UPSC Physical Geography – Chapter 3: Interior of the Earth (22 MCQs)

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UPSC Physical Geography – Chapter 3: Interior of the Earth (22 MCQs) – 21 questions, subject: Geography. Every question has the correct answer with a one-line explanation; tap "Show Answer". Free practice for TNPSC, UPSC, SSC, Bank and RRB exams – Shanmugam IAS Academy, Coimbatore.

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1.  

The most important source of information about the Earth's interior is:

Correct Answer: C [seismic waves]

Explanation:

Seismic waves pass through the whole Earth, and their speed, refraction and shadow zones reveal the layers and the liquid outer core.

2.  

The deepest borehole on the Earth, the Kola borehole, reached a depth of about:

Correct Answer: B [12 km]

Explanation:

The Kola Superdeep Borehole in Russia reached 12,262 m in 1989, still within the continental crust.

3.  

S-waves cannot pass through:

Correct Answer: B [liquids]

Explanation:

S-waves are transverse and travel only through solids; liquids such as the outer core stop them.

4.  

The seismic shadow zone lies between:

Correct Answer: C [105° and 145°]

Explanation:

Between 105° and 145° from the epicentre neither P- nor S-waves are recorded directly, forming the shadow zone.

5.  

The waves that cause the most damage to buildings are:

Correct Answer: D [surface waves]

Explanation:

Surface waves arrive last and move the ground at the surface, causing most of the damage to buildings.

6.  

The boundary between the mantle and the core is the:

Correct Answer: A [Gutenberg discontinuity]

Explanation:

2,900 km.

7.  

The asthenosphere is important because it is:

Correct Answer: D [the main source of magma and the layer over which plates move]

Explanation:

The weak, partly molten asthenosphere in the upper mantle supplies magma and lets the rigid lithospheric plates move over it.

8.  

The term NIFE refers to the composition of the:

Correct Answer: D [core]

Explanation:

nickel and iron.

9.  

Consider the following statements:

1. The outer core of the Earth is liquid.
2. The Earth's magnetic field is generated in the outer core.
3. The inner core is liquid because of very high temperature.

Which of the statements given above is/are correct?

Correct Answer: B [1 and 2 only]

Explanation:

The outer core is liquid and its motion generates the magnetic field; the inner core is solid owing to enormous pressure.

10.  

Assertion (A): S-waves are not recorded beyond 105° from the epicentre.

Reason (R): S-waves cannot travel through the liquid outer core.

Correct Answer: A [Both A and R are true, and R is the correct explanation of A]

Explanation:

S-waves vanish beyond 105° because they cannot cross the liquid outer core, so R directly explains A.

11.  

The rigid outer shell made of the crust and the uppermost mantle is called the:

Correct Answer: C [lithosphere]

Explanation:

The lithosphere is the rigid shell of the crust plus the uppermost mantle, resting on the weak asthenosphere.

12.  

The oceanic crust is made largely of:

Correct Answer: D [sima]

Explanation:

The thinner, denser oceanic crust is made mainly of silica and magnesium, hence the name sima.

13.  

In the upper crust, temperature rises with depth at a commonly cited average rate of about:

Correct Answer: D [1 °C per 32 m]

Explanation:

About 1 °C for every 32 m is the commonly cited near-surface rate, roughly 30 °C per km of depth.

14.  

The point on the surface directly above the focus of an earthquake is the:

Correct Answer: B [epicentre]

Explanation:

The epicentre is the point on the surface vertically above the focus, or hypocentre, of an earthquake.

15.  

The solid inner core was discovered by:

Correct Answer: B [Inge Lehmann]

Explanation:

1936.

16.  

Arrange the following in chronological order:

1. Gutenberg discontinuity
2. Kola borehole reaches about 12 km
3. Lehmann discontinuity
4. Moho discovered

Select the correct answer using the code given below:

Correct Answer: A [4-1-3-2]

Explanation:

1909, 1914, 1936, 1989.

17.  

The mean density of the whole Earth compared with surface rocks is:

Correct Answer: A [much higher]

Explanation:

about 5.5 against about 3 g/cm³.

18.  

Melting of polar ice affects the Earth's axis because:

Correct Answer: B [water moves towards the equator and redistributes mass]

Explanation:

(b) Correct (Prelims 2025).

19.  

The Mohorovičić (Moho) discontinuity separates the:

Correct Answer: D [crust and the mantle]

Explanation:

about 35 km below the continents, less below the oceans.

20.  
UPSC Prelims 2025

Consider the following statements:

Statement I: Scientific studies suggest that a shift is taking place in the Earth's rotation and axis.

Statement II: Solar flares and associated coronal mass ejections bombarded the Earth's outermost atmosphere with tremendous amount of energy.

Statement III: As the Earth's polar ice melts, the water tends to move towards the equator.

Which one of the following is correct in respect of the above statements?

Correct Answer: B [Both Statement II and Statement III are correct but only one of them explains Statement I]

Explanation:

both are true, but only ice melt (Statement III) explains the shift.

21.  
UPSC Prelims 2023

Consider the following statements:

1. In a seismograph, P waves are recorded earlier than S waves.
2. In P waves, the individual particles vibrate to and fro in the direction of waves propagation whereas in S waves, the particles vibrate up and down at right angles to the direction of wave propagation.

Which of the statements given above is/are correct?

Correct Answer: C [Both 1 and 2]

Explanation:

P-waves are fastest and arrive first; P-wave particles move along the direction of travel, S-wave particles at right angles.

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