October 3, 2022 [GRADE 7 SOCIAL STUDIES NOTE AND EXERCISE BY EDUCATION AND TECHNOLGY TEAM, DEREJE B.

UNIT ONE 2.1 Inner planets

PHYSICAL CHARACTERISTICS OF THE EARTH  The four planets closest to the Sun - Mercury, Venus, Earth,
and Mars are the inner planets.
1.1. Origin of the earth and the solar system  They exist in solid state.
 Scientists believe that the sun, planets and other smaller bodies  Astronomers call them the “terrestrial planets” because
in the solar system were formed from a large flammable of hot they have solid and rocky surfaces.
swirling gases.  Compared to the outer planets, the inner planets are small in
size.
 The flammable gas was loosely packed gases, largely made
up of hydrogen and helium, and dust particles. 1. Outer planets
 Jupiter, Saturn, Uranus, and Neptune are the outer planets
 Gradually, the gases and dust particles drew together of our solar system.
because of gravitational pull and formed a thin disc.  These planets are farthest from the Sun.
 The outer planets are much larger than the inner planets.
 Through time, the disc split into rings and kept spinning.  Since they are mostly made of gases, they are also called gas
The spinning rings at the center formed the sun. The outer giants.
rings resulted in the formation of the eight planets, including
the earth. Note: Till August 2006, Pluto was considered a planet. However, in a Meeting of
the International Astronomical Union, a decision was taken that Pluto like other
 Geologists estimate that the earth was formed 4.6 billion years celestial objects (Ceres, 2003 and UB313) discovered may be called “dwarf
ago. planets”.
Members of the solar system
3. Asteroids
1. The Sun  An asteroid is a relatively small rocky body that orbits the
 The sun is a huge and made up of extremely hot gases at the sun.
 Most asteroids in our solar system are found in the main
center of solar system.
asteroid belt.
 It provides the pulling force that binds the solar system.  They are found between the orbits of Mars and Jupiter.
2. Planets
 The word „planet‟ comes from the Greek word “Planetai” 4. Meteoroids
which means „wanderers‟.  The crushing of asteroids can cause small pieces of the
 There are eight planets in our solar system. asteroid to break off.
 All the planets revolve around the Sun on paths called  The broken pieces of asteroid are called meteoroids.
orbits.  When a meteoroid enters the earth‟s atmosphere, it
 The orbit is elliptical in shape. vaporizes and turns into a meteor
 In order of their distance from the sun, they are classified in  A meteor is a streak of light in the sky.
to two; inner planets and outer planets.  Because of their appearance, these streaks of light are
sometimes called “shooting stars”.
 October 3, 2022 [GRADE 7 SOCIAL STUDIES NOTE AND EXERCISE BY EDUCATION AND TECHNOLGY TEAM, DEREJE B.]

 When meteoroids survive their trip through earth‟s  Oxygen is primarily produced by plants.
atmosphere and land on the earth‟s surface they are called  Nitrogen and oxygen accounts for about 99% of the gases.
meteorites.
1.2.2. Internal structure of the earth
1.2 External components and internal structure of the earth
 The four physical environmental components or sub systems are
1.2.2.1 Sources of information about the internal parts of
the:
 lithosphere (land), the earth
 hydrosphere(water),
 biosphere (living things) and A. Direct sources
 atmosphere (air).
i. Mining: is the process of extracting useful materials from the
The lithosphere: is the solid or rock part of the Earth. earth.
 It is the coolest and most rigid part of the Earth.  The gold mining that is being undertaken in the Republic of
 It is an irregular surface with various landforms. South Africa enabled human beings to secure rock sample
 The surface of the lithosphere is very uneven. from a depth of 3 – 4 km beneath the surface.
 There are highest mountains like Ras Dejen (Ras Dashen),
and lowest places like Dallol depression in Ethiopia. ii. Volcanic eruption
 When the molten material (magma) thrown in to the surface
The Hydrosphere: contains all of the water on earth in liquid, solid of the earth, during volcanic eruption it becomes available for
and vapor form. laboratory analysis.
 The oceans are covers nearly 71 % of the earth‟s surface and
97 % of earth‟s water. iii. Deep ocean drilling projects
 The deepest hole dug for research purpose by far is on the
The Biosphere: is part of the earth‟s surface where living things Kola Peninsula in Russia, referred as the “Kola well” with a
exist. depth of 12km.
 It is concentrated near the surface in a zone that extends  This and many deep drilling projects have provided large
from the ocean floor upward for several kilometers into the volume of information through the analysis of materials
atmosphere. collected at different depth.

