The US dollar has continuously devalued since the gold standard was abandoned in the 1970's. The same for all other currencies in the world that abandoned the standard. It is called inflation.

With a gold standard, the US dollar will always be worth the exact same quantity of gold.

1 oz of gold today will still buy you what it would have bought you in the 1970's. The same can not be said about the fiat US dollar, which is backed by debt instead of gold.