Exercise Solutions Available
Step-by-step answers for all textbook questions in this chapter
Lithosphere I — Endogenetic Processes — Exercise Solutions Guide
Solve every exercise on your own first, then cross-check your answers here. Understanding why an answer is correct matters more than memorising it.
I. Multiple Choice Questions (MCQs)
Q1. The layer of the Earth immediately below the crust is the
(a) Outer core (b) Inner core (c) Mantle (d) Lithosphere
Q2. The point of origin of an earthquake inside the Earth is called the
(a) Epicentre (b) Focus (c) Crater (d) Seismograph
Q3. Which type of volcanic eruption is characterised by slow-moving lava flows?
(a) Explosive (b) Shield (c) Flood basalt (d) Composite
Q4. The super-continent proposed by Alfred Wegener is called
(a) Gondwanaland (b) Laurasia (c) Pangaea (d) Panthalassa
Q5. The Ring of Fire is associated with
(a) Volcanoes and earthquakes around the Atlantic Ocean (b) Volcanoes and earthquakes around the Pacific Ocean (c) Tsunami occurrences in the Indian Ocean (d) Mountain formation in the Himalayas
Q6. When two oceanic plates collide, which feature is formed?
(a) Rift valley (b) Ocean trench (c) Mid-ocean ridge (d) Fold mountain
Q7. The instrument used to measure seismic waves is called a
(a) Barometer (b) Thermometer (c) Seismograph (d) Hygrometer
Q8. Which of the following is an example of a dormant volcano?
(a) Mt. Fuji (b) Barren Island (c) Mt. Kilimanjaro (d) Mt. Vesuvius
Q9. The Earth's core is primarily composed of
(a) Silicon and aluminium (b) Iron and magnesium (c) Nickel and iron (d) Silicon and magnesium
Q10. Transform plate boundaries are characterised by
(a) Plates moving towards each other (b) Plates moving away from each other (c) Plates sliding past each other (d) Plates rotating in place
Q11. Tsunami waves are caused by
(a) Strong winds over the ocean (b) Underwater volcanic eruptions and earthquakes (c) Tidal forces of the moon (d) Ocean currents
Q12. Which layer of the Earth's interior is in a semi-solid (plastic) state?
(a) Crust (b) Asthenosphere (c) Lithosphere (d) Inner core
II. True or False
1. The crust is the thickest layer of the Earth.
2. The epicentre is the point on the Earth's surface directly above the focus.
3. Continental drift theory was proposed by Alfred Wegener.
4. Shield volcanoes are formed by explosive eruptions.
5. The mid-Atlantic ridge is an example of a divergent plate boundary.
6. The inner core of the Earth is in a liquid state.
7. Volcanoes are only found on land.
8. The Himalayas were formed by the collision of the Indian and Eurasian plates.
9. A seismograph measures the magnitude of an earthquake.
10. Tsunami waves in the open ocean are very tall and easily visible.
III. Fill in the Blanks
1. The outermost solid layer of the Earth is called the ___.
2. The boundary between the crust and the mantle is called the ___ discontinuity.
3. The liquid layer of the Earth's core is called the ___.
4. The theory of plate tectonics explains that the lithosphere is divided into several large and small blocks called ___.
5. When one plate slides beneath another at a convergent boundary, the process is called ___.
6. The Richter scale measures the ___ of an earthquake.
7. The Depression formed at the top of a volcanic cone is called the ___.
8. The super-ocean that surrounded Pangaea was called ___.
9. The point on the Earth's surface directly above the earthquake focus is called the ___.
10. The Hawaiian Islands are an example of ___ volcanoes.
IV. Match the Following
| Column A | Column B |
|---|---|
| 1. Crust | a. NiFe (Nickel and Iron) |
| 2. Mantle | b. SiAl (Silicon and Aluminium) |
| 3. Core | c. SiMa (Silicon and Magnesium) |
| 4. Focus | d. Point of origin inside the Earth |
| 5. Epicentre | e. Point on the surface directly above focus |
1 → b — The continental crust is predominantly composed of silicon and aluminium (SiAl), making it lighter and less dense than the oceanic crust. 2 → c — The mantle is mainly composed of silicon and magnesium (SiMa), making it denser than the crust but less dense than the core. 3 → a — The core is composed primarily of nickel and iron (NiFe), making it the densest layer of the Earth. 4 → d — The focus (hypocentre) is the exact point inside the Earth where an earthquake originates. 5 → e — The epicentre is the point on the Earth's surface located directly above the focus, where the earthquake is felt most intensely.
V. Short Answer Questions (2-3 marks)
Q1. What are endogenetic processes? Name two examples.
