Continental Drift

Notes

The Continental Drift Theory was proposed by the German meteorologist Alfred Wegener in 1912 (published in The Origin of Continents and Oceans, 1915). He argued that all continents were once joined in one supercontinent, Pangaea, surrounded by a single ocean, Panthalassa.

Break-up of Pangaea

About 200 million years ago, Pangaea split into Laurasia (north: North America, Europe, Asia) and Gondwanaland (south: South America, Africa, India, Australia, Antarctica), separated by the Tethys Sea. The name Gondwanaland was given by Eduard Suess.
The continents drifted to their present positions through the Mesozoic and Cenozoic. India broke away from Gondwanaland about 120-150 million years ago and moved north.

Evidence

Jig-saw fit of the coasts of Africa and South America (Bullard's fit at the 1,000-fathom line).
Geological: rocks of the same age and type on both sides of the Atlantic (e.g., the Gondwana system); tillite (glacial deposits) in India, South Africa and South America; placer gold deposits in Ghana whose source is in Brazil.
Palaeontological: fossils of Mesosaurus (a freshwater reptile) in Brazil and South Africa; the Glossopteris flora across the southern continents.
Climatic: coal in Antarctica indicates a tropical past.
Palaeomagnetism later supported drift.

Wegener's forces: pole-fleeing force (centrifugal force due to Earth's rotation) and tidal force (Sun and Moon), both far too weak to move continents.

Criticism: the forces were inadequate; continents could not plough through the rigid ocean floor; the theory could not explain mountain building or why the drift began in the Mesozoic. It was replaced by plate tectonics, which explains the mechanism (seafloor spreading, convection currents).

Basis	Continental Drift	Plate Tectonics
Proposed	Wegener, 1912	McKenzie, Parker, Morgan, 1967
Moving units	Continents	Lithospheric plates (carrying continents and oceans)
Mechanism	Pole-fleeing and tidal forces	Convection, slab pull, ridge push

Key Points

Wegener (1912): Pangaea and Panthalassa; Laurasia and Gondwanaland; Tethys Sea.
Evidence: jig-saw fit, Mesosaurus, Glossopteris, tillite, placer gold.
Forces: pole-fleeing and tidal; considered inadequate.
Gondwanaland named by Suess.
Replaced by plate tectonics.

MCQs

Q1. The Continental Drift Theory was proposed by:

(a) Harry Hess
(b) Alfred Wegener
(c) Arthur Holmes
(d) Eduard Suess
Ans: (b).

Q2. The single ocean surrounding Pangaea was called:

(a) Tethys
(b) Panthalassa
(c) Pacific
(d) Atlantic
Ans: (b).

Q3. The fossil flora found across the southern continents, supporting drift, is:

(a) Glossopteris
(b) Mesosaurus
(c) Archaeopteryx
(d) Gondwana
Ans:
(a). Mesosaurus is a reptile, not a plant.