The Class 8 is an important year in a student’s life and Maharashtra State Board Social Science Grography is one of the subjects that require dedication, hard work, and practice. It’s a subject where you can score well if you are well-versed with the concepts, remember the important formulas and solving methods, and have done an ample amount of practice. Worry not! Home Revise is here to make your Class 8 journey even easier. It’s essential for students to have the right study material and notes to prepare for their board examinations, and through Home Revise, you can cover all the fundamental topics in the subject and the complete Maharashtra State Board Class 8 Social Science Grography Book syllabus.
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
(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
Answer A: (ii) Continental and oceanic crust
Answer B: (i) Silica
Answer C: (iv) Iron-nickel
Answer D: (ii) Solid state
Answer E: (i) Iron
Answer F: (iv) Continental crust
Answer G: (i) Primary 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.
(B) The core of the earth’s interior is made up of hard rock
(C) Secondary waves cannot pass through the outer core.
(D) Continental crust is made up of silica and magnesium
Answer A: The statement is right.
Answer B: The statement is wrong. Our Earth is divided into two core Outer core and Inner core. The outer core is made up of liquid state and the inner core is made up of solid state.
Answer C: The statement is right.
Answer D: The statement is wrong because 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?
(B) Why is the upper mantle called the asthenosphere?
(C) Magnetosphere of the earth is a result of rotation. Explain.
Answer A: The uppermost layer of the earth’s surface is in solid state and is called the crust. The two parts of the crust are Oceanic Crust and Continental Crust. Oceanic Crust is the second layer of the crust. It is made up of silica and magnesium. It was earlier called Sima. Continental Crust continents are mainly composed of Silica and Aluminum. Because of their high proportion in this layer, the layer was earlier known as Sial.
Answer B: The upper layer of the 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.
Answer C: The difference between the temperatures of the outer and inner core gives rise to vertical currents. The earth’s rotation gives them 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. 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 the magnetosphere.
Q 4. Draw neat diagrams, label them and explain.
(A) The interior of the earth
(B) Magnetic pole and equator
Answer A:
Answer B:
Q 5. Give geographical reasons:
(A) There are discontinuities in the interior of the earth.
(B) There is a 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.
(D) The thickness of the crust below the continents is less as compared to oceans.
(E) Earth is protected because of the magnetosphere.
Answer A: There is a discontinuity between the continental crust and oceanic crust. It was first deduced by a scientist called Conrad and is named after him as Conrad discontinuity. There is discontinuity between crust and mantle too. This discontinuity was deduced by a scientist called Mohorovicic. It has been named after him as Moho discontinuity. There is discontinuity between mantle and core too. It has been named after Gutenberg, a scientist, who discovered it.
Answer B: As we go deeper inside the earth, the pressure increases. The lithosphere is made of silica and aluminium (SIAL) and silica and magnesium (SIMA). They are solid but not very dense. Then comes the outer mantle, it is made of solid rocks which are denser than SIAL and SIMA. The inner mantle is hotter and denser than the outer mantle. The core is made up of Nickel and Iron. Outer core is in molten state due to high temperature. The outer core is in solid state due to the extremely high pressure.
Answer C: Below the crust lies the mantle. Mantle can be divided into two layers: upper and lower mantle. The upper layer 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. Mantle begins at a depth of around 42km from the earth’s surface.
Answer D: Both the continental crust and oceanic crust are thick but the oceanic crust is much more dense than the continental crust. Both these crusts are less denser than mantle but since continental crust has lower density than the other one, it has a higher elevation than the ocean floor. Their densities vary mainly because they are made of different types of rocks that also have varying densities which greatly affects their elevation.
Answer E: The Earth ’s magnetosphere protects the planet from solar winds and high-energy particles by redirecting this energy around the planet. When charged particles approach the Earth, the magnetosphere affects them due to their magnetic properties. Particles blown by the solar wind simply sweep around the Earth, while slower radioactive particles may become part of the Earth ’s radiation belts, held safely above the surface by the magnetosphere.