MORE DETAILS ABOUT THE OUTER AND INTERNAL STRUCTURE OF THE EARTH
PHYSICAL GEOGRAPHY

MORE DETAILS ABOUT THE OUTER AND INTERNAL STRUCTURE OF THE EARTH

The structure of the earth is grouped into two zones. These are 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. These zones or layers are:

  1. Lithosphere.
  2. Hydrosphere.
  3. Atmosphere.
  4. Biosphere.

 

  1. LITHOSPHERE (CHARACTERISTICS)
  • The lithosphere is the solid portion of the earth.
  • It is the outermost layer or zone of the earth crust.
  • It is made up of rocks and mineral materials.
  • It represents 30% of the earth surface.
  • It forms the land mass which is about 10-50km thick.
  • The outermost layer of the land mass is made up of loose materials like gravel, sand and soils.

 

IMPORTANCE OF LITHOSPHERE TO MAN

  • Lithosphere forms the basis of all human settlement.
  • All mineral resources are derived from lithosphere.
  • It aids transportation through construction of roads, railways, airport, etc.
  • All farming activities are carried out on lithosphere.
  • Most human activities like mining, trading, etc. are carried out on lithosphere.

 

  1. HYDROSPHERE (CHARACTERISTICS)
  • The hydrosphere is the liquid portion of the earth.
  • It covers about 70% or 2/3 of the earth’s crust.
  • It holds water in various forms. Solid e.g. ice, liquid like water and as gases e.g. water vapour.
  • It includes all forms of fresh water like lakes, rivers, water vapour.
  • It also includes ocean water which is salty.
  • Ocean water accounts for about 97% of the hydrosphere.

 

IMPORTANCE OF HYDROSPHERE TO MAN

  • Hydrosphere provides water for domestic uses e.g. washing, drinking, cooking, etc.
  • It provides a medium of transportation.
  • It also provides water for industrial uses.
  • It provides food in form of fish, prawns, etc. to man.
  • It provides employment e.g. fishermen.
  • It’s a medium for sport e.g. swimming, diving, etc.
  • It can also be used to generate electricity e.g. hydro-electric power.
  • It is used in agriculture in form of rain or irrigation.
  • It is also serves as tourist centres e.g .rivers and beaches.

 

  1. ATMOSPHERE (CHARACTERISTICS)
  • The atmosphere is the gaseous portion of the earth.
  • It is a layer of gases surrounding the earth.
  • Over 99% lies within 30km of the earth surface.
  • Its density decreases progressively with elevation.
  • It contains water in form of vapour in lower layers.
  • Weather phenomenon – cloud, rain and snow are largely confined in the atmosphere.
  • It contains 78% Nitrogen, 21% Oxygen, 0.03% Carbon dioxide and 0.97% rare or inert gases.

 

IMPORTANCE OF ATMOSPHERE TO MAN

  • The atmosphere is the habitat of some living organisms.
  • It provides oxygen for animals and plants for respiration.
  • It provides carbon dioxide for photosynthesis by plants.
  • It provides oxygen for the combustion or burning.
  • It provides nitrogen for plants (protein synthesis).
  • It acts as green house.
  • Atmosphere is a medium of communication e.g. air routes.
  • It contains ozone layer which acts as protective cover for living organisms against the burning effects of ultraviolet rays of the sun.

 

  1. BIOSPHERE (CHARACTERISTICS)
  • The biosphere is the zone of the earth occupied by living organisms.
  • It is a layer of life which exists on earth surface and the lithosphere.
  • It has a maximum thickness of only a few kilometres.
  • It is a narrow zone where complex biological and chemical activities occur.
  • It includes organisms like plants, animals and micro-organisms.

 

IMPORTANCE OF BIOSPHERE TO MAN

  • Plants in the biosphere provide food for man.
  • It also provides a source of energy like firewood for man.
  • Plants also provide clothing materials like cotton and wool for man.
  • It provides shelter in form of timber for man.
  • It provides raw materials like timber, hides and skin, cotton for industries.
  • Activities within the biosphere provide employment for man.
  • It aids the balancing and purification of atmospheric gases e.g. carbon dioxide during respiration and oxygen, during photosynthesis.

 

  • THE INTERNAL STRUCTURE OF THE EARTH

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

  • Crust (Lithosphere).
  • Mantle (Mesosphere).
  • Core (Barysphere).

 

  1. THE CRUST OR LITHOSPHERE (CHARACTERISTICS)

The crust is sub-divided into upper and lower parts.

  • The upper part of the earth crust consists of granite rocks and forms the continent. The main minerals here are silica and aluminium, collectively referred to as The upper earth crust has average density of 27.
  • 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. The lower crust has a density of 3.0. The sial, therefore, is lighter than the sima. The sial and sima are 5-6km below the ocean and 48km below the surface of the continent. The lithosphere lies above the mantle. It forms the soil and sustains life.

 

  1. THE MANTLE OR MESOSPHERE (CHARACTERISTICS)
  • The mantle is found just beneath the crust.
  • It is about 2897km thick.
  • It is very dense.
  • Its main mineral is olivine.
  • It is plastic and semi-liquid form.
  • Has average density of about 3.3.
  • It is a middle layer which surrounds the core.

 

  1. THE CORE OR BARYSHERE (CHARACTERISTICS)
  • The core is the innermost part of the earth.
  • It is about 3476km in radius or width all round.
  • 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 (3500*F).
  • The core is also subjected to constant temperature and pressure.
  • It is in molten state.

The correct arrangement of the layers of the earth crust from the surface to the interior is sial, sima, mantle and core.

 

INTERACTIONS WITHIN AND BETWEEN THE FOUR ZONES

  1. Within the Lithosphere
  • The rocks wither to form the soil.
  • The rocks also change to minerals like coal, petroleum, gold, etc.

 

  1. Within the Hydrosphere
  • Water from seas and oceans evaporates to form clouds and rainfall.
  • Water from rivers, streams and rainfall combine to form the water in seas and oceans.

 

  1. Within the Atmosphere
  • Water vapour combines to form cloud and rain.
  • Oxygen is taken in by plants and animals to release carbon dioxide.
  • Carbon dioxide is taken in by plants to release oxygen.

 

  1. Within the Biosphere
  • Animals depend on plants for their food.
  • The decomposition of animals provides manure for plants.
  • Micro-organisms in the soil promote plants growth.
  • Animals provide carbon dioxide for plants during respiration.
  • Plants provide oxygen for animals during photosynthesis.

 

INTERACTIONS BETWEEN THE FOUR ZONES

  • Plants and animals can be found in lithosphere, atmosphere and hydrosphere.
  • Plants in biosphere derive their nutrients from the soil (lithosphere).
  • Most human activities are mainly carried out on lithosphere.
  • Gases like oxygen and carbon dioxide are made constant in the atmosphere through respiration and photosynthesis.
  • Sunlight from the atmosphere is required by plants to carry out photosynthesis.
  • Atmosphere contains water vapour from the hydrosphere.
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