All questions of Geomorphology (Part 1) for Delhi Police Constable Exam

Explanation:

Volcanoes and earthquakes are natural phenomena that occur due to the movement of tectonic plates. These plates make up the Earth's crust and are constantly shifting and colliding with each other. The majority of volcanoes and earthquakes in the world are located at plate margins.

Plate Margins:

Plate margins are the boundaries where two tectonic plates meet. There are three main types of plate boundaries:

1. Divergent Boundaries: This is where two plates move away from each other. This movement creates a gap between the two plates which magma rises up to fill, creating new crust. This is where most of the world's volcanoes are located.

2. Convergent Boundaries: This is where two plates move towards each other. This movement can cause one plate to be forced under the other, creating a subduction zone. This can cause earthquakes and volcanic eruptions.

3. Transform Boundaries: This is where two plates slide past each other horizontally. This can cause earthquakes but rarely causes volcanic eruptions.

Conclusion:

In conclusion, the majority of volcanoes and earthquakes in the world are located at plate margins. The movement of tectonic plates at these boundaries causes geological activity such as volcanic eruptions and earthquakes. Understanding plate tectonics and plate boundaries is important for predicting and mitigating the risks associated with these natural phenomena.

The question is asking about the incorrect statement but here both statement are correct so the option (D) is correct.

Oldest Rocks in the World

The oldest rocks in the world are found in Western Australia.

Evidence

- The rocks in Western Australia are known as the Jack Hills group and have been dated to be 4.4 billion years old.
- These rocks were formed during the Hadean Eon, which lasted from the formation of the Earth around 4.6 billion years ago to the beginning of the Archean Eon around 4 billion years ago.
- The rocks contain tiny zircon crystals which have been used to determine their age.
- The zircon crystals have been found to be up to 4.4 billion years old, making them the oldest known rocks in the world.

Importance

- The discovery of these rocks in Western Australia has important implications for our understanding of the early Earth.
- It suggests that the planet was able to cool and solidify much faster than previously thought.
- It also suggests that conditions on the early Earth were more hospitable for life than previously thought, as life is believed to have emerged around 3.5 billion years ago.

Conclusion

In conclusion, the oldest rocks in the world are found in Western Australia and are known as the Jack Hills group. These rocks have been dated to be 4.4 billion years old and contain tiny zircon crystals which have been used to determine their age. The discovery of these rocks has important implications for our understanding of the early Earth and the emergence of life.

Explanation:

Pole fleeing force is a term used to describe the outward-directed force associated with the spinning of the Earth. This force is also known as centrifugal force. It is the force that causes objects at or near the Earth's equator to experience a slight outward push. This force is due to the rotation of the Earth on its axis.

The centrifugal force is a result of the Earth's rotation, which causes the equator to bulge outwards slightly and the poles to flatten slightly. It is important to note that the pole fleeing force is not responsible for the bulging at the Earth's poles, which is primarily caused by the Earth's rotation and the gravitational pull of the Sun and Moon.

The pole fleeing force is an important factor to consider when studying the Earth's rotation. It influences the Earth's shape, the distribution of mass within the Earth, and the motion of the Earth's oceans and atmosphere.

Conclusion:

In summary, the pole fleeing force is the outward-directed force associated with the spinning of the Earth. It is not responsible for the bulging at the Earth's poles but is an important factor to consider when studying the Earth's rotation.

Subduction is a geological process that occurs at convergent plate boundaries, where two tectonic plates come together. It involves one tectonic plate sinking beneath another plate into the Earth's mantle. This process is responsible for the formation of deep-sea trenches, volcanic arcs, and earthquakes.

1. Convergent Plate Boundaries:
Convergent plate boundaries are locations where two tectonic plates collide. There are three types of convergent plate boundaries:
- Oceanic-Oceanic Convergence: When two oceanic plates collide, one plate is usually denser and older, causing it to subduct beneath the other plate.
- Oceanic-Continental Convergence: When an oceanic plate collides with a continental plate, the denser oceanic plate will subduct beneath the less dense continental plate.
- Continental-Continental Convergence: When two continental plates collide, neither plate is dense enough to subduct. Instead, the collision results in the formation of mountains and a process known as continental collision.

