Copper was used to make knives as early as 5,000 BC- but once people started mixing tin and copper to make a harder metal, the bronze age began. Bronze is mixture of copper and tin and sometimes other metals- The tin is mined separately and then added to molten copper to create bronze. As a molten material, the metal could be poured into forms to create different styles of tools and weapons, ift could also be worked cold. Lighter then stone and easier to shape it quickly replaced stone tools in the areas of the world where it was available.
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