Continental drift theory - Evidences and Limitations

Continental drift theory - Evidences and Limitations

Question - Throw some light on Theory of continental drift. Provide some evidences to support it and its limitation

Wegener took inspiration from a map of continents to explain the earth's geologic history. Trained as a meteorologist, he was intrigued by the exact fit of Africa's and South America's shorelines. He then gathered an impressive amount of evidence to show that earth's continents were once connected in a single supercontinent.

Thus, proposed in 1912 by Alfred Wegener, continental drift theory explained why similar looking animal and plant fossils and similar rock formations are found on different continents. This theory attempted at explaining how continents shift position. He maintained that around 200 million years ago, the supercontinent Pangaea began to split apart and broke into two large continental landmasses, Laurasia in the northern hemisphere and Gondwanaland in the southern hemisphere. Laurasia and Gondwanaland further continued to break apart into the various smaller continents that exist today.

Evidences to support the theory:

Wegener's theory was based partly on what appeared to him a remarkable fit of the South American and African continents. Apart from this coal deposits which are usually found in tropical climates were found in the North Pole. Wegener concluded that the North Pole could have been located near the equator when it was part of Pangaea.

The fossils of the same species were found in South America and South Africa. It is not possible for these organisms to travel over the vast water bodies of present day. The only way to explain it was that these two pieces of land were once connected.

Finally there were signs of glaciation at South America and Africa and the patterns of the marks left behind are similar in both continents, leading Alfred to believe they were connected.

He was aware that fossil plants and animals such as mesosaurs, a freshwater reptile found only South America and Africa during the Permian period, could be found on many continents. He also matched up rocks on either side of the Atlantic Ocean like puzzle pieces in order to support his theory. For example, the Appalachian Mountains in US and Caledonian Mountains in Scotland fit together, as do the Karroo strata in South Africa and Santa Catarina rocks in Brazil.

This was all more than a mere coincidence.

Limitations to the theory:

The scientists were reluctant in accepting the theory because there was not enough satisfactory explanation to the forces or mechanism that caused these continents to move such great distances, until the 1960s, when the concept of plate tectonics was introduced.

In other words, he could not explain what it was that made the continents move. When the Plate Tectonics Theory was proposed, mantle convection currents was the given mechanism to explain what made them move. Since the continents floated on the plates, the Plate Tectonic Theory provided the much needed mechanism for Wegner's Continental Drift theory. At once it was readily accepted by most all geologists.

The use of the jigsaw puzzle analogy as one of the evidences of his theory, too was not taken well. The argument was that it was not a perfect fit, whereas the continent's true shape was discovered not to be the shore line around them, but the edges of their continental shelves. With those outlines, the continents took on a very good fit for the puzzle pieces.

Another problem was that he believed that the continents "plowed" through the rocks of the ocean basins. Most geologists did not believe that this could even be a possible option.

In spite of all the criticism, Wegener was able to keep Continental Drift part of the discussion until his death. To strengthen his case he drew insights from the fields of geology, geography, biology and paleontology.

Plate tectonics, a modern update of the old ideas of Wegener about "plowing" continents, understands continental motion through the mechanism of seafloor spreading. New rock is created by volcanism at mid-ocean ridges and is returned to the earth's mantle at ocean trenches.

Despite his stupendous evidence for continental drift, Wegener never lived to see his theory gain a wide acceptance. He died in 1930 at age 50 of a probable heart attack while on a scientific expedition in Greenland.