2. Subduction Process:
Subduction occurs when one tectonic plate is forced beneath another plate. The process can be explained in the following steps:
- As the two plates converge, the denser plate starts to sink into the mantle beneath the less dense plate.
- The sinking plate creates a deep-sea trench, which is a long, narrow depression in the ocean floor.
- As the subducting plate sinks deeper into the mantle, it begins to melt due to the increasing pressure and temperature.
- The melted rock, called magma, is less dense than the surrounding mantle, causing it to rise through the overlying plate.
- The rising magma leads to the formation of a volcanic arc, which is a line of volcanoes on the overriding plate.
- Along with volcanic activity, subduction zones are also prone to intense earthquakes due to the movement and interaction of the plates.

3. Geological Consequences:
The subduction process has several geological consequences:
- Formation of Volcanic Arcs: The rising magma from the subducting plate leads to the formation of volcanic arcs, such as the Pacific Ring of Fire.
- Deep-sea Trenches: Subduction zones are associated with the formation of deep-sea trenches, which are the deepest parts of the Earth's oceans.
- Earthquakes: Subduction zones are highly seismically active, with frequent and often powerful earthquakes occurring due to the interaction of the plates.
- Recycling of Material: Subduction allows for the recycling of crustal material back into the Earth's mantle, playing a crucial role in the Earth's geochemical cycles.

In conclusion, subduction is the process by which one tectonic plate sinks beneath another plate at convergent plate boundaries. This process is responsible for the formation of deep-sea trenches, volcanic arcs, and earthquakes, and plays a significant role in the geology and dynamics of the Earth's crust.

Difference between Extrusive and Intrusive Rocks

Introduction
Extrusive and intrusive rocks are two types of igneous rocks that differ in their formation, texture, and the duration of their formation. Understanding these differences is important in the study of geology and helps in identifying and classifying various rock formations.

Formation
1. Extrusive Rocks: Extrusive rocks are formed from magma, which is molten rock that reaches the Earth's surface through volcanic activity. When magma erupts from a volcano, it cools rapidly and solidifies to form extrusive rocks. Examples of extrusive rocks include basalt, obsidian, and pumice.

2. Intrusive Rocks: Intrusive rocks, on the other hand, are formed from lava, which is magma that has reached the Earth's surface. Instead of erupting, lava flows out of the volcano and cools slowly beneath the surface. This slow cooling allows for the formation of large mineral crystals, resulting in coarse-grained textures. Examples of intrusive rocks include granite, gabbro, and diorite.

Texture
1. Extrusive Rocks: Extrusive rocks have a fine-grained texture due to their rapid cooling. As the magma cools quickly at the surface, there is insufficient time for large mineral crystals to form. Instead, small crystals or even glassy structures are observed in extrusive rocks.

2. Intrusive Rocks: Intrusive rocks have a coarse-grained texture because of their slow cooling process. As the magma cools slowly beneath the surface, there is ample time for large mineral crystals to develop. These crystals are often visible to the naked eye and contribute to the coarse-grained appearance of intrusive rocks.

Duration of Formation
1. Extrusive Rocks: Extrusive rocks are formed relatively quickly, as the magma reaches the surface and cools rapidly. This process typically takes place over a short duration of time, such as days or weeks.

2. Intrusive Rocks: In contrast, the formation of intrusive rocks occurs over a much longer duration of time. The slow cooling of lava beneath the surface can take thousands or even millions of years, allowing for the growth of large mineral crystals.

Conclusion
In summary, extrusive and intrusive rocks differ in their formation, texture, and the duration of their formation. Extrusive rocks are formed from magma, have a fine-grained texture, and are formed relatively quickly. In contrast, intrusive rocks are formed from lava, have a coarse-grained texture, and are formed over a longer duration of time. Understanding these differences is essential in the study of igneous rocks and helps in identifying and classifying various geological formations.

