WBBSE Solutions For Class 8 Geography Chapter 1 Interior Of The Earth Topic A Sources And Evidences About The Interior Of The Earth

Chapter 1 Interior Of The Earth

The radius of the earth is 6370 km.

Robinson Deep is the world’s deepest mine (3-4km deep). It is a gold mine located in South Africa.

The temperature of the earth increases at a rate of about 1°C per 33 meter depth.

The deepest artificial hole dug on the surface of the earth is in the Kola Peninsula in north-western Russia. It is 12km deep.

Magma is a substance of the earth’s interior that remains in a molten and viscous state due to tremendous heat and pressure, mixed with gas and vapour.

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When molten magma reaches the surface of the earth through any weak region or a fault, it is known as lava.

Temperature increases with depth in the result, the interior of the earth. As a tremendous heat is generated which remains stored inside the earth and is called geothermal energy.

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The measure of mass content in a unit volume of a substance is known as its density.

The average density of the earth is only 2.6-3.3 grams/cubic cm. The average density of the matter near the earth’s interior is 11 grams/cubic cm which can increase up to 13-14 grams/cubic cm at the center. The average density of the earth is 5.5 grams/ cubic cm with respect to artificial satellites.

Seismic waves reveal information about the interior of the earth.

P waves can travel through both solids and liquids.

S waves cannot travel through liquid or semi-liquid materials.

The earth’s interior has three layers.

The layer of rocks above the mantle is called the earth’s crust. It can be further divided into SIAL and SIMA.

The oceanic crust is a heavier layer composed of silicon and magnesium. This layer is known as SIMA.

The uppermost part of the crust which forms the base of the continents is composed of silicon and aluminum. Hence, this layer is known as SIAL.

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

Conrad’s discontinuity lies between SIAL and SIMA.

The layer just below the crust having the same density is known as the mantle. The mantle can be further divided into two layers-Crofesima and Nifesima.

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

The lower part of the mantle extending from about 700km-2000km is called Nifesima (Ni+Fe+Si+Ma) because it constitutes of nickel, iron, silicon, and magnesium.

The Mohorovicic discontinuity lies between the crust and the mantle.

The Repetti discontinuity lies between Crofesima and Nifesima.

The asthenosphere is a definite layer that lies on the upper part of the mantle consisting of substances that are molten and soft in nature.

Lithosphere is formed of the earth’s crust and upper part of the mantle.

The innermost layer which encircles the centre of the earth and is subsequent to the crust and the mantle is known as the core. It can further be divided into the inner core and the outer core.

The layer surrounding the centre of the earth is known as inner core. The layer which encircles the inner core is called outer core.

The Gutenberg discontinuity lies between the mantle and the core.

The Lehman discontinuity lies between the inner and the outer core.

Chapter 1 Topic A Sources And Evidence About The Interior Of The Earth Short Analytical Type Questions

Question 1. By what means has man got so much knowledge about the earth’s interior?
Answer:

Man Got So Much Knowledge About The Earth’s Interior:-

We have come to know about the interior of the earth from two types of sources.

These are discussed below

Direct sources:

  1. Deep cavities, bored on the crust to take out rock materials for research
  2. Analysis of the emitted lava
  3. Research on mineral content, chemical properties, and temperature of water from hot springs.

2. Indirect sources:

  1. Analysis of the speed of seismic waves.
  2. Besides this, the gravitational force proposed by Newton has already proved that the heavier and denser materials will be found as we move toward the centre of the earth.

Question 2. Why are we unable to reach the centre of the earth?
Answer:

We Unable To Reach The Centre Of The Earth:-

We cannot reach the centre of the earth due to the following reasons

Excessive temperature:

Temperature increases with increasing depth from the earth’s surface at a rate of about 1°C/33 metre, soaring as high as 5000°C at the core.

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Enormous pressure:

Pressure also increases with increasing depth. Due to tremendous pressure and weight of the overlying materials, it is not possible for us to reach the centre of the earth.

Lack of oxygen:

If we move from the crust to the core of the earth, there is a shortage of oxygen due to the non-existence of the atmosphere.

