Here's why:
* P-waves are compressional waves. This means they travel by pushing and pulling the material they pass through, much like a spring.
* P-waves can travel through solids, liquids, and gases. This makes them unique because they can pass through the Earth's core, which is primarily liquid iron and nickel.
* S-waves (secondary waves) are shear waves. They travel by moving material perpendicular to their direction of travel. S-waves cannot travel through liquids, so they do not penetrate the Earth's core.
Therefore, P-waves are the only type of body wave that can penetrate the Earth's core.
