Rocks and Earth Sciences Archives

1. Which one of the following is not a characteristic of continental shel

Which one of the following is not a characteristic of continental shelves ?

Sites of productive fishing grounds

Oil and gas reserves

Sites of submarine canyons

Large stores of sand and gravel

This question was previously asked in

UPSC CISF-AC-EXE – 2017

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While submarine canyons can cut across continental shelves, they are more characteristic features of continental slopes, not the shelf itself as a defining characteristic.

Continental shelves are gently sloping underwater extensions of continents, known for shallow depths and abundant marine life.

Continental shelves are important for fishing grounds due to their biological productivity and are significant sources of oil and gas reserves. They also accumulate large amounts of sediment, forming stores of sand and gravel. Submarine canyons are steep-sided valleys cut into the seabed.

2. Which one of the following are the most widespread inorganic pelagic d

Which one of the following are the most widespread inorganic pelagic deposits on the ocean floor?

Red clay

Radiolarian ooze

Volcanic dust

Calcareous ooze

This question was previously asked in

UPSC CISF-AC-EXE – 2017

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Red clay is the most widespread inorganic pelagic deposit on the ocean floor.

Pelagic deposits are deep-sea sediments. Red clay is composed of fine-grained detrital material, volcanic ash, and cosmic dust, accumulating slowly in areas away from continental margins and where biogenic sedimentation is low, typically in the deepest ocean basins.

Radiolarian ooze and calcareous ooze are examples of biogenic pelagic deposits, formed from the remains of marine organisms. Volcanic dust can contribute to red clay but is not the deposit itself.

3. Consider the following statements with respect to the ‘asthenosphere’

Consider the following statements with respect to the ‘asthenosphere’ :

1. It extends from the lower crust to the upper mantle.
2. It is the main source of the magma that finds its way to the surface of the Earth during volcanic eruptions.

Which of the statements given above is/are correct?

1 only

2 only

Both 1 and 2

Neither 1 nor 2

This question was previously asked in

UPSC CBI DSP LDCE – 2023

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Statement 2 correctly identifies the asthenosphere as a major source of magma, while Statement 1 inaccurately describes its location.

The asthenosphere is the highly viscous, mechanically weak and ductile region of the upper mantle, below the lithosphere. It extends roughly from about 100 km to 400 km depth. Statement 1 is incorrect because the asthenosphere is entirely within the upper mantle and does not extend into the lower crust. Statement 2 is correct because partial melting occurs within the asthenosphere due to its temperature and pressure conditions, generating magma that contributes to volcanic activity.

The lithosphere, which comprises the rigid crust and uppermost part of the mantle, floats on the ductile asthenosphere. The movement of tectonic plates (parts of the lithosphere) is facilitated by the plastic flow within the asthenosphere.

4. Subduction zone with reference to plate tectonics is associated with w

Subduction zone with reference to plate tectonics is associated with which of the following plate boundaries?

1. Convergent boundaries
2. Divergent boundaries

Select the correct answer using the code given below.

1 only

2 only

Both 1 and 2

Neither 1 nor 2

This question was previously asked in

UPSC CBI DSP LDCE – 2023

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The correct option is A.

– Subduction zones occur at **convergent plate boundaries** where one tectonic plate slides beneath another plate into the Earth’s mantle. This typically happens when an oceanic plate converges with a continental plate or another oceanic plate.
– Divergent plate boundaries are where plates move apart, leading to the creation of new crust (e.g., mid-ocean ridges). Subduction does not occur at divergent boundaries.

Convergent boundaries can also result in continental collision (e.g., formation of Himalayas) where subduction may not occur or is incomplete. Subduction zones are associated with deep ocean trenches, volcanic arcs, and significant seismic activity.

5. Which one of the following is not an erosional landform?

Which one of the following is not an erosional landform?

Esker

Pediment

Point bar

Stack

This question was previously asked in

UPSC CBI DSP LDCE – 2023

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The correct option is C.

