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Chapter 4

Earth's Structure

Class 9 - Veena Bhargava Geography Solutions

Answer the following questions

Question 1

What do you understand by lithosphere?

Answer

Earth's outer shell of crystalline surface rock, ranging from 4 to 48 km in thickness from oceanic crust to mountain ranges is known as lithosphere.

Question 2

Name the two layers of lithosphere.

Answer

The two layers of lithosphere are:

  1. Sial
  2. Sima

Question 3

What do you understand by mantle?

Answer

It is the layer of silicate rock between the crust and the outer core. The depth of Mantle varies between 35 to 2900 km. It consists of dense and rigid rocks containing magnesium and iron. The Mantle is divided into two parts:

  1. the Upper Mantle or Asthenosphere
  2. the Lower Mantle or the Mesosphere

Question 4

What is the position of mantle in the Earth?

Answer

The mantle layer lies between the crust and the core of earth. Its upper boundary is marked by Mohorovicic Discontinuity and its lower boundary is marked by the Gutenburg Discontinuity.

Question 5

What is core? By what other name is it known as?

Answer

The central part of earth that probably consists of dense nickel and iron alloy (Nife) is known as core. It is also known as Barysphere. It's temperature is estimated to be about 2700°C.

Question 6

State the composition of the SIAL layer.

Answer

SIAL layer consists of Silica and Aluminium.

Question 7

State the properties of the core of the Earth.

Answer

The properties of the core of the Earth are:

  1. It consists of Nickel and Iron with a temperature estimated to be 2700°C.
  2. The inner core also consists of nickel and iron and is forced into a solid state by increased pressure.

Question 8

What is Earth’s crust composed of?

Answer

The earth's crust consists of two layers - SIAL and SIMA.

The material of the upper or continental part of the earth's crust, characterized by relatively low density is called the SIAL layer.The SIAL layer has predominance of Silica and Aluminium. It is also known as granite layer which floats on SIMA.

The lowest layer of the earth's outer crust that underlies the SIAL is SIMA layer. It consists of Silica and Magnesium and it is also known as basaltic layer.

Question 9

What does 'Nife' mean?

Answer

'Nife' is the name given to the core of the Earth as it is rich in Nickel and Ferrous(iron) alloy.

Question 10

Why does the temperature increase as we go down(underground)?

Answer

High pressure in the interior of the earth exercises a powerful influence on the temperature and physical state of the earth. The temperature of the earth's interior goes on increasing at the rate of 1°c for every 32 metres. Thus, the temperature increase as we go down(underground).

Question 11

How does Sial differ from Sima?

Answer

S.
No.		SialSima
1.This is the uppermost layer of the earth's crust.This is below the Sial layer.
2.Its thickness is nearly 20 km.Its average thickness is about 25 to 30 km.
3.It is composed of Silica(Si) and Aluminium(Al).It is composed of Silica(Si) and Magnesium(Mg).
4.It is not a continuous layer. It is not found on ocean basin.It is a continuous layer.
5.It is less dense.It is more dense.
6.It is Granite layer.It is Basaltic layer.

Question 12

Name the two most important and abundant chemical elements present in the Earth's crust.

Answer

The two most important and abundant chemical elements present in the Earth's crust are Silica and Oxygen.

Question 13

What is meant by Mohorovicic Discontinuity?

Answer

The contact zone of the Crust and Mantle is called Mohorovicic Discontinuity.

Question 14

What is mantle composed of?

Answer

The Mantle layer is composed of magnesium and iron silicates, along with substantial quantities of sulphides in the upper mantle and nickel and iron in the lower mantle.

Define the following terms

Question 1

Crust

Answer

Earth's outer shell of crystalline surface rock, ranging from 4 to 48 km in thickness from oceanic crust to mountain ranges is called Crust.

Question 2

Mantle

Answer

The layer of Iron and Magnesium silicate rock and nickel and iron alloy between the crust and the outer core with depth varying from 35 to 2900 km is called Mantle.

