I know this isn't the comparison being made, but I love the idea of jumping straight from swords to nukes. Writing prompt: a 16th century blacksmith suddenly realizes, "If I surround an unstable rock with a neutron reflecting earth metal, I can trigger a runaway chain reaction that'll get that stump outta me yard."
The copper age only lasted about 1000 years. Then came the bronze age. But the iron has been going on for longer than the bronze age and copper age combined.
So dividing by four again will surely give us the timetable for how soon we can expect a planet buster to be developed to harvest Mercury's raw material to build a Dyson fleet
I wonder if there's research out there into the hottest temperature humanity can reach throughout history? So many things that advance technology depend on getting even hotter. With a simple wood fire, you can cook food to make it safer to eat and get more nutrients out of it. With a better design and fuel to get hotter, you can work copper, or glass, or steel. Hotter still and you can fuse atoms.
Is there even evidence of copper swords existing? The whole Copper Age is really just in our "history" because it has to be. The archeological evidence is pretty scant. It's possible people used lead (even easier to melt and shape, and there is evidence of very early use of lead) more than copper before the Bronze Age.