The layers of the earth according to their physical properties:
Lithosphere.
Asthenosphere.
Mantle.
Outer Core.
Inner Core.
The Core
At the centre is the densest of the three layers, the core. It is mostly metallic iron with small amounts of nickel and other elements. The outer boundary of core is at a depth of 2,900 kilometres.
The Mantle
The thick shell of the dense, rocky matter that surrounds the core is called the mantle. The mantle consists of iron-magnesium-silicates and it is less dense than the core but denser than the outermost compositional layer, which also consists of rocky matter. The outer boundary of the mantle is at a depth from 8-70 km.
The Crust
The outermost compositional unit is the crust. While the core and the mantle have nearly constant thicknesses, the thickness of the crust is different in different places. The crust beneath the oceans, which is called oceanic crust, has an average thickness of about 8 km, whereas the thickness of the continental crust ranges from 30 to 70 km. The oceanic crust is basalt while the continental crust has a granitic composition.
Layers of Differing Physical Properties
In addition to compositional layering, other changes occur within the earth. Most important, there are changes in physical properties such as rock strength and solid versus liquid. Except for the outer boundary of the core, the boundaries of the layers of different physical properties do not coincide with the boundaries of the layers of different chemical composition.
The layers of different physical properties outward from the centre of the Earth are as follows: inner core, outer core, mesosphere, asthenosphere, and lithosphere.
The inner structure of the Earth
Layers of differing chemical composition: core, mantle, crust. Layers of differing physical properties: inner core, outer core, mesosphere, asthenosphere, lithosphere. Note that the crust is a thinner layer inside the lithosphere. The oceanic crust and continental crust are different in composition. The Inner and Outer Core
Within the core an inner region exists where pressures are so great that iron is solid despite its high temperature. The solid centre of the Earth is in the inner core. Surrounding the inner core is a zone where temperature and pressure are so balanced that the iron is molten and exists as a liquid. This is the outer core. The difference between the inner and outer cores is not one of the composition (the compositions are believed to be the same). Instead, the difference lies in the physical states of the two: one is a solid, the other is a liquid.
The Mesosphere
The strength of a solid is controlled by both temperature and pressure. When a solid is heated, it loses strength. When it is compressed, it gains strength. Differences in temperature and pressure divide the mantle and crust into three strength regions. In the lower part of the mangle, the rock is so highly compressed that it has considerable strength even though the temperature is very high. Thus, a solid region of high temperature but also relatively high strength exists within the mantle from the core-mantle boundary (at 2,883 km depth) to a depth of about 350 km and is called the mesosphere ("intermediate, of middle, sphere").
The Asthenosphere
Within the upper mantle, from 350 to between 100 and 200 km below the Earth’s surface, is a region called the asthenosphere ("weak sphere"), where the balance between temperature and pressure is such that rocks have little strength. Instead of being strong, like the rocks in the mesosphere, rocks in the asthenosphere are weak and easily deformed, like butter or warm tar. As far as geologists can tell, the compositions of the mesosphere and the asthenosphere are the same. The difference between them is one of physical properties; in this case the property that changes is strength.
The Lithosphere
Above the asthenosphere is the outermost strength zone, a region where rocks are cooler, stronger, and more rigid than those in the plastic asthenosphere. This hard outer region, which includes the uppermost mantle and all of the crust, is called the lithosphere ("rock sphere"). It is important to remember that despite the fact that the crust and mantle differ in composition, it is rock strength, not rock composition, that differentiates the lithosphere from the asthenosphere.
The difference in strength between rock in the lithosphere and rock in the asthenosphere is a function of temperature and pressure. At a temperature of 1300°C and the pressure reached at a depth of 100 km, rocks of all kinds lose strength and become readily deformable. This is the base of the lithosphere beneath the oceans, or, as it is most colloquially termed, the oceanic lithosphere. The base of the continental lithosphere, by contrast, is about 200 km deep.
Mark Please~ ^.^
