WBBSE Solutions For Class 8 Geography Chapter 1 Interior Of The Earth Topic B Layers In The Interior Of The Earth

Chapter 1 Topic B Layers In The Interior Of The Earth Analytical Type Questions

Question 1. What do you know about the major layers in the interior of the earth? Give a detailed account of the crust.
Answer:

Major Layers in the interior of the earth:

The region from the crust to the core, which is equal to the average radius of the earth, i.e., 6370km, is called the interior of the earth. Below the earth’s surface, the density of materials goes on increasing.

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The interior of the earth can be divided into three layers

  1. Core
  2. Mantle and
  3. Crust.

WBBSE Solutions For Class 8 Geography Chapter 1 Interior Of The Earth Topic B Layers In The Interior Of The Earth Structure of the earth's interior

 

Crust:

The layer of rocks above the mantle is known as the earth’s crust. This layer is made up of lighter materials like silicon, aluminum, and magnesium, which has hardened due to differences in temperature and pressure.

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Constituents:

The crust is generally formed of igneous rocks like granite and basalt. The rocks of the crust are rich in various minerals. Soil lies on top of the crust.

The oxygen content of the earth’s crust is 47%, which is more than the amount present in the atmosphere. It can be found in the earth’s crust in different chemical compounds. Silicon is the second chief constituent of the earth’s crust.

Depth:

The depth of the crust is around 5km beneath the oceans and 60 km beneath the continents. So, the average depth of the crust is taken as 30km.

Temperature:

Of all the earth’s layers, the crust is the coolest.

Mobility:

An increase in temperature gives rise to a convection current in the asthenosphere, which makes the crust composed of lithospheric plates, move or drift.

 

WBBSE Solutions For Class 8 Geography Chapter 1 Interior Of The Earth Topic B Layers In The Interior Of The Earth The Earth's Crust

 

Divisions of the crust:

The crust can be divided into two parts- SIAL and SIMA.

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SIAL:

It is composed of silicon (Si) and aluminum (Al). It is basically the continental crust which is absent beneath the oceans and is composed of lighter rock materials like granite. It is, at places, 60 km deep. It is lighter than SIMA and is discontinuous.

SIMA:

The comparatively heavy part of the crust is called SIMA. It is formed of silicon (Si) and magnesium (Mg). The entire sea bed extends all over SIMA and so this is the oceanic crust.

This layer is mainly composed of basalt. The SIMA layer is 5 km deep with an average density of 2.9 grams/cubic cm.

Question 2. Give a detailed account of the mantle of the earth.
Answer:

Mantle Of The Earth:-

The layer just below the crust having the same density is known as the mantle. It constitutes of iron, chromium, silicon, magnesium, etc. It lies just above the core.

Divisions of the mantle:

Mantle has been divided into two parts- Nifesima or inner mantle and Crofesima or outer mantle. The inner mantle is named after its components— nickel (Ni), iron (Fe), silicon (Si) and magnesium (Mg).

Similarly, the outer mantle also gets its name from its constituent materials-chromium (Cr), iron (Fe), silicon (Si) and magnesium (Mg).

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Density:

The density of this layer ranges between 3.4-5.6 gram/cubic cm.

Depth:

The entire mantle extends up to a depth of 2900 km. The outer mantle lies between 30- 700km while the inner one lies between 700- 2900km.

Temperature:

The average temperature of the mantle is about 2000°C-3000°C.

 

Question 3. Give a detailed account of the earth’s core.
Answer:

Earth’s Core:-

The innermost layer which encircles the center of the earth and is subsequent to the crust and the mantle is known as the core. Due to the gravitational pull of the earth, heavier and denser materials gathered around its centre.

This layer is also called the centrosphere of the earth. The core is mainly made up of very heavy metals like nickel and iron and so it is called Nife (Ni-Fe).

Divisions of the core:

The core has been divided into two layers, based on temperature, pressure, and density.

These are

  1. The inner core and
  2. The outer core.

Inner core is the layer that lies surrounds the centre of the earth and the layer which encircles the inner core is called the outer core.

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The materials present in the outer core are semi-solid, while those in the inner core are solid due to tremendous overlying pressure. The density of the inner core is much greater than that of the outer one.

The outer core rotates around the axis of the earth in a semi-solid state. Ferrous elements in this layer, being in the viscous state, develop an electromagnetic field due to very high velocity. This has led to the formation of the magnetism of the earth.

