How long does it take for carbon to become a fossil fuel

Conversion of carbon to fossil fuels takes hundreds of millions of years beneath the earth-crust.

Explanation:

Conversion of carbon to fossil fuels takes hundreds of millions of years beneath the earth-crust. Fossil fuel is formed by the anaerobic decomposition of dead remains of the plants and animals. When the remains of the plants and animals get buried under the earth surface under high temperature and pressure it starts converting into fossil fuels. Coal, natural gas and petroleum are the extracts of the fossil fuel.

Millions of years.

Explanation:

Fossil fuels are fuels formed by natural processes. It involves decomposition of dead and decaying animals, marine and plants for over million years. This some times take more than hundred million years to convert into fuel. This is why they are called non renewable resources of energy. The decomposition of dead plant species forms coal and decomposition animals of land and sea forms crude oil and gas.