Khan Academy Static

How do we know what the Earth is made up of? Has someone dug to the core? No, but we humans have been able to see how earthquake (seismic) waves have been bent and reflected through our planet to get a reasonable idea of what is down there.

10678_Seismic_waves.html

10680_Refraction_of_seismic_waves.html

10679_Why_S_waves_only_travel_in_solids.html

10681_The_mohorovicic_seismic_discontinuity.html