South America has been going on since the Paleozoic era, hundreds of millions of years longer, so the classic idea of a folded mountain range as the result of a collision had to be revised as well.

Heat build-up and welding torches

Just as the relationship between the hot rock masses on the rise and the Earth’s crust is more nuanced than was previously believed. The lithosphere operates as a barrier layer to the surface like a heat blanket as a hot rock bubble rises, increasing the temperature of the rock underneath. Like a blowtorch, this accumulated heat may ultimately dissolve whole continents, as happened with Gondwana about 140–130 million years ago, when it split in two.

Starting with Wegener’s method, the last century’s plate tectonics brought about a paradigm shift in the way scientists saw the planet. As our knowledge of Earth expands, so does our appreciation of the planet as a whole, and with this comes a modest but profound shift in the idea of plate tectonics.

By Bertie Atkinson

Bertie Atkinson is a history writer at Malevus. He writes about diverse subjects in history, from ancient civilizations to world wars. In his free time, he enjoys reading, watching Netflix, and playing chess.