2.1. Direct Sources

Our knowledge about the structure and interior of the earth from direct observation is very limited. No instrument has been invented so far which can see through the interior of the earth directly. The deepest depth of an oil well drilled so far is 8 kilometers. The deepest mine of the world is Robinson Deep in South Africa. Its depth is less than 4 kilometer.

Besides mining, scientists have taken up a number of projects to penetrate deeper depths to explore the conditions in the crustal portions. Scientists world over are working on two major projects such as “Deep Ocean Drilling Project” and “Integrated Ocean Drilling Project”. The deepest drill at Kola, in Arctic Ocean, has so far reached a depth of 12 km. This and many deep drilling projects have provided large volume of information through the analysis of materials collected at different depths.

Volcanoes are yet another major source of direct information – they tell us about the composition and characteristics of the materials found inside the Earth. However, it is difficult to ascertain the depth of the source of such material.