Discuss how the changes in shape and sizes of continents and ocean basins of the planet take place due to tectonic movements of the crustal masses. (2025, 15 Marks)

Paper	GS Paper 1
Word Limit	250 words
Syllabus Topic	Salient Features of World’s Physical Geography – Plate Tectonics

Model Answer

The Earth’s lithosphere is broken into about seven major and several minor plates. They move slowly over the soft asthenosphere. This movement keeps changing the shape and size of continents and ocean basins.

Basis of the Theory

• Continental Drift (Wegener, 1912): all continents were joined as Pangaea, surrounded by Panthalassa.
• Sea-floor spreading (Harry Hess, 1960s) and plate tectonics explained how plates move.

How Continents and Ocean Basins Change

• Divergent boundaries: Plates move apart and new crust forms. The Mid-Atlantic Ridge widens the Atlantic. The East African Rift is splitting Africa; the Red Sea is a young ocean.
• Convergent boundaries: Ocean crust sinks by subduction, shrinking oceans and forming trenches like the Mariana Trench. The Pacific is slowly shrinking.
• Continental collision: The Indian plate hit the Eurasian plate, closing the Tethys Sea and raising the Himalayas.
• Transform boundaries: Plates slide past each other, e.g. the San Andreas Fault.
• Break-up of Pangaea: It split into Laurasia and Gondwanaland, then into today’s continents.

Driving Forces

• Mantle convection currents (Arthur Holmes), ridge push and slab pull.
• Oceans open and close in a long cycle, called the Wilson Cycle.
• The Indian plate is still moving north, so the Himalayas are still rising.

Conclusion

Continents and oceans are not fixed; they are always changing. Understanding plate movements helps India prepare for earthquakes, tsunamis and volcanic hazards.

Related PYQs

• Define mantle plume and explain its role in plate tectonics. (2018)
• Describe the characteristics and types of primary rocks. (2022)
• How are the fjords formed? Why do they constitute some of the most picturesque areas of the world? (2023)

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