**Earth's Structure:** Crust (30–40 km continental, 5–7 km oceanic) → Mantle (2900 km) → Outer Core (2200 km) → Inner Core (1250 km). Lithosphere = crust + upper mantle. Asthenosphere = semi-molten layer below.
**Plate Tectonics:** Large slabs move a few cm/year due to mantle convection. Three types: continental (carry continents), oceanic (carry ocean floors), mixed (both).
**Plate Boundaries:** (1) Convergent—plates collide → fold mountains (Himalaya) or subduction (earthquakes, volcanoes). (2) Divergent—plates separate → magma rises → new crust (Mid-Atlantic Ridge). (3) Transform—plates slide past → earthquakes (San Andreas Fault).
**Landforms:** Mountains, valleys, plateaus, plains, deserts, coastal features—all formed by weathering, erosion, deposition, crustal movement.
**Ring of Fire:** Pacific Ocean rim; 80% global earthquakes & volcanoes occur here due to converging plate boundaries.
**India's Risk:** Indo-Australian plate collides with Eurasian plate → earthquake vulnerability (2001 Gujarat example).
Q1. Who gave the theory of plate tectonics?
Answer: A — W.J. Morgan is credited with giving the important theory of plate tectonics that explains Earth's crust movement.
Q2. What is the thickness of the continental crust?
Answer: C — Continental crust is 30–40 km thick, while oceanic crust is only 5–7 km thick.
Q3. Which layer of Earth allows tectonic plates to move?
Answer: B — The semi-molten asthenosphere beneath the lithosphere allows tectonic plates to move slowly.
Q4. If two oceanic plates move away from each other at a divergent boundary, what forms?
Answer: C — At divergent boundaries, magma rises from below and creates new oceanic crust, forming mid-ocean ridges like the Mid-Atlantic Ridge.
Q5. Which of the following is NOT a type of tectonic plate boundary?
Answer: D — There are only three main types of plate boundaries: convergent, divergent, and transform; subduction is a process occurring at convergent boundaries, not a separate boundary type.
Q6. Ramesh observes that the Himalayan Mountains are still growing at a slow rate. Which plate boundary concept explains this?
Answer: B — The Himalaya form at a convergent boundary where the Indo-Australian plate collides with the Eurasian plate, causing continuous uplift.
Q7. Why do most earthquakes and volcanoes occur along the Ring of Fire?
Answer: B — The Ring of Fire marks where multiple tectonic plates meet around the Pacific Ocean, causing 80% of the world's earthquakes and volcanoes.
Q8. Which of the following best explains why the 2001 Gujarat earthquake caused severe damage in India?
Answer: B — India sits on the Indo-Australian plate that collides with the Eurasian plate, creating earthquake risk; high population density means greater human cost.
Q9. When an oceanic plate collides with a continental plate at a convergent boundary, what typically occurs?
Answer: B — In oceanic-continental convergence, the denser oceanic plate subducts under the continental plate, triggering earthquakes and volcanic arcs.
Q10. According to Varāhamihira in the Bṛihatsaṁhitā, earthquakes (bhūkampa) were attributed to which forces?
Answer: B — Varāhamihira identified four elemental forces—Vāyu, Agni, Indra, and Varuṇa—linked to specific regions and constellations, showing ancient Indian earthquake understanding.
What is plate tectonics?
Plate tectonics is the theory that Earth's crust is broken into large, slow-moving pieces called tectonic plates that reshape the surface.
Name the three main layers of Earth.
The three layers are crust (outermost), mantle (thick and hot middle layer), and core (innermost, extremely hot).
What is the lithosphere?
The lithosphere is the rigid outer layer of Earth composed of the crust and upper mantle, and is broken into tectonic plates.
What causes tectonic plates to move?
Convection currents in the mantle, caused by heat from Earth's core, push and pull the tectonic plates.
Describe a convergent plate boundary.
A convergent boundary is where two plates move towards each other, forming fold mountains or causing subduction and volcanic activity.
What is the Ring of Fire?
The Ring of Fire is an area around the Pacific Ocean where 80% of the world's earthquakes and volcanoes occur along plate boundaries.
Define a landform.
A landform is a natural feature on Earth's surface formed by weathering, erosion, deposition, and crustal movement, such as mountains or valleys.
What happens at a divergent plate boundary?
At a divergent boundary, plates move away from each other, magma rises, and new crust forms, creating features like mid-ocean ridges.
What is the asthenosphere?
The asthenosphere is a semi-molten layer beneath the lithosphere that allows tectonic plates to move slowly.
Why is India at risk of earthquakes?
India is at risk of earthquakes because it lies on the Indo-Australian plate that is colliding with the Eurasian plate, creating tectonic stress.
Define plate tectonics and explain why the theory is important for understanding Earth's surface. [2 marks]
State that plate tectonics explains movement of Earth's crust in broken pieces called plates. Explain it helps predict earthquakes, volcanoes, and landform formation.
Compare convergent and divergent plate boundaries, and explain the landforms or features that result from each type of boundary. [3 marks]
Convergent: plates move toward each other → fold mountains (Himalaya) or subduction with earthquakes/volcanoes. Divergent: plates move apart → magma rises → new crust and mid-ocean ridges form.
Explain why India is vulnerable to earthquakes and discuss the potential impact of a major earthquake on human life and the environment in a densely populated country like India. Use the 2001 Gujarat earthquake as an example. [5 marks]
Explain Indo-Australian plate collision with Eurasian plate creates tectonic stress in India. Discuss how dense population, infrastructure damage, casualties, and environmental destruction increase vulnerability. Reference Gujarat 2001: thousands killed, extensive property damage, economic loss, and displacement of people.
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