Continental Drift | Geography Optional for UPSC (Notes) PDF Download

Introduction - Continental Drift

Alfred Wegener, a versatile German scientist proficient in meteorology, polar exploration, astronomy, and geology, is commonly acknowledged as the pioneer of the continental drift theory. In a lecture in 1912, Wegener unveiled his revolutionary idea of 'continental drift,' profoundly altering our comprehension of the Earth's geological phenomena.

Continental Drift Theory (Alfred Wegener)

• Proposer and Concept Origin: Alfred Wegener introduced the Continental Drift Theory, proposing that Earth's entire landmass was once part of a unified supercontinent called "Pangaea" (meaning "all Earth").
• Ancient Ocean Surrounding Pangaea: Wegener suggested that Pangaea was surrounded by a vast ocean known as "Panthalassa" (meaning "all ocean").
• Commencement of Continental Drift: According to Wegener's theory, the process of continental drift commenced around 200 million years ago.
• Gradual Breakup and Movement: The theory posits that Pangaea began to break apart, and the individual landmasses started moving gradually to their present locations.
• Ongoing Shifts: Wegener proposed that the movement of continents is an ongoing process, indicating that the landmasses continue to shift even in contemporary times.

Wegener became interested in this idea due to several intriguing questions he had:

1. How could tropical ferns have grown in locations such as London, Paris, Bonn, and even Greenland?
2. Why are coal belts found in the extremely cold tundra regions?
3. How can evidence of glaciers be found in tropical areas like Brazil, the Indian Peninsula, Australia, and the Congo Basin?

Considering these points, Wegener came up with two possible explanations:

• The climate zones may have shifted from one region to another, while the continents remained stationary.
• The climate zones stayed in place, but the continents moved.

Since climate zones are determined by factors such as the Earth's tilt and the sun's position, it seemed unlikely that they would shift. Therefore, Wegener concluded that the more plausible explanation was that the continents had changed their positions over time.

The Direction of  Drift

The theory of continental drift, proposed by Alfred Wegener, suggests that the continents have moved in two primary directions:

• Jigsaw Fit: The shapes of the continents, especially the coastlines of Africa and South America, fit together like pieces of a puzzle, indicating that they were once joined.

• Geological Structure: The geological structures on the continents' coastlines show remarkable similarities, suggesting they were once connected. For example, the Appalachian Mountains in North America align with the old Hercynian Mountains in Ireland, Wales, and central Europe.

Geological Structure

• Permo-Carboniferous Glaciations:
  • Evidence of ancient glaciations is identified in locations including Brazil, Falkland Islands, South Africa, the Indian Peninsula, and Australia.
  • This implies that these landmasses were previously connected, challenging explanations based on the current arrangement of land and water.
• Fossil Remains Consistency:
  • Similar fossil remains of terrestrial animals are present on both sides of the Atlantic, indicating a past connection between the continents.
  • The nature of these fossils suggests that the animals could not have traversed the Atlantic Ocean through swimming.
• Paleoclimatic Indicators:
  • Coal deposits, typically formed in tropical regions, are discovered in temperate and polar regions.
  • This finding suggests a historical shift in continents, as it is inconsistent with the current locations of these coal-forming regions.
• Biological Migration Patterns:
  • Certain animal species, like the lemming, exhibit migratory patterns implying past continent connection.
  • Lemmings migrating westward across North America and entering the Atlantic Ocean suggest the existence of an ancient route connecting North America and Europe.

Criticism of Continental Drift Theory

The continental drift theory, while quite persuasive, also faced significant criticism and controversy, largely due to the speculative nature of some aspects of the theory and insufficient supporting evidence. The most contentious part of this theory was the proposed forces that caused the drift.

• Critique of Gravitational Forces:
  • Experts argued that if the gravitational forces of the moon or sun were potent enough to break up the landmass, it should have halted Earth's rotation, rendering it stationary.
  • The rotational speed required for landmass drift would have been so high that it would have propelled the atmosphere and other entities into outer space, escaping Earth's gravitational pull.
• Limitation of Historical Knowledge:
  • Another challenge was the limited understanding of Earth's history preceding the Carboniferous period.
  • The proposed drift primarily considered northward and westward movements, leaving unaddressed why other directions were not involved.
• Sial over Sima Criticism:
  • The concept of sial (continental crust) floating over sima (oceanic crust) faced criticism. It was later revealed that the lithosphere actually floats on the aesthenosphere.
  • The explanation for mountain formation, such as the Rockies and Andes, due to friction with sima was seen as self-contradictory.
• Failure to Explain Certain Features:
  • The continental drift theory lacked an explanation for the formation of oceanic ridges and island arcs.
  • Despite its groundbreaking nature, the theory faced significant criticism, prompting the development of the more comprehensive plate tectonics theory.

Conclusion

Alfred Wegener's continental drift theory significantly changed our understanding of the Earth's geological processes. The theory suggests that Earth's landmasses were once combined into a single supercontinent, Pangaea, which broke apart and moved to their current positions over time. While the theory provided an explanation for various geological, paleoclimatic, and biological evidence, it faced significant criticism due to its speculative nature and insufficient supporting evidence. These criticisms eventually led to the development of the more comprehensive plate tectonics theory.

Frequently Asked Questions (FAQs) of Continental Drift

What is the Continental Drift Theory and who proposed it?

The Continental Drift Theory was proposed by German scientist Alfred Wegener. It suggests that all of Earth's land was once combined into a single supercontinent called Pangaea, which later broke apart and moved to their current positions, continuing to shift even today.

What were the two main directions of continental drift according to Wegener's theory?

Wegener's theory suggests that the continents have moved in two primary directions: towards the Equator and towards the West. The equatorward drift contributed to the formation of various mountain ranges, while the westward drift led to the separation of the Americas from Europe and Africa, and the formation of the Atlantic Ocean.

What evidence supports the Continental Drift Theory?

Some key evidence supporting the Continental Drift Theory includes the jigsaw fit of continents' coastlines, similarities in geological structures, evidence of Permo-Carboniferous glaciations, fossil remains, paleoclimatic evidence, and biological evidence such as migratory patterns of certain animal species.

Why was the Continental Drift Theory criticized?

The theory faced significant criticism mainly due to the speculative nature of some aspects, insufficient supporting evidence, and the inability to explain certain geological phenomena. Critics argued that the proposed forces causing the drift were not plausible, and the theory could not account for the Earth's history before the Carboniferous period or explain the formation of oceanic ridges and island arcs.

How does the Continental Drift Theory relate to the Plate Tectonics Theory?

The Continental Drift Theory was a precursor to the Plate Tectonics Theory. While the former focused on the movement of continents, the latter expanded upon this idea by considering the movement of Earth's lithospheric plates. The criticisms of the Continental Drift Theory led scientists to develop the more comprehensive Plate Tectonics Theory, which is now widely accepted as the explanation for Earth's geological processes.