What do you understand by the theory of continental drift? Discuss the prominent evidences in its support.

What do you understand by the theory of continental drift? Discuss the prominent evidences in its support. [GS1, 2013]

Continental drift is the idea that the present continents have not always remained in their current positions but have moved slowly over geological time.

Alfred Wegener, a German meteorologist, proposed in 1912 that the continents were once united into a single large landmass called Pangaea, surrounded by a universal ocean named Panthalassa. Pangaea later broke apart — first into a northern block, Laurasia, and a southern block, Gondwanaland — and its fragments gradually drifted to form the present continents.

Some prominent evidences in its support:

1. Matching shape of continents. E.g., the eastern coastline of South America appears to fit into the western coastline of Africa, like two pieces of a jigsaw that were once joined.
2. Similar rocks and mountain systems. E.g., mountain belts in eastern North America continue geologically into parts of western Europe, which is best explained if the two shores once formed one continuous belt.
3. Distribution of identical fossils. E.g., fossils of Glossopteris, an ancient plant, have been found in India, Africa, Australia, South America and Antarctica. A land plant could not have spread across wide oceans, so the continents carrying its remains must once have been joined.
4. Evidence of past climatic conditions. E.g., coal deposits occur in Antarctica, indicating that it once supported dense vegetation under a warmer climate and therefore lay far from its present polar position.
5. Similar mineral and sedimentary deposits. E.g., Gondwana coal-bearing formations found in India have parallels in other southern continents.

Key limitation:

Wegener could not satisfactorily explain what force moved the continents. The polar-fleeing force and tidal force he suggested were shown to be far too weak to drag continents across the ocean floor, and the theory remained neglected for decades. Later, the theory of plate tectonics supplied the mechanism (explained that continents are carried on large moving lithospheric plates, while processes such as seafloor spreading create and rearrange ocean basins).

Although Wegener’s original theory lacked a convincing mechanism, its central insight was correct. The evidences he assembled — the jigsaw fit of coastlines, the continuity of mountain belts, the spread of Glossopteris and the coal of Antarctica — all survive within plate tectonics, which treats drifting continents as the surface expression of moving lithospheric plates.