NCERT Class 11

Distribution of Oceans and Continents Notes

Distribution of Oceans and Continents Class 11 Geography Notes

These Distribution of Oceans and Continents Class 11 Notes explain the origin, movement and present arrangement of continents and oceans on Earth. The chapter discusses Continental Drift Theory, Sea Floor Spreading, Plate Tectonics and the movement of the Indian Plate in detail.

These notes are useful for UPSC, SSC, Railways, State PSC, CUET, CBSE Board Exams and other competitive examinations because Continental Drift, Sea Floor Spreading and Plate Tectonics are among the most important topics in Physical Geography.

NCERT Pages: 27–35

Table of Contents

Chapter Overview

NCERT Pages: 27–35

This chapter explains how continents and oceans have continuously changed their positions through geological time. It discusses Wegener’s Continental Drift Theory, evidence supporting continental drift, sea floor spreading, plate tectonics and the movement of the Indian Plate leading to the formation of the Himalayas.

Major Topics Covered

  • Continental Drift Theory
  • Pangaea and Panthalassa
  • Evidence of continental drift
  • Tillite deposits
  • Sea floor spreading
  • Plate tectonics
  • Plate boundaries
  • Movement of Indian Plate
  • Formation of Himalayas

Continental Drift Theory

NCERT Page: 27

These notes explain Wegener’s Continental Drift Theory and the concept of moving continents.

Continental Drift

  • Alfred Wegener proposed the Continental Drift Theory in 1912.
  • According to Wegener:
    • All continents were once joined together.
    • This supercontinent was called Pangaea.
    • A mega ocean called Panthalassa surrounded it.
  • Around 200 million years ago, Pangaea split into:
    • Laurasia
    • Gondwanaland
Term Meaning
Pangaea Supercontinent
Panthalassa Mega ocean
Laurasia Northern continental mass
Gondwanaland Southern continental mass

Evidence in Support of Continental Drift

NCERT Pages: 27–28

Matching of Continents (Jig-Saw Fit)

  • Coastlines of Africa and South America fit together remarkably.
  • Bullard (1964) demonstrated best fit using computer mapping.

Rocks of Same Age Across Oceans

  • Rock belts of Brazil match with those of western Africa.
  • Jurassic-age marine deposits occur along both coasts.
Important Fact: Suggests Atlantic Ocean did not exist before Jurassic period.

Tillite Deposits

NCERT Page: 28

These notes explain glacial tillite evidence supporting continental drift.

  • Tillite is sedimentary rock formed by glacier deposits.
  • Gondwana tillite deposits found in:
    • India
    • Africa
    • Antarctica
    • Australia
    • Madagascar
    • Falkland Islands
Significance:
  • Indicates common glacial history.
  • Supports continental drift.

Distribution of Fossils

NCERT Page: 28

Fossil Location
Lemurs India, Madagascar, Africa
Mesosaurus South Africa and Brazil
Significance:
  • Freshwater and land species could not cross oceans.
  • Suggests continents were previously connected.

Sea Floor Spreading Theory

NCERT Pages: 30–31

  • Proposed by Harry Hess in 1961.
  • New crust forms at mid-ocean ridges.
  • Ocean floor spreads outward.

Key Observations

Observation Importance
Youngest rocks near ridges New crust formation
Older rocks away from ridges Crust spreading
Thin sediments Young ocean floor
Deep earthquakes at trenches Subduction zones

Plate Tectonics Theory

NCERT Pages: 31–32

  • Proposed in 1967 by McKenzie, Parker and Morgan.
  • Earth’s lithosphere divided into plates.
  • Plates move over asthenosphere as rigid units.

Major Plates of Earth

Plate Type
Pacific Plate Oceanic
Eurasian Plate Continental
African Plate Continental
Indo-Australian Plate Mixed

Types of Plate Boundaries

NCERT Page: 33

Divergent Boundaries

  • Plates move away from each other.
  • New crust generated.
  • Example: Mid-Atlantic Ridge.

