These DAV Class 7 SST Book Solutions Pdf and DAV Class 7 SST Chapter 3 Question Answer – The Surface and the Interior of the Earth are thoughtfully prepared by experienced teachers.
DAV Class 7 SST Ch 3 Question Answer – The Surface and the Interior of the Earth
DAV Class 7 SST Ch 3 Solutions – The Surface and the Interior of the Earth
Something To Know
A. Tick (✓) the correct option.
Question 1.
Living organisms do not survive inside the earth due to
(a) high temperature
(b) cool temperature
(c) presence of gases
(d) excessive water
Answer:
(a) high temperature
Question 2.
Earthquakes and volcanoes are caused by
(a) internal disturbance
(b) external disturbance
(c) overpopulation
(d) gradation
Answer:
(a) internal disturbance
Question 3.
Respective layers of the earth from top to bottom are
(a) crust, core, mantle
(b) crust, mantle, core
(c) core, crust, mantle
(d) core, mantle, crust
Answer:
(b) crust, mantle, core
Question 4.
The full form of SIMA is
(a) silica and mica
(b) silica and magnesium
(c) silica and magma
(d) silica and magnetite
Answer:
(b) silica and magnesium
Question 5.
The original rock from which Gneiss formed is
(a) limestone
(b) shale
(c) granite
(d) quartzite
Answer:
(c) granite
B. Fill in the blanks.
1. Earth was formed about …………….. million years ago.
2. The behaviour of …………… waves tells us about the earth’s interior.
3. The ………….. of crust varies from place to place.
4. Rocks are classified into three groups on the basis of their …………….
5. The ………….. of the earth is rich in iron and nickel.
Answer:
1. 4,600
2. seismic
3. thickness
4. formation
5. core
C. Give a single term for each of the following statements.
Question 1.
It is the hardest substance.
Answer:
Diamond.
Question 2.
The molten rock material present inside the earth.
Answer:
Magma.
Question 3.
Rocks which are formed due to cooling and solidification of magma inside the earth.
Answer:
Sedimentary rocks.
Question 4.
Shaking and trembling of the earth’s surface.
Answer:
Earthquake.
Question 5.
A naturally occurring solid substance made up of a mixture of minerals.
Answer:
Rock.
D. Answer the following questions in brief.
Question 1.
What is the special feature of sedimentary rocks?
Answer:
Sedimentary rocks are layered.
Question 2.
How is a metamorphic rock formed?
Answer:
Rocks which originally are igneous or sedimentary in nature, get changed in character and appearance due to heat and pressure to form metamorphic rocks.
Question 3.
What is lava?
Answer:
Lava is actually fine red molten magma coming out from the interior of the earth on its surface.
Question 4.
Why are igneous rock called primary rocks?
Answer:
Igneous rocks are called primary rocks as they were formed first over the earth’s surface.
Question 5.
What are sediments?
Answer:
The agents of denudation break the rocks into small rock pieces. These rock pieces are then carried by rivers and deposited on the river
beds or sea beds. These deposits are called sediments.
E. Answer the following questions.
Question 1.
Differentiate between the P-Wave and the S-Wave.
Answer:
Both are types of seismic waves. The P-Wave, also known as Primary Wave can travel through both solid and liquid mediums and is faster in speed. But the S-Wave, also known as Secondary Wave, can travel through only a solid medium and that too at a slower speed.
Question 2.
Write two characteristics of each of the following:
(a) Crust
(b) Mantle
(c) Core
Answer:
(a) Crust:
- It is the uppermost layer over the earth’s surface.
- It is the thinest of all the layers.
(b) Mantle:
- It is a very thick layer of rocks and lie just beneath the crust.
- The entire mantle is not homogenous.
(c) Core:
- It is the innermost layer of the earth with a radious of 3,470 km.
- It is mainly made up of nickel and iron and is, therefore, called nife.
Question 3.
What are fossil fuels? Name any two fossil fuels and specify their importance.
Answer:
Sometimes, the remains of animals and plants get buried and trapped under the layers and over a period of time get converted into coal, oil and natural gas. These are called fossil fuels. Coal, oil and natural gas are fossil fuels. These are of great economic importance all over the world as a major source of energy. India is highly dependent on coal for meeting its commercial energy requirements. Natural gas is considered environment friendly fuel. It is not only a source of energy but also an industrial raw material in the petrochemical industry. Petroleum (oil) provides fuel for heat and lighting and raw materials for a number of manufacturing industries.
Question 4.
