why would crude oil in soil would be considered pollution?

Question

if u can in your answer can u please include the word concentration in the right form

Answer 1

all life forms on earth are made up of carbon
when these carbon organisms are buried in the soil for millions of years their oxygen and other molecules and elements and compounds are taken by the soil and the only element left is carbon with other elements
this gives us natural gas crude oil and coal

Answer 2

Oil is formed in the rock layers. If crude oil moves out of the rocks into the soil in high enough concentration then it would pollute the soil preventing plants from growing.

Answer 3

big j didn't use the word "concentration" in his answer. although it was a good one.