Internal Structure of Earth - Practice Test 3

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

1. Q1.The depth of the Mantle extends up to:

   • A.100 km
   • B.2900 km✓ Correct Answer
   • C.5150 km
   • D.6371 km

   Explanation: The mantle extends from the Moho to about 2,900 km deep.

2. Q2.The Outer Core extends from:

   • A.0 to 100 km
   • B.2900 km to 5150 km✓ Correct Answer
   • C.5150 km to 6371 km
   • D.100 to 2900 km

   Explanation: The Outer Core is between the Gutenberg discontinuity (2900 km) and Lehmann discontinuity (5150 km).

3. Q3.The temperature at the center of the Earth is estimated to be around:

   • A.1000°C
   • B.3000°C
   • C.5000°C - 6000°C✓ Correct Answer
   • D.10,000°C

   Explanation: The core temperature is about 5000°C to 6000°C, similar to the Sun's surface.

4. Q4.Oceanic crust is thinner but ___ than continental crust.

   • A.Lighter
   • B.Denser✓ Correct Answer
   • C.Softer
   • D.Older

   Explanation: Oceanic crust (Basalt) is denser than Continental crust (Granite).

5. Q5.Who discovered the crust-mantle discontinuity?

   • A.Gutenberg
   • B.Andrija Mohorovicic✓ Correct Answer
   • C.Conrad
   • D.Lehmann

   Explanation: Andrija Mohorovicic identified the abrupt change in seismic velocities.

6. Q6.The core forms approximately what percentage of Earth's volume?

   • A.1%
   • B.15-16%✓ Correct Answer
   • C.50%
   • D.84%

   Explanation: The core makes up about 15-16% of Earth's volume (but 32% of mass).

7. Q7.Which mineral group is most common in the Earth's crust?

   • A.Silicates✓ Correct Answer
   • B.Oxides
   • C.Carbonates
   • D.Sulphides

   Explanation: Silicates (Feldspar, Quartz) form the majority of the crust.

8. Q8.Which is the most abundant mineral in the Earth's crust?

   • A.Quartz
   • B.Feldspar✓ Correct Answer
   • C.Mica
   • D.Olivine

   Explanation: Feldspar is the most abundant mineral group.

9. Q9.Is the Earth's interior uniform in composition?

   • A.Yes, completely
   • B.No, it is layered✓ Correct Answer
   • C.Yes, only rocks
   • D.No, it is hollow

   Explanation: The Earth is differentiated into layers of varying composition and density.

10. Q10.The transition zone between the Outer and Inner Core is:

    • A.Moho
    • B.Gutenberg
    • C.Lehmann✓ Correct Answer
    • D.Conrad

    Explanation: The Lehmann Discontinuity separates the liquid outer core from the solid inner core.

11. Q11.What happens to pressure as we go deeper into the Earth?

    • A.Increases✓ Correct Answer
    • B.Decreases
    • C.Remains same
    • D.Becomes zero

    Explanation: Pressure increases tremendously with depth.

12. Q12.Which layer is the main source of magma?

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

    Explanation: The Asthenosphere contains partially molten rock.

13. Q13.The rigid outer part of the Earth consisting of the crust and upper mantle is:

    • A.Lithosphere✓ Correct Answer
    • B.Asthenosphere
    • C.Mesosphere
    • D.Core

    Explanation: Lithosphere means 'rocky sphere'.

14. Q14.S-waves disappear at an angle of ___ from the epicenter.

    • A.105°✓ Correct Answer
    • B.90°
    • C.140°
    • D.60°

    Explanation: Beyond 105 degrees, the liquid outer core blocks S-waves.

15. Q15.What is the average thickness of the Continental Crust?

    • A.5 km
    • B.30-50 km✓ Correct Answer
    • C.100 km
    • D.2900 km

    Explanation: It averages around 35-40 km but can be up to 70 km under mountains.

16. Q16.Which of these is not a layer of the Earth?

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

    Explanation: Photosphere is a layer of the Sun.

17. Q17.The term 'Barysphere' is sometimes used for:

    • A.The Core / Interior✓ Correct Answer
    • B.The Atmosphere
    • C.The Crust
    • D.The Water bodies

    Explanation: Barysphere refers to the heavy interior core of the Earth.

18. Q18.Which rock type is the primary constituent of the continental crust?

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

    Explanation: Granitic rocks dominate the continents.

19. Q19.The velocity of seismic waves changes when they:

    • A.Enter a medium of different density✓ Correct Answer
    • B.Travel straight
    • C.Stop
    • D.Reflect only

    Explanation: Changes in density and elasticity of layers cause refraction and speed change.

20. Q20.The lower mantle is in which state?

    • A.Liquid
    • B.Solid✓ Correct Answer
    • C.Gas
    • D.Plasma

    Explanation: The Lower Mantle (Mesosphere) is solid due to high pressure.