Worksheet Solutions: Distribution of Oceans and Continents | Geography Class 11 - Humanities/Arts PDF Download

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Q1: According to Alfred Wegener, all the continents formed a single continental mass called ________.
Ans: Pangaea.
Pangaea was a supercontinent that Wegener proposed existed around 200 million years ago, and it means "all earth" in Greek.

Q2: The mega-ocean surrounding Pangaea was named ________.
Ans: Panthalassa.
Panthalassa was the vast ocean that surrounded Pangaea, and it means "all water" in Greek.

Q3: Pangaea first broke into two large continental masses known as ________ and ________.
Ans: Laurasia and Gondwana.
Laurasia and Gondwana were the northern and southern components formed when Pangaea began to split.

Q4: The sedimentary rock formed from deposits of glaciers is called ________.
Ans: Tillite.
Tillite is a type of sedimentary rock that forms from the deposits left by glaciers. It provides evidence of past glaciation.

Q5: The distribution of identical species of plants and animals on either side of marine barriers led to the concept of ________.
Ans: Continental drift.
This observation of similar species on continents separated by oceans raised questions about how these species could have been connected in the past, contributing to the concept of continental drift.

Q6: The force responsible for drifting of continents due to the Earth's rotation is called ________.
Ans: Tidal forces.
Wegener suggested that the gravitational pull of the moon and the sun, causing tides in oceanic waters, could play a role in the movement of continents over millions of years.

Q7: The theory of plate tectonics was introduced by ________.
Ans: Alfred Wegener.
Alfred Wegener proposed the theory of continental drift in the early 20th century, which laid the foundation for the modern theory of plate tectonics.

Q8: Divergent boundaries are associated with the creation of ________.
Ans: New crust.
Divergent boundaries occur when tectonic plates move away from each other, and as they separate, new oceanic crust is formed through volcanic activity.

Q9: The slowest rate of plate movement occurs along the ________.
Ans: Transform boundaries.
Transform boundaries are characterized by plates sliding past each other horizontally, and they typically have slower rates of movement compared to divergent or convergent boundaries.

Q10: The boundary where two plates neither produce nor destroy crust as they slide past each other is called ________.
Ans: Transform boundary.
Transform boundaries are characterized by lateral movement of tectonic plates, where crust is neither created nor destroyed.

Assertion and Reason Based

Q1: Assertion: The shorelines of Africa and South America have a remarkable match.
Reason: This match is due to the gravitational pull of the moon and the sun.
(a) Both assertion and reason are true, and the reason is the correct explanation of the assertion.
(b) Both assertion and reason are true, but the reason is not the correct explanation of the assertion.
(c) Assertion is true, but the reason is false.
(d) Assertion is false.
Ans: (c)
While the assertion is true, the reason provided is not accurate. The remarkable match between the shorelines of Africa and South America is a significant piece of evidence supporting continental drift, but it is not primarily due to the gravitational pull of the moon and the sun. Instead, it is due to the fact that these continents were once part of a single landmass (Pangaea) and have since drifted apart.

Q2: Assertion: Seafloor spreading supports the theory of continental drift.
Reason: Seafloor spreading occurs when new oceanic crust is formed through volcanic activity.
(a) Both assertion and reason are true, and the reason is the correct explanation of the assertion.
(b) Both assertion and reason are true, but the reason is not the correct explanation of the assertion.
(c) Assertion is true, but the reason is false.
(d) Assertion is false.
Ans: (a)
In this case, both the assertion and the reason are true and well-aligned. Seafloor spreading is a key mechanism that supports the theory of continental drift. As new oceanic crust is formed at mid-ocean ridges through volcanic activity, it provides evidence of the movement of tectonic plates and the separation of continents.

Q3: Assertion: Plate boundaries where crust is neither produced nor destroyed are called transform boundaries.
Reason: Transform boundaries are associated with the creation of new crust.
(a) Both assertion and reason are true, and the reason is the correct explanation of the assertion.
(b) Both assertion and reason are true, but the reason is not the correct explanation of the assertion.
(c) Assertion is true, but the reason is false.
(d) Assertion is false.
Ans: (b)
The assertion is correct in defining transform boundaries, but the reason is incorrect. Transform boundaries are indeed places where tectonic plates slide past each other horizontally, without creating or destroying crust. However, they are not associated with the creation of new crust; that occurs at divergent boundaries.

Q4: Assertion: The Indian Plate is currently moving away from the Eurasian Plate.
Reason: The collision between the Indian Plate and the Eurasian Plate caused the formation of the Himalayas.
(a) Both assertion and reason are true, and the reason is the correct explanation of the assertion.
(b) Both assertion and reason are true, but the reason is not the correct explanation of the assertion.
(c) Assertion is true, but the reason is false.
(d) Assertion is false.
Ans: (a)
Both the assertion and reason are true and aligned. The Indian Plate is not currently moving away from the Eurasian Plate; in fact, it is still colliding with it. The collision between these two plates did indeed cause the formation of the Himalayas, which is a well-established geological fact.

