As the Stone Age evolved into the Bronze Age, metals began to play a dominant role. There are places where copper occurs on the land surface as native copper metal-solid, malleable copper (Figure 12-5a). Somewhere, somehow copper-bearing materials were melted, perhaps first in pottery kilns, where the minerals may have been used for glazes. In several cultures, melting and processing copper into ornaments, utensils, and tools was the beginning of metalworking (Figure 12-5b). However, combining molten copper with molten tin was the significant technological breakthrough. The resulting mixture of metals, or alloy-bronze-is much stronger and more durable than either pure copper or pure tin. When people discovered how to make bronze, it changed their world.