Chapter 2 - Interior of the Earth
Q 1. Tick ✓ the correct options in the box
(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
Ans: Option (ii) – Continental and oceanic crust
(B) Which element is found in both mantle and crust ?
(i) Silica
(ii) Magnesium
(iii) Aluminium
(iv) Iron
Ans: Option (iv) – Iron
(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
Ans: Option (i) – Iron-magnesium
(D) The inner core is in which state?
(i) Gaseous
(ii) Solid state
(iii) Semi-solid state
Ans: Option (i) – Gaseous
(E) The outer core is made up of
(i) Iron
(ii) Gold
(iii) Hydrogen
(iv) Oxygen
Ans: Option (iv) – Oxygen
(F) The layer of the earth on which we live.
(i) Mantle
(ii) Core
(iii) Crust
(iv) Continental crust
Ans: Option (i) – Mantle
(G) Which seismic waves can travel through liquid medium?
(i) Primary waves
(ii) Secondary Waves
(iii) Surface waves
(iv) Oceanic waves
Ans: Option (ii) – Secondary Waves
Q 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.
Ans: Right
(B) The core of the earth’s interior is made up of hard rock
Ans: Wrong
Correct statement: The core of the earth’s interior is made up of elements, viz. iron and nickel.
(C) Secondary waves cannot pass through the outer core.
Ans: Right
(D) Continental crust is made up of silica and magnesium
Ans: Wrong
Correct statement: Continental crust is made up of silica and aluminum.
Q 3. Answer the following
(A) What are the two parts of the crust? What is the basis of classification?
Ans:
(i) The continental crust and the oceanic crust are the two parts of the crust.
(ii) The continental crust mainly comprises Silica (Si) and Aluminium (Al) in higher proportions. It is also called Sial.
(iii) The oceanic crust is composed of Silica (Si) and Magnesium (Ma). It is also called Sima.
(iv) The crust is classified mainly on the basis of its thickness as well as the composition of minerals.
(B) Why is the upper mantle called the asthenosphere?
Ans:
(i) The mantle lies below the crust.
(ii) The upper portion of the mantle is called the ‘asthenosphere’. The word ‘astheno’ means weak.
(iii) It is in a liquid state, and it is from this weaker zone that the molten rock materials, i.e., magma, find their way to the surface during volcanic eruptions.
(iv) Epicenters of deep-seated earthquakes are also found here.
(v) Therefore, the upper mantle is called the ‘asthenosphere’.
(C) Magnetosphere of the earth is a result of rotation. Explain.
Ans:
(i) The average temperature of the outer core of the earth is around 5000° C. The average temperature of the inner core of the earth is around 6000° C. This difference in temperature results in the formation of vertical currents.
(ii) The rotation of the earth gives eddy (circular) motion to these currents.
(iii) Electric currents develop in these spiral eddies of liquid iron, leading to the generation of the magnetic field of the earth. This magnetic field is called the magnetosphere.
(iv) In this way, the magnetosphere is formed due to the rotation of the earth.
Q 4. Draw neat diagrams, label them and explain.
(A) The interior of the earth
Ans:
(B) Magnetic pole and equator
Ans:
Q 5. Give geographical reasons:
(A) There is variety in the interior of the earth.
Ans:
(i) There is a difference between the elements, temperatures, and pressure found in the three parts of the interior of the earth, viz., the crust, mantle, and core.
(ii) In the interiors of the earth, transitional areas are found between;
(a) continental crust and oceanic crust
(b) crust and mantle
(c) upper mantle and lower mantle
(d) mantle and core and
(e) outer core and inner core
(iii) Therefore, there are discontinuities in the interior of the earth.
(B) There is correlation between the density of metals and their location in the interior of the earth.
Ans:
(i) The rocks found in the crust have a predominance of the compounds silicon, aluminium, magnesium, etc. These compounds are lighter in weight. Therefore, they are found in the upper layer of the interior of the earth.
(ii) The elements like iron and nickel are found in the core of the earth. These elements are heavier in weight. Thus, metals with low density are found in the upper level of the interior of the earth, and metals with high density are found in the lower level of the interior of the earth.
(iii) Thus, there is a correlation between the density of metals and their location in the interior of the earth.
(C) Mantle is the centre of earthquakes and volcanic eruptions.
Ans:
(i) The rocks in the upper 100 to 200 km of the mantle melt due to the heat, and magma is created.
(ii) Magma chambers are found in this layer of the earth.
(iii) Due to the heat and pressure, energy waves are created in the mantle. These energy waves move in a vertical direction, and magma comes out on the surface of the earth during volcanic eruptions.
(iv) Thus, the mantle is the centre of earthquakes and volcanic eruptions.
(D) The thickness of the crust below the continents is less as compared to oceans.
Ans:
(i) The density of the crust below the continents is 2.65 to 2.90 g/cm³. The density of the crust below the oceans is 2.90 to 3.3 g/cm³.
(ii) As the density of the crust below the continents is comparatively low, it keeps floating on the mantle. It does not subduct into the mantle. As a result, the thickness of the crust below the continents is found to be high.
(iii) As the density of the crust below the ocean is comparatively high, it subducts into the mantle, leading to its low thickness.
(iv) Thus, the thickness of the crust below the continents is greater as compared to the oceans.
(E) Earth is protected because of the magnetosphere.
Ans:
(i) The ozone layer protects the earth from ultraviolet radiation.
(ii) The earth’s magnetosphere serves to deflect most of the solar wind, whose charged particles would otherwise strip away the ozone layer.
(iii) In this way, the earth is protected because of the magnetosphere.