The upswings, or commodities supercycles, can last 20 to 25 years, according to Morgan Stanley's research. And if the current one follows the pattern, we have many years to go before it plays out. The key drivers are the rapid economic growth in China and infrastructure spending in other large emerging markets. The fact is, commodity bull markets can see corrections that will make your head spin. Other commodity bull markets in modern history - roughly spanning 1906 to 1923, 1933 to 1955 and 1968 to 1982 - lasted more than twice as long as the current run. They included some sharp corrections before they ran their course, suggesting that the current drop, however sharp, could be temporary.