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).