Rocks and Earth Sciences

31. Which one of the following is not an agent of metamorphism?

Which one of the following is not an agent of metamorphism?

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Heat
Compression
Decomposition
Solution
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UPSC NDA-2 – 2018
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Metamorphism is the process by which existing rocks are transformed into new types of rock by high temperature, high pressure, and/or chemically active fluids. Heat, pressure (often resulting in compression), and chemically active fluids (which can involve solution and redeposition of minerals) are the primary agents of metamorphism. Decomposition, which is the breakdown of substances, typically organic matter, is not a process that drives the transformation of rocks under metamorphic conditions.
The three main agents of metamorphism are heat, pressure, and chemically active fluids. These agents cause mineralogical, textural, and/or chemical changes in the parent rock without complete melting.
Heat can be provided by geothermal gradient, contact with magma, or friction along faults. Pressure can be lithostatic (confining pressure from overlying rocks) or directed pressure (differential stress). Chemically active fluids are typically hot water or gas mixtures that circulate through the rock, dissolving and transporting ions, leading to the formation of new minerals. Decomposition is a biological and chemical process associated with weathering and breakdown, distinct from the high-energy transformations of metamorphism.

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32. Match List I with List II and select the correct answer using the code

Match List I with List II and select the correct answer using the code given below the Lists :

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List I
(Geomorphic Agent)		 List II
(Feature)
A. Ground water 1. Plunge pool
B. Running water 2. Horns
C. Glacier 3. Playas
D. Wind 4. Lapies

Code :

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4 1 2 3
3 2 1 4
3 1 2 4
4 2 1 3
This question was previously asked in
UPSC NDA-2 – 2016
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The correct answer is A) 4 1 2 3. This matches the features to their primary geomorphic agents:
– Ground water (A) is a significant agent in karst landscapes, forming features like sinkholes, caves, and Lapies (also known as Karren), which are solutional features on limestone or dolomite surfaces. So, A-4.
– Running water (B), particularly rivers, is responsible for erosional features like valleys, canyons, and waterfalls. Plunge pools are common erosional features found at the base of waterfalls, carved by the impact and turbulence of falling water. So, B-1.
– Glacier (C) is a powerful erosional and depositional agent in high latitudes and altitudes. Glacial erosion shapes mountains, creating features like cirques, arêtes, and sharp, pyramidal peaks called Horns (or pyramidal peaks) formed when several cirques meet. So, C-2.
– Wind (D) is a dominant geomorphic agent in arid and semi-arid regions. Wind can erode, transport, and deposit sediment, forming features like sand dunes, loess deposits, and erosional landforms. Playas are flat, dry lakebeds found in desert basins, which are depositional features associated with ephemeral lakes and wind processes (deflation and deposition). So, D-3.
– Groundwater creates dissolution features in soluble rocks (karst).
– Running water (rivers) creates features like valleys and erosional landforms at waterfalls (plunge pools).
– Glaciers carve distinctive landscapes in mountainous and polar regions (horns, cirques, U-shaped valleys).
– Wind shapes arid landscapes through erosion, transport, and deposition (playas, dunes).
– Lapies are small-scale solution features that can form on rock surfaces exposed to rainfall or covered by a thin soil layer, often part of larger karst systems shaped by groundwater.
– Horns are characteristic features of glaciated mountain ranges, resulting from the headward erosion of multiple cirques around a peak.
– Playas are temporary lakes; when they dry, the flat surface is often subject to wind deflation and deposition of fine sediments.

33. An up fold in rock is:

An up fold in rock is:

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graben
horse
anticline
syncline
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UPSC NDA-2 – 2015
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The correct option is C, anticline.
In structural geology, an up fold in rock layers, where the limbs dip away from the hinge and the oldest strata are typically in the core, is called an anticline. Conversely, a down fold, where the limbs dip towards the hinge and the youngest strata are in the core, is called a syncline. Graben and horst are fault-related structures; a graben is a down-dropped block bounded by normal faults, and a horst is an uplifted block bounded by normal faults.
Folds in rock strata result from compressional forces acting on the Earth’s crust. Anticlines and synclines often occur together in fold belts. The shape of the fold can vary from gentle waves to tight, overturned folds.

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34. Which one of the following describes the Lithosphere?

Which one of the following describes the Lithosphere?

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Upper and lower mantle
Crust and upper mantle
Crust and core
Mantle and core
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UPSC NDA-2 – 2015
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The Lithosphere is defined as the rigid outer part of the Earth, consisting of the crust and the uppermost part of the mantle. It is situated above the asthenosphere, which is a more ductile layer of the upper mantle.
Understanding the layered structure of the Earth (Crust, Mantle, Core) and the physical properties of these layers (Lithosphere, Asthenosphere, Mesosphere, etc.) is key.
The lithosphere is broken into tectonic plates that move over the asthenosphere. The thickness of the lithosphere varies, being thinner under oceanic crust and thicker under continental crust.

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35. Which one of the following combinations of stalactites and stalagmites

Which one of the following combinations of stalactites and stalagmites occurrences is correct?

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Stalactites hang as icicles of different diameters and stalagmites hang from the floor of the caves
Stalactites hang as icicles of different diameters and stalagmites rise up from the floor of the caves
Stalactites rise up from the floor of the caves and stalagmites hang as icicles of different diameters
Stalactites hang as icicles of different diameters and stalagmites also hang as icicles of different diameters
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UPSC NDA-2 – 2015
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Stalactites are formations that hang from the ceiling of caves, typically formed by the slow dripping of mineral-rich water, often appearing like icicles. Stalagmites are formations that rise up from the floor of caves, formed by the accumulation of material from the dripping water from above.
The distinction between stalactites (hanging) and stalagmites (rising) is a common geological concept.
These formations are types of speleothems, usually found in limestone caves, formed by the deposition of calcium carbonate dissolved in water.

