Distribution of Oceans and Continents Short and Long Important Question Class 11 Geography Chapter-4 Book-Fundamental of Physical Geography

 

Question - Explain the basic difference between continental drift theory and plate tectonics theory

Answer - 

1. Continental Drift Theory

• According to Alfred Wegener, all the continents were connected into a single landmass.

• All the continents of today were part of this landmass and it was surrounded by a large ocean.

• This large continent was named Pangaea.

• The vast ocean was named Panthalassa 

• About 200 million years ago, the division of this large continent, Paigea, began.

• Pagaea first split into two large continental bodies, Laurasia and Gondwanaland.

2. Plate tectonics theory

• A tectonic plate is a large block of solid rock composed of continental and oceanic lithosphere.

• The lithosphere includes the crust and the upper mantle, whose thickness is 5 to 100 km in the oceans and about 200 km in the continental regions.

• A plate may also be called a continental or oceanic plate, depending on whether the majority of the plate is associated with an ocean or a continent.

Question –  Explain the difference between divergent boundary and convergent boundary.

Answer - 

1. Divergent boundary

• When two plates move away from each other in opposite directions and new crust is formed, they are called divergent plates. 

• The places where plates move away from each other are also called spreading sites.

2. Convergent boundary

• When one plate subducts beneath another and where the crust is destroyed, that is a convergent boundary. 

• The place where the plates sink is also called the subduction zone. 

Convergence can happen in three ways

1. Between oceanic and continental plates 

2. Between two oceanic plates 

3. Between two continental plates.

Question -  Which forces did Wegener hold responsible for continental drift?

Answer - 

According to Wegener there are two reasons for continental displacement 

1. Polar flying force – The continents moved out of their positions due to the rotation of the earth 

2. Tidal force Tidal force is related to the attraction of the Sun and the Moon. This force of attraction can cause displacement of continental blocks.

 

Question:  According to the plate tectonics theory, how many plates is the Earth divided into?

Answer - 

important large plate 

• Antarctic Plate

• North American Plate

• South American Plate

• pacific oceanic plate

• Indo-Australian New Zealand Plate.

• African Plate 

• Eurasian Plate

Important small plates 

• Cocos 

• Nazca Plate

• Arabian Plate

• philippine plate

• Carolyn Plate

Question –  How many parts is the sea floor divided into with depth?

Answer -  

Division of the sea floor 

1. Continental margin

• This is the area between the continental margin and the deep ocean basin. 

• It includes continental shelf, continental slope, continental rise and deep ocean trenches etc.

2. Deep sea basin

• These vast plains are found between the continental coasts and mid-ocean ridges. 

• Abyssal plains are areas where sediments carried from the continents are deposited away from their coasts.

3. Mid-ocean ridge

• The mid-ocean ridge forms a chain of interconnected mountains. 

• Submerged in ocean water, it is possibly the longest mountain range found on the Earth's surface.

Question -  What evidence can be given in favour of displacement of continents. Give details.

Answer - 

What is the evidence in favor of the displacement of continents?

1. Similarities between continents

•  If we look carefully at the shape of the continents, we will find that there is a wonderful similarity between their opposite coastlines.

2. Similarity in age of rocks across oceans

• The rocks of two continents which are far away from each other at present have similar ages. For example, a strip of 200 crore years old rock formations is found on the coast of Brazil (South America) and West Africa. This shows that both the continents were together in ancient times.

3. Tillite

• These are sedimentary rocks formed by glacial deposition. Patterns of such deposits are found in six different landmasses of the Southern Hemisphere, which is evidence of their existence together in ancient times.

4. Placer deposits

• Gold-bearing veins are found in Brazil while placer deposits are found in Ghana, proving that South America and Africa were once one place.

5. Distribution of fossils

• On some continents, remains of organisms are found that are not currently found in that place