Grade 7 Social Studies Textbook PDF

GRADE 7 Unit One Physical Characteristics of the Earth SOCIAL STUDIES STUDENT TEXTBOOK GRADE 7 Addis Ababa City Administration Education Bureau...

GRADE 7 Unit One Physical Characteristics of the Earth SOCIAL STUDIES STUDENT TEXTBOOK GRADE 7 Addis Ababa City Administration Education Bureau Addis Ababa / Ethiopia / 2014 E.C. 1  GRADE 7 Unit One Physical Characteristics of the Earth Social Studies Student Textbook Take Good Care of This Textbook This textbook is the property of your school. Take good care not to damage or lose it. Here are 10 ideas to help take care of the book: 1. Cover the book with protective material, such as plastic, old newspapers or magazines. 2. Always keep the book in a clean dry place. 3. Be sure your hands are clean when you use the book. 4. Do not write on the cover or inside pages. 5. Use a piece of paper or cardboard as a bookmark. 6. Never tear or cut out any pictures or pages. 7. Repair any torn pages with paste or tape. 8. Pack the book carefully when you place it in your school bag. 9. Handle the book with care when passing it to another person. 10. When using a new book for the first time, lay it on its back. Open only a few pages at a time. Press lightly along the bound edge as you turn the pages. This will keep the cover in good condition. 2  Social Studies GRADE 7 Unit One StudentofTextbook Physical Characteristics the Earth SOCIAL STUDIES STUDENT TEXTBOOK GRADE 7 Authors Abebe Yibeltie Yayehyirad (MA) Dessalew Awaye Derese (BA) Mulugeta Dires Fetene (MA) Tegegn Degelo Someno (MA) Editors, Reviewers and Evaluators Solomon Wondimu Metaferia (MA) Belay Belete Birhanu (MA) Coordinator : Getachew Talema Atinafu Addis Ababa City Administration Education Bureau 3  GRADE 7 Unit One Physical Characteristics Student ofTextbook the Earth Social Studies ©Addis Ababa City Administration Education Bureau First edition 2022 Addis Ababa Acknowledgment This textbook development and publishing would not have been possible without the commitment and support of Ato Zelalem Mulatu - the AAEB head. He deserves deep gratitude for his patient guidance, enthusiastic encouragement and useful critiques.Special thanks should also be given for his advice and assistancein keeping the progress on schedule. Each of the members of the management - Ato Adimassu Dechasa, Ato Dagnaw Gebru, Ato Samson Melese, W/ro Abebech Negash, Ato Sisay Endale and Ato Desta Mersha has played a significant role in providing professional guidance, valuable support, and constructive recommendations for the realization of this project. Special thanks should go to primary and secondary school principals that had great share in inspiring their teachers to successfully accomplish their duty and play key role in concerted effort to a tremendous success. PHOTO CREDIT: Bahru Zewde, A history of modern Ethiopia (1855- 1991), Addis Ababa University Press, 2005. Fleischer, M and Raymond, M., Data of Geochemistry. United States Government Printing Office. Washington: 1967; MoE, Geography Students Text book for Grade 10, 2011; https://spaceplace.nasa.gov/; https://www.worldatlas.com; https://starchild.gsfc.nasa.gov; https://www.nationalgeographic.org; https://www.reporterethiopia.com; https://www.indiamart.com; https://www.CK-12foundation. While every attempt has been made to trace and acknowledge copy right, the authors and publishers apologies for any accidental infringement where copyright has proved untraceable. 4  GRADE 7 Unit One Physical Characteristics of the Earth Social Studies Student Textbook Contents Introduction Pages Unit 1: Physical Characteristics of the Earth 1.1 Origin of the earth and the solar system............................................2 1.2 Shape and movements of the earth.....................................................8 1.3 External components and internal structure of the earth................12 1.4 Materials forming the crust of the Earth........................................19 1.5 The distribution and economic value of the different rock types in Ethiopia................................................................................24 - Unit Summary - Glossary - Review Exercise Unit 2: Human Evolution and World Population 2.1 Human Evolution.....................................................................................33 2.2 Trend of World Population......................................................................38 2.3 People and the Development of Transportation................................58 - Unit Summary - Glossary - Review Exercise Unit 3: Human and Natural Resources 3.1 Human-Environment relationships (reciprocal relationship)...........................................................................................74 3.2 Population- resource relationship (over population, optimal population and under population)....................................................76 3.3 Types of Natural Resources.................................................................80 3.4 Factors affecting natural resources in Ethiopia................................84 - Unit Summary - Glossary - Review Exercise Unit 4. Ancient Civilizations and Medieval History of the World 4.1 Ancient world civilizations..................................................................95 4.2 Medieval history of the world..........................................................111 - Unit Summary - Glossary - Review Exercise I  GRADE 7 Unit One Social Studies Physical Characteristics Studentof the Earth Textbook Unit 5: Ancient History of Africa 5.1 Ancient kingdom of Egypt.............................................................125 5.2 The kingdom of Nubia.....................................................................131 5.3 The kingdom of Meroe....................................................................133 - Unit Summary - Glossary - Review Exercise Unit 6: States and Peoples of Ancient and Medieval Ethiopia 6.1 Aksum, Lalibela and Gondar........................................................142 6.2 Islamic Sultanates...........................................................................159 6.3 Population movements, interaction and integration (Gada and other indigenous organizations)...........................................163 6.4 Economic base of states: agriculture, trade and trade routes, taxation............................................................................................169 - Unit Summary - Glossary - Review Exercise Unit 7: Contemporary Global Issues 7.1 Environment....................................................................................181 7.2 Demographic “overload”.................................................................193 7.3 Terrorism1.......................................................................................195 7.4 Human trafficking..........................................................................197 - Unit Summary - Glossary - Review Exercise II  GRADE 7 Unit One Physical Characteristics of the Earth Unit One Physical Characteristics of the Earth Unit learning outcomes After studying this unit, you will be able to: Explain the origin of the earth and the solar system; Explain the origin of the earth and the solar system; Evaluate the shape and movement of the earth and their effects Describe Describe thethefour fourcomponents components ofof the earth earth and andtheir theirinteraction; interaction; Explain the earth’s internal layers and their characteristics; Explain the earth’s internal layers and their characteristics; Identify direct and indirect sources of information regarding the interior Identify layers ofthedirect earth;and indirect sources of information regarding the interior layers of Identify major the earth; elements, minerals and rocks forming the crust of the earth; Identifythe Analyze major elements, spatial minerals distribution andand rocks forming economic the crust importance of of the earth; rocks in Ethiopia. Analyze the spatial distribution and economic importance of rocks in Ethiopia. Main contents 1.1 Origin of the earth and the solar system 1.2 Shape and movement of the earth 1.3 External components and internal stucture of the earth 1.4 Materials forming the crust of the earth 1.5 The distribution and economic value of different rock types in Ethiopia Unit Summary Glossary Review Exercise 1  GRADE 7 Unit One Physical Characteristics of the Earth 1.1. Origin of the earth and the solar system Competency: After studying this lesson, you will be able to: Discuss how the earth and other members of the solar system were originated and evolved to the present state These are the words you should try to learn for this lesson Top 5 words  Solar system  Planet  Meteoroid  Sun  Asteroids More Key words  Inner planet  Outer planet  Dwarf planets  Orbit A. The origin of the Earth Start-up questions 9 What do you understand about the origin of the Earth and the solar system? 