Geography UGC NET UPSC 1

Assertion (A) : The ocean floors are much younger than continents. 

Reason (R) : Owing to their low density and consequent buoyancy, the ocean floors are not forced down into the mantle in subduction zone. 

Codes : 

(A) Both (A) and (R) are true and (R) is the correct explanation of (A) 

(B) Both (A) and (R) are true and (R) is not a correct explanation of (A) 

(C) (A) is true, but (R) is false 

(D) (A) is false, but (R) is true

The correct answer is (B) Both (A) and (R) are true and (R) is not a correct explanation of (A).

Explanation:

Assertion (A) states that the ocean floors are much younger than continents, which is true. This is due to a process called seafloor spreading, where new oceanic crust is formed at mid-ocean ridges through volcanic activity. As the new crust forms, it pushes older crust away, resulting in a continuous creation and movement of oceanic crust. Therefore, the ocean floors tend to be relatively young compared to continents.

Reason (R) states that the ocean floors are not forced down into the mantle in subduction zones due to their low density and buoyancy. While it is true that oceanic crust is denser than the underlying mantle, it is not the primary reason why ocean floors are younger than continents. The primary reason, as mentioned earlier, is seafloor spreading, not the lack of subduction. In reality, subduction does occur in certain regions where oceanic crust converges with continental crust, leading to the recycling of older oceanic crust into the mantle.

Hence, while both statements (A) and (R) are true, (R) does not provide an accurate explanation for why ocean floors are younger than continents, making option (B) the correct choice.