Here's a breakdown:

* Pressure: The weight of the overlying rock layers creates immense pressure. This pressure increases significantly with depth.

* Temperature: Earth's internal heat increases with depth, leading to higher temperatures. This heat can come from radioactive decay within the Earth's core.

These conditions can significantly alter the properties of rocks:

* Density: Rocks become denser under pressure.

* Mineralogy: High temperatures and pressure can cause minerals to transform, creating new minerals and rock types.

* Behavior: Rocks can become ductile (bendable) at depth, allowing them to flow slowly over time.

Let me know if you'd like to explore any of these aspects in more detail!