Explain how earthquake waves give scientists evidence that part of the earth’s core is liquid.

Two types of seismic waves are released when an earthquake occurs: they are called P-waves (primary-waves) and S-waves (secondary waves). One of the main difference between the two types of waves is that P-waves are able to travel through solids and liquids, while S-waves travel only through solids.
When an earthquake happens, seismic waves are detected in different locations of the world, because from the hypocenter they travel everywhere. However, S-waves do not reach the opposite side of Earth, because they cannot travel through the outer core which is liquid, so only the P-waves are detected on the other side of Earth and this is a proof that the outer core is liquid.