Internal Structure of Earth - Practice Test 2

Attempt the quiz above first, then review every question with its correct answer and a short explanation below.

1. Q1.The Repetti Discontinuity separates:

   • A.Crust and Mantle
   • B.Upper and Lower Mantle✓ Correct Answer
   • C.Outer and Inner Core
   • D.Mantle and Core

   Explanation: The Repetti Discontinuity separates the Upper Mantle from the Lower Mantle.

2. Q2.The Lehmann Discontinuity separates:

   • A.Outer and Inner Core✓ Correct Answer
   • B.Upper and Lower Crust
   • C.Mantle and Core
   • D.Upper and Lower Mantle

   Explanation: The Lehmann Discontinuity separates the liquid Outer Core from the solid Inner Core.

3. Q3.Continental Crust is thicker than Oceanic Crust. True or False?

   • A.True✓ Correct Answer
   • B.False
   • C.Both are equal
   • D.Cannot be determined

   Explanation: Continental crust (30-50 km) is much thicker than Oceanic crust (5-10 km).

4. Q4.Oceanic Crust is mainly composed of which type of rock?

   • A.Granite
   • B.Basalt✓ Correct Answer
   • C.Sandstone
   • D.Limestone

   Explanation: Oceanic crust is primarily made of Basalt (mafic rocks).

5. Q5.Continental Crust is mainly composed of:

   • A.Basalt
   • B.Granite✓ Correct Answer
   • C.Iron
   • D.Magnesium

   Explanation: Continental crust is granitic (felsic) in nature.

6. Q6.Which seismic wave travels fastest?

   • A.P-waves✓ Correct Answer
   • B.S-waves
   • C.L-waves
   • D.Rayleigh waves

   Explanation: Primary (P) waves are the fastest seismic waves.

7. Q7.Which seismic wave cannot pass through the liquid core?

   • A.P-waves
   • B.S-waves✓ Correct Answer
   • C.Both
   • D.None

   Explanation: Secondary (S) waves are shear waves and cannot travel through liquids.

8. Q8.The shadow zone of P-waves appears between:

   • A.105° and 145°✓ Correct Answer
   • B.90° and 100°
   • C.105° and 180°
   • D.30° and 60°

   Explanation: P-waves are refracted by the core, creating a shadow zone between 105° and 145° from the epicenter.

9. Q9.The shadow zone of S-waves extends beyond:

   • A.90°
   • B.105°✓ Correct Answer
   • C.145°
   • D.180°

   Explanation: S-waves cannot pass through the core, so their shadow zone is beyond 105° (covering the entire other side).

10. Q10.Which layer generates the Earth's magnetic field?

    • A.Inner Core
    • B.Outer Core✓ Correct Answer
    • C.Mantle
    • D.Crust

    Explanation: The movement of molten iron in the Outer Core generates the dynamo effect (magnetic field).

11. Q11.The density of the Earth's core is approximately:

    • A.2.7 g/cm³
    • B.5.5 g/cm³
    • C.13 g/cm³✓ Correct Answer
    • D.100 g/cm³

    Explanation: The core density ranges from 9.9 to 13 g/cm³.

12. Q12.The volume of the Mantle is what percentage of Earth's total volume?

    • A.1%
    • B.15%
    • C.84%✓ Correct Answer
    • D.50%

    Explanation: The mantle makes up about 84% of Earth's volume.

13. Q13.The volume of the Crust is approx what percentage of Earth's total volume?

    • A.1%✓ Correct Answer
    • B.15%
    • C.30%
    • D.50%

    Explanation: The crust makes up only about 0.5% to 1% of Earth's volume.

14. Q14.Magma chambers are usually found in the:

    • A.Outer Core
    • B.Asthenosphere / Upper Mantle✓ Correct Answer
    • C.Lower Mantle
    • D.Inner Core

    Explanation: The Asthenosphere provides the molten rock (magma) for volcanoes.

15. Q15.Which instrument records seismic waves?

    • A.Barometer
    • B.Seismograph✓ Correct Answer
    • C.Thermometer
    • D.Hygrometer

    Explanation: A Seismograph (or Seismometer) records the ground motion caused by seismic waves.

16. Q16.L-waves (Surface Waves) are responsible for:

    • A.Early warning
    • B.Transmission through core
    • C.Maximum destruction on surface✓ Correct Answer
    • D.Measuring depth

    Explanation: Surface waves (Love and Rayleigh) cause the most damage to structures.

17. Q17.The approximate radius of the Earth is:

    • A.3200 km
    • B.6400 km✓ Correct Answer
    • C.12800 km
    • D.5000 km

    Explanation: The mean radius is 6,371 km (approx 6,400 km).

18. Q18.Which layer is responsible for plate tectonics?

    • A.Asthenosphere
    • B.Inner Core
    • C.Lower Mantle
    • D.Lithosphere sliding on Asthenosphere✓ Correct Answer

    Explanation: Tectonic plates (Lithosphere) move over the semi-fluid Asthenosphere.

19. Q19.The density of Sial is ___ than Sima.

    • A.Higher
    • B.Lower✓ Correct Answer
    • C.Equal
    • D.Variable

    Explanation: Sial (Continental, ~2.7 g/cm³) is lighter than Sima (Oceanic, ~3.0 g/cm³).

20. Q20.Which element is abundant in the mantle?

    • A.Iron and Nickel
    • B.Silica and Magnesium (Olivine)✓ Correct Answer
    • C.Gold and Silver
    • D.Helium

    Explanation: The mantle is rich in silicate minerals like Olivine and Pyroxene (Mg, Fe silicates).