Q5: Assertion: The concept of plate tectonics emphasizes the dynamic nature of the Earth's surface.
Reason: Heat generated from radioactive decay is the primary driving force behind plate movement.
(a) Both assertion and reason are true, and the reason is the correct explanation of the assertion.
(b) Both assertion and reason are true, but the reason is not the correct explanation of the assertion.
(c) Assertion is true, but the reason is false.
(d) Assertion is false.
Ans: (a)
Both the assertion and reason are true and well-explained. Plate tectonics emphasizes that the Earth's surface is dynamic, with tectonic plates constantly in motion. The heat generated from radioactive decay is indeed one of the primary driving forces behind the movement of tectonic plates.

Very Short Answer Type Questions

Q1: What does "Pangaea" mean?
Ans: "Pangaea" means a supercontinent that existed about 300 million years ago, which included all the present-day continents fused together.

Q2: How does the radiometric dating of rocks across continents support continental drift?
Ans: Radiometric dating of rocks across continents shows similarities in rock formation and age, supporting continental drift.

Q3: What is the significance of tillite in the evidence for continental drift?
Ans: Tillite is a sedimentary rock formed from glacier deposits, providing evidence of past glaciation and continental drift.

Q4: Explain the concept of Lemuria in the context of continental drift.
Ans: Lemuria was a proposed landmass connecting India, Madagascar, and Africa based on the distribution of lemurs.

Q5: Where are Mesosaurus skeletons found, and why is their distribution significant?
Ans: Mesosaurus skeletons are found in the Southern Cape province of South Africa and Iraver formations of Brazil. Their distribution suggests continental drift.

Q6: What are placer deposits, and how do they relate to continental drift?
Ans: Placer deposits are rich in gold and occur in Ghana, derived from the Brazil plateau when the two continents were adjacent.

Q7: How do plate tectonics cause earthquakes and volcanoes?
Ans: Plate tectonics cause earthquakes and volcanoes at plate boundaries due to the movement of plates.

Q8: Define seafloor spreading and its role in continental drift.
Ans: Seafloor spreading is the process of new oceanic crust formation at mid-ocean ridges, supporting continental drift.

Q9: Name three types of plate boundaries and briefly describe each.
Ans: Divergent boundaries, convergent boundaries, and transform boundaries.

Q10: What is the driving force behind plate movement according to plate tectonics?
Ans: The driving force behind plate movement is the convection of the Earth's mantle caused by heat from radioactive decay and residual heat.

Short Answer Type Questions

Q1: Describe the evidence provided by the matching shorelines of Africa and South America for the continental drift theory.
Ans: The matching shorelines of Africa and South America provide strong evidence for the continental drift theory. The coastlines of these two continents fit together almost perfectly, suggesting that they were once joined together. The shapes of the continents, such as the bulge of Brazil fitting into the Gulf of Guinea, support the idea that they were once part of a single landmass. This observation indicates that the continents have moved apart over time, supporting the concept of continental drift.

Q2: Explain the significance of rocks of the same age found on different continents. How does this support continental drift?
Ans: Rocks of the same age found on different continents provide evidence for continental drift. When rocks of the same age and composition are found on different continents, it suggests that these continents were once connected and have since moved apart. This phenomenon is known as "matching fossils" or "corresponding rock types." The presence of identical fossils or rock formations on separate continents indicates that these landmasses were once contiguous and later separated, supporting the theory of continental drift.

Q3: Discuss the concept of "tillite" and its role in providing evidence for continental drift.
Ans: Tillite is a type of sedimentary rock formed from the compacted and lithified glacial till, which consists of various sizes of rock fragments and unsorted sediments. The presence of tillite in regions that are now located in tropical or subtropical climates provides evidence for continental drift. Tillite is typically associated with glaciers and is formed in cold, high-latitude environments. However, tillite deposits have been found in regions such as Africa and India, which are currently located near the equator. This suggests that these regions were once located near the South Pole and experienced glacial conditions, supporting the theory of continental drift.

Q4: How do placer deposits in Ghana relate to the continental drift theory?
Ans: Placer deposits in Ghana, specifically gold deposits, provide evidence for continental drift. Ghana is known for its rich placer gold deposits, which are found in riverbeds and other sedimentary environments. The presence of these gold deposits suggests that Ghana was once part of a landmass that contained gold-bearing rocks. This landmass is believed to be the supercontinent of Gondwana, which included present-day Africa, South America, Antarctica, Australia, and the Indian subcontinent. The existence of placer gold deposits in Ghana supports the idea that these continents were once connected and have since drifted apart.

