THE EARTH’S STRUCTURE

WEEK 8                                                                                

DATE………………

SUBJECT: GEOGRAPHY

CLASS: SS 1   

TOPIC: THE EARTH’S STRUCTURE

CONTENT:

             I. Outer Structure of the earth

(a) Major Spheres of the Earth:

(i) The Atmosphere

(ii) The Lithosphere (iii) The Hydrosphere (iv) The Biosphere. (b) Relationship between the three major spheres

(atmosphere, lithosphere and hydrosphere) (c) Relevance to Human activities. 

             II. Inner Structure of the earth –

(i) The Crust – SIAL and SIMA, Mohorovisic-discontinuity (ii) The Mantle (iii) The Core.

SUB-TOPIC 1: THE STRUCTURE OF THE EARTH

The structure of the earth is grouped into the outer structure and the internal structure of the earth. The outer structures of the earth consist of four zones or layers. Three are made up of physical constituents, which consist of the three different states of matter; which are solid, liquid and gaseous substances. While the fourth which is made up of the Biological constituents, consist of living organisms.

These outer structures of the earth includes: –

i. The Atmosphere, ii. The Hydrosphere, iii. The Lithosphere and iv. The Biosphere.

The Atmosphere: –

This is the gaseous envelope or layer surrounding the earth. It extends from the earth’s surface upwards to about 600km above the surface of the earth. The atmosphere is made up of different gases in varying proportions and it is held to the earth by the gravitational force of the earth. The atmosphere protects life on earth from the harmful ultraviolet rays of the sun, which causes skin cancer. The atmosphere also regulates temperature on earth, as it absorbs most of the heat radiated from the earth’s surface and thus making the earth a hospitable place for human beings and other living organisms.

The Hydrosphere: –

This is the watery layer of the earth and it covers about 71% of the earth’s surface. It is made up of all the water bodies on earth such as; oceans, seas, lakes, rivers, streams etc. and also the water vapour in the air. The water in the hydrosphere is in constant motion due to the forces of evaporation, condensation, precipitation and transpiration. The water cycle or hydrological cycle is the continuous process by which water is evaporated from the surface of the earth, condenses as rain or snow in the atmosphere and falls back to the surface of the earth.

The External and Internal Structure of the Earth

THE ATMOSPHERE: The atmosphere is the portion of the earth that consists of gases. These mixtures of various gases and other matter, forms and envelops round the earth. The atmosphere is loosely called “Air”, around us but in the real fact the atmosphere contain more than just air. The pure air in it, is made up of the following gases:

Nitrogen ——– ———————–78%

Oxygen ——————————— 21%

Argon and Neon (rare gases——- 0.93%

Carbon dioxide ———————-0.03%

The atmosphere also contains water vapour and dust particles. The atmosphere also is made up of four layers which include:

1. the troposphere,
2. ii. the stratosphere,
3.  iii. the mesosphere and
4. iv. The thermosphere.

The troposphere is the lowest and nearest to the earth, while the thermosphere, otherwise known as the ionosphere is the uppermost part of the earth.

EVALUATION

1. Mention the three physical constituents of the outer structure of the earth.
2. Describe the atmosphere.
3. Outline the different atmospheric gases and their percentage.
4. List the different layers of the atmosphere, indicating the nearest and the uppermost layers to the earth.
5. What is meant by air?
6. The Lithosphere: –
7. This is the solid outer layer of the earth and it consists of the crust and the uppermost part of the mantle. The lithosphere is broken into several large and small pieces called plates. These plates move on the molten mantle below and they interact with each

THE LITHOSPHERE: The lithosphere or the crust is the outer solid part of the earth. The lithosphere comprises of two distinct parts; the upper part consists of granite rocks and forms the continents comprising of the landmasses, which is marked by irregular surface features known as landforms, e.g. mountains, plateau, hills, plains, etc.; its main mineral compositions are Silica and Alumina, collectively referred to as SIAL.

The lower part is a continuous zone of thicker rocks forming the ocean floor, comprising of silica, iron and magnesium collectively called the SIMA. 

THE HYDROSPHERE: The hydrosphere is the liquid components of the earth where there is water. It consists of oceans, sea, river, lake, streams and other forms of water bodies. The water bodies consist of 71% of the earth surface. The ocean and the sea make up 97% of them. To these water bodies, the water locked up in frozen ice sheet and glaciers, underground water and water vapour forms part of the total water bodies.

THE BIOSPHERE: The biosphere is the world of living organisms, which includes Man, plants, animals and micro-organisms like bacteria and fungi. These organisms dwell on Lithosphere (land), Hydrosphere (water) and Atmosphere (air) around us. They obtain their energy from the sun convert it into use, interact and depend on one another for existence.

