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Class 11 Geography Chapter 4 Distribution of Oceans And Continents
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Distribution of Oceans And Continents
Chapter: 4
PART-1
GEOGRAPHY
TEXTUAL QUESTION & ANSWER
(a) Multiple choice questions.
Q.1. Who amongst the following was the first to consider the possibility of Europe, Africa and America having been located side by side?
(i) Alfred Wagener
(ii) Antonio pellegrini
(iii) Abraham Ortelius
(iv) Edmond Hess
Ans: (iii) Abraham Ortelius
Q.2. Polar fleeing force relates to-
(i) Revolution of the earth.
(ii) Gravitation
(iii) Rotation of the earth.
(iv) Tides
Ans: (iii) Rotation of the earth.
Q.3.Which one of the following is not a minor plate?
(i) Nazca
(ii) Arabia
(c) Philippines
(iv) Antarctica
Ans: (iv) Antarctica
Q.4. Which one of the following facts was not considered by those while discussing the concept of seafloor spreading?
(i) Volcanic activity along the mid- oceanic ridges.
(ii) Stripes of normal and reverse magnetic field observed in rocks of the ocean floor.
(iii) Distribution of fossils in different continents.
(iv) Age of rocks from the ocean floor.
Ans: (iii) Distribution of fossils in different continents.
Q.5. Which one of the following is the type of plate boundary of the Indian plate along the Himalayan mountains?
(i) Ocean-continent convergence.
(ii) Divergent boundary
(iii) Transform boundary
(iv) Continent- Continent Convergence
Ans: (iv) Continent- Continent Convergence
(b) Answer the following questions in about 30 words.
Q.1. What were the forces suggested by Wegener for the movement of the continents?
Ans: Wegener suggested that the movement responsible for the drifting of the continents was caused mainly by the following two force:
(a) pole fleeing force.
(b) Tidal force.
The pole fleeing force relates to the rotation of the earth. The tidal force is due to the attraction of the moon and the sun develops tides in oceanic waters.
Q.2. How are the convection currents in the mantle initiated and maintained?
Ans: The possibility of conventional current in the mantle of the earth’s interior was introduced by Arthur Holmes in 1930. To him convection currents are generated due to radioactive elements causing thermal differences in the mantle portion. These currents move in radial directions.
Q.3. What are the major differences between the transform boundary and the convergent or divergent boundary of plates?
Ans: In case of a transform boundary the crust is neither produced nor destroyed as the plates slide horizontally past each other. But the diverge boundaries new crust is generated or in case of convergent boundaries crust is destroyed as one plate dives under another.
Q.4. What is the location of the Indian landmass during the formation of the Deccan Traps?
Ans: Initially,India was a large island situated off the Australian coast, in a vast ocean. The Tethys sea separated it from the Asian continent till about 225 million years ago. India is supposed to have started her northward journey about 200 million years ago at the time when Pangaea broke. During the movement of the Indian plate towards the Asiatic plate, by the outpouring of lava, the Deccan Traps was formed. About 140 million years before the present the Indian landmass was located as south as 50° latitude.
| Sl. No. | CONTENTS |
| Chapter 1 | Geography As A Discipline |
| Chapter 2 | The Origin and Evolution of the Earth |
| Chapter 3 | Interior of the Earth |
| Chapter 4 | Distribution of Oceans And Continents |
| Chapter 5 | Minerals and Rocks |
| Chapter 6 | Geomorphic Processes |
| Chapter 7 | Landforms and Their Evolution |
| Chapter 8 | Composition and Structure of Atmosphere |
| Chapter 9 | Solar Radiation, Heat balance, and Temperature |
| Chapter 10 | Atmospheric Circulation and Weather Systems |
| Chapter 11 | Water in the Atmosphere |
| Chapter 12 | World Climate and Climate Change |
| Chapter 13 | Water (Oceans) |
| Chapter 14 | Movements of Ocean Water |
| Chapter 15 | Life on the Earth |
| Chapter 16 | Biodiversity And Conservation |
| Chapter 17 | Indian Location |
| Chapter 18 | Structure and Physiography |
| Chapter 19 | Drainage System |
| Chapter 20 | Climate |
| Chapter 21 | Natural Vegetation |
| Chapter 22 | Soils |
| Chapter 23 | Natural Hazards and Disasters |
(c) Answer the following questions in about 150 words.
Q.1. What is the evidence in support of the continental drift theory?
Ans: To support the continental drift theory, Wegener collected a lot of evidence, from various sources Among them the following are worth mentioning.
(a) The matching of continents: The shorelines of Africa and South America facing each other have a remarkable and unmistakable match. The matching situation or the jig-saw-fit prove that once all the landmasses were united one.
(b) Rocks of the same age across the oceans : From the radiometric dating methods it is clear that the rock formation of both coasts are the same age.
(c)Tillite: Tillite is the sedimentary rock formed out of deposits of glaciers. It is found in six different landmasses of the southern hemisphere ( Africa, Falkland Islands, Madagascar, Antarctica, Australia and India). The glacial Tillite provides unambiguous evidence of paleoclimates and also of drifting of continents.
(d)Placer Deposits: The occurrence of rich placer deposits of gold in the Ghana coast and the Brazil plateau prove the continental drift theory.
(e) Distribution of fossils: The presence of Lemurs in three countries respectively India, Madagascar and Africa, prove that once all the landmasses were united one.
(f) The Plate tectonics also support the continental drift theory of Alfred Wegener.
Q.2. Bring about the basic difference between the drift theory and plate tectonics.
Ans: The basic difference between the drift theory and plate tectonics are given below:
(a) The continental drift theory was postulated by Alfred Wegener in 1912.
(b) Continental drift theory believed that all the present continents were united one. He named the supercontinent Pangaea.
(c) Drift theory considers the horizontal movement only.
(d) Continental drift theory explained only the origin and distribution of ocean and continents.
Plate tectonics:
(a) In 1967, Mekenzie, Parker and Morgan forwarded the plate tectonics ideas.
(b) According to the plate tectonics theory, the upper part of the earth (lithosphere) is made of some blocks untitled as plates.
(c)It takes into account the subduction of plates besides horizontal movement.
(d)Plate tectonics theory is a theory which is able to explain the origin and distribution of Oceans and continents, earthquakes, volcanic activity,sea-floor spreading and fold mountains on earth’s surface.
Q.3. What were the major post- drift discoveries that rejuvenated the interest of scientists in the study of distribution of Oceans and continents?
Ans: For Continental drift, most of the evidence was collected from the continental areas in the form of distribution of flora and fauna or from other deposits. A number of discoveries during the post- drift period added new Ocean and continents. Particularly the information collected from the ocean floor mapping provided new dimensions for the study of distribution of Oceans and continents.
Some facts are given below: (a) Most of the volcanic eruptions are scattered all along the mid- oceanic ridges, Which bring out the lava to 6 surfaces in such areas.
(b) The presence of conventional current in the mantle, which helps to move the land blocks from one place to another.
(c) Information about the sea floor spreading.
(d) The rocks of the oceanic crust are much younger than the continental one which is another discovery of the post drift period.
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