First proposed by Alfred Wegener, the meteorologist, the theory of continental drift supports the belief that the Earth’s continents once were a single landmass. This landmass, which was named “Pangaea,” broke up, and its various parts drifted away from one another. Centuries ago, trips around the world from travellers showed outlines from every continent around the world. Later on, early mapmakers wondered why these continents fit together so well. Early geologists thought that the continents had started in the places they laid in the present day. Finally, however, a meteorologist constructed a theory that would change the way people would look at the world.
The Theory of Continental Drift is a theory that proves that the continents were once joined together, making only one single landmass. A meteorologist proposed this theory by the name of Alfred Wegener. His theory states that the continents were once one and have drifted apart. Wegener named this landmass “Pangaea,” which translates “All Lands” Then, he gathered evidence from around the world from landforms, fossils, and climate. He then gathered his evidence and put it in a book titled “The Origin of Continents and Oceans,” published in 1915. But Wegener’s theory was rejected because he could not provide evidence on the force that moved the continents.
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The Earth has a magnetic field that causes a compass needle to always point toward the North magnetic pole, located near the rotation pole. The Earth’s magnetic field would be expected if a giant bar magnet was located at the centre of the Earth. The magnetic field is composed of lines of force. Initial studies of how the position of the Earth’s magnetic pole varied with time were conducted in Europe. These studies showed that the magnetic pole had moved through time. When similar measurements were made on rocks of various ages in North America, a different magnetic pole path was found.
This either suggested that (1) the Earth has had more than one magnetic pole at various times in the past (not likely), or (2) that the different continents have moved relative to each other over time. Studies of ancient pole positions for other continents confirmed the latter hypothesis and seemed to confirm the theory of Continental Drift. Exploration of the seafloor had been in progress at a slow but gradually accelerating pace during the nineteenth century and the first four decades of this century.
There was a rapid increase in geological and geophysical exploration of the seafloor after the Second World War. Hess suggested in 1958 that seafloor too may be in motion, and it may be carrying the continents with it. It turns out that the theory of continental drift provides a consistent and straightforward explanation for these paleomagnetic results. Hess’s idea explained neatly why the drifting continents did not leave any scars on the seafloor. It also shifted the spotlight from the mechanism of continental drift that had bothered Wegener greatly. In time, Hess’s poetry became known as the seafloor spreading hypothesis.
A fossil is any evidence of ancient life. At the beginning of the 20th Century, fossil evidence was also found to support continental drift. Identical fossilized plant and animal species have been found in many different places on different continents. It seems complicated to believe that such similar organisms would exist so far away from each other or that they could have swum from one continent to another. It is more likely that these life forms once lived altogether on a single continent, as shown in the following image. An example of this would be that the same animal fossils have been found in places like South America and Africa, which could only have happened if they were joined initially.
Palaeoclimatology is the study of changes in climate taken on the scale of the entire history of Earth. Glaciers covered Parts of all the continents in the Southern Hemisphere in their geological past. Glaciers grind and smooth the rocks across which they move, and leave grooves where rocks that were caught in the ice grated over the bottom rocks. When the ancient scour marks on the continents in the Southern Hemisphere are studied, it appears as if the ancient glaciers were formed in the oceans and moved towards the land. But no glacier we know of functions in this way. Glaciers usually form in high-lying regions and then move slowly downwards in the direction of the oceans.
However, if we could move the continents back to recreate Gondwana, all ancient glacier parts would fit neatly into one another without being separated by oceans. While the ancient fossils on different continents were often similar or identical, the exploring naturalists were finding out that living plants and animals on the different continents were often very different. The naturalists were discovering whole new groups of animals and plants on nearly every island and continent they visited. Most biological species seemed to be unique to the region or continent in which they were found. How could these seemingly contradictory observations be reconciled? Plate tectonics provided the answer.
When the different landmasses were connected, the same or closely related plants and animals inhabited each other. After the landmasses were separated, the different populations were geographically isolated from each other by great distances from the ocean. Life on the different continents had apparently evolved into different species because the populations were isolated from each other by such great distances. It is possible to correlate, or link, the breakup of the continents with the types of animals found on each. The longer the period of separation, the more differences between species were found. For example, all of the indigenous (native) mammals found in Australia are marsupials. There are no naturally occurring placental mammals.
This suggests that Australia broke away before placental mammals had evolved. In geographic isolation from the rest of the world, Australia’s mammals were able to evolve into many highly sophisticated forms found nowhere else. A geologic record of ancient plate tectonic activity is preserved in mountain belts around the world. Suture zones that indicate boundaries between ancient mobile plates can be dated to determine when continents joined and contiguous mountain belts reveal the placement of continents along ancient subduction zones. The Alps and the Himalayas are examples of much more recent mountain-building episodes. The formation of the Alps began about 50 million years ago with the northward movement of the African plate.
Although Africa has not made contact with Eurasia, small plates caught between the two larger plates have been pushed up against Europe causing mountain building there. The Himalayas formed when northbound India crashed into Asia. The eastern edge of India made the first contact with Indochina perhaps 45 million years ago and the plate continued advancing northward until contact with Eurasia was attained 15 million years ago. The Himalayan crust is extremely thick possibly due to the wedging of the Indian plate beneath the Eurasia plate. These and other mountain belts contribute to our understanding of plate movements and the closing of ancient oceans.
The weakness of Wegner’s theory and the reason it was not readily accepted by geologists was that he proposed that the continents slide over the ocean floor. Geophysicists disagreed, stating the ocean floor did not have enough strength to hold the continents and too much frictional resistance would be encountered. Confounded by his critics on the evidence for drift in the geological past, Wegener turned to geodetic data in the form of longitude measurements around Greenland to establish that continents may be drifting today. Since then, phenomenal advances have occurred in geodetic measuring techniques. Many geodetic methods today utilize the technologies of space. They include very long baseline interferometry with radio waves from distant quasars, laser ranging and the GPS. All yield highly precise and repeatable measurements.
In conclusion, it was an important day in 1912 when Wegener proposed his theory. Le Grand views the subsequent developments related to the idea of continental drift as the stuff of myth and legend. In one inspired paragraph, he equates continental drift with Cinderella and its critics with her vain stepsisters. He compares the geophysicists of the 1950s and early 1960s with Cinderella’s Fairy Godmother who waved the Magnetic Wand. Cinderella went to the Ball and married the Prince represented by the seafloor spreading hypothesis and the plate tectonics theory.
The history of science is replete with instances where ideas popular in one period were discarded subsequently. Thus I cannot end in the normal style of fairy tales by saying. The idea of continental drift lived happily ever after. Changes may be anticipated. How and when I can.t say. But, as of now, GPS results provide a reasonable basis to infer that continents drift and all other earth sciences observations may be reconciled in light of this fact.