Depth:

The depth of the core is 2900km- 6370 km, out of which the outer core is nearly 2900 km-5100km deep while the inner core is nearly 5100km-6370km deep.

Temperature:

The core records about 5000°C temperature. However, the temperature does not remain uniform throughout the core.

 

WBBSE Solutions For Class 8 Geography Chapter 1 Interior Of The Earth Topic B Layers In The Interior Of The Earth Core of the earth

 

Density:

Although the density is not uniform throughout the core, the average density ranges from 9.1-13.1 grams/cubic cm.

Question 4. Compare the three layers of the earth’s interior.
Answer: A comparative study of the layers there of the earth’s interior is given in the following table

WBBSE Solutions For Class 8 Geography Chapter 1 Interior Of The Earth Topic B Layers In The Interior Of The Earth Layers there of the earth's interior

 

Chapter 1 Topic B Layers In The Interior Of The Earth Short Analytical Type Questions

Question 1. Write the differences between SIAL and SIMA.
Answer: The differences between SIMA and SIAL are

WBBSE Solutions For Class 8 Geography Chapter 1 Interior Of The Earth Topic B Layers In The Interior Of The Earth Differences between SIMA, SIAL

 

Question 2. Give a short account of the lines of discontinuity between various layers of the earth’s interior.
Answer:

The Lines Of Discontinuity Between Various Layers Of The Earth’s Interior:-

The place of separation where the seismic waves change their velocity from the crust to core, is called a line of discontinuity.

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There are five such lines

  1. Gutenberg Discontinuity: This exists between the core and mantle.
  2. Mohorovicic Discontinuity: This exists between the mantle and the crust.
  3. Conrad Discontinuity: This exists between the SIAL and SIMA layers.
  4. Lehman Discontinuity: between the inner core and the outer core.
  5. Repetti Discontinuity: This exists between the Nifesima and the Crofesima.

Question 3. What do you know about the asthenosphere?
Answer:

Asthenosphere:-

Asthenosphere is a definite layer that lies on the upper part of the mantle consisting of substances that are molten and soft in nature. The major plates of the earth float on this layer.

Scientists have not yet been able to define the uppermost or the lowest borders of the asthenosphere. They have developed some idea about it only after doing research on P and S waves and their movements.

It is expected that the asthenosphere can extend up to a depth of about 100-250km. P and S waves slow down here and so it is called a ‘slow layer.

 

WBBSE Solutions For Class 8 Geography Chapter 1 Interior Of The Earth Topic B Layers In The Interior Of The Earth Asthenosphere

 

Question 4. Write the differences between the outer core and the inner core.
Answer:

The differences between the outer and inner core are

WBBSE Solutions For Class 8 Geography Chapter 1 Interior Of The Earth Topic B Layers In The Interior Of The Earth Differences between Out and Inner Core

 

Question 5. Though the mantle and the core have nearly the same thickness, the mantle occupies 84% of the total volume of the earth. Can you say how this has happened?
Answer:

Though the mantle and the core have nearly the same thickness, the mantle occupies 84% of the total volume of the earth.

The mantle extends to about 2900 km below the earth’s crust. Below the mantle, the core covers a region which is about 3500km in radius. The core contains the heaviest metals of the earth-iron and nickel.

As they have very high density, they remain compact. On the other hand, the constituents of the mantle (Cr, Fe, Si, Mg) are less dense, and hence they spread over a larger area. So, the mantle makes up about 84% of the earth’s volume.

Earth’s Discontinuity

Question 6. Why does density vary in different layers of the Interior of the Earth?
Answer:

Density Vary In Different Layers Of The Interior Of The Earth:-

We all know that the different layers of the earth have different densities. For example, the upper layer of the crust has an average density of 2.9 grams/cubic cm, the average density of mantle is 3.4-5.6 gram/cubic cm and that of the core is 9.1-13.1 gram/cubic cm.

The main causes behind this varying densities are as follows

Class 8 Geography Chapter 8 Question Answer

Heavier materials gather in the centre of the earth, while lighter materials move away due to the rotation of the earth.

The earth is gradually cooling and in this process, the heavier materials are slowly settling down towards the centre of the earth.

Question 7. Explain the convection current in the asthenosphere with the help of a simple experiment.
Answer:

Convection Current In The Asthenosphere

The substances of the asthenosphere are in a molten state. These move up and down by the process of convection. The tectonic plates floating on the asthenosphere drift apart due to this process. This can be proved by a simple experiment.

