Geologists apply various methods to study the layers of the Earth. Which of the following is a method used to study the Earth’s layers?

A. Scientists use seismic waves to map the atmospheric conditions above Earth's crust.
B. Scientists map seismic waves to determine the atomic structure of materials that lie beneath Earth's surface.
C. Scientists measure vibrations of Earth's surface using a compass (an instrument that is sensitive to Earth's magnetic field).
D. Scientists measure the time it takes for seismic waves to reach a seismograph (an instrument that measures seismic waves).