Question – Explain in detail the evidence given in the proof of continental drift theory. – 23 November 2021
Continental drift theory was proposed by Alfred Wegener in 1912. According to this theory, all the continents were connected by a continental landmass called Pangea, which was surrounded by a vast ocean called Panthalassa. According to Wegener’s argument, about 200 million years ago [Mesozoic Era], the vast continent of Pangea split and began to move in all four directions.
Over time, Pangea split into two large continental landmass – Laurasia and Gondwana land. Larasia and Gondwanaland then gradually split into several smaller continents (the present continental form).
The major evidences given by Alfred Wegener to support the continental drift theory are:
- Similarities in Shape of Coastlines (jig-saw-fit): The face-offs of South America and Africa show a striking resemblance, in particular, the bulge of Brazil coincides with the Gulf of Guinea. It appears that the west coast of India, Madagascar and the east coast of Africa were intertwined. North and South America on the one hand and Africa and Europe on the other, share similarities with the Mid-Atlantic Ridge.
- Similar orogenic belts: If the east coast of South America and the west coast of Africa are fitted together, there are orogenic belts from the two continents that have the same age and structural tendency. For example, near Accra (West Africa) in Ghana there is a clear boundary between rocks older than 2000 million years and present-day rocks (about 400 million years old).
- Tillite Deposits: Tillites are sedimentary rocks formed by glacial deposits. The patterns of the Gondwana range of sediments found in India are found in different landmass of the Southern Hemisphere such as Africa, Falkland Islands, Madagascar, Antarctica and Australia. The base beds of the Gondwana range have dense tillage indicating extensive and prolonged snow cover or glaciation. This similarity of the sediments of the Gondwana range shows that there has been a similarity in the history of these lands. Glacial tillite rocks provide clear evidence of ancient climate and displacement of continents.
- Similarity in age of rocks in the oceans: corresponds to a strip of 200 million year old rock groups found off the coast of Brazil and off the coast of West Africa. The Gondwana range sediment patterns found in India are found in six different landmasses in the Southern Hemisphere. Similar patterns are found in Africa, the Falkland Islands, Madagascar, Antarctica and Australia. It is a surprising fact to find large deposits of gold with veins of gold on the Ghana coast and also in Brazil.
- Placer deposits: The presence of large gold deposits on the Ghana coast and the absence of native rocks are surprising facts. The gold deposits found in Ghana may have originated from the Brazilian plateau during the period when the two continents were connected to each other.
- Distribution of fossils: Homologous species of plants and animals living on land or in fresh water have been found on both opposite sides of the oceanic barrier. Small crawling creatures called mesosaurs can only live in shallow salt water. Their bones are found in only two regions – the Southern Cape Province of South Africa and the Eravar Rock Group of Brazil. At present the two places are 4,800 km apart and an ocean exists between them. Similarly, the presence of Glossopteris vegetation in Carboniferous rocks of India, Australia, South Africa, Falkland Islands, Antarctica etc. confirms the fact that these landmass were once interconnected in the past.
Wegener’s theory has been criticized on the basis of polar or polar flying force and tidal force, which are not believed to be capable of displacing continents. Presently, theories such as ‘Sea floor spreading theory’ and ‘Plate tectonics theory’ have become more relevant than continental drift theory, which offer a different explanation regarding the displacement of continents.