The relative position of landmass and ocean basins is referred to as the distribution of continents and oceans. The movements of tectonic plates take place over millions of years, which moves at a rate of 2-10 cm/year. The movement of tectonic plates by this slow speed causes movements of hundreds to tens of thousands of kilometers over millions of years, bringing change in size, shape, and depth of the ocean basins, and distribution of oceans and continents on Earth’s surface. Oceans comprise 69% whereas continents comprise 29% of the Earth’s surface.
The following major theories were proposed during different times regarding the distribution of Oceans and Continents
Continental Drift Theory
Seafloor Spreading Theory
Plate Tectonics Theory
Continental Drift Theory:
The continental drift refers to the horizontal movement of the continents on a vast scale.
In 1908, F. B. Taylor proposed the continental drift hypothesis. Then in 1910, and 1912, Alfred Wegener, advocated that continents had drifted apart, and suggested mechanisms by which this might have occurred.
Taylor’s Hypothesis
According to Taylor’s hypothesis, there were two landmasses in the past, one in the northern hemisphere, Laurasia, and the other in the southern hemisphere, Gondwana Land.
With time, these landmasses start spreading outward towards the equator, more or less radially from the polar regions.
Taylor suggested that this land spreading was due to the sudden increase of tidal action of the moon, which was sufficient to increase the rate of rotation of the earth and also dragged the continents away from the pole.
However, Taylor’s hypothesis fails to justify, that how could these tidal forces increase the Earth’s rate of rotation, and the equatorial movement of continents. He also fails to explain, the drifting of South America and Africa.
Wegener’s Hypothesis
Wegener suggested that till the end of the Carboniferous period, the present-day continents were one supercontinent called Pangea, surrounded by the world ocean called Panthalassa.
In the late Palaeozoic period, probably during Permian or in early Mesozoic time Pangea broke into pieces and the separated continental blocks began to migrate away from each other.
After Pangea broke apart, the African block (Gondwana land) and the Eurasian block (Laurasia) moved towards the equator, America drifted towards the west, the Atlantic Ocean created between North and South America in the west Europe and Africa in the East, and Australia swung to the east.
India after getting separated from Africa moved north. It left Madagascar behind and collided with the northern plate resulted the formation of the great Himalayan mountain chain.
These hypotheses were based on palaeontological and paleoclimatic evidence, such as the presence of the plant fossil Glossopteris, in late Palaeozoic age rocks of South America, Africa, India, and Australia, which suggests that these continents were once joined.
The similarity of Precambrian rocks of Central Africa, South India, Brazil, and Australia.
Evidence of widespread glaciation towards the Palaeozoic era was found on the continents of the South hemisphere.
The shift of climate belts through geological time is related to Polar wandering, i.e. the apparent movement of the earth’s geographic north and south pole.
To be continued…
