Wegener’s Unbelievable Revelation: Continents Moving, Seriously?
In 1910, Alfred Wegener, a meteorologist from Germany, discovered a surprising fact while briefly looking at a map. He noted that the lines of the East Coast of South America and the West Coast of Africa have remarkably similar shapes. Was this just a coincidence? Or was there a bigger story behind it?
To solve all these questions, Wegener explored and studied his discovery. As a result, he published a book called “The Origin of Continents” in 1912. In this book, Wegener first proposed the theory of continental drift. He argued that the continents were originally one, and over time, the continents on both sides of the Atlantic drifted in their respective directions.
His claim was simple. The continents are made up of relatively low-density granite, so they can float on the denser basaltic oceanic crust. The core idea of Wegener’s continental drift theory was that the continents are not fixed to the Earth’s core and float like icebergs.
However, his theory faced a lot of criticism in the academic community at the time. The claim that continents can float was a hard story to imagine for many scholars. They rebutted Wegener, saying, “Are you saying that these enormous continents can float around? Stop talking nonsense. Isn’t the meteorologist making this baseless claim? Bring the evidence and shut up.”
Despite this, Alfred Wegener did not abandon his theory. He published another book called “The Origin of Continents and Oceans” in 1915. In this book, he argued as follows:
“If you look at the continents of the Earth now, they are divided into Africa, Australia, North America, Europe, etc. However, at the end of the Permian period of the Paleozoic era, 300 million to 250 million years ago, all the continents would have been a supercontinent, that is, Pangaea. This supercontinent began to divide again 200 million years ago, and the continents moved, and then it would have taken on the current shape of the Earth.”
So, what was the Earth’s environment like during the time of Pangaea when all the continents were together? Wegener claimed that the inland temperature would have formed a lot of dry climates compared to now.
Next, he assumed that giant mountains would have formed, so large that even clouds could not reach the inland areas of Pangaea. In such an environment, a very large desert would have appeared. And with the continents together, the shallow seas where creatures primarily live would have been limited to narrow areas around Pangaea.
These assumptions overlap with the time of the Permian mass extinction, when more than 95% of the existing species disappeared in a massive extinction event. The main cause of this Permian mass extinction is presumed to be a volcanic explosion, and the volcanic activity that occurs when continents come together may have had a significant impact on the species.
So, on what basis was Wegener’s continental drift theory established? The first evidence is that the shape of the east coast of South America and the west coast of Africa is remarkably similar. It looked as if two puzzle pieces fit perfectly.
The second evidence is the continuity of geological structures. The geological structures of the Appalachian Mountains in North America, the Caledonian Mountains in Scotland, and the Gletscher, Cabot faults, which are very far apart, were similar, and this was evidence supporting his claim.
The third evidence is the distribution of fossils. Wegener noted the distribution of plant fossil Glossopteris and reptile fossil Mesosaurus. These fossils were evenly distributed in several continents, including Africa and South America, which was evidence suggesting that organisms lived together in Pangaea and then separated.
The fourth evidence is the traces of glaciers. Currently, in South America, Africa, India, Australia, etc., which belong to tropical or temperate regions, large glacial sedimentary layers formed at the end of the Paleozoic era are distributed. If you combine all these sedimentary layers, you can see that the continents are all connected with Antarctica in the center.
Lastly, the fifth evidence is climatological evidence. Coal layers created in the forest climate, salt, gypsum, limestone, etc., created in arid climates are commonly found in South America, Australia, Antarctica, etc., and this was evidence supporting his claim. In addition, evidence was presented that the Atlantic is relatively younger than the Pacific. This means that the Pacific was the original ocean, and the Atlantic was a sea formed later as the continents moved.
Through various evidences, Wegener claimed the theory of continental drift. However, his theory had a crucial limitation. He could not explain the fundamental force that moves continents. Because of this limitation, existing geologists began to attack Wegener. In 1928, the American Petroleum Geological Society even held a symposium to refute the theory of continental drift.
Despite this, Wegener did not give up his theory. He was undoubtedly an outstanding meteorologist and published numerous papers and books. Even if he was not recognized in the field of geology, he insisted on his theory to the end.
Eventually, in 1930, Wegener went on an expedition to Greenland to collect evidence for the theory of continental drift. In this expedition, he and his team revealed that the thickness of the inland glacier is 1800m. However, Wegener disappeared during this expedition, and his voice fell silent forever.
Backing Up Wegener’s Theory: Solid Evidence for Continents Moving
The Continental Drift Theory proposed by Wegener was largely ignored by geologists. The reason was that there was a lack of explanation for the fundamental force that moves continents. However, after Wegener’s death, the development of observational equipment and the sophistication of research methods led to the discovery of evidence supporting the continental drift theory. These evidences provided us with insights into how earth’s continents move, and with the advancement of geological evidence and observational equipment, Wegener’s continental drift theory was widely accepted in the scientific community.
The first evidence supporting the continental drift theory is the mantle convection theory proposed by Holmes in 1929. The earth is composed of inner core, outer core, mantle, and crust. The layer called mantle, located just below the crust, is made up of a somewhat movable viscoelastic solid. This mantle is under tremendous pressure and temperature, and the mantle closer to the core is hotter, and the mantle closer to the crust is cooler. This temperature difference creates the convection of the mantle. This convection moves the crust. At this time, the hard mantle and crust are called lithosphere, and the fluid mantle below the lithosphere is called asthenosphere. The lithosphere is moved by being pulled by the asthenosphere.
However, Holmes’ mantle convection theory could not accurately explain the depth or size of the mantle convection. Moreover, at that time, there was no way to prove it with experimental evidence or observation, so, like the continental drift theory, it was not accepted at that time.
Next, the second evidence supporting the continental drift theory is the seafloor spreading theory. With the advancement of human science, we have come to understand more about the underwater terrain. It was discovered that giant canyons and mountains located deep in the sea are distributed all over the earth. Based on this fact, the seafloor spreading theory was announced.
The seafloor spreading theory is based on the fact that the direction of the earth’s magnetic field is not always constant and changes at a certain period. The most recent reversal of the magnetic field was 780,000 years ago. As the mantle convects, the material of the mantle penetrates the oceanic crust and creates mountains in the sea. When the material of the mantle cools down and becomes rock, it arranges the magnetic direction according to the magnetic field of the earth at that time. By analyzing this rock, you can find out the magnetic direction and age of the rock when it was created. This is clear evidence that continents are moving.
In this way, Wegener’s continental drift theory evolved into plate tectonics. Plate tectonics suggests that areas with many earthquakes are located on the boundary of the plate, and the thickness of the plate is about 100km. According to the theory, the lithosphere is divided into six large plates and 12 small plates. These plates move like a kind of fluid, and their movement directions and relative speeds are different. The interaction of these plates can explain natural phenomena such as earthquakes and volcanoes, and almost all geological phenomena.
However, plate tectonics has a limitation that it cannot perfectly explain the movement of the earth’s continental crust in the mantle. To compensate for this, plume tectonics was proposed in the 1990s. Plume tectonics explains the flow of a hot lump inside the earth rising or descending. This flow of plume itself creates the movement of the mantle and moves the plate.
Currently, scientists are trying to explain the geological phenomena of the earth more accurately by using both plate tectonics and plume tectonics. And in the future, the continents of the earth are expected to merge again to become a single giant continent called ‘Pangaea Ultima’. We will look at this in more detail in the next posting.