• Alfred Wegener proposed the Continental Drift theory in 1912. He was a German meteorologist, polar explorer, astronomer, and geologist, also known as the father of continental drift.
• The theory explains the movement of continents across the ocean bed. This process takes millions of years to complete.
• According to Wegener, all the continents were once a single mass called Pangaea (which means all earth). This supercontinent was surrounded by a mega ocean called Panthalassa (meaning all water).
• Later as Pangaea broke apart, it formed Laurasia and Gondwanaland. It again further broke apart into smaller continents that we know today.
• Thus Wegener proposed that continents are floating and constantly drifting on the earth’s surface.
• His hypothesis became the basis of present day plate tectonic theory.

Various Stages of CDT

• First stage: during the Carboniferous period, Pangea was surrounded by Panthalassa.
• Second stage: around 200 million years ago in the Jurassic period, Pangaea began to split into Laurasia and Gondwanaland.
• Third stage: during the Mesozoic epoch, the Tethys Sea filled the area between Laurasia and Gondwanaland and gradually broadened.
• Fourth stage: around 100 million years ago, North and South America drifted westward, resulting in the emergence of the Atlantic Ocean. The Rockies and Andes were formed by this drift.
• Fifth stage: the Orogenetic Stage, in which mountain-building activity took place.

Forces Responsible for Continental Drift

• There are two factors responsible for continental drift:
  • The first factor is a combined action of gravitational forces, pole-fleeing force, and buoyancy force, causing the drift to be equatorward because the planet is not perfectly round and has a bulge at the equator.
  • The ‘pole-fleeing force’ is caused by an increase in centrifugal force from the poles towards the equator.
  • The second factor is tidal currents caused by the Earth’s rotation, causing the drift to be westward.
• However, these two factors were eventually found to be insufficient reasons for continent drifting.
• This is considered a criticism of Wegener’s theory.

Evidence in support of CDT

• The Matching of Continents (Jig-Saw-Fit):
  • When facing one another, the shorelines of South America and Africa form a similarity. Similarly, when matched, Africa, Madagascar, and India’s east coast all fit together.
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• Geological Structure:
  • There is a remarkable similarity in geological structure along the two coasts of the Atlantic.
  • The Appalachian mountains of North America come up to the coast and continue across the ocean in the old Hercynian Mountains of southwest Ireland, Wales, and central Europe.
  • The opposite coasts of Africa and Brazil display even greater resemblance in their structure and rocks.
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• Permo-carboniferous glaciations:
  • These are strong proof that at one point in time, landmasses were assembled together.
  • Evidence of this glaciation is found in Brazil, Falkland island, South Africa, the Indian peninsula, and Australia.
  • It is difficult to explain these extensive glaciations based on the existing distribution of landmass and water.
  • According to Wegener, at the time of Pangaea, the South Pole was situated near Durban on the present coast of South Africa.
• Distribution of Fossils:
  • Identical species and animals were found on both sides of the marine barrier, providing evidence through distribution of fossils.
  • For example, Mesosaurus, a freshwater crocodile-like reptile that lived between 286 and 258 million years ago, is only found in Southern Africa and Eastern South America.
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• Paleoclimatic Evidence:
  • Coal deposits have been found in temperate and polar regions, but coal is formed in tropical regions, providing paleoclimatic evidence.
• Biological evidence:
  • The migratory pattern of some animal species, such as lemmings, also hints towards the joined landmass, as they have the tendency to migrate westwards for the search of land, but they fall in the Atlantic because they have not forgotten their route when the landmasses were joined.

Criticism of CDT

• The continental drift theory faced a lot of criticism and controversy despite being convincing.
• The greatest criticism of this theory was due to the controversial forces stated to have caused the drift.
  • Experts argued that if the gravitational force of the moon or sun was so strong to cause the landmass to break, it would have stopped the rotations of the earth and made it stationary.
  • Also, In order to cause a drift in a landmass, the required rotations should have been at such a high speed that it would have thrown the atmosphere and everything else in the outer space away from the earth’s gravitational pull.
• The Precarboniferous history was not known, which raised questions about the theory’s accuracy.
• It was not clear why only northward and westward drift occurred.
• The idea of Sial floating over Sima was criticized as in reality, the lithosphere is floating on aesthenosphere.
• The theory’s explanation for the formation of mountains (Rockies and Andes) due to friction by Sima was considered self-contradictory.
• The theory also did not explain the formation of oceanic ridges and Island arcs.

Conclusion

• The Continental Drift Theory was rejected by most scientists and was disputed for decades after Wegener’s death in 1930.
• The idea of conventional currents in the upper mantle was developed in the 1920s, but Wegener was unable to incorporate it into his theory before he died.
• Despite its rejection, the theory’s central premise remained a driving force behind subsequent hypotheses such as plate tectonics and seafloor spreading.