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Chapter 4

Earth's Structure

Class 9 - Total Geography Morning Star


Short Answer Questions

Question 1

Name the sources of information about forces operating inside the earth.

Answer

Information about forces operating inside the earth is taken by the study of seismic waves, materials thrown up by volcanoes and the evidence from the theories of the origin of the earth.

Question 2

In which part of the earth is NIFE found? What is it composed of?

Answer

The core of the earth is called NIFE. It is composed of Nickel (Ni) and Iron (Fe).

Question 3

What are the consequences of the pressure and temperature in the interior of the earth?

Answer

The extreme temperature of 4400°C to about 6000°C and high density and pressure have compressed the molten rock material at the inner core to solid state. The outer core is in a molten state.

The temperature at the mantle ranges from about 1000°C to around 3700°C. The upper mantle is cooler and made of solid rocks. The lower mantle is hotter and denser than the upper mantle. Lower mantle is solid due to high pressure while upper mantle is in partially molten state.

The crust, a layer of 60 km, breadth, is made of solid rocks with a density of 2 – 3, g/cm3. The density goes on increasing to 3-4g/cm3 in the mantle and 10-13 g/cm3 in the core.

Question 4

How do the meteorites help scientists to know about the interior of the earth?

Answer

The earth is said to be constituted of the same materials as the meteorites. So, scientists study meteorites to know more about the interior of the earth.

Question 5

What is the composition of the earth's crust?

Answer

The crust of the earth is a sphere of solid rocks. It is only 1% of earth's mass. It is made up of rocks with large content of silicates, feldspar, mica etc.

The crust is divided into two broad divisions- SIAL and SIMA. SIAL is composed of Silica and Aluminium while SIMA is composed of Silica and Magnesium.

Question 6

What is the lithosphere?

Answer

The crust of the earth is called lithosphere as it is a sphere of solid rocks with a thickness of 60 km below high mountains and just 5-10 km below the oceans.

Question 7

Name the three layers of the earth's interior.

Answer

The three layers of the earth's interior are Core, Mantle and Crust.

Question 8

Describe the mantle. State its two chief characteristics.

Answer

Mantle lies below the crust. It makes up 84% of the earth's total volume. Mantle is divided into two parts- the upper mantle and the lower mantle.

Two chief characteristics of mantle are-

  1. It has an average thickness is 2900 km.
  2. The temperature varies between about 1000°C to around 3700°C.

Question 9

Where is asthenosphere found? In which form does it exist?

Answer

Asthenosphere is found at the depth of around 100-410 km. It exists in partially molten form.

Question 10

Write one difference between Moho Discontinuity and Gutenberg Discontinuity.

Answer

Moho DiscontinuityGutenberg Discontinuity
Moho Discontinuity is the boundary between crust and mantle.Gutenberg Discontinuity is the boundary between mantle and core.

Question 11

Why is the earth's interior in most part found in a solid state despite great heat and pressure?

Answer

The solid state of the inner core is due to high density and pressure which have compressed molten rock material.

Distinguish between the following

Question 1

Crust and Core

Answer

CrustCore
The crust is the outermost layer of the earth.The core is the innermost layer of the earth.
Crust is about 60 km thick below high mountains and just 5-10 km below the oceans.Core is about 7000 km in diameter.
Crust has relatively low temperatures.Core has very high temperature ranging from 4400°C to about 6000°C.
Crust is inhabited by living organisms.Core is inhabitable.

Question 2

Sial and Sima

Answer

SialSima
Sial floats on top of Sima.Sima lies under Sial.
Sial has less density.Sima has more density.
Sial is composed of Silica and Aluminium.Sima is composed of Silica and Magnesium.
Sial forms the continents.Sima makes up the ocean floor.

Question 3

Gutenberg Discontinuity and Mohorovicic Discontinuity.