The Atmosphere: is the envelope of air that surrounds the earth. B. Indirect Sources
 It is a mixture of gases, Nitrogen (78%), oxygen (21%),  The indirect sources of information about the internal part of
Argon ( 0.93%), Carbon dioxide 0.03%) the earth are obtained from earth quake wave and by
Gases including methane, and water vapor make up the rest studying the meteorites that fall to the earth.
of the atmosphere.
 Nitrogen enters the atmosphere when volcanoes erupt and i. Earth quake wave/ Seismic Wave
 The shaking of the earth caused due to release of energy,
when dead plants and animals decay.
which generates wave that travel in all direction.
 October 3, 2022 [GRADE 7 SOCIAL STUDIES NOTE AND EXERCISE BY EDUCATION AND TECHNOLGY TEAM, DEREJE B.]

 The wave generated by an earth quake tells us a lot of things C. Core

about the material property of the interior of the earth.  The core is the innermost layer of the earth. It is composed
mainly of Nickel (Ni) and Iron (Fe) hence it is also called as
Note: Because the speed of the seismic waves depends on density, we can use NIFE.
the travel-time of seismic waves to map change in density with depth and  The cores temperature is about 60000C.
show that the Earth is composed of several layers  The core constitutes nearly 15% of earth‟s volume.
 The core has two layers:
1. Inner core that is solid
ii. Study of meteorites that fall to the earth In the inner core the force of gravity is so intense that the
 The materials and the structures observed in the meteorites molten metal (iron and nickel) is compressed in to a
are similar to that of the earth. solid material
 Since the earth is a celestial body like that of the meteorite, it 2. Outer core that is liquid (or semi-liquid).
can easily inferred that our earth also contain iron and nickel
in its core.
Note: You can think of the earth like an apple with three layers – skin, flesh
Note: Celestial bodies are objects in the universe such as stars, planets, and core. Except, in the earth; the layers are called the crust, the mantle and
asteroids and moon. the core.

1.2.2.2. Internal structure of the earth 1.3 Materials forming the crust of the Earth
 The structure of the earth‟s interior is basically divided into
crust, mantle and core. 1.3.1 Major Elements
A. Crust: is the outermost and thinnest layer of the earth.  About 98% of the total crust of the earth is composed of eight
 It has two different parts: continental crust and oceanic elements.
crust.
 The average thickness of continental crust is about 30 to 40  The most abundant elements in the Earth‟s crust are
km while that of Oceanic crust is oxygen, silicon, aluminum, iron, calcium, sodium,
5 to 6 km thick. potassium, and magnesium.
 The crust consists of hard and strong rock. Major
constituent elements of the crust are Silica (Si) and
Aluminum (Al) and thus, it is often termed as SIAL.

B. Mantle: is thickest portion of the earth below the

crust
 The mantle is about 2,900km thick, and takes up 84% of
Earth‟s volume. The major constituent elements of the
mantle are Silicon and Magnesium and hence it is also
termed as SIMA.
 October 3, 2022 [GRADE 7 SOCIAL STUDIES NOTE AND EXERCISE BY EDUCATION AND TECHNOLGY TEAM, DEREJE B.]

Most Abundant Elements In Earth's Crust

1. Oxygen - 46.1% 6.Sodium - 2.36%  There are two main types of igneous rocks. These are extrusive
and intrusive igneous rocks.
2. Silicon - 28.2% 7.Magnesium - 2.33%
A. Extrusive igneous rock: They are also called
3. Aluminium - 8.23% 8.Potassium - 2.09% volcanic rocks.
 They are formed when magma cools and solidifies on the
4. Iron - 5.63% 9.Titanium - 0.565% surface of the earth.
 An abundant and important example is basalt and obsidian.
5. Calcium - 4.15% 10.Hydrogen - 0.140%
B. Intrusive igneous rocks : They are also called
plutonic rock.
 They are formed when magma cools and crystallizes within the
1.3.2 Major Minerals interior of earth.
 The materials that the earth‟s crust is made of are called rocks,  Granite is the most abundant intrusive igneous rock.
and all rocks are made of minerals. Note: 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
 The building block of rocks are minerals 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.
 Minerals are inorganic solids with a specific internal structure
and a definite chemical composition. 2. Sedimentary rock
 The term sedimentary was derived from the Latin term
 Major rock forming minerals are minerals found in abidance like “sedimentum”, which means
Silicates, Oxides, Carbonates, and Sulfides etc… settling (laid down).

1.3.3 Major rocks that form the crust  Sedimentary rocks are formed when sediments come to
settle in a certain areas by various erosion agents.

On the base of formation rocks are classified into: igneous,  Most of these types of rocks are formed in rivers, seas and
sedimentary and metamorphic rocks oceans.

