Samacheer Kalvi 7th Social Science Interior of the Earth Exercise Solutions

How to Use This Page

This page provides complete exercise solutions for Chapter 1: Interior of the Earth from the Samacheer Kalvi 7th Social Science textbook (Geography, Term 1). Read each question, attempt it on your own first, then compare with the answers below. Use the Key Concepts section for a quick revision before exams.

Key Concepts (Quick Recap)

• Three Layers of the Earth: Crust (outermost, thinnest), Mantle (middle, 84% of volume), Core (innermost, also called Barysphere)
• SIAL: Upper crust — Silica + Alumina; granite rocks; forms continents; less dense
• SIMA: Lower crust — Silica + Magnesium; basaltic rocks; forms ocean floors; denser
• NIFE: Core — Nickel + Ferrous (Iron); extremely high temperature and pressure
• Discontinuities: Mohorovicic (Crust-Mantle boundary), Weichart-Gutenberg (Mantle-Core boundary)
• Earthquakes: Sudden movement of a portion of Earth's crust; measured by Richter Scale; recorded by Seismograph
• Earthquake Waves: P waves (longitudinal), S waves (transverse), L waves (surface)
• Volcanoes: Active (erupt frequently, ~600 worldwide), Dormant (sleeping, may erupt), Extinct (eroded tops)
• Pacific Ring of Fire: Circum-Pacific belt with two-thirds of world's volcanoes
• Tsunami: Japanese term for huge waves caused by undersea earthquakes
• Tectonic Movements: Movement of lithospheric plates over the asthenosphere

Exercise Solutions

I. Choose the Correct Answer (MCQs)

Q1. Nife is made up of ________

• a) Nickel and ferrous ✓
• b) Silica and aluminum
• c) Silica and magnesium
• d) Iron and magnesium

Q2. Earthquake and volcanic eruption occur near the edges of ________

• a) Mountain
• b) Plains
• c) Plates ✓
• d) Plateaus

Q3. The magnitude of an earthquake is measured by ________

• a) Seismograph
• b) Richter scale ✓
• c) Ammeter
• d) Rotameter

Q4. The narrow pipe through which magma flows out is called a ________

• a) Vent ✓
• b) Crater
• c) Focus
• d) Caldera

Q5. ________ Volcano is known as the lighthouse of the Mediterranean Sea.

• a) Stromboli ✓
• b) Krokota
• c) Fujiyana
• d) Kilinanjaro

Q6. ________ belt is known as the "Ring of Fire."

• a) Circum-Pacific ✓
• b) Mid-Atlantic
• c) Mid-Continental
• d) Antarctic

Q7. The structure of the Earth is compared to ________

• a) Apple ✓
• b) Orange
• c) Egg
• d) Mango

Q8. Which is called the Blue Planet?

• a) Mars
• b) Earth ✓
• c) Venus
• d) Jupiter

Q9. The Earth is covered by water at ________

• a) 51%
• b) 71% ✓
• c) 61%
• d) 81%

Q10. The outer core is rich in ________

• a) Iron ✓
• b) Nickel
• c) Silica
• d) Aluminium

Q11. The radius of the Earth is ________ kms.

• a) 6370
• b) 6371 ✓
• c) 6731
• d) 6713

Q12. The mantle forms ________ of the Earth's volume.

• a) 48%
• b) 68%
• c) 84% ✓
• d) 94%

Q13. The crust forms ________ of the Earth's volume.

• a) 5%
• b) 10%
• c) 50%
• d) 1% ✓

Q14. How many active volcanoes are in the world?

• a) 500
• b) 600 ✓
• c) 700
• d) 800

Q15. How many major zones of volcanic activities are in the world?

• a) Two
• b) Four
• c) Three ✓
• d) Five

Q16. The upper part of the Earth's crust is called ________

• a) SIMA
• b) NIFE
• c) SIAL ✓
• d) Mantle

II. Fill in the Blanks

1. The core is separated from the mantle by a boundary called Weichart-Gutenberg discontinuity. 2. The earthquake waves are recorded by an instrument known as Seismograph. 3. Magma rises to the surface and spreads over a vast area is known as Lava. 4. An example of an active volcano is Mauna Loa in Hawaii (or Mt. Stromboli / St. Helens / Pinatubo). 5. Seismology is the study of earthquakes. 6. The oceanic crust is composed mostly of dense rocks. 7. The upper part of the crust consists of granite rocks. 8. The sial and the sima together form the Earth's crust. 9. Mantle is separated from the crust by a boundary called Mohorovicic discontinuity. 10. The core is also known as Barysphere. 11. The outer core is rich in iron. 12. The crust forms 1% of the Earth's volume. 13. The movement of the Earth's lithospheric plates is termed as tectonic movements. 14. A trench is formed between two plates. 15. The earthquake is measured by the Richter scale. 16. The earthquake is a volcanic activity. 17. Tsunami is a Japanese term. 18. On 26th December 2004, a tsunami occurred in Tamil Nadu. 19. The opening of a volcano is usually circular in form. 20. The semi-molten state of interior Earth is called magma.