Q5: Explore the distribution of Lemurs and Mesosaurus and their implications for continental drift.
Ans: The distribution of Lemurs and Mesosaurus provides evidence for continental drift. Lemurs are primates found exclusively in Madagascar, while Mesosaurus is a reptile found only in South America and Africa. The existence of these unique and geographically isolated species suggests that these landmasses were once connected. The limited ability of these organisms to disperse across vast bodies of water supports the concept of continental drift. The presence of Lemurs in Madagascar and Mesosaurus in both South America and Africa indicates that these continents were once contiguous and later separated, further supporting the theory of continental drift.

Q6: Describe the forces responsible for driving the movement of continents according to Wegener.
Ans: According to Wegener, the movement of continents is driven by the forces of "continental drift." He proposed that continents are not static but rather move horizontally over the Earth's surface. Wegener suggested two main forces responsible for this movement: (1) "polar wandering," which involves the movement of continents towards or away from the Earth's poles, and (2) "tidal forces," which are caused by the gravitational pull of the Moon and Sun. These forces, combined with the concept of "continental plowing," where continents push through the oceanic crust, were believed to be the driving mechanisms for the movement of continents.

Q7: What is seafloor spreading, and how does it support the theory of plate tectonics?
Ans: Seafloor spreading is the process by which new oceanic crust is formed at mid-ocean ridges and spreads outward. As magma rises to the surface at these ridges, it cools and solidifies, creating new crust. The older crust is pushed away from the ridge and gradually moves laterally. This process supports the theory of plate tectonics as it provides a mechanism for the movement of tectonic plates. The spreading of the seafloor allows for the continuous creation of new crust, which pushes older crust away from the ridges. This movement of oceanic plates influences the motion of the adjacent continental plates, leading to the shifting and rearrangement of continents over geological timescales.

Q8: Explain the role of convection currents in the mantle in the context of tectonic plate movement.
Ans: Convection currents in the mantle play a crucial role in tectonic plate movement. The mantle, which is the layer of hot, semi-fluid rock beneath the Earth's crust, experiences convection due to temperature differences. Warmer material near the core rises, while cooler material near the surface sinks. This movement generates convection currents that drive the motion of tectonic plates. As the warmer mantle material rises, it pushes against the underside of the lithosphere, causing it to move. This movement can result in the separation of plates at mid-ocean ridges or the subduction of one plate beneath another at convergent boundaries. Convection currents in the mantle provide the energy needed to drive the motion of tectonic plates and are a fundamental component of the theory of plate tectonics.

Long Answer Type Questions

Q1: Discuss the continental drift theory proposed by Alfred Wegener. Include details about Pangaea, the breakup of continents, and the evidence supporting this theory.
Ans: The continental drift theory, proposed by Alfred Wegener in the early 20th century, suggests that the continents were once joined together in a single supercontinent called Pangaea and have since drifted apart to their current positions.
Wegener proposed this theory based on several lines of evidence:

• Pangaea, which means "all lands" in Greek, was a supercontinent that existed around 300 million years ago. According to Wegener's theory, Pangaea began to break apart into smaller continents, which eventually drifted to their current positions. This breakup process occurred over millions of years and is known as continental drift.
• One piece of evidence supporting the continental drift theory is the fit of the coastlines. When the continents are brought together, the coastlines of continents such as South America and Africa seem to fit together like puzzle pieces. This suggests that they were once joined together.
• Another piece of evidence is the distribution of fossils. Similar fossils of plants and animals have been found on different continents that are now far apart. For example, fossils of the freshwater reptile Mesosaurus have been found in both South America and Africa. This indicates that these continents were once connected.
• Furthermore, the presence of similar rock types and geological structures on different continents supports the continental drift theory. For instance, the Appalachian Mountains in North America and the Caledonian Mountains in Europe have similar rock formations and structures, suggesting that they were once part of the same mountain range.
• The discovery of ancient glacial deposits in regions that are currently too warm for glaciation is another evidence for continental drift. For example, glacial deposits from the Permian period have been found in South America, Africa, India, and Australia, which implies that these continents were once located near the South Pole.

Overall, these lines of evidence provided by Wegener and subsequent research support the theory of continental drift and have led to the development of the modern theory of plate tectonics.

Q2: Explain the concept of plate tectonics and the types of plate boundaries. Provide examples for each type of boundary.
Ans: Plate tectonics is the scientific theory that describes the movement and interaction of large sections of the Earth's lithosphere, known as tectonic plates. These plates are composed of the crust and the upper part of the mantle and float on the semi-fluid asthenosphere below.
There are three main types of plate boundaries: divergent boundaries, convergent boundaries, and transform boundaries.

