Class 11 Geography Important Chapter 4 Continental Drift and Plate Tectonic Theory

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Class 11 Geography Important Chapter 4 Continental Drift and Plate Tectonic Theory

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Continental Drift and Plate Tectonic Theory

Chapter: 4

SECOND UNIT : OUR EARTH

IMPORTANT QUESTION AND ANSWER

Answer The Following Questions:

1. Who is the founder of the Continental Drift Theory?

Ans: The founder of the Continental Drift Theory is Alfred Wegener.

2. What is Pangaea?

Ans: According to Alfred Wegener, Pangaea was a supercontinent that existed in the ancient geological past and contained all the major landmasses of the Earth.

3. Into how many parts did Pangaea break and what were they?

Ans: Pangaea broke into two parts — (i) Laurasia in the north and (ii) Gondwanaland in the south.

4. After which year did the modern development of the Plate Tectonic Theory occur?

Ans: The modern development of the Plate Tectonic Theory took place after 1960.

5. How many types of plates are there?

Ans: There are three types of plates.

6. In which year did Alfred Wegener publish his theory?

Ans: Alfred Wegener published his theory in 1912.

7. Up to what depth does the Lithosphere extend?

Ans: The Lithosphere extends up to about 100 kilometres in depth.

8. What does the word “Pangaea” mean?

Ans: The word “Pangaea” means “the land of all continents united.”

9. What is meant by Continental Drift?

Ans: According to Alfred Wegener, due to the forces caused by the Earth’s rotation and tidal action, the continents drifted from their original positions to new ones. The entire process of continental movement and re-establishment is called Continental Drift.

10. In which year did Tuzo Wilson suggest that the Earth’s crust is composed of polygonal pieces of different sizes?

Ans: In 1965, Tuzo Wilson suggested that the Earth’s crust is composed of polygonal pieces of various sizes.

Long Question & Answer:

1. What is meant by seafloor mapping?

Ans: Earlier, people believed that the ocean floor was a flat and featureless surface. However, in the first half of the 20th century, scientists discovered that the ocean floor also contains various landforms like mountains, plateaus, ridges, and trenches similar to those on land.

(i) Ocean deeps and submerged mountain chains are found not far from the coasts.

(ii) Many mid-ocean ridges contain active volcanoes.

(iii) The rocks of the ocean floor are younger than continental rocks.

(iv) Rocks of similar age are found on both sides of mid-ocean ridges, suggesting symmetrical formation.

These discoveries through seafloor mapping have greatly helped explain the scientific distribution of continents and oceans on Earth.

2. Describe the later studies related to the Continental Drift Theory.

ns: Wegener’s data supporting continental drift were mostly based on continental evidence and lacked information from the oceans, which cover about 71% of the Earth’s surface. Hence, he could not explain whether continents are currently moving or stationary.

Later, with the advancement of science after World War I, new technologies like seafloor mapping, paleomagnetism, and oceanic drilling provided new evidence. These studies proved that both continents and oceans are dynamic and that the process of plate movement continues today.

3. Discuss the forces responsible for Continental Drift.

Ans: According to Alfred Wegener, two types of forces were responsible for the movement of continents:

(i) Centrifugal force generated by the Earth’s rotation, which caused the equatorial bulge.

(ii) Tidal force caused by the gravitational pull of the Moon and the Sun, which moved continents westward.

Wegener believed that these forces acted continuously over millions of years, causing the separation of the Americas from the main continental mass.

Although modern scientists accept continental movement, they believe Wegener’s proposed forces were insufficient to cause such massive displacements.