Question.
Examine the plate tectonic theory. (UPPSC 2017)
Provide a critical account of the theory of Plate Tectonics. ( UPPSC 1990)
Answer.
Plate tectonic theory is a modern scientific theory that explains the following:
- Current position and direction of motion of continental and oceanic crust.
- How did the major landforms like fold mountains, volcanic mountains, trenches, etc. originate?
- It explains the occurrence and pattern of natural disasters especially terrestrial disasters like earthquakes and volcanoes.
According to plate tectonics theory,
- The lithosphere is made up of the crust and the upper solid part of the mantle that lies above the asthenosphere. The thickness of the lithospheric plates is about 50 to 100 km.
- The lithosphere is divided into 7 major parts and about 15 minor parts which are called tectonic plates or plates.
- Tectonic plates can include both oceanic crust and continental crust. But depending on the majority of shares, plates can be classified as oceanic plates or continental plates.
- Continental plates are lighter than oceanic plates. The thickness of oceanic plates (about 50 km) is much less than that of continental plates (about 50 to 100 km), but they are heavier than continental plates.
- These tectonic plates move vertically and horizontally over the asthenosphere.
- Earth's major landforms such as mountains, trenches, volcanic activity, and earthquakes occur around the margins of plates.
- The plate has three sides- convergent, divergent, and transverse plates.
Evidence regarding the correctness of plate tectonic theory:
- With respect to fold mountains, plate tectonics theory has rightly stated that fold mountains are formed either at the convergence boundary of continental-continental plates or at the convergence boundary of oceanic and continental plates. For example, the Himalayas are formed at the convergence boundary of the two continental plates.
- The theory also explains correctly in relation to volcanic activities and volcanic mountains. It occurs at the convergence boundary of the ocean–continental convergence, ocean-to-oceanic convergence, and ocean-to-ocean plate divergence boundary.
- The earthquake zone occurs in all three margins of the plates.
- It is able to give correct answers regarding the origin of major landforms such as fold mountains, volcanic mountains, mid-oceanic ridges, trenches, etc.
- According to plate tectonic theory, supercontinents( Pangaea) and superoceans (Panthalassa) were one of the patterns of motion of plates in geological time scales.
- It is also able to explain the driving force of tectonic plates that move through convection cells inside the lower mantle.
Criticism of Plate Tectonic Theory:
- It did not provide any information about the equilibrium force between the crust and the asthenosphere. The theory did not answer how the high mountain region is balanced on the moving asthenosphere.
- Some volcanoes and some sources of earthquakes are not found even on the margins of tectonic plates. The theory does not give any answer about this either.
- The theory hasn't given much information about how the convection cells in the lower mantle are working.
- According to the laws of physics, there must be friction between the lithosphere and the asthenosphere due to the movement of Plates, but this force of friction is not explained in theory.
Barring a few regions, plate tectonic theory has almost succeeded in explaining the origin of various landforms on the Earth's crust and is the most accepted scientific theory.
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