• Divergent boundaries occur where tectonic plates move away from each other. This leads to the upwelling of material from the mantle, creating new crust. An example of a divergent boundary is the Mid-Atlantic Ridge, where the North American Plate and the Eurasian Plate are moving apart, creating new oceanic crust.
• Convergent boundaries occur where tectonic plates collide with each other. There are three types of convergent boundaries:
  a. Oceanic-Continental Convergent Boundaries: In this case, an oceanic plate subducts beneath a continental plate. This results in the formation of deep ocean trenches and the volcanic activity on the continental plate. The subduction of the Nazca Plate beneath the South American Plate, forming the Andes Mountains, is an example of an oceanic-continental convergent boundary.
  b. Oceanic-Oceanic Convergent Boundaries: Here, one oceanic plate subducts beneath another oceanic plate. This leads to the formation of volcanic island arcs. The subduction of the Pacific Plate beneath the Philippine Sea Plate, creating the Mariana Islands, is an example of an oceanic-oceanic convergent boundary.
  c. Continental-Continental Convergent Boundaries: When two continental plates collide, neither subducts due to their low density. Instead, the collision results in the formation of large mountain ranges. The collision between the Indian Plate and the Eurasian Plate, giving rise to the Himalayas, is an example of a continental-continental convergent boundary.
• Transform boundaries occur where tectonic plates slide past each other horizontally. These boundaries are characterized by intense seismic activity. The San Andreas Fault in California is an example of a transform boundary, where the Pacific Plate and the North American Plate are sliding past each other.
  
  

Q3: Analyze the movement of the Indian plate, its history, and the impact on the Himalayas. Include key geological events in this process.
Ans: The Indian plate is one of the major tectonic plates on Earth and has played a significant role in shaping the geology of the Indian subcontinent and its surrounding regions. The movement of the Indian plate began around 50 million years ago and has had a profound impact on the formation of the Himalayas.
In the past, the Indian plate was located in the southern hemisphere and was part of the supercontinent Gondwana. Around 200 million years ago, Gondwana began to break apart, and the Indian plate started moving northward.
Around 50 million years ago, the Indian plate began to collide with the Eurasian plate. This collision occurred at a convergent boundary, where the Indian plate, consisting of continental crust, collided with the Eurasian plate, also consisting of continental crust. As a result of this collision, the Indian plate was forced beneath the Eurasian plate, leading to intense compression and deformation.
The ongoing collision between the Indian plate and the Eurasian plate has resulted in the uplift of the Himalayas, the highest mountain range on Earth. The Himalayas continue to rise at a rate of a few millimeters per year due to the ongoing convergence between the two plates.
The collision between the Indian plate and the Eurasian plate has also led to the formation of other geological features, such as the Tibetan Plateau. The Indian plate has been pushing against the Eurasian plate, causing the crust to thicken and uplift, resulting in the formation of the high-altitude Tibetan Plateau.
Overall, the movement of the Indian plate and its collision with the Eurasian plate have had a profound impact on the geological history of the region, resulting in the formation of the Himalayas and other associated geological features.

Q4: Elaborate on the role of convection currents in the mantle and their influence on tectonic plate movement. Discuss how this concept has evolved over time in understanding continental drift.
Ans: Convection currents in the mantle play a crucial role in driving the movement of tectonic plates. The mantle is a semi-fluid layer of the Earth's interior, and convection currents are large-scale movements of material driven by temperature differences.
The concept of convection currents in the mantle and their influence on tectonic plate movement has evolved over time in understanding continental drift. Initially, Alfred Wegener proposed the idea of continental drift based on the observation of the fit of coastlines and the distribution of fossils, but he did not provide a mechanism for how continents could move.
Later, in the 1960s, the theory of plate tectonics emerged, which incorporated the concept of convection currents in the mantle as the driving force behind the movement of tectonic plates. According to this theory, the heat generated from the core of the Earth causes the mantle to convect, forming convection cells. These cells involve the upward movement of hot material and the downward movement of cooler material.
As the hot material rises, it creates a pressure gradient that pushes the tectonic plates apart at divergent boundaries. The cooler material sinking back down into the mantle at subduction zones creates a downward force that drives the motion of tectonic plates at convergent boundaries.
This understanding of convection currents in the mantle and their influence on tectonic plate movement has been supported by various lines of evidence. For example, seismic activity and the distribution of earthquakes and volcanic activity align with plate boundaries, indicating the regions where tectonic plates interact.
Furthermore, the observation of the symmetrical magnetic striping on the seafloor, discovered in the 1960s, provided strong evidence for seafloor spreading and the movement of tectonic plates. This striping is a result of the alternating magnetic polarity of the Earth's magnetic field, which is preserved in the rocks as they solidify from magma at mid-ocean ridges.
Overall, the concept of convection currents in the mantle as the driving force behind tectonic plate movement has become a fundamental part of our understanding of continental drift and the theory of plate tectonics. Ongoing research and technological advancements continue to refine our understanding of these processes.