Questions: Earth's Layers: Crust, Mantle, and Core
3 questions to test your understanding
Score: 0 / 3
Question 1 Multiple Choice
Which of Earth's layers is the thickest?
AThe crust
BThe mantle
CThe outer core
DThe inner core
The mantle is about 2,900 km thick, making it by far the thickest layer. The crust is only 5-70 km thick. The outer core is about 2,200 km thick and the inner core has a radius of about 1,200 km.
Question 2 True / False
The mantle is a layer of liquid lava beneath the crust.
TTrue
FFalse
Answer: False
The mantle is mostly solid rock, not liquid. However, it is extremely hot (up to about 4,000 degrees Celsius near the core) and under enormous pressure. Over very long time periods, the solid rock in the mantle flows very slowly, like thick putty. Small pockets of melted rock (magma) can form in the upper mantle, but the layer as a whole is solid.
Question 3 Short Answer
If we have never drilled past the crust, how do scientists know what the inside of Earth is like?
Think about your answer, then reveal below.
Model answer: Scientists study seismic waves from earthquakes. These waves travel at different speeds and bend when they pass through different materials. By analyzing how seismic waves travel through Earth, scientists can determine the density, state (solid or liquid), and composition of each layer.
Seismic waves are like an X-ray of the planet. P-waves travel through both solids and liquids but change speed at layer boundaries. S-waves cannot travel through liquids at all, which is how scientists discovered the outer core is liquid — S-waves disappear in a 'shadow zone' behind the core.