III. Match the Following

Match A (Textbook Exercise):

Match B (Additional Exercise):

IV. Assertion and Reason

Q1.

• A: The structure of the Earth may be compared to that of an Apple.
• R: The interior of the Earth consists of crust, mantle, and core.

Q2.

• A: The Pacific Ocean includes two-thirds of the world's volcanoes.
• R: The boundary along the Eastern and Western coast areas of the Pacific Ocean is known as the Pacific Ring of Fire.

• A: A greater danger in an earthquake is the falling of buildings.
• R: Earthquake may cause changes in the Earth's surface.

• A: The Himalayan region and the Ganga-Brahmaputra valley are prone to earthquakes.
• R: A number of earthquakes have been experienced in the Brahmaputra valley.

V. Very Short Answers (1-2 sentences)

Q1. Name the outermost layer of the Earth. The crust is the outermost layer of the Earth.

Q2. What is SIAL? SIAL is the upper part of the crust, consisting of Silica and Alumina, forming the continental rocks.

Q3. Name the movement of the Earth's lithospheric plates. The movement of the Earth's lithospheric plates is called Tectonic Movements.

Q4. Give an example of an extinct volcano. Mt. Popa of Myanmar is an example of an extinct volcano. Other examples include Mt. Kilimanjaro and Mt. Kenya.

Q5. What are the three concentric layers of the Earth? The three concentric layers are the Crust, the Mantle, and the Core.

Q6. What are the causes of earthquakes? Earthquakes are caused by sudden slipping of the Earth's crust along fractures/faults, sudden shifting of landmass causing upheavals, and volcanic activity.

Q7. What are the types of earthquake waves? There are three types: P waves (longitudinal), S waves (transverse), and L waves (surface waves).

Q8. What is Magma? Magma is the molten rock material within the Earth, together with gases, in a semi-molten state.

Q9. What is a Caldera? A caldera is a large, basin-shaped crater caused by violent explosions that blow away the entire top of a volcanic cone.

VI. Short Answers (3-5 sentences)

Q1. What is the Mantle? The mantle is the layer beneath the crust, forming about 84% of the Earth's volume. It is separated from the crust by the Mohorovicic discontinuity. The mantle is in a semi-molten state, and its upper portion (the asthenosphere) flows and moves the lithospheric plates.

Q2. Write a note on the Core of the Earth. The core is the innermost layer of the Earth, also called the Barysphere. It is separated from the mantle by the Weichart-Gutenberg discontinuity. The core has two parts: the outer core (rich in iron, in liquid state) and the inner core (composed of Nickel and Ferrous/Nife, in solid state). The central core has extremely high temperature and pressure, making it impossible to obtain samples from.

Q3. Define an Earthquake. An earthquake is a sudden movement of a portion of the Earth's crust that produces shaking or trembling. It is caused by sudden slipping of the crust along fractures or faults, sudden shifting of landmass, or volcanic activity. The point of origin inside the Earth is called the focus, and the point on the surface directly above it is called the epicentre.

Q4. What is a Seismograph? A seismograph is an instrument that records earthquake waves. It detects and records the intensity, direction, and duration of seismic waves. The magnitude of an earthquake is then measured using the Richter Scale — earthquakes of magnitude 2.0 or less are slight, above 5.0 cause damage from falling objects, above 6.0 are very strong, and 7.0 or above are classified as major earthquakes.

Q5. What is a Volcano? A volcano is a vent or opening in the Earth's crust through which hot magma erupts from deep below the surface. The opening is usually circular in form. When magma reaches the surface, it is called lava. Volcanoes are classified as active, dormant, or extinct based on the periodicity of eruption.

Q6. Name the three types of volcanoes based on the periodicity of eruption. The three types are: (1) Shield volcano, (2) Cinder-cone volcano, and (3) Composite volcano. Alternatively, based on eruption frequency: (1) Active volcanoes (erupt frequently, e.g., Mauna Loa, Stromboli), (2) Dormant volcanoes (no activity for many years but may become active, e.g., Vesuvius, Mt. Fujiyama), and (3) Extinct volcanoes (tops eroded away, e.g., Mt. Popa, Mt. Kilimanjaro).

