Plate Tectonics Theory - Geography Ebooks | TheGeoecologist

Question 1

What are the four main evidences supporting the Continental Drift Theory?

Accepted Answer

The four main evidences are: (1) Jigsaw fit of coastlines (e.g., South America-Africa), (2) Fossil correlations (Mesosaurus, Glossopteris across separated continents), (3) Matching rock formations and mountain belts (Cape Fold Belt–Ventania, Appalachians–Caledonians), and (4) Paleoclimatic indicators (Permo-Carboniferous glacial tillites in now-tropical regions, coal in Antarctica).

Question 2

How does Seafloor Spreading provide the mechanism missing in Wegener's theory?

Accepted Answer

Harry Hess (1961) proposed that mid-ocean ridges are sites of new oceanic crust formation via magma upwelling. This creates a conveyor belt: crust forms at ridges, moves laterally, and is consumed at subduction zones. Magnetic striping (Vine-Matthews-Morley, 1963) and age progression from ridges confirmed this mechanism, validating mantle convection as the driving force.

Question 3

What are the three types of plate boundaries and their associated landforms?

Accepted Answer

(1) Divergent: Plates move apart → mid-ocean ridges (oceanic), rift valleys (continental). (2) Convergent: Plates collide → subduction zones with trenches/volcanic arcs (oceanic-oceanic, oceanic-continental), collisional mountains like Himalayas (continental-continental). (3) Transform: Plates slide past → strike-slip faults (San Andreas), shallow earthquakes, no volcanism.

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Distribution of Oceans and Continents: NCERT Class 11 Geography Chapter 4 Complete Guide