Answer

Moho DiscontinuityGutenberg Discontinuity
Moho Discontinuity is the boundary between crust and mantle.Gutenberg Discontinuity is the boundary between mantle and core.
It is found at about 8 km beneath the oceans and about 32 km beneath the continents.It begins at a depth of 2800 km.

Structured Questions

Question 1(a)

Describe the layers of the interior of the earth and their chemical composition.

Answer

The layers of the interior of the earth are as follows:

1. Crust — It is the topmost layer of the earth. It is made up of rock with large content of silicates, feldspar, mica etc. It also contains silica and aluminium.

2. Mantle — It lies between the crust and core. It can be divided into upper and lower crust. Upper crust is solid while lower crust is partially molten. It is mainly composed of oxygen, silicon and magnesium.

3. Core — Core is the innermost inaccessible part of the earth. It is mainly composed of Nickel and Iron.

Question 1(b)

There are two transitional zones between the two consecutive layers of the interior of the earth. Name them and state their chief characteristics.

Answer

The transitional zone between crust and mantle is Moho Discontinuity which is the dividing zone between solid and semi-solid state of rocks due to the increasing temperature as the depth increases. It is found at about 8 km beneath the oceans and about 32 km beneath the continents.

The boundary between mantle and core is known as Gutenberg Discontinuity. it begins at the depth of 2800 km. Below this zone, both density and temperature goes on increasing.

Question 1(c)

Give a geographical reason for each of the following:

(i) Temperature starts rising gradually towards the interior of the earth.
(ii) The asthenosphere is in a semi-molten state.
(iii) The inner core of the earth is in a solid state.

Answer

(i) Due to enhancing density and pressure the temperature goes on increasing gradually towards inside of the interior of the earth.

(ii) The asthenosphere is in a semi-molten state because of high temperature, pressure and density.

(iii) The inner core of the earth is in a solid state due to high density and pressure.

Question 1(d)

Look at the figure on the side and answer the questions:

Label the parts 1, 2, 3, 4, 5. Name the state (solid, liquid or gas) in which each part exists. Earth's structure, Total Geography ICSE Class 9.

(i) Label the parts: (1), (2), (3), (4) and (5).
(ii) Name the state (solid, liquid or gas) in which each part exists.
(iii) Which part of the earth is suitable for human habitation? Why?

Answer

(i) The parts are:

(1) Atmosphere
(2) Crust
(3) Mantle
(4) Core
(5) Ocean

(ii) The states are:

(1) Atmosphere - Gaseous state
(2) Crust - Solid state
(3) Mantle - Semi-molten and solid state
(4) Core - Solid state
(5) Ocean - Liquid state

(iii) Crust is suitable for human habitation due to favourable conditions for survival, i.e. atmosphere for air, lithosphere for settlement due to ideal temperature, hydrosphere for hydrological cycle for providing rainfall and fresh water bodies on the earth and oceans for navigation and trade routes etc.

Question 2(a)

State two chief characteristics of the earth's crust.

Answer

Two chief characteristics of the earth's crust are-

  1. It is a sphere of solid rocks with a thickness of 60 km below high mountains and just 5-10 km below the oceans.
  2. It is made up of rocks with large content of silicates, feldspar, mica etc.

Question 2(b)

Which layer is responsible for earth's magnetic field? Why?

Answer

The core of the earth is responsible for earth's magnetic field as it is composed of iron and nickel.

Question 2(c)

Give a geographical reason for each of the following:

(i) Nife is so called.

(ii) The core of the earth is the most inaccessible part of the earth.

(iii) The earth's crust undergoes many changes.

Answer

(i) Nife is so called as Ni stands for Nickel and Fe stands for Iron.

(ii) The core of the earth is the most inaccessible part of the earth because it lies thousands of kilometers deep inside the earth.

(iii) The earth's crust undergoes many changes due to the forces of nature.

Question 2(d)

Draw a well labelled diagram to show the interior of the earth.

Answer

Draw a well labelled diagram to show the interior of the earth. Earth's structure, Total Geography ICSE Class 9.
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