Seismology: inside the Earth

Earthquake waves recorded worldwide revealed that Earth has a crust, mantle, liquid outer core and solid inner core.

Richard Oldham identified the core in 1906, Andrija Mohorovičić the crust-mantle boundary in 1909, and Inge Lehmann the solid inner core in 1936. Seismographs later became the tool that mapped plate boundaries and detected nuclear tests.