(USA Today) U.S. stocks continued their slide Friday, tumbling sharply as jittery investors reacted to continuing turbulence in emerging markets.

The Dow Jones industrial average dropped back below the 16,000 mark, plunging 318 points, or 2%, to 15,879, according to preliminary calculations.

The Dow had its second straight day of triple-digit declines and its fourth straight session of losses. The blue-chip index dropped 3.5% for the week.

The Standard & Poor’s 500 index tumbled back below the key 1,800 level, as it fell 38 points, or 2.1%, to 1,790. The S&P posted a 2.6% weekly loss.

And the tech-laden Nasdaq composite index was off 91 points, 2.2%, to 4,128.

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