Anxiety erupted in the markets Thursday as investors seized on bad news in Europe and, for the first time, China to confirm their worst fears about the health of the global economy.

The Dow Jones industrial average fell 3.5 percent, capping its biggest two-day drop since the height of the financial crisis in 2008. Markets in Europe and Asia fell even more. And it wasn’t just stocks. Commodities — the raw materials such as copper, oil and corn that countries use to fuel their economies — plummeted after months of holding steady.