The Bronze Age began and ended at different times in different places, depending on when bronze came into common use for the manufacture of tools, weapons, ornaments, etc. and when it was effectively superseded by iron. In very broad terms, the Bronze Age may be considered to span the 3rd and 2nd millenniums BC. Bronze was probably first created in the early part of the 4th millennium in the Middle East. By the end of the 2nd millennium, iron was increasingly in use as the primary component in metalwork throughout the Aegean and the Middle East.
Invention of bronze
Bronze is an alloy of copper (Cu, 29) and tin (Sn, 50) with the tin content ranging from 15% to 25% depending on intended usage. By the 4th millennium BC, copper had been in use for a long time but, as it is a soft metal, a harder alternative was sought. Copper yields under pressure because of internal slippage of crystals. All metals are made up of crystal layers which slide over one another until they part (i.e., they have little resistance to pressure and do not bind together).
To prevent this slippage, the fine crystals must be made gritty so that they will lock together and remain rigid, offering high resistance to pressure. In modern terms, some of the copper atoms in the crystals must be replaced by other types of atom. Where the atoms in the crystals are not of the same kind, the structure will be more rigid. In simple terms, this means the creation of an alloy by merging copper and another substance, not necessarily in equal proportions. As it happens, copper ores and tin ores are often found together. Whether by luck or by experiment, tin and copper were smelted together and bronze was discovered. The paradox here is that tin is even softer than copper, but the two together formed an alloy harder than both. The tin atoms provide the crystals with a "roughness" which prevents slippage.
Virtually all dates used in a chronology of the Neolithic and Bronze Ages are approximate and some are pure speculation. Broadly, the timespan of the Neolithic was from c.9700 BC (also when the Holocene Epoch is estimated to have begun) until the beginning of the third millennium. As with the Bronze Age which superseded it, the Neolithic began and ended at different times in different places. It began in the Fertile Crescent of the Middle East but was not fully established in Western Europe until the end of the 5th millennium (c.4000 BC).
That was perhaps only a couple of centuries before people in the Middle East discovered bronze (c.3800 BC), which was to revolutionise society by providing more durable tools and weapons. Later in the 4th millennium came two of history's most significant inventions – writing and the wheel. In Mesopotamia, the Sumerians developed cuneiform, a system of writing using combinations of wedge-shaped strokes, usually impressed on clay which was then dried out and stored as tablets. That was perhaps around 3600 BC and may have preceded the invention of the wheel and axle, tentatively dated c.3500 BC, by the Elamites of western Iran, whose capital was Susa. Whatever its original purpose, its adaptability was quickly appreciated as it was soon in use both in pottery and on wagons.
By the end of the 4th millennium (c.3000 BC), increasing usage of bronze for the manufacture of tools, weapons, ornaments and other implements was signalling the beginning of the Bronze Age in the Middle East, Egypt, the Levant and the Aegean.