Q7. What is the Crust? The crust is the outermost layer of the Earth, about 35 km thick on continental masses and about 5 km thick on oceanic floors. It has two parts: the upper part (SIAL) consisting of silica and alumina, and the lower part (SIMA) consisting of silica and magnesium. SIAL is lighter than SIMA. The crust forms only about 1% of the Earth's volume.

Q8. What are Tectonic Movements? Each lithospheric plate moves over the asthenosphere (the semi-molten part of the upper mantle), and this movement is termed tectonic movements. These movements cause changes on the Earth's surface and result in phenomena like earthquakes and volcanic activity.

Q9. What is the Asthenosphere? The asthenosphere is the part of the mantle that flows and moves the plates of the Earth. It lies in the upper portion of the mantle, below the lithosphere, and is in a semi-molten (plastic) state that allows the lithospheric plates to move over it.

Q10. How can earthquakes be recorded and measured? Earthquake waves are recorded by a seismograph and measured by the Richter Scale. Earthquakes of magnitude 2.0 or less are slight; above 5.0 cause damage from falling objects; above 6.0 are very strong; and 7.0 or above are classified as major earthquakes.

Q11. Give a note on the Tsunami of 2004. On 26th December 2004, a massive tsunami in the Indian Ocean swept coastal areas of Indonesia, India, Sri Lanka, Thailand, and other countries, causing immense damage to life and property. In Tamil Nadu, coastal areas were severely affected.

Q12. What is a Tsunami? A tsunami is a Japanese term for huge waves caused in the sea by an earthquake. Tsunamis are common along the coasts of Japan and other Pacific regions. The waves can travel at great speed across the ocean and cause devastating damage when they reach the shore.

Q13. Write a note on Barren Island. Barren Island is located in the Andaman Sea, approximately 138 km northeast of the territory's capital. It is the only active volcano from Sumatra to Myanmar. Its last eruption occurred in 2017.

VII. Detailed Answers (Paragraph-length)

Q1. Write about the effects of an earthquake. Earthquakes cause widespread destruction. In mountainous regions, they trigger landslides that can bury entire settlements. Buildings, especially mud and brick structures, collapse, causing loss of life and property. Earthquakes can also cause fire hazards by damaging gas pipelines and electrical systems. Underground water systems get disturbed, leading to flooding or water scarcity. Large earthquakes can cause tsunami waves in coastal areas, resulting in devastating loss of life and property, as seen in the 2004 Indian Ocean tsunami. The shaking can also cause cracks in the ground, damage roads and bridges, and disrupt communication and transportation networks.

Q2. Describe the classification of volcanoes based on eruptions. Volcanoes are classified into three types based on their eruption pattern:

• Active Volcanoes: These erupt frequently. There are about 600 active volcanoes in the world, most of which lie in the Pacific Ring of Fire. Examples include Mauna Loa in Hawaii (the world's biggest active volcano), Mt. Stromboli (known as the lighthouse of the Mediterranean Sea), St. Helens, and Pinatubo.

• Dormant Volcanoes: These have shown no sign of activity for many years but may become active at any time. They are also called "sleeping volcanoes." Examples include Vesuvius (Italy), Mt. Fujiyama (Japan), and Mt. Krakatoa (Indonesia).

• Extinct Volcanoes: These are volcanoes whose tops have been eroded away over time. They have not erupted in recorded history and are unlikely to erupt again. Examples include Mt. Popa (Myanmar), Mt. Kilimanjaro (Tanzania), and Mt. Kenya (Kenya).

Q3. Name the major zones of volcanic activity and explain any one. There are three major zones of volcanic activity in the world:

1. Circum-Pacific Belt (Pacific Ring of Fire): This is the convergent oceanic plate boundary zone that includes volcanoes along the eastern and western coasts of the Pacific Ocean. It is popularly called the "Pacific Ring of Fire" and includes approximately two-thirds of the world's volcanoes. This zone extends from New Zealand through Indonesia, the Philippines, Japan, the Aleutian Islands, and down the western coast of the Americas.

2. Mid-Continental Belt: This zone includes volcanoes in the Mediterranean region, the Himalayan region, and the Ganga-Brahmaputra valley.

3. Mid-Atlantic Belt: This zone includes volcanoes along the mid-Atlantic ridge, where tectonic plates are diverging.

Q4. Explain the divisions of Earth Movements. Lithospheric plate movements cause changes and forces on the Earth's surface. These movements are classified into two types:

• Endogenic Forces: These forces act in the interior of the Earth. They are responsible for phenomena like earthquakes and volcanic eruptions. Endogenic forces can further be classified into sudden forces (like earthquakes and volcanic eruptions that cause sudden changes) and slow forces (like mountain building that causes gradual changes over millions of years).

