The history of metal is a long and fascinating one. Before the metal ages, the Stone Age reigned for perhaps millions of years. During that long period, humans learned to shape stones into useful implements, including stone tools and sharp-edged flint blades.
By around 6,000 B.C., people picked up bits of gold which they learned to form into jewelry. They discovered silver by about 4,000 B.C., and eventually used it to make jewelry, coins and bars for commerce. Both metals were scarce and quite soft and malleable, which made them useless for tools and weapons.
As people learned to find and use more practical metals, three distinct “metal ages” began toward the end of the Stone Age, each one overlapping the next. These include the Copper Age, Bronze Age, and Iron Age.
By about 4,200 B.C., people began to pick up small nodules of copper and used them to make green or blue paints or to fashion ornaments by hammering flat into various shapes. Repeated heating and hammering resulted in annealing, which made the metal harder but also brittle. In this way, they made simple flat axes and daggers.
They also learned to melt pure copper over a fire and poured it into simple molds. Later they learned how to “smelt” the copper from ore, by melting it at 1200 °C and combining it with charcoal to precipitate out the pure copper.
Copper was still a scarce commodity, so stone continued to be the primary material for many tools until the Bronze Age.
Bronze is an alloy made primarily of copper with about 10 percent tin and small amounts of other elements. In the late Copper Age, around 4,500 years ago, metalsmiths in China and the Middle East learned how to purify tin from ore and then combine it with copper. The resulting alloy was much stronger and tougher than copper, making it useful for many applications and replacing copper and stone implements in many locations.
Bronze of different types was developed around the world, and used in ploughs, swords, axes, spearheads, armor, helmets, and shields, as well as artistic decorations and scientific implements.
After the Bronze Age, the Iron Age began about three thousand years ago between 1200 B.C. and 1000 B.C. As people became more adept at mining and metalworking, they learned to make useful objects from the iron found in meteorites dropped from space. Later, they learned to smelt iron ores, which are quite common, creating superior weapons and agricultural implements.
Iron is stronger and more plentiful than copper and tin, and became much cheaper than bronze so that regular farmers could afford iron ploughs. The result was an agricultural explosion that altered the pattern of societies.
Iron remained the primary metal of industry for more than two thousand years – until the discovery of steel.