What is some direct evidence scientists used to determine that earth has liquid layers beneath the crust?

Seismic-Wave Data

Explanation: In 1909, Andrija Mohorovičić, a Croatian seismologist, discovered the boundary between the crust and the mantle by observing the sudden increase of seismic waves as they passed from the crust to the mantle. During an earthquake, energy is released in waves that travel throughout Earth's layers. ... Seismic wave data shows that S waves do not pass through the outer core, and thus this part of the planet's interior must be liquid.

It is said that the average kinetic energy of the molecules in a gas system is directly proportional to its temperature. We use this to solve the temperature. We do as follows:

Kinetic Energy = (3/2) nRT
4265 = (3/2) (1)(8.314) (T)
T = 341.99 K = 68.84 degrees Celsius