Short answers, pulled from the story.
The Bronze Age is an archaeological and anthropological term for a phase of material culture defined by the production or trading of bronze, copper alloyed with tin, arsenic, or other metals. It is the middle period of the three-age system, following the Stone Age and preceding the Iron Age, and had begun in much of the Old World by 3000 BC.
Bronze was rare and expensive mainly because of difficulties obtaining enough tin, which occurs in relatively few places, unlike the very common copper. The scarcity meant some societies used bronze only for weapons or elite art, while ordinary farmers largely kept using stone tools, and bronze was keenly recycled.
The oldest known bronze was produced by the Maykop culture of the North Caucasus, which discovered bronze independently as early as the mid-4th millennium BC. The Maykop culture only had arsenical bronze. A disputed tin-alloy bronze foil from the Vinča culture site at Pločnik, Serbia, dated to the mid-5th millennium BC, may be even earlier.
West Asia and the Near East entered the Bronze Age first, beginning with the rise of the Mesopotamian civilization of Sumer in the mid-4th millennium BC. These cultures developed the earliest practical writing systems, cuneiform in Mesopotamia and hieroglyphs in Egypt.
The Aegean Bronze Age collapse has been attributed to the failure of the trade network, the exhaustion of the Cypriot forests that supplied charcoal for bronze production, and the spread of iron tools that ended the justification for the tin trade. The Thera eruption around 1600 BC, 110 km north of Crete, may have triggered instability through tsunami damage and the loss of the Minoan navy.
The Americas did not have a conventional Bronze Age, as archaeology there uses a five-period system instead, though cultures such as the Moche, Inca, and Calchaquí smelted copper and bronze. On the Australian continent, no evidence of metalworking has been found before European settlement in 1788.