Earth’s Discontinuity

 

WBBSE Solutions For Class 8 Geography Chapter 1 Interior Of The Earth Topic B Layers In The Interior Of The Earth Convection Process

 

Experimental procedure:

A wide glass beaker full of water is taken and two light wooden blocks are placed in the beaker. The entire setup is then put on a stove and after a while, it is seen that, water gets heated and starts rising up from the bottom.

As the water gradually gets heated up, the pieces of wood move away from their previous positions along the edge of the beaker.

Inference:

Similarly, the process of convection goes on in the asthenosphere which ultimately makes the plates move.

Question 8. Draw a diagram showing the layers of the earth’s interior.
Answer: The diagram showing the layers of the earth’s interior is given below

 

WBBSE Solutions For Class 8 Geography Chapter 1 Interior Of The Earth Topic B Layers In The Interior Of The Earth Layers of The Earth interior

 

Chapter 1 Topic B Layers In The Interior Of The Earth Short Answer Type Questions

Question 1. Why do the matters lying close to the earth’s centre have greater density?
Answer:

Matters Lying Close To The Earth’s Centre Have Greater Density:-

The core of the earth is composed of heavy metals like iron and nickel. During the formation of the earth, hot and denser matter moved towards the earth’s centre due to its gravitational pull.

The lighter materials, on the other hand, like silicon ad aluminium stayed afloat and later solidified to form the crust. So, all the denser materials are lying close to the earth’s centre.

Question 2. What do you mean by crust of the earth?
Answer:

Crust Of The Earth:-

The layer of rocks above the mantle is known as the earth’s crust. Its main constituents are silicon, aluminium, and magnesium. It is a very thin layer with an average depth of 30km.

Class 8 Geography Chapter 8 Question Answer

Question 3. What do you mean by SIMA?
Answer:

SIMA:-

The oceanic crust is a comparatively heavy layer and mainly consists of igneous rocks like basalt. It is composed of silicon (Si) and magnesium (Mg). This layer is thus known as SIMA. The average density of this layer is 2.9 grams/cubic cm.

Question 4. What do you mean by SIAL?
Answer:

SIAL:-

The uppermost part of the crust which forms the base of the continents, is the lightest of all the layers. It mainly consists of granite. It is composed of silicon (Si) and aluminum (Al).

Hence, this layer is known as SIAL. It is a discontinuous layer and is also lighter than SIMA.

Question 5. What are lines of discontinuity?
Answer:

Lines Of Discontinuity:-

The places between the crust and the core where the seismic waves change their velocity, are called lines of discontinuity. There are several lines of discontinuity such as, Conrad discontinuity, Mohorovicic discontinuity, etc.

Question 6. Define Crofesima.
Answer:

Crofesima:-

The mantle extends from 30km-2900km, out of which, the upper part of the mantle extends from 30km-700km. This layer constitutes of chromium, iron, silicon, magnesium, etc., and hence, it is called Crofesima (Cro+Fe+Si+Ma).

Question 7. Define Nifesima.
Answer:

Nifesima:-

The lower part of the mantle, extending from about 700km-2900 km, is called Nifesima (Ni+Fe+Si+Ma), since it constitutes of nickel, iron, silicon, and magnesium.

Question 8. What are the constituents of the various layers of the earth’s interior?
Answer: The constituents of the various layers of the earth’s interior are as follows

WBBSE Solutions For Class 8 Geography Chapter 1 Interior Of The Earth Topic B Layers In The Interior Of The Earth Layers

 

Chapter 1 Topic B Layers In The Interior Of The Earth Multiple Choice Questions

Choose The Correct Option

Question 1. The hard outer surface of the earth is called

  1. Plate
  2. Nife
  3. Crust
  4. Soil

Answer: 3. Crust

Question 2. The principal rock that forms the oceanic crust is

  1. Mudstone or shale
  2. Basalt
  3. Granite
  4. Dolorite

Answer: 2. Basalt

Question 3. The SIAL layer is made up of

  1. Granite
  2. Limestone
  3. Basalt
  4. Mudstone/Shale

Answer: 3. Basalt

Question 4. ________ is seen in between SIAL and SIMA layers.