Convergent Boundaries

  • One plate subducts below another.
  • Crust destroyed.
Type Example
Oceanic-Continental Andes
Oceanic-Oceanic Island arcs
Continental-Continental Himalayas

Transform Boundaries

  • Plates slide horizontally past each other.
  • Crust neither created nor destroyed.
  • Transform faults generally perpendicular to ridges.

Movement of the Indian Plate

NCERT Page: 34

  • India was once a large island near Australia.
  • Tethys Sea separated India from Asia.

Timeline

Event Approximate Time
Pangaea breakup 200 million years ago
Deccan Trap volcanism 60 million years ago
Collision with Asia 40–50 million years ago
Important Facts:
  • Himalayas formed due to continent-continent convergence.
  • Himalayan uplift continues even today.

Important Topics

Important Topic NCERT Page
Continental Drift Theory 27
Fossil evidence 28
Sea floor spreading 30–31
Plate tectonics 31–32
Plate boundaries 33
Indian Plate movement 34

Important Questions

Very Short Answer Questions

  1. Who proposed the Continental Drift Theory? (NCERT Page 27)
  2. What is Pangaea? (NCERT Page 27)
  3. Define Panthalassa. (NCERT Page 27)
  4. What is tillite? (NCERT Page 28)
  5. What is Sea Floor Spreading? (NCERT Page 30)
  6. Define lithosphere. (NCERT Page 32)
  7. What is a subduction zone? (NCERT Page 33)
  8. What is Ring of Fire? (NCERT Page 29)

Short Answer Questions

  1. Explain Continental Drift Theory. (NCERT Page 27)
  2. Discuss fossil evidence supporting continental drift. (NCERT Page 28)
  3. Explain convection current theory. (NCERT Page 28)
  4. Describe ocean floor configuration. (NCERT Page 29)
  5. Explain Sea Floor Spreading Theory. (NCERT Pages 30–31)
  6. Describe types of plate boundaries. (NCERT Page 33)
  7. Explain movement of Indian Plate. (NCERT Page 34)

Long Answer Questions

  1. Discuss evidences supporting Continental Drift Theory. (NCERT Pages 27–28)
  2. Explain Sea Floor Spreading and its significance. (NCERT Pages 30–31)
  3. Describe Plate Tectonics Theory and plate boundaries. (NCERT Pages 31–33)
  4. Explain the role of convection currents in plate movement. (NCERT Pages 33–34)
  5. Describe the movement of the Indian Plate and formation of Himalayas. (NCERT Page 34)

FAQs

1. Who proposed Continental Drift Theory?

Alfred Wegener proposed the Continental Drift Theory in 1912. (NCERT Page 27)

2. What is Pangaea?

Pangaea was the supercontinent containing all landmasses. (NCERT Page 27)

3. What is Sea Floor Spreading?

Formation of new oceanic crust at mid-ocean ridges is called sea floor spreading. (NCERT Pages 30–31)

4. What drives plate movement?

Mantle convection currents drive tectonic plates. (NCERT Pages 33–34)

5. How were Himalayas formed?

Himalayas formed due to collision of Indian and Eurasian plates. (NCERT Page 34)

Quick Revision Summary

  • Alfred Wegener proposed Continental Drift Theory.
  • Pangaea means “all Earth”.
  • Panthalassa means “all water”.
  • Gondwana tillites support continental drift.
  • Mesosaurus fossils found in Brazil and South Africa.
  • Mantle convection currents were proposed by Arthur Holmes.
  • Mid-ocean ridges are volcanic zones.
  • Pacific volcanic belt is called Ring of Fire.
  • Harry Hess proposed Sea Floor Spreading.
  • Oceanic crust is younger than continental crust.
  • Lithosphere moves over asthenosphere.
  • Divergent boundaries create new crust.
  • Convergent boundaries destroy crust.
  • Indian Plate collided with Eurasian Plate.
  • Himalayas are still rising.
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