Endogenetic processes are forces that originate from within the Earth's interior. They are responsible for building up landforms on the surface. Two major examples are volcanism (eruption of magma onto the surface) and diastrophism (plate movements that cause folding, faulting, and mountain building). Earthquakes are also a result of endogenetic processes.
Q2. Distinguish between the focus and the epicentre of an earthquake.
The focus (hypocentre) is the point deep within the Earth where an earthquake originates — where the rocks first fracture and energy is released. The epicentre is the point on the Earth's surface that lies directly above the focus. Damage is usually greatest near the epicentre, and its location helps seismologists map earthquake distribution.
Q3. What is continental drift? Who proposed it?
Continental drift is the theory that the continents were once joined together as a single super-continent called Pangaea and have since slowly moved (drifted) apart to their present positions. This theory was proposed by the German meteorologist Alfred Wegener in 1912. Evidence supporting the theory includes the jigsaw-fit of continents (especially South America and Africa), fossil distributions across oceans, and matching rock formations on separate continents.
Q4. List three types of plate boundaries.
The three types of plate boundaries are: (1) Convergent boundaries — where plates move towards each other, causing subduction, folding, and mountain formation; (2) Divergent boundaries — where plates move apart, creating mid-ocean ridges and rift valleys; and (3) Transform boundaries — where plates slide past each other horizontally, causing earthquakes along fault lines such as the San Andreas Fault.
Q5. What is a tsunami? How is it caused?
A tsunami is a series of large ocean waves generated by a sudden displacement of the sea floor. It is most commonly caused by powerful underwater earthquakes, but volcanic eruptions and landslides can also trigger tsunamis. In the open ocean, tsunami waves are low and have long wavelengths, but they gain enormous height and destructive power as they approach shallow coastal waters.
Q6. Name the three layers of the Earth's interior and state one characteristic of each.
The three layers are: (1) Crust — the outermost, thinnest solid layer; continental crust is granitic (SiAl) while oceanic crust is basaltic (SiMa). (2) Mantle — the thickest layer (about 2,900 km), composed of semi-solid rock that flows slowly; contains the asthenosphere. (3) Core — the innermost layer made of nickel and iron (NiFe); the outer core is liquid while the inner core is solid due to extreme pressure.
Q7. What are the different types of volcanoes based on the nature of eruption?
Based on eruption type, volcanoes are classified as: (1) Shield volcanoes — formed by quiet eruptions of low-viscosity basaltic lava (e.g., Hawaiian volcanoes). (2) Composite volcanoes — formed by alternating layers of lava and ash from both explosive and quiet eruptions (e.g., Mt. Fuji). (3) Caldera volcanoes — formed when a violent eruption empties the magma chamber, causing the volcanic cone to collapse into a large depression. (4) Flood basalt volcanoes — formed by highly fluid lava that flows over vast areas, creating plateaus.
Q8. What is the Ring of Fire?
The Ring of Fire is a horseshoe-shaped zone around the Pacific Ocean, stretching from New Zealand along the eastern coast of Asia, across to the western coast of the Americas. It is the most seismically and volcanically active region in the world, containing about 75% of all active volcanoes and experiencing about 90% of all earthquakes. This activity results from the numerous subduction zones around the Pacific plate margins.
VI. Detailed Answer Questions (5 marks)
Q1. Explain the structure of the Earth's interior with a neat diagram description.
The Earth's interior consists of three major layers, each with distinct properties:
Crust: The outermost solid layer, ranging from 5 km (oceanic) to about 40 km (continental) in thickness. The continental crust is composed mainly of silicon and aluminium (SiAl) and is granitic in nature. The oceanic crust is composed of silicon and magnesium (SiMa) and is basaltic and denser. The boundary between the crust and the mantle is called the Mohorovicic (Moho) discontinuity.
Mantle: Extending from the Moho discontinuity to about 2,900 km depth, the mantle is the thickest layer. The upper part contains the asthenosphere, a semi-solid, plastic zone that allows tectonic plates to move. The lower mantle is more rigid. Rock in the mantle flows very slowly over geological time, driving convection currents that power plate tectonics.
Core: The innermost layer, divided into the outer core (liquid, about 2,900-5,150 km depth) and the inner core (solid, from 5,150 km to the centre at 6,371 km). The core is composed primarily of nickel and iron (NiFe). Temperatures reach up to 5,000 degrees Celsius. The liquid outer core generates the Earth's magnetic field through convection currents, while the inner core remains solid due to immense pressure despite the extreme heat.
Q2. Explain the theory of plate tectonics and the three types of plate boundaries with examples.
