The history of refined metals is thought to begin with the use of copper about 11,000 years ago. Gold, silver, iron (as meteoric iron), lead, and brass were likewise in use before the first known appearance of bronze in the fifth millennium BCE. Subsequent developments include the production of early forms of steel; the discovery of sodium —the first light metal —in 1809; the rise of modern alloy steels ; and, since the end of World War II, the development of more sophisticated alloys.