Class 8 Geography Chapter 2 Interior of the Earth answers

std 8 Geography Chapter 2 Interior of the Earth answers

Std 8 geography lesson 2 Interior of the Earth solutions

Exercises

Q 1. Tick the correct options.

(A) There are two layers in the crust.

          (i) Inner and outer crust

          (ii) Continental and oceanic crust

          (iii) Surface and oceanic crust

          (iv) Mantle and Core

Answer: (ii) Continental and oceanic crust

(B) Which element is found in both mantle and crust ?

(i) Silica

(ii) Magnesium

(iii) Aluminium

(iv) Iron

Answer: (ii) Magnesium

(C) Which of these minerals are found in the core of the earth?

(i) Iron-magnesium

(ii) Magnesium-nickel

(iii) Aluminium- Iron

(iv) Iron-nickel

Answer: (iv) Iron – nickel

(D) The inner core is in which state?

(i) Gaseous

(ii) Solid state

(iii) Semi-solid state

Answer: (i) Gaseous

(E) The outer core is made up of

(i) Iron

(ii) Gold

(iii) Hydrogen

(iv) Oxygen

Answer: (i) Iron

(F) The layer of the earth on which we live.

(i) Mantle

(ii) Core

(iii) Crust

(iv) Continental crust

Answer: (iv) Continental crust

(G) Which seismic waves can travel through liquid medium?

(i) Primary waves

(ii) Secondary Waves

(iii) Surface waves

(iv) Oceanic waves

Answer: (i) Primary waves

2. Tell whether right or wrong. Correct the wrong statement

(A) The density of various materials is not the same in the interior of the earth.

Answer: Correct

(B) The core of the earth’s interior is made up of hard rock.

Answer: Incorrect

The Inner core is made up of elements like iron and nickel.

(C) Secondary waves cannot pass through outer core.

Answer: Correct

(D) Continental crust is made up of silica and magnesium

Answer: Incorrect

Continental crust is made up of silica and aluminium.

Q 3. Answer the following

(A) What are the two parts of the crust? What is the basis of classification?

(i) Continental crust and the Oceanic crust are the two parts of the crust.

(ii) The part of the crust lying below the continent is known as the continental crust.

(iii) The part of the crust lying below the ocean is known as the oceanic crust.

(B) Why is the upper mantle called the asthenosphere?

Answer: The upper mantle is more in liquid state. Here, one finds magma chambers. It is through these chambers that magma comes out on the earth’s surface during volcanic eruptions. ‘Astheno” means ‘weak’, since this layer is a weak layer, it is called asthenosphere.

(C) Magnetosphere of the earth is a result of rotation. Explain.

Ans. The difference between the temperatures of the outer and inner core gives rise to vertical currents. The earth’s rotation gives them eddy (circular) motion. Electric currents develop in these spiral eddies of liquid iron and thus magnetic field is generated. It is sometimes called the geo-dynamo too. This magnetic field of the earth is functional even outside the earth’s surface for quite a distance. As a result, a cover develops around the earth because of the magnetic field. The earth’s atmosphere is protected from solar winds coming from the sun. The magnetic field thus developed around the earth, is called magnetosphere. This is the fifth and an important sphere of the earth.

Q 4. Draw neat diagrams, label them and explain.

(A) The interior of the earth

Answer: Refer to figure 2.2 on page 12 of your text book.

THE CRUST : The uppermost layer of the earth’s surface is in solid state and is called the crust. It can be divided into two sub-layers.

Continental crust and Oceanic crust.

MANTLE : Below the crust lies the mantle. Mantle can be divided into two layers: upper and lower mantle.

CORE : The part of the earth’s interior extending from the mantle upto the centre of the earth is the core. This layer can be divided into outer core and inner core.

(B) Magnetic pole and equator

Answer: Refer to figure 2.3 (B) on page 13 of your text book.

Q 5. Give geographical reasons:

(A) There are discontinuities in the interior of the earth.

Answer: There is a variation in the density, thickness, temperature and material found in the layers of the earth. Therefore, there is discontinuity in the crust, mantle and core of the earth.

(B) There is correlation between the density of metals and their location in the interior of the earth.

Answer: Metals with low density are found in upper level in the interior of the earth and the metals with high density are found in the lower level in the interior of the earth. The compounds of silicon, aluminium, magnesium, etc. are found in the crust of the earth. These compounds are lighter in weight. Therefore, they are found in the upper layer of the earth. The elements like iron, nickel are found in the core of the earth. These elements are heavier in weight. Thus we see that there is correlation between the density of metals and their location in the interior of the earth.

(C) Mantle is the centre of earthquake and volcanic eruptions.

Answer: The upper mantle is more in liquid state. Here, one finds magma chambers. It is through these chambers that magma comes out on the earth’s surface during volcanic eruptions. This layer is also known as asthenosphere. Epicenters of deep seated earthquakes are usually found here. The internal energy released due to endogenetic movements occurring in this layer is responsible for mountain-building, rifts, volcanic eruptions earthquakes, etc.

(D) The thickness of the crust below the continents is less as compared to oceans.

Answer:

The density of the crust below the continents is 2.65 to 2.90 gm/cm3 and the density of the crust below the oceans is 2.90 to 3.3 gm/cm3.  As the density of the crust below the continents is comparatively low, the thickness of the crust below the continents is high. On the other hand as the density of the crust below the ocean is comparatively high, the thickness is low. Thus, the thickness of the crust below the continents is more as compared to oceans.

(E) Earth is protected because of the magnetosphere

Answer: The difference between the temperatures of the outer and inner core gives rise to vertical currents. The earth’s rotation gives them eddy (circular) motion. Electric currents develop in these spiral eddies of liquid iron and thus magnetic field is generated. It is sometimes called the geo-dynamo too. This magnetic field of the earth is functional even outside the earth’s surface for quite a distance. As a result, a cover develops around the earth because of the magnetic field. The earth’s atmosphere is protected from solar winds coming from the sun. The magnetic field thus developed around the earth, is called magnetosphere which protects the earth from the ultra violet rays of the sun.

ACTIVITY : Prepare a model of the earth’s interior.