Scientists are able to use body waves to determine what make up the different layers of the earth interior. What characteristics to the body waves have that allow scientists to do this?

Body waves are waves that moves within the earth. They propagate within the earth and have very interesting capabilities in different mediums.

There are two main types of body waves:

Primary waves or P-waves; these types of waves can move within any material medium such as solid, liquid or gases. They are compressional waves in nature. They usually arrive in a seismic station first. Secondary waves or S-waves or Shear waves causes shearing. They move only in solids as liquids and gases cannot be sheared.

On a seismograph, wherever we cannot see an S-wave suggests that liquids or gases are present because they will not allow this wave to pass through.

Whenever we see P-waves, solids, liquids and gases are present.

This is a very important property used to investigate the subsurface.