Here under Structure of the Earth, you will find reference information about the interior of the earth.
The detailed study of the interior of the earth is generally undertaken by geologists and specialists in Earth Science. But we need its elementary knowledge in geography because this understanding is essential to follow the nature of changes going on the earth's surface. The uplift of great mountains, the subsidence of parts of the crust, its expanding or contracting, are related to deep-laid internal forces operating from within the earth.
Evidences about Earth's Interior. Exploring the earth beneath our feet is a more difficult task than mapping the moon. A scientist can look far into space but such is not possible in the case of earth's interior.
Only the upper part of the earth's crust, just below its surface, could be known more or less by direct observations. The lower part is beyond the reach of direct observations and our knowledge about it is based upon indirect scientific evidences. These indirect sources are temperature and pressure inside the earth, density of its different shells, behavior of earthquake waves and evidence from meteorites. Still uncertainties persist about the actual state of matter in the innermost zone around earth's core. The different scientific observers also do not agree on a precisely uniform thickness and classification of the layers of earth's interior.
By using a seismograph, a graphic recording of the earthquake waves or vibrations is made, and scientists are able to get sonic idea of the kind of rocks, which are found below the earth's surface. There is a change in the course and velocity of the waves on crossing the boundaries of different zones inside the earth. If the ground through which the waves travel is solid, they behave in one way. If it is liquid, the waves behave in a different way. Their velocity in both the cases differs. There are three types of waves known as or longitudinal or primary waves. 'S' or transversal or secondary and the long L or surface waves, which are recorded by a seismograph. the velocity of the first two types of waves increases with depth but only up to 2,900 kilometers. Afterwards, 'S' waves passing across the direction of their movement do not pass and the 'P' waves traveling in the direction of their movement generally pass at a reduced velocity. The long 'L' waves do not pass and do not go deeper in the earth. The 'S' waves cannot pass through a liquid and are transmitted only through a rigid or a solid body. The velocity of the 'P' waves passing through inner core again increases as compared to their passage through the outer core. This data briefly point out that the inner core of the earth is of solid iron and the outer core has probably the properties of a liquid. The meteorites belonging to our solar family are another source of our information for a better understanding of the earth's structure. Their outer layer is burnt during their fall to the earth. As the stony materials of meteorites are similar to those found on the earth's surface, these are scarcely recognized. But the composition of the meteorites consisting of heaviest materials confirms the similar composition of inner core of the earth.
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