GEOLOGY

Detailed explanation-1: -Seismic waves tell us that the Earth’s interior consists of a series of concentric shells, with a thin outer crust, a mantle, a liquid outer core, and a solid inner core. P waves, meaning primary waves, travel fastest and thus arrive first at seismic stations. The S, or secondary, waves arrive after the P waves.

Detailed explanation-2: -When seismic waves encounter a rock of a different density, it may reflect off of that layer, or bend as it travels across the boundary. By noting these patterns of reflection and refraction, one can determine the presence and depth of layers within Earth.

Detailed explanation-3: -Scientists can tell by observing the seismic waves that are recorded all over the surface of the earth from distant earthquakes. The seismic waves are reflected (bounced off) layers of different density, and they are refracted (bent) when they enter layers of different density.