9 Where did the Earth come from, and how it is formed? The origin of the Earth is intimately related to the formation of the solar system. Some scientists believe that the sun, planets and other smaller bodies in the solar system were formed from a large flammable of hot swirling gases. The flammable was loosely packed gases, largely made up of hydrogen and helium, and dust particles. Gradually, the gases and dust particles drew together because of gravitational pull and formed a thin disc. Through time, the disc split into rings and kept spinning. 2  GRADE 7 Unit One Physical Characteristics of the Earth Focus The spinning rings at the center formed the sun.The outer rings Till August 2006, Pluto was considered resulted in the formation of the a planet. However, in a Meeting of eight planets, including the earth. the International Astronomical Union, Geologists estimate that the earth a decision was taken that Pluto like was formed 4.6 billion years ago other celestial objects (Ceres, 2003 and UB313) discovered may be called “dwarf planets”. B. Members of the solar system Our solar system is made up of a star, eight planets and countless smaller bodies such as dwarf planets, asteroids and meteoroids. I. The Sun The sun is the centre of the solar system. It is huge and made up of extremely hot gases. It Things to do! provides the pulling force that binds the solar system. The sun The earth orbit the Sun at a is the ultimate source of heat distance of about 150 million km. and light for the solar system. Light travels at a speed of 300,000 But that tremendous heat is not kilometers/second. How long does it take sunlight to reach the Earth? felt so much by humans because This sounds like a strange question, despite being our nearest star, but think about it. it is far away from us. The sun is about 150 million km away from the earth. Focus The sun is a star, just like many of the stars that you can see in the night sky. It is the largest object, comprising 99.8% of the system’s mass. 3  GRADE 7 Unit One Physical Characteristics of the Earth II. Planets Start-up questions What is a planet? What is the name of the planet we live in? The word ‘planet’ comes from the Greek word “Planetai” which means ‘wanderers’. There are eight planets in our solar system. All the planets revolve around the Sun on paths called orbits. The orbit is elliptical in shape. In order of their distance from the sun, they are classified in to Figure 1.1 The Planets two; inner planets and outer planets. Inner planets The four planets closest to the Sun - Mercury, Venus, Earth, and Mars are the inner planets. They exist in solid state. Astronomers call them the “terrestrial planets” because they have solid and rocky surfaces. Compared to the outer planets, the inner planets are small in size. Outer planets Jupiter, Saturn, Uranus, and Neptune are the outer planets of our solar system. These planets are farthest from the Sun. The outer planets are much larger than the inner planets. Since they are mostly made of gases, they are also called gas giants. 4  GRADE 7 Unit One Physical Characteristics of the Earth III. Asteroids Apart from the stars and planets, there are numerous tiny bodies which also move around the sun. An asteroid is a relatively small rocky body that orbits the sun. Most asteroids in our solar system are found in the main asteroid belt. They are found between the orbits of Mars and Jupiter. Figure 1.2 Asteroids belt IV. Meteoroids Sometimes one asteroid can crush into another. This can cause small pieces of the asteroid to break off. The broken pieces of asteroid are called meteoroids. When a meteoroid enters the earth’s atmosphere, it vaporizes and turns into a meteor: a streak of light in the sky. Because of their appearance, these streaks of light are sometimes called “shooting stars”. Sometimes meteoroids don’t vaporize completely in the atmosphere. In fact, sometimes they survive their trip through earth’s atmosphere and land on the earth’s surface. When they land on earth, they are called meteorites. Figure 1.3 Asteroid and Meteoroid 5  GRADE 7 Unit One Physical Characteristics of the Earth Figure 1.4 Constellations Interesting Fact! While watching the night sky, you may observe various patterns formed by different groups of stars, these are called constellations. Today there are a total of 88 constellations that cover the entire night sky including the Andromeda (Princess of Ethiopia), Cassiopeia (Queen of Ethiopia) and Cepheus (King of Ethiopia). You can see the patterns of constellation on figure 1.4. Latin Name English Name or Description Andromeda Princess of Ethiopia Apus Bird of Paradise Aquarius Water bearer Cassiopeia Queen of Ethiopia Cetus Sea monster (whale) Cepheus King of Ethiopia Gemini Twins Source: https://starchild.gsfc.nasa.gov/docs/StarChild/questions/88constellations.html 6  GRADE 7 Unit One Physical Characteristics of the Earth Things to do! Why the stars are not visible at the day time? You’ll need: 1 torch, 1 sheet of plain paper, pencil and a needle. Steps: 1. Place the torch in the centre of the paper with its glass front touching the paper. 2. Now draw a circle around the torch. 3. Perforate the paper with the needle within the circled area. 4. Now place the perforated circle part of the paper on the glass front and cover the paper around the torch with a rubber band. 5. Take care that the switch of the torch is not covered. 6. In a dark room, stand at some distance facing a plain wall, switch off all other lights. Now flash the torch light on the wall. You will see numerous dots of light on the wall, the like stars shine at night. 7. Switch on all the lights in the room. All dots of light will be almost invisible. 8. You may now compare the situation with what happens to the bright objects of the night sky after the sun rises in the morning. After you practice at home write a report and present to the class. 7  GRADE 7 Unit One Physical Characteristics of the Earth Activity 1.1 A. Individual work 1. What is ‘Solar System’? 2. Name all the planets according to their distance from the sun. 3. Which one is the nearest planet to the sun? B. Group discussion Discuss the following question in small groups and present your discussion outcome through your group representative. How the earth and other members of the solar system were originated and evolved to the present state? 1.2 Shape and movements of the earth Competency: After studying this lesson, you will be able to:- E Evaluate the shape and movement of the earth and their effects A. The shape of earth Start-up Start-up questions questions estions Start-up questions Whatdoisyoutheunderstand shape of about earth? 9 What the origin of the Earth and the solar system? Start-up How docan questions we prove the shape ofhow theof Where 9 What didyou the Earth come understand from, about and the origin itearth? is theformed? Earth and the solar system? 9 What Wheredoevidence What didyou iscome there theunderstand Earth that about from,theEarth howisof origin and it spherical? theformed? is Earth and the solar system? 9 Where did the Earth come from, and how it is formed? These are the words you should try to learn for this lesson. Top eight words understand about the origin of the Earth and the solar system? Spheroid Revolution Axis Equinox Rotation Season Orbit Solstice 8  GRADE 7 Unit One Physical Characteristics of the Earth Earth is one of eight planets in our solar system. The earth’s shape is not perfectly round. It has a slightly greater radius at the Equator. It is an oblate spheroid (spherical) shape. Earth does not have a perfect spherical shape. This is due to the gravitational force caused by the Earth’s rotation. As a result, it is bulging in the middle; whereas slightly flattened at North and South Poles. Evidences of earth’s shape There are various physical evidences that prove the earth’s shape is not perfectly spherical. If the shape of the earth were a flat disc, then the rising Sun would have been seen at all places at the same time. But this does not happen. Places in the east see the rising Sun earlier. When a ship approaches land, its funnel or mast is seen first and then the hull. If the Earth had been flat, the whole ship would have been seen at the same time. These evidences prove that earth’s shape is not flat but an oblate spheroid. The following illustrations show what the actual shape of the earth looks like. The illustrations help you to have a better understanding on the shape of the earth. Figure 1.5 shape of the earth B. Movements of the Earth Start-up Start-up questions questions estions Start-up Whatdoare questions movement? 