Class 11 Geography - WEST-BENGAL
Distribution of Oceans and Continents
The chapter 'Distribution of Oceans and Continents' in Class 11 Geography explores how the earth's surface evolved from a single supercontinent into the current arrangement of landmasses and water bodies. Students study Alfred Wegener's Continental Drift Theory, the evidence supporting it like fossil distribution and matching coastlines, and the driving forces he proposed. The chapter further progresses into modern scientific breakthroughs including Paleomagnetism, Sea Floor Spreading by Arthur Holmes and Harry Hess, and the comprehensive Plate Tectonic Theory. Mastering this chapter is crucial for WBBSE board exams as it forms the foundational base for geomorphology and internal earth processes.
Start Learning FreeKey Concepts
Continental Drift Theory
Proposed by Alfred Wegener in 1912, this theory states that all continents were once a single supercontinent called Pangea, surrounded by a mega-ocean called Panthalassa, which eventually broke apart and drifted to their present positions.
Pangea and Panthalassa
Pangea represents the massive single landmass comprising all modern continents, while Panthalassa was the gigantic primeval ocean that enclosed it before the continental drift began.
Convectional Current Theory
Proposed by Arthur Holmes, this theory suggests that intense radioactive heat generated in the mantle creates thermal convection currents, which act as the primary driving force behind the movement of crustal plates.
Sea Floor Spreading
Introduced by Harry Hess, this concept explains that new oceanic crust is continuously formed at mid-ocean ridges through volcanic activity and spreads outward, while older crust is consumed at deep-sea trenches.
Plate Tectonics
A unifying geological theory stating that the Earth's lithosphere is broken into several rigid tectonic plates that float on the semi-fluid asthenosphere, interacting at convergent, divergent, and transform boundaries.
Important Formulas
Board Exam Info
In the West Bengal Council of Higher Secondary Education (WBBSE) Class 11 Geography annual examinations, this chapter generally carries around 6 to 9 marks. Questions typically include 1-mark objective questions (MCQs/SAQs), 3-mark short explanatory questions (such as evidences of continental drift or forces of drift), and 5-mark long descriptive essay-type questions focusing on Plate Tectonics or Sea Floor Spreading.
Frequently Asked Questions
What were the main evidences given by Alfred Wegener for Continental Drift?
Wegener provided several evidences including the Jigsaw fit of continents (like South America and Africa), fossil remains of identical plants and species across separated oceans, matching rock formations of same ages, and glacial tillite deposits in tropical regions.
What was the main drawback of Wegener's Continental Drift Theory?
The primary flaw was that Wegener could not provide a scientifically valid or powerful driving force for the movement of continents, incorrectly attributing it solely to tidal forces and gravitational differential forces which are too weak.
How is Sea Floor Spreading different from Continental Drift?
While Continental Drift focuses on continents moving across the ocean floor, Sea Floor Spreading proves that the oceanic crust itself is moving, being continuously created at mid-ocean ridges and destroyed at subduction zones.
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