GC Leong Test: The Earth and the Crust - UPSC MCQ

To determine the correct statements, let's analyze each one:

1. Fold Mountains: This statement is correct. Fold Mountains are formed by the folding of geosyncline sediments under compressible tectonic forces. They are often associated with volcanic activities, particularly in regions around the circum-Pacific belt where tectonic activity is significant.

2. Block Mountains: This statement is incorrect. Block Mountains are typically formed due to tensional forces rather than compressional forces. These forces cause the earth's crust to break and create faults, leading to blocks of the crust either subsiding or being uplifted.

3. Volcanic Mountains: This statement is correct. Volcanic Mountains are also known as mountains of accumulation. They are formed by the accumulation of lava and volcanic materials from eruptions, which build up over time to create these mountains.

Thus, statements 1 and 3 are correct, making Option C the correct answer.

1. Himalaya - Volcanic Mountain: Incorrect. The Himalayas are Fold Mountains, formed by the folding of the Earth's crust due to tectonic forces, not volcanic activity.

2. Vosges - Block Mountain: Correct. The Vosges in France are an example of Block Mountains, which are formed due to faulting and are characterized by large blocks of the Earth's crust that have been uplifted.

3. Fuji Yama - Volcanic Mountain: Correct. Mount Fuji in Japan is a classic example of a Volcanic Mountain, which is formed by the accumulation of lava from volcanic eruptions.

4. Nilgiris - Residual Mountain: Correct. The Nilgiris in India are considered Residual Mountains, which are remnants of ancient mountain ranges that have been eroded over time.

Fold Mountains are primarily formed by the folding of geosyncline sediments under compressible tectonic forces. This process results in the elevation of rock strata to great heights, giving rise to Fold Mountains. These mountains are closely associated with volcanic activities and are known for their mineral-rich resources like Tin, Copper, Gold, and Petroleum. The Himalayas, Alps, Rockies, Andes, and other well-known mountain ranges are examples of Fold Mountains resulting from this geological process.

Explanation:

• Statement-I says that the mantle is heated by the core and that this heating leads to convection currents, which drive plate movements.
• Statement-II explains the heating process in more detail, linking the heat from the outer core to the convection currents in the mantle, which directly influences plate tectonics, and thus explains the heating process mentioned in Statement-I.

Correct Answer: (a) Both Statement-I and Statement-II are correct and Statement-II explains Statement-I.

1. Granite Rocks : Sima
- Incorrect. Granite rocks are typically associated with the continental crust, known as SIAL, which is rich in silicon and aluminum. Sima, on the other hand, refers to the oceanic crust, which is rich in silicon and magnesium.
2. Basaltic Rocks : SIAL
- Incorrect. Basaltic rocks are primarily associated with the oceanic crust, known as Sima. SIAL refers to the continental crust which is high in silicon and aluminum.
3. Mantle : Lithosphere and Aesthenosphere
- Correct. The mantle is divided into two sub-layers: the upper mantle, which is part of the lithosphere (along with the crust), and the lower mantle, which is known as the asthenosphere.
4. Core : Nife
- Correct. The core of the Earth is composed mainly of nickel (Ni) and iron (Fe), hence the term Nife. The core is divided into the inner and outer core.
Pairs 3 and 4 are correctly matched, making a total of two correctly matched pairs. Therefore, the correct answer is Option B: Only two pairs.

Tectonic plateaus are formed by earth movements that cause uplift, resulting in plateaus of considerable size with a fairly uniform altitude. Examples include the Deccan Plateau, Meseta Plateau, and Harz Plateau. These plateaus are characterized by their formation due to tectonic forces shaping the landscape.

1. Statement 1 is correct. Igneous rocks are indeed formed through the cooling and solidification of molten material, such as magma. This process often results in a crystalline structure. These rocks do not contain fossils because they are formed from molten material.

2. Statement 2 is incorrect. Sedimentary rocks are generally non-crystalline and are often stratified. They are known to contain fossils of animals, plants, and other microorganisms, which suggests a different characteristic than being crystalline. The presence of fossils is a defining feature of sedimentary rocks due to the accumulation and compaction of organic material over time.

3. Statement 3 is incorrect. Metamorphic rocks are formed from the transformation of pre-existing rocks (either igneous or sedimentary) under heat and pressure, which alters their structure and mineral composition. This process typically destroys any fossils that might have been present in the original rock. Metamorphic rocks do not exhibit stratification, as the process of metamorphism often results in the re-crystallization of minerals into a denser, more compact form without layering.

Therefore, only statement 1 is correct.

In the given statements, Statement-I correctly explains that Fold Mountains are termed as mountains of elevation due to the uplifting of rock strata by compressible tectonic forces. However, Statement-II inaccurately describes Block Mountains as being formed due to faults caused by tension or compression forces, leading to the subsidence or rising of sections of the earth's crust. Block Mountains are actually formed due to faulting caused by tension forces, not compression forces. This difference in the formation processes of Fold Mountains and Block Mountains clarifies that Statement-I is correct while Statement-II is incorrect.

Statement-I correctly describes the characteristics of igneous rocks, stating their crystalline structure, absence in strata, and lack of fossils. Statement-II correctly describes the formation process of sedimentary rocks, emphasizing their origin through the deposition of sediment layers along water bodies over time. While both statements are independently correct, they relate to different types of rocks and do not provide explanatory connections to each other. Therefore, Option B is the accurate choice as both statements are correct without one explaining the other.

- The Earth's crust is primarily composed of two types: the continental crust and the oceanic crust.
- The continental crust is rich in silica (SiO₂) and aluminum (Al), often referred to with the acronym "sial."
- This composition makes it less dense than the oceanic crust, which is rich in silica and magnesium "sima".
The elements silicon and magnesium (sima) are prominent in the denser oceanic crust, while the lighter silica and aluminum (sial) dominate the continental crust.
Therefore Correct Answer- Option B