9 What youearth’s understand about the origin of the Earth and the solar system? Start-up questions Whatdodid 9 Where What isyou the difference theunderstand between Earth comeabout from, and the rotation how origin it is of and revolution? theformed? Earth and the solar system? Start-up questions Explain 9 Where What how dodidyou rotation theunderstand Earth and comeabout revolution from,the and howof origin it isaffect the Earthdays, formed? years and the solarand seasons system? Howdo What 9 Where long thedoes didyou Earthitcome take understand for the about from, Earth origin and howto of itrotate is on its theformed? Earth andaxis? the solar system? 9 Where did the Earth come from, and how it is formed? 9  GRADE 7 Unit One Physical Characteristics of the Earth There is nothing stationary in the universe. The planets, moons, and other heavenly bodies in the universe rotate and revolve at different speeds. Earth has two movements. These movements are called rotation and revolution. i. Rotation Rotation is the movement of the earth on its axis. The earth takes about 24 hours to complete one rotation around its axis. Earth rotates from west to east, so the sun appears to rise in the east and set in the west.  It’s axis of rotation is tilted at an angle of 231/2° and is perpendicular to the Earth’s orbit. This tilt influences the amount of daylight (temperature) and other weather patterns from season to season. Effects of Earth’s Rotation Start-up questions Start-up questions estions 9 What Whatdocauses day and about you understand night?the origin of the Earth and the solar system? 9 Where The rotation of thedidEarth the Earth hascome from, and how the following it is formed? effects: 1.Day and Night Rotation creates a diurnal cycle of light and darkness, temperature, and humidity changes. As the earth rotates on its axis, understand about the origin of the Earth and the solar system? half of the earth faces the sun and half of the earth faces away from the sun. 2.High and Low Tide Figure 1.6 Day and night on the earth High and low tide is a result of the gravitational pull between the sun and the e Earth come from, and how it is formed? moon. When the earth rotates, the sun and the moon pulls it, however, one of the force is usually stronger than the other. Hence, we will experience high and low tide. ii. Revolution of the Earth Start-up questions Start-up questions estions Start-up questions 9 What What doisyou earth’s revolution? understand about the origin of the Earth and the solar system? Start-up questions 9 How Where long What dodidyou does the Earthit come takeabout understand for the from,Earth and to of how origin revolve it is around theformed? Earth and thethe Sun? solar system? 9 What Where What doare didyoueffects the Earth of understand the come earth’s from, about and the revolution? howof origin it is theformed? Earth and the solar system? 9 Where did the Earth come from, and how it is formed? 10  GRADE 7 Unit One Physical Characteristics of the Earth Revolution is the movement of the earth around the sun in a fixed path or orbit. Time for one revolution is 365¼ days or one year and the speed of earth’s revolution is 68,000 miles per hour. The Effects of Revolution of the Earth a. variation in the length of day and night The revolution of the earth gives impression that the sun is moving north and south of the equator. The equator faces the sun directly on March 21 and September 23. During these two days the day and night are equal throughout the earth. These two days are called equinoxes. On June 21, the tropic of cancer faces the sun. This is known as summer solstice. It is the longest day in the Northern hemisphere and longest night in the southern hemisphere. On December 21, the Tropic of Capricorn faces the sun. This is known as the winter solstice. It is the longest day in southern hemisphere and longest night in northern hemisphere. b. Seasons The revolution of the earth causes the four seasons namely summer (kiremt), autumn (Meher), winter (Bega) and spring (Belg / Tsedey). The following illustration shows the effects of earth’s revolution. Winter Spring Autumn Summer Figure 1.7 helps you to summarize the effects of rotation and revolution of the earth.. 11  GRADE 7 Unit One Physical Characteristics of the Earth Activity 1.2 Individual work 1. How does the rotation of Earth cause day and night? 2. What effect does the tilting of the earth on its axis have? 3. Why are there not always 12 hours of day light and 12 hours of dark everywhere in the world each day? Things to do Form a group that consists of 5 or 6 members and conduct the following activities. 1. Take a ball to represent the earth and a lighted candle to represent the sun. 2. Mark a point on the ball to represent a town “X”. 3. Place the ball in such a way that the town “X” is in darkness. 4. Now rotate the ball from left to right. After you did aforementioned activities, write what you observed. 1.3 External components and internal structure of the earth Competencies: After studying this lesson, you will be able to State the four components (subsystems) of the earth and their constant interaction; Distinguish the difference and similarity between direct and indirect sources information about the internal parts of the earth 12  GRADE 7 Unit One Physical Characteristics of the Earth These are the words you should try to learn for this lesson Top 5 words  Atmosphere  Hydrosphere  Components  Biosphere  Lithosphere More Key Words  Core  Crust Mantle 1.3.1. External Components of the earth Start-up questions 9 Do you know what each of these spheres represents - lithosphere, hydrosphere, biosphere and atmosphere? 9 Are these external components or sub systems interacted? The physical environment of the earth can be divided into four components or sub systems. They are the “lithosphere” (land), “hydrosphere” (water), “biosphere” (living things) and the “atmosphere” (air). A. The lithosphere The lithosphere is the solid or rock part of the Earth. It is the coolest and most rigid part of the Earth. It is an irregular surface with various landforms such as mountains, plateaus, plains and valley etc Things to do! Word Origin Many words used in a language may have been Discuss the following question in small groups and present your discussion outcome taken from some other languages. The following through your group representative. words are having origin from Greek words. 1. List the name of highest mountains, Atmos– meaning vapor major rivers, and plants grow in your locality. Hydro – meaning water 2. Associate the features you have listed Bio – meaning Life with the components of the earth (to which components of the earth they Lithos – meaning Stone belong? The surface of the lithosphere is very uneven. There are highest mountains like Ras Dejen (Ras Dashen (4620 m above sea level) and lowest places like Dallol (116 m below sea level) in Ethiopia. 13  GRADE 7 Unit One Physical Characteristics of the Earth B. The Hydrosphere The hydrosphere is the water section of the earth. The hydrosphere contains all of the water on earth in liquid, solid and vapor form. They can be found in oceans, seas and lakes etc. The oceans are the most prominent features of the hydrosphere, covering nearly 71 percent of the earth’s surface and 97 percent of earth’s water. C. The Biosphere The biosphere is part of the earth’s surface where living things exist. It is concentrated near the surface in a zone that extends from the ocean floor upward for several kilometers into the atmosphere. D. The Atmosphere Atmosphere is the envelope of air that surrounds the earth. It is a mixture of gases. The most abundant gas in the atmosphere is Nitrogen (78%). Nitrogen enters the atmosphere when volcanoes erupt and when dead plants and animals decay. The second most abundant gas in earth’s atmosphere is oxygen (21%). Oxygen is primarily produced by plants. Nitrogen and oxygen Figure 1.8 Composition of the accounts for about 99 % of the gases. Gases atmosphere including argon, carbon dioxide, methane, and water vapor make up the rest of the atmosphere. Things to do! Discuss the following question in small groups and present your discussion outcome through your group representative. State the four external components of the earth and discuss their interaction. 