🪨 Introduction 

Understanding the internal structure of the Earth is fundamental for every mining engineer. DGMS exams test your ability to relate geological formations with mining hazards, stability, and mineral occurrence.
The Earth is composed of three main layers — the Crust, Mantle, and Core, separated by discontinuities like Mohorovičić (Moho) and Gutenberg.

---

🧭Layers of the Earth Crust

• The outermost solid shell of the Earth.
• Average thickness:
• 35 km under continents (continental crust)
• 5–10 km under oceans (oceanic crust)
• Composed mainly of silica (Si) and alumina (Al) — hence called SIAL.
• Dominant rocks: Granite (continental), Basalt (oceanic).
• Temperature: ~0°C to 870°C at base.

---

Mantle

• Lies below the crust up to ~2900 km.
• Divided into upper and lower mantle.
• Made of silicate minerals rich in magnesium and iron — hence called SIMA.
• Semi-solid plastic layer — Asthenosphere — allows tectonic plate movement.
• Temperature: 870°C to 2200°C.

---

Core

• Extends from 2900 km to Earth’s center (~6371 km).
• Composed of nickel and iron (NIFE).
• Outer core: molten; Inner core: solid due to immense pressure.
• Source of Earth’s magnetic field.
• Temperature: ~5000–7000°C.

---

🧪  Major Discontinuities

1. Mohorovičić Discontinuity (Moho): Between crust & mantle.
2. Gutenberg Discontinuity: Between mantle & core.
3. Lehmann Discontinuity: Between outer & inner core.

These boundaries represent changes in seismic wave velocity and material composition.

---

🌋  DGMS Exam Relevance

• Understanding layers helps in ore formation processes (igneous/sedimentary).
• Crucial for mine hazard prediction – e.g., geothermal gradient, rock pressure.
• Geological mapping & drilling depend on structural knowledge.

---

⚡ Quick One-Liners

• Earth’s radius = 6371 km
• Crust composition = SIAL
• Mantle composition = SIMA
• Core composition = NIFE
• Moho discontinuity separates crust & mantle
• Gutenberg discontinuity separates mantle & core
• Lehmann discontinuity separates outer & inner core

---

These layers are separated by discontinuities — Moho, Gutenberg, and Lehmann.
Understanding them is vital for predicting geological stability, mine planning, and assessing ore deposits.

---

🎯 25 MCQs (DGMS Pattern) 

  Q1. The average thickness of the Earth’s crust under continents is: A. 5–10 km
B. 20 km
C. 35 km
D. 50 km
E. 100 km
Answer: C.
Solution: Continental crust is ~35 km thick.

---

Q2. The Earth’s crust mainly consists of: A. Iron & Nickel
B. Silica & Alumina
C. Magnesium & Iron
D. Sulphur & Carbon
E. Calcium & Sodium
Answer: B.
Solution: SIAL = silica + alumina.

---

Q3. Which discontinuity separates crust from mantle? A. Lehmann
B. Gutenberg
C. Moho
D. Conrad
E. Asthenosphere
Answer: C.
Solution: Mohorovičić (Moho) discontinuity marks this boundary.

---

Q4. The main elements of Earth’s core are: A. Fe & Ni
B. Si & Al
C. Mg & Ca
D. Na & K
E. Cu & Zn
Answer: A.
Solution: NIFE = Nickel + Iron.

---

Q5. Earth’s radius is approximately: A. 3500 km
B. 4500 km
C. 6371 km
D. 8000 km
E. 9000 km
Answer: C.
Solution: Earth’s radius = 6371 km.

---

Q6. The semi-fluid layer that allows tectonic plates to move is: A. Lithosphere
B. Asthenosphere
C. Hydrosphere
D. Atmosphere
E. Magnetosphere
Answer: B.
Solution: Asthenosphere is the mobile layer of mantle.

---

Q7. The outer core is: A. Solid
B. Liquid
C. Gaseous
D. Mixed
E. Semi-solid
Answer: B.
Solution: Outer core is molten, inner core is solid.

---

Q8. The boundary between outer and inner core is called: A. Moho
B. Lehmann
C. Gutenberg
D. Conrad
E. Sima
Answer: B.
Solution: Lehmann discontinuity divides core layers.

---

Q9. The main source of Earth’s magnetic field is: A. Crustal rocks
B. Mantle heat
C. Core movement
D. Volcanoes
E. Solar winds
Answer: C.
Solution: Generated by movement of molten iron in outer core.

---

Q10. The Moho discontinuity is discovered using: A. Drilling
B. Seismic waves
C. Satellite imagery
D. Mining
E. Borehole samples
Answer: B.
Solution: Identified by change in seismic wave velocity.