Question 3. Why do we not get any direct information about the earth’s interior?
Answer:

We Not Getting Any Direct Information About The Earth’s Interior:-

We have been able to gather information about the earth’s interior to some limited extent. A 12km deep hole is the deepest extent to which we have been able to reach the earth’s interior directly.

However, this depth is too negligible compared to the depth of the earth (6370 km). Beyond this accessed limit, we fail to gather knowledge about the earth’s interior directly due to enormous temperature and massive pressure inside the earth.

Thus, we have to depend on the indirect sources to know about the earth’s interior.

Question 4. What is geothermal energy?
Answer:

Geothermal Energy:-

Temperature increases with depth in the interior of the earth. Usually, temperature increases at a rate of 1°C per 33 m. This tremendous heat generated and stored inside the earth is called geothermal energy.

When electricity is generated using this geothermal energy, it is called geothermal power. This power is now utilised by many nations. For example, Iceland produces 30% of its total electricity using geothermal energy.

The USA is the leading producer of electricity from geothermal energy in the world.

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Question 5. The outer surface of the earth is cool, but the earth is hot inside. Why?
Answer:

The Outer Surface Of The Earth Is Cool, But The Earth Is Hot Inside

The earth came into existence about 460 crore years ago. It was a very hot ball of fire at that stage. With time, it gradually cooled developing a hard covering all around called the crust.

However, the innermost part of the earth is still hot. The temperature there is about 5000°C. This temperature and the tremendous pressure from the overlying layers have kept the centre of the earth in a solid state.

Question 6. What are the differences between magma and lava?
Answer:

Differences Between Magma And Lava:-

The differences between magma and lave are as follows

WBBSE Solutions For Class 8 Geography Chapter 1Interior Of The Earth Topic A Differences Between Magma And Lava

 

Chapter 1 Topic A Sources And Evidence About The Interior Of The Earth Short Answer Type Questions

Question 1. What lies underneath the hard surface on which we stand?
Answer: We stand on the hard surface of the earth, which is known as the crust. Just below the crust, there are hot, malten, semi-solid, and solid materials, up till the centre of the earth. These form the mantle and the core.

Beneath the surface on which we stand, there lies a layer of groundwater also.

Differentiate Between Magma And Lava

Question 2. Has anyone ever seen the interior of the earth?
Answer: Man has penetrated up to a depth of 12km into the earth’s interior. Beyond this limit, it is not possible for man to directly reach the interior of the earth due to enormous pressure and temperature.

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Thus, nobody has directly ever seen the interior of the earth.

Question 3. How much one has to dig up to see the centre of the earth?
Answer: To reach the centre of the earth, one has to dig a tunnel equal in length to the radius of the earth, i.e., 6370 km. Man’s greatest endeavour has been a 12km deep tunnel in the Kola Peninsula of north-western Russia. It is the longest artificial tunnel.

Question 4. How far has it been possible to know about the interior of the earth?
Answer: It is not possible to reach the interior of the earth directly in order to gather information about it. However, several branches of science such as Physics, Mathematics, Seismology have contributed greatly in studying the characteristics of the earth’s interior.

Question 5. What is magma?
Answer:

Magma:-

Magma is a substance of the earth’s interior that remains in a molten and viscous state due to tremendous heat and pressure, mixed with gas and vapour. The space under the crust that contains magma is called the magma chamber.

Question 6. What is lava?
Answer:

Lava:-

When molten magma reaches the surface of the earth through any weak region or a fault, it comes out in the form of lava. Thus, lava is actually an external appearance of magma on earth.

Question 7. Why is hot and molten lava ejected out of the crater of a volcano?
Answer:

Hot And Molten Lava Ejected Out Of The Crater Of A Volcano because:-

In the interior of the earth, temperature increases with increasing depth, soaring as high as 5000°C in the inner core. The pressure in this region is very high as well. Due to this, the rocks and minerals remain in a molten and viscous state.

By any chance, if there is a release of pressure, these hot and molten rock materials gush out through a vent in the form of lava which we term as a volcano.

Differentiate Between Magma And Lava

Question 8. What is a hot spring?
Answer:

Hot Spring:-

The groundwater stored in different layers of the earth gets heated and starts to boil when it comes in contact with geothermal heat.

When this hot and boiling water gushes out from underground through any weak zone or a crack on the earth’s surface, it is called a hot spring.

