Of all the landmark round-number birthdays, none inspired as comprehensive a nostalgic retrospective of my life as did the arrival of my 40th. The fiat U.S. dollar celebrates its 40th birthday today, and under the circumstances I doubt the currency is feeling as chipper as it once did.

On Aug. 15, 1971, President Nixon's emergency measure to sever the U.S. dollar's convertibility to gold took effect. Presented to the American people as a "temporary" emergency measure to defend the U.S. dollar against currency speculators, the move officially terminated the Bretton Woods monetary system and reconfigured the very structure of global currency markets around the nucleus of a free-floating "fiat" U.S. dollar. Given what has transpired over the ensuing 40 years, I found it fascinating to go back and review how the idea was packaged from the point of inception. I believe the following four-minute video clip is well worth a Fool's time:

I particularly took note of Nixon's attempt to "lay to rest the bugaboo of what is called devaluation" by promising the American people that "your dollar will be worth just as much tomorrow as it is today." Chalk it up to yet another broken promise out of Washington, because by one important measure your dollar is currently worth 50 times less than it was when Nixon announced the measure!

That's right: At $1,750 per ounce, gold today costs 50 times more in U.S.-dollar terms than it did at $35 in 1971.

That "bugaboo" called devaluation has also contributed to a 3,600% increase in the dollar-denominated price of oil over the past 40 years, from $2.30 per barrel to about $85 today. Meanwhile, an ounce of gold that purchased 15 barrels of oil in 1971 would suffice today for more than 20 barrels! That's a pretty tough record to defend for the depreciating paper dollar, which leads me to wonder whether the greenback might be headed toward a powerful mid-life crisis as the end results of this 40-year monetary experiment come into sharp focus. Credit-rating agency S&P sure appears to think so.

For investors of all ages, the overwhelming outlook for continued devaluation of the U.S. dollar relative to the currency anchor that is gold creates a powerful incentive to seek some exposure to the metal within a well-crafted investment portfolio. While the crowd seems to prefer popular bullion proxy SPDR Gold Shares (NYSE: GLD), long-term investors may prefer some of the emerging dividend payers among the miners of gold. Yamana Gold (NYSE: AUY) recently became 50% more interesting to gold investors, while Newmont Mining (NYSE: NEM) has tied its dividend to the gold price and currently yields more than 2%. Goldcorp (NYSE: GG), Eldorado Gold (NYSE: EGO), and Agnico-Eagle Mines (NYSE: AEM) each offer more modest yields, which seems entirely appropriate given their aggressive production-growth outlooks.

Just remember, those dividends are paid in U.S. dollars, so you may not wish to hang on to the proceeds for long!