TOPIC: STRUCTURE OF THE EARTH

The structure of the earth is grouped into two zones: The outer structure and the internal structure.

THE OUTER STRUCTURE OF THE EARTH

The outer structure of the earth is made up of four zones or layers:

(i) Lithosphere

(ii) Hydrosphere

(iii) Atmosphere

(iv) Biosphere

(A) Lithosphere: This is the solid portion of the earth. It is the outermost zone of the earth which is made up of rocks and mineral materials. It represents 30% of the earth surface.

Importance:

(a) It forms the basis for all human settlement.

(b) All mineral resources are derived here.

(c) It aids transportation through construction of roads, railways, airports, etc.

(d) It aids farming activities.

(e) Most human activities like mining, trading, etc are done here.

(B) Hydrosphere: This refers to the liquid portion of the earth. It includes the oceans, seas, rivers, streams and springs, lakes, etc. It covers 70% of the earth’s crust.

Importance:

(a) Provides water for domestic uses.

(b) Provides medium for transportation.

(c) Provides water for industrial uses.

(d) Provision of food (fishes, prawns, etc).

(e) Provision of employment.

(f) Serves as tourist centre.

(g) Generation of hydro-electric power (HEP).

(C) Atmosphere: This is the gaseous portion of the earth. It contains 78% nitrogen, 21% oxygen, 0.03% carbon dioxide and 0.097% rare gases.

Importance:

(a) It is the habitat of some living organisms.

(b) It provides oxygen for respiration.

(c) It provides carbon dioxide for photosynthesis.

(d) It provides oxygen for combustion.

(e) It provides medium of transportation.

(f) It provides nitrogen for protein synthesis in plants.

(D) Biosphere: This is the zone of the earth where living things are found.

Importance:

(a) Plants provide food for man.

(b) Provision of employment.

(c) Provision of raw materials.

(d) Balancing and purification of the atmosphere.

INTERNAL STRUCTURE OF THE EARTH

The internal structure of the earth is made up of three concentric layers which are:

(a) The crust (Lithosphere)

(b) The mantle (Mesosphere)

(c) The core (Barysphere)

The Crust: This is subdivided into upper and lower crust. The upper crust consists of granite rocks and forms the continent. The main minerals here are silica and aluminium, collectively referred to as SIAL. It has an average density of 2.7.

The lower part of the earth crust consists of basalt rocks and forms the ocean floor. It contains minerals like silica, iron and magnesium, collectively referred to as SIMA. It has an average density of 3.0.

The Mantle: This zone is found just beneath the crust. It is about 2900km thick with a density of 3.3. Its main mineral is olivine. It is plastic and in semi-liquid form.

The Core: This is the innermost part of the earth. It is about 3500km in radius. It contains two minerals, iron and nickel, collectively referred to as NIFE. The temperature of the core is estimated to be as high as 2000°C. It is in molten state.

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STRUCTURE OF THE EARTH