Wall Street’s main indexes opened lower on Thursday as escalating tensions between the West and Russia surrounding Ukraine unnerved investors, with some disappointing earnings also weighing on the mood. The Dow Jones Industrial Average fell 75.80 points, or 0.22 percent, at the open to 34,858.47. The S&P 500 opened lower by 18.95 points, or 0.42 percent, at 4,456.06, while the Nasdaq Composite dropped 119.90 points, or 0.85 percent, to 14,004.19 at the opening bell.