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 land masses were connected, the same or closely related plants and animals inhabited each.
After the land masses were separated, the different populations were geographically isolated from each other by great distances of 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 which 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 north-bound India crashed into Asia. The eastern edge of India made 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 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 utilise the technologies of space. They include very long base line 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.
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