Overview of Metallic and Non-Metallic Minerals
Understanding the distribution of metallic and non-metallic minerals is essential in geology and resource management. Let’s analyze each statement to clarify their correctness.
Statement 1: Metallic Minerals in Igneous and Metamorphic Rocks
- Metallic minerals are typically found in igneous and metamorphic rocks because these rocks are formed under high temperatures and pressures, conditions conducive to the formation of metallic deposits.
- Large plateaus, often formed by volcanic activity or tectonic uplift, are common locations for these types of minerals.
Statement 2: Non-Metallic Minerals in Sedimentary Formations
- Sedimentary rock formations, particularly in plains and young fold mountains, are known to contain non-metallic minerals like limestone, gypsum, and salt.
- The formation processes of these rocks often involve sedimentation, which leads to diverse mineral deposits that are primarily non-metallic.
Statement 3: Organic Formation of Sedimentary Rocks
- Sedimentary rocks can indeed form organically. For instance, limestone can form from the accumulation of shells and coral, while coal is created from the remains of plant material.
- This process illustrates the biological contribution to sedimentary rock formation, confirming that not all sedimentary rocks are purely clastic or chemical in origin.
Conclusion
- All three statements are correct. Therefore, the correct answer is option 'D': All of the above.
- This understanding is crucial for resource exploration and management in various geological settings, particularly in the context of sustainable development and environmental considerations.

The correct answer is option 'D': All of the above.

Earthquakes are a natural phenomenon that occurs when there is a sudden release of energy in the Earth's crust, causing the ground to shake. They are most prone to occur in areas where certain geological conditions exist. Let's examine each option to understand why they are all correct:

1. Active Volcanoes:
- Volcanic activity often occurs in areas where tectonic plates meet, resulting in the formation of active volcanoes. These areas are known as volcanic zones or volcanic arcs.
- Volcanic eruptions are associated with the movement of magma from beneath the Earth's surface. As the magma rises, it can cause the surrounding rocks to fracture and create pathways for seismic waves to propagate, leading to earthquakes.
- Additionally, the pressure exerted by the magma can cause the Earth's crust to deform, resulting in stress accumulation and subsequent release in the form of earthquakes.

2. Large Reservoirs:
- Large reservoirs, such as those created by the construction of dams, can also trigger earthquakes. This phenomenon is known as reservoir-induced seismicity.
- When a reservoir is filled with water, the weight of the water puts additional stress on the underlying rocks and increases the pore pressure within them. This can destabilize the rocks and trigger seismic activity.
- The increased pore pressure can reduce the effective stress between rock grains, making them more susceptible to sliding along pre-existing fault planes and generating earthquakes.

3. Tectonic Fault Planes:
- Tectonic fault planes are areas where two tectonic plates meet and interact. These interactions can result in the accumulation of stress along the fault lines.
- When the stress exceeds the strength of the rocks, it can cause them to fracture and slip, resulting in an earthquake. The release of accumulated stress along fault planes is the most common cause of earthquakes worldwide.
- Some well-known examples of tectonic fault planes include the San Andreas Fault in California and the Himalayan Frontal Thrust in the Himalayas.

In conclusion, earthquakes are most prone to occur in areas where there are active volcanoes, large reservoirs, and tectonic fault planes. These geological conditions contribute to the build-up and release of stress within the Earth's crust, leading to seismic activity. Therefore, the correct answer is option 'D': All of the above.

The Mid-Ocean Ridge system forms the most extensive chain of mountains on Earth, with more than 90% of the mountain range lying in the deep ocean - with a total length of about 60,000 km. Mid-ocean ridges are geologically important because they occur along divergent plate boundaries, where the new ocean floor is created as the Earth’s tectonic plates spread apart. As the plates separate, some molten rock rises to the seafloor, producing enormous volcanic eruptions of basalt, and building the longest chain of volcanoes in the world. Because most of these eruptions occur deep under the water, they often go unnoticed.

Geothermal energy

The primary source of energy that drives the movement of tectonic plates is geothermal energy. Geothermal energy is the heat that comes from the Earth's core, where radioactive decay produces high temperatures. This heat causes convection currents in the mantle, which is the layer beneath the Earth's crust where tectonic plates float.

How geothermal energy drives tectonic plate movement

- The heat from the Earth's core causes magma to rise towards the surface, creating a convection current in the mantle.
- This movement of magma pushes and pulls on the tectonic plates, causing them to move.
- As the plates move, they interact with each other at their boundaries, leading to phenomena such as earthquakes, volcanic eruptions, and the formation of mountain ranges.

