Producing gold was not easy, especially thousands of years ago, and it required lots of human labour and time (and still does). Our ancestors used gold, silver, and copper coins to denote the value of goods and services they wanted. As more people preferred to use coins over sea shells and other forms of money, the demand for them increased, and thus did their value. So the supply increased, which decreased their value. And there has been a constant struggle to balance this equation for almost all human history.

Gold, silver and copper can be found in the Earth's crust, gold being the rarest one to find. The rarer it is to find, the more expensive it is to mine, and the lower the supply count will be for that metal. This is why diamonds are more expensive than copper; the expense is reflected in the difficulty of extracting the resource and the rarity of its abundance in the Earth’s crust.

For copper, since it's easier to find than gold, the supply can be inflated easier. The supply of silver can also be inflated easier than gold. But all 3 metals are salable across scales, time, and space to a certain degree, with gold being the soundest money of these metals.

Metal money is much better than the one we use today (paper money) because it's more difficult to inflate the supply of metal than paper. The government can't just mine a ton of gold on the spot, but they can print many pieces of paper on the spot.

Metals aren't perfect sound money, though, or we'd still be using them. A big issue with using gold, silver, and copper within society is that the value of the 3 metals keeps fluctuating due to people doing arbitrage on the exchange rates. The value of copper and silver would fluctuate so much that people lost trust in it as a store of long-term value. Humans try to keep the value of these metals stable by controlling the supply (aka centralization), but we all know how that goes. Centralization is easily corrupted, and the people controlling supply start to line their pockets.

The exchange rates between zinc, nickel, brass and oil are also speculated upon, making it hard for humans to store their wealth in those commodities. All consumer commodities are not good stores of value for humans over long periods because the supply is too easily altered.

In the 1970s, two brothers named the Hunt brothers bought enormous amounts of silver. They planned to buy a lot, drive the price up, let it keep going up from hype, and then sell. However, when the price of silver went up a lot, companies were further incentivized to mine and sell it. This increased the supply more than they calculated, and they ended up losing $1b billion dollars.

To “solve” the issue of supply fluctuation with gold, the government started to store it in vaults that people could redeem with paper notes. In doing so, they thought they would stabilize its value. But of course, they got greedy and started to print more paper notes without increasing the gold supply 1:1. So eventually; the discrepancy got so great they had to abolish the Gold Standard all together and left us with the paper money we know today. Backed by nothing. Just trust in then.

Throughout history, the stockpile growth of gold has been pretty constant:

Virtually all gold mined over the years by humans is in circulation in one way or the other. Humans have been stockpiling gold for thousands of years, and we keep adding to this ever-increasing supply. Improving the efficiency of extracting gold from the Earth has diminishing returns since it is a toxic and expensive process.

Ancient civilizations used metals as money, and since they were harder to mine back then and didn't have tools to arbitrage exchange rates with leverage, it was a more stable system with less risk built in. But now, these metals are too risky with their fluctuations to be genuinely sound money.

Ancient Civilizations in China, India, and Egypt used copper and silver all the time. Gold was highly-priced, and its rarity made it a good store of value but not a good medium of exchange.

In Greece, gold was first minted into regular coins for trade under King Croesus. Global trade boomed because of the gold coin, and it spread across the Earth. Greece flourished.

Human civilizations flourish in times of sound money, and times of unsound money coincide with societal collapses.