1. The study of Earth’s interior is primarily based on—
a) Direct drilling
b) Volcanic activity
c) Seismic waves
d) Fossils
Answer: c) Seismic waves
Explanation: Since direct access is limited, scientists study earthquake-generated seismic waves to infer Earth’s interior.
2. The average radius of the Earth is about—
a) 3,276 km
b) 5,276 km
c) 6,371 km
d) 7,500 km
Answer: c) 6,371 km
Explanation: The Earth’s mean radius is approximately 6,371 km.
3. The innermost layer of the Earth is—
a) Crust
b) Mantle
c) Outer core
d) Inner core
Answer: d) Inner core
Explanation: The solid inner core is Earth’s deepest layer, mainly composed of iron and nickel.
4. The Mohorovičić discontinuity (Moho) separates—
a) Mantle and outer core
b) Crust and mantle
c) Inner core and outer core
d) Lithosphere and asthenosphere
Answer: b) Crust and mantle
Explanation: The Moho marks the boundary between Earth’s crust and mantle.
5. The core of the Earth is mainly composed of—
a) Oxygen and silicon
b) Iron and nickel
c) Magnesium and aluminum
d) Sodium and potassium
Answer: b) Iron and nickel
Explanation: Earth’s core is metallic, made primarily of iron and nickel (NiFe).
6. The outer core of Earth is in which state?
a) Solid
b) Liquid
c) Semi-solid
d) Gas
Answer: b) Liquid
Explanation: The outer core is liquid metal, responsible for Earth’s magnetic field.
7. The inner core of Earth is—
a) Solid
b) Liquid
c) Semi-molten
d) Gas
Answer: a) Solid
Explanation: Despite high temperatures, pressure keeps the inner core solid.
8. The crust is thickest under—
a) Continents
b) Oceans
c) Islands
d) Rivers
Answer: a) Continents
Explanation: Continental crust averages 35 km thick (up to 70 km under mountains), while oceanic crust averages 5–10 km.
9. The crust is primarily composed of—
a) Basalt and granite
b) Iron and nickel
c) Carbonates and sulphates
d) Argon and nitrogen
Answer: a) Basalt and granite
Explanation: Continental crust is granitic, while oceanic crust is basaltic.
10. The mantle extends to a depth of about—
a) 30 km
b) 100 km
c) 2,900 km
d) 5,200 km
Answer: c) 2,900 km
Explanation: The mantle lies between the crust and core, up to ~2,900 km deep.
11. The Gutenberg discontinuity separates—
a) Crust and mantle
b) Mantle and outer core
c) Outer core and inner core
d) Lithosphere and asthenosphere
Answer: b) Mantle and outer core
Explanation: Gutenberg discontinuity lies at ~2,900 km depth between mantle and outer core.
12. The Lehmann discontinuity lies between—
a) Crust and mantle
b) Mantle and outer core
c) Outer core and inner core
d) Lithosphere and asthenosphere
Answer: c) Outer core and inner core
Explanation: Lehmann discontinuity (at ~5,150 km depth) separates the liquid outer core from solid inner core.
13. Which part of Earth generates its magnetic field?
a) Crust
b) Mantle
c) Outer core
d) Inner core
Answer: c) Outer core
Explanation: Movement of liquid iron in the outer core creates Earth’s magnetic field.
14. The lithosphere includes—
a) Crust only
b) Mantle only
c) Crust and uppermost mantle
d) Core
Answer: c) Crust and uppermost mantle
Explanation: The rigid lithosphere consists of crust plus upper mantle, broken into tectonic plates.
15. Beneath the lithosphere lies—
a) Asthenosphere
b) Mesosphere
c) Outer core
d) Moho
Answer: a) Asthenosphere
Explanation: The asthenosphere is a ductile, partially molten layer on which lithospheric plates float.
16. The average density of Earth is about—
a) 2.5 g/cm³
b) 3.3 g/cm³
c) 5.5 g/cm³
d) 7.9 g/cm³
Answer: c) 5.5 g/cm³
Explanation: Earth’s mean density is 5.5 g/cm³, higher than surface rocks, indicating a dense metallic core.