1. Igneous rock  Contrary to other rocks, sedimentary rock has layers which
 The word igneous was derived from the Latin word indicate the amount of sediment deposited at a time.
“ignis”, which means fire.
 Igneous rocks are formed when molten rock (magma) cools  The bottom layer is the oldest and the hardest of all the
and solidifies either on the surface or inside the surface. layers deposited above it while the top layer is the youngest
 Magma that gets to the surface is called lava. and the softest.
 October 3, 2022 [GRADE 7 SOCIAL STUDIES NOTE AND EXERCISE BY EDUCATION AND TECHNOLGY TEAM, DEREJE B.]

 Sedimentary rocks contain fossils which

indicate evidences of past events. B. Economic importance of rocks in Ethiopia

 These rocks are ware house of major energy resources, such i. Source of fuel: Sedimentary rocks like coal are a
as coal, petroleum and natural gas. source of fuel for industrial use.

2. Metamorphic rock ii. Construction purpose: Rocks like granite and

sandstone are quarried and used for road, bridge
 Metamorphic rocks get their name from the Greek words and building construction. Rocks like marble can be
“meta” meaning change, and “morpho” meaning form. polished as an ornament for decorating floors, walls
of buildings
 Metamorphic rock results from changes of pre-existing
igneous, sedimentary, and even other metamorphic rocks iii. Source of food nutrient: Rock salt such as sodium chloride from
through heat and pressure inside the earth‟s crust. sedimentary rock provide minerals used in cooking.

 They are also called changed rocks. iv. Formation of soil: Soils are formed from the disintegration of
rocks though weathering.
 Example: Marble which is formed from
limestone (sedimentary rock).

Note: Metamorphism involves the transformation of preexisting

rocks. Heat and pressure are the most important agents of change of
igneous and sedimentary rocks into metamorphic rocks.

1.4 The distribution and economic value of the

different rock types in Ethiopia

A. Distribution of rocks
 Igneous rocks cover large areas in the central part of
Ethiopia.
 Eastern Ethiopia is mainly covered with sedimentary rocks.
 Metamorphic rocks are found in the northern, western and
southern edges of the country.
 October 3, 2022 [GRADE 7 SOCIAL STUDIES NOTE AND EXERCISE BY EDUCATION AND TECHNOLGY TEAM, DEREJE B.]

Exercise One Instruction: Choose the best answer from the given options
1.During the formation of solar system, the swirling gas were
Instruction: Write true if the statement is correct and false if it is largely:
wrong. A. Nitrogen and Oxygen C. Helium and Hydrogen
1. Pluto is the ninth planet in the solar system. B. Methane and Water vapor D. Silicon and Iron
2. Earth is among outer planets. 2.Which of the following is incorrect regarding planet?
3. The sun comprises 50% of solar system‟s mass. A. They are eight.
4. The most abundant elements on earth is aluminum B. They revolve around the earth
5. Resources such as coal and petroleum are associated with C. They are all dominated by solid matter
sedimentary rock type. D. They have elliptical orbit
6. Rock is a source of human nutrient. 3.One is among gas giant planet.
A. Neptune C. Mars
Instruction: Match Items under column B with their B. Earth D. Mercury
corresponding items listed under column A 4.Which one refers to “shooting star”?
A. Meteoroids C. Asteroids
A B B. Meteorites D. Meteor
1. Dominated by solid Ni & Fe A. Gypsum 5.One is incorrect about biosphere.
2. Dominated by Liquid Ni & Fe B. Pyrites & Galena A. It overlaps with hydrosphere and lithosphere
3. Dominated by semiliquid Si & Mg C. Inner core B. It is the realm of living things.
4. Silicate minerals D. Quartz & Magnetite C. It is limited on the land surface of the earth.
5. Oxide minerals E. Outer core D. It extends to and interact with atmosphere.
6. Sulfides minerals F. Crus t 6. Identify intrusive igneous rock
G. Mica & Feldspar A. Marble C. Sandstone
B. Basalt D. Granite
Instruction: Complete the following statements with the
appropriate word/ or phrase Instruction: Answer the following questions by writing short
1.The rocky body revolves around the sun between the orbit of Mars responses
and Jupiter is ___________. 1. What is the most important reason for the sun‟s intense heat
2.The most abundant gas in the atmosphere is ________. not to cause harm on the earth?
3.The gold mining in Republic of South Africa enabled to gather 2. How is meteoroids formed?
earth‟s internal information from the depth of _________km. 3. Describe lithosphere
4.Major constituents of the crust are _________ and __________. 4. What are direct sources for information regarding internal
5.Magma that gets to the surface of the earth is known as part of the earth?
_____________. 5. What is metamorphism in rock formation?
6.The central Ethiopia is largely covered by _______ rock. 6. What are the two most important agents of rock
metamorphosis?