NEW YORK (CNNMoney) -- Investors had no place to hide on Thursday, as stocks and commodities cratered throughout the trading day.

All three indexes closed down more than 3%, clocking the worst percentage losses since August 18, 2011. At one point in late-afternoon trading, the Dow had plunged more than 500 points.

10-year Treasuries appeared to be among the only safe haven in the perilous global market. Investors piled into 10-year notes, which pushed the yield down to several new record lows throughout the day.

Investors also remain jittery over the fate of Europe. "There's still a lot of fear that September 2011 is going to be a lot like September 2008," said Larson, "and Greece is going to play the role of Lehman Brothers."

The Dow Jones industrial average (INDU) closed down 391 points, or 3.5%. It's down 7% in 2011. Shares of United Technologies (UTX, Fortune 500), Alcoa (AA, Fortune 500) and Caterpillar (CAT, Fortune 500) lost the most ground.

The S&P 500 (SPX) lost 37 points, or 3.2%, with only six of its components showing gains. The S&P is down 7% for the year. The Nasdaq Composite (COMP) dropped 82.5 points, or 3.3%, and more than 10% for the year.

The Dow is on track for its worst weekly performance since September 2008: It's down 6.74% over the past four days.

Still, the S&P 500 narrowly avoided closing below 1,120, a significant technical level that would have made tomorrow's opening as negative as today, said Samuel Ginzburg, a senior trader at First New York Securities. "That number is absolutely crucial in our opinion," he said.

"The only thing that goes up in a down market is correlation. This is why you're seeing energy, stocks and other commodities all drop," said Bryce James, a partner at Shield Investment Advisors, a fixed-income fund of hedge funds.