17. The oceanic crust is mainly composed of—
a) Granite
b) Basalt
c) Limestone
d) Sandstone
Answer: b) Basalt
Explanation: Oceanic crust is basaltic, denser than continental granite.
18. The continental crust is mainly composed of—
a) Basalt
b) Granite
c) Iron
d) Gabbro
Answer: b) Granite
Explanation: Continental crust is granitic, lighter than oceanic crust.
19. Which seismic waves cannot pass through liquid?
a) P-waves
b) S-waves
c) L-waves
d) Surface waves
Answer: b) S-waves
Explanation: S-waves (shear waves) cannot travel through liquids, proving the outer core is liquid.
20. Which seismic waves are the fastest?
a) P-waves
b) S-waves
c) Surface waves
d) L-waves
Answer: a) P-waves
Explanation: Primary (P) waves are fastest and arrive first at seismic stations.
21. The depth of the Moho discontinuity beneath continents is about—
a) 5–10 km
b) 20–30 km
c) 35 km average
d) 100 km
Answer: c) 35 km average
Explanation: The Moho is deeper under continents (~35 km) than oceans (~5–10 km).
22. The asthenosphere lies at what depth?
a) 0–10 km
b) 30–100 km
c) 100–400 km
d) 2,900–5,100 km
Answer: c) 100–400 km
Explanation: Asthenosphere is a weak, ductile layer of upper mantle at ~100–400 km depth.
23. The temperature at Earth’s center is estimated to be—
a) 500°C
b) 1,500°C
c) 3,000°C
d) 5,000–6,000°C
Answer: d) 5,000–6,000°C
Explanation: The inner core reaches ~5,000–6,000°C, similar to Sun’s surface.
24. The term “SIAL” refers to—
a) Oceanic crust (Silica + Magnesium)
b) Continental crust (Silica + Aluminum)
c) Mantle composition
d) Core composition
Answer: b) Continental crust (Silica + Aluminum)
Explanation: Continental crust is rich in silica and aluminum, hence “SIAL”.
25. The term “SIMA” refers to—
a) Core composition
b) Oceanic crust (Silica + Magnesium)
c) Continental crust
d) Lithosphere
Answer: b) Oceanic crust (Silica + Magnesium)
Explanation: Oceanic crust is mainly basaltic, rich in silica and magnesium – “SIMA”.
26. Which is the thinnest layer of the Earth?
a) Crust
b) Mantle
c) Outer core
d) Inner core
Answer: a) Crust
Explanation: The crust is Earth’s outermost and thinnest layer (5–70 km).
27. The average thickness of oceanic crust is about—
a) 70 km
b) 50 km
c) 30 km
d) 5–10 km
Answer: d) 5–10 km
Explanation: Oceanic crust is very thin compared to continental crust.
28. Which part of the Earth is responsible for volcanic eruptions?
a) Inner core
b) Outer core
c) Mantle
d) Crust
Answer: c) Mantle
Explanation: Magma originates from the mantle and erupts through the crust.
29. The average thickness of continental crust is about—
a) 5 km
b) 35 km
c) 70 km
d) 100 km
Answer: b) 35 km
Explanation: Continental crust is ~35 km thick, reaching up to 70 km under mountains.
30. Which element is the most abundant in Earth’s crust?
a) Oxygen
b) Silicon
c) Iron
d) Magnesium
Answer: a) Oxygen
Explanation: Oxygen makes up ~47% of Earth’s crust by weight.
31. Which element is the second most abundant in Earth’s crust?
a) Silicon
b) Iron
c) Magnesium
d) Calcium
Answer: a) Silicon
Explanation: Silicon is ~28% of the crust, mainly in silicate minerals.
32. Which two elements together make up about 75% of Earth’s crust?
a) Iron and nickel
b) Silicon and oxygen
c) Magnesium and aluminum
d) Calcium and sodium
Answer: b) Silicon and oxygen
Explanation: Together they form silicates, the dominant crustal minerals.
33. The “Conrad Discontinuity” separates—
a) Continental crust and oceanic crust
b) Upper and lower mantle
c) Lithosphere and asthenosphere
d) Outer and inner core
Answer: a) Continental crust and oceanic crust
Explanation: It separates the granitic upper crust from basaltic lower crust.
