We say fossil fuels will last only for a few hundred years. Comment.

Fossil fuels will last only for a few hundred years because they are exhaustible natural resources. If consumed at a rate faster than the rate at which these are formed in nature, they will get exhausted very soon.

Once the present stock of these gets exhausted, no new supplies of these fossil fuels will be available to us in the near future because it required millions of years for the conversion of dead organisms into these fuels.