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The development of earth science theories and immense advancement of technology led to new discoveries about our planet, mother Earth. Around the time of 1940’s to 1950’s geologists have developed a different perspective of our planet. They have developed new and advanced theories about the formation of our planet and how it is changing every day.
Plate tectonics is derived from a greek word ‘tekton’ meaning construction worker or mason. Plate tectonics is a theory in geology. This theory primarily explains the proof of the large movements of the earth’s lithosphere. The lithosphere is the outermost layer of solid rock of a planet. The lithosphere consists of the uppermost mantle and the crust. These two are joined together across the Mohorovicic discontinuity. Under the lithosphere lies the athenosphere. The athenosphere is weak, hot and includes the deeper part of the upper mantle.
This plate tectonic theory was an expanded and detailed version of the previous theory of continental drift originated in the early 20th century. It also touched the seafloor spreading theory originated around 1960’s. Now, below the lithosphere lies the athenosphere. This athenosphere has lesser viscosity and also shear strength. This athenosphere can also flow like a liquid. However the displacement is very small and is measured on the geological time scale. The lithosphere is hard. Athenosphere is relatively more fluid. Again below the athenosphere lies the deeper mantle. However this mantle is rigid and hard. The reason stated for this is believed to be because of low temperature. However, it is because of very high pressure. Thus there are alternating layers of hard then relatively soft and then a hard layer again.
Now, the lithosphere is broken into small plates or regions called as tectonic plates. These tectonic plates are further divided into major tectonic plates and minor tectonic plates. In case of our planet earth, there are seven major and a large number of minor plates. The seven major plates are-
1> The African plate. This plate covers Africa.
2> The Antarctic Plate. This plate covers Antarctica.
3> The Australian Plate. This plate covers Australia.
4> The Eurasian Plate. This plate covers the continents Asia and Europe.
5> The North American Plate. This plate covers North America and also south east Siberia
6> The South American Plate. This plate covers South America.
7> The Pacific Plate. This plate covers the Pacific ocean.
Except for the Pacific plate which is a oceanic plate, all others are continental plates. Some important minor plates are the Indian Plate, the Arabian Plate, the Caribbean Plate.
The lithospheric plates are located on the athenosphere. These plates move with respect to each other at one of the three types of the plate boundaries. This movement is the cause of earthquakes. It is also responsible for volcanic activity, mountain building, and formation of ocean trenches. The plates are usually about hundred kilometers thick. The main constituent of these plates is lithospheric mantle. There is a layer of crustal material over this.
However, The lateral movement of the plates is slow. It is typically at speeds of 0.66 to 8.50 centimeters per year. Its magnitude can be grasped from the fact that, that’s about the same speed with which human nails grow!
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