So you can easily say bronze requires a more advanced civilization than does iron, given the more complicated trade routes required. In that sense, developing Bronze before smelted iron is partially a historical/geological artifact (although one replicated in the Americas). the southern half of Africa was cut off from European and Asian sources of tin but geographical barriers (and there are no tin sources in Africa itself), so they skipped Bronze and went straight to Iron smelting.
This is an interesting one because it touches on the evolution of bronze. Early bronze was made from nearby co-occurring deposits, including arsenic bronze which was made from the arsenic that is often found along with copper. However because tin was much rarer than copper, and because there was a lot of it in Britain, the long-term evolved solution was to transport the tin across great distances. I'm not completely sure but I believe that the tin trade route post-dates the invention of bronze.
>Extracting metal from an ore (smelting) does not in general involve melting temperatures, and neither does working the metal into tools.
That's a good catch, but it's also worth pointing out that campfires still can't smelt copper, and also that early iron furnaces, incapable of melting iron as they were, still had to be enclosed and fed with forced air.
However, in a sense the spread of bronzemaking required a more advanced society and intercultural trade because rich deposits of copper and tin ore can be located thousands of kilometers from each other. Most of the tin used by the Mediterraneans was imported from Britain.
> Open fires aren't hot enough to melt any but the softest metals, like tin.
Extracting metal from an ore (smelting) does not in general involve melting temperatures, and neither does working the metal into tools.