NCERT Solutions Class 11 Geography Chapter 4: Distribution of Oceans and Continents– This article includes free NCERT Solutions Class 11 Geography Chapter 4: Distribution of Oceans and Continents according to the latest CBSE Syllabus 2023-24, and guidelines.
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NCERT Solutions Class 11 Geography Chapter 4: Distribution of Oceans and Continents
1. Multiple choice questions
Question 1(i).
Who amongst the following was the first to consider the possibility of Europe, Africa, and America having been located side by side?
(а) Alfred Wegener
(b) Antonio Pellegrini
(c) Abraham Ortelius
(d) Edmond Hess.
Answer:
(c) Abraham Ortelius
Question 1(ii). Polar fleeing force relates to:
(a) Revolution of the Earth
(b) Gravitation
(c) Rotation of the earth
(d) Tides.
Answer:
(c) Rotation of the earth
Question 1(iii). Which one of the following is not a minor plate?
(a) Nazca
(b) Arabia
(c) Philippines
(d) Antarctica.
Answer:
(d) Antarctica
Question 1(iv). Which one of the following facts was not considered by those while discussing the concept of sea floor spreading?
(a) Volcanic activity along the mid- oceanic ridges
(b) Stripes of normal and reverse magnetic field observed in rocks of ocean floor
(c) Distribution of fossils in different continents
(d) Age of rocks from the ocean floor.
Answer:
(c) Distribution of fossils in different continents
Question 1(v). Which one of the following is the type of plate boundary of the Indian plate along the Himalayan Mountains?
(а) Ocean-continent convergence
(b) Divergent boundary
(c) Transform boundary
(d) Continent-continent convergence.
Answer:
(d) Continent-continent convergence.
2. Answer the following questions in about 30 words.
Question 2(i). What were the forces suggested by Wegener for the movement of the continents?
Answer:
Wegener proposed that the movement responsible for the shifting of the continents resulted from two forces: the pole-fleeing force and the tidal force.
The pole-fleeing force is associated with the Earth’s rotation, which causes a bulge at the equator due to the Earth not being a perfect sphere. This bulge is a consequence of the Earth’s rotation.
The tidal force is generated by the gravitational pull of the moon and the sun, which creates tides in the oceans. Wegener hypothesized that these forces would gradually exert their influence over millions of years.
Question 2(ii). How are the convectional currents in the mantle initiated and maintained?
Answer:
In the 1930s, Arthur Holmes explored the idea of convection currents happening within the mantle layer. These currents are created by radioactive elements, which lead to variations in temperature within the mantle.
Holmes proposed that a system of such currents exists throughout the mantle. This was his attempt to address the question of force that caused many scientists at the time to reject the theory of continental drift.
Question 2(iii). What is the major difference between the transform boundary and the convergent or divergent boundaries of plates?
Answer:
The major difference between the transform boundary and the convergent or divergent boundaries of plates are as follows:
Transform Boundaries: These occur when plates slide horizontally past each other, without either creating or destroying crust.
Convergent Boundaries: At these boundaries, one plate moves beneath another, leading to the destruction of crust.
Divergent Boundaries: Here, new crust forms as plates move away from each other.
Question 2(iv). What was the location of the Indian landmass during the formation of the Deccan Traps?
Answer:
Approximately 140 million years ago, the subcontinent was positioned as far south as 50°S latitude. As the Indian plate moved towards the Asiatic plate, a significant event occurred: the eruption of lava and the creation of the Deccan Traps. This began around 60 million years ago and persisted for an extended period.
It’s important to note that during this time, the subcontinent remained close to the equator. Around 40 million years ago and onwards, the formation of the Himalayas began. Scientists suggest that this process is ongoing, with the height of the Himalayas continuing to increase even today.
3. Answer the following questions in about 150 words.
Question 3(i) . What are the evidences in support of the continental drift theory?
Answer:
Various pieces of evidence were presented to support the theory of continental drift. Here are some of them:
Continental Fit (Jig-Saw-Fit): Africa and South America have shorelines that remarkably match each other, suggesting they were once connected.
