Geography: Inner Part of Earth and Plate Tectonics
Inner Part of the Earth:
Our understanding of the internal structure of the Earth us derived from studies of earthquakes. The shock waves sent out by an earthquake indicate the physical nature of the regions through which they pass.
Lithosphere:
The lithosphere is the top crust of the Earth on which our continents and ocean basins rest. it is thickest in the continental regions where it has an average thickness of 40 km and thinnest in the oceans where it may have a maximum thickness of 10 to 12 km
Mohorovic Discontinuity : An imaginary line that separates Mantle and Crust.
Gutenberg-Wiechert Discontinuity : A separation between the Mantle and the Core.
Plate Tectonics:
The Lithosphere is broken-up into tectonic plates and it rides on the Asthenosphere a layer just above Mantle. They move in relation to each other along their edges.
Basically in 3 ways:
- Convergent bound-Aries (collision or destructive)
- Divergent boundaries (Spreading or constructive)
- Transformation boundaries (conservative)
Such movements results in Earthquakes, volcanic activities, mountain buildings. Plate tectonics describes the motions of Earth's lithosphere as huge plates mostly resembling a continent or region on the surface.
The Forces acting behind:
- Friction
- Gravitation
- External Forces like Tidal
- Rotation of the Earth, etc.,,
Plate Tectonics tells us that it is not only the continents that are in motion, but the oceans as well. This is so, because the top crust of the Earth is not a complete single shell of granite and basalt, but a mosaic of several rigid segments, called plates. The theory of plate tectonics explains how the Earth's crust is moving in vast, rigid sections (plates) and is a modern revolution in our understanding of the plates. These plates include not only the Earth's solid upper crust, but also parts of the denser mantle below called Asthenosphere, and carry the continents and oceans on their backs like mammoth rafts. The plates with an average thickness of 100 km float on the Asthenosphere and move continuously against one another at a rate of upto 20 cm a year. Continents form only a part of the plates, the surrounding oceans form the rest of the plates. It is the plates containing both continents and oceans that move. The relation of inter-plates. It is the plates containing both continents and oceans that move. The relation of Inter-Plate. It is the plates containing both continents and oceans that move.
The relation of Inter-Plate movement is defined by the type of plate margin:
- Constructive
- Destructive
- Conservative
Constructive Plates:
Movement is obvious in the Atlantic Oceans. At the mid-ocean ridge, new ocean floor is continuously being produced as the Americas move further apart from Europe and Africa.
Destructive Plate:
Is found on all sides of Pacific Ocean, as the various plates slide down beneath the surrounding lithosphere.
Conservative Plate:
Arises where adjacent plates slide past one another along transform faults, such as the San Andreas fault.
i. African Plate - Continental
ii. Antarctic Plate - Continental
iii. Australian Plate - Continental
iv. Indian Plate - Continental (Indian Sub-Continent + Indian Ocean)
v. Eurasian Plate - Continental (Asia + Europe)
vi. North American Plate - Continental (North America + North East Siberia)
vii. South America Plate - Continental
viii. Pacific Plate - Oceanic
Notable Minor Plates: Arabian Plate, Caribbean Plate, Juan de Fuca Plate, Cocos Plate, Nazaca Plate, Phillippine Plate, Scotia Plate.............
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