  1. Gutenberg discontinuity
  2. Conrad discontinuity
  3. Moho discontinuity
  4. Lehman discontinuity

Answer: 4. Lehman discontinuity

Question 5. The distance of the mantle from the crust is about

  1. 6371km
  2. 2900km
  3. 5100km
  4. 2500km

Answer: 2. 2900km

Class 8 Geography Chapter 8 Question Answer

Question 6. The temperature of the mantle is about

  1. 1000°C-2000°C
  2. 2000°C-3000°C
  3. 5000°C-6000°C
  4. 6000°C-7000°C

Answer: 2. 2000°C-3000°C

Question 7. The upper part of the mantle (30km- 700km) is known as

  1. Nifesima
  2. Nife
  3. Crofesima
  4. SIAL

Answer: 3. Crofesima

Question 8. The lower layer of the mantle (700km- 2900km) is called

  1. Nifesima
  2. SIMA
  3. Crofesima
  4. SIAL

Answer: 1. Nifesima

Question 9. The depth of the lithosphere is about

  1. 200km
  2. 100km
  3. 50km
  4. 20km

Answer: 2. 100km

Question 10. The innermost layer of the earth is the

  1. Core
  2. Nifesima
  3. Mantle
  4. Crofesima

Answer: 1. Core

Question 11. The average density of the core is

  1. 1-5.5 gram/cubic cm
  2. 5.5-9.7 gram/cubic cm
  3. 9.1-13.1 gram/cubic cm
  4. 8.5-16.2 gram/cubic cm

Answer: 3. 9.1-13.1 gram/cubic cm

Question 12. Due to extreme heat and pressure, the materials of the inner core remain

  1. In a liquid state
  2. In a dense and elastic state
  3. In a solid state
  4. In a gaseous state

Answer: 3. In a solid state

Question 13. The distance of the core from the crust or the earth’s surface is

  1. 2900km
  2. 100km
  3. 6370km
  4. 4000km

Answer: 3. 6370km

Question 14. The depth of the core is about

  1. 4000km
  2. 3470km
  3. 2800km
  4. 99km

Answer: 2. 3470km

Question 15. The radius of the earth from the centre to the surface is about

  1. 6400km
  2. 6434km
  3. 6370km
  4. 6390km

Answer: 3. 6370km

Question 16. The radius of the core is about

  1. 2895km
  2. 3500km
  3. 3470km
  4. 6720km

Answer: 3. 3470km

Question 17. The outer core and the inner core are separated by

  1. Conrad discontinuity
  2. Gutenberg discontinuity
  3. Lehman discontinuity
  4. Mohorovicic discontinuity

Answer: 3. Lehman discontinuity

Question 18. 84% of the total area of the earth is occupied by the

  1. Core
  2. Mantle
  3. Lithosphere
  4. Hydrosphere

Answer: 2. Mantle

Class 8 Geography Chapter 8 Question Answer

Chapter 1 Topic B Layers In The Interior Of The Earth Very Short Answer Type Questions Fill In The Blanks

Question 1. The oceanic floor, formed of silica and magnesium, is called ________.
Answer: SIMA

Question 2. The crust below the continents has a depth of ________ km.
Answer: 60

Question 3. The average depth of the earth’s crust is about ________ km.
Answer: 30

Question 4. The layer between the core and the crust of the earth is called ________.
Answer: Mantle

Question 5. The mantle extends up to a depth of ________ km from the surface of the earth.
Answer: 2900

Question 6. The outer part of the mantle is called ________.
Answer: Crofesima

Question 7. Nifesima is the ________ part of the mantle.
Answer: Inner

Question 8. The surface of separation between the mantle and the crust of the earth is called ________ Discontinuity.
Answer: Mohorovicic

Question 9. The lithosphere has a depth of ________ km.
Answer: 100

Question 10. The core is formed of ________ and ________.
Answer: Nickel, ferrous(iron)

Question 11. The approximate temperature of the centrosphere is about ________ °C.
Answer: 5000

Question 12. The average density of the core ranges from ________ gram/cubic cm.
Answer: 9.1-13.1

Question 13. The surface of separation between the core and the mantle is called ________ Discontinuity.
Answer: Gutenberg

Question 14. The constituents of the core are in a molten state but those of the mantle are in a ________ state.
Answer: viscous

Question 15. The distance between the crust and the core of the earth is ________ Km.
Answer: 6370

Question 16. The centrosphere is also known as ________.
Answer: Core/Nife

 

Write True Or False

Question 1. The distance between the centre and the surface of the earth is the same as the radius of the earth.
Answer: True

Question 2. The average temperature inside the earth is about 115°C.
Answer: False

Question 3. The primary constituents of the core are silicon and magnesium.
Answer: False

Question 4. A portion of the earth’s crust (47%) constitutes of nitrogen.
Answer: False