14  GRADE 7 Unit One Physical Characteristics of the Earth The components (sub systems) of the earth are highly interacted each other. The interaction of these systems influences every environment on Earth. High mountains, for example, often have lower temperatures than valleys or hills. In high- Lithosphere altitude mountain ranges, the lithosphere Figure 1.9 Components of the interacts with the thinner air and precipitation earth and their interaction to create a cool or even icy climate zone. Over time, plants and animals have adapted to live in these unique environments How do earth’s spheres interact? The earth is an integrated system that consists of rock, air, water, and living things that all interact with each other. Scientists divide this system into four parts. These are the lithosphere, hydrosphere, biosphere and atmosphere. The spheres are closely connected. For example, Many birds (biosphere) fly through the air (atmosphere), while water (hydrosphere) often flows through the soil (lithosphere). Human beings from the (biosphere) walk on the ground (the lithosphere); breath the air (the atmosphere); and drink the water (the hydrosphere). We could not exist without any one of these systems. Humans (biosphere) built a dam out of rock materials (lithosphere) Humans (biosphere) harness energy from the water (hydrosphere) by having it spin turbines (lithosphere) to produce electricity. 1.3.2 Internal structure and sources of information about the internal parts of the earth 1.3.2.1. Sources of information about the internal parts of the earth Start-up questions List out the various sources of information about the interior of the earth. How do we get information about the interior of the earth? Human lives on the surface of a globe that has a radius of nearly 6500 15  GRADE 7 Unit One Physical Characteristics of the Earth km, yet no one has ever penetrated more than a few kilometers below the solid earth. The knowledge about the internal parts of the earth is obtained from direct sources and indirect sources. A. Direct sources The direct source of information about the internal parts of the earth includes rock materials from mining areas and molten magma from volcanic eruptions. Besides scientist are working on “deep ocean drilling projects”. i. Mining Mining is the process of extracting useful materials from the earth. The gold mining that is being undertaken in the Republic of South Africa enabled human beings to secure rock sample from a depth of 3 – 4 km beneath the surface. ii. Volcanic eruption Volcanic eruption forms another source of direct information. When the molten material (magma) thrown in to the surface of the earth, during volcanic eruption it becomes available for laboratory analysis. iii. Deep ocean drilling projects Many holes have been dug for research purpose. The deepest hole by far is on the Kola Peninsula in Russia, referred as the “Kola well”. The deepest drill at Kola, has so far reached a depth of 12km. This and many deep drilling projects have provided large volume of information through the analysis of materials collected at different depth Figure 1.10 The Kola Super deep holes, A. Indirect Sources the deepest manmade hole on Earth The vast interior of the earth is largely inaccessible to direct study. The indirect sources of information about the internal part of the earth are obtained from earth quake wave and by studying the meteorites that fall to the earth. i. Earth quake wave An earth quake wave is one of the most important sources of information about the interior of the earth. An earth quake is simply the shaking of 16  GRADE 7 Unit One Physical Characteristics of the Earth the earth. It is a natural event. It is caused due to release of energy, which generates wave that travel in all direction. The wave generated by an earth quake tells us a lot of things about the material property of the interior of the earth. ii. Study of meteorites that fall to the earth The materials and the structures observed in the meteorites are similar to that of the earth. The analysis indicated that the core of the meteorites consists of iron and nickel. Since the earth is a celestial body like that of the meteorite, it can easily inferred that our earth also contain iron and nickel in its core. 1.3.2.2. Internal structure of the earth Start-up questions List out the various sources of information about the interior of the earth. How do we get information about the interior of the earth? The structure of the earth’s interior is basically divided into three layers. These are crust, mantle and core. A. Crust The crust is the outermost and thinnest layer of the earth. It has two different parts: continental crust and oceanic crust. The average thickness of continental crust is about 30 to 40 km. Figure Figure1.11 Structure 1.8 Structure of of thethe Earth Earth In contrast, oceanic crust is between 5 to 6 km thick. The crust consists of hard and strong rock. Major constituent elements of the continental crust are Silica (Si) and Aluminum (Al) and thus, it is often termed as SIAL. The major constituent elements of the oceanic crust are Silicon (Si) and Magnesium (Mg) and thus, it is often termed as SIMA. B. Mantle The portion of the interior below the crust is called the mantle. The mantle is about 2,900km thick, and takes up 84% of Earth’s volume. The mantle is the thickest layer of the earth. The major constituent elements of the mantle are Silicon and Magnesium and hence it is also termed as SIMA. The upper mental has solid rocks whereas, the lower part with molten rock called magma. 17  GRADE 7 Unit One Physical Characteristics of the Earth C. Core The core is the innermost layer of the Focus earth. It is composed mainly of Nickel (Ni) and Iron (Fe) hence it is also called You can think of the earth like an apple as NIFE. The core´s temperature is with three layers – skin, flesh and core. about 60000c. The core constitutes Except, in the earth, the layers are called nearly 15% of earth’s volume. The core the crust, the mantle and the core. has two layers: an inner core that is solid and an outer core that is liquid (or semi-liquid). In the inner core, the force of gravity is so intense that the molten metal (iron and nickel) is compressed in to a solid material.. Activity 1.3 A. Individual work 1. Name the three layers of the earth? 2. Which layers of the earth are the outermost and the thinnest? 3. List out the various sources of information about the interior of the earth? 4. Which layer of the earth accounts about 15% of the earth’s volume? 5. Using the following picture, label the layers of the earth that make up the structure of the earth? A ------------ B ------------ C ------------ D ------------ B. Group discussion Discuss the following questions in small groups and present your discussion outcome through your group representative. 1. State the four components (sub systems) of the earth and explain their constant interaction? 2. Discuss why inner core becomes solid? 18  GRADE 7 Unit One Physical Characteristics of the Earth 1.4 Materials forming the crust of the Earth Competencies: After studying this lesson, you will be able to Identify major elements, minerals and rocks forming the crust of the earth; Analyze how and why different earth’s materials are differentiated into different layers; These are the words you should try to learn for this lesson  Elements  Sedimentary rock  Continental crust  Minerals  Volcanic rock  Oceanic crust  Igneous rock  Plutonic rock  Metamorphism  Metamorphic rock More key words  Oxygen  Rock  Lava  Basalt  Magma  Granite 1.4.1. Major Elements Start-up questions 9 What type of materials makes up the earth’s crust? 9 Name the major elements present in the earth’s crust? Earth’s crust is made up of several elements. These elements are in a solid form in the outer layer of the earth and in hot and molten form in the interior. About 98% of the total crust of the earth is composed of eight elements. As you can see from the table (table 1.1) the most abundant elements in the Earth’s crust are oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium. 19  GRADE 7 Unit One Physical Characteristics of the Earth Table 1.1 Weight percentages of the most abundant elements the earth’s crust Elements Relative abundance (%) Oxygen (O) 46.6 Silicon (Si) 27.72 Aluminum (Al) 8.13 Iron (Fe) 5.00 Calcium (Ca) 3.63 Sodium (Na) 2.83 Potassium (K) 2.59 Magnesium (Mg) 2.09 Others 0.41 Source: Data of Geochemistry, sixth edition, Michael Fleischer (1967) 1.4.2. Major Minerals Start-up question 9 What are the major minerals forming the crust of the earth? The materials that the earth’s crust is made of are called rocks, and all rocks are made of minerals. There are many known mineral species, but the vast majority of rocks are formed by combination of a few common minerals, called rock forming minerals. Minerals, the building blocks of rocks, are inorganic solids with a specific internal structure and a definite chemical composition. Major rock forming minerals are those minerals which are found in abundance in the rocks of the earth’s crust. Refer the (table 1.2) which shows the major rock forming minerals: such as silicates, Oxides, Carbonates, Sulfides etc are the major rock forming minerals. 