Being burried under soil and mud changes vegetation into peat through extreme heat and pressure in a swamp over a long period of time.
After a long time, the moss can form into a peat.
Moss forms into peat through extreme heat and pressure over time.
What forms into peat through extreme heat and pressure over time?
  * bamboo
  * desiccation
  * burrs
  * elms
  * moss
  * coal
  * candy
  * meat