Significance of geothermal energy in plate tectonics

- Geothermal energy is crucial in maintaining the dynamic nature of the Earth's crust, as it provides the energy needed for the movement of tectonic plates.
- Without geothermal energy, the Earth's crust would be static, and essential geological processes such as continental drift and seafloor spreading would not occur.

In conclusion, geothermal energy is the primary source of energy that drives the movement of tectonic plates, playing a fundamental role in shaping the Earth's surface and influencing geological events.

The correct answer is option 'C': Both 1 and 2.

Explanation:
1. Magnetically susceptible minerals get aligned to the Earth’s magnetic field during the period of rock formation.
- This statement is correct. Certain minerals, such as magnetite, contain magnetic properties and can align themselves with the Earth's magnetic field during the formation of rocks. As magma cools and solidifies, these minerals can become aligned and preserve the magnetic field direction at the time of their formation. This phenomenon is known as paleomagnetism and is used by geologists to study the Earth's magnetic history and plate tectonics.

2. Foliated metamorphic rocks are formed within the Earth’s interior under extremely high pressures that arc unequal in different directions.
- This statement is also correct. Foliation is a texture exhibited by certain metamorphic rocks, where minerals are aligned in parallel layers or bands. This alignment is a result of the extreme pressures and temperatures experienced during metamorphism. The unequal pressures in different directions cause the minerals to recrystallize and align perpendicular to the direction of highest stress, resulting in the characteristic foliation. Examples of foliated metamorphic rocks include slate, schist, and gneiss.

In conclusion, both statements are correct. Magnetically susceptible minerals can align with the Earth's magnetic field during rock formation, and foliated metamorphic rocks form under unequal pressures within the Earth's interior. These processes provide valuable information about the Earth's history and geological processes.

Subduction Boundary
A subduction boundary is not a type of plate boundary. Below is an explanation of the other three types of plate boundaries:

Convergent Boundary
- Convergent boundaries occur when two tectonic plates collide with each other.
- The collision can result in the formation of mountain ranges, deep ocean trenches, and volcanic arcs.
- Subduction zones, where one plate is forced underneath another, are a common feature of convergent boundaries.

Transform Boundary
- Transform boundaries are where two tectonic plates slide past each other horizontally.
- These boundaries are characterized by frequent earthquakes as the plates grind against each other.
- The San Andreas Fault in California is a famous example of a transform boundary.

Divergent Boundary
- Divergent boundaries are where two tectonic plates move away from each other.
- This movement creates a gap which is filled with magma from below the Earth's crust, leading to the formation of new crust.
- Mid-ocean ridges, such as the Mid-Atlantic Ridge, are examples of divergent boundaries.
In conclusion, while subduction zones are associated with convergent boundaries, they are not a distinct type of plate boundary like convergent, transform, and divergent boundaries.

Answer:

Rocks That Make Up the Crust of Earth

The crust of the Earth is made up of various types of rocks, but some of them make up for large portions of it. These rocks are:

1. Granitic rocks
2. Basaltic rocks

Explanation:

Granitic rocks are igneous rocks that are light-colored and have a coarse-grained texture. They are formed from the slow cooling of magma beneath the Earth's surface. They are found in the continental crust and make up a large portion of it.

Basaltic rocks, on the other hand, are dark-colored igneous rocks that have a fine-grained texture. They are formed from the rapid cooling of lava on the Earth's surface. They are found in the oceanic crust and make up a significant portion of it.

Pumice rocks and obsidian rocks are also types of igneous rocks, but they do not make up large portions of the Earth's crust. Pumice rocks are formed from the rapid cooling of lava that is rich in gas bubbles, while obsidian rocks are formed from the rapid cooling of lava that is rich in silica.

Conclusion:

Therefore, the correct answer to this question is option 'B' - 1 and 2 only, as granitic rocks and basaltic rocks make up for large portions of the Earth's crust.

Mount Aso is located in Japan and is an active volcano. However, the statement that it was an active volcano a few decades back, but is an inactive volcano now is incorrect. Therefore, statement 1 is incorrect.