Rocks of Similar Age Across Oceans: Ancient rocks dating back 2,000 million years found along the Brazilian coast align with those in western Africa. The earliest marine deposits in South America and Africa are from the Jurassic age, implying that there was no ocean between them before that time.
Tillite: This sedimentary rock, formed from glacier deposits, is found in the Gondwana system across six different landmasses of the Southern Hemisphere. The presence of thick tillite at the base indicates extensive glaciation, with counterparts found in Africa, Falkland Islands, Madagascar, Antarctica, Australia, and India. This suggests that these landmasses had similar histories and provides evidence of continental drift.
Placer Deposits: The discovery of rich gold placer deposits on the Ghana coast, without any local source rock, suggests they originated from the Brazilian plateau when the two continents were adjacent.
Fossil Distribution: The presence of lemurs in India, Madagascar, and Africa suggests the existence of a contiguous landmass called “Lemuria.”
Mesosaurus fossils, adapted to shallow brackish water, are found in Southern Cape province of South Africa and Iraver formations of Brazil, despite these locations being 4,800 km apart with an ocean separating them.
Question 3(ii). Bring about the basic difference between the drift theory and Plate tectonics.
Answer:
|
Aspect |
Drift Theory |
Plate tectonics |
|---|---|---|
|
Main Idea |
Suggests a past super continent (Pangaea) split into continents |
Proposes earth’s lithosphere divided into major and minor plates |
|
Scope |
Focuses on continental movement |
Covers movement of both continents and oceans |
|
Evidence |
Jig-Saw-Fit, Placer Deposits, Fossil Distribution, etc. |
Based on scientific analysis of processes within Earth’s surface |
|
Predictions |
Doesn’t make future predictions |
Predicts ongoing movement of plates into the future |
Question 3(iii). What were the major post-drift discoveries that rejuvenated the interest of scientists in the study of distribution of oceans and continents?
Answer:
During the post-war era, several discoveries contributed new insights to geological studies. Ocean floor mapping, in particular, provided valuable data for understanding the distribution of oceans and continents.
Arthur Holmes proposed that convection currents in the mantle, generated by radioactive elements, played a significant role. He suggested a system of such currents throughout the mantle, aiming to address concerns that led many scientists to dismiss the continental drift theory.
Further examination of the ocean floor revealed intricate features beyond a simple flat surface. Post-war expeditions meticulously mapped ocean relief, unveiling submerged mountain ranges and deep trenches, primarily near continent margins.
Notably, mid-oceanic ridges emerged as active sites for volcanic activity. Dating of oceanic crust rocks revealed their relative youth compared to continental counterparts.
Additionally, rocks located equidistant from the crest of mid-oceanic ridges displayed striking similarities in composition and age on both sides of the ridge.
Conclusion
In this article, we provided free NCERT Solutions for NCERT Solutions Class 11 Geography Chapter 4: Distribution of Oceans and Continents, adhering to the latest CBSE syllabus for 2023-24. The study of the distribution of oceans and continents has undergone significant evolution, with numerous discoveries reshaping our understanding of the Earth’s structure and geological processes.
Distribution of Oceans and Continents- FAQs
Who first proposed the idea of Europe, Africa, and America once being connected?
The first to consider the possibility of these continents being joined was Abraham Ortelius.
What forces did Wegener suggest were responsible for continental movement?
Wegener proposed two forces: the pole-fleeing force, associated with the Earth’s rotation, and the tidal force, caused by gravitational pull from the moon and sun.
What distinguishes a transform boundary from convergent or divergent boundaries?
Transform boundaries involve horizontal sliding of plates, without crust creation or destruction, unlike convergent boundaries where one plate sinks beneath another, or divergent boundaries where new crust forms as plates move apart.
Where was the Indian landmass during the formation of the Deccan Traps?
Approximately 140 million years ago, the Indian landmass was positioned around 50°S latitude, close to the equator.
What were some major post-drift discoveries that renewed scientific interest in ocean and continent distribution?
Post-war expeditions revealed intricate ocean floor features, such as submerged mountain ranges and deep trenches. Additionally, the recognition of convection currents in the mantle and the youthfulness of oceanic crust rocks provided further insights into Earth’s geological processes.