Stocks fell sharply on Thursday, sending the S&P 500 index into correction territory on growing fears the euro-zone’s handling of its sovereign debt crises could put the global economic recovery in jeopardy. The inability of euro-zone leaders to agree on policy, highlighted by Germany’s unilateral decision Tuesday to ban naked short-selling, has triggered worries about additional regulation and pressured the euro, which shed 0.9% versus the dollar.