Earth's Layers — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. Scientists study Earth's interior by analyzing seismic waves produced by earthquakes.
Seismic waves travel through Earth's layers and reveal information about density and state of matter.
2. Seismic waves travel faster through dense solid rock than through liquid material.
P-waves move faster through solid rock than liquid. This speed difference helps identify layers.
3. Scientists cannot study Earth's deep layers directly because we cannot drill that far down.
The deepest borehole ever drilled reached only about 12 km — far short of the mantle.
4. When seismic waves hit a boundary between two different layers, they bend or bounce back.
At layer boundaries, waves refract or reflect, revealing where one layer ends and another begins.
5. The instrument used to detect and record earthquake waves is called a seismograph.
A seismograph records the vibrations of seismic waves on a strip chart or digital display.
6. Seismic waves that stop or slow down in the outer core prove that layer is liquid.
S-waves cannot travel through liquids. Their disappearance at the outer core proves it is liquid.
7. By studying how waves change speed, scientists can map the layers inside Earth.
Speed changes at boundaries. Faster = denser solid; slower or stopped = liquid layer.
8. The deeper inside Earth you go, the higher the temperature and pressure become.
Both temperature and pressure increase with depth due to gravitational compression and radioactive decay.
9. Earthquake waves give scientists evidence about materials they cannot see or touch.
Seismic wave data is indirect evidence that reveals composition and state of Earth's interior.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
Seismic waves
→ Energy that travels through Earth after an earthquake
A machine that detects and records earthquake vibrations
Seismograph
→ A machine that detects and records earthquake vibrations
Waves that travel only through solids and stop in liquids
P-waves
→ The fastest seismic waves that move through both solids and liquids
Energy that travels through Earth after an earthquake
S-waves
→ Waves that travel only through solids and stop in liquids
The fastest seismic waves that move through both solids and liquids
Seismic waves=energy that travels(idx2); Seismograph=machine that records(idx0); P-waves=fastest, through solids and liquids(idx3); S-waves=only through solids(idx1)