GED Science TestEarth and Space ScienceHard
A seismologist is studying the propagation of seismic waves through Earth's interior after a major earthquake. They notice that a particular type of wave, which travels only through solids, is completely absent in recordings taken from receivers on the opposite side of the Earth from the earthquake's epicenter. This observation is key evidence for the existence of which Earth layer?
- AInner Core
- BMantle
- CCrust
- DOuter Core
Show answer & explanationAnswer & explanation
Correct answer: D. Outer Core
The description refers to S-waves (shear waves), which can only travel through solid material. Their complete absence on the opposite side of the Earth (the S-wave shadow zone) indicates that they encountered a liquid layer that absorbed them. This liquid layer is the Earth's outer core, composed of molten iron and nickel.
Why the other options are wrong
- A. The inner core is solid, allowing S-waves to pass through if they reached it.
- B. The mantle is mostly solid, allowing S-waves to pass.
- C. The crust is solid, allowing S-waves to pass.
S-wave Shadow Zone
An area on Earth's surface where seismographs cannot detect S-waves after an earthquake, providing evidence for a liquid outer core.
- S-waves (shear waves) cannot travel through liquids.
- The liquid outer core absorbs S-waves, creating a shadow zone spanning 103° to 180° from the epicenter.
- This phenomenon was crucial in determining the liquid nature of the outer core.
Memory trick: S-Waves Stop, Liquid's Proof, Outer Core's Roof.