Answer:
Coal is a dark-colored sedimentary rock and is often considered as a fossil fuel. These are formed from the plants and trees that were buried millions of years ago, under the earth's surface. These plants and trees that have been deposited must have formed in the tropical region because both the tropics receive a maximum amount of sunlight and rainfall that favors the growth and expansion of trees.
These plants after getting buried undergone a significantly high level of compaction due to the weight of the overlying sediments and rocks. Moreover, they were subjected to extremely high pressure and temperature condition, as a result of which the oxygen is eliminated and the carbon remained and over a due course of time, it gave rise to the formation of coal.
Thus, Compaction is highly important for the formation of coal.