The correct statements about Mount Aso are:

Location:
- Mount Aso is located in Japan.

Activity:
- Mount Aso is an active volcano.
- The explosions in Mount Aso can be of high intensity at times.

Therefore, the correct answer is option 'D' (2 only).

Sandstone is a sedimentary rock formed by sedimentation of sand grains.

Convection currents in the mantle are the primary cause of tectonic plate movements on the Earth's surface. These convection currents occur due to the transfer of heat from the core to the mantle, creating a cycle of rising and sinking material within the mantle.

- **What are convection currents?**
Convection currents are the circular motion of fluids (in this case, the semi-solid mantle) caused by density differences due to temperature variations. When a fluid is heated, it becomes less dense and rises, while cooler, denser fluid sinks.

- **The role of convection currents in tectonic plate movements**
1. **Heat transfer from the core**: The Earth's core is extremely hot, and this heat is transferred to the mantle above it. The heat causes the mantle material to expand and become less dense, leading to the formation of convection currents.
2. **Rising and sinking of mantle material**: As the mantle material near the core heats up, it becomes less dense and rises towards the Earth's surface. This rising material carries the tectonic plates above it.
3. **Plate movement**: As the hot mantle material reaches the surface, it spreads out, causing the tectonic plates to move laterally. This is known as divergent plate boundaries. At other locations, the cooler, denser mantle material sinks back into the mantle, creating a downward force on the tectonic plates. This is known as convergent plate boundaries.
4. **Creation of subduction zones**: When two tectonic plates collide, one plate may override the other and sink beneath it. This process is called subduction and occurs at convergent plate boundaries. It is facilitated by the downward force created by the sinking of cooler mantle material.

- **Other factors and their roles**
While convection currents are the primary cause of plate movements, other factors can also influence them to some extent. These include:
- **Earth's rotation**: The rotation of the Earth can affect the direction and speed of plate movements but is not the primary cause.
- **Gravitational forces from the Moon**: The gravitational pull of the Moon causes tides on Earth, but its effect on tectonic plate movements is relatively small compared to convection currents.
- **Solar radiation**: Solar radiation primarily affects climate and weather patterns on Earth but does not directly cause tectonic plate movements.

In conclusion, convection currents in the mantle are the main driving force behind tectonic plate movements on the Earth's surface. These currents are caused by the transfer of heat from the core to the mantle, creating a cycle of rising and sinking material that leads to the lateral movement and collisions of tectonic plates.

Answer:

Factors responsible for changes on Earth's surface:

There are several factors responsible for bringing changes on the surface of the Earth. Some of the major factors are discussed below:

1. Tectonic forces:

Tectonic forces include processes like plate tectonics, earthquakes, volcanic eruptions, and mountain building. These forces are responsible for the creation of new landforms and the destruction of existing ones. Plate tectonics is the key process that drives the movement of the Earth's crust.

2. Gravitational force:

The gravitational force of the Earth is responsible for many changes on its surface. It causes erosion, weathering, and mass wasting. Erosion is the process by which the surface of the Earth is worn away by the action of water, wind, or ice. Weathering is the breakdown of rocks into smaller pieces due to the action of weather. Mass wasting is the downhill movement of soil and rock under the influence of gravity.

3. Electromagnetic radiation:

Electromagnetic radiation from the sun is responsible for many changes on the Earth's surface. It causes weather patterns, ocean currents, and the growth of plants. The sun's energy is also responsible for the water cycle, which is the process by which water evaporates from the surface of the Earth and is later returned as precipitation.

Correct answer:

All of the above (1, 2, and 3) are responsible for bringing changes on the surface of the Earth.

Explanation:

Alpine mountain building phase is the recent phase to which the Himalayan mountains belong to. The Ural Mountains were not formed during the Alpine orogeny (mountain building phase).

Therefore, the correct answer is option 'A' - 1 only.

- Alpine Mountain Building Phase
The Alpine mountain building phase is the most recent phase and began about 40 million years ago. This phase is ongoing and still forming mountains today in areas such as the Himalayas, the Alps, and the Andes.

- Himalayan Mountains
The Himalayan Mountains are a range of fold mountains located in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. They were formed during the ongoing Alpine mountain building phase.

