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.

nacl or sodium chloride is an ionic compound. this is because an ionic compound pertains to a compound that consists of positively and negatively charged ions. in this case, na (sodium) has a tendency to lose one electron when it reacts with with other atoms, so the resulting sodium ion contains 11 protons and 10 electrons, thus making it positively charged (na+), when chlorine reacts, it usually gains one electron to form an ion called chloride, thus making it negatively charged ( since the ions are oppositely charged, they attract.