34. The “Repetti Discontinuity” separates—
a) Crust and mantle
b) Mantle and outer core
c) Upper and lower mantle
d) Outer and inner core
Answer: c) Upper and lower mantle
Explanation: It lies at ~1,000 km depth, dividing upper and lower mantle.
35. Which layer of Earth is known as the “mesosphere” (not atmosphere)?
a) Outer mantle
b) Lower mantle
c) Inner core
d) Crust
Answer: b) Lower mantle
Explanation: The lower mantle (660–2,900 km depth) is sometimes called the mesosphere.
36. Which layer of the Earth is directly involved in plate tectonic movement?
a) Inner core
b) Outer core
c) Lithosphere
d) Asthenosphere
Answer: d) Asthenosphere
Explanation: The ductile asthenosphere allows lithospheric plates to move over it.
37. Earthquake shadow zones are formed because—
a) S-waves cannot pass through liquid outer core
b) P-waves travel straight lines
c) Crust blocks the waves
d) Inner core absorbs waves
Answer: a) S-waves cannot pass through liquid outer core
Explanation: This creates an S-wave shadow zone, while P-waves bend, creating their own shadow zone.
38. The seismic shadow zone of P-waves lies between—
a) 0°–103°
b) 103°–143°
c) 143°–180°
d) 0°–90°
Answer: b) 103°–143°
Explanation: P-waves are refracted at the core-mantle boundary, creating a 103°–143° shadow zone.
39. The density of Earth increases with depth due to—
a) Temperature decrease
b) Pressure increase
c) Composition change
d) Both b and c
Answer: d) Both b and c
Explanation: Density rises from crust (~2.7 g/cm³) to core (~13 g/cm³) because of pressure and composition.
40. Which discontinuity marks the boundary between lithosphere and asthenosphere?
a) Moho
b) Repetti
c) Conrad
d) Low-velocity zone
Answer: d) Low-velocity zone
Explanation: The lithosphere-asthenosphere boundary is identified by a low-velocity zone of seismic waves.
41. The most abundant metal in Earth’s crust is—
a) Iron
b) Aluminum
c) Magnesium
d) Calcium
Answer: b) Aluminum
Explanation: Aluminum is the most abundant metallic element in the crust (~8%).
42. The most abundant element in Earth as a whole is—
a) Oxygen
b) Silicon
c) Iron
d) Nickel
Answer: c) Iron
Explanation: Iron dominates the core, making it the most abundant element in the entire Earth.
43. Which layer is responsible for convection currents driving plate tectonics?
a) Inner core
b) Asthenosphere
c) Crust
d) Lithosphere
Answer: b) Asthenosphere
Explanation: Convection currents in the asthenosphere move tectonic plates.
44. The Kola Superdeep Borehole (Russia) reached a depth of—
a) 2 km
b) 5 km
c) 12 km
d) 25 km
Answer: c) 12 km
Explanation: It’s the deepest artificial borehole, far less than Earth’s total crust thickness.
45. The D’’ (D double-prime) layer is located—
a) At Moho discontinuity
b) At crustal base
c) At the core-mantle boundary
d) Within the asthenosphere
Answer: c) At the core-mantle boundary
Explanation: D’’ is a thin boundary layer above the outer core (~2,900 km depth).
46. Which layer of Earth is about 2,900 km thick?
a) Crust
b) Mantle
c) Outer core
d) Inner core
Answer: b) Mantle
Explanation: The mantle extends from ~30 km to 2,900 km depth.
47. The thickness of the outer core is about—
a) 100 km
b) 700 km
c) 2,200 km
d) 3,500 km
Answer: c) 2,200 km
Explanation: The outer core is ~2,200 km thick, liquid, extending from 2,900–5,100 km.
48. The thickness of the inner core is about—
a) 200 km
b) 500 km
c) 1,200 km
d) 2,500 km
Answer: c) 1,200 km
Explanation: The solid inner core has a radius of ~1,200–1,220 km.
49. The asthenosphere is characterized by—
a) Brittle rocks
b) Partial melting and ductility
c) Solid iron
d) Volcanic deposits
Answer: b) Partial melting and ductility
Explanation: Rocks in the asthenosphere are soft and flow slowly.