20  GRADE 7 Unit One Physical Characteristics of the Earth Table 1.2 Major rock forming minerals Mineral group Example Silicates Mica, feldspar, olivine Oxides Quartz, Magnetite Carbonates Calcite, Dolomite etc Sulfides Pyrite, Galena Sulfates Gypsum Chlorides Rock salt 1.4.3. Major rocks forming the crust Start-up questions 9 List the major rocks forming the crust of the earth? 9 How are different rocks formed? On the basis of their mode of formation (origin), rocks of the Earth’s crust are classified into three. These are igneous, sedimentary and metamorphic rocks. 1. Igneous rock The word igneous was derived from the Latin word “ignis”, which means fire. Igneous rocks are formed when molten rock (magma) cools and solidifies either on the surface or inside the surface. Sometimes the hot rock erupts, on the surface. Magma that gets to the surface is called lava. There are two main types of igneous rocks. These are extrusive and intrusive igneous rocks. A. Extrusive igneous rock Extrusive igneous rocks are also called volcanic rocks. They are formed when magma cools and solidifies on the surface of the earth. An abundant and important example is basalt and obsidian. Figure 1.12 Types of Ignous rocks 21  GRADE 7 Unit One Physical Characteristics of the Earth A. Intrusive igneous rocks Intrusive igneous rocks are also called plutonic rock. They are formed when magma cools and crystallizes within the interior of earth. Granite is the most abundant intrusive igneous rock. Focus Magma is a name for molten rock material found below the Earth’s surface, and this name changes to lava when magma reaches the Earth’s surface. It is produced in the earth’s interior at a depth of about 60 to 200km where temperature is between 900 oc and 1600oc 2. Sedimentary rock The term sedimentary was derived from the Latin term “sedimentum”, which means settling (laid down). Sedimentary rocks are formed when sediments come to settle in a certain areas after they have been transported in to those areas by various erosion agents. Most of these types of rocks are formed in rivers, seas and oceans. Sedimentary rock differ from other types of rocks for the fact that it has layers. A layer indicates the amount of sediment deposited at a time. The bottom layer is the oldest and the hardest of all the layers deposited above it while the top layer is the youngest and the softest.Sedimentary rocks contain fossils which indicate evidences of past events. These rocks are ware house of major energy resources, such as coal, petroleum and natural gas. Figure 1.13 Sedimentary rocks, laid down in layers 2. Metamorphic rock Start-up questions How metamorphic rocks are formed? What is Metamorphism? What are the agents of metamorphism? 22  GRADE 7 Unit One Physical Characteristics of the Earth Metamorphic rocks get their name from the Greek words “meta” meaning change, and “morpho” meaning form. Metamorphic rock results from changes in other kinds of rocks. They are produced from pre-existing igneous, sedimentary, and even other metamorphic rocks through heat and pressure inside the earth’s crust. Sometimes they are called changed rocks. Marble is an example of metamorphic rock. It is formed from limestone (sedimentary rock). Focus Metamorphism involves the transformation of pre existing rocks, i.e igneous and sedimentary rock and other qualitatively different rocks. Heat and pressure are the most important agents of change of igneous and sedimentary rocks into metamorphic rocks. Heat and Pressure Limestone Marble Activity 1.4 A. Individual work 1. How the different types of rocks are formed? 2. Mention the names of the different types of igneous rocks? 3. List the major elements forming the crust of the earth? 4. List the major minerals forming the crust of the earth? 5. What are the most important agents of metamorphism? B. Group discussion Discuss on the following question in small groups and present your discussion outcome through your group representative. 1. State the main difference between intrusive and extrusive igneous rock? 2. Discuss on the major elements, mineral and rocks forming the crust of the earth 23  GRADE 7 Unit One Physical Characteristics of the Earth 1.5 The distribution and economic value of the different rock types in Ethiopia Competency: After studying this lesson, you will be able to Describe the distribution and economic value of the different rock types in Ethiopia Start-up questions 9 Which areas of Ethiopia are largely covered by igneous, sedimentary and metamorphic rocks? 9 List the different uses of rocks in your locality? A. Distribution of rocks The igneous, sedimentary and metamorphic rocks are found in different parts of Ethiopia. As you can see from the map (figure 1.11) igneous rocks cover large areas in the central part of the country. Eastern Ethiopia is mainly covered with sedimentary rocks. Metamorphic rocks are found in the northern, western and southern edges of the country. Figure 1.14 Distribution of the major outcropping rocks in Ethiopia 24  GRADE 7 Unit One Physical Characteristics of the Earth B. Economic importance of rocks in Ethiopia Rocks have a broad range of uses that make them significantly important to human life. These include: I. Source of fuel: Sedimentary rocks like coal are a source of fuel for industrial use. II. Construction purpose: Some rocks like granite and sandstone are quarried and used for road, bridge and building construction. Rocks like marble can be polished as an ornament for decorating floors, walls of buildings etc III.Source of food nutrient: Rock salt such as sodium chloride from sedimentary rock provide minerals used in cooking. IV. Formation of soil: Soils are formed from the disintegration of rocks. Table 1.3 Economic importance of rocks Major Rocks Associated mineral Importance Metallic minerals, such as - gold, -Decorative and Jewelry materials - nickel, Metamorphic -Construction, - diamond, rock -Electrical wire making, - copper, - uranium, iron, -industrial machinery platinum and lead production etc Sedimentary Mineral fuels, such as - Energy sources rock - coal - Construction - petroleum - Writing materials - natural gas - limestone, and gypsum Igneous rock Basalt, granite, sand etc - Building and construction materials 25  GRADE 7 Unit One Physical Characteristics of the Earth Activity 1.5 A. Individual work 1. What type of rock is dominant in Addis Ababa and its surrounding? (refer figure 1.10, distribution of the major outcropping rocks in Ethiopia) 2. List down the uses of rocks? B. Group discussion Discuss on the following question in small groups and present your discussion outcome through your group representatives. 1. Is it possible to learn of past conditions of the earth by studying sedimentary rocks? 2. In a group, walk around your school compound and its surroundings. Collect samples of several types of rocks and bring them back to the classroom. Finally, report to the class about the uses of rocks you have collected in your locality? 26  GRADE 7 Unit One Physical Characteristics of the Earth UNIT SUMMARY In this unit, we have discussed the physical characteristics of the earth. We discussed how the earth and other members of the solar system were originated and evolved to the present. Besides, We explained the external components and internal structure of the earth and examined the materials forming the crust of the earth. Finally, we have described the distribution and economic value of the different rock type in Ethiopia. The origin of the earth is related to the formation of the solar system. The sun and the sun’s family (planets, asteroids, meteors etc) were formed from a large filament of hot whirling gases. Finally as a result of long time processes the sun and the planets were formed. Geologists estimate that the earth was formed 4.6 billion years ago. The earth’s shape is not perfectly round. It is an oblate spheroid, Rotation is the movement of the earth on its axis. Effects of rotation include day and night, High and Low Tide. Revolution is the movement of the earth around the sun in a fixed path or orbit Effects of revolution are seasons, varying the length of day and night,. The four components (sub systems) of the earth are the lithosphere, hydrosphere, biosphere and the atmosphere. The knowledge about the internal parts of the earth is obtained from direct sources and indirect sources. The internal structure of the earth is divided in to three major components: the crust, the mantle and the core. The materials that the Earth’s crust is made of are called rocks, and all rocks are made of minerals. On the basis of their mode of origin, rocks of the Earth’s crust are classified into three: igneous, sedimentary and metamorphic rocks.  