The theory of plate tectonics states that the Earth's lithosphere is divided into several large and small rigid blocks called tectonic plates, which float on the semi-solid asthenosphere below. These plates move due to convection currents in the mantle. Their movement causes major geological features and events. The three main types of plate boundaries are:
Convergent boundaries (plates move towards each other): When two plates collide, several outcomes are possible. When an oceanic plate meets a continental plate, the denser oceanic plate subducts beneath the continental plate, forming ocean trenches and volcanic mountain ranges (e.g., the Andes). When two continental plates collide, they form fold mountains (e.g., the Himalayas formed by the collision of the Indian and Eurasian plates). When two oceanic plates converge, the denser one subducts, forming trenches and volcanic island arcs.
Divergent boundaries (plates move apart): As plates separate, magma rises from the mantle to fill the gap, creating new crust. On the ocean floor, this creates mid-ocean ridges (e.g., the Mid-Atlantic Ridge). On land, divergent boundaries create rift valleys (e.g., the East African Rift Valley).
Transform boundaries (plates slide past each other): Plates move horizontally in opposite directions along a fault. No crust is created or destroyed. These boundaries cause powerful shallow earthquakes. The San Andreas Fault in California, where the Pacific Plate slides past the North American Plate, is the best-known example.
Q3. Describe the types of volcanoes and their global distribution.
Volcanoes are classified into four main types based on the nature of their eruptions and the materials they eject:
Shield Volcanoes: These are built by multiple quiet eruptions of low-viscosity basaltic lava that can flow over long distances, creating broad, gently sloping sides resembling a warrior's shield. The Hawaiian Islands (Mauna Loa) and the Deccan Traps of India are examples. They rarely cause violent explosions but can produce extensive lava fields.
Composite Volcanoes (Stratovolcanoes): Formed by alternating layers of lava flows and volcanic ash from both explosive and quiet eruptions. They have steep, symmetrical cones and are the most common type of volcano. Mt. Fuji (Japan), Mt. Vesuvius (Italy), and Mt. St. Helens (USA) are examples. They can produce devastating pyroclastic flows.
Caldera Volcanoes: Formed when a massive eruption empties the magma chamber beneath a volcano, causing the volcanic cone to collapse into a large depression called a caldera. Crater Lake in Oregon (USA) and the caldera of Santorini (Greece) are notable examples. Caldera-forming eruptions are among the most destructive volcanic events.
Flood Basalt Provinces: Formed by highly fluid basaltic lava that erupts through fissures and flows over vast areas, creating extensive plateaus. The Deccan Traps (India) and the Columbia Plateau (USA) are examples.
Global Distribution: Most volcanoes are distributed along plate boundaries. The Ring of Fire around the Pacific Ocean accounts for about 75% of all active volcanoes. Other major volcanic zones include the Mid-Atlantic Ridge, the East African Rift, and the Mediterranean belt. Some volcanoes also occur at hotspots (e.g., Hawaii), which are not at plate boundaries.
Q4. Write about earthquakes — causes, types of seismic waves, and effects.
Causes: Earthquakes are caused by the sudden release of energy stored in the Earth's crust due to the movement of tectonic plates. This release occurs when rocks along a fault line fracture after accumulating stress beyond their elastic limit. Other causes include volcanic activity, human activities such as dam construction and mining, and underground nuclear tests. The point of origin inside the Earth is called the focus, and the point on the surface directly above it is the epicentre.
Types of Seismic Waves: Earthquakes generate two main types of seismic waves: (1) Body waves — which travel through the Earth's interior. These include P-waves (Primary or compressional waves), which are the fastest and can travel through solids, liquids, and gases; and S-waves (Secondary or shear waves), which are slower and can only travel through solids. (2) Surface waves — which travel along the Earth's surface and cause the most destruction. They include Love waves and Rayleigh waves.
Effects: Earthquakes cause widespread destruction including collapse of buildings and infrastructure, loss of life, fires from broken gas lines, landslides, soil liquefaction, and tsunamis (when they occur under the ocean). The 2004 Indian Ocean earthquake (magnitude 9.1-9.3) triggered a devastating tsunami affecting multiple countries, killing over 2,30,000 people.
Measurement: Earthquake magnitude is measured using the Richter scale (each unit increase represents a tenfold increase in amplitude). The Mercalli scale measures earthquake intensity based on observed effects and damage.
Q5. Explain Alfred Wegener's Continental Drift Theory — its evidence and limitations.
