The positions of the continents and ocean bodies have not been same in the past. The fact that continents shift their positions was proposed as early as in 1596. However, it was Alfred Wegener, a German a geophysicist and meteorologist, who put forth the theory of Continental drift with evidences in 1912.
Theory of Continental Drift
According to Wegener, about 300 million years all the continents had formed a single mass, called Pangaea which meant all earth. It was surrounded by a mega ocean called Panthalasa which meant all water. About 200 million years ago, the super-continent began to split apart. Pangaea first broke into two large continental landmasses, Laurasia in the northern hemisphere and Gondwanaland in the southern hemisphere. Laurasia and Gondwanaland then continued to break apart into the various smaller continents that exist today.
Evidences
Wegener put forward evidences to support his arguments. Important among these are the matching of shorelines of South America and Africa, identical geological structures and identical fossil species along the coastal parts of Africa and South America.
According to Wegener the drifting of continents after the break-up of Pangaea explained not only the matching fossil occurrences but also the evidence of dramatic climate changes on some continents. For example, the discovery of fossils of tropical plants (in the form of coal deposits) in Antarctica led to the conclusion that this frozen land previously must have been situated closer to the equator.
Wegener thought that the continents were moving through the earth's crust, like icebreakers plowing through ice sheets. According to him the movement responsible for the drifting of the continents was caused by pole-fleeing force (Centrifugal force due to rotation of the earth) and tidal force.
Criticism
Opponents of Continental Drift Theory pointed out that the centrifugal and tidal force were not large strong enough to move continents.
Wegener’s Theory of Continental Drift did not receive much acceptance when it was proposed. Since Wegener proposed his theory, scientists have carried out extensive exploration of earth’s crust and ocean floor. The evidences that have been gathered clearly suggest that continents drift.
Continental Drift and Plate Tectonics
The reason behind continental drift, which Wegener could not explain convincingly, is now explained by Plate Tectonic Theory. According to this theory earth’s crust is divided into major and minor rigid plates called tectonic plates. These plates move relative to each over the underlying asthenosphere. The slow movement of hot, softened mantle
that lies below the rigid plates is the driving force behind the plate movement.
Important Points
1. Alfred Wegener, a German a geophysicist and meteorologist, put forth the theory of Continental drift in 1912.
2. About 300 million years all the continents had formed a single mass, called Pangaea. It was surrounded by a mega ocean called Panthalasa.
3. Pangaea first broke into two large continental landmasses, Laurasia in the northern hemisphere and Gondwanaland in the southern hemisphere.
4. Wegener proided evidences for his proposal such as identical geological structures and identical fossils along the coastal parts of Africa and South America.
5. Wegener argued that movement responsible for the drifting of the continents was caused centrifugal force due to rotation of the earth and tidal force.
6. Opponents of Continental Drift Theory pointed out that the centrifugal and tidal force were not large strong enough to move continents.
7. The reason behind continental drift, which Wegener could not explain convincingly, is now explained by Plate Tectonic Theory.
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