Some important MCQs related to 12th Geology Exam with Explanations -2

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Unit 1: General Geology

1. The outermost layer of the Earth is known as:
a) Mantle
b) Core
c) Crust
d) Lithosphere
Answer: c) Crust
Explanation: The crust is the Earth's outermost solid layer. It is thin and composed of various rocks and minerals, and it supports life. The lithosphere includes both the crust and the uppermost part of the mantle.

2. The Earth’s lithosphere is divided into:
a) 7 major and many minor plates
b) 5 major and 10 minor plates
c) 3 major and several minor plates
d) 10 major and no minor plates
Answer: a) 7 major and many minor plates
Explanation: The lithosphere is divided into tectonic plates that float on the semi-fluid asthenosphere. Examples include the Pacific Plate, Indian Plate, and Eurasian Plate.


3. What is the age of the Earth, as determined by radiometric dating methods?
a) 3.5 billion years
b) 4.6 billion years
c) 5.5 billion years
d) 6.5 billion years
Answer: b) 4.6 billion years
Explanation: Radiometric dating, particularly using isotopes like uranium-lead, has determined the Earth's age to be approximately 4.6 billion years.

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Unit 2: Petrology

4. Which of the following rocks is an example of sedimentary rock?
a) Granite
b) Marble
c) Limestone
d) Basalt
Answer: c) Limestone
Explanation: Limestone is a sedimentary rock primarily composed of calcium carbonate. It forms from the accumulation of biological debris like shells and corals or through chemical precipitation.


5. The texture of igneous rocks is determined by:
a) The color of the rock
b) The rate of cooling of magma or lava
c) The composition of magma
d) The amount of water present
Answer: b) The rate of cooling of magma or lava
Explanation: Slow cooling of magma results in coarse-grained textures (e.g., granite), while rapid cooling of lava results in fine-grained textures (e.g., basalt).


6. Which of the following is a characteristic feature of metamorphic rocks?
a) Fossils
b) Banding or foliation
c) Vesicular texture
d) Glassy texture
Answer: b) Banding or foliation
Explanation: Metamorphic rocks often exhibit foliation or banding due to the alignment of minerals under high pressure and temperature.


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Unit 3: Structural Geology

7. The point within the Earth where an earthquake originates is called:
a) Epicenter
b) Focus
c) Fault
d) Seismic zone
Answer: b) Focus
Explanation: The focus, or hypocenter, is the location inside the Earth where the earthquake starts. The epicenter is the point on the Earth's surface directly above the focus.

8. Which of the following is a strike-slip fault?
a) San Andreas Fault
b) Himalayan Fault
c) Andes Fault
d) Normal Fault in East Africa
Answer: a) San Andreas Fault
Explanation: A strike-slip fault is characterized by horizontal movement. The San Andreas Fault in California is a well-known example of this type of fault.


9. Which type of stress causes folding in rocks?
a) Tensional stress
b) Compressional stress
c) Shear stress
d) None of the above
Answer: b) Compressional stress
Explanation: Compressional stress pushes rock layers together, causing them to bend and form folds such as anticlines and synclines.
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Unit 4: Paleontology

10. The Jurassic period is part of which era?
a) Paleozoic
b) Mesozoic
c) Cenozoic
d) Precambrian
Answer: b) Mesozoic
Explanation: The Jurassic period belongs to the Mesozoic era, known as the "Age of Reptiles," which includes dinosaurs and the first birds.


11. Which of the following is an example of a trace fossil?
a) Dinosaur bones
b) Shell imprints
c) Burrows and footprints
d) Petrified wood
Answer: c) Burrows and footprints
Explanation: Trace fossils represent the activity of organisms, such as footprints, burrows, or feeding marks, rather than the remains of the organism itself.


12. The oldest known fossils are of:
a) Trilobites
b) Stromatolites
c) Dinosaurs
d) Ammonites
Answer: b) Stromatolites
Explanation: Stromatolites are layered structures formed by cyanobacteria. They are the oldest known fossils, dating back more than 3.5 billion years.

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