In time, the pressure of the massive weight of rock and mud which covered the organic matter created heat, which changed this matter over a period of several hundred million years to oil (remains of ancient marine organisms), coal (remains of ancient swamps and forests), and natural gas.
(the massive weight of rock and mud; covered; the organic matter) (the pressure of the massive weight of rock and mud; created; heat, which changed this matter over a period of several hundred million years; T:In time) (heat; changed; this matter; T:over a period of several hundred million years)
the massive weight of rock and mud the pressure of the massive weight of rock and mud heat
covered created changed
the organic matter
heat, which changed this matter over a period of several hundred million years T:In time
this matter T:over a period of several hundred million years