Why is the knowledge of the earth’s interior based on indirect observation?
Answer:
The intensive heat neither allows us to dig deep nor there is any possibility of living organism deep inside the earth. It is, therefore, we have little knowledge about the earth’s interior. Whatever knowledge we have, is based on indirect observations.
Question 5.
What are minerals? On what basis can the minerals be identified? Give examples.
Answer:
A naturally occurring substance that has a definite chemical composition is called a mineral. Minerals are not evenly distributed over space. They are concentrated in a particular area or rock formations. There are over three thousand minerals. They are identified on the basis of their colour, hardness and lustre. On the basis of composition, minerals are classified mainly as metallic and non-metallic minerals. The metallic minerals contain metal in raw form. Iron ore, bauxite, manganese, etc. are some of its examples. The non-metallic minerals do not contain metals. Limestone, mica and gypsum are examples of such minerals.
Value-Based Questions
A very high magnitude earthquake that struck central Nepal, killed over 8,700 people and destroyed thousands of houses. Most of the people got trapped inside the buildings. Narrow lanes, high rise buildings, improper construction material and technically weak structures took the maximum toll. Inspite of all odds, everybody-be the neighbours, local government or international organisations, lent the helping hand to the needy people. It has been proved by the people that humanity excels in all the situations.
- Is the nature totally responsible for this misery or are we at a fault somewhere? Explain.
- Which human values were seen in action in all those who helped the earthquake victims? Mention any five with examples.
Answer:
Do yourself with the help of Internet.
Something To Do
Question 1.
Take a thermocol sheet, plastic clay and bright colours to make a model of the earth’s interior showing its major layers. Label it.
Ans.
Do it with the help of the figure given in the textbook.
Question 2.
Group the following rocks under three headings-Igneous, Sedimentary and Metamorphic.
(a) Granite
(b) Marble
(c) Coal
(d) Clay
(e) Gneiss
(f) Slate
(g) Limestone
(h) Basalt
(i) Sandstone
(j) Shale
Answer:
| Igneous Rocks | Sedimentary Rocks | Metamorphic Rocks |
| Granite
Basalt |
Coal
Clay Limestone Sandstone Shale |
Marble
Gneiss Slate |
DAV Class 7 Social Science Chapter 3 Question Answer – The Surface and the Interior of the Earth
A. Tick (✓) the correct option.
Question 1.
The uppermost layer of the earth’s interior is called
(a) mantle
(b) crust
(c) core
(d) rock
Answer:
(b) crust
Question 2.
The core of the earth is rich in
(a) iron
(b) nickel
(c) aluminium
(d) both (a) and (b)
Answer:
(d) both (a) and (b)
Question 3.
An example of igneous rock is
(a) limestone
(b) granite
(c) marble
(d) chalk
Answer:
(b) granite
Question 4.
Granite changes into metamorphic as
(a) gneiss
(b) marble
(c) slate
(d) none of them
Answer:
(a) gneiss
Question 5.
Which one of the following groups of rocks is the correct example of sedimentary rocks?
(a) Clay, shale and chalk
(b) Marble, genesis and slate
(c) Granite, basalt and sandstone
(d) Limestone, basalt and shale
Answer:
(a) Clay, shale and chalk
B. Very Short Answer Type Questions
Question 1.
What do you mean by sea level?
Answer:
The surface of the earth is not uniform. There are huge mountains and deep valleys, vast stretches of plains and plateaus. This variation in terms of height and depth varies from high mountains to lowlands and sea-bed and is measured from a base line called the sea level.
Question 2.
Which is the highest point of the earth’s surface?
Answer:
Mount Everest in the Himalayas.
Question 3.
Which is the lowest point of the earth’s surface?
Answer:
The lowest point of the earth’s surface is the bottom of the Marina Trench in the Pacific Ocean.
Question 4.
Why is there no possibility of living organisms deep inside the earth?
Answer:
There is no possibility of any living organisms deep inside the earth because its temperature is very high.
Question 5.
What are the two main types of seismic waves?
Answer:
1. P-Wave or Primary Wave
2. S-Wave or Secondary Wave.
Question 6.
Mention one difference between sial and sima.
Answer:
Sial is made of lighter rock material and is on an average of 35 km beneath the continents. Sima, on the other hand, is made of heavier rock material and is on average of 4-7 km thick beneath the ocean.
Question 7.
What is the depth of the upper mantle?
Answer:
The upper mantle is upto 100 km in depth.
Question 8.
Give an example of hard rock.
