Detailed, Step-by-Step NCERT Solutions for Class 11 Geography Chapter 11 Distribution of Oceans and Continents Questions and Answers were solved by Expert Teachers as per NCERT (CBSE) Book guidelines covering each topic in chapter to ensure complete preparation.
Distribution of Oceans and Continents NCERT Solutions for Class 11 Geography Chapter 4
Distribution of Oceans and Continents Questions and Answers Class 11 Geography Chapter 4
Question 1.
Multiple choice questions :
(i) Who amongst the following was the first to consider the possibility of Europe, Africa and America having been located side by side?
(a) Alfred Wegner
(b) Abraham Ortelius
(c) Antonia Pellegrini
(d) Edmond Hess
Answer:
(b) Abraham Ortelius.
(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.
(iii) Which one of the following is not a minor plate?
(a) Nazca
(b) Arabia
(c) Philippines
(d) Antarctica
Answer:
(d) Antarctica.
(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 fiel 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.
(v) Which one of the following is the type of plate boundary of the Indian plate along the Himalayan mountains?
(a) Ocean-continent convergence
(b) Divergent boundary
(c) Transform boundary
(d) Continent-continent convergence
Answer:
(d) Continent-continent convergence.
Question 2.
Answer the following questions in about 30 words each :
(i) What were the forces suggested by Wegner for the movement of the continents?
Answer:
(1) Pole fleeing force and
(2) Tidal force.
These were the two forces suggested by Wegner for the movement of the continents. He believed that these forces would become effective when applied over many million years.
(ii) How are the convectional currents in the mantle initiated and maintained?
Answer:
These currents are generated due to radioactive elements causing thermal differences in the mantle portion. The currents move in radial direction and develop in cell patterns.
(iii) What is the major difference between the transform boundary and the convergent or divergent boundaries of the plates?
| Convergent or Divergent boundaries | Transform boundaries |
| (0 These are known as subduction boundaries. | (i) These are known as transform boundaries. |
| (ii) These boundaries are destructive, consumptive or converging boundaries. | (ii) These are conservative. |
| (iii) These are identified with oceanic trenches and island arcs. | (iii)Two plates slide by each other. |
(iv) What was the location of Indian landmass during the formation of Deccan Traps?
Answer:
(a) India was in the southern hemisphere when the volcanie activity began and was drifting northward during the span of this activity.
(b) Deccan Trap flows having an altitude of around 600 m (2000 ft.) and above were found to be magnetized normally.
Question 3.
Answer the following questions in about 150 words each :
(i) What are the evidences in support of continental drift theory?
Answer:
There were a number of evidences offered in support of the continental drift. Some of them are given below :
(1) The matching of continents : The shorelines of Africa and S. America facing each other have a remarkable and unmistakable match. The match was tried at 1000 fathom line instead of the present shoreline. However, with slight modification, a reasonably good and acceptable map of the continents was demonstrated.
(2) Rocks of same age across the oceans: The radiometric dating methods developed in recent period have facilitated correlating the rock formation from different continents across the vast ocean. The earliest marine deposits along the coastline of either S. America or Africa are of Jurassic age. This suggests that the ocean did not exist prior to that time.
(3) Tillite: Tillite are the sedimentary rocks formed out of deposits of glaciers. The Gondawana system of sediments is known to have its counterpart in six different landmasses of southern hemisphere. At the base, the system has thick tillite indicating extensive and prolonged glaciation. Overall resemblance of the Gondawana type sediments clearly demonstrate that these landmasses had remarkably similar histories. The glacial tillites provide unambiguous evidence of palaeoclimates and also of drifting of continents.
(ii) Bring about the basic difference between the drift theory I and plate tectonics.
Answer:
The basic concept regarding continental drift was that all the
continents formed a single continental mass – a protocontinent. This covered about all the present continents and was surrounded by an ocean. This was named PANGAEA. It was argued that around 200 million years ago, the super continent pangaea began to split apart. Pangaea first broke into two large continental landmasses, Laurasia in the Northern Hemisphere and Gondawana in the Southern Hemisphere. A number of evidences were offered in support of the continental drift.
Plate tectonic : According to plate tectonic theory, the earth’s lithosphere is divided into six major and some minor plates. At present, Antarctica and the surrounding ocean, Americas with western Atlantic floor, Pacific floor, India to Australia and New Zealand, Africa with eastern Atlantic floor, Eurasia and adjacent ocean are the major plates.
Cocos plate, Nazca plate, Arabian plate, Philippine plate, Caroline plate and Fuji plate are minor plates. These plates are moving over the globe throughout the history of the earth. The plate boundaries are the most active areas along which there is always some kind of tectonic activity going on.
(iii) What were the major post drift discoveries that rej uvenated the interest of scientists in the study of distribution of oceans and continents?
Answer:
The positions of the continents and the ocean bodies have not been the same in the past. The oceans and continents will not continue to enjoy their present position in times to come. If this is so, then the question arises what were their positions in the past? Why and how do they change their positions? How do the scientists know this?
Observe the shape of the coastline of Atlantic ocean.
There is symmetry between the coastlines on either side of the ocean. Many scientists thought of this similarity and considered the possibility of the two Americas, Europe and Africa to be once joined. From the known records of the history of science, it was Abraham Ortelius, a Dutch map maker, who first proposed such a possibility as early as 1596.
Antonio Pellegrini drew a map showing the three continents together. Wegner’s theory was based on the remarkable fit of the south American and African continents and the occurrences of unusual geologic structures and of plant and animal fossils found on the matching coastlines of two continents widely separated by the Atlantic ocean. The presence of identical fossil species along the coastal parts of Africa and South America was convincing evidence of the fact that two continents lay side by side in the past.