Fossil fuels are considered exhaustible natural resources because they take millions of years to form from the dead remains of plants and animals that get buried deep inside the Earth. This formation process requires very high temperature and pressure conditions, which cannot be artificially replicated in laboratories. Due to the extremely slow formation rate and finite supply of fossil fuels, the amount available is limited and cannot be quickly replenished. Hence, when we use fossil fuels at the current rate, their reserves will eventually be exhausted and cannot be replaced within a human timescale, making them exhaustible resources.

In summary:

• Fossil fuels form over millions of years from organic material under high temperature and pressure.
• They are found in limited quantities and their slow formation means they cannot be renewed quickly.
• Use at current rates leads to eventual depletion of reserves.
• This makes fossil fuels exhaustible natural resources.