Chapter 4: Distribution of Oceans and Continents
Geography - Fundamental of Physical Geography • Class 11
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Chapter Analysis
Intermediate10 pages • EnglishQuick Summary
The chapter 'Distribution of Oceans and Continents' discusses the theories and evidence regarding the dynamic nature of earth's lithospheric plates and their movements over geological time. It covers the theory of Continental Drift originally proposed by Wegener, which suggests that the continents were once a single supercontinent, Pangaea, and have since drifted to their current positions. The chapter also introduces plate tectonics, explaining how plates move and interact through different types of boundaries. Additionally, it looks into sea floor spreading, the mapping of ocean floors, and the significance of mid-oceanic ridges in understanding Earth's geological history.
Key Topics
- •Continental Drift Theory
- •Plate Tectonics
- •Types of Plate Boundaries
- •Sea Floor Spreading
- •Mid-Oceanic Ridges
- •Earthquake and Volcano Distribution
- •Convectional Currents in Mantle
- •Historical Geology of Continents
Learning Objectives
- ✓Understand the concept of continental drift and its historical development.
- ✓Identify different types of plate boundaries and their characteristics.
- ✓Explain the process of sea-floor spreading and its significance.
- ✓Discuss the evidence supporting plate tectonics.
- ✓Analyze the distribution of earthquakes and volcanoes in relation to tectonic activity.
- ✓Evaluate the role of palaeomagnetic studies in the study of Earth's geological past.
Questions in Chapter
Who amongst the following was the first to consider the possibility of Europe, Africa and America having been located side by side?
Answer: Alfred Wegener
Page 35
Polar fleeing force relates to:
Answer: Rotation of the earth
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Which one of the following is not a minor plate?
Answer: Antarctica
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Which one of the following facts was not considered by those while discussing the concept of sea floor spreading?
Answer: Distribution of fossils in different continents.
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Which one of the following is the type of plate boundary of the Indian plate along the Himalayan mountains?
Answer: Continent-continent convergence
Page 35
What were the forces suggested by Wegener for the movement of the continents?
Page 36
How are the convectional currents in the mantle initiated and maintained?
Page 36
What is the major difference between the transform boundary and the convergent or divergent boundaries of plates?
Page 36
What was the location of the Indian landmass during the formation of the Deccan Traps?
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What are the evidences in support of the continental drift theory?
Page 36
Bring about the basic difference between the drift theory and Plate tectonics.
Page 36
What were the major post-drift discoveries that rejuvenated the interest of scientists in the study of distribution of oceans and continents?
Page 36
Additional Practice Questions
Explain the role of sea-floor spreading in the development of plate tectonics theory.
mediumAnswer: Sea-floor spreading explains how new oceanic crust is formed at mid-ocean ridges and gradually moves outward. This helps in understanding how tectonic plates expand and converge, providing evidence for the broader theory of plate tectonics.
Describe the significance of the Mid-Atlantic Ridge in the study of tectonic movements.
mediumAnswer: The Mid-Atlantic Ridge is a divergent boundary where two plates are moving apart, allowing magma to rise and form new crust. Its study provides insights into the process of crustal generation and helps validate the theory of sea-floor spreading.
Discuss the importance of palaeomagnetic studies in understanding continental drift.
hardAnswer: Palaeomagnetic studies involve analyzing the magnetic properties of rocks to track past movements of tectonic plates. These studies provide historical records of plate positions, supporting the theory of continental drift.
Explain the concept of tectonic plates and their movement.
easyAnswer: Tectonic plates are massive slabs of Earth's lithosphere that float over the semi-fluid asthenosphere beneath them. Their movement is driven by forces such as mantle convection, ridge push, and slab pull, which cause interactions at plate boundaries.
What are the different types of plate boundaries and how do they affect geological features?
mediumAnswer: Plate boundaries can be divergent, convergent, or transform. Divergent boundaries form new crust, convergent boundaries destroy crust and can form mountains, while transform boundaries cause earthquakes.
Why is the concept of Pangaea important in the study of Earth's geological history?
mediumAnswer: Pangaea represents a time when all continents were joined, providing a starting point for understanding the subsequent movement and current layout of continents, shedding light on past climates and biological evolution.
How did the theory of continental drift evolve into the theory of plate tectonics?
hardAnswer: Continental drift proposed that continents moved over Earth's surface. Advances in oceanography revealed sea-floor spreading, leading to the understanding that entire plates, not just continents, were moving, which became the foundation of plate tectonics.
Illustrate the process of oceanic trench formation and its implications for tectonic activity.
hardAnswer: Oceanic trenches form at convergent boundaries where an oceanic plate subducts beneath another plate, leading to volcanic activity and earthquakes, highlighting the dynamic nature of tectonic interactions.
Analyze the evidence that led to the acceptance of the plate tectonics theory.
hardAnswer: Evidence includes matching geological and fossil records across continents, the presence of parallel magnetic stripes on ocean floors, and the worldwide distribution of earthquakes and volcanoes, all supporting the concept of moving plates.
How do plate tectonics affect climate and natural disasters?
mediumAnswer: Plate movements can alter climate by repositioning landmasses and ocean currents. They also cause natural disasters such as earthquakes, volcanic eruptions, and tsunamis, impacting human life and infrastructure.