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Question 9. Why does boiling water come out of hot springs?
Answer:

Boiling Water Come Out Of Hot Springs:-

Temperature in the interior of the earth increases with depth and so, groundwater starts boiling under extreme heat. This water comes out through the faults on the earth’s surface as hot springs. For example- Manikaran in Himachal Pradesh has such a hot spring.

Question 10. Try to know about geothermal power stations located in different parts of India.
Answer: The geothermal power stations of India are

  1. Manikaran, Himachal Pradesh
  2. Puga Valley. Ladakh
  3. Tatapani, Chhattisgarh.

Question 11. What is your idea about the density of the earth?
Answer:

Idea About The Density Of The Earth:-

The measure of mass content in a unit volume of a substance is known as its density. Hence, the density of matter is the quantity of mass present in it, in an area of one cubic cm.

Similarly, the total mass content in the entire volume of the earth is known as the earth’s density. The average density of the earth is 5.5 grams/ cubiccm with respect to artificial satellites.

Question 12. What are the different types of seismic waves produced by earthquakes?
Answer:

Different Types Of Seismic Waves Produced By Earthquakes:-

There are three types of seismic waves produced by earthquakes

  1. Por primary waves
  2. S or secondary waves and
  3. L or surface waves.

Question 13. What do you mean by P wave?
Answer:

P Wave:-

The P or primary wave is the wave that can pass through both solid and liquid materials. It is the fastest wave to reach the epicenter of an earthquake.

Question 14. What is S wave?
Answer:

S Wave:-

The S or secondary wave travels through solid materials only. It cannot travel through liquid or semi-liquid materials. It reaches the epicenter of an earthquake just after P wave.

Question 15. What do you know about the interior of the earth?
Answer:

Interior Of The Earth:-

The interior of the earth refers to the layers of the earth that lie below its surface. It can be divided into three layers

  1. The core
  2. The mantle and
  3. The crust.

Question 16. What is a crater?
Answer:

Crater:-

The topmost outlet of a volcano through which lava is ejected is called a crater. Usually, a volcano has one main crater and several sub-craters.

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Question 17. What do you mean by L wave?
Answer:

L Wave:-

L wave is a surface wave moving parallel to the crust from the epicenter of an earthquake. Although it is slower than the P and S waves, it is the most destructive and violent of all the waves.

Chapter 1 Topic A Sources And Evidence About The Interior Of The Earth Multiple Choice Questions

Choose the correct option

Question 1. Robinson Deep is located in

  1. Australia
  2. Germany
  3. South Africa
  4. Argentina

Answer: 3. South Africa

Question 2. The deepest mine in the earth is a

  1. Coal Mine
  2. Diamond Mine
  3. Copper Mine
  4. Gold Mine

Answer: 4. Gold Mine

Question 3. The approximate age of the earth is

  1. 220 crore years
  2. 460 crore years
  3. 370 crore years
  4. 550 crore years

Answer: 2. 460 crore years

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Question 4. The average density of the earth’s surface is

  1. 2.6-3.3 gram/cubic cm
  2. 5.0-5.5 gram/cubic cm
  3. 11.0 gram/cubic cm
  4. 13-14 gram/cubic cm

Answer: 1. 2.6-3.3 gram/cubic cm

Question 5. The seismic wave that can penetrate all the layers in the interior of the earth, is the

  1. P wave
  2. L wave
  3. S wave
  4. R wave

Answer: 1. P wave

Question 6. Who wrote the book ‘Journey to the Centre of the Earth’?

  1. Agatha Christie
  2. H. G. Wells
  3. Jules Verne
  4. A. Huxley

Answer: 3. Jules Verne

Question 7. At present, the approximate age of the universe is about

  1. 1300 crore years
  2. 1500 crore years
  3. 1400 crore years
  4. 1600 crore years

Answer: 3. 1400 crore years

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Question 8. The most destructive surface is the- wave on the earth’s

  1. P wave
  2. S wave
  3. L wave
  4. X wave

Answer: 3. L wave

Chapter 1 Topic A Sources And Evidence About The Interior Of The Earth Fill In The Blanks

Question 1. Temperature increases by about 1°C for every ________ m increase in depth from the surface of the earth.
Answer: 33