- Ural Mountains
The Ural Mountains are a range of fold mountains located in western Russia, separating Europe and Asia. They were formed during the Variscan orogeny, which occurred about 300 million years ago, and not during the Alpine mountain building phase.

Therefore, statement 1 is correct, and statement 2 is incorrect.

**Introduction:**
Volcanoes are geological features that occur when magma, gas, and other materials from the Earth's interior are released through openings in the Earth's surface. They are typically found in specific geological locations that are associated with tectonic plate boundaries or areas of geological activity. In this context, we will explore the likelihood of the occurrence of volcanoes in the given geological locations.

**Coastal Mountain Ranges:**
Coastal mountain ranges are formed by the collision or subduction of tectonic plates. These tectonic activities create intense pressure and heat, leading to the melting of rocks and the formation of magma. As the magma rises through cracks and fissures in the Earth's crust, it can erupt onto the surface and form volcanoes. Notable examples of volcanic activity in coastal mountain ranges include the Cascade Range in North America and the Andes in South America.

**Off-Shore Islands:**
Off-shore islands, especially those located near tectonic plate boundaries, are commonly associated with volcanic activity. These islands are often formed by volcanic eruptions that occur underwater. As the magma rises and reaches the surface, it cools and solidifies, eventually forming new landmasses. Well-known examples of volcanic islands include the Hawaiian Islands, which were formed by a hotspot beneath the Pacific Plate.

**Midst of Deep Ocean Beds:**
Deep ocean beds are generally associated with tectonic plate boundaries, which are hotspots for volcanic activity. Underwater volcanic eruptions can occur along mid-ocean ridges, where tectonic plates are diverging, or at subduction zones, where one tectonic plate is being forced beneath another. These volcanic activities contribute to the formation of seamounts and underwater volcanoes. One such example is the Axial Seamount located off the coast of Oregon in the United States.

**Conclusion:**
Based on the geological processes and locations described, it is evident that volcanic activity is likely to occur in all three given geological locations: coastal mountain ranges, off-shore islands, and the midst of deep ocean beds. These areas are associated with tectonic plate boundaries, where the conditions for magma generation and eruption are favorable. Therefore, the correct answer is option 'D': All of the above.

Fold mountains are formed due to compressive action of forces in the Earth's crust. These are driven by magmatic convection.

Observing Earth's Structure through Earthquake Waves

Assertion (A): The structure of Earth can be understood by observing the passage of earthquake waves through different layers of earth.

Reason (R): Some type of earthquake waves do not travel through liquid material in Earth’s layers.

Explanation:

The Earth's interior structure can be understood by observing the passage of earthquake waves through different layers of the Earth. The waves generated by an earthquake travel through the Earth's interior and are recorded on seismographs placed at different locations on the surface. These waves are of two types - body waves and surface waves.

Body Waves:
Body waves are seismic waves that travel through the Earth's interior. There are two types of body waves: P waves (primary waves) and S waves (secondary waves).

P Waves:
P waves are the fastest seismic waves and can travel through solid, liquid, and gas materials. They arrive at the seismograph station first and can move through the Earth's interior in a straight line.

S Waves:
S waves are slower than P waves and can only travel through solid materials. They arrive at the seismograph station second and move through the Earth's interior in a zigzag pattern.

Surface Waves:
Surface waves are the waves that travel on the Earth's surface. They are slower than body waves but are more destructive. There are two types of surface waves: Love waves and Rayleigh waves.

Love Waves:
Love waves are the fastest surface waves and move the ground from side to side. They are responsible for most of the damage during an earthquake.

Rayleigh Waves:
Rayleigh waves are slower than Love waves and move the ground up and down. They are responsible for the rolling motion felt during an earthquake.

Conclusion:

The assertion is correct. The structure of the Earth can be understood by observing the passage of earthquake waves through different layers of the Earth. The reason is also correct. Some type of earthquake waves, such as S waves, do not travel through liquid material in the Earth's layers. This is because liquids cannot support shear stresses, which are necessary for S waves to propagate. Hence, option (A) is correct, and option (B) is the appropriate explanation of (A).

