The knowledge about the interior of earth is very limited. The sources of information regarding the earth’s interior can be classified into two parts. These are direct sources and, indirect sources. Among the direct sources, the important ones are volcanic eruption and, mining areas and drilling projects.
Among the indirect sources, the important ones are seismic activity and, gravity force.
Magma, which comes out during volcanic eruption is used in laboratory for research and analysis.
Mining areas and drilling projects provide information through the analysis of materials collected at different depths.
Gravity force gives information about the distribution of mass of the material in the earth’s crust.
Seismic waves are the most important source regarding information about the interior of the earth.
The two types of earthquake waves are surface waves, which travel only on the surface of the earth, and, body waves, which travel deep beneath the earth.
The earth’s surface is primarily composed of rocks, metal and water. The surface of the earth is solid and the temperature inside the earth increases with its depth.
The three layers of earth are crust, mantle and, core. Crust is the outermost layer of earth. The crust consists mainly of silicon, aluminum, and magnesium. Earth’s crust is divided into two parts – oceanic crust, which is also known as Sima, and continental crust, which is also known as Sial. Mantle is the middle shell, which lies below the crust. It is rich in magnesium and silicon. Mantle can be divided into the inner mantle and the outer mantle. Outer mantle is made up of rocks. Inner mantle consists of sulphides and oxides of silicon and magnesium. Core is the innermost layer of earth. It consists of two parts – inner core, which contains solid nickel and iron and, outer core, which contains liquid nickel and iron.
The Mohorovicic Discontinuity, or "Moho," is the transition zone between earth's crust and the uppermost section of the mantle. Gutenberg Discontinuity is the boundary between the core and the mantle. Earth functions as a magnet. Without magnetic field, the surface will not be protected from solar radiation and life will not exist on earth.