Forgive me, I'm feeling contrary today.

Fred J. McCall wrote:

The only way we would ever 'use it all up' is if there is some
critical use for which absolutely no substitute exists at any price.
Then it will stay very expensive so that price exceeds the cost of
getting it out of the ground and we'll keep pumping it up until there
is no more.

Note that the preceding is pretty much an economically impossible
situation, since there are no uses for anything that are infinitely
valuable and for which no possible substitute will do.

How about phosphorus? It's been proposed as the ultimate limiting
factor for the size of the human population the Earth will support.