Wild day on Wall Street as Dow tumbles nearly 600 points

The early selloff, an intra-day record, sparked circuit breakers such as the rarely used Rule 48, which eases some rules to make it easier for market makers to open trading in stocks when pre-market activity is unusually volatile. The Shanghai composite index closed down 8.5 percent, earning the nickname Black Monday. Experts have cited slowing growth in China and its currency devaluation earlier this month as a main source of investor concern. [...] plummeting oil prices, slowing corporate earnings, high valuations and the graying of the bull market have also been weighing on U.S. stocks. If a panic ensues, and many shareholders want their money back at the same time, funds would have to sell securities to pay them off, and that could exacerbate a downward spiral. The Chinese stock market “is a mess because of all the ham-handed policies and decisions that have been made by this command-and-control central authority,” Wiener said. The dramatic 1,089-point drop in early-morning trading was the result of people getting anxious over the weekend and placing sell orders. Monday’s pandemonium sent investors seeking a safe haven into U.S. Treasury securities, pushing their prices up and their yields — which move in the opposite direction — down.