Question 3

Core

Answer

The central part of earth that probably consists of dense nickel and iron alloy is known as core.

Question 4

Nife

Answer

The core of earth consists of nickel and iron alloy and is known as Nife.

Distinguish between the following pairs

Question 1

Crust and Core

Answer

S.
No.		CrustCore
1.The crust is the outermost layer of the earth.The core is the innermost layer of the earth.
2.Crust is about 60 km thick below high mountains and just 5-10 km below the oceans.Core is about 7000 km in diameter.
3.Crust has relatively low temperatures.Core has very high temperature ranging from 4400°C to about 6000°C.
4.Crust is inhabited by living organisms.Core is uninhabitable.

Question 2

Sial and Sima

Answer

S.
No.		SialSima
1.This is the uppermost layer of the earth's crust.This is below the Sial layer.
2.Its thickness is nearly 20 km.Its average thickness is about 25 to 30 km.
3.It is composed of Silica(Si) and Aluminium(Al).It is composed of Silica(Si) and Magnesium(mg).
4.It is not a continuous layer. It is not found on ocean basin.It is a continuous layer.
5.It is less dense.It is more dense.
6.It is Granite layer.It is Basaltic layer.

Diagram

Question 1

Draw a self-explanatory diagram showing the composition and structure of the Earth.

Answer

Below diagram shows the composition and structure of the Earth:

Draw a self-explanatory diagram showing the composition and structure of the Earth. Earth's Structure, Geography by Veena Bhargava Goyal Brothers Prakashan Solutions ICSE Class 9.

Choose the correct option

Question 1

What is the rate of change of temperature inside the earth?

  1. Temperature decreases at the rate of 1°C for every 32 metres of descent.
  2. Temperature increases at the rate of 1°C for every 32 metres of descent.
  3. Temperature remains constant
  4. Temperature decreases at the rate of 32°C for every 1 metre of descent.

Answer

Temperature increases at the rate of 1°C for every 32 metres of descent.

Question 2

Sial is the part of ............... .

  1. Mantle
  2. Core
  3. Crust
  4. Sima

Answer

Crust

Question 3

Sima is composed of ............... & ...............

  1. Silica & Aluminium
  2. Silica & Nickel
  3. Silica & Magnesium
  4. Silica & Ferrous

Answer

Silica & Magnesium

Question 4

Gutenburg Discontinuity separates ............... & ...............

  1. Crust & Core
  2. Core & Mantle
  3. Mantle & crust
  4. Sial & Sima

Answer

Core & Mantle

Question 5

Mesosphere is another name of ............... .

  1. Crust
  2. Core
  3. Mantle
  4. Sima

Answer

Mantle

Question 6

Asthenosphere remains in ............... state.

  1. Liquid
  2. Molten
  3. Partially Molten
  4. Solid

Answer

Partially Molten

Question 7

Gutenburg Discontinuity is placed at ............... km depth from the surface.

  1. 3270
  2. 2900
  3. 32
  4. 1000

Answer

2900

Question 8

Which of the following layer is also called Barysphere?

  1. Mantle
  2. Asthenosphere
  3. Core
  4. Continental crust

Answer

Core

Question 9

Inner core is solid due to

  1. high temperature
  2. high pressure
  3. high density
  4. low pressure

Answer

high pressure

Question 10

Which of the following rocks and mineral composition is correct for Continental crust?

  1. Basalt, Si, Al.
  2. Granite, Si, Ma.
  3. Granite, Si, Al.
  4. Basalt, Granite, Si, Ma.

Answer

Granite, Si, Al.

Question 11

The average density of earth expressed in g/cm3 is

  1. 5.5
  2. 2.7
  3. 11
  4. 4.3

Answer

5.5

Question 12

Which of the following discontinuity is found between crust & mantle?

  1. Conrad
  2. Gutenberg
  3. Mohorovicic
  4. Lehmann

Answer

Mohorovicic

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