I remember reading an article in a magazine, way before the Internet, that said there could not have been enough plants and animals on the Earth, even taking into account a billion years, to account for the amount of petroleum being pumped out of the ground.
While coal is definitely a ‘fossil fuel’, you can actually see imprints of plants in it, petroleum is not.
Science has never fully explained just where liquid petroleum comes from, and how it got ‘down there’ in the first place.................