SOLAR SYSTEM

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: -So scientists rely on seismic waves-shock waves generated by earthquakes and explosions that travel through Earth and across its surface-to reveal the structure of the interior of the planet. Thousands of earthquakes occur every year, and each one provides a fleeting glimpse of the Earth’s interior.

Detailed explanation-3: -The two main types of waves are body waves and surface waves. Body waves can travel through the Earth’s inner layers, but surface waves can only move along the surface of the planet like ripples on water.

Detailed explanation-4: -These recordings made by a seismograph are called seismograms. Seismic waves travel at different speeds when they pass through different types of material, so by studying seismograms, scientists can learn a lot about Earth’s internal structure.

Detailed explanation-5: -The types of waves that are useful for understanding Earth’s interior are called body waves, meaning that, unlike the surface waves on the ocean, they are transmitted through Earth materials. Imagine hitting a large block of strong rock (e.g., granite) with a heavy sledgehammer (Figure 9.3).

Detailed explanation-6: -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.