Answer:
Granite.
Question 9.
Give an example of soft rock.
Answer:.
Clay or chalk.
Question 10.
What are the most common minerals that occur inside the earth?
Answer:
Iron, silver, gold, mica, bauxite and lead.
Question 11.
On what basis are minerals identified?
Answer:
Minerals are identified on the basis of their colour, hardness and lustre.
Question 12.
Name a few minerals which are of economic importance.
Answer:
Iron, gold, uranium, fertilizers, lead, etc.
C. Short Answer Type Questions
Question 1.
What is an earthquake? Write about it briefly.
Answer:
Earthquake is the shaking and trembling of the earth’s surface, caused by internal movements. The shock waves generated by an earthquake have their origin at a focus inside the earth. These waves, then, travel towards the earth’s surface in different directions and with different speeds. The speed of these waves depends upon the nature of the material they pass through.
Question 2.
What is a rock? Mention three features of rocks.
Answer:
A rock is a naturally occurring solid substance made up of a mixture of minerals.
Features of Rocks:
- They can be as hard as granite and as soft as clay or chalk.
- They are found in different shapes, sizes and colours.
- There are a variety of rocks found on the earth’s crust.
Question 3.
How are intrusive and extrusive rocks formed?
Answer:
Intrusive and extrusive rocks are two types of igneous rock. Extrusive Rocks. Lava is a fiery red molten magma coming out from the interior of the earth’s surface. When this molten lava comes on the earth’s surface, it rapidly cools down and becomes solid. Rocks formed in such a way on the crust are called extrusive igneous rocks. They have very fine grained structure. For example, basalt. Intrusive Rocks. Sometimes the molten magma cools down deep inside the earth’s crust. Solid rocks so formed are called intrusive igneous rocks. Since they cool down slowly they form large grains. For example, granite.
D. Long Answer Type Questions
Question 1.
Describe the different layers of the earth’s interior.
Answer:
The earth’s interior is made up of three layers –
(i) the crust
(ii) the mantle and
(iii) the core.
(i) Crust – It is the uppermost layer over the earth’s surface. It is the thinnest of all the layers. Beneath the sedimentary rocks of the solid earth, the rocks are such in sial i.e. silica + aluminium. Sial is made of a lighter rock material and is on an average of 35 km beneath the continents. Beneath the sial lies sima, rocks rich in silica and magnesium. Sima is made of heavier rock material and is on an average of 4-7 km thick beneath the ocean.
(ii) Mantle – Just beneath the crust lies the mantle which extends upto to a depth of 2900 km. below the crust. The entire mantle is not homogenous. The mantle is subdivided into two parts namely, the upper mantle and the lower mantle.
(iii) Core – It is the innermost layer of the earth. It has a thickness of 3,470 km. It is mainly made up of nickel and iron and is called nife (ni-nickel and fe-ferrous i.e., iron). The core is further divided into inner core and outer core.
Question 2.
Describe all the three types of rocks.
Or
Give an account of igneous, sedimentary and metamorphic rocks.
Answer:
There are three major types of rocks –
1. Igneous Rocks – The word ‘igneous’ means ‘coming out of life’. The igneous rocks are formed due to intensive heat and pressure where molten magma comes out and solidifies over the earth’s surface as lava. It is of two types—intrusive rocks and extrusive rocks.
- Intrusive rocks – Sometimes the molten magma cools down deep inside the earth’s crust. Solid rocks so formed are called intrusive igneous rocks. Since they cool down slowly, they form large grains. Granite is an example of such rock.
- Extrusive rocks-When the molten magma cools over the earth’s surface, it forms extrusive igneous rocks. Basalt is an example of extrusive rocks.
2. Sedimentary Rocks – The igneous rocks roll, crack and hit each other and are broken down into small rock pieces called sediments. These sediments are transported and deposited by wind, water, etc. These loose sediments are compressed and hardened to form layers of rocks. These types of rocks are called sedimentary rocks. Sandstone, limestone, clay, shale, chalk are some examples of sedimentary rocks. These rocks may contain fossils of plants, animals and other micro-organisms that once lived on them.
3. Metamorphic Rocks – Rocks which organically are igneous or sedimentary in nature, get changed in character and appearance due to heat and pressure. These types of rocks are called metamorphic rocks. For example, granite is igneous but changes into metamorphic as gneiss. The limestone is a sedimentary rock but changes into metamorphic as marble.
Question 3.
Draw a neat and labelled picture of the rock cycle.
Answer:
