The idea of Continental Drift is very old and has been known to several explorers in the past from the Age of Discovery. Over the period various geologists have found the Continental Drift Theory evidence. The following geological facts were observed for a long time, which remained unexplained until recent times.
The configuration of the land masses of the American continents and the continents of the eastern hemisphere is such that if the two land masses are put together, the curves fit into one another.
The mountains of America, the Rockies, and the Andes are situated on the western boundaries of the continents as if they had been folded by pressure from the east.
The mountains of central Asia and Europe seem to have been formed by a push from the south against the landmass of the northern parts of these continents.
The rocks formed in South India, in what is known as the Gondwana lands, are identical to those of South Africa.
The fossils found in the cold regions of the Earth have been identified as remains of plants belonging to warmer regions, so either the climate has undergone a radical change or these regions were once situated in the warmer parts of the Earth and have subsequently shifted to the colder north.
The flora of many places situated at great distances from one another shows great similarity, as if they evolved from the same ancestors.
Continental Drift Theory
Alfred Wegener, a German meteorologist, noted the similar coastal outlines of western Africa and the eastern coast of South America. He speculated that the continents were not only located nearby but were once a single land mass, a supercontinent called Pangaea. He was the one who pioneered the Continental Drift theory in 1912.
According to the Continental Drift Theory, the whole mass of land was once a huge agglomeration of the masses of the present-day continents. Thai mass was named Pangea. At some time in the Paleozoic age in the Upper Carboniferous period, this mass broke into fragments that were detached from the west and south and began drifting apart due to differential gravitational forces.
The mass on the west side later formed the American continents. Its western side was the first to stop drifting while the eastern side continued drifting, and the pressure led to the further folding up of the western margin, leading to the formation of the Andes and Rockies.
The second mass broke off from the southern part of Africa and was divided into two. One portion moved to the northeast and the other to the southwest. The northeast portion gave rise to the formation of peninsular India while pressing against the southern margin of Asia, creating the mighty Himalayas and other mountains in central Asia.
The other portion towards the southeast formed the Antarctic, Australia, and New Zealand. This drifting process continued till the Eocene period, and the continents achieved their current state by the Quaternary period.
Sir Francis Bacon commented in 1620 that such similarities were not accidental. In 1756, Theodor Lilienthal discovered biblical evidence of these separations and drifting. In 1800, Alexander von Humboldt retained the idea that the Atlantic was a huge river valley with its sides separated by a great volume of water through which Noah’s Ark sailed.
S.W. Carey, a geologist, postulated that the Earth was expanding due to heat generated inside by the disintegration of radioactive minerals. This expansion caused cracks in Pangaea, which grew further, leading to the formation of oceans in between.
Such cracks are called rift valleys and were discovered in Africa. The Red Sea is an example. The expulsion of lava led to the formation of ridges that further expanded the ocean,s leading to the separation of the continents.
Thus, most scientists consider Alfred Wegener to be the real pioneer of the modern theory of Continental Drift.
Continental Drift Theory Evidence
In 1861, Antonio Snider-Pelligrini described the fitting together of the continents that border the Atlantic.
Later, J.H. Pepper explained the occurrence of identical fossil plants in European and North American coal deposits in 1861.
Plant fossils were also discovered from the coal-bearing rocks of Bengal and Bihar, showing peculiar leaves that were later found to be similar to those found in Australia, South Africa, and South America.
In the 19th century, the Balnford brothers discovered enormous coal beds held by unrounded boulders, embedded in the rock strata in the 200 million-year-old coal deposits near Talcher in Orissa. These were called the Talcher Bed.
Geologists believe that such humongous boulders could only have been brought by the glaciers, a phenomenon they call erratic.
A similar discovery was also made near the bank of the Penganga in Madhya Pradesh. The Talcher Bed also had striated pavement underneath it.
The discovery of Glossopteris from Antarctica under the ice revealed that the South Pole was not always covered in ice when the coal beds were being deposited in the southern hemisphere. The discovery of similar rocks, vertebrates, and invertebrates from these areas supports this theory. Moreover, the discovery of fossilized bones of a small animal called Mesosaurus was also made in Africa, Argentina, and Brazil.
Conclusion
The Continental Drift theory made way for the modern theory of Plate tectonics. The plate tectonics theory was introduced by the Canadian geophysicist and geologist John Tuzo Wilson in 1965. He published his work in the Nature where he defined the nature of the plates and plate boundaries along with its continuous motion of rigid plates with respect to one another. According to the plate tectonics theory,
The Earth is made thin rigid plates or pieces of lithosphere.
Theseplates move horizontally with respect to one another.
They interact with each other and their boundaries.
Such interactions are associated with tectonic activities such as creation of mountains, earthquakes, volcanoes, etc.
A historical account of how continental drift and plate tectonics provided the framework for our current understanding of palaeogeography. Geological Magazine , Volume 156 , Issue 2 , February 2019 , pp. 182 – 207. DOI: https://doi.org/10.1017/S0016756818000043
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