Question 5. Convection currents in the asthenosphere cause the movement of the crustal plates.
Answer: True

Question 6. A weak layer called the asthenosphere lies just above the core.
Answer: False

Question 7. The Conrad Discontinuity separates SIAL and SIMA.
Answer: True

Question 8. The Mohorovicic Discontinuity separates Crofesima and Nifesima.
Answer: False

Question 9. The SIAL layer is basically formed of igneous rocks like granite.
Answer: True

Question 10. The SIAL is actually the oceanic crust.
Answer: False

Question 11. The crust lies above all other layers of the interior of the earth.
Answer: True

Question 12. The approximate temperature at a depth of 30km from the surface of the earth will be 760°C.
Answer: False

Question 13. The SIAL is made up of silicon, aluminum, and iron.
Answer: False

Question 14. The crust comprises of oxygen, silicon, aluminium, etc.
Answer: True

Question 15. The approximate temperature of the mantle is about 15000°C.
Answer: False

Question 16. The earth’s crust is hard and solid and the outer core is semi-solid.
Answer: True

Question 17. The core consists of metals like iron and nickel and so the earth has magnetic property.
Answer: True

Question 18. The SIMA layer is also called the asthenosphere.
Answer: False

Question 19. The radius of the earth’s core is about 3470km.
Answer: True

Question 20. The mantle is basically composed of nickel, chromium, magnesium, iron, and silicon.
Answer: True

 

Chapter 1 Topic B Layers In The Interior Of The Earth Match The Columns

1.WBBSE Solutions For Class 8 Geography Chapter 1 Interior Of The Earth Topic B Layers In The Interior Of The Earth Match the Following 1

Answer: 1. B, 2. E, 3. D, 4. C, 5. A

2.WBBSE Solutions For Class 8 Geography Chapter 1 Interior Of The Earth Topic B Layers In The Interior Of The Earth Match the Following 2

Answer: 1. E, 2. C, 3. A, 4. D, 5. B

 

Answer In One Or Two Words

Question 1. How many layers are there in the interior of the earth and what are they?
Answer: Three layers-core, mantle and crust.

Question 2. What does oceanic crust mainly consist of?
Answer: Basalt.

Question 3. What is continental crust made up of?
Answer: Granite.

Question 4. Which one is heavier magnesium or aluminum?
Answer: Aluminium (Density of aluminium > Density of magnesium).

Question 5. Name the layer that lies above the core and below the crust.
Answer: Mantle.

Question 6. What are the divisions of the mantle?
Answer: Nifesima and Crofesima.

Question 7. What is the depth of the lithosphere?
Answer: 100km.

Question 8. In which sphere of the earth’s interior do seismic waves have the lowest velocity?
Answer: Asthenosphere.

Question 9. Where does the Lehman Discontinuity exist?
Answer: Between inner and outer core.

 

Choose The Correct Option

Question 1. The layer between Conrad discontinuity and Mohorovicic discontinuity is called-

  1. Sial
  2. Inner core
  3. Sima
  4. Outer core

Answer:  3. Sima

Question 2. Aesthenosphere originates from a-

  1. Greek word
  2. German word
  3. Russian word
  4. Italian word

Answer: 1. Greek word

Question 3. Convection currents in magma is found in-

  1. Sial
  2. Lower mantle
  3. Upper mantle
  4. Inner core

Answer: 3. Upper mantle

Question 4. Diameter of the earth is about-

  1. 6370km
  2. 3185 km
  3. R 6371km
  4. 12740km

Answer:  4. 12740km

 

Fill In The Blanks

Question 1. The plane of separation between the inner core and the outer core is the _________ discontinuity.
Answer: Lehman

Question 2. The main constituents of the core are __________ and _________.
Answer: Nickle, iron

 

Write True or False

Question 1. Different discontinuities are named after the person who discovered them.
Answer: True

Question 2. We know more about the mantle and the core than the earth’s crust.
Answer: False

 

Answer In One Or Two Words

Question 1. Which layer inside the earth is also known as the ‘zone of low velocity’?
Answer: Asthenosphere

Question 2. Who first coined the terms SIAL and SIMA?
Answer: Edward suess

Question 3. Write the name of a layer present inside the earth which can deflect seismic waves.
Answer: Outer core

Question 4. What does oceanic crust mainly consist of?
Answer: Basalt

 

Answer The Following Questions

Question 1. What do you mean by a line of discontinuity?
Answer:

Line Of Discontinuity:-

The places between the crust and the core where the seismic waves change their velocity, are called lines of discontinuity. There are several lines of discontinuity such as, Conrad discontinuity, Mohorovicic discontinuity, etc.