50. Which discontinuity separates the upper and lower mantle?
a) Lehmann
b) Gutenberg
c) Repetti
d) Conrad
Answer: c) Repetti
Explanation: The Repetti discontinuity (~1,000 km depth) marks this boundary.
51. The primary source of information about Earth’s interior comes from—
a) Volcanic rocks
b) Mines
c) Seismic waves
d) Ocean drilling
Answer: c) Seismic waves
Explanation: Seismology provides the most reliable data about Earth’s internal structure.
52. The rocks of the upper mantle are mainly—
a) Granite
b) Basalt
c) Peridotite
d) Sandstone
Answer: c) Peridotite
Explanation: The mantle is dominated by peridotite, rich in olivine and pyroxene.
53. The temperature at the Moho discontinuity is about—
a) 200°C
b) 400°C
c) 800°C
d) 1,000°C
Answer: d) 1,000°C
Explanation: Temperatures at the crust–mantle boundary are around 1,000°C.
54. The seismic discontinuity at 660 km depth is associated with—
a) Moho
b) Repetti
c) Mantle transition zone
d) Lehmann
Answer: c) Mantle transition zone
Explanation: At ~660 km, mineral transformations mark the mantle’s upper-lower boundary.
55. The Earth’s crust makes up only about what percentage of Earth’s volume?
a) 1%
b) 5%
c) 10%
d) 25%
Answer: a) 1%
Explanation: Crust is extremely thin compared to mantle and core.
56. The lower mantle is also called—
a) Asthenosphere
b) Mesosphere
c) Lithosphere
d) D-layer
Answer: b) Mesosphere
Explanation: The lower mantle (660–2,900 km depth) is termed the mesosphere.
57. The Kola Superdeep Borehole could penetrate only a fraction of the crust. Its depth was—
a) 5 km
b) 8 km
c) 12 km
d) 20 km
Answer: c) 12 km
Explanation: It reached 12.2 km, less than 0.2% of Earth’s radius.
58. Which region of Earth is responsible for volcanism and earthquakes?
a) Crust and upper mantle
b) Outer core
c) Inner core
d) Lower mantle
Answer: a) Crust and upper mantle
Explanation: Tectonic activity originates in the lithosphere and asthenosphere.
59. The asthenosphere plays a key role in—
a) Plate tectonics
b) Ocean currents
c) Volcanic gases
d) Atmosphere formation
Answer: a) Plate tectonics
Explanation: Its ductility enables lithospheric plates to move.
60. Which method helps determine the thickness of the crust?
a) Drilling
b) Gravity survey
c) Seismic survey
d) Magnetic survey
Answer: c) Seismic survey
Explanation: Seismic waves reveal the depth of discontinuities like the Moho.
61. What percentage of Earth’s volume is occupied by the mantle?
a) 50%
b) 67%
c) 83%
d) 90%
Answer: c) 83%
Explanation: Mantle is the largest layer, making up about 83% of Earth’s volume.
62. The inner core is solid because—
a) It is colder
b) High pressure prevents melting
c) It has less iron
d) It is crystallized basalt
Answer: b) High pressure prevents melting
Explanation: Enormous pressure keeps the core solid despite high temperatures.
63. The outer core extends from a depth of—
a) 1,000–2,000 km
b) 2,900–5,150 km
c) 3,500–6,371 km
d) 5,200–6,371 km
Answer: b) 2,900–5,150 km
Explanation: The liquid outer core lies between mantle and solid inner core.
64. The solid inner core has a radius of about—
a) 500 km
b) 1,220 km
c) 2,500 km
d) 3,000 km
Answer: b) 1,220 km
Explanation: The inner core’s radius is ~1,220 km.
65. Earth’s magnetic field protects us mainly from—
a) Meteors
b) Solar wind
c) UV radiation
d) Earthquakes
Answer: b) Solar wind
Explanation: The magnetosphere deflects harmful charged particles from the Sun.
66. Which layer of Earth is least accessible to direct study?
a) Crust
b) Mantle
c) Outer core
d) Inner core
Answer: d) Inner core
Explanation: The inner core is inaccessible due to depth and pressure; only indirect evidence exists.
67. The geotherm refers to—
a) Seismic wave velocity
b) Variation of temperature with depth
c) Rock density
d) Earth’s pressure gradient
Answer: b) Variation of temperature with depth
Explanation: The geotherm shows how temperature increases with depth inside Earth.
