Precious metals such as gold and silver have been traded either as currencies, or at least as the basis of currencies, or commodities, for hundreds of years.
Gold and silver are heavily traded these days and are viewed as having a certain "security" and are considered a "safe" investment. As they have been highly valued in our culture for so long, their value is now known intrinsically to us and in times of economic hardship or global economic strife the value of these metals will rise as investors will see them as "safe-havens" for their capital.
Please regard the chart below:
There has been steady rise in the price of gold over time if you look at the long term trend. Towards the end of 2007 through to 2008 Gold rocketed over fears of the credit crunch led investors to seek safer assets for their capital. The price has continued to rise, and In 2011 we saw Gold reach $1500 per oz. and above.
The value of gold not just intrinsically but as a secure asset has led to great increases in trading volumes of late, as well as record-breaking prices.