https://www.theregister.co.uk/2018/10/19/earths_hidden_core/

The Earth’s core is solid, according to a pair of geophysicists who claim to have solved an 80-year-old conundrum concerning the planet's center.

The suggestion that our home world has a liquid outer core containing a smaller solid inner core was put forward by Danish seismologist Inge Lehmann in the 1930s. Scientists have been searching for direct evidence ever since.