EVALUATION:

1. State the two distinct parts of the lithosphere and describe their mineral compositions.
2. Describe the term hydrosphere.
3. Why is the biosphere a unique sphere?

SUB-TOPIC 2: THE RELATIONSHIP BETWEEN THE THREE MAJOR SPHERES AND ITS RELEVANCE TO HUMAN ACTIVITIES

The lithosphere is made up of the rock materials; the atmosphere consists of the gases that envelop the earth; the hydrosphere consists of the liquid substances-that is all the natural bodies of water on the outer earth. The intersect of these three (Atmosphere, Lithosphere and Hydrosphere) gives rise to the sphere of life (Biosphere). See Diagram bellow

The Relationship between the major spheres of the Earth

The lithosphere which is the solid part of the earth is where all living organisms including man lives and survive; though not without the support of the other two spheres (Hydrosphere and Atmosphere).

The atmosphere which consists of the different gases that envelops the earth is the very source of energy to all living organisms. The sun is the ultimate source of energy from which plants and other organisms derive their source of energy to produce their own food, on which other animals including man depend on for survival. Oxygen, Nitrogen, carbon dioxide and the rare gases are other atmospheric composite that enhances the survival of living organisms on the Biosphere.

The hydrosphere, which consist of all natural water bodies of the earth, from which plants, animal, and other living organisms including man depend on for survival. Therefore these three spheres (atmosphere, lithosphere and hydrosphere) are very essential for every living organism in the biosphere.

EVALUATION:

1. What is the name given to the intersect of the three major spheres?
2. Explain the relationship that exist among these spheres.

SUB-TOPIC 3: RELEVANCE OF THESE SPHERES TO HUMAN ACTIVITIES

The Atmosphere, the Lithosphere and the Hydrosphere, which intersects to form the Biosphere, are very relevant to Human activities in the following ways:

Atmosphere

1. It serves habitat for some living organism.
2. It provides oxygen for plants and animals for respiration.
3. It provides carbon dioxide for photosynthesis by plants.
4. It contains ozone layer which acts as protective cover for living organism against the burning effects of ultra violet rays of the sun.
5. It acts as green house.
6. It is a medium of communication e.g. air routes.

Hydrosphere

1. It provides water for domestic uses e.g. drinking, washing, bathing, etc.
2. It provides water for industrial uses.
3. It serves as a means of transportation.
4. It provides employment opportunities for the people dwelling in the riverine areas.
5. It is used for generating electricity.
6. It is also used for irrigation purpose.
7. It serves as tourist centre e.g. bar beach.

          Lithosphere

1. Lithosphere forms the basis of all human settlement.
2. It serves as a source of all mineral resources.
3. It aids transportation through construction of roads, railways and airports.
4. All forms of farming activities are carried out on lithosphere.
5. It forms basis for most human activities such as mining, trading, etc.

 EVALUATION:

1. Outline the importance of the spheres of the earth to human activities

SUB- TOPIC 4: Internal structure of the earth

LITHOSPHERE (CRUST)

This is the solid portion of the earth that contains mineral substances broadly called Sial and Sima. The upper part of lithosphere is made of Silica and aluminium (sial) and the lower part silica and magnesium (sima). The density of sial is 2.7 while that of sima is 3.0. Silica floats on sima. The boundary of lithosphere and mantle is called Mohorovisic discontinuity.

MANTLE (MESOSPHERE OR SUBSTRATUM)

Mantle is also called mesosphere. It is found beneath the lithosphere. It has high density and contains a kind of rock called olivine. The boundary between the mantle and the core is called Gutenberg discontinuity.

CORE (BARYSPHERE) 

The core or barysphere comes after the mantle and is made up of Iron and Nickel (Nife). It has a very hot temperature of 1927°c and so is in a state of fluid. The rock is known to be crystalline in nature.

EVALUATION:

1. State three internal structure of the earth.
2. Draw a well labelled diagram to show the internal structure of the earth.
3. Describe the main features of the two of the parts shown in 2 above. (WASSCE, 2002).

GENERAL EVALUATION

1. Briefly describe the interaction within each zone of the outer part of the earth.
2. Describe the main characteristics of each of the following: (i) atmosphere (ii) lithosphere                                       (iii) hydrosphere
3. Outline the importance of either the biosphere or hydrosphere to man.
4. Name the zones in the outer structure of the earth.
5. Outline three characteristics of the following: crust, mantle and core.

