Class 11 Geography - CBSE
Distribution of Oceans and Continents
The chapter 'Distribution of Oceans and Continents' in CBSE Class 11 Geography explores how the Earth's present-day landmasses and water bodies assumed their current positions. It covers 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 dives into Arthur Holmes' Convectional Current Theory and the groundbreaking Plate Tectonic Theory, which unifies concepts of seafloor spreading, paleomagnetism, and plate boundaries. Understanding these tectonic processes is vital for board exams as it forms the bedrock of physical geography and explains global earthquakes and volcanism.
Start Learning FreeKey Concepts
Continental Drift Theory
Proposed by Alfred Wegener in 1912, it suggests that all continents were once a single supercontinent named Pangea, surrounded by a mega-ocean called Panthalassa, before breaking apart and drifting.
Convectional Current Theory
Put forward by Arthur Holmes, this theory explains that intense thermal convection currents generated within the mantle's radioactive decay serve as the primary driving force behind plate and continental movement.
Seafloor Spreading
Introduced by Harry Hess, this concept states that constant volcanic eruptions along mid-oceanic ridges create new oceanic crust, pushing older crust away and widening the ocean basins.
Plate Tectonics
The modern unifying theory which states that the Earth's lithosphere is broken into rigid fragments called tectonic plates that float on the semi-fluid asthenosphere, interacting at convergent, divergent, and transform boundaries.
Paleomagnetism
The study of the record of Earth's magnetic field preserved in magnetic minerals in rocks over time, which provided definitive proof for seafloor spreading and continental drift.
Important Formulas
Board Exam Info
In the CBSE Class 11 Geography board-level exams, this chapter typically carries around 4 to 6 marks. Common question types include direct theory questions (e.g., evidence of Continental Drift), differentiating between types of plate boundaries, short notes on seafloor spreading, and map-based questions identifying major tectonic plates.
Frequently Asked Questions
What were the main evidences given by Wegener for Continental Drift?
Wegener cited matching coastlines (Jigsaw fit of Africa and South America), fossil distribution of identical species across separated oceans, matching rock types of the same age across oceans, and tillite deposits in tropical regions.
Why was Wegener's Continental Drift Theory initially rejected?
Wegener could not provide a logical, physically plausible driving force for the movement of continents. He suggested tidal force and earth's rotation, which physicists proved were far too weak to move massive landmasses.
What is the difference between continental drift and plate tectonics?
Continental drift only suggested that continents moved through the ocean floor driven by weak forces, whereas plate tectonics proves that rigid lithospheric plates carrying both oceans and continents move over the asthenosphere driven by mantle convection.
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