Question 2. Geothermal energy produces approximately ________ % of the electricity in Iceland.
Answer: 30

Question 3. The degree of compactness of a substance is known as its ________.
Answer: Density

Question 4. The main source which provides knowledge about the interior of the earth is ________.
Answer: Seismic waves

Question 5. An important geothermal power plant of India is located in the state of ________.
Answer: Himachal Pradesh

Question 6. With the increase of temperature, the volume of a material ________.
Answer: Increases

Question 7. With the increase of pressure, the volume ________.
Answer: Decreases

Chapter 1 Topic A Sources And Evidence About The Interior Of The Earth Write True Or False

Question 1. The hot and molten material found inside the earth is called lava.
Answer: False

Question 2. Bakreshwar in West Bengal has a cold spring.
Answer: False

Question 3. The S wave can pass through both liquids and semi-solids.
Answer: False

Question 4. The P wave is the fastest among all the seismic waves.
Answer: True

Question 5. The P wave cannot probe into the core of the earth.
Answer: False

Question 6. Eruption of lava provides us with knowledge about the earth’s interior.
Answer: True

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Question 7. The S wave can pass through the core of the earth.
Answer: False

Question 8. Immense heat inside the earth can generate geothermal energy.
Answer: True

Question 9. Seismology is the study of earthquakes.
Answer: True

Question 10. The velocity of seismic waves depends on the density of the materials present inside the earth.
Answer: True

Question 11. The velocity of all types of seismic waves is the same.
Answer: False

Chapter 1 Topic A Sources And Evidence About The Interior Of The Earth Match The Columns

WBBSE Solutions For Class 8 Geography Chapter 1Interior Of The Earth Topic A Match the columns

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

Chapter 1 Topic A Sources And Evidence About The Interior Of The Earth Answer In One Or Two Words

Question 1. Where is the deepest artificial borehole of the world located?
Answer: Kola Peninsula in north-western Russia.

Question 2. At what rate does the temperature inside the earth increase?
Answer: 1°C per 33m of depth.

Question 3. Name the hot molten material found inside the earth.
Answer: Magma.

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Question 4. Which country in the world produces the maximum amount of electricity from geothermal energy?
Answer: The United States of America.

Question 5. Which waves help us to learn about the interior of the earth?
Answer: Seismic waves.

Question 6. Which waves can travel through any and every medium?
Answer: P waves.

Question 7. Which waves can pass only through solid medium?
Answer: S waves.

Question 8. Give another name for L waves.
Answer: Surface waves.

Chapter 1 Topic A Sources And Evidence About The Interior Of The Earth Choose The Correct Option

Question 1. The average density of the earth is

  1. 5.9gram/cubic cm
  2. 6.9 gram/cubic cm
  3. 5.5 gram/cubic cm
  4. 7.5 gram/cubic cm

Answer: 3. 5.5 gram/cubic cm

Question 2. Which of the following provides us with knowledge about the interior of the earth?

  1. Precipitation
  2. Wind velocity
  3. Human settlement
  4. Seismic waves

Answer: 4. Seismic waves

Chapter 1 Topic A Sources And Evidence About The Interior Of The Earth Fill In The Blanks

Question 1. S waves cannot penetrate the ________ of the earth.
Answer: Core

Question 2. Bakreswar in West Bengal has ________.
Answer: Hot springs

Chapter 1 Topic A Sources And Evidence About The Interior Of The Earth Write True Or False

Question 1. The inner part of the earth is easily accessible to man.
Answer: False

Question 2. Temperature decreases with the increase in depth inside the earth.
Answer: False

Chapter 1 Topic A Sources And Evidence About The Interior Of The Earth Answer The Following Questions

Question 1. What are the different types of seismic waves?
Answer:

Different Types Of Seismic Waves:-

There are three types of seismic waves produced by earthquakes

  1. Por primary waves
  2. S or secondary waves and
  3. L or surface waves.

Question 2. What are the different sources for acquiring knowledge about the earth’s interior?
Answer:

Different Sources For Acquiring Knowledge About The Earth’s Interior:-

The sources which provide us with knowledge about the earth’s interior are

  1. Volcanic eruptions
  2. Water from hot springs
  3. Digging boreholes and deep mining
  4. Nature of seismic waves.

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