Earth is divided into four spheres, the atmosphere, the hydrosphere, the biosphere, and the lithosphere. Spheres of the earth are explained in the previous post: Spheres of the Earth. As this chapter is about the interior of the Earth, therefore, we will discuss in this post only the Lithosphere of the Earth.
The upper solid layer of the Earth is known as Lithosphere. The upper mantle and the crust of the Earth are collectively called the Lithosphere. This region of lithosphere rests on a hot soft plastic-like layer: the Asthenosphere. Heat source inside mantle keep Asthenosphere in motion. Bright spots are zones in crust 15 to 20 km below the surface of Earth. It is layer, which reflect seismic waves more in lithosphere. The crust and the lithosphere as a whole is composed of many segments called the lithosphere plates are also known as tectonic plates. They move in response to the plastic flow in the hot Asthenosphere. In some mountains, the tectonic plates have come together in huge collisions.
Composition of Lithosphere:
So far as the composition of lithosphere is concerned, it is composed of many elements with different propositions. According to Clarke and Washington, it is made of igneous rocks (95%), shale (4%), sandstone(0.75%) and limestone(0.25%). These are composed of many elements which includes Oxygen(46.7%), Silicon(27.6%), Aluminimum(8.0%), Iron(5.0%), Calcium(3.6%), Sodium(2.7%), Potassium (2.0%), Magenisium(2.6%), Titanium(0.6%), and Hydrogen(0.14%). These elements are found in the form of compounds such as Anhydite (Calcium Sulphate/CaSo4), Aragonite (Calcium Carbonate/CaCO3), Calcite (Calcium Carbonate/CaCo3), Chalcedony (Silicon/SiO2), and Dolomite (Calcium Magnesium Carbonate (CaMg.CO3) 2 .
The Earth’s crust together with upper mantle (Lithosphere) is divided into segments separated along the ridges called lithosphere plates. They help us understand drifting movement of the continents. The scientists have concluded that if the ocean flours can move and spread then the continents can also do so. The plates can cause destruction if they move in appositive direction and collide. Collision results in earthquakes, volcanism and mountain building. There are many plates out which of the following are more important.
- The specific plates (South Alaska to Antarctic plates)
- The North American plate (North America)
- The African plate (African and Madagascar)
- The South American plate (Westward from 20oN).
- The Eurasian plate (Eurasia: North of Himalaya)
- The Austalian India plate (Australia & India).
- The Anstarctic plate ( Anstarctic Landmass).
- The Nazca plate (Between South American and Pacific Plates)
- The Caribbean Plate ( Cantral America & Caribean)
- The Cocos Plate (Oceanic of Latin America)
- The Scotic plate ( South of Latin America)
- Jaun de Fuca plate ( US-Canada boundary: N.America)
- Philippine Plate (Between Pacific & Eurasian plates)
- Arabian Plate (Arabia)