Question 2. Why does the earth have a magnetic field?
Answer:

The Earth Have A Magnetic Field:-

Due to immense heat and pressure, the outer core is in a semi-solid condition. It rotates around the axis of the earth. Ferrous elements of this layer being in develops electromagnetic field due to high velocity which, in turn, forms the magnetism of the earth.

Question 3. Differentiate between Crofesima and Nifesima.
Answer:

Differentiate Between Crofesima And Nifesima:-

WBBSE Solutions For Class 8 Geography Chapter 1 Interior Of The Earth Topic B Layers In The Interior Of The Earth Difference between Crofesima and Nifesima

 

Question 4. Write the characteristics of the core of the earth.
Answer:

The characteristics of the core are

  1. It is almost 3500 km thick,
  2. It is composed of very heavy metals like Nickel (Ni) and Iron (Fe). Thus, it is also known as Nife.
  3. The average density of this layer ranges from 9.1-13.1 gram/ cubic cm.
  4. Average temperature of this layer is about 5000°C.
  5. Density, temperature, and pressure do not remain uniform throughout the core.

 

Chapter 1 Topic B Layers In The Interior Of The Earth Conceptual Questions And Answers

 

Who am I?

 

Question 1. ‘I lie below the oceans and at the base of the continents for about 5km-60km. I am composed of Si, Mg, Al, etc.-Who am I?
Answer: Crust of the earth

Question 2. ‘I am an oceanic crust, formed of silica and magnesium. I am mainly basaltic in nature.’ -Who am I?
Answer: SIMA

Question 3. I am the surface of separation between SIAL and SIMA. After studying S and P waves, an Austrian geologist had proved my existence.’ Who am I?
Answer: Conrad Discontinuity

Question 4. I am the central part of the earth, made up of Ni and Fe, and having an average temperature of 5000°C.’-Who am I?
Answer: Core of the earth

 

Scrambled Words

1. R D C N O A
2. S E H A N T S E O E R P H
3. N R I N E C R E O
4. I C M G A E N T
5. T R E N H S O C R E P E

Answers:

  1. CONRAD
  2. ASTHENOSPHERE
  3. INNER Core
  4. MAGNETIC
  5. CENTROSPHERE

 

Fill Up The Blanks In The Knowledge Hive

Question 1. Fill up the blanks in the knowledge hive with information on the Mantle.

 

WBBSE Solutions For Class 8 Geography Chapter 1 Interior Of The Earth Topic B Layers In The Interior Of The Earth Fill up the blanks

Answers:

  1. It extends till 2900km under the earth’s crust.
  2. The upper layer of the mantle is called asthenosphere.
  3. The density of this layer is 3.4- 5.6 gram/cubic cm.
  4. It can be further divided into two layers-Crofesima and Nifesima.
  5. The temperature of this layer is about 2000°C-3000°C.

 

Answer With Reference To The Illustration

Question 1. The layers of the earth’s interior are given in the diagram below. Write the name of each layer marked 1, 2, 3, 4.

 

WBBSE Solutions For Class 8 Geography Chapter 1 Interior Of The Earth Topic B Layers In The Interior Of The Earth earth layers

Answers:

  1. Crofesima
  2. Nifesima
  3. Outer core
  4. Inner core

2. Write the names of the different layers of the earth and the lines of discontinuity in the given diagram.

 

WBBSE Solutions For Class 8 Geography Chapter 1 Interior Of The Earth Topic B Layers In The Interior Of The Earth Different Layers of the earth

Answers:

  1. SIAL
  2. Conrad Discontinuity
  3. SIMA
  4. Mohorovicic Discontinuity
  5. Gutenberg Discontinuity
  6. Lehman Discontinuity
  7. Upper mantle
  8. Lower mantle
  9. Outer core
  10. Inner core

 

Crossword

 

WBBSE Solutions For Class 8 Geography Chapter 1 Interior Of The Earth Topic B Layers In The Interior Of The Earth Crossword

 

CLUES

Down:

1. Upper layer of the earth’s crust.
3. Hot and molten material below the crust that forms lava on cooling.

Across:

2. Lower layer of the earth’s crust.
4. Layer between the earth’s crust and the outer core.
5. One of the chief constituents of the SIAL layer.

