NCERT Solutions for Class 11 Geography (Fundamental of physical geography) Chapter 4 Distribution of Oceans and Continents

NCERT
SOLUTIONS
CLASS - 11th

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Book : Fundamental of Physical Geography Ncert Solutions | Chapter - 4 Social Science Geography

Class : 11th

Subject : Geography

Chapter : 4

Chapter Name : Distribution of Oceans and Continents

Q1 Multiple Type 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 Wegener (c) Abraham Ortelius

(b) Antonio Pellegrini (d) Edmond Hess

(ii) Polar fleeing force relates to:

(a) Revolution of the Earth (c) Rotation of the earth

(b) Gravitation (d) Tides

(iii) Which one of the following is not a minor plate?

(a) Nazca (c) Philippines

(b) Arabia (d) Antarctica

(iv) Which one of the following facts was not considered by those while discussing the concept
of sea floor spreading?

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Book : Fundamental of Physical Geography Ncert Solutions | Chapter - 4 Social Science Geography

(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.

(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.

(i) (c) Abraham Ortelius

(ii) (c) Rotation of the earth

(iii) (d) Antarctica

(iv) (c) Distribution of fossils in different continents.

(v) (d) Continent -continent convergence

Page : 38 , Block Name : Multiple choice questions.

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Book : Fundamental of Physical Geography Ncert Solutions | Chapter - 4 Social Science Geography

Q2 Answer the following questions in about 30 words-

(i) What were the forces suggested by Wegener for the movement of the Continents?

(ii) How are the convectional currents in the mantle initiated and maintained?

(iii) What is the major difference between the transform boundary and the convergent or
divergent boundaries of plates?

(iv) What was the location of the Indian landmass during the formation of the Deccan Traps?

Answer.

(i) Wegener suggested that the movement responsible for the drifting of the continents was
caused by pole- fleeing force and tidal force. This force relates to the rotation of the earth. The
earth isn’t a perfect sphere; it has a bulge at the equator. He believed that these forces; when
applied over many million years shall become effective.

(ii) The convectional currents is initiated by the thermal difference caused by radioactive
elements in the mantle. They are maintained due to the repetitive process where the hot material
in the mantle rises up from greater depths and the cold material goes down from above.

(iii) A transform boundary is where the crust is neither created nor destroyed as the plates slide
horizontally past each other, whereas in a convergent or divergent boundary there is creation of a
new crust either by destruction as one plate dives under other which is the case in the former type
or by generation of new crust as the plates pull away from each other as is the case in the latter.

(iv) The Deccan Traps were formed during the movement of the Indian plate towards the
Eurasian plate. At that time, Indian landmass was located in the south of the equator.

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Book : Fundamental of Physical Geography Ncert Solutions | Chapter - 4 Social Science Geography

Page : 38 , Block Name : Very short answer

Q3 Answer the following questions in about 150 words.

(i) What are the evidences in support of the continental drift theory?

(ii) Bring about the basic differences between the drift theory and Plate tectonics.

(iii) What were the major post-drift discoveries that rejuvenated the interest of scientists in the
study of distribution of oceans and continents?

Answer.

(i) The evidences in support of the continental drift theory are :
(a) T ​ he shorelines of continents are matching that
​ he Matching of Continents (Jig-Saw-Fit) T

means that the margins of the continents are such that there is a jig saw fit amongst them.
Example is the boundary of Africa and South America f​ acing each other have a remarkable and
unmistakable match.
(b) ​Rocks of Same Age Across the Oceans:​The belt of ancient rocks of 2,000 million years from
Brazil coast matches with those from western Africa. The earliest marine deposits along the
coastline of South America and Africa are of the Jurassic age. This suggests that the ocean did
not exist prior to that time.
(c ) Tillite : ​It is the sedimentary rock formed out of d​ eposits of glaciers. The Gondawana
system of sediments from India is known to have its counterparts in six different landmasses of
the Southern Hemisphere. The glacial tillite provides unambiguous evidence of palaeoclimates
and also of drifting of continents.
(d) ​Placer Deposits: ​The occurrence of rich placer deposits of gold in the Ghana coast and the
absolute absence of source rock in the region is an amazing fact. The gold bearing veins are in

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Book : Fundamental of Physical Geography Ncert Solutions | Chapter - 4 Social Science Geography

Brazil and it is obvious that the gold deposits of the Ghana are derived from the Brazil plateau
when the two continents lay side by side.
(e) D ​ hen identical species of plants and animals adapted to living on
​ istribution of Fossils: W

land or in fresh water are found on either side of the marine barriers, a problem arises regarding
accounting for such distribution. The observations that Lemurs occur in India, Madagascar and
Africa led some to consider a contiguous landmass ‘Lemuria’ linking these three landmasses.

(ii)

Drift theory:

The Drift theory was given by Alfred Wegener in 1912.

Drift theory suggested that:
→There was a super continent called Pangea. Over time, this super continent split apart to
form the seven continents we have today.
→This theory mainly covers the movement of continents amongst other things.
→The evidences in support of drift theory includes; Placer Deposits and others.
→ ​It doesn’t give any future prediction.

Plate Tectonics :

The plate Tectonics theory Provided that :
→It’s a theory of global tectonics proposing that the earth’s lithosphere is divided into seven
major and some minor plates.
→It is based on the fact that the rigid most outer shell of a planet is divided into Tectonic
plates.
→It covers both continents and oceans.
→It is based on scientific analysis of the processes inside the earth’s surface.
→This theory says that all plates shall continue to move in the future period as well.

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Book : Fundamental of Physical Geography Ncert Solutions | Chapter - 4 Social Science Geography

(iii) A number of post drift discoveries during the post- war period added new information to
geological literature. The information collected from the ocean floor mapping provided new
dimensions for the study of distribution of oceans and continents.

➔ All along the midoceanic ridges, volcanic eruptions are common and they bring huge
amounts of lava to the surface in this area.
➔ The oceanic crust rocks are much younger than the continental rocks. The age of rocks in
the oceanic crust is nowhere more than 200 million years old.
➔ The sediments on the ocean floor are unexpectedly very thin.
➔ Rocks closer to the mid oceanic ridges are normal polarity and are the youngest. The age
of rocks increases as one move away from the crest.
➔ The deep trenches have deep- seated earthquake occurrences while in the mid oceanic
ridge areas, the quake foci have shallow depths.

Page : 38 , Block Name : Very Long Answer

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