Fact 1: Being burried under soil and mud changes vegetation into peat through extreme heat and pressure in a swamp over a long period of time.

Fact 2: Fossils are typically preserved when they are buried under many layers of sand and mud.

Given the two facts above, answer the question "being preserved under many layers changes vegetation into peat through extreme what?" with the following options: 
- Physical weathering
 - Wet weather
 - heat and mud
 - Time and energy
 - scarce resources
 - heat and pressure
 - heat and vegetation
 - sand and pressure


 

      heat and pressure   