PHYSICAL GEOGRAPHY
TOPIC: – STRUCTURE OF THE EARTH
The earth is a system which composed of two zones. These are
1) Outer zone
2) Inner zone
Thus, the structure of the earth consists of external structure and internal structure.
INTERNAL STRUCTURE / CONCENTRIC ZONE OF THE EARTH
The internal structure of the earth consists of three zones. These are
i) Lithosphere/crust
ii) Mesosphere/Mantle
iii) Barysphere / Core.
LITHOSPHERE / CRUST
Is the outermost and thinnest zone of the earth which found between 8 – 50km or 5 – 30 miles.
– It is largely composed of igneous rocks.
– Other types of rocks also exist as a result of changes on the earth’s surface. When subjected to forces or any stress.
– Igneous rocks are hard and brittle.
– The crust also consist of two layers are sial and sima layers.
THE SIAL LAYER
Is the outer layer of the crust which rich in silica and Aluminium minerals.
– The sial layer consist of granites rocks with density of about 2.65.
– The sial for the basis of the continent.
– The presence of silica and aluminium minerals collectively form SIAL layer.
THE SIMA
– Is the layer which found beneath the sial.
– Is the inner layer of the crust which separated from sial layer by the zone called Conrad discontinuity line.
– The sima layer is composed by silica and magnesium.
– It has the density of about
– It forms the basis of ocean floor.
Note: – Sial and sima layer together forms the crust.
MESOSPHERE / MANTLE
Mesosphere or mantle which found between the crust and core.
– It lies beneath the crust
– It separated from the crust by the zone of separation called Mohorovic discontinuity line has temperature which may reaches to.
– It consist of denser rock to about 3.03 –
– It consist of pale green minerals called Olivine (Ferromagnesium silicate) in form of ultra basic rock
– It consists of lower and upper mantle.
– The upper mantle is rigid and crust to form a large layer called lithosphere.
– The lower mantle is less rigid and forms the moltern layer within the earth’s interior called asthenosphere.
– Asthenosphere is the molten layer layer which responsible for the balancing movement of the earth’s material called isostatic readjustment.
– Asthenosphere has been investigated is found between 100 to 200km below the upper surface.
THE BARYSHERE / CORE
The core is the innermost zone of the internal structure of the earth.
– It has diameter of about 69000km (4300 miles) density of about.
– The core is also classified into two parts i.e. the outer and inner core.
– It separated from the mantle by zone of separation called Gutenberg discontinuity
– The outer core is liquid in nature because of temperature of up to
– The outer core is consist of nickel and Iron (NIFE)
– It estimated to be 2100km
– Its density is about.
– The inner core is solid in nature because of high pressure exerted from different parts toward the center
– It composed mainly by iron
– Its density is about 16 – 17
– It has diameter of about 2600 – 2700km. (1600 – 1700 miles)
– The temperature at the center is about
Note
i) The average density of the whole earth is about 5.17gm/cm3
ii ) The total mass of the earth is about 5.976 x 1021 tons.
EXTERNAL STRUCTURE OF THE EARTH
External structure of the earth consists of four main layers’. These are
- Atmosphere
- Hydrosphere
- Lithosphere / Land mass
- Biosphere
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THE ATMOSPHERE
– Is the thin layer of gases held on the earth by gravitation’ attraction.
– It composed by abiotic (non living matter) and biotic living organism.
– Non living matter found in the atmosphere includes mixture of gases, water vapor and dust particles.
– The living organism include the smallest or microscopic organisms like bacteria
COMPOSITION OF ATMOSPHERE
Atmosphere is the outer zone or external structure of the earth composed by Abiotic and Biotic components.
ABIOTIC COMPONENTS OF ATMOSPHERE.
The abiotic components of the atmosphere include the following.
- Mixture of various gases.
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These include Nitrogen (78%), oxygen (21%), argon (0.009%) and carbon dioxide (0.03%).
– Other gases include neon, helium, Krypton, xenon and other which are present in minite (small proportion) percentage.
- Water vapor.
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Is the colorless and odorless (smell less) gas in the form of water which makes up a perfect mixture with other gases.
– The degree to which water vapor is present in the atmosphere is called humidity.
– Humidity is very important to weather as condensed to form clouds and fog.
– Excess water vapor brings about precipitation in form of rain, hail, snow and sleet.
– Water vapor is capable of absorbing heat which penetrates into the atmosphere in the form of radiant energy from the sun to the earth.
– It is also act as a blanket which prevents the rapid escape of heat from the earth’s surface and therefore maintain heat budget.
- Dust particles.
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The dust particles may exposed to the atmosphere naturally or artificially
– Natural dust particles are those caused by natural phenomena like winds and volcanic eruptions
– Artificial dust particles are those derived from industrial pollutions such as soot and ashes. It includes the particles caused by other man’s activities like construction, mining and farming activities
– The function of dust particles serve as a nuclear or center around which water vapor condenses to produce clouds.
