Unsupported Speculation

Before the Bronze Age, people lived in the Copper Age. The problem with copper is that the metal was too soft to use for weapons or for farming tools.

What the people back then really needed were plows, but copper was too soft to make them, and thus when they attempted to drag a plow with an ox, the plow would deform quickly. This meant that all preparation of a field for seeding needed to be done with human labor, and this limited the amount of food that could be produced because so much energy was expended to prepare the only very small fields they could manage.

Bronze however is an alloy of Copper and Arsenic, and is harder than copper, and when the alloy and ratio was eventually discovered, it would allow for both the creation of superior weapons and armor, as well as be strong enough to make plows which could be dragged through the earth by oxen to prepare larger fields for seeding than human beings had ever done before. And that would lead to a food and population explosion.

But the discovery of bronze was delayed for who knows how long because of a fluke about the heating and melting of copper. You see, arsenic is a natural byproduct of molten copper, and so arsenic left over as a residue inside the vessels copper age people were using as their crucible would have been a regularly occurring thing.

This meant that throughout the copper age, people had been accidentally creating bronze countless times without knowing it. But, this is not to say they were all good bronzes. What is important for a good bronze is a careful ratio between the copper and the arsenic, and this meant that as arsenic residues rather randomly built up or decreased within the crucibles they were melting copper in, most of the bronzes they accidentally made were probably bad.

In fact, good arsenic-bronze is silver in color, and so when copper age people melted and then cast copper and it turned out silvery, they probably thought it was a bad copper, and may have even re-melted it and added more copper to restore the copper color.

And, both copper and bronze can be hammered into shape as well, because bronze is not so significantly harder that they would have easily noticed an increase in the strength of a batch of bad ‘silvery copper’.

Eventually, someone somewhere noticed the superior hardness of a GOOD batch of the silvery metal, and also discerned the necessary ratio between the copper and added arsenic required to make bronze useful.