From the source, coal was formed by ancient plants in an anaerobic environment after a long period of change. These plants are transformed into solid substances rich in carbon under the action of underground pressure and high temperature. After millions of years of sedimentation, pressure and geological processes, marine microorganisms and small biological remains have formed liquid compounds containing carbon and hydrogen, which are the main components of what we call "oil". Oil and coal are two different fossil fuels, and there are obvious differences in essence.