People used silver for a long time too, but it was demonetized in 20th century.
http://www.dailyreckoning.com.au/silver-a-brief-history-of-d...
http://www.dailyreckoning.com.au/silver-a-brief-history-of-d...
In the USA, gold was demonetized (1933) before silver (1965) in the currency when used in the USA. The dollar was convertible into gold internationally however.
The international gold window was closed by Nixon in 1971.