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Plate Tectonics and Continental Drift for UPSC Prelims

1. Introduction to Plate Tectonics

Plate tectonics is the scientific theory that Earth's lithosphere is divided into large, rigid plates that move relative to one another. This movement explains continental drift, earthquakes, volcanic activity, and the formation of mountain ranges and ocean basins.

Key Facts

  • Number of Major Plates: 7 (Pacific, North American, Eurasian, African, Antarctic, Indo-Australian, South American)
  • Speed of Movement: 1-10 cm per year (about as fast as fingernails grow)
  • Theory Developed: 1960s, building on continental drift theory
  • Significance: Explains Earth's topography, seismic zones, and volcanic belts

Important Facts for UPSC

  • The lithosphere (crust + upper mantle) is divided into tectonic plates.
  • Plate movements are driven by mantle convection currents.
  • The theory unified earlier concepts of continental drift and seafloor spreading.

2. Continental Drift Theory

Alfred Wegener's Theory (1912)

Proposed that continents were once joined in a supercontinent called Pangaea (meaning "all Earth"), which began breaking apart about 200 million years ago.

Era Supercontinent Description
Late Paleozoic to Early Mesozoic Pangaea Single supercontinent surrounded by Panthalassa ocean
Jurassic Period Laurasia (North) and Gondwana (South) Pangaea split into two major landmasses
Cretaceous to Present Modern continents Further breakup into current continental configuration

Important Facts for UPSC

  • Wegener couldn't explain the mechanism of drift, leading to initial rejection.
  • The theory was later supported by seafloor spreading evidence in the 1960s.
  • India was part of Gondwana before drifting north to collide with Eurasia.

3. Evidence Supporting Continental Drift

Key Evidence

Important Facts for UPSC

  • The Glossopteris flora (fossil plant) is found across southern continents.
  • The Appalachian Mountains (USA) align with mountains in Scotland and Scandinavia.
  • Coal deposits in Antarctica indicate it was once in warmer latitudes.

4. Types of Plate Boundaries

Boundary Type Description Geological Features Examples
Divergent Plates move apart Mid-ocean ridges, rift valleys Mid-Atlantic Ridge, East African Rift
Convergent Plates move toward each other Mountains, trenches, volcanoes Himalayas, Andes, Mariana Trench
Transform Plates slide past each other Earthquakes, fault lines San Andreas Fault (California)

Convergent Boundary Subtypes

Important Facts for UPSC

  • The "Ring of Fire" around the Pacific is a convergent boundary zone.
  • Divergent boundaries create new crust; convergent boundaries destroy it.
  • Transform boundaries often cause shallow but powerful earthquakes.

5. Forces Behind Plate Movements

Driving Mechanisms

Important Facts for UPSC

  • Slab pull is considered the dominant driving force.
  • Convection currents move at about 1-20 cm/year.
  • Hotspots (like Hawaii) show absolute plate motion over stationary mantle plumes.

6. Major and Minor Tectonic Plates

Plate Name Type Area (million km²) Notable Features
Pacific Plate Major (Oceanic) 103.3 Ring of Fire, Hawaii hotspot
Eurasian Plate Major (Continental) 67.8 Contains Europe and most of Asia
Indo-Australian Plate Major 58.9 Colliding with Eurasian Plate (Himalayas)
Nazca Plate Minor (Oceanic) 15.6 Subducting under South America (Andes)

Important Facts for UPSC

  • The Indo-Australian Plate is breaking into Indian and Australian plates.
  • The Philippine Sea Plate is a notable minor plate with complex boundaries.
  • Turkey sits on the Anatolian Plate, a microplate causing frequent earthquakes.

7. The Indian Plate and Its Movement

Key Features

Effects of Indian Plate Movement

Important Facts for UPSC

  • The collision is responsible for the formation of the Himalayas, Karakoram, and Hindu Kush ranges.
  • Deccan Traps (volcanic province) formed as India passed over the Réunion hotspot.
  • India's northward push causes frequent earthquakes in the Himalayan region.

8. Landforms Created by Plate Tectonics

Landform Plate Boundary Formation Process Examples
Fold Mountains Convergent (C-C) Continental collision compresses crust upward Himalayas, Alps, Appalachians
Ocean Trenches Convergent (O-O or O-C) Subduction creates deep troughs Mariana Trench, Peru-Chile Trench
Mid-Ocean Ridges Divergent Seafloor spreading creates underwater mountain chains Mid-Atlantic Ridge, East Pacific Rise
Rift Valleys Divergent (Continental) Crust stretches and fractures East African Rift, Rhine Valley

Important Facts for UPSC

  • The East African Rift may eventually split Africa, creating a new ocean.
  • The Himalayas contain the world's highest peaks, including Everest.
  • Island arcs like Japan form where two oceanic plates converge.

9. Associated Natural Hazards

Earthquakes

Most occur along plate boundaries, especially convergent and transform boundaries. The circum-Pacific belt ("Ring of Fire") is particularly active.

Volcanoes

Common at convergent boundaries (subduction zones) and divergent boundaries. Hotspots like Hawaii can occur within plates.

Tsunamis

Often generated by undersea earthquakes at subduction zones (e.g., 2004 Indian Ocean tsunami).

Important Facts for UPSC

  • India's earthquake zones: Himalayan (high risk), Indo-Gangetic (moderate), Peninsula (low).
  • Barren Island (Andamans) is India's only active volcano.
  • The 2001 Bhuj earthquake occurred on an intraplate fault, showing risk beyond boundaries.

10. UPSC Relevance and Preparation Tips

Why Important for UPSC?

Preparation Tips

Important Facts for UPSC

  • Previous UPSC questions have asked about the Ring of Fire, Himalayan formation, and evidence for continental drift.
  • Understand the difference between continental drift (Wegener) and plate tectonics (modern theory).
  • Note that the theory explains mineral and fossil fuel distribution patterns.