– Esker: A long, winding ridge composed of stratified sand and gravel, deposited by glacial meltwater streams flowing in tunnels within or under a glacier. This is a **depositional** landform.
– Pediment: A broad, gently sloping erosional surface cut into bedrock or thin veneer of alluvium at the foot of a mountain front in arid or semi-arid regions. This is primarily an **erosional** landform.
– Point bar: An alluvial deposit that accumulates on the inside bend of a meandering stream or river. This is a **depositional** landform.
– Stack: A geological landform consisting of a steep and often vertical column or columns of rock in the sea near a coastline, formed by wave erosion. This is an **erosional** landform.

The question asks which one is *not* an erosional landform. Both Esker and Point bar are depositional landforms and therefore fit this description. Given that only one option can be selected, there might be an issue with the question having two correct answers among the options provided (A and C). However, following standard classifications, both are definitively non-erosional (i.e., depositional). If forced to choose one, or assuming a single correct answer is expected, both A and C represent landforms primarily built by deposition of sediment rather than sculpted by erosion. Without further context or clarification, both A and C are technically correct. Based on a common understanding and prominent examples, both Esker (glacial deposition) and Point Bar (fluvial deposition) are key depositional features.

6. Consider the following statements : Statement-I : Rainfall is one of

Consider the following statements :

Statement-I : Rainfall is one of the reasons for weathering of rocks.
Statement-II : Rain water contains carbon dioxide in solution.
Statement-III : Rain water contains atmospheric oxygen.

Which one of the following is correct in respect of the above statements?

Both Statement-II and Statement-III are correct and both of them explain Statement-I

Both Statement-II and Statement-III are correct, but only one of them explains Statement-I

Only one of the Statements II and III is correct and that explains Statement-I

Neither Statement-II nor Statement-III is correct

This question was previously asked in

UPSC IAS – 2024

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Statement-I is correct. Rainfall is a major agent of weathering. This includes physical weathering (e.g., the impact of raindrops, wetting and drying cycles) and chemical weathering. Statement-II is correct. Rainwater absorbs carbon dioxide from the atmosphere, forming weak carbonic acid (H₂CO₃) in solution. Statement-III is correct. Rainwater also absorbs oxygen from the atmosphere. Both carbon dioxide (as carbonic acid) and oxygen dissolved in rainwater contribute significantly to chemical weathering processes. Carbonic acid reacts with minerals like calcium carbonate (carbonation), and dissolved oxygen causes oxidation of iron-bearing minerals (oxidation). Therefore, both Statement-II and Statement-III describe components of rainwater that are responsible for chemical weathering, which is a type of weathering caused by rainfall. Thus, both statements are correct and both explain Statement-I by describing mechanisms through which rainfall causes weathering.

– Rainfall causes both physical and chemical weathering.
– Chemical weathering involves reactions between rock minerals and substances in rainwater.
– Carbon dioxide in rainwater forms carbonic acid, causing carbonation.
– Oxygen in rainwater causes oxidation.

Chemical weathering is particularly effective in warm and humid climates where rainfall is abundant. The presence of dissolved substances like CO2 and O2 in rainwater significantly enhances its chemical reactivity with rocks.

7. Consider the following statements : 1. The Earth’s magnetic field ha

Consider the following statements :

1. The Earth’s magnetic field has reversed every few hundred thousand years.
2. When the Earth was created more than 4000 million years ago, there was 54% oxygen and no carbon dioxide.
3. When living organisms originated, they modified the early atmosphere of the Earth.

Which of the statements given above is/are correct ?

1 only

2 and 3 only

1 and 3 only

1, 2 and 3

This question was previously asked in

UPSC IAS – 2018

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The correct answer is C) 1 and 3 only.

This question assesses understanding of Earth’s history, including its magnetic field and atmospheric evolution.

1. The Earth’s magnetic field does undergo polarity reversals, where the magnetic North and South poles switch places. Geological records show that these reversals have occurred irregularly throughout Earth’s history, on average every few hundred thousand years. Statement 1 is correct.
2. When the Earth formed over 4 billion years ago, the atmosphere was primarily composed of volcanic gases like water vapor, carbon dioxide, and nitrogen, with little to no free oxygen. An atmosphere with 54% oxygen is not consistent with early Earth conditions; oxygen became abundant much later due to biological activity. Statement 2 is incorrect.
3. The origin and evolution of life, particularly photosynthetic organisms like cyanobacteria, fundamentally altered the Earth’s atmosphere. Through photosynthesis, these organisms consumed carbon dioxide and produced oxygen, leading to the gradual oxygenation of the atmosphere over billions of years (the Great Oxidation Event). Statement 3 is correct.
Therefore, statements 1 and 3 are correct.

