Question

Fossil fuels are made by the decay of living things. Because living things are always dying and decaying, why are fossil fuels not a renewable source of energy?

Answer 1

Because it takes millions of years of pressure under the right conditions for dead creatures to become fossil fuels, and we're running out of the resource faster than it could ever be replenished. 

Answer 2

Fossil fuels are made of dead and decaying organism but the fossils are formed by a certain process which takes thousands of years to form coal or other fossils.

Though it takes a very small amount of time for a substance to die but it takes thousands of years to form fossil.

As it takes much time to be converted into a form where it can be used as fossil. It is considered as non renewable source of energy.