Rocks are used as a source of fuel, construction and serves as a source of food nutrients 27  GRADE 7 Unit One Physical Characteristics of the Earth Glossary Asteroids: a relatively small rocky crust and the core layers of the earth body that orbits the sun. Meteors: Shooting star; fragment of Atmosphere: the envelope of air solid matter which enters the upper that surrounds the earth, held in atmosphere from outer space. place by gravity. Minerals:naturally occurring Axis :an imaginary line on which the Earth rotates. inorganic solids with a specific internal structure and a definite Biosphere: part of the earth’s surface where living things exist. chemical composition. Celestial bodies: refers to the sun, Orbit: the path each planet follows the moon, and all those objects when it moves around the sun shining in the night sky. Planet: a spherical object that orbits Constellation: The patterns of around a star stars seen in the sky Revolution: is the movement of the earth around the sun in a fixed path or Core: the central layer of the earth orbit. which is composed of nickel and Rock: a solid material that comprises iron. the earth’s crust. They are made of Crust: the outer surface or layer of minerals. In turn minerals are made the earth up of elements. Equinox : are days in which day and night are of equal duration. Rotation : is the movement of the earth on its axis. Hydrosphere: is the water surface Season :is a period of the year that of the Earth including oceans, seas caused by the earth’s revolution. and lakes. Solar system: the sun, the eight Lithosphere: the solid or rock part planets and all other objects that of the Earth. revolve around the sun Magma: Molten rock beneath the Solstice : are days when the Sun surface of the earth. reaches its farthest northern and southern Mantle: an intermediate layer of declinations. the earth. It is found between the Spheroid : ellipsoid, is a sphere flattened at the poles.. 28  GRADE 7 Unit One Physical Characteristics of the Earth REVIEW EXERCISE FOR UNIT ONE I. True or False Direction: Write “True” if the statement is correct and write “False” if it is incorrect 1. The core of the earth consists of nickel and iron. 2. The layer of the earth beneath the mantle is core. 3. The crust is the innermost layer of the earth. 4. Mineral fuels such as coal, petroleum and natural gas are associated with metamorphic rocks. 5. An earth quake wave enables us to acquire information about the interior of the earth. 6. Rock is a solid material that comprises the earth’s crust. II. Matching Direction: Match the items in column “A” with items in “B” A B 1 Lithosphere A. The water section of the earth 2 Hydrosphere B. The cultural landscape of the Earth 3 Atmosphere C. The part of the earth that supports all sorts of life 4 Biosphere D. The gaseous envelop of the Earth E. The solid or rock part of the earth 29  GRADE 7 Unit One Physical Characteristics of the Earth III. Multiple choices Direction: Choose the correct answer from the given options. 1. The type of rock that shows layered arrangement is: A. Igneous B. Metamorphic C. Sedimentary D. Magma 2. Which is the third nearest planet to the sun? A.Venus B. Mercury C. Earth D. Mars 3. How long does it take for the Sun’s light to reach Earth? A. 10 minutes B. 8 minutes C. 7 minutes D. 12 Minutes 4. Which of the following two important elements constitute the earth’s innermost core? A. Potassium and Magnesium C. Nickel and Iron B. Silicon and Aluminum D. Magnesium and Silicon ______5.The earth rotates around its axis from __________. A. North to sout B. South to North C. East to West D. West to East ______6.Variations in the length of daytime and night time from season to season are due to A. the earth’s rotation on its axis B. the earth’s revolution round the sun in an elliptical manner C. latitudinal position of the place D. revolution of the earth on a tilted axis IV. Fill in the blank Direction: Fill the following blanks with appropriate word(s) 1. The star from which we get light and heat is. 2. All the planets revolve around the Sun on a path called which is in shape. 3. is naturally occurring inorganic solid with a specific internal structure and a definite chemical composition. V. Short answer Direction: Give short answers for the following questions. 1. How are the earth and other members of the solar system formed? 2. How many planets are there in our solar system?. 3. Write down the direct and indirect sources of information about the interior of the earth? 4. What are the reasons that we know that earth is spherical? 5. How many rotations does the Earth make around its axis in a day? 30  GRADE 7 Unit One Physical Characteristics of the Earth Check List Put a tick (√) mark in each of the boxes for activities you can perform I can 1. Discuss how the earth and other members of the solar system were originated and evolved to the present state 2. Evaluate the shape and movement of the earth and their effects 3. State the four components (sub-systems) of the earth and their constant interaction 4. Distinguish between direct and indirect sources of information about the internal parts of the earth 5. Identify major elements, minerals and rocks forming the crust of the earth 6. Analyze how and why different earth’s materials are differentiated into different layers 7. Describe the distribution and economic value of the different rock types in Ethiopia. 31  GRADE 7 GRADE 7 Unit Two Human Evolution and World Population Unit Two Human Evolution and World Population Unit learning outcomes After studying this unit, you will be able to: Explain the origin of human beings; Point out the archeological sites that show the origin of earlier human beings; Discuss world population growth distribution; Calculate different demographic rates; Evaluate the role of different mode of transportation; Identify and show significant road signs Main Contents 2.1 Human Evolution 2.2 Trend of World Population 2.3 People and the Development of Transportation Unit summary Review Exercise 32  GRADE 7 GRADE 7 Unit Two Human Evolution and World Population 2.1 Human Evolution Competencies: After studying this lesson, you will be able to Point out archeological sites that show the origin of earlier human beings; Examine the historical routes humankind has passed through over time; These are the words you should try to learn for this lesson Top 10 words  Evolution  Homo  Homo erectus  Fossil  Hominids  Homo sapiens  Genus homo  Homo habilis  Pre-history  Bi-pedal More key words  Archeology  creationist 2.1.1 Archeology and archeological works Start-up question 9 What is archeology? Archeology is the science in which archeologists dig out material objects and fossils of the past. It helps us in the study of pre-history. Pre-history was the distant past before the beginning of writing and recording. Fossils are the remains of dead plants, human beings and animals. Therefore, the study of fossils and other material remains of the past help us to reconstruct what happened before the art of writing started. 33  GRADE 7 GRADE 7 Unit Two Human Evolution and World Population Figure 2.1 Artifacts and fossils 2.1.2 Origin of the first human beings Start-up question 9 Distinguish the difference between the Creationist theory and the scientific theory? With regard to the origin of human beings, there are two theories suggested. These are: creationist theory and scientific (evolution) theory Creationist theory said that human beings were created by God. Those who believe in the assumption that God creates humans and the whole universe are Creationists. The Scientific theory believes that human beings and other living things are the result of gradual and natural process of changes that took millions of years. Charles Darwin (1809-1882) explained about evolutionary process. Hominids were the ancestors of human beings. Human beings belong to the species called homo sapiens. Australopithecines (southern ape) were the earliest (the first) human species that appeared in Africa around 6 million years ago. Its fossils were discovered in Ethiopia, Kenya, South Africa and Chad. 34  GRADE 7 GRADE 7 Unit Two Human Evolution and World Population The fossil remains of Australopithecus Afarensis, Known as Lucy or Dinikensh, was found in 1974 at Hadar, in the Afar region, Ethiopia. Afarensis may have been ancestor of Genus Homo. 2.1.3 Historical paths human kind passes over time There are different species that belong to genus homo: homohabilis, homo erectus and homo sapiens. The homo habilis (handy human being) is considered to be the oldest human being that appeared in Africa. Its fossils were found at Olduvai Gorge in Tanzana, at lake Turkana in Kenya and in the Omo valley in Ethiopia. Homo erectus (up right walking human being) was the first human being to master the use of fire and the earliest species to migrate from Africa to other part of the world. Its fossils were discovered in Ethiopia in the Omo Basin, Melka-Kunture, Konso-Gardula and Middle Awash. Homo sapiens (wise human being) were very similar to modern human being. Fossils of this species were found in the Awash and Omo valleys and in the areas near Dire Dawa. Modern beings appeared about 40,000 years ago in Africa. They are different in many ways from their ancestors. They have large brains, are bi-pedal and walk erect, use languages, develop culture, invent tools and transmit knowledge from generation to generation. 