Question 1

Question 8What is Earth’s crust composed of?

Accepted 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 2

Question 10Why does the temperature increase as we go down(underground)?

Accepted 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 3

Question 11How does Sial differ from Sima?

Accepted Answer

S.No.SialSima1.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 4

Question 12Name the two most important and abundant chemical elements present in the Earth's crust.

Accepted Answer

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

Question 5

Question 13What is meant by Mohorovicic Discontinuity?

Accepted Answer

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

Question 6

Question 14Assertion (A): The thickness of the lithosphere is very fragile compared to the nature and composition of the earth.Reason (R): There are continuous changes in the earth's crust due to forces of nature.Both A and R are true and R is the correct explanation of A.Both A and R are true but R does not explain A.A is true but R is false.A is false but R is true.

Accepted Answer

Both A and R are true and R is the correct explanation of A.Explanation — Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A) because the lithosphere, though solid, is thin and constantly affected by natural forces like earthquakes and volcanic activity, leading to its fragile state.

Question 7

Question 15What life sustaining unit contains only one per cent of the earth's mass?biospherelithospherecrustmantle

Accepted Answer

crust/lithosphere

Question 8

Question 16Mohorovicic discontinuity is found at about ............... beneath the oceans and ............... beneath the continents.8 km, 32 km36 km, 10 km60 km, 6 km40 km, 4 km

Accepted Answer

8 km, 32 km

Question 9

Question 17Extending upwards, the earth is enveloped by a blanket of gases. Name it.LithosphereHydrosphereAtmosphereChamber

Accepted Answer

Atmosphere

Question 10

Question 18The diameter of the core is about ............... km.5000600070008000

Accepted Answer

7000

Question 11

Question 19Name the layer of the earth that is fragile as compared to the rest of the layers of the earth. Different theories suggest that this layer undergoes changes to give earth a new shape.MantleCoreCrustAsthenosphere

Accepted Answer

Crust

Question 12

Question 1Crust and Core

Accepted Answer

S.No.CrustCore1.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 13

Question 3Core is working as a magnetic field.

Accepted Answer

The Earth’s core, especially the outer core, is made up of molten iron and nickel. Due to the rotation of the Earth, these liquid metals move and generate electric currents. This movement of electrically charged fluid produces a magnetic field around the Earth.This phenomenon is called the dynamo effect, and it is the reason why the Earth behaves like a giant magnet, with a North and South Magnetic Pole.

Question 14

Question 6Name the three layers of the earth's interior. Name their boundaries.

Accepted Answer

The three layers of the earth's interior are Core, Mantle and Crust.The boundaries between the three layers of the earth's interior are:Gutenberg Discontinuity — It lies between the mantle and the core.Mohorovicic Discontinuity — It lies between the crust and the mantle.

Question 15

Question 7Describe the mantle. State its two chief characteristics.

Accepted 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-Its average thickness is 2900 km.The temperature varies between about 1000°C to around 3700°C.

Question 16

Question 9What happens to the P and S waves at the Gutenberg Discontinuity?

Accepted Answer

At the Gutenberg Discontinuity, there is an abrupt change in the seismic waves (generated by earthquakes or explosions) that travel through the earth. Primary seismic waves (P waves) decrease in velocity while secondary seismic waves (S waves) disappear completely.

Question 17

Question 1(d)Look at the figure on the side and answer the questions:(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?

Accepted 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 18

Question 2(a)State two chief characteristics of the earth's crust.

Accepted Answer

Two chief characteristics of the earth's crust are-It is a sphere of solid rocks with a thickness of 60 km below high mountains and just 5-10 km below the oceans.It is made up of rocks with large content of silicates, feldspar, mica etc.

Question 19

Question 2What would happen if the earth's core no longer remain hot and the magma cools and hardens inside the earth? Give reasons to support your answer.

Accepted Answer

If the Earth's core were to cool down and the magma inside the Earth were to cool and harden, it would have serious consequences.The Earth's magnetic field, generated by the molten iron in the outer core, would weaken or disappear, leaving the surface exposed to harmful cosmic radiation.Tectonic activity would halt, which could cause earthquakes and volcanic eruptions to cease. This will impact nutrient recycling. Over time, this could also lead to the formation of a supercontinent, as there would be no mechanism to break apart the continents.Geothermal energy availability would be affected.The Earth's rotation would slow down, leading to longer days and shorter nights. This would have significant effects on the climate and the seasons.

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