---

Q11. The layer directly below crust is: A. Core
B. Lithosphere
C. Mantle
D. Troposphere
E. Hydrosphere
Answer: C.
Solution: Mantle lies beneath crust.

---

Q12. The continental crust mainly consists of: A. Basalt
B. Granite
C. Gabbro
D. Andesite
E. Peridotite
Answer: B.
Solution: Granite-rich crust forms continents.

---

Q13. Oceanic crust mainly consists of: A. Granite
B. Basalt
C. Sandstone
D. Limestone
E. Quartzite
Answer: B.
Solution: Basalt forms oceanic crust.

---

Q14. The mantle is composed mostly of: A. SIAL
B. SIMA
C. NIFE
D. Iron oxides
E. Silicates of sodium
Answer: B.
Solution: SIMA = silica + magnesium.

---

Q15. The innermost solid part of Earth is: A. Mantle
B. Crust
C. Outer Core
D. Inner Core
E. Moho
Answer: D.
Solution: Inner core is solid due to pressure.

---

Q16. The temperature at the Earth’s core is approximately: A. 1000°C
B. 2200°C
C. 5000–7000°C
D. 10,000°C
E. 900°C
Answer: C.
Solution: Inner core temperatures reach 7000°C.

---

Q17. Which layer contributes to volcanic activity? A. Core
B. Crust
C. Mantle
D. Asthenosphere
E. Lithosphere
Answer: D.
Solution: Asthenosphere supports magma movement.

---

Q18. Earthquake waves provide data about: A. Ocean salinity
B. Earth’s interior
C. Rock strength
D. Wind speed
E. Surface erosion
Answer: B.
Solution: Seismic studies reveal internal layers.

---

Q19. The uppermost rigid layer is called: A. Lithosphere
B. Mesosphere
C. Asthenosphere
D. Troposphere
E. Crustal zone
Answer: A.
Solution: Lithosphere = crust + upper mantle.

---

Q20. Which layer has the highest density? A. Crust
B. Mantle
C. Core
D. Lithosphere
E. Asthenosphere
Answer: C.
Solution: Core (NIFE) is densest. 

  Q21. The thermal gradient in Earth’s crust is defined as:
A. Increase of temperature with depth
B. Increase of pressure with altitude
C. Decrease of gravity with depth
D. Variation of seismic velocity
E. None of the above
Answer: A.
Solution: Thermal gradient = rate of increase of temperature with depth (~30°C/km). 

  Q22. The Mohorovičić discontinuity (Moho) separates:
A. Crust and Mantle
B. Mantle and Core
C. Inner and Outer Core
D. Lithosphere and Hydrosphere
E. Mantle and Asthenosphere
Answer: A.
Solution: The Moho marks the boundary between Earth's crust and mantle. 

  Q23. The Appellate Medical Board constituted under Rule 29K operates under which statutory authority?
A. Ministry of Coal
B. Directorate General of Mines Safety (DGMS)
C. Ministry of Labour & Employment
D. State Mining Department
E. Ministry of Mines
Answer: B.
Solution: DGMS is the statutory authority for mine health, safety, and medical supervision.

  Q24. Seismic methods are primarily used in mining geology for:
A. Measuring mine air velocity
B. Detecting subsurface rock structure and faults
C. Determining mine humidity
D. Estimating ore assay value
E. Measuring gas concentration
Answer: B.
Solution: Seismic exploration detects discontinuities and structures like faults or ore zones. 

  Q25. In mining areas, mineral zoning occurs primarily due to:
A. Uniform temperature
B. Hydrothermal activity and pressure variation
C. Biological decomposition
D. Sedimentation alone
E. Chemical weathering only
Answer: B.
Solution: Hydrothermal and pressure-temperature variations create mineral zones, vital for exploration planning. 

  🧩 Conclusion 

 Rule 29K of the Mines Rules, 1955 empowers miners to appeal for a fair medical re-examination under DGMS oversight, ensuring transparency and worker welfare.
Understanding such statutory rights is vital not only for legal compliance but also for mine managers and engineers appearing for DGMS First/Second Class Examinations.
Moreover, DGMS emphasizes integrating geological understanding (like structural zones, thermal gradients, and seismic safety) in managerial decision-making — making these topics essential for holistic exam preparation. The internal structure of the Earth forms the basis for understanding mineral formation, tectonics, and mine design. For DGMS exams, remember key data:

• Earth’s layers (Crust, Mantle, Core)
• Major discontinuities (Moho, Gutenberg, Lehmann)
• Composition (SIAL, SIMA, NIFE)

---

👉 Practice Geology & Earth Structure MCQs with OnlineMiningExam’s Daily Quizzes, Mock Tests & Video Classes to ace your DGMS exam.
Visit 🔗 www.onlineminingexam.com | 📞 Call/WhatsApp: 9971114020

---

---

• 
  

---