35  GRADE 7 GRADE 7 Unit Two Human Evolution and World Population Focus There are three stages through which the Homo species passed before the emergence of modern humans. These are:- 1. Homo habilis: able to make tools 2. Homo erectus: able to erect upright and walk 3. Homo sapiens: knowledge is the distinctive feature of modern human Figure 2.2 Human evolution from Homo habilis to Homo erectus 36  GRADE 7 GRADE 7 Unit Two Human Evolution and World Population Activity 2.1 A. Individual work Using the reference materials, write very short notes on the following terms: 1. Archaeology 2. Fossils 3. Hominids, 4. Creationist theory 5. Evolutionary theory B. Group discussion: Discuss on the following questions in small groups and present your discussion outcome through your group representatives. 1. List the sites where the fossils of Homo erectus were discovered in Ethiopia. 2. By using the map of Africa indicate the location of archeological sites that show the origin of early human being. 37  GRADE 7 GRADE 7 Unit Two Human Evolution and World Population 2.2 Trends of world population Competencies: After studying this lesson, you will be able to Predict future world population growth pattern on the basis of present and past population growth rate Calculate different demographic rates such as growth, mortality, fertility, net-migration and etc.; Identify types and causes of population movement; Locate densely and sparsely populated regions on world population map; Evaluate growth trend of Ethiopian population in line with world population growth; These are the words you should try to learn for this lesson Top 10 words  Birth rate  Fertility  Mortality  City  Immigrant  Migration  Death rate  Hamlet  Population  Emigrant More key words  Dependency ratio  Natural increase Population explosion  Infant mortality  Settlement  Population Cluster Start-up questions 9 What do you mean by human population? 9 What factors have contributed to the growth of world population? Human population refers to the total number of human inhabitants of a specified area, such as a city, country, or continent, at a given time. Population is one of the most critical factor that determine the socio-economic and environmental conditions of every country in the world. 38  GRADE 7 GRADE 7 Unit Two Human Evolution and World Population The world’s population has been experiencing continuous growth since the th 15 century. The UNDP estimated that world population reached 6 billion with an annual growth rate of 1.5% by 2000 A.D. The number added to world population per year would increase from 80 million to 90 million if the growth rate of 1.5% continues, and world population would double in a period of 40-50 years from about 2000 A.D. Such rapid and dramatic growth rate of the world population is known as population explosion. Focus Population doubling time is length of time needed by a population to double itself. It can be calculated using the following formula:- 70 Doubling Time = growth rate Example: suppose the population growth rate of country A in 2010 were 2%. How many years will it take the population to double? Doubling time = = 35 years Factors that contribute for rapid population growth The rapid increase in the size of the human population is attributed to many factors. These include:  Advancements in scientific knowledge, agriculture, industry, medicine;  Improvement in peoples living conditions;  Humans ability to control famine and disease, which have been major killers of humans;  The relatively lower cost of importing vaccines, antibiotics, insecticides, and high-yielding varieties of seeds. 39  GRADE 7 GRADE 7 Unit Two Human Evolution and World Population As indicated in (Table 2.1) below, by 1750 there were only about 791 million peoples in the world. However, in a matter of 250 years, the world population reached over 6 billion. The growth of human population between 1750 and 2000 has been very rapid. Table 2.1 Trends in world population growth (1750-2050) Region Population size (in millions) Years 1750 1800 1850 1900 1950 2000 2050 (Estimate) Asia 502 635 809 947 1,437 3,689 5,369 Africa 106 107 111 133 228 797 1,846 Europe 163 203 276 408 546 727 642 Latin America 16 24 38 74 166 523 480 and the Caribbean North America 2 7 26 82 221 481 722 Oceania 2 2 2 6 12 30 45 Total 791 978 1,262 1,650 2,556 6,073 9,104` Source :- Microsoft Encarta (2009) 40  GRADE 7 GRADE 7 Unit Two Human Evolution and World Population Trend and growth rate of Ethiopian population According to the 2007 Census, the population of Ethiopia was 73,918 505. The country’s population is among the fastest growing in the world It was estimated that, in 1900, Ethiopia had only 11.8 million persons. As shown in (Table 2.2), this number increased to about 12.9 million in 1920 and to 23.5 million in 1960. The table shows that, in 1960, the country had twice the population it had in 1900. These values show that, during those decades, it took 60 years for the population to double in size. In contrast, since 1960, the time required for the population to double has been on the decline. This is because of rapid rate of population growth. As shown in (Table 2.2)the growth rates of the Ethiopian population since 1900 increased by less than 1.0% until about 1920. Regarding worldwide efforts to control malaria and other diseases in the 1950s, the growth rate rises from year to year and reached 2.8% in 1970 and 3.1% in 1984. According to the results of the three censuses, there was a slight decline in the population growth rate over recent decades, changing from 3.1 percent in 1984 to 2.9 percent in 1994, and to 2.6 percent in 2007. This was mainly the result of the government’s efforts to regulate fertility rates through the delivery of family planning services. Table 2.2 Population estimate and growth rate in Ethiopia (1900-2007) Year 1900 1920 1940 1960 1970 1984 1994 2007 Population (million) 11.8 12.9 16.3 23.5 29.5 42.6 53.5 73.9 Growth rate (%) 0.2 1.0 1.5 2.2 2.8 3.1 2.9 2.6 Source: Central Statistical Authority (CSA) 1994 and 2007 41  GRADE 7 GRADE 7 Unit Two Human Evolution and World Population Activity 2.2 A. Group discussion Discuss on the following question in small groups (based on Table 2.1 and 2.2) and present your discussion outcome through your group representative. 1. Identify the two continents whose population growth rates differ the most? 2. Discuss the consequences of any rapid population growth you have observed in your locality? What measures do you suggest to correct the situation? 3. Discuss about the growth and distribution pattern of Ethiopian population? 2.2.1 Components of population dynamics Start-up question 9 What are the components of population dynamics? The main components of population dynamics/ determinants are fertility, mortality and migrations. Fertility and mortality are biological factors, while migration is purely non-biological. The combined effect of the three factors controls the changes in population size and composition. A. Fertility Start-up questions 9 What do you mean by fertility? 9 What factors affect the fertility of a society? 