The Theory: Alfred Wegener, a German meteorologist, proposed the Continental Drift Theory in 1912. He suggested that around 200 million years ago, all the continents were joined together as a single super-continent called Pangaea, surrounded by a super-ocean called Panthalassa. Pangaea gradually broke apart, and the continents drifted to their current positions over millions of years.
Evidence supporting the theory: 1. Jigsaw-fit of continents: The coastlines of South America and Africa fit together remarkably well, like pieces of a puzzle. 2. Fossil evidence: Identical fossils of the fern Glossopteris and the reptile Mesosaurus have been found in South America, Africa, India, Antarctica, and Australia — continents now separated by vast oceans. 3. Rock formations: Matching rock types, ages, and mountain chains are found on opposite sides of the Atlantic (e.g., the Appalachian Mountains match the Scottish Highlands). 4. Glacial evidence: Glacial deposits and striations from the same geological period are found in now-tropical regions of South America, Africa, and India, suggesting these landmasses were once near the South Pole. 5. Paleoclimatic evidence: Coal deposits (formed from tropical plants) found in Antarctica indicate it was once in a warmer latitude.
Limitations: Wegener could not explain the mechanism driving continental drift. He proposed that tidal forces and the centrifugal force of Earth's rotation caused the movement, but physicists demonstrated these forces were far too weak. Additionally, Wegener's estimated rate of drift (250 cm/year) was vastly exaggerated. Without a viable mechanism, the scientific community largely rejected the theory until the 1960s, when the theory of plate tectonics provided the explanation — convection currents in the mantle drive plate movement.
Common Mistakes
1. Confusing endogenetic and exogenetic processes: Endogenetic processes originate from within the Earth (earthquakes, volcanoes, plate movements) and build landforms up. Exogenetic processes are external forces (weathering, erosion, deposition) that wear landforms down. Remember: endo = within, exo = outside.
2. Mixing up focus and epicentre: The focus is inside the Earth; the epicentre is on the surface directly above it. A simple trick: "focus is found deep, epicentre is on the epidermis (surface)."
3. Stating the inner core is liquid: The inner core is solid because immense pressure prevents the iron-nickel alloy from melting, despite temperatures exceeding 5,000 degrees Celsius. Only the outer core is liquid.
4. Confusing continental crust and oceanic crust composition: Continental crust is SiAl (Silicon + Aluminium) — lighter and granitic. Oceanic crust is SiMa (Silicon + Magnesium) — denser and basaltic. This density difference explains why oceanic crust subducts beneath continental crust at convergent boundaries.
5. Saying shield volcanoes are explosive: Shield volcanoes are characterised by quiet, non-explosive eruptions of fluid basaltic lava. Composite volcanoes are the explosive type. The key difference is lava viscosity — thin (basaltic) lava forms shields; thick (andesitic/rhyolitic) lava forms composite volcanoes.
6. Confusing the Richter scale and Mercalli scale: The Richter scale measures earthquake magnitude (energy released) using instruments, expressed as a number (e.g., 7.2). The Mercalli scale measures earthquake intensity (observed damage and effects) qualitatively using Roman numerals (e.g., IX). They measure different things.
7. Forgetting that tsunamis are caused by underwater events, not surface winds: Tsunamis are generated by sudden displacement of the sea floor due to underwater earthquakes, volcanic eruptions, or landslides. They are entirely different from wind-generated ocean waves in both origin and behaviour.
Exam Checklist
- [ ] Can describe all three layers of the Earth's interior (crust, mantle, core) with composition and properties
- [ ] Can distinguish between SiAl and SiMa, and between oceanic and continental crust
- [ ] Can explain the Mohorovicic, Gutenberg, and Repetti discontinuities
- [ ] Can define and give examples of convergent, divergent, and transform plate boundaries
- [ ] Can explain Wegener's Continental Drift Theory with at least four pieces of evidence and its limitations
- [ ] Can differentiate between focus and epicentre of an earthquake
- [ ] Can list and explain the four types of volcanoes with examples
- [ ] Can describe the Ring of Fire and its significance
- [ ] Can explain tsunami formation and why they become destructive near coasts
- [ ] Can distinguish between P-waves and S-waves
- [ ] Can explain why the inner core is solid while the outer core is liquid
- [ ] Can define key terms: subduction, lithosphere, asthenosphere, Pangaea, Panthalassa, caldera
Internal Links
- [Class 9 Social Science — Lithosphere I Endogenetic Processes Guide](/school/tamil-nadu-state-board/class/9/social/lithosphere-i-endogenetic-processes)
- [All Class 9 Social Solutions](/school/tamil-nadu-state-board/class/9/social/solutions)
- [Class 9 Social Science Subject Guide](/school/tamil-nadu-state-board/class/9/social)