Answers:

Down:

1. SIAL
3. MAGMA

Across:

2. SIMA
4. MANTLE
5. ALUMINIUM

 

Chapter 1 Topic B Layers In The Interior Of The Earth Advanced Questions And Answers

Question 1. Discuss the mechanism of capturing geothermal energy and also state the advantages and disadvantages of this energy.
Answer:


Mechanism Of Capturing Geothermal Energy:

Heat generated and stored inside the earth is called geothermal energy. This energy can be used to generate electrical energy which can be used for various purposes.

Earth Discontinuity

In areas of hot springs and volcanic regions, wells are dug to obtain the rising hot water and steam. This steam is then used to rotate a turbine which, in turn, is connected to a generator that generates electricity.

Capturing Geothermal Energy Advantages:

  1. It is a renewable and non-exhaustible form of energy.
  2. It does not cause environmental pollution.
  3. There is no wastage of energy and the maintenance cost is also very low.

Capturing Geothermal Energy Disadvantages:

  1. The initial cost of setting up the necessary infrastructure is very high.
  2. Per unit cost of production is also high.
  3. It can only meet the needs of the locally situated consumers.

Question 2. Why is the asthenosphere also known as a ‘Low-Velocity Zone’?
Answer:

The Asthenosphere Also Known As A ‘Low-Velocity Zone’:-

Immediately beneath the lithosphere, at a depth of 100km-250 km, a definite soft and molten layer is present. This is known as the asthenosphere.

This layer lies on the upper mantle. Seismic waves (P and S waves) pass relatively slowly through this layer, as compared to the overlying lithosphere. Thus, this layer is called a ‘Low-velocity Zone’ (LVZ).

Question 3. Why is the asthenosphere called a sphere of agitation or eruptions?
Answer:

Asthenosphere Called A Sphere Of Agitation Or Eruptions:-

The asthenosphere lies on the upper part of the mantle and is composed of substances that are soft and molten in nature. Magma originates in this layer due to changes in temperature and pressure in the interior of the earth.

This magma erupts through the weaker regions or faults on the surface. Landforms also change after these eruptions and so this is called a sphere of agitation or eruptions.

Chapter 1 Topic B Layers In The Interior Of The Earth Formative

Participation

This segment will indicate how much the students have actively participated and taken initiative during the class.

The interior of the Earth is made up of several layers. With reference to this, answer the following:

Question 1. How can we know about the interior of the earth?
Answer: By analysing seismic waves/ Lava from volcanic craters/…….

Question 2. How do we know that the interior of the earth is hot?
Answer: From volcanic eruptions/ Water coming out from hot springs/…

Question 3. What are the different types of seismic waves?
Answer: P wave/ S wave /…

Question 4. What are the different divisions in the interior of the earth?
Answer: The crust/ The mantle/ The core.

Question 5. Name some seismologists who discovered various discontinuities inside the earth.
Answer: Conrad/ Gutenberg/ Lehman/…

Question 6. What are the major elements present in the interior of the earth?
Answer: Iron/ Oxygen/ Silicon/…..

Question 7. How does pressure and temperature change as we proceed to the interior of the earth?
Answer: Pressure increases as we proceed further inside the earth/ Temperature increases as we proceed further inside the earth.

Interpretation And Application

This segment will test whether the students have understood the topics, or whether they are just mugging up.

Question 1. Take an iron plate and an aluminium plate of same dimension on your hand and see which one weighs heavier and why?
Answer: The iron plate weighs heavier than the aluminium plate due to greater density of the iron plate. Density of iron is 7.873 gram/cubic cm whereas that of aluminium is 2.70 gram/cubic cm.

This is the reason why an iron plate weighs more than an aluminium plate of same dimension.

Question 2. Imagine how thin the skin is with respect to the whole apple. Which portion of the apple is compared with the mantle? Which part of an apple resembles the core?
Answer:

  1. The skin of the apple can be compared to the Earth’s crust
  2. The flesh of the apple can be compared to the mantle
  3. The core of the apple, where the seeds lie can be compared to the earth’s core.

 

 

WBBSE Solutions For Class 8 Geography Chapter 1 Interior Of The Earth Topic B Layers In The Interior Of The Earth Apple

 

Question 3. You have an idea about the exterior and interior of the earth. Which one attracts you more and why?
Answer: We live on the earth’s surface. We regularly get to see different kinds of landforms, flora and fauna. We see the lofty mountains, deserts, oceans and seas and diversity among the plants and animals.

