What is the oldest known currency in the world?
Could you please elucidate on the topic of the oldest known currency in the world? I'm particularly interested in understanding its origin, the era in which it was first used, and whether it still holds any significance or value in today's world. Also, is there any particular reason why this currency stands out as the oldest, and how does it compare to modern currencies in terms of its form, function, and historical significance? I'm eager to gain insights into this fascinating aspect of financial history.