NCERT CH4 OCEAN AND CONTINENTS

Question 1

What is the proportion of land and water on the earth surface?

Answer 1

71% OCEANS

29% LAND

Question 2

Who first proposed that all the continents were once joined together?

Answer 2

Abraham Ortelius, a Dutch map maker in 1596

Question 3

Who drew a map showing the three continents joined together?

Answer 3

Antonio Pellegrini

Question 4

Who gave the CONTINENTAL DRIFT THEORY?

Answer 4

ALFRED WEGENER, a German meteorologist in 1912

Question 5

What is the CONTINENTAL DRIFT THEORY?

Answer 5

According to CDT, there existed one big landmass called PANGAEA which was surrounded by one superocean called PANTHALASSA.
200 Million years ago, Pangaea split into two large continental masses LAURASIA on the north and GONDWANALAND on the south. They were separated by the TETHYS SEA.
Both these landmasses continued to split and drift to form the present continents.

Question 6

What are the evidences in support of CONTINENTAL DRIFT THEORY?

Answer 6

1. Jig-saw fit of the continents
2. Rocks of same age across the oceans
3. Tillite deposits
4. Placer deposits
5. Distribution of fossils

Question 7

What are the forces behind the drifting of continents according to CDT?

Answer 7

1. Polar fleeing force

2. Tidal force

Question 8

What are the drawbacks of CDT?

Answer 8

1. Doesn’t explain why the drift began only in the mesozoic era
2. Doesn’t consider oceans
3. Proofs heavily dependent upon assumptions that are generalistic
4. Forces like buoyancy, tidal force, gravity are too weak to move continents