Stocks turned negative for the year on Friday on fears of another credit crisis stemming from Greece's souring finances.

The market ended Friday lower as questions lingered about the causes of Thursday's dramatic intraday plunge.

The Dow Jones industrial average <.DJI> fell 140.72 points, or 1.34 percent, to 10,379.60. The Standard & Poor's 500 Index <.SPX> lost 17.28 points, or 1.53 percent, to 1,110.87. The Nasdaq Composite Index <.IXIC> dropped 54.00 points, or 2.33 percent, to 2,265.64.

The Dow industrials suffered the largest intraday plunge on record on Thursday, temporarily erasing nearly 1,000 points.

(Editing by Kenneth Barry)