• Exogenic Forces: These forces work on the surface of the Earth. They include weathering, erosion, and deposition by rivers, wind, glaciers, and sea waves. These forces continuously shape and reshape the Earth's surface features.

Q5. What are the causes of Volcanic Activity? Volcanic activity is caused by the extreme temperature and pressure inside the Earth. Temperature increases at approximately 10 degrees Celsius per 35 metres of depth. This creates a semi-molten state of rock material called magma. Under great pressure, magma dissolves large volumes of combustible gases. When this pressurised magma finds a weak spot in the Earth's crust (such as a fracture or fault line), the volcanic material bursts through the surface, causing an eruption. The gases expand rapidly, pushing the magma upward through vents and craters, resulting in lava flows, ash clouds, and pyroclastic material.

Q6. Describe the distribution of Earthquakes and Volcanoes in the world. Earthquakes: About 68% of all earthquakes occur in the Pacific Ring of Fire, which encircles the Pacific Ocean. About 31% occur in the Mediterranean-Himalayan belt and Asia Minor. The remaining percentage occurs in Northern Africa, Rift Valley areas, and the Ganga-Brahmaputra Valley.

Volcanoes: Volcanoes are located in intensely folded or faulted regions. There are approximately 600 active volcanoes in the world, plus thousands of dormant and extinct ones. They occur along coastal mountain ranges, offshore islands, and mid-ocean ridges. The volcanic belts largely coincide with the principal earthquake belts, as both are caused by tectonic plate boundaries. The three major volcanic zones are: the Circum-Pacific belt (containing two-thirds of all volcanoes), the Mid-Continental belt, and the Mid-Atlantic belt.

Q7. Are Volcanoes Destructive or Constructive? (HOTS) Volcanoes are both destructive and constructive:

Constructive effects: Volcanic ash provides rich soil nutrients that make the land fertile for agriculture. Volcanic eruptions form plateaus and plains over time. Volcanoes also cool the Earth by releasing interior heat. Minerals and geothermal energy from volcanic regions are valuable resources.

Destructive effects: Volcanoes cause earthquakes, floods, mudslides, and rockfalls. Volcanic dust and ash harm living things, damage crops, and disrupt air travel. Lava flows destroy everything in their path. Toxic gases released during eruptions can be fatal.

Distinguish Between

SIAL vs. SIMA

Active Volcano vs. Dormant Volcano

Common Mistakes

1. Confusing Seismograph and Richter Scale: A seismograph records earthquake waves; the Richter Scale measures the magnitude. They are different instruments/concepts. 2. Mixing up SIAL and SIMA: SIAL = Silica + Alumina (continents, lighter); SIMA = Silica + Magnesium (ocean floors, denser). 3. Confusing Magma and Lava: Magma is inside the Earth; Lava is what magma is called after it reaches the surface. 4. Reversing discontinuity names: Mohorovicic separates Crust from Mantle; Weichart-Gutenberg separates Mantle from Core. 5. Confusing Vent and Crater: A vent is the narrow pipe through which magma flows; a crater is the bowl-shaped opening at the top. 6. Mixing up Active, Dormant, and Extinct volcanoes: Active = erupts frequently; Dormant = sleeping, may erupt; Extinct = eroded tops, unlikely to erupt. 7. Forgetting the core's two parts: The outer core is liquid (iron-rich); the inner core is solid (Nickel and Ferrous/Nife).

Exam Checklist

• [ ] Can you name the three layers of the Earth and their characteristics?
• [ ] Can you distinguish between SIAL and SIMA?
• [ ] Do you know the two discontinuities (Mohorovicic and Weichart-Gutenberg)?
• [ ] Can you define earthquake, seismograph, Richter Scale, and tsunami?
• [ ] Can you name the three types of earthquake waves (P, S, L)?
• [ ] Can you classify volcanoes as Active, Dormant, and Extinct with examples?
• [ ] Do you know the three major zones of volcanic activity?
• [ ] Can you explain what the Pacific Ring of Fire is?
• [ ] Can you distinguish between Active and Dormant volcanoes?
• [ ] Can you explain why the Earth's interior is very hot?
• [ ] Can you explain both the destructive and constructive effects of volcanoes?
• [ ] Do you know what happened in the 2004 tsunami?
• [ ] Can you explain the difference between endogenic and exogenic forces?
• [ ] Do you know the Richter Scale magnitudes and their effects (2.0 slight, 5.0+ damaging, 7.0+ major)?