Continental Drift | The Basic Theory Of Plate Tectonics | Geology

Continental Drift is horizontal movements of continents with respect to one another and to the basins in geologic time.
In the early 1900s Alfred Wegener, a German Earth Scientist proposed the idea that the continents as we believe are not stationary, but as a matter of fact, have been drifting about on the earth’s surface over millions of years of geologic time. Continental drift theory is the basis for the theory of plate tectonics.

Continental Drift

Have you ever imagined, our Earth becoming a global village having no more different continents but just one? Alternatively, will you believe if I say that Antarctica was once a warm landmass with dense tropical rain forests growing on it? If the answer is no, then probably you should explore this fascinating theory of continental drift because appearances can be deceptive in the field of geology.

Snider-Pellegrini Wegener fossil map
Like Clouds drift in the sky, the continents also drift in the same manner but at a minimal rate of about a few centimetres per year. It takes millions of years for a continent to move to a much noticeable different location.
Wegener also suggested that a super-continent existed 200 million years ago in which all the major continents of the world were clubbed together, and have since then broken apart and migrated to their present locations which we see today in our world map. He named this super-continent “Pangea” which is entirely appropriate because it is a Greek term for ‘entire Earth.’

Evidence In Support Of Wegener’s Hypothesis Of Continental Drift

  • Jigsaw Puzzle Fit Of The Continents

Wegner noticed that the coastlines of South America and Africa fit like the pieces of a puzzle. This was not a coincidence because it indicates that the two continents were once united and had since then drifted apart. 

  • Fossil Evidence

Similar species of fossils were recognized between the east coast of South America and the west coast of Africa. For example, the fern Glossopteris which grew in a sub-polar climate was found in the rocks of Africa, Australia, India, and South America. This indicated that the landmasses were once a part of Gondwanaland.

Fossils of the reptile Mesosaurus were found at two different continents that were thousands of kilometres apart. There was no logical reason for explaining how those reptiles could have travelled through the saltwater separating the east coast of South America and the west coast of Africa. The idea of land bridges seemed improbable and continental drift was a better explanation which unfolded that the continents of Africa and South America were connected when Mesosaurus existed on the planet. Later on, the two continents moved apart carrying away the fossils with them, and an ocean basin was born.
  • Orogenic Belts

On reconstructing the continents, Wegner found that the Appalachian Mountain belt forms a continuous chain with mountains on Greenland and in Northern Europe. This was inferred after correlating the type of rocks and their age which were found to be similar in both the mountain chains. 
  • Paleoclimatic Evidence of Continental Drift

The palaeoclimatic evidence is ancient climate indicators like plant species and depositional environments for sedimentary rocks that show similarities in palaeoclimatology data.
‘Glacial evidence has been found in warm regions, and bituminous coal has been found in cold regions like Antarctica.’ Rocks deposited by glaciers that existed 250 million years ago are found in similar-aged rocks of southern Africa, South Africa, India, and Australia. The strange thing is that much of this land presently lies within 30 degrees of the equator.
Therefore the presence of similar glacial rocks in southern continents indicates that these continents were once a part of Gondwanaland covered by a single continental glacier. Another evidence is the fossils in the coalfields of the Appalachians which are indigenous to a warm subtropical climate but are presently located in a temperate climate.
Despite all these pieces of evidence Wegner’s ideas were not generally accepted within the scientific community because he failed to explain the mechanism that was driving the movement of continents on the earth’s surface.
It was only in the 1950s when discoveries and research on seafloor spreading, magnetic reversals, palaeomagnetism and polar wandering garnered support for the theory of continental drift and it was finally accepted.

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