Interior of the earth, Temperature of earth, Density of earth, Pressure of earth, Gravitational force and Magnetic Surveys, Meteorites, Moon, Earthquake waves
As we know Human life is largely influenced by the physiography of the region. Therefore, it is necessary that one gets acquainted with the forces that influence landscape development. Also to understand by the earth shakes or how a Tsunami wave is generated, it is necessity that we know important details of the Earth’s Interior.
What is the Sources of Information About Earth
Most of the information about the interior of earth is based on interference drawn from different sources with direct and indirect.
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 Kilometer. 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. Scientist world over are working on to 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 sources of direct information that 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.
2. Indirect Sources
The centre of the earth downward is 6,371 kilometers away from the surface of Earth. In comparison to this distance the depth of a deep well or a mine is insignificant. It is therefore, necessary to take help of indirect scientific evidences to know about the interior of the earth. These sources in two temperature, pressure and density of earth, behaviour of seismic waves meteors, the moon etc.
These sources maybe classified into three groups-
(a) Artificial sources such as temperature, pressure and density.
(b) Evidences from the theories of origin of earth.
(c) Natural Sources example: volcanic eruption, earthquakes, meteors and seismology.
Temperature Of Earth
Temperature goes on increasing with the increase in depth inside the Earth. This is clearly proved while going down in mine or deep wells. The volcanic eruptions or hot water is springs also confirm this fact that temperature increasing towards the interior of the earth. On an average there is a rise of 1 degree Celsius temperature for every 32 meters of depth. This rapid increase in temperature continues to great depth there after the temperature increases slowly.
The main reason for the increase in the heat and temperature in the interior of the earth are the following:
1. Radioactive disintegration within rocks which liberates heat
2. Internal and external forces
3. Chemical reactions
It is tempting to think that under the conditions of this enormous temperature in the interior of the earth nothing can be found in solid state. Under such conditions all existing rocks should be either in liquid or gaseous state. But it is not so. Along with the increase in temperature with depth, pressure too increase in the interior of the earth. The pressure is lacs of times more than the pressure exercise by atmospheric layers on the surface of the water in oceans.
For this reason due to enormous pressure, liquid state rocks of the core have the properties of solids. It is possible that these rocks might be in plastic state. It is why these rocks have elasticity. Due to the pressure of over lying layers on the Earth’s interior these rocks do look solid up to 2,900 km depth. Sometimes due to lessening of over lying pressure, the rocks in the interior meltdown and the fluids comes to the surface or is in the process of finding its way to the surface of the Earth. A volcanic eruption is one such example.
Density of Earth
In accordance with the Newton’s laws of gravity the Earth’s density has been calculated to be 5.5 gms per cubic centimetre. However it is surprising that the rocks near the surface of the earth have an average density of 2.7 only. This density is less than half the average density of the earth as a whole. From this it is clear that the density too increases with the increase in depth. The earth’s internal part is compose of very dance rocks, their density must be in the range of 8 to 10. The density of the central part of the core is still more. Higher density could be due to heavy metals like Nickel and Iron at the centre as well as due to pressure and overlying layers.
Pressure of Earth
Just like density and temperature and pressure too increase with increase in depth inside the earth. Some Earth scientists believe that due to the weight of the overlying layers the pressure goes on increasing with depth and others think that materials of the interior of the earth are heavier since birth of the earth. Thee happenings due to change in pressure inside the earth affect the physical features on the surface of the earth.
Gravitation force on Earth
The gravitation force 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 centre at the equator being the greater than that at the poles. The gravity values also differ according to the mass of material. The uneven distribution of mass of material within the earth influences this value. The reading of the gravity at different places is influence by many other factors. These readings differ from the expected values. Such a difference is called gravity anomaly. Gravity anomalies give us information about the distribution of mass of the material in the crust of the earth. Gravity anomalies also inform us about the distribution of molten material In the crust of the earth.
Magnetic Surveys of Earth
The earth also acts like a huge magnet. The rapid spinning of earth creates electric currents in its centre that creates a magnetic field around the earth. The magnetic field is strongest at the magnetic north and south poles. The magnetic north and south poles do not coincide with geographic north and south poles. In fact the earth’s magnetic field keeps on changing magnetic service provide information about the distribution of magnetic materials in the crustal portion and thus provide information about the distribution of materials in this part.
Meteorites on Earth
The space debris, while entering the atmospheric layers of earth get burn due to the friction of air. Only the heavier objects whose outer layers have been burnt fall to the earth. Man has discovered many such meteorites and after examining them obtained evidences about the interior of the earth. Thee meteorites which have been examine are of two types ,(i) Rock and (ii) Metals . The metallic meteorites chiefly contain heavy materials like Iron and Nickel. The meteorites too have originated during the formation of solar system.It is therefore very much in order to believe both the meteorites and earth are of similar materials.
The Moon and Earth
The first information about the earth’s interior had been obtain through the study of the Moon. There are several ways of determining the moon’s orbit around earth. Among these one of the important factors is earth’s mass. Remember, their is closed relationship between the mass and Earth’s gravitation. The movements of the moon and its distance from earth provide the basis for determining the mass of the earth by earth scientists.
Evidence from Theories
The earth was mostly in a volatile state during its primordial stage. Due to gradual increase in density the temperature inside has increased. As a result the material inside started getting separated depending on the densities. This allowed heavier materials to sink towards the centre of the earth and the lighter once to move towards the surface. With passage of time it cooled further and solidified and condensed into a smaller size.
This later lead to the development of the outer surface in the form of a crust. During the formation of the moon, due to the giant impact the earth was further heat up. It is through the process of differentiation that the earth forming material got separate into different layers. Starting from the surface to the central parts. We have layers like the crust, mental outer core and inner core. From the crust to the core the density of material increases.
Earthquakes are cause by the movements in the interior of the earth. Movements cause waves inside the earth just as waves are generate on the surface of water in a lake when a stone is throw into it. Incidently majority of the earthquakes originate in the upper mantle. The earthquake waves are measure on the seismograph. The study of earthquake waves helps earth scientists to get a lot of information about the types of rocks and layered composition in the interior of the earth.
Earthquake waves are basically of two types- body waves and surface waves. Body waves are generate due to the release of energy at the focus and move in all directions travelling through the body of the earth. Hence, the name body waves. The body waves interact with the surface rocks and generate new set of waves called surface waves. These waves move along the surface. The velocity of waves changes as they travel through materials with different densities. The denser the material, the higher is the velocity. Their direction also changes as they reflect or refract when coming across materials with different densities.