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The theory of continental drift is an attempt to explain the present arrangement of continents and ocean basins. The idea of continental drift is very old as Abraham Ortelius in 1596. The concept was independently and more fully developed by Alfred Wegner, a German meteorologist and geophysicist, in his book ‘Origin of Continents and Oceans’ published in 1915.
In his theory it is presumed that in the geological past all the continents were ‘united’ together. This Parent continent was known as Pangea (Pan = All + gea = Earth). The Pangea was surrounded by a huge sea ‘Panthalassa (Pan = All + thalassa = ocean) representing Primeval Pacific Ocean.
Wegner hypothesized that the surface of super continent (Pangea) broke up to form:
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(i) Lurasia (North America, Greenland and whole Eurasia, North of Indian sub-continent) and
(ii) The Gondwana Land (S. America, Africa, Madagascar).
Now Malagasy, Peninsular India, Australia and Antarctica, in the carboniferous period about 300 million (30 crore) years back. He opined that continents are made up of SIAL (Sillicon and Aluminium) and ocean basins of SIMA (Sillicon and Magnesium).
Wegnar developed this concept while trying to explain the climate of the past.
The puzzling questions in his mind were:
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(1) Why should tropical ferns (vegetation) have grown in temperate countries like England, Germany, France and Greenland?
(2) Why the Glaciers have covered parts of Brazil, Peninsular India, Australia and Congo Basin?
These climate changes may be explained in two ways:
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(a) If the continents reclaimed stationery at their places, the climate zones might have shifted from one region to another.
(b) If the climatic zones remained stationery, the landmasses might have been displaced and drifted. Since climatic zones are controlled by the heat from the sun, their shift cannot be explained. It is more probable that the landmass have changed their position. According to Wegner, the continents drifted in two directions: towards Equator and towards West.
Evidence in Support of Continental Drift:
(1) Geographical similarities in opposing coast of the Atlantic Ocean. ‘Jigsaw-fit’ of the opposing coasts of Atlantic ocean.
(2) Fossils of glossopteris (a fern-like plant) have been found in rocks of the same age from South America, India and Australia. Fossils of Lystrosaurus (Lizard type animal) have been found in South Africa, India, and Antarctica. There is no way that such huge animals travelled across oceans if lands were not adjoining earlier.
(3) Folded Mountain ranges at Cape of Good Hope and rocks of Buenos Aires (Argentina) resemble.
Wegner was however, criticized for failing to explain the forces that would permit continents to plough through the ocean of rocks. Wegner died in Greenland in 1930. The idea of continental drift got revived in 1950s and 1960s.
In 1940, seismologist Hugo Benioff plotted the location of deep earthquakes at the edges of Pacific ocean. He plotted 30,000 earthquakes and established the ring of fire. The Continental Drift Theory became basis of Plate Tectonic Theory.