Properties of Lava:

Basic Lava:
- Basic lavas are the hottest lavas and are highly fluid.
- These lavas have low viscosity and can flow easily.
- They have a low gas content and therefore, do not cause explosive volcanoes.
- Basic lava is also called as mafic lava.

Acid Lava:
- Acid lavas are highly viscous and cause less explosive volcanoes.
- These lavas have a high gas content and therefore, tend to be explosive.
- Acid lava is also called as felsic lava.

Correct Answer:
- Statement 1 is correct as basic lavas are hot and highly fluid.
- Statement 4 is correct as acid lava is also called felsic lava.
- Therefore, option 'A' is the correct answer.

Incorrect statements:
- Statement 2 is incorrect as basic lava does not cause explosive volcanoes.
- Statement 3 is incorrect as acid lavas are highly viscous and tend to be explosive.

Volcanic Origin of Galapagos Islands:
- The first statement is correct. The Galapagos Islands are of volcanic origin. They were formed by volcanic activity over millions of years. The islands are located on the Nazca Plate, a tectonic plate in the Pacific Ocean.

Unique Adaptations and Endemic Species:
- The second statement is also correct. The Galapagos Islands have a unique ecosystem with diverse and distinct plant and animal species. The islands' harsh and isolated conditions, including stark rocky landscapes and limited freshwater sources, have created challenges for survival.
- Many species have adapted to these conditions over time, resulting in the evolution of new endemic species found only on the Galapagos Islands. These adaptations can include changes in physical characteristics, behavior, and feeding habits.

Galapagos Islands and Darwin's Theory of Evolution:
- The third statement is correct as well. The Galapagos Islands were instrumental in the development of Charles Darwin's Theory of Evolution. Darwin visited the islands during his famous voyage on the HMS Beagle in the 1830s.
- The unique and diverse species he encountered on the islands, such as the Galapagos finches and giant tortoises, played a crucial role in shaping his ideas about natural selection and the process of evolution.
- Darwin observed variations among these species, which he later concluded were adaptations to different ecological niches. This led him to propose that species could change over time through the process of natural selection, where those individuals with advantageous traits are more likely to survive and reproduce.

Conclusion:
- In conclusion, all three statements are correct. The Galapagos Islands are volcanic in origin and were never attached to any continent. The unique environment and limited resources on the islands have led to the evolution of new endemic species. Moreover, the Galapagos Islands played a pivotal role in the development of Darwin's Theory of Evolution.

Formation of Esker:
An Esker is a long, winding ridge of gravel and sand that is deposited by meltwater streams flowing beneath a glacier or ice sheet. These landforms are typically found in areas that were once covered by glaciers and icebergs.

Process of Formation:
1. **Glacial Melting:** When glaciers and icebergs melt, they release large amounts of water that flow underneath the ice.
2. **Transportation of Sediments:** As the meltwater streams flow, they carry sediments such as gravel and sand with them.
3. **Deposition:** The sediments are deposited in the form of a long, winding ridge as the meltwater streams slow down and deposit their load of sediments.
4. **Formation of Esker:** Over time, as the glacier or ice sheet retreats, the eskers are left behind as evidence of the melting ice.

Characteristics of Esker:
- Eskers can range in size from a few meters to several kilometers in length.
- They typically have a sinuous shape and can be several meters high.
- Eskers are often found in groups or clusters, known as eskers systems.
In conclusion, eskers are landforms that are formed by the melting of icebergs and glaciers, specifically by the deposition of sediments carried by meltwater streams. These unique landforms provide valuable insights into the history of glacial activity in a region.

Seafloor Spreading at Divergent Boundaries
Seafloor spreading occurs at divergent boundaries where tectonic plates move away from each other. This process is responsible for the formation of new oceanic crust.

Process of Seafloor Spreading
- Magma rises from the mantle and creates new crust at the mid-ocean ridges.
- As the magma cools, it solidifies to form new oceanic crust.
- The newly formed crust pushes the older crust away from the mid-ocean ridge, leading to the spreading of the seafloor.

Evidence for Seafloor Spreading
- Age of the seafloor: The further away from the mid-ocean ridge, the older the seafloor gets, providing evidence for the continuous creation of new crust.
- Magnetic striping: Alternating bands of magnetic polarity on the seafloor provide evidence for seafloor spreading.

