Structure of Earth
The interior structure of the Earth is layered in spherical shells, like an onion. Earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core.
The structure of mechanically can be divided into
- mesospheric mantle
- outer core
- inner core
The interior of Earth is divided into 5 important layers. Chemically, Earth can be divided into
- upper mantle
- lower mantle
- outer core
- Inner core
|0–60||0–37||Lithosphere (locally varies between 5 and 200 km)|
|0–35||0–22||… Crust (locally varies between 5 and 70 km)|
|35–60||22–37||… Uppermost part of mantle|
|100–200||210-270||… Upper mesosphere (upper mantle)|
|660–2,890||410–1,790||… Lower mesosphere (lower mantle)|
The average density of Earth is 5,515 kg/m3. Since the average density of surface material is only around 3,000 kg/m3, we must conclude that denser materials exist within Earth’s core. Seismic measurements show that the core is divided into two parts, a “solid” inner core with a radius of ~1,220 km and a liquid outer core extending beyond it to a radius of ~3,400 km.
The inner core is generally believed to be composed primarily of iron and some nickel. It is not necessarily a solid, but, because it is able to deflect seismic waves, it must behave as a solid in some fashion.
The liquid outer core surrounds the inner core and is believed to be composed of iron mixed with nickel and trace amounts of lighter elements.
Earth’s mantle extends to a depth of 2,890 km, making it the thickest layer of Earth. The upper mantle is divided into the lithospheric mantle and the asthenosphere. The upper and lower mantle are separated by the transition zone. The lowest part of the mantle next to the core-mantle boundary is known as the D″ layer. The mantle is composed of silicate rocks that are rich in iron and magnesium relative to the overlying crust
The crust ranges from 5–70 km in depth and is the outermost layer. The thin parts are the oceanic crust, which underlie the ocean basins (5–10 km) and are composed of dense (mafic) iron magnesium silicate igneous rocks, like basalt. The thicker crust is continental crust, which is less dense and composed of (felsic) sodiumpotassium aluminium silicate rocks, like granite.