68. Which zone is known as the “Low Velocity Zone” (LVZ)?
a) Inner core
b) Asthenosphere
c) Moho
d) Lower mantle
Answer: b) Asthenosphere
Explanation: Seismic waves slow down in the partially molten asthenosphere.
69. What is the estimated pressure at Earth’s center?
a) 100,000 atm
b) 1 million atm
c) 3 million atm
d) 3.5–3.6 million atm
Answer: d) 3.5–3.6 million atm
Explanation: Extreme pressure exists at the inner core.
70. Which discontinuity is found at ~100 km depth?
a) Moho
b) Conrad
c) Lithosphere–asthenosphere boundary
d) Gutenberg
Answer: c) Lithosphere–asthenosphere boundary
Explanation: The L–A boundary lies around 80–120 km.
71. The thickness of Earth’s lithosphere varies between—
a) 1–5 km
b) 10–50 km
c) 50–200 km
d) 500–1,000 km
Answer: c) 50–200 km
Explanation: Lithosphere thickness depends on tectonic setting.
72. The seismic wave that travels through both solids and liquids is—
a) P-wave
b) S-wave
c) L-wave
d) R-wave
Answer: a) P-wave
Explanation: Primary (compressional) waves pass through all mediums.
73. Which wave travels only through solid materials?
a) P-wave
b) S-wave
c) L-wave
d) R-wave
Answer: b) S-wave
Explanation: Shear waves cannot move through liquids, hence blocked by outer core.
74. Earth’s average crustal thickness is—
a) 20 km
b) 30 km
c) 50 km
d) 100 km
Answer: b) 30 km
Explanation: Average crust thickness: ~35 km under continents, ~7 km under oceans.
75. The mantle’s composition is dominated by—
a) Silica + Aluminum
b) Silica + Magnesium
c) Iron + Nickel
d) Calcium + Sodium
Answer: b) Silica + Magnesium
Explanation: The mantle is SIMA-rich, with silicate minerals of magnesium and iron.
76. The boundary between crust and mantle is called—
a) Lehmann discontinuity
b) Gutenberg discontinuity
c) Moho discontinuity
d) Repetti discontinuity
Answer: c) Moho discontinuity
Explanation: The Mohorovičić discontinuity (Moho) separates Earth’s crust and mantle.
77. The density of the crust compared to the mantle is—
a) Higher
b) Lower
c) Equal
d) Same at all depths
Answer: b) Lower
Explanation: Crust is lighter (2.7–3.0 g/cm³), mantle is denser (~3.3–5.5 g/cm³).
78. Which part of the Earth has the lowest density?
a) Crust
b) Mantle
c) Outer core
d) Inner core
Answer: a) Crust
Explanation: Crust is the lightest layer, made mostly of granitic and basaltic rocks.
79. Which layer is believed to be the source of basaltic magma?
a) Crust
b) Upper mantle
c) Outer core
d) Inner core
Answer: b) Upper mantle
Explanation: Partial melting in the upper mantle (asthenosphere) produces basaltic magma.
80. The mantle is made up predominantly of—
a) Peridotite
b) Granite
c) Basalt
d) Gabbro
Answer: a) Peridotite
Explanation: Peridotite (olivine-rich rock) dominates mantle composition.
81. Earth’s internal heat is mainly due to—
a) Primordial heat + Radioactive decay
b) Solar radiation
c) Meteorite impacts only
d) Atmospheric greenhouse effect
Answer: a) Primordial heat + Radioactive decay
Explanation: Leftover heat from formation and isotope decay maintain Earth’s heat.
82. The Dʺ (D double-prime) layer is located—
a) At crust–mantle boundary
b) Within lithosphere
c) Just above core–mantle boundary
d) In the outer core
Answer: c) Just above core–mantle boundary
Explanation: Dʺ lies at ~2,700–2,900 km depth, at base of the mantle.
83. The average density of mantle rocks is—
a) 2.5 g/cm³
b) 3.3 g/cm³
c) 5.5 g/cm³
d) 10 g/cm³
Answer: b) 3.3 g/cm³
Explanation: Mantle density averages ~3.3 g/cm³, increasing with depth.
