NCERT Book Class 11 Geography (Fundamental of Physical Geography) Chapter 3 Interior of the Earth

18 FUNDAMENTALS OF PHYSICAL GEOGRAPHY

CHAPTER

INTERIOR OF THE EARTH

W
hat do you imagine about the nature SOURCES OF INFORMATION ABOUT THE INTERIOR
of the earth? Do you imagine it to be The earth’s radius is about 6,378 km. No one
a solid ball like cricket ball or a can reach the centre of the earth and make
hollow ball with a thick cover of rocks i.e. observations or collect samples of the material.
lithosphere? Have you ever seen photographs Under such conditions, you may wonder how
or images of a volcanic eruption on the scientists tell us about the earth’s interior and
television screen? Can you recollect the the type of materials that exist at such depths.
emergence of hot molten lava, dust, smoke, fire Most of our knowledge about the interior of
and magma flowing out of the volcanic crater? the earth is largely based on estimates and
The interior of the earth can be understood only inferences. Yet, a part of the information is
obtained through direct observations and
by indirect evidences as neither any one has nor
analysis of materials.
any one can reach the interior of the earth.
The configuration of the surface of the earth Direct Sources
is largely a product of the processes operating The most easily available solid earth material
in the interior of the earth. Exogenic as well as is surface rock or the rocks we get from mining
endogenic processes are constantly shaping areas. Gold mines in South Africa are as deep
the landscape. A proper understanding of the as 3 - 4 km. Going beyond this depth is not
physiographic character of a region remains possible as it is very hot at this depth. Besides
mining, scientists have taken up a number of
incomplete if the effects of endogenic processes
projects to penetrate deeper depths to explore
are ignored. Human life is largely influenced
the conditions in the crustal portions. Scientists
by the physiography of the region. Therefore, world over are working on two major projects
it is necessary that one gets acquainted with such as “Deep Ocean Drilling Project” and
the forces that influence landscape “Integrated Ocean Drilling Project”. The
development. To understand why the earth deepest drill at Kola, in Arctic Ocean, has so
shakes or how a tsunami wave is generated, it far reached a depth of 12 km. This and many
is necessary that we know certain details of the deep drilling projects have provided large
interior of the earth. In the previous chapter, volume of information through the analysis of
you have noted that the earth-forming materials collected at different depths.
materials have been distributed in the form of Volcanic eruption forms another source of
obtaining direct information. As and when the
layers from the crust to the core. It is interesting
molten material (magma) is thrown onto the
to know how scientists have gathered
surface of the earth, during volcanic eruption
information about these layers and what are it becomes available for laboratory analysis.
the characteristics of each of these layers. This However, it is difficult to ascertain the depth of
is exactly what this chapter deals with. the source of such magma.