SUMMARY

1. The earth is made up of three main layers: crust, mantle and core. The lithosphere (crust) is the solid outer layer of the earth. The mantle is found beneath the lithosphere and is made up of a kind of rock called olivine. The core or barysphere is found after the mantle and is made up of iron and nickel. The earth’s atmosphere, lithosphere and hydrosphere are very relevant to human activities in the following ways:
2. The atmosphere serves habitat for some living organism, provides oxygen for plants and animals for respiration, provides carbon dioxide for photosynthesis by plants, contains ozone layer which acts as protective cover for living organism against the burning effects of ultra violet rays of the sun, acts as green house, is a medium of communication e.g. air routes.
3. The lithosphere forms the basis of all human settlement, serves as a source of all mineral resources, aids transportation through construction of roads, railways and airports, all forms of farming activities are carried out on lithosphere, forms basis for most human activities such as mining, trading, etc.
4. The hydrosphere provides water for domestic and agricultural use, provides a medium for transportation e.g. through canals and rivers, provides a habitat for aquatic plants and animals, is a source of food e.g. fish farming, is a source of minerals e.g. salt, provides a medium for recreation e.g. swimming and rowing.
5. The biosphere is the zone that contains all forms of life while the lithosphere is the solid outer layer of the earth. The hydrosphere is the zone that contains all the water on earth while the atmosphere is the gaseous layer that surrounds the earth. The core is the central part of the earth.
6. 3.Interaction within each zone of the outer part of the Earth
7. The atmosphere, lithosphere and hydrosphere interact with each other in the following ways:
8. -The atmosphere contains air which is necessary for the survival of all living organisms on earth
9. The earth is made up of three major spheres namely, the lithosphere, the hydrosphere and the atmosphere. The biosphere is the zone where all these three spheres intersect. These spheres are relevant to human activities in various ways. The internal structure of the earth consists of the crust, mantle and core.

WEEKEND ASSIGNMENT

Objective Test:

1. The structure of the earth is divided into ——————- a. 2 parts b. 4 layers c. 5 layers d. 3 parts
2. Which of this part of the lithosphere comprises of landmasses and irregular features a. sima b. sial c. silica                        d. magnesium
3. The mineral contents of the upper part of the earth’s crust are collectively called the sial because it is composed mainly of (A) silica and olivine (B) alumina and olivine (C) silica and alumina (D) alumina and phosphate.
4. In which part of the atmosphere does rain clouds develop? (A) Troposphere (B) Stratosphere (C) Thermosphere              (D) Exosphere.
5.  The hydrosphere covers the total of ——— percent of the earth surface  a. 71% b. 93% c. 75% d. 97%
6. Which of the following is not a constituent material of the biosphere?  a. man b. animals c. rocks d. micro organisms.
7. The layer of the atmosphere where most of the weather conditions are found is called the ——————. a. Stratosphere b. Troposphere c. Mesosphere d. Ionosphere
8. The deep hot inner part of the earth can be classified as —————- a. core b. lithosphere c. mantle d. crust
9. Mantle is also called —————– a. sial b. sima c. mesosphere d. biosphere
10. The solid outermost layer of the earth is known as ———————- a. mesosphere b. lithosphere c. crust d. atmosphere
11. The total volume of the water on earth’s surface is called ————- a. hydrosphere b. biosphere c. ionosphere d. stratosphere
12. A layer of air that envelopes the earth is known as —————- – a. hydrosphere b. biosphere c. ionosphere d. stratosphere
13. The solid outermost layer of the earth is known as ———————- a. mesosphere b. lithosphere c. crust d. atmosphere
14. The total volume of the water on earth’s surface is called ————- a. hydrosphere b. biosphere c. ionosphere d. stratosphere
15. A layer of air that envelopes the earth is known as —————- – a. hydrosphere b. biosphere c. ionosphere d. stratosphere
16. The deep hot inner part of the earth can be classified as —————- a. core b. lithosphere c. mantle d. crust
17. The layer of the atmosphere where most of the weather conditions are found is called the ——————. a. Stratosphere b. Troposphere c. Mesosphere d. Ionosphere
18. Which of the following is not a constituent material of the biosphere? a. man b. animals c. rocks d. micro organisms
19. The hydrosphere covers the total of ——— percent of the earth surface – a. 71% b. 93% c. 75% d. 97%
20. In which part of the atmosphere does rain clouds develop? (A) Troposphere (B) Stratosphere (C) Thermosphere (D) Exosphere.

ESSAY

1. Briefly discuss on the activities of man that can lead to the depletion of the ozone layer.
2. With the aid of a diagram illustrate the relationship between the atmosphere, hydrosphere and the lithosphere.
3. What is the significance of a study of the spheres of the earth?
4. What are the three main layers of the earth?
5. What is the difference between sial and sima?
6. What is Earth’s magnetic field?
7. What are the two types of crust?
8. What is the Mohorovičić discontinuity?