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Our idea of the structure of the interior of the Earth is much lower. This is because it is not possible to predict from above what is in the earth's interior with a circumference of 7400 km, what is its condition, what is formed by matter, its depth or how much and it is not possible for human beings to collect information artificially to a great depth. Geologists have been able to collect data up to a depth of only a few kilometers above the surface of the earth by direct observation.
The sources from which the idea of the interior of the earth is derived are mainly divided into two parts. Namely - indirect source and indirect source
Indirect sources are those from which we cannot directly gather information about the interior of the earth, but the analysis of those sources helps us to understand the structure of the interior. Such as meteors or cosmic objects, the gravitational force of the earth, the magnetism of the earth and seismic waves.
Direct Sources - The sources from which we get an idea of the interior of the earth directly are called direct sources. Such as - surface rock, mineral extraction, deep ocean excavation and eruption.
However, among the direct sources, from mineral extraction and deep ocean mining, we can know very little about the depth of the interior of the earth. For example, the deepest mining area in the world extends to a depth of only 5 km. Ocean Drilling has been able to dig up to a maximum of 12 km.
What we now know about the interior of the Earth is largely due to the analysis of the kinetic nature of the indirect source seismic waves. There are two main types of seismic waves that change their speed and direction according to the nature and density of matter inside the earth, such as - P wave and S wave . Although P waves and S waves are created simultaneously, P waves are caught on seismographs much later than S waves, mainly because seismic waves change their velocity as they flow through solid and liquid media. For example, the P wave can be detected in seismographs long ago because it can flow through all media, but the S wave can be detected in seismographs much later because it cannot flow through liquid and gaseous media.
Therefore, an analysis of the kinetic nature of these seismic waves around the world gives a thorough idea of the structure of the earth's interior. Based on the kinetic nature of these seismic waves, the interior of the earth is divided into three main layers , namely , crust, gurumandala and kendramandala .
The inner layers of the earth are discussed in detail .
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