STRUCTURE OF ATMOSPHERE
According to the temperature changes, atmosphere divided into two zones. These are
- Homosphere
- Heterosphere.
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HOMOSPHERE
Homosphere is the layer which found between 0 – 80km above the sea level.
– This is the lowest part of the atmosphere which composed of uniform composition gas of uniform composition of gases and temperature
– Homosphere consist of three layers. These are
i) Troposphere
– This layer extends by 0 – 15km above the sea level.
– Troposphere is the first layer of homosphere located nearest to the earth
– It contains water vapor, gases and dust particles
– It is the layer of atmosphere which support life on the earth due to the presence of plenty oxygen gas.
– All processes of rainfall formation take place in this layer and the temperature decreases as the altitude increases at the rate of per every 100 meters or per every 1000 meters.
Note: – This situation where by temperature decreases as altitude increases is called lapse rate and because it occur near to the ground is called environmental Lapse rate.
⇒The upper limit of Troposphere which separates it to the next later is called Tropopause.
Tropopause makes the upper limit of troposphere to the next layer called stratosphere.
ii) Stratosphere
Stratosphere exists between 15 – 48 km above the sea level.
– This is the second layer of homosphere which lies above the tropopause.
– It is also composed of water vapor, dust particles and various gases
– It is the layer of atmosphere which characterized by high concentration of Ozonic gases. This gases form Ozone layer which found particularly at 20 – 35 km in the stratosphere
– The Ozonosphere or ozone layer is the layer which form a shield or cover that prevent the earth’s surface from destroying by the sun rays.
– It prevents the direct incoming of harmful rays from the sun to fall direct on the earth’s surface.
– The temperature remains unchanged about between 20 – 35 km from the earth’s surface. Then temperature increases with height to about at the upper limit of stratosphere called stratopause.
– The increase in temperature with height is referred to as temperature invasion.
iii) Mesosphere
– This layer extends between 48- 80 kilometers above the sea level.
– Mesosphere is the third part of the homosphere where temperature decreases as the altitude increases.
– It separated from the stratosphere by the zone of separation called stratopause.
– The upper limit of mesosphere is called mesopause.
– Mesopause record minimum temperature of this zone that may fall to making this zone to be coldest.
– It is at this zone where strong upper air streams of wind like jet streams are experienced.
HETEROSPHERE
– Is the second layer of atmosphere which extends from 80km towards the interplanetary space
– Heterosphere divided into two layers which include.
- Thermosphere
- Exosphere
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THERMOSPHERE
– Is the lower part of heterosphere where temperature increases as the altitude increases from – i.e. temperature invasion. This is because; there is no water vapor or dust particle in this zone.
EXOSPHERE
– Is the part of heterosphere which found above the thermosphere.
– It has high temperature through it has little significance as it has not been greatly researched.
Note: – Within the heterosphere, there is also a scientific significant layer called ionosphere.
– Ionosphere consists of some ions which influence radio waves. This is because, ionosphere is electrically charged with free electrons that allow the passage of radio waves, television waves and telephone or mobile phone waves.
THE HYDROSPHERE
– Is the layer of water bodies of the earth including all oceans, rivers, precipitation and underground water.
– It is estimated that 75% of the Earth’s surface is covered by water bodies.
THE LITHOSPHERE / LAND MASS
– Is the whole solid body of the earth with various landforms such as mountains, valleys and plateaus.
– The lithosphere is also known as the crust.
– It includes all land masses. The major land mass is called continent and the minor land mass is called islands.
THE BIOSPHERE
– Biosphere is the complex zone which comprises all living things.
– It includes a lower level of atmosphere and the upper level of lithosphere and hydrosphere.
– Biosphere receives substantial supply of energy from the sun which gives it condition necessary for life and does not occur in any part of the solar system.
– The living organisms that inhibit biosphere interact with each other and their environment.
– The sum of all these interaction components is called the ecological system or ecosystem.
– Biosphere comprises all living organism both macro and micro organisms living in water bodies, soils and on air.
FUNCTION OF ATMOSPHERE
1) Insulation
Atmosphere is an insulator it acts as a shield or blanket and therefore regulates temperature during the night and during the winter.
2) Filtration. The atmosphere is the filter. It filters solar insulation and percent ultra violet rays of certain length due to the presence of ozone layer in the stratosphere.
3) Scientific function. Atmosphere is the scientific field
– It is the field through which the scientific experiments and observation carried out. Example ionosphere layer of atmosphere reflects some electromagnetic waves and ration signals back to the earth.
4) It supports much on hydrological cycle.
The surface water, evaporation, condensation and precipitation formation take place in the atmosphere.
5) It support life some gases particularly oxygen is important for living organisms
– Air has weight which contributes to the occurrence of atmospheric pressure variations without which breathing would be impossible.
– Wind movement and direction that balances temperature, humidity and precipitation also result from pressure variations.