The Theory of Continental Drift (as well as a brief overview on Pangaea)
The existence of ‘Pangea’ and the notion of ‘Continental drift was suggested by German meteorologist Alfred Lothar Wegener. He stated that — “About 300 million years ago, Earth didn’t have 7 continents, but instead one super-continent called Pangaea (Greek for ‘All Lands’), which was surrounded by a single ocean, namely Panthalassa”.
Continental drift is the theory of the gradual movement of continents across the Earth’s surface over some time.
The thought of Continental Drift, proposed during 1912 by Wegener, was not accepted by the majority of scientists as the reason behind the movement of continents was not proven or disclosed. Wegener himself could not understand how modern-day tectonic plates moved from their positions as he somewhat calculated that the force that drove the movement of continents would have to be. His thoughts regarding the movement of continents related to centrifugal, tidal force and pseudo-force, but when he released this thought, the wider scientific community rejected it as calculations showed that the force was insufficient.
Another way he elucidated the westward movement of the Americas was by the gravitational effect of the sun and the moon. “Wegener’s inability to provide an adequate explanation of the forces responsible for continental drift and the prevailing belief that the earth was solid and immovable resulted in the scientific dismissal of his theories.”
As currently established by science, the outer shell of Earth, known as the Lithosphere, is broken into plates.
2 types of crust form these plates:
- Continental Crust — Thick, made of the rock Granite, not very dense — only about 2.7 grams per cubic centimetre
- Oceanic Crust — Thin, denser than continental crust as it is made of salt which has a density of about 3 grams per cubic centimetre.
All these crusts, along with the rigid mantle, make up the top layer of Earth. Beneath this, there is a melted, bubble-gum texture later called the Asthenosphere. In some sense, the plates float on the Asthenosphere. As the “plasma” in the Asthenosphere can move, a current known as a Convection Current occurs, driving plate motion. This happens when hot material becomes less dense and rises to the top of the Asthenosphere, and then it cools down, becoming denser, and sinks back down. This process drives the motion of the plate and is how contemporary scientists explain continental drift.
Though ongoing science has verified this, Alfred Wegener was unaware of this knowledge.
However, he found many pieces of evidence supporting his notion of Continental Drift, which he later published in his book, ‘The Origins of Continents and Oceans’.
The first piece of major evidence he established was, in fact, the apparent fit of the continents. This can be seen extending along the Eastern coast of South America, and the Western coast of Africa. During the late 1800s, about 300 years after the first accurate map of the world was released (Credited to Martin Waldseemülle during 1507 based on findings by multiple expeditions), it was known that the continents distinctly resembled pieces in a puzzle, but this was merely deemed a coincidence. Nonetheless, Wegener could not believe in the apparent, obvious resemblance, and this became his first proof of continental drift.
Following this, after conducting dozens of research expeditions, he came across another piece of evidence that further supported his idea; Fossil Correlation. During the many expeditions, he found the same fossils around one coast, as also in the corresponding coast that he believed would have been adjoined to the former.
A very valid example was of the Mesosaurus, a freshwater reptile found during the late Permian Period and Mesozoic Period. Its fossils were only found in the southern tip of South America and the southern tip of Africa. Wegener noted that the Mesosaurus could not have evolved in 2 places at the same time, and the freshwater reptile could not have made the journey across the modern-day salty Atlantic ocean — again backing his theory of Continental Drift — as the continents must have once been together in one landmass, and that area (where the Mesosaurus was found) must have been a place where that species thrived. More similar examples include Cynognathus, Lystrosaurus, and a tree known as Glossopteris.
Per contra, even though his evidence of Fossil correlation seemed to be credible, most geologists rejected his theory as some of the explanations given by him differed with other theories that were fully accepted. A precedent of this would be that in his evidence, he used fossils from different modern-day continents. Albeit, an established theory circulating was that there was a land bridge formed between continents, examples being Africa and South America.
Wegener’s penultimate primary confirmation of Continental Drift was Geological Structures, and Rock and Mountain correlation. This corroboration was found during another scientific expedition led by determined Wegener. The findings of that expedition were later disclosed. To summarize his findings, rock formations across vast oceans such as the Pacific ocean have had a similar resemblance, and have been of the same age and type. i.e. North East Mountains of modern-day America and mountains on the north-west coast of UK and Scandinavia; similar resemblance, same age, same type.
Finally, likely Wegener’s most compelling data to his proof was Paleoclimate Data. This part of his proof stated and started with the fact that when glaciers move across Earth, they leave Glacial Striations (deep, orderly scratches in rocks they have travelled through)
These Glacial striations were found in the Amazon rainforest and hot jungles of central Africa. The only reason for this was, these modern-day continents were once close to the poles as glaciers cannot form near the equator due to the intense amount of sunlight.
He also saw that Bituminous coal, made from compacted plant remains, were formed from plants originating from humid, sticky jungles. Strangely enough, all the Bituminous coal formed in jungles and dense shrubbery were found only in modern-day Antarctica, Australia, North America, European Russia, Ukraine, and more parts of Russia. This evidence, collected by Wegener himself, suggested that these frigid areas might have once been closer to the equator and been able to sustain jungles.
These above pieces of evidence were enough for Alfred Wegener to convince himself and the minority of the scientific population of Continental Drift, but it was only until April 29th 1967 that scientists had fully delved into geophysics, used advance sonar mapping systems, and accepted the theory to its entirety.
I think that the concept of Continental Drift is credible, accurate, and explains fossil and geological phenomena to its plentitude. It also helps scientists to justify seismic activity and the formation of volcanoes, mountain ranges, and earthquakes.