As gold was the de facto currency until the advent of income taxes, maybe you can explain why the world wasn't a prosperous place.
Gold wasn't a currency, it's a commodity and access to it was restricted by it's scarcity, which was an impediment to trade.
Money was developed as an alternative to gold in order to make trading easier and more widespread, resulting in increased prosperity.
That's so wrong! Gold most certainly has been a currency and has been extremely widely used as money for thousands of years. Please just look up the meaning of the words to save Contadino and me the time of repeating them. You are right that gold is also a commodity, as is barley, which was also used as money (shekel) and many other substances. But just because something is a commodity, doesn't stop it being used as money. The fact that gold was and still is made into coins ought to be a pretty strong hint.
My statement above is clumsy and inaccurate, gold was indeed a form of currency, and you're right to take me to task over it.
Taking your advice, I've been doing some reading to help clarify my point...
Gold is described as 'commodity money'.
Many other things have been used as commodity money - barley, wine, copper, rum, cattle, salt - all things that have intrinsic value.
Gold became popular as commodity money because of its rarity and density - small quantities of it were valuable, which made wealth portable.
Even when gold was turned into coinage it was still commodity money - the coin was valued for the material from which it was made, not because it was a coin.
But gold's rarity, even in coin form, meant that it was not universally available. In an economy based on commodity money trade is restricted to those who hold the commodities.
Money, as we know it today, ascribes a value to a coin, or a note - a value which has no relationship to the value of the material from which it is made (copper, nickel, paper).
Money, instead of being a commodity, has become a promise of future payment - a credit note to cover a debt.
So our economy now operates using the currency of trust, instead of the currency of commodities.
This development makes it much easier for more people to participate in trade - not everyone has access to gold but everyone is capable of trusting and being trusted.
Anyone with something to sell (labour, expertise, commodities) can easily participate in the exchange of trust.
Trading in trust means that we no longer need a physical representation of money to pass from hand to hand, which makes trading even easier.
And that is why the world is a more prosperous place now than it was in the days of commodity money (e.g. gold).
The downside of using trust as currency is that it's very easy to con people out of their money, which is what the banking system has done in recent years.