84. Which discontinuity is at ~5,100 km depth?
a) Moho
b) Gutenberg
c) Repetti
d) Lehmann
Answer: d) Lehmann
Explanation: Lehmann discontinuity separates liquid outer core from solid inner core.
85. Which statement is correct about the outer core?
a) Solid, rich in silicon
b) Solid, rich in iron
c) Liquid, rich in iron and nickel
d) Semi-solid, rich in basalt
Answer: c) Liquid, rich in iron and nickel
Explanation: The outer core is molten Fe–Ni alloy, creating Earth’s magnetic field.
86. The asthenosphere is important because—
a) It forms the rigid plates
b) It is the source of convection currents
c) It is the densest layer
d) It produces seismic shadow zones
Answer: b) It is the source of convection currents
Explanation: Heat-driven convection in asthenosphere drives plate movements.
87. Which layer has the maximum thickness?
a) Crust
b) Mantle
c) Outer core
d) Inner core
Answer: b) Mantle
Explanation: Mantle is ~2,900 km thick, the thickest Earth layer.
88. Which waves are the fastest seismic waves?
a) P-waves
b) S-waves
c) L-waves
d) Surface waves
Answer: a) P-waves
Explanation: Primary waves move fastest, ~6–14 km/s.
89. The inner core is mostly composed of—
a) Granite
b) Peridotite
c) Iron and nickel
d) Silica and magnesium
Answer: c) Iron and nickel
Explanation: Core is NiFe-rich, mostly iron (~85%) and nickel.
90. The “shadow zone” proves that—
a) Mantle is solid
b) Inner core is molten
c) Outer core is liquid
d) Crust is thin
Answer: c) Outer core is liquid
Explanation: S-waves stop at outer core, and P-waves bend, forming shadow zones.
91. Earth’s magnetic field is generated by—
a) Solidification of crust
b) Convection in outer core
c) Mantle conduction
d) Inner core crystallization
Answer: b) Convection in outer core
Explanation: The geodynamo effect in liquid outer core produces the magnetic field.
92. The temperature gradient inside Earth is about—
a) 10°C/km
b) 25–30°C/km in crust
c) 50°C/km
d) 100°C/km
Answer: b) 25–30°C/km in crust
Explanation: This geothermal gradient applies in the upper crust.
93. The innermost solid part of Earth is under what pressure?
a) 10,000 atm
b) 100,000 atm
c) 1 million atm
d) 3.5 million atm
Answer: d) 3.5 million atm
Explanation: Enormous pressure keeps the inner core solid.
94. What is the estimated temperature at Earth’s core?
a) 1,500°C
b) 3,000°C
c) 5,000–6,000°C
d) 10,000°C
Answer: c) 5,000–6,000°C
Explanation: Similar to Sun’s surface, core temperatures are ~6,000°C.
95. Which layer is also called the “sima layer”?
a) Continental crust
b) Oceanic crust
c) Mantle
d) Outer core
Answer: b) Oceanic crust
Explanation: Oceanic crust is silica + magnesium (SIMA).
96. Which layer is called the “sial layer”?
a) Continental crust
b) Oceanic crust
c) Mantle
d) Inner core
Answer: a) Continental crust
Explanation: Continental crust is silica + aluminum (SIAL).
97. Which part of Earth is described as “plastic” in behavior?
a) Lithosphere
b) Asthenosphere
c) Outer core
d) Inner core
Answer: b) Asthenosphere
Explanation: Ductile rocks here allow plate movement.
98. Which discontinuity was discovered using seismic data in 1909
a) Moho
b) Gutenberg
c) Lehmann
d) Conrad
Answer: a) Moho
Explanation: Mohorovičić discovered it by studying earthquake waves.
99. The fluid outer core plays a major role in—
a) Plate tectonics
b) Ocean currents
c) Magnetic field generation
d) Earthquakes
Answer: c) Magnetic field generation
Explanation: Convection in outer core drives the geodynamo.
100. The study of Earth’s internal structure using seismic waves is called—
a) Geodesy
b) Seismology
c) Geomorphology
d) Petrology
Answer: b) Seismology
Explanation: Seismology is the science of earthquake waves and Earth’s interior.