Scientists use siesmic waves also known as s-waves. These only go through solid layers not liquid. So when they reach a liquid level the wave shoots back and the scientists are able to determine what layers are solid and which are not.
An excellent experiment is to heat sodium thiosulfate in a water bath. The solid crystals will dissolve into the water in the hydrated crystals forming a supersaturated solution. ... Placing a small crystal in the supersaturated solution will cause the liquid to turn solid.