42  GRADE 7 GRADE 7 Unit Two Human Evolution and World Population Fertility refers to the actual reproductive performance of a population. The growth of world population depends largely on human fertility. This is so because any society replenishes itself through the process of human fertility. Measures of fertility Fertility can be determined using different methods, but the most commonly used measure of fertility is birth rate. Birth Rate (BR) Birth rate is the most common and simplest index of fertility. It is simply the number of live births observed in one year among one thousand people in a given region. Birth rate can be expressed as a number of live births per thousand people. BR= P×K Where B is the total number of live births during a year, P is mid-year total population and K is a constant, conventionally 1000. Example If the number of live births in a population of 50,686,000 was 150,800, the birth rate is: 150,800 BR= B×K= × 1000= 2.9 births per1000 per year P 50,686,000 Factors of Fertility Distribution Various factors affect fertility distribution in the world including  Low access to contraceptives;  Backwardness and poverty;  Low status of women; 43  GRADE 7 GRADE 7 Unit Two Human Evolution and World Population  Need of children for labour;  Children are considered as symbol of virility and  Low educational background. B. Mortality Start-up questions 9 What is mortality? 9 What factors affect mortality? Mortality refers to the occurrence of death in the human population. Mortality rates are higher in the developing countries than in the developed ones. This difference is caused by variations in standards of living, nutrition, medical services, personal hygiene and environmental sanitation. Measures of Mortality Mortality can be measured in a number of ways, including the use of death rate and infant mortality rate. Death rate (DR): is the ratio of the total registered deaths of a specified year in a region to the total mid-year population, multiplied by 1000. 44  GRADE 7 GRADE 7 Unit Two Human Evolution and World Population D DR= × 𝐾𝐾𝐾𝐾 where DR is crude death rate, D stands for total observed P deaths, P is total mid-year population, and k is a constant, 1000. Example In a hypothetical region, the total number of deaths observed in 2011 was 21,000, and the total mid-year population was 7,000,000. What is death rate? D DR= × 𝐾𝐾𝐾𝐾= 21,000 × 1000=3/1000.This number indicates that P 7,000,000 the deaths of 3 persons were observed for each 1000 people per year. Focus Rate of natural increase refers to the difference between the number of live births and the number of deaths occurring in a year. Rate of natural increase = Birth rate-Death rate Infant mortality is the death of young children aged below one year. Major factors that attributed for high death rate are the following:  Low standard of living  Low access to health facilities  Poor nutrition, and sanitary practices  Civil war and political instability  Wide spread of famine and starvation  High incidence of disease and infections 45  GRADE 7 GRADE 7 Unit Two Human Evolution and World Population C. Migration Start-up questions 9 What is migration? 9 Why do people migrate? Migration refers to the movement of humans from one place to another. Migration takes place with two major factors. These are: I. Push factors: impose pressure on peoples to migrate, which includes poor employment, civil war, and harsh climate etc. II. Pull factors: attract peoples to migrate, which include good job opportunity, favorable climate and good welfare service. An emigrant (out migrant) is a person who is leaving one country to live in another. An immigrant (in migrant) is a person who is entering a country from another to make a new home. Measures of migration Immigration rate indicates the number of people arriving at a destination per 1000 people in a given year Emigration rate indicates the number of departing people from an area of origin per 1000 people in a given year. 46  GRADE 7 GRADE 7 Unit Two Human Evolution and World Population Net Migration Rate (NMR): shows the net effect (balance) of immigration and emigration in an area. It can be expressed as an increase or decrease per 1000 people in the area in a given year. Activity 2.3 A. Individual Work 1. What are the factors that led fertility differences in developed and developing countries? 2. What are the major factors that attributed for high death rate in the world? B. Group work Discuss on the following questions in small groups. 1. The number of live births for place “A” was 2400, and its mid-year population was 160,000. Find BR. 2. The number of deaths for place “B” was 219,300, and its mid-year population was 19,297,000. Calculate DR. 3. Assume the number of emigrants and immigrants are 30,000 and 150,000 respectively, if total population is 100 million. Calculate NMR? 47  GRADE 7 GRADE 7 Unit Two Human Evolution and World Population 2.2.2 Population characteristics Start-up question 9 What are the major characteristics of population? The structure or composition of population can be classified in to two categories; these are biological and cultural characteristics. Biological characteristics include race, ethnicity, sex and age and cultural characteristics comprise of education, health, nutrition, religion and occupation. Age structure is the distribution of a given population into age groups. There are two important statistical tools used to understand age structure. These are: age groups and population pyramid. Age groups: in the broad age groups, age structures are;  Young age, 0-14 (the young dependent population),  Working age, 15-64 (the economically active population)  Old age, 65+ (the elderly dependent population). Population Pyramid: implies the graphic representation of the age distribution of a given population by sex. Look the Figure given below which show the population of Ethiopia. 48  GRADE 7 GRADE 7 Unit Two Human Evolution and World Population Figure 2.3 Typical example of population pyramid Population Pyramid of Ethiopia for 2007 Source: PCC. In general, population pyramids of developing countries like Ethiopia have very broad bases, showing the dominance of the young-age population. sex Structure Start-up question 9 What is sex structure? The sex structure of a population is shown by sex ratio, which is the ratio of male population to female population. Sex ratio is usually expressed as the number of males per 100 females in a population Sex ratio = male population X 100 Female population 49  GRADE 7 GRADE 7 Unit Two Human Evolution and World Population Age dependency ratio Start-up questions 9 What is age dependency ratio? 9 Is the dependency ratio of your locality or city high or low? Why? Age dependency ratio (ADR) is the relationship between the working or economically active population and the non-working population. In Ethiopia, the age dependency ratio is very high. In other words, the dependency burden of the young and old age populations on the working or economically active population is very heavy. ADR = Example: Suppose region “A” has the number of dependent population (under-15 years) is 6,247,000. The number of old age (dependent) population > 64 is 6,217,000 and number of independents (15 – 64 years) is about 27,160,000. What will be the ADR? ADR = (population of aged 0 14) + (population of aged 65+) x 100 population of aged (15-64) = =82.7% 50  GRADE 7 GRADE 7 Unit Two Human Evolution and World Population Activity 2.4 A. Individual work. Try to calculate individually in the class 1. Assume total students of a given school were 3000. Out of this 1650 were females. What is sex ratio? 2. Suppose region “A” has the number of dependent population under-15 years is 12,191,000, number of old age (dependent) population > 64 is 5,127,000 and the number of independents 15 – 64 = 29,120,000. Calculate ADR? 2.2.3 Population distribution Start-up question 9 What factors have influenced the distribution of world population? Population distribution refers to the way people inhabit and occupy the earth’s surface. Generally, the distribution of population in the world is uneven. Factors of population distribution The major factors of population distribution can be classified in to two groups. These are: physical factors and human factors. 51  GRADE 7 GRADE 7 Unit Two Human Evolution and World Population Physical Factors The most significant physical factors affecting the distribution of population are:  Natural resources (water, soil, vegetation and minerals etc) The nature of topography (slope and altitude) Climate condition (mainly rainfall and temperature) Human factors The major factors affecting distribution of population includes:  Socio-economic factors ( job opportunities, availability of technology)  Political factors (civil war, political unrest)  Type of farming and transportation facilities,  Social organization Spatial distribution of world population 1. Densely Populated Regions There are three main belts of high population density and concentration in the world. These areas are also called “Population Clusters”. These regions are: A. Asiatic population belt B. Peninsular Europe C. North-eastern North America A. Asiatic Population Belt: The region accounts for about 60