"Over millions of years, the remains of these animals and plants were covered by layers of sand, silt, and rock. Heat and pressure from these layers turned the remains into what we now call crude oil or petroleum. The word petroleum means rock oil or oil from the earth."
Oil is the only resource I know of that is a finite supply, only available on earth, not asteroids or other planets.
This stuff is truly fascinating.
I think I am in love.