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36. Which of the following statements regarding Earth’s internal structure

Which of the following statements regarding Earth’s internal structure is/are correct?
1. The oceanic crust is heavier than the continental crust.
2. Most of the Earth’s internal heat is contained within the mantle.
3. Large convective cells in the crust circulate heat and drive plate-tectonic processes.

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3 only
1 and 2 only
2 and 3 only
1, 2 and 3
This question was previously asked in
UPSC NDA-1 – 2024
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Statements 1 and 2 are correct, while statement 3 is incorrect.
Statement 1 is correct. Oceanic crust, primarily composed of basalt, has a higher density (about 3.0 g/cm³) than continental crust, which is mainly granitic in composition (density around 2.7 g/cm³). This difference in density explains why oceanic plates subduct beneath continental plates. Statement 2 is correct. While the Earth’s core is hotter, the mantle, being the largest layer by volume (about 84% of Earth’s volume), contains a significant portion of the Earth’s internal heat, generated from primordial heat and radioactive decay. This heat drives convection within the mantle. Statement 3 is incorrect. Large convective cells responsible for driving plate tectonics are located within the Earth’s *mantle*, not the crust. The crust is the rigid outer shell that is broken into tectonic plates, which move atop the convecting mantle.
The Earth’s internal structure consists of the crust, mantle, outer core (liquid), and inner core (solid). Temperature increases with depth, but the state of matter depends on pressure and composition as well.

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37. Which one of the following is found in the innermost part of the Earth

Which one of the following is found in the innermost part of the Earth ?

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Conrad discontinuity
Moho discontinuity
Guttenberg discontinuity
Lehmann discontinuity
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UPSC NDA-1 – 2023
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The correct answer is D) Lehmann discontinuity.
The Earth is structured in layers: crust, mantle, outer core, and inner core. Discontinuities are boundaries where seismic waves change speed due to changes in material properties. The Lehmann discontinuity is located at a depth of approximately 5150 km and separates the liquid outer core from the solid inner core. Since the inner core is the innermost part of the Earth, the Lehmann discontinuity is found at the boundary of this innermost region.
– The Conrad discontinuity is a theoretical or regional boundary within the continental crust.
– The Moho discontinuity (Mohorovičić discontinuity) is the boundary between the Earth’s crust and the mantle (around 35-70 km under continents, 5-10 km under oceans).
– The Guttenberg discontinuity (also known as the Wiechert–Gutenberg discontinuity or Core–mantle boundary) is the boundary between the Earth’s mantle and the outer core (around 2900 km depth).

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38. Weathering, mass wasting, erosion and transportation are indicators of

Weathering, mass wasting, erosion and transportation are indicators of which one of the following processes?

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Denudation
Endogenetic process
Diastrophism
Mountain building
This question was previously asked in
UPSC NDA-1 – 2022
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The correct answer is A) Denudation.
Denudation is the overall process that causes the wearing away of the Earth’s surface by moving water, ice, wind, and waves. It encompasses several processes, including weathering (breakdown of rock), mass wasting (movement of rock and soil downslope under gravity), erosion (removal and transportation of material), and transportation (movement of eroded material).
Endogenetic processes originate within the Earth (like diastrophism and mountain building). Diastrophism is large-scale deformation of the crust. Mountain building (Orogeny) is a specific type of diastrophism. The listed processes (weathering, mass wasting, erosion, transportation) are exogenetic processes acting on the surface.

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39. Consider the following statements: 1. Rocks do not remain in their o

Consider the following statements:

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  • 1. Rocks do not remain in their original form for long and undergo transformation.
  • 2. Transformation of rocks is caused by weathering, erosion and metamorphic action.

Which of the statements given above is/are correct?

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1 only
2 only
Both 1 and 2
Neither 1 nor 2
This question was previously asked in
UPSC NDA-1 – 2022
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The correct answer is C) Both 1 and 2.
Statement 1 is correct: Rocks are continuously undergoing transformation through the rock cycle (igneous to sedimentary, sedimentary to metamorphic, etc.). They are not static entities. Statement 2 is correct: Transformation is indeed caused by various processes. Weathering and erosion break down rocks, which is a necessary step in the formation of sedimentary rocks. Metamorphic action (heat and pressure) directly transforms existing rocks into metamorphic rocks. These processes are key drivers of the rock cycle.
The rock cycle illustrates how rocks change from one type to another. Weathering, erosion, deposition, compaction, cementation (leading to sedimentary rocks), heat, and pressure (leading to metamorphic rocks), melting, and solidification (leading to igneous rocks) are all processes involved in the transformation of rocks.

40. Which one of the following is likely to be the most prevalent form of

Which one of the following is likely to be the most prevalent form of weathering in hot-tropical desert areas?

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Mechanical
Chemical
Biological
Leaching
This question was previously asked in
UPSC NDA-1 – 2022
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The correct answer is A) Mechanical.
Hot tropical desert areas are characterized by extreme diurnal (daily) temperature variations and lack of moisture. Mechanical weathering, such as thermal stress (repeated expansion and contraction of rocks due to large temperature swings) and salt crystal growth (where infrequent water evaporates leaving salt crystals that exert pressure), is the dominant form of weathering in these environments.
Chemical weathering requires water, which is scarce in hot deserts, making it less prevalent compared to mechanical processes. Biological weathering can occur but is generally limited by the lack of life forms compared to more humid environments. Leaching is a chemical process requiring water.

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