Continental Drift Theory: continents cover 29 per cent of the surface of the earth and the remainder is under oceanic waters. The positions of the continents and the ocean bodies, as we see them in the map, have not been the same in the past. Their position is still changing. To answer the questions arises what were their positions in the past? Why and how do they change their positions? many theories are published. One of them is Continental Drift Theory

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Continental Drift

Abraham Ortelius, a Dutch map maker, was the first one to propose the possibility of the two Americas, Europe and Africa to be once joined together as early as 1596. Antonio Snider drew a map showing the three continents together in 1858, but this was so much opposed to the scientific view then prevailing that nobody took notice of it. In 1910, F.B. Taylor of America invoked the hypothesis of horizontal displacement of continents or continental drift with a view to explaining the distribution of mountain ranges.

Continental Drift Theory

In 1912 Alfred Wegener (a German meteorologist) postulated that all the continents once were together forming a single continent.
According to him, about 250 million years ago, the earth was made up of a single landmass called Pangaea (meaning “all lands”), and a single ocean surrounding it called as Panthalassa.

Over a long period of time, probably 200 million years ago, they drifted apart and gradually moved to form their present position.

First, Pangaea broke into two landmasses namely Laurasia in the north and Gondwana in the south. Tethys sea was formed between Laurasia and Gondwana. Laurasia further split into Eurasia and North America. Gondwana land split into Africa, South America, Antarctica, Australia, and India.

Various Stages of Continental Drift Theory

  • First Stage: The first stage occurred during the Carboniferous period, when Pangea, a supercontinent, was encircled by Panthalassa, a mega-ocean.
  • Second Stage: In the second stage around 200 million years ago in the Jurassic period, the supercontinent, Pangaea, began to split. Pangaea first broke into large continental masses as Laurasia and Gondwanaland formed the northern and southern components respectively.
  • Third Stage: In the third stage, the Tethys Sea progressively filled the area between Laurasia and Gondwanaland during the Mesozoic epoch, and it gradually broadened.
  • Fourth Stage: In the fourth stage around 100 million years ago when North and South America drifted westward, resulting in the emergence of the Atlantic Ocean. The Rockies and Andes were formed by the westward drift of North and South America.
  • Orogenetic Stage: The Orogenetic Stage in which mountain-building activity took place is the fifth stage.

Note: The Himalayas and Alps were constructed by the folding of Tethys Sea deposits.

Forces Responsible for Drifting of Continents

According to Wegener, the drift was in two directions:

  1. Towards the equator due to the interaction of forces of gravity, pole-fleeing force (due to centrifugal force caused by earth’s rotation) and buoyancy (ship floats in water due to buoyant force offered by water)
  2. Westwards due to tidal currents because of the earth’s motion (earth rotates from west to east, so tidal currents act from east to west, according to Wegener).
  • Wegener suggested that tidal force (gravitational pull of the moon and to a lesser extent, the sun) also played a major role.
  • The polar-fleeing force relates to the rotation of the earth. Earth is not a perfect sphere; it has a bulge at the equator. This bulge is due to the rotation of the earth (greater centrifugal force at the equator).
  • Centrifugal force increases as we move from poles towards the equator. This increase in centrifugal force has led to pole fleeing, according to Wegener.
  • Tidal force is due to the attraction of the moon and the sun that develops tides in oceanic waters (tides explained in detail in oceanography).
  • According to Wegener, these forces would become effective when applied over many million years, and the drift is continuing.

Evidences to support continental drift theory

Wegener put forward certain evidences to support the continental drift theory. The continental drift theory is supported by the following evidences.

1. Jigsaw Fit:

The corresponding edges of the continents fit together. For example, the western side of Africa and the eastern side of South America fit together. Similarly, when matched, Africa, Madagascar, and India’s east coast all fit together. The best fit is obtained if the coastlines are matched at a depth of 1,000 meters below current sea level

Eastern South American and West African coastlines show the best jigsaw fit

2. Geological Fit: Rocks of Same Age Across the Oceans:

Radiometric dating techniques have been used to correlate rock development across continents. It suggests that the 2,000 million-year-old strip of ancient rocks off the coast of Brazil corresponds to the mountain ranges of Western Africa.

