Describe how fossil fuels were formed.

When the ancient plants and animals died, they decomposed and became buried under layers and layers of mud, rock, and sand. Eventually, hundreds and sometimes thousands of feet of earth covered them. In some areas, the decomposing materials were covered by ancient seas, then the seas dried up and receded. Hence, these materials away from the reach of oxygen, got converted into fossil fuels due to the chemical effects of pressure, heat and bacteria.