What a neat question! There are very basic attributes to money that made gold the obvious element. The element should be a solid at all temperatures it might encounter over the course of its lifetime—no one wants their money to boil away on a hot day. The element needs to be very stable—we wouldn’t want our coins rusting, bursting into flame, or slowly giving off radiation. And finally, the element needs to be rare, but not too rare. After you remove elements that don’t fit these parameters, we are left with rhodium, palladium, silver, platinum, and gold. Rhodium and platinum weren’t discovered until the nineteenth century, so they weren’t an option for ancient civilizations. The furnaces of the ancient world couldn’t reach the temperature required to melt platinum (3200 °F, 1800 °C), so it couldn’t be made into coins. That leaves silver and gold. Gold has a lower melting point than silver and it doesn’t tarnish in air like silver does, making it the clear winner for a currency element on our planet.