The concept of plate tectonics has been derived from the isostasy and continental drift theory. Elaborate citing suitable examples.
The modern concept of Plate tectonic theory was postulated in 1960′. It is based on the understanding of various theories argued earlier to explain the movement of the earth’s crust.
- For the first time in 1915 crustal movement was proposed by Alfred Wegener in his theory of “continental drift.” Wegener proposed that the continents float over the heavier matter underlying them. This is why continents were once united into a single supercontinent named Pangaea, meaning all earth in ancient Greek. He suggested that Pangaea broke up long ago and that the continents then moved to their current positions. He called his hypothesis continental drift.
He argued this on the basis of several shreds of evidence as follows:
- Identical rocks of the same type and age are found on both sides of the Atlantic Ocean. Wegener said the rocks had formed side-by-side and that the land had since moved apart.
- Mountain ranges with the same rock types, structures, and ages are now on opposite sides of the Atlantic Ocean.
- The Appalachians of the eastern United States and Canada, for example, are just like mountain ranges in eastern Greenland, Ireland, Great Britain, and Norway. Wegener concluded that they formed as a single mountain range that was separated as the continents drifted.
- Ancient fossils of the same species of extinct plants and animals are found in rocks of the same age but are on continents that are now widely separated. Wegener proposed that the organisms had lived side by side, but that the lands had moved apart after they were dead and fossilized.
However, Wegener failed to explain the reason for continents floating over the earth. He didn’t have an explanation for why and how the continents moved. Later several theories like seafloor spreading, paleomagnetism, and isostasy built the understanding of crustal movement over heavier underlying matter.
The concept of isostasy later explains lighter element float over denser material. The theory argued that
lighter crust must be floating on the denser underlying mantle. It also explained how different topographic heights can exist on the Earth’s surface on the basis of Isostatic equilibrium. Therefore, understanding the dynamics of isostasy helps us figure out more complex phenomena such as mountain building, sedimentary basin formation, the break-up of continents, and the formation of new ocean basins.
Starting from the development of continental drift theories, later several theories such as seafloor spreading, isostasy, and understanding of asthenosphere lead to the development of modern plate tectonic theory. Since its emergence in the 1960s, plate tectonic theory has gained widespread acceptance as the model of Earth processes.