Interior of the Earth – NDA Geography PYQs

Question 1 [NDA 2009-II]
The Earth’s crust is the thinnest:
(a) Under the mountain ranges
(b) Under continental masses
(c) At ocean bottoms
(d) At mid-oceanic ridges

Answer: (c) At ocean bottoms
The oceanic crust is only 5–10 km thick — the thinnest part of the Earth’s crust. Under mountain ranges, the crust is actually the thickest — mountains have deep roots extending into the mantle. Under continental masses in general, the crust is 30–50 km thick.

---

Question 2 [NDA 2015-II]
Which one of the following describes the Lithosphere?
(a) Upper and lower mantle
(b) Crust and upper mantle
(c) Crust and core
(d) Mantle and core

Answer: (b) Crust and upper mantle
The lithosphere includes the crust and the uppermost solid portion of the mantle. It is the rigid outer shell of the Earth that is broken into tectonic plates. It does not include the deeper mantle, the core, or just the crust alone.

---

Question 3 [NDA 2019-II]
Lithosphere consists of:
(a) Upper and lower mantle
(b) Crust and core
(c) Crust and uppermost solid mantle
(d) Mantle and core

Answer: (c) Crust and uppermost solid mantle
The lithosphere consists of the crust and the uppermost solid part of the mantle — together forming the rigid outer shell of the Earth. This question is essentially the same as NDA 2015-II but worded differently. The answer is always the same concept.

Question 4 [NDA 2021-I]
The maximum depth of Lithosphere is found in the:
(a) Pacific Ocean
(b) Siberian Plain
(c) Patagonian Desert
(d) Himalayan Mountains

Answer: (d) Himalayan Mountains
The lithosphere is thickest under the Himalayan Mountains — because the continental crust there is at its greatest depth, with deep roots extending into the mantle. The Himalayas were formed by the collision of two continental plates, which pushed the crust to its greatest thickness.

---

Question 5 [NDA 2021-II]
Which one of the following best describes the Lithosphere?
(a) Upper and lower mantle
(b) Crust and core
(c) Crust and upper mantle
(d) Lower mantle and core

Answer: (c) Crust and upper mantle
This is the third time NDA has asked this question in different forms. The lithosphere = crust + upper mantle. It does not include the core or the lower mantle.

---

Question 6 [NDA 2022-II]
Which of the following statements is/are correct?

1. The Earth’s crust is brittle in nature.
2. The mean thickness of the oceanic crust is 15 km, whereas that of the continental crust is around 30 km.

(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2

Answer: (a) 1 only
Statement 1 is correct — the crust is indeed brittle; it fractures under stress. Statement 2 is wrong — the oceanic crust is about 5–10 km thick, not 15 km. The continental crust average of 30 km is broadly correct, but the oceanic crust figure is wrong.

Question 7 [NDA 2023-I]
Which one of the following is found in the innermost part of the Earth?
(a) Conrad discontinuity
(b) Moho discontinuity
(c) Gutenberg discontinuity
(d) Lehmann discontinuity

Answer: (d) Lehmann discontinuity
The Lehmann discontinuity at approximately 5,100 km depth separates the liquid outer core from the solid inner core. It is the deepest of all known discontinuities. From shallowest to deepest: Conrad → Moho → Gutenberg → Lehmann.

---

Question 8 [NDA 2024-I]
Which of the following statements regarding Earth’s internal structure is/are correct?

1. The oceanic crust is heavier than the continental crust.
2. Most of the Earth’s internal heat is contained within the mantle.
3. Large convective cells in the crust circulate heat and drive plate-tectonic processes.

(a) 3 only
(b) 1 and 2 only
(c) 2 and 3 only
(d) 1, 2 and 3

Answer: (b) 1 and 2 only
Statement 1 is correct — oceanic crust (SIMA) is denser than continental crust (SIAL). Statement 2 is correct — the mantle contains most of Earth’s internal heat. Statement 3 is wrong — the convective cells that drive plate tectonics are in the MANTLE, not in the crust. The crust is too thin and rigid for convective cells.

---