There are 2 types of sources to study Earth’s interior- Direct and Indirect.
Most of our knowledge about the interior of the earth is largely based on estimates and inferences. Yet, a part of the information is obtained through direct observations and analysis of materials.
Volcanic eruption forms another source of obtaining direct information. As and when the molten material (magma) is thrown onto the surface of the earth, during volcanic eruption it becomes available for laboratory analysis.
Gravitation is an indirect source. The gravitation force (g) is not the same at different latitudes on the surface. It is greater near the poles and less at the equator. This is because of the distance from the center at the equator being greater than that at the poles. The gravity values also differ according to the mass of material. Gravity anomalies give us information about the distribution of mass of the material in the crust of the earth.
Seismic activity is one of the most important sources of information about the interior of the earth. The study of seismic waves provides a complete picture of the layered interior.
Mining activity is both a direct as well as an indirect source for Earth’s interior. The most easily available solid earth material is surface rock or the rocks we get from mining areas. Besides mining, scientists have taken up a number of projects like “Deep Ocean Drilling Project” and “Integrated Ocean Drilling Project”. These have provided large volume of information through the analysis of materials collected at different depths.
Mining is also an indirect source as we can analyze the properties of matter at different depths. We know through the mining activity that temperature and pressure increase with the increasing distance from the surface towards the interior in deeper depths. Moreover, it is also known that the density of the material also increases with depth.
Other important indirect sources are meteorsand magnetic field.
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