8. Which of the following processes is/are part of the Rock Cycle? 1. L

Which of the following processes is/are part of the Rock Cycle?

1. Lithification
2. Metamorphism
3. Solidification

Select the answer using the code given below:

1 only

1 and 2 only

2 and 3 only

1, 2 and 3

This question was previously asked in

UPSC CAPF – 2024

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The correct answer is D) 1, 2 and 3.

The Rock Cycle describes the transitions through geologic time among the three main rock types: sedimentary, metamorphic, and igneous. Key processes involved in these transitions include lithification, metamorphism, and solidification (also known as crystallization).

Lithification is the process by which unconsolidated sediments are compacted and cemented together to form sedimentary rocks. Metamorphism involves the transformation of existing rock types (igneous, sedimentary, or other metamorphic rocks) into metamorphic rocks by heat, pressure, or chemically active fluids. Solidification is the cooling and hardening of molten rock (magma or lava) to form igneous rocks. Weathering, erosion, deposition, melting, and uplift are also crucial processes in the rock cycle, facilitating the transformation and movement of rock material between the different types and locations.

9. Consider the following statements about rock structure : 1. Conglome

Consider the following statements about rock structure :

1. Conglomerates are clastic sedimentary rocks.
2. Slate is a non-clastic sedimentary rock.
3. Granite is a plutonic igneous rock.
4. Basalt is an extrusive igneous rock.

Which of the statements given above are correct ?

1, 2 and 3 only

3 and 4 only

1 and 2 only

1, 3 and 4 only

This question was previously asked in

UPSC CAPF – 2023

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Statement 1 is correct: Conglomerates are clastic sedimentary rocks formed by the cementation of rounded gravel, pebbles, and boulders. Clastic rocks are composed of fragments of pre-existing rocks or minerals. Statement 3 is correct: Granite is a common type of felsic intrusive igneous rock. Intrusive igneous rocks are also known as plutonic rocks, forming from magma that cools and solidifies slowly beneath the Earth’s surface. Statement 4 is correct: Basalt is a common type of mafic extrusive igneous rock. Extrusive igneous rocks, also known as volcanic rocks, form from lava that erupts onto the surface and cools rapidly. Statement 2 is incorrect: Slate is a fine-grained, foliated metamorphic rock, formed by the metamorphism of shale or mudstone. It is not a sedimentary rock, and clastic/non-clastic classification applies to sedimentary rocks, not metamorphic rocks.

Rocks are classified into igneous, sedimentary, and metamorphic based on their formation process. Sedimentary rocks can be clastic or non-clastic. Igneous rocks can be intrusive (plutonic) or extrusive (volcanic). Metamorphic rocks are formed by transformation of existing rocks.

Clastic sedimentary rocks are formed from weathered and eroded fragments (clasts) of other rocks. Non-clastic sedimentary rocks are formed by chemical precipitation or accumulation of organic matter (e.g., limestone, coal). Metamorphic rocks like slate form under heat and pressure.

10. Solifluction is a geomorphic process involving a special type of soil

Solifluction is a geomorphic process involving a special type of soil flow that is noticed in

desert regions

karst regions

permafrost regions

savanna regions

This question was previously asked in

UPSC CAPF – 2022

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The correct answer is C) permafrost regions.

– Solifluction is a specific type of mass wasting process common in cold climates, particularly in regions with permafrost.
– It involves the slow flow of water-saturated soil down a slope. This occurs when the surface layer of soil (active layer) thaws in summer but is underlain by impermeable permafrost, preventing drainage and causing the soil to become saturated and mobile.

– Permafrost is ground (soil, rock, or sediment) that remains frozen for at least two consecutive years. It is found in high latitudes and high altitudes.
– While slow mass movement (creep) can occur in various environments, solifluction specifically refers to the saturated flow condition over a frozen layer and is characteristic of permafrost environments or places with seasonal ground freezing that mimics the effect.