Question 1. Select 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
(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
(D) The inner core is in which state?
(i) Gaseous
(ii) Solid state
(iii) Semi-solid state
(E) The outer core is made up of
(i) Iron
(ii) Gold
(iii) Hydrogen
(iv) Oxygen
(F) The layer of the earth on which we live.
(i) Mantle
(ii) Core
(iii) Crust
(iv) Continental crust
(G) Which seismic waves can travel through liquid medium?
(i) Primary waves
(ii) Secondary Waves
(iii) Surface waves
(iv) Oceanic waves
Question 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.
(B) The core of the earth’s interior is made up of hard rock
Answer :
Incorrect.
Correct statement : The core of the earth’s interior is made up of elements, viz iron and nickel.
(C) Secondary waves cannot pass through outer core.
(D) Continental crust is made up of silica and magnesium
Answer :
Incorrect.
Correct statement : Continental crust is made up of silica and aluminium.
Question 3. Answer the following
(A) What are the two parts of the crust? What is the basis of classification?
Answer :
- The crust is divided into two parts: continental crust and oceanic crust.
- The crust is classified according to whether it is under land or under the ocean.
- The continental crust is the section of the crust that is underneath the continent.
- The oceanic crust is the section of the crust that is underneath the ocean.
(B) Why is the upper mantle called the asthenosphere?
Answer :
- The upper mantle is called the asthenosphere because it is a weak layer where rock material deforms more readily and magma formation takes place.
- The rocks in the upper 100 to 200 km of the mantle melt due to the heat and magma is created. Magma chambers are found in this layer of the earth.
- Due to the heat and pressure, the energy waves are created in mantle. These energy waves move in vertical direction and magma comes out on the surface of the earth by volcanic eruptions.
- These endogenitic movements continuously occur in the upper layer of the mantle. Therefore, the upper layer of the mantle is known as the asthenosphere.
(C) Magnetosphere of the earth is a result of rotation. Explain.
Answer :
- The average temperature of the earth's outer core is roughly 5000° C. The average temperature of the earth's inner core is roughly 6000° C. Vertical currents are formed as a result of the temperature difference.
- These currents move in eddy (circular) motion due to the rotation of the earth.
- Electric currents form in these spiral eddies of liquid iron, resulting in the formation of the earth's magnetic field. This magnetic field is known as the magnetosphere.
- The magnetosphere is produced in this fashion as a result of the earth's rotation.
Question 4. Draw neat diagrams, label them and explain.
(A) The interior of the earth
(B) Magnetic pole and equator
Question 5. Give geographical reasons:
(A) There is variety in the interior of the earth.
Answer :
There is a difference between the elements, temperatures and the pressure found in the three parts of the interior of the earth, viz. crust, mantle and core.
In the interiors of the earth, the transitional areas are found between
- continental crust and oceanic crust
- crust and mantle
- upper mantle and lower mantle
- mantle and core
- outer core and inner core.
Therefore, there are discontinuities or variety in the interior of the earth.
(B) There is correlation between the density of metals and their location in the interior of the earth.
Answer :
- Silicon, aluminium, magnesium, and other substances predominate in the rocks found in the crust. These substances are lighter in weight. As a result, they are located in the higher layer of the earth's interior.
- Elements such as iron and nickel are found in the core of the earth. These are the heavier elements.
- Thus, metals with low density are found at the higher level of the earth's interior, whereas metals with high density are found in the lower level.
- Thus, 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 :
- Heat causes the rocks in the top 100 to 200 km of the mantle to melt, resulting in the formation of magma. That layer of the earth contains magma chambers.
- Energy waves are formed in the mantle as a result of heat and pressure. These energy waves flow upward, and volcanic eruptions release magma onto the earth's surface.
- As a result, the mantle is the source of earthquakes and volcanic eruptions.
(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. 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, it keeps floating on the mantle. It does not subduct into mantle. As its effect, the thickness of the crust below the continents is found to be high.
- As the density of the crust below the ocean is comparatively high, it subducts into mantle leading to its low thickness. 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 ozone layer protects the earth from ultraviolet radiation.
- The earth’s magnetosphere serves to deflect most of the solar wind, whose charged particles would otherwise strip away the ozone layer.
- In this way, the earth is protected because of the magnetosphere.
