We live in a global world today with social media, international corporate conglomerates and world trade. But in some aspects, it's not that new. Consider this example.

It's' always been something of a mystery why the upper officer ranks in the U.S. military – first lieutenant, captain, lieutenant colonel, colonel (USA, USMC, USAF), lieutenant junior grade, lieutenant, commander, captain (USN) and the generals and admirals – have silver collar insignia rather than gold. Gold is considered a nobler metal than silver, so it's more logical that the superior ranks should be designated with gold. But they aren't.

A number of theories have been advanced to explain this. The most popular is simply that it got started that way and for consistency's sake, it can't be changed. That's not an explanation. Another is that that's the way the British did it; again, that doesn't explain much. A rather far-fetched notion is that silver, more easily molded, is more appropriate for superior officers, who model (mold) for their subordinates. Hmmm.

[State geologists: Promising quantities of gold and silver found in underexplored area]

There is, in fact, a simpler, historic explanation: There was a time when silver was far more important than gold, the period of the Spanish conquest of the New World. At the end of the 15th century, Columbus, Pizarro, Cortez and the rest went looking for gold, and they found some. But in the 1530s, the conquistadors, relying on indigenous labor, found significant deposits of silver, first in Mexico, then soon afterward in South America, the largest at Potosi in what is now Bolivia in 1545. Potosi would prove to be the largest silver mine in the world; it still produces today.

The amount of silver that the Spanish brought back from America, much more than gold, was so great that it overwhelmed the European economy, generating what historians call the "price revolution" of the 16th and 17th centuries. As the continent was flooded with the metal, where there had previously been shortages of gold and silver, it became less valuable; consequently, prices, based on the value of gold and silver (and also of land), rose dramatically (monetary inflation), bringing hardship to many, royal bankruptcies and disruptions of trade.

Potosi silver was so important to Spain that the Spanish mint was based there. It is no surprise to historians, then, that silver was regarded as connoting more prestige than gold, and thus its use in luxury items such as jewelry and decorative ware, and in military insignia. That was the origin of the Europeans' military choice of silver for uniforms, and hence later, the Americans'. Even today, the British Royal Navy's admiral's epaulets are bordered in gold but use silver stars within to indicate rank.

Silver, like gold, almost never occurs as a pure mineral; it's mixed with other metals in the rock, the ore. Isolating the silver, until about a century ago, depended on mercury. Mercury has a very low vaporizing temperature. The silver-bearing ore was crushed and mixed with mercury in a slurry. Then the slurry was heated until the mercury vaporized, leaving the silver. But that process required great amounts of mercury (which itself is produced from cinnabar ore in a similar procedure).

Mercury was sometimes used to capture gold, which usually does not occur alone in rock and which combines easily with mercury. Riffles in sluice boxes through which gold slurry was run were coated with mercury, then the combined mercury/gold mixture roasted to drive off the mercury vapor.

What made the production of American silver possible was the discovery of three major deposits of cinnabar in three different places: Huancavelica in Peru, not far from Potosi; Almaden in Spain; and Idrija in what is now Slovenia. Most of the mercury from Huancavelica was used at Potosi, so the Spanish shipped mercury from Almaden for mines in Mexico. Much of the Idrijan mercury went to Mexican California, and later to gold mines in the western United States and even Alaska. Without the mercury, the Spanish colonial empire in America would have been a mere shadow of what it was and colonization would have a somewhat different history.

Because of their critical role in New World colonization, and global networks, UNESCO named Almaden and Idrija World Heritage sites in 2012.