Structural Geology MCQ with answer and solution

Concept

The mantle lies between the crust and the outer core. It goes from the Moho down to the Gutenberg discontinuity at about 2,900 km depth.

Step-by-step solution

1. The Earth has three main layers: crust, mantle and core. 2. The crust ends at the Mohorovicic (Moho) discontinuity, about 5 to 70 km deep. 3. The mantle continues down to the Gutenberg discontinuity. 4. The Gutenberg discontinuity is at about 2,900 km depth. 5. So the answer is (A) 2,900 km.

Explanation

The mantle starts at the base of the crust (Moho) and ends at the core-mantle boundary (Gutenberg discontinuity). This boundary is about 2,900 km deep. It is the thickest layer of the Earth.

Why the other options are wrong

2,800 km, 2,600 km and 2,700 km are all less than the standard value of about 2,900 km for the mantle's lower boundary.

Shortcut

Remember: Moho = top of the mantle, Gutenberg = 2,900 km = bottom of the mantle.

Common mistake

Confusing the mantle depth with the outer core boundary (about 5,150 km) or the Earth's radius (about 6,371 km).