Geomorphology
Climatology
Oceanography

Class 8: Continental Drift Theory Current Theory

Topics Covered in this Lecture

  1. Basic Postulates of Continental Drift Theory
  2. Evidences Supporting the Theory
  3. Stages of Drift Theory
  4. Critical Evaluation
  5. Concretional Current Theory


It is one of the earliest theory which talks about rifting and drifting of the continents.

Assumptions

  1. SIAL floats on SIMA without any resistance.

  2. Forces responsible for the drift are-


    a- tidal force resulting in the westward movement of the continents.


    b- centrifugal force and the force of buoyancy which resulted in the northward movement of the continents.

Theory

  • Before the Carboniferous period, there was a supercontinent – Pangea surrounded by a superocean-Panthalassa.

  • After the Carboniferous period, In the Mesozoic era, the Pangea broke into two parts, the northern part was known as Lauretia/Angara land while the Southern part was known as Gondwanaland. This phase is known as the “opening of Tethys”.

  • In the later period, Angara land further broke into North America and Eurasia, while the Gondwanaland broke into South America, Africa, Peninsula India, Madagascar, Australia, and Antarctica.

  • The westward movement of both the Americas resulted in the opening up of the S-shaped Atlantic ocean.

  • The northward movement of peninsular India resulted in the formation of the Indian Ocean. The Tethys sea was reduced in size to form the present-day the Mediterranean Sea.

  • According to him, mountains were formed because of fiction between SIAL and SIMA while the trailing margins of the continents gave rise to Island Arc festoons.

Criticism

  1. He could not explain the force that is responsible for drifting.

  2. Also, not unable to explain the trigger mechanism for the breaking of continents after the Carboniferous period.

  3. He cannot explain the sequence of how the continents moved.

  4. His explanation of mountain building and island arc is full of errors.

Evidences

  1. Jig-Saw fit- If we attach all the continents, they fit well.

  2. Rocks of the same age across the coast of Atlantic. In fact, the mountains of Scandinavia, Ireland, and the Appalachians are geologically similar.

  3. Gold deposits in Ghana while the gold-bearing rocks are in South America.

  4. Distribution of fossils, Glossopetrius flora in Brazil, Africa, Peninsular India, and Antarctica. Similarly, the above regions have evidence of glaciation.

  5. The behavior of some animals. For example, Lemmings have a tendency to run towards the west whenever there is an increase in population.

Practice Questions-

  1. Who has given the continental drift theory? Write about its significance.

  2. Elaborate the theory of continental drift with its assumptions and evidences.
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