We also get to see different human races and cultures of the world. All these things are known to us. In comparison to the exterior of the earth, the interior of the earth is quite unknown.

Nobody has been able to penetrate to the centre of the earth. We have to depend on the indirect sources to know about the interior of the earth. So, the exterior of the earth is more fascinating.

Question 4. If temperature increases by 1°C for every 33m increase in depth inside the earth, what will be the temperature of the Robinson Deep? [Average temperature on the earth’s surface = 15°C]
Answer: Depth of the Robinson Deep = 3km = 3000m
We know, for every 33m of depth, temperature increases by 1°C
∴ For every 1m of depth, temperature increases by 1/33°C
∴ For every 3000m of depth, temperature increases by 3000/33°C = 90.90°C
∴ Temperature of the Robinson Deep = 90.90°C + 15°C 105.90°C

Question 5.Find out the density of the compounds (Silicon, Aluminium, Magnesium, Iron, Chromium, Nickel) available in different layers of the earth. If required, you can take help from your teacher or your Geography book. Make a list of these compounds according to their density. Check that your list matches the division of layers of the interior of the earth.
Answer:

 

WBBSE Solutions For Class 8 Geography Chapter 1 Interior Of The Earth Topic B Layers In The Interior Of The Earth compounds

Surface of the earth:

It has two layers

  1. SIAL is composed of silicon and aluminium, even though aluminium’s density is more than that of magnesium.
  2. SIMA is composed of silicon and magnesium and is present beneath the SIAL. The elements in this layer have some impurities, which lead to the increase in their densities as compared to the elements of the SIAL layer.

These two layers are light, i.e., their average density is 2.2-2.9 gram/cubiccm. Thus, they form the outermost layer of the interior of the earth.

The mantle:

The outer mantle consists of silicon, magnesium, iron, and chromium. The inner mantle consists of silicon, magnesium, iron, and nickel.

The core:

It is composed of only the heaviest metals-nickel and iron. Thus, this layer is situated at the center of the earth.

Aesthetics And Creativity

This segment will check the aesthetic sense and creativity of the students.

Question 1. Make a collage by collecting incidents of volcano, earthquakes, hot springs in West Bengal or India.
Answer: A collage is made by collecting incidents of volcano, earthquakes, and hot springs in West Bengal and India-

WBBSE Solutions For Class 8 Geography Chapter 1 Interior Of The Earth Topic B Layers In The Interior Of The Earth incidents of valcano, earthquakes

Question 2. Take some cobbles, stones, and soil. Fill half a glass with water. Pour all those materials into the glass, stir them, and see what happens.
Answer:

Experimental procedure:

A clean, transparent glass with half filled water is taken. Some cobbles, stones, and soil are put into the glass and stirred thoroughly.

Observation:

The glass is left undisturbed for more than 10 minutes so that the contents in it may settle down. It is seen that the cobbles are in the bottom layer of the glass, while the stones are in the middle layer, and the soil sits at the top. Above all a layer of clear water is seen.

Conclusion:

It is understood from this experiment that cobbles are the heaviest and densest. So the bottom part of the glass is occupied by them. Next is the stone layer which occupies the middle part.

Soil particles are the lightest and so they appear at the top. Thus, it can be said that denser materials settle at the bottom due to gravitational pull while lighter materials float on the top.

WBBSE Solutions For Class 8 Geography Chapter 1 Interior Of The Earth Topic B Layers In The Interior Of The Earth Set up of The experiment

Resemblance with the earth’s structure:

Different constituents of the earth’s interior are also arranged according to their density from the earth’s crust to the centre of the earth.

Similar to the observation of the above experiment, the denser materials (iron and nickel) are found near the earth’s core whereas the lighter materials (aluminium and silicon) are found near the earth’s crust.

Question 3. Make a model of the earth’s interior with the help of a thermocol.
Answer:

1. Thermocol Materials required:

Thermocol, knife, colours, brushes, chart papers, scissors, and glue.

WBBSE Solutions For Class 8 Geography Chapter 1 Interior Of The Earth Topic B Layers In The Interior Of The Earth A model Of the earth interior

 

2. Thermocol Procedure:

  1. A spheroidal thermocol is taken and triangular section is cut out of it from the surface.
  2. The edges are left uneven to make it similar with the surface of the earth.
  3. Next, lines are drawn to demarcate different layers of the earth’s interior on the inner side of the spheroid.
  4. These are then painted individually.
  5. Finally, labellings are done on the chart papers and stuck on the model.

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