The Structure of the Earth – meaning, types and various groups
The earths’ structure is divided into groups namely:
1.) The External/Outer zone or Structure and
2.) The Internal zone or Structure.
The External /Outer Layer of the Earth.
The outer structure of the earth is made up of the following layers:
1) Atmosphere
2) Hydrosphere &
3) Biosphere
The Atmosphere.
The atmosphere is composed of a mixture of gases which forms an envelope around the earth. The atmosphere contains 78% Nitrogen, 21% oxygen, 0.03% Carbon dioxide and 0.97% inert gases. The atmosphere is of great importance to both man and other living organisms:
a) It provides gases which are essential for respiration.
b) It provides nitrogen for plant.
c) It contains the ozone layer which acts as a protective cover for living organism against the burning effects of ultra violet rays of the sun.
d) It acts as the habitat of some living organisms.
The Hydrosphere.
The hydrosphere refers to the water masses which include rivers, oceans and seas. It is the liquid potion of the earth and it occupies about 70%of the total earth crust. The hydrosphere holds water in both solid and gaseous form. The importance of the hydrosphere to man and other organisms are as follows:
1) It provides for both domestic and industrial uses.
2) It creates employment for the people dwelling in the riverine area.
3) It can also be used to generate electricity.
4) It is used for irrigation scheme.
5) It encourages tourism.
The Biosphere.
The Biosphere is the biological active part of the earth. It consists of plant, animals and microorganisms. This concept can be subdivided into Biocycles namely:
1) Fresh Water Biocycles
2) Salt Water Biocycles
3) Terrestrial Biocycles
Both the fresh water and salt and salt water are under the aquatic Biocycles wheareas with terrestrial Biocycles, it is possible to recognise zones where certain life forms are adapted to environment. Therefore terrestrial biocycle can be divided into the following ‘Biochores’ which are;
1) Forest Biochores
2) Grassland Biochores
3) Desert Biochores
The forest biochore is made up mainly rain and deciduous forest whilst the grassland biochore is made up of Guinea, Sudan and Sahel Savanna. The desert biochores is a bare earth surface.
The importance of the various biochores in the biosphere to man are;
1) They produce plants which provide food for man.
2) They provide sources of energy to man.
3) They aid the balancing and purification of atmospheric gases.
4) They provide raw materials such as timber,hides and skin,cotton etc.
5) They create employment for man – agriculture.
THE INTERNAL STRUCTURE OF THE EARTH
The internal structure of the earth is made up of three concentric layers.
a) The Lithosphere
b) The Mantle or Mesosphere
c) The Core or Barysphere
What is the Lithosphere made up of?
The lithosphere comprises of two parts namely:
• Sial and
• Sima.
The ‘Sial’ has a relative density of 2.7 and consists of granite rock while ‘Sima’ is denser in weight with a relative density of 3.0 and comprises of basaltic rocks.
‘Sial’ is rich in mineral constituent known as silica and Alumina whilst ‘Sima’ is rich in silica and magnesium.
What is the Mesophere or Mantle made of?
The Mesosphere lies beneath the lithosphere. It is a very thick layer rich in a mineral constituent called ‘Olivine’.
What is the Barysphere made up of?
The inner-most layer is known as ‘Core’ which was generally believed to be in liquid state because of the high pressure and temperature in the interior. Barysphere is made up of mineral constituent known as ‘Nickel’.
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