Oil and Time

As I write I am sitting in the Atlanta airport waiting for my wife who is returning from a short trip.  To my right is the giant skeleton of a Yangchuanosaurus.  To me it looks like a tyrannosaurus rex, but what do I know?  I know Job 41 describes such a creature as this.  So, how many of these monsters had to die and be buried to make oil?  The plaque describes five hundred million years of life on Earth.  Could each of the 'days' of the Genesis account be fifty or a hundred million years?  Could something else be creating oil in the Earth?  Maybe some sub-organic plant life?