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

Fact 2: Most coal is fossil peat.

Given the two facts above, answer the question "What is coal made out of?" with the following options: 
- heat
 - rocks
 - fossils
 - water
 - trees
 - energy
 - power
 - calcite


 

   fossils      