Earth's Layers Quiz

Grade 8 · Science · Quiz

10 questions on Earth's structure, composition, seismic waves, and the lithosphere and asthenosphere.

Questions

1. Which layer of Earth is the thinnest?

   1. Mantle
   2. Outer core
   3. Crust
   4. Inner core
   Show answer

   Answer: Crust

   The crust is only 5–70 km thick — the thinnest layer compared to the mantle (~2,900 km) and core layers.

2. Earth's magnetic field is generated by:

   1. The solid inner core spinning
   2. The movement of liquid iron in the outer core
   3. The crust's magnetic minerals
   4. Solar wind interacting with the mantle
   Show answer

   Answer: The movement of liquid iron in the outer core

   Convection currents of liquid iron and nickel in the outer core create electrical currents that generate Earth's magnetic field.

3. The mantle is composed primarily of iron and nickel.

   Show answer

   The mantle is made of silicate rocks (containing silicon and oxygen). Iron and nickel make up the core.

4. What is the asthenosphere?

   1. The outermost layer of Earth
   2. The semi-fluid upper mantle on which tectonic plates float
   3. The boundary between the mantle and the core
   4. The solid inner portion of the core
   Show answer

   Answer: The semi-fluid upper mantle on which tectonic plates float

   The asthenosphere is the ductile, partially molten upper mantle layer that allows tectonic plates to move.

5. What drives convection currents in the mantle?

   1. The Moon's gravitational pull
   2. Heat from Earth's core
   3. Solar radiation
   4. Plate collisions
   Show answer

   Answer: Heat from Earth's core

   Heat from the core heats the lower mantle, causing material to rise, cool, and sink — creating convection currents that move tectonic plates.

6. The ___ includes the crust and upper mantle and is broken into tectonic plates.

   Show answer

   The rigid lithosphere rides on the more fluid asthenosphere below it.

7. Which type of crust is denser — oceanic or continental?

   1. Continental
   2. Oceanic
   3. They have the same density
   4. Density varies with depth only
   Show answer

   Answer: Oceanic

   Oceanic crust is made of basalt, which is denser than the granite that makes up continental crust.

8. Seismic waves travel at the same speed through all of Earth's layers.

   Show answer

   Seismic waves change speed and bend when they pass between layers of different density and composition — this is how scientists map Earth's interior.

9. What is the approximate temperature at Earth's inner core?

   1. 100°C
   2. 1,000°C
   3. 5,400°C
   4. 50,000°C
   Show answer

   Answer: 5,400°C

   Earth's inner core reaches about 5,400°C — comparable to the surface temperature of the Sun.

10. Why is Earth's inner core solid despite being extremely hot?

    1. It is made of a material that doesn't melt
    2. Extreme pressure from layers above prevents it from melting
    3. It is cooler than the outer core
    4. It rotates too fast to stay liquid
    Show answer

    Answer: Extreme pressure from layers above prevents it from melting

    The immense pressure from all of Earth's overlying layers raises the melting point of iron, keeping the inner core solid.

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