Significance of Seafloor Spreading
Seafloor spreading plays a crucial role in plate tectonics and the movement of Earth's lithosphere. It helps in the recycling of oceanic crust and the formation of new crust, contributing to the dynamic nature of the Earth's surface.

East South American and West African coasts do not have good natural harbours.

The correct answer is option 'D' - All of the above.

Explanation:
The action of endogenic forces, which include processes like volcanic activity, faulting, and folding, is not uniform. This non-uniformity leads to an uneven and varied crustal surface. This can be attributed to several factors, including variation in crustal thickness, variation in geothermal gradients, and volcanism in the lithosphere.

1. Variation in crustal thickness:
The crust of the Earth is not uniform in thickness. It varies from place to place, with some regions having thicker crust and others having thinner crust. This variation in crustal thickness can be attributed to different geological processes, such as the collision of tectonic plates, the formation of mountain ranges, and the presence of deep-seated faults. The variation in crustal thickness results in an uneven crustal surface.

2. Variation in geothermal gradients:
Geothermal gradient refers to the rate at which temperature increases with depth in the Earth's interior. The geothermal gradient is not constant throughout the Earth's crust. It varies from region to region due to factors like heat flow from the mantle, presence of thermal anomalies, and local geologic conditions. This variation in geothermal gradients can lead to variations in the physical properties of rocks, such as their strength and viscosity, which in turn influence the action of endogenic forces and contribute to an uneven crustal surface.

3. Volcanism in the lithosphere:
Volcanism refers to the eruption of molten rock (magma) onto the Earth's surface. Volcanic activity is a common manifestation of endogenic forces and is associated with the movement of tectonic plates and the formation of volcanic landforms, such as volcanoes, lava flows, and volcanic ash deposits. Volcanism occurs in certain regions where there are active volcanic systems, such as the Ring of Fire in the Pacific Ocean. The presence of volcanism leads to localized uplift and subsidence of the Earth's crust, resulting in an uneven surface.

In conclusion, the action of endogenic forces is not uniform, and factors such as variation in crustal thickness, variation in geothermal gradients, and volcanism in the lithosphere contribute to the uneven and varied crustal surface. Therefore, the correct answer is option 'D' - All of the above.

Explanation:

Gutenberg Discontinuity:
The Gutenberg Discontinuity is the boundary between Earth's silicate mantle and its liquid iron-nickel outer core. It is located at a depth of about 2,900 kilometers beneath the Earth's surface.

Composition:
- The silicate mantle is composed of solid rock, while the outer core is made up of liquid iron and nickel.
- This boundary marks the transition from solid to liquid within the Earth's interior.

Seismic Waves:
- The Gutenberg Discontinuity is identified based on the behavior of seismic waves as they pass through the Earth's interior.
- Seismic waves change speed and direction when they encounter different materials, allowing scientists to map the Earth's interior structure.

Importance:
- Understanding the Gutenberg Discontinuity is crucial for studying the Earth's internal dynamics and processes.
- It helps scientists determine the composition and properties of different layers within the Earth.

Conclusion:
The Gutenberg Discontinuity is a significant boundary within the Earth's interior, marking the transition between the solid silicate mantle and the liquid iron-nickel outer core. Studying this boundary provides valuable insights into the Earth's composition and structure.

Salient Features of Fold Mountains

Fold mountains are formed by the folding of the Earth's crust. They are characterized by certain salient features, which are discussed below.

1. Conical Peaks:
Fold mountains are most likely to have conical peaks due to the volcanic activity associated with them. The magma below the surface rises and solidifies to form a cone-shaped structure.

2. Vertical Displacement:
Fold mountains are created when large areas of the Earth's crust are broken and displaced vertically, leading to the formation of fold structures.

3. Associated Volcanism:
Fold mountains are often associated with volcanism, either from the mountain core or its vicinity. This is due to the movement of tectonic plates, which leads to the formation of magma chambers and volcanic eruptions.

Correct Option
None of the above statements is correct as the first statement is incorrect. Fold mountains are most likely to have conical peaks due to the associated volcanic activity.