  • Similarities can also be found between the Caledonian and Appalachian mountains.
  • It also implies that the early marine deposits along Africa’s and South America’s coastlines date from the Jurassic period, implying that the ocean did not exist before then.
Geological fit of opposing continental coastline

3. Tectonic Fit:

  • Fragments of an old fold mountain belt between 450 and 400 million years ago are found on widely separated continents today.
  • Pieces of the Caledonian fold mountain belt are found in Greenland, Canada, Ireland, England, Scotland and Scandinavia. When these land masses are re-assembled the mountain, belt forms a continuous linear feature.
Caledonian/Acadian mountain belts at the end of the Caledonian. Present day coastlines in grey.

4. Glacial Deposits:

  • Today, glacial deposits formed during the Permo-Carboniferous glaciation (about 300 million years ago) are found in Antarctica, Africa, South America, India and Australia.
  • If the continents haven’t moved, then this would suggest an ice sheet extended from the South Pole to the equator at this time – which is unlikely as the UK at this time was also close to the equator and has extensive coal and limestone deposits.
  • If the continents of the southern hemisphere are re-assembled near the South Pole, then the Permo-Carboniferous ice sheet assumes a much more reasonable size
Evidence from the Permo-Carboniferous glaciation

5. Fossil Evidence:

  • There are many examples of fossils found on separate continents and nowhere else, suggesting the continents were once joined. If Continental Drift had not occurred, the alternative explanations would be:
  • The species evolved independently on separate continents – contradicting Darwin’s theory of evolution.
  • They swam to the other continent/s in breeding pairs to establish a second population. 
  • The fossil of a Fern tree, about 360 million year old, has been found only in India and Antarctica.
Fossil Evidence

Certain identical rare fossils have been found in different continents. The fossils of Mesosaurus (a small Permian reptile), for example, have been found only in Africa and South America.

  • Tillite: Tillite is a type of sedimentary rock formed by glacier deposits. The Gondwana system of sediments from India has been discovered to have parallels in six different landmasses of the Southern Hemisphere, including Africa, the Falkland Islands, Madagascar, Antarctica, Australia, and India. It reveals that the antiquity of both landmasses was strikingly similar.
  • Placer Deposits: Gold placer deposits can be discovered along the Ghana coast (West Africa). However, there is no source rock in the immediate vicinity. The fact that gold-bearing veins may be found in Brazil is incredible.
    • When the two continents are laid side by side, it appears that Ghana’s gold reserves are sourced from the Brazil plateau.
  • Distribution of Fossils: Identical species and animals were found on both sides of the marine barrier. 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.

Criticisms of Theory of Continental Drift

  • Wegener discusses how buoyancy, tidal currents, and gravity all play a role. These, however, were insufficient to move continents.
  • He favors westward or equatorial travel, but movements have occurred in all directions.
  • Alfred Wegener was unable to explain the pre-carboniferous period of time. He didn’t say why the drift started in the Mesozoic era and not earlier.
  • Oceans were not taken into account in the theory.
  • Oceanic ridges and Island arcs were not explained by the idea.
  • Large-scale motions are thought to be impossible due to the rigidity of the Earth’s crust.
  • Wegener’s theories failed to provide a convincing mechanism for supporting the displacement of bigger masses during long voyages.

Extra Point for Theory of Continental Drift

‘Enchanted rock is a pink’ coloured ancient Granite rock located in Texas Which attracts tourists

Continental Drift Theory UPSC

Question can be asked in the UPSC based on distribution of Ocean and Continent, Theory of Continental Drift, Plate tectonics theory and Seafloor spreading theory.

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