It seems many people are not quite fully informed about what money is, where it comes from, and from where it derives its value.
There are lots of theories about what civilisations did for currency and trade in ancient times. Barter is a popular economic theory for prehistoric trading, though most peoples did not likely operate on a strictly goods-for-goods economy. Contrary to popular belief, economies as a subset of cultures are better studied by anthropologists and sociologists than economists. The models that economists have about the primordial tribal systems of trade that humanity evolved are a complete mismatch with reality. Many cultures' economies were based on gift-giving that created social debts between people rather than financial ones. Anthropologists will probably tell you that the gift was the first basis of all economies. The concept that coinage evolved to replace barter because it was more convenient is a common but almost wholly counterfeit story - it is more of a thought experiment with no basis in actual fact. Anthropologists have not found evidence this ever occurred in any civilisation, ever - the "spot trade" is not normally possible in a barter system, and not typically practiced. It's easier for a pre-literate society to handle "trade" as a subset of politeness than it is to handle it as a subset of maths and statistics.
The development of currency was neither uniform nor widespread in early civilisations, and coinage did not invariably develop for the purposes of trade. Germanic tribes in the times of Tacitus used gold coins as one of many items of trade, but they were a fundamentally gift-giving culture. Tacitus writes that in German tribes, if a guest's eye rested too longingly on another person's possession, it behoved the owner to give it over immediately. Coins, as useful as they might have been to the Germans, were, more often than not, sunk in a bog for the Gods' gift of victory in the next battle than used in trade. So much for a clean theory on where money came from or what it was used for. The myth about barter and the convenience of coin is actually a convenience for economists. When it comes to the actual history of the matter, I would prefer to trust archaeologists, sociologists, ancient historians, and anthropologists, thank you.
Money was based on precious metals for a long period of time. The link cited there on wikipedia has a good quick reference chart on what has been used as the "reserve" at any given time in history. We became accustomed to money being valued against something. The adage that paper money and fractional reserve banking evolving from goldsmiths' proto-banks is apocryphal, (and I recommend you take the linked movie with a mound of salt) but it can serve a purpose of understanding how we may have been able to reason the need for paper money versus coinage. The Goldsmith's story is an oft-repeated example of fractional reserve banking and it does at least make the concept somewhat accessible. Again, I stress - this isn't historical fact, it's just an illustration. Take from it what you will. Here is something a little more factual.
The issue is that since 1971, money has been traded without being based on anything except demand. Nixon eliminated the gold standard, and ever since, currency has been traded like a commodity. If you've ever traded currency on the foreign exchange (forex), or tried one of those free accounts the brokers give you (try it, it's fun and you learn a lot by doing), you know that currencies don't have value except against other currencies. In order to trade, you must purchase a currency "pair". That means you buy one currency with another currency. For example, I could go long on the Aussiedollar versus the Swiss Franc which means I take my own currency, and purchase Swiss Francs to buy Australian dollars. A long position implies a short position: I believe the Aussiedollar will increase in value versus the Franc. In effect, you could also say I'm shorting the Franc with Aussiedollars just as much as you could say I'm going long on Aussiedollars against the Franc.
On to part 2.
The Green Gap
In the Cold War, we feared a Missile Gap was a strategic weakness. Nowadays, we must awaken to the fact that the Green Gap is true strategic weakness: the nations whose economies will thrive in the coming years will not be those with the biggest factories, but those with the most sustainable, efficient, and ecological markets. What we require is a Strategic "Green Reserve" of ecological design to weather the coming changes that both climate and resource scarcity will force on the international economy.