Here's why:

* P-waves are compressional waves: They travel through the Earth by compressing and expanding the material they pass through, similar to how sound waves travel.

* Solid, liquid, and gas: P-waves can travel through all three states of matter, making them capable of traversing the entire Earth.

* Higher speed: Because of their compressional nature, P-waves can travel faster than other types of seismic waves, like S-waves.

This speed is why P-waves are the first to arrive at a seismograph after an earthquake.