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Earth structure and geomorphology

Geography

Useful for: UPSC Civil Services, OSSC RHT — Regular High School Teacher, OSEPA Upper Primary — Arts, OSSC Geography, OSSSC Govt TGT Arts, SSB Lecturer (Degree Colleges), SSB TGT Arts

Overview

Seismic waves reveal the Earth’s layered interior; plate tectonics explains earthquakes, volcanoes and mountain building.

Key points

Layers: crust, mantle, outer core (liquid), inner core (solid).
Discontinuities: Mohorovičić (crust–mantle), Gutenberg (mantle–core), Lehmann (outer–inner core).
P-waves pass through solids and liquids; S-waves only through solids — so S-waves do not cross the liquid outer core.
The seismic shadow zone lies between about 105° and 145° from the epicentre.
Wegener proposed continental drift (1912) with a supercontinent, Pangaea; Harry Hess proposed sea-floor spreading.
Plate boundaries: divergent (mid-ocean ridges), convergent (subduction, fold mountains such as the Himalaya), transform (e.g. San Andreas Fault).

Explanation

The Himalaya formed by the collision of the Indian and Eurasian plates.
Ring of Fire around the Pacific marks subduction zones.
Hotspots (e.g. Hawaii) form volcanoes away from boundaries.
Earthquake magnitude is measured on the Richter or moment-magnitude scale.
Palaeomagnetism supports sea-floor spreading.

Step by step

Identify the concept, law or fact asked.
Recall the definition, formula, example or year.
Apply it and eliminate mismatched options.

Examples

Statement: "S-waves pass through the outer core." → Incorrect.
Statement: "The Gutenberg discontinuity separates mantle and core." → Correct.
Statement: "The San Andreas Fault is a transform boundary." → Correct.

Traps and advanced points

Trap: Mixing discontinuities.
Trap: Letting S-waves cross liquids.
Trap: Calling the Himalaya a divergent boundary.

Quick revision

Moho, Gutenberg, Lehmann.
S-waves only in solids.
Divergent, convergent, transform.

Practice MCQs

From the perspective of definition and scope, which one of the following statements about Earth Interior & Plate Tectonics is correct?
1. Earth Interior & Plate Tectonics has no exceptions or limitations in exam analysis.
2. The lithosphere is broken into plates moving over the weaker asthenosphere.
3. Earthquakes and volcanoes are randomly distributed and show no systematic relationship with plate boundaries.
4. Earth Interior & Plate Tectonics is unrelated to institutions, processes or real-world applications.
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Answer: (b) The lithosphere is broken into plates moving over the weaker asthenosphere.. The lithosphere is broken into plates moving over the weaker asthenosphere.
Consider the following statements on Earth Interior & Plate Tectonics, focusing on definition and scope: 1. Earthquakes and volcanoes are randomly distributed and show no systematic relationship with plate boundaries. 2. The lithosphere is broken into plates moving over the weaker asthenosphere. Which of the statements given above is/are correct?
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Read chapter notes · Similar questions
Show answer
Answer: (b) 2 only. Statement 2 is correct; Statement 1 is a common misconception.
With reference to Earth Interior & Plate Tectonics (definition and scope), consider the following statements: 1. Earthquakes and volcanoes are randomly distributed and show no systematic relationship with plate boundaries. 2. Convergent, divergent and transform boundaries produce different combinations of earthquakes, volcanism and crustal change. Which of the statements given above is/are correct?
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Read chapter notes · Similar questions
Show answer
Answer: (b) 2 only. Only statement 2 is correct.
From the perspective of institutional design, which one of the following statements about Earth Interior & Plate Tectonics is correct?
1. Convergent, divergent and transform boundaries produce different combinations of earthquakes, volcanism and crustal change.
2. Local winds may arise from thermal or topographic contrasts and can differ sharply from planetary wind systems.
3. Rivers, glaciers, wind and waves create distinctive erosional and depositional landforms.
4. Similar-looking landforms can have different origins, so process matters more than visual resemblance alone.
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Answer: (a) Convergent, divergent and transform boundaries produce different combinations of earthquakes, volcanism and crustal change.. Convergent, divergent and transform boundaries produce different combinations of earthquakes, volcanism and crustal change.
Consider the following statements on Earth Interior & Plate Tectonics and Monsoon System, focusing on practical application: 1. Earthquakes and volcanoes are randomly distributed and show no systematic relationship with plate boundaries. 2. The Indian monsoon depends only on local land heating and is unaffected by ocean-atmosphere variability. Which of the statements given above is/are correct?
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
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Answer: (d) Neither 1 nor 2. Neither statement is correct; both are common misconceptions.
With reference to Earth Interior & Plate Tectonics (institutional design), consider the following statements: 1. Earthquakes and volcanoes are randomly distributed and show no systematic relationship with plate boundaries. 2. Subduction recycles oceanic lithosphere and is associated with trenches and volcanic arcs. Which of the statements given above is/are correct?
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
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Answer: (b) 2 only. Only statement 2 is correct.
From the perspective of working mechanism, which one of the following statements about Earth Interior & Plate Tectonics is correct?
1. Tides are primarily driven by gravitational interactions involving the Moon and Sun.
2. Subduction recycles oceanic lithosphere and is associated with trenches and volcanic arcs.
3. Latitudinal energy imbalance drives atmospheric and oceanic circulation.
4. River-source-mouth and upstream-downstream relations are especially useful for map elimination.
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Answer: (b) Subduction recycles oceanic lithosphere and is associated with trenches and volcanic arcs.. Subduction recycles oceanic lithosphere and is associated with trenches and volcanic arcs.
Consider the following statements on Earth Interior & Plate Tectonics, focusing on working mechanism: 1. Subduction recycles oceanic lithosphere and is associated with trenches and volcanic arcs. 2. Earthquakes and volcanoes are randomly distributed and show no systematic relationship with plate boundaries. Which of the statements given above is/are correct?
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Read chapter notes · Similar questions
Show answer
Answer: (a) 1 only. Statement 1 is correct; Statement 2 is a common misconception.
Consider the following statements on Earth Interior & Plate Tectonics, focusing on institutional design: 1. Earthquakes and volcanoes are randomly distributed and show no systematic relationship with plate boundaries. 2. Convergent, divergent and transform boundaries produce different combinations of earthquakes, volcanism and crustal change. Which of the statements given above is/are correct?
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Read chapter notes · Similar questions
Show answer
Answer: (b) 2 only. Only statement 2 is correct, so the answer is (B) 2 only. Statement 2 is correct; Statement 1 is a common misconception.
With reference to Earth Interior & Plate Tectonics (working mechanism), consider the following statements: 1. Earthquakes and volcanoes are randomly distributed and show no systematic relationship with plate boundaries. 2. Plate tectonics links continental drift, sea-floor spreading and global patterns of seismicity. Which of the statements given above is/are correct?
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Read chapter notes · Similar questions
Show answer
Answer: (b) 2 only. Only statement 2 is correct, so the answer is (B) 2 only. Statement 1 is incorrect — it is an overstated or wrong claim. Correct position: Convergent, divergent and transform boundaries produce different combinations of earthquakes, volcanism and crustal change. Statement 2 is correct.