Continental Drift: Theory and Evidences of Continental Drift and Continental Fit
The Lithosphere is always in a state of work in progress. In 1912, a German geologist named Alfred Wegener came up with an outlandish theory known as continental drift. His theory was based upon the following clues.
Continental Fit
One of the first clues he had was that the continents were once joined once, by noting the jigsaw puzzle–like geometry of Africa’s west coast and South America’s east coast. This was called “Continental Fit”.
Fossils
Fossils of Mesosaurus, a freshwater reptile, have only been found in Africa and South America. The fossil remains of Cynognathus, a land reptile, are found in South America and Africa. A fern called Glossopteris was found fossilized on all of the southern continents. Since these continents all have different climates now, Wegener proposed that they once all shared a similar climate as one landmass. The evidence of another land reptile, Lystrosaurus, was found in Africa, India, and Australia.
Coal Fields
He noticed the presence of coal fields in the temperate regions, while they could only be formed in the Tropical regions.
Glacial Flow
Wegener noticed that all over the southern hemisphere there are glacier deposits left over from millions of years ago. India, which is now located above the equator, shows signs of glaciers moving across it from the south. Since, it can not be explained without continental drift why would glaciers move toward India from the equator? The clue Wegener had was of a single giant ice sheet that moved outward from Antarctica.
Similarity in Rocks
The similarity in the rock structure on opposite sides of the Atlantic was another clue.
So, Wegener proposed that the present continents were once joined in a super continent named Pangaea and later the drifted apart. Wegener proposed that the Pangaea broke into continents and the new continents drove away themselves in two directions viz. Equatorward and Westward movements. He said that the movements towards the equators were because of the gravitational differential forces and force of buoyancy. The Westward movement occurred because of the tidal force of sun and moon.
He proposed that the Pangaea began to separate into the Gondwanaland and Angaraland in the Carboniferous period and the space between the two was filled with water that was called Tethys Sea. Later the Gondwanaland disrupted during the Cretaceous period and with this, the Indian subcontinent (peninsula) , Madagaskar, Australia and Antarctica broke away from the Gondwanaland. Similarly the North America broke away from the Angaraland and drifted westward due to Tidal forces. He went on further proposing that South America broke way from Africa and moved westwards due to Tidal forces. This theory was interesting and thrilling but Wegener was unable to explain what the forces behind this drift were. So, the result was that Alfred Wegener was derided by the scientific community; his proposal was called “geopoetry”. However, the later discoveries in deep-sea science led Wegener’s basic proposition to be accepted as fact, and today a good deal is known about how the continental drift occurs.
Paleomagnetism
Earth has a magnetic field that causes a compass needle to always point toward the North magnetic pole. When the magnetic minerals cool down, the domains within the magnetic mineral take on an orientation parallel to any external magnetic field present at the time they cooled below this temperature. Using this, it can be determined what was the orientation of the magnetic field present at the time the rock containing the mineral cooled, and thus be able to determine the position of the magnetic pole at that time. Magnetite is the most common magnetic mineral in the Earth’s crust. The studies showed that the magnetic pole had apparently moved through time. When similar measurements were made on rocks of various ages in North America, however, a different path of the magnetic pole was found. This would first imply that either the Earth has had more than one magnetic pole at various times in the past, which can not happen. The second implication is that the different continents have moved relative to each other over time. This led to the confirmation of the theory of continental drift.
