Some important MCQs related to 12th Geology Exam with Explanations -5

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Unit 1: General Geology

1. The process by which the Earth's layers separated based on density is called:
a) Subduction
b) Differentiation
c) Plate tectonics
d) Convection
Answer: b) Differentiation
Explanation: Differentiation is the process in which the Earth’s materials separated into layers of differing densities, forming the core, mantle, and crust.

2. Which of the following represents the Earth's innermost layer?
a) Crust
b) Outer core
c) Inner core
d) Mantle
Answer: c) Inner core
Explanation: The Earth's inner core is solid and primarily composed of iron and nickel, with temperatures exceeding 5,000°C.

3. What drives the movement of tectonic plates?
a) Magnetic field
b) Mantle convection
c) Ocean currents
d) Solar radiation
Answer: b) Mantle convection
Explanation: The heat from the Earth’s interior causes mantle convection, which drives the movement of tectonic plates.


Unit 2: Petrology

4. Which rock type forms when magma cools slowly beneath the Earth's surface?
a) Extrusive igneous rock
b) Intrusive igneous rock
c) Metamorphic rock
d) Sedimentary rock
Answer: b) Intrusive igneous rock
Explanation: Intrusive igneous rocks, such as granite, form when magma cools slowly underground, allowing large crystals to develop.

5. Which of the following is a foliated metamorphic rock?
a) Marble
b) Quartzite
c) Schist
d) Basalt
Answer: c) Schist
Explanation: Schist is a foliated metamorphic rock characterized by its parallel mineral alignment, which forms under directed pressure.

6. The presence of fossils in a rock indicates that it is most likely:
a) Igneous
b) Metamorphic
c) Sedimentary
d) Volcanic
Answer: c) Sedimentary
Explanation: Fossils are typically preserved in sedimentary rocks, as these form under conditions suitable for the preservation of organic remains.


Unit 3: Structural Geology

7. A fault in which the hanging wall moves down relative to the footwall is called a:
a) Normal fault
b) Reverse fault
c) Strike-slip fault
d) Transform fault
Answer: a) Normal fault
Explanation: A normal fault occurs when extensional forces cause the hanging wall to move downward relative to the footwall.


8. The San Andreas Fault is an example of a:
a) Normal fault
b) Reverse fault
c) Transform fault
d) Thrust fault
Answer: c) Transform fault
Explanation: The San Andreas Fault is a transform fault where two tectonic plates slide past each other horizontally.

9. The point inside the Earth where an earthquake originates is called the:
a) Epicenter
b) Focus
c) Fault plane
d) Rift zone
Answer: b) Focus
Explanation: The focus is the point within the Earth where an earthquake originates. The epicenter is the point on the surface directly above the focus.

Unit 4: Paleontology

10. Which of the following is considered a "living fossil"?
a) Trilobites
b) Coelacanth
c) Ammonites
d) Pterosaurs
Answer: b) Coelacanth
Explanation: Coelacanths are ancient fish thought to be extinct but were discovered alive in the 20th century, earning them the title of "living fossils."


11. The term "index fossil" refers to:
a) Fossils found in all types of rocks
b) Fossils used to determine the age of rock layers
c) Fossils preserved in volcanic rocks
d) Fossils of the oldest organisms
Answer: b) Fossils used to determine the age of rock layers
Explanation: Index fossils are species that were widespread but existed for a short geological period, making them useful for dating rock layers.


12. Which fossil organism is commonly associated with the Cambrian period?
a) Trilobites
b) Dinosaurs
c) Brachiopods
d) Mammoths
Answer: a) Trilobites
Explanation: Trilobites were dominant marine organisms during the Cambrian period and are widely used as index fossils for this time.
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Unit 5: Economic Geology

13. The principal ore of copper is:
a) Bauxite
b) Hematite
c) Chalcopyrite
d) Magnetite
Answer: c) Chalcopyrite
Explanation: Chalcopyrite (CuFeS₂) is the most important ore for copper production, providing a major source of this metal.


14. Which mineral is known as "fool’s gold"?
a) Galena
b) Pyrite
c) Magnetite
d) Hematite
Answer: b) Pyrite
Explanation: Pyrite is often called "fool’s gold" because of its metallic luster and pale brass-yellow color, which resembles gold.


15. Which of the following is NOT a fossil fuel?
a) Coal
b) Petroleum
c) Natural gas
d) Uranium
Answer: d) Uranium
Explanation: Uranium is not a fossil fuel but a radioactive element used as fuel in nuclear reactors.

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