Chemical boundary between the crust and the mantle, where chemical composition changes and so does density
Gutenberg discontinuity
Boundary between the mantle and outer core, stony to metallic composition
Lehmann discontinuity
Boundary between outer core and inner core, liquid to solid
Data sources
Earthquakes
Magnetism
Meteorites
Thermal energy
Gravity anomalies
Earthquakes
Make waves that travel across the earth's surface and down through the earth, changing direction and speed as they travel. Seismic recorders placed around the earth give us data on these waves
