On January 6, 1912, at a geological conference held in Frankfurt, the German scholar Alfred Lothar Wegener presented his theory of continental drift. Later, in 1915, he published the book "The Origin of Continents and Oceans". Wegener was a climatologist, and his primary area of study was the variation and distribution of climates in the geological past. During his research, he discovered evidence of both equatorial (tropical) and Arctic climates in locations where their presence seemed impossible. To resolve this, he proposed two possibilities -
(A) Either the Sun did not exert control over these climatic zones, or
(B) The Earth’s large landmasses (continents) had shifted (drifted) from their original positions.
It was this second hypothesis that led Wegener to formulate his theory.
Continental Drift Theory
According to Wegener, during the Carboniferous period of the Paleozoic Era (approximately 360 million years ago), all the continents were joined together. A single vast supercontinent, which Wegener named ‘Pangaea,’ existed on Earth, surrounded by a vast ocean he called ‘Panthalassa.’ Pangaea was composed of ‘sial’ (silica and aluminum) and floated upon a denser layer of ‘sima’ (silica and magnesium). A shallow sea known as the ‘Tethys Sea’ lay in the middle of Pangaea. To the north of this sea was the ‘Angaraland’ (or Laurasia) landmass, which included North America and Eurasia. To the south of the Tethys Sea lay ‘Gondwanaland,’ comprising South America, Africa, Madagascar, Australia, peninsular India, and Antarctica. The South Pole was located near the present-day South African coast (Natal) that is, near the center of Pangaea. At the end of the Carboniferous period, Pangaea began to break apart and drift, moving in two directions -
(A) Towards the equator, and
(B) Towards the west.
The movement
towards the equator was driven by the interplay between gravitational forces
and buoyancy, while the westward drift was caused by the tidal forces exerted
by the Sun and the Moon. Due to these tidal forces, peninsular India,
Madagascar, Australia, and Antarctica separated and drifted away. Similarly,
North and South America drifted westward; however, the resistance encountered
from the underlying ‘sima’ layer led to the formation of the Rocky and Andes
mountain ranges. It is through this process of continental drift that the
present-day configuration of the continents and oceans has emerged. According
to Wegener, this displacement continues even today.
Arguments in Support of the Theory
1. According to Wegener, if the two coastlines of the Atlantic Ocean were brought together, they would fit each other precisely. Similarly, the eastern coast of North America could be joined with the western coast of Europe. The bulge of Brazil could easily fit into the Gulf of Guinea.
2. There is a striking similarity between the rocks and mountain ranges found along the Atlantic coastlines. Their geological history and structure are also identical. The mountains in Europe, Africa, and the Americas share a similar composition. The Brazilian Plateau, the plateau of Southern Africa, the Deccan Plateau, and the Australian Plateau are structurally similar. Furthermore, similar minerals are found in both Southern Africa and South America. Thus, geological evidence also supports this theory.
3. The lemmings a specific type of animal found in Scandinavia migrate westward and perish in the Atlantic Ocean; this behavior suggests an instinctual drive to reach a landmass located to the west.
4. Fossils of the small reptile "Mesosaurus" have been discovered exclusively in Southern Africa and Brazil, which serves as evidence that these regions were once connected.
5. Evidence of glaciation dating back to the Carboniferous period has been found in widely separated regions such as the Falkland Islands, Southern Africa, Brazil, and Australia which confirms the former existence of the supercontinent Pangea.
