As civil engineer, we built everything on the surface of earth. So it is important to know the structure of earth.
Our planet earth was formed some 4500 million years ago. During this time period it has gone through many changes. Previously it was a ball of molten mass and gradually as the time elapsed, the surface of the earth became solid.
The radius of earth is 6470 km. As shown in the figure, earth consists of following 3 regions.
- Crust
- Mantle
- Core
1. Crust
Crust is the upper most part of the earth. The thickness of earth crust is not same in every area. It may be as much as 40 km thick in continental areas and as little as 7 km thick in oceanic areas. Civil engineers are interested in only about 20 to 30 m of depth of earth crust. The solid part of the earth crust is called rock by engineer. The remaing loose part are called soils, gravel etc.
2. Mantle
The mantle consists of two parts
- Outer mantle
- Inner mantle
Outer mantle is in semi solid state. The thickness of outer mantle is 850 km. Inner mantle is in plastic state. The thickness of inner mantle is 2000 km.
3. Core
Core is the inner most part of the earth. Core of the earth consist of heavy metals, mostly iron of mass density 8 g/cm3. Core consists of two parts,
- Outer core
- Inner core
Outer core is in liquid state and its thickness is 2100 km. inner core is in solid state and its thickness is 1470 km.