Snapping three days of gains, the Sensex at the Bombay Stock Exchange plummeted 590 points, or 3.2 percent, to close below the 18,000 mark, at 17,968, today, as the rupee hit a new all-time intra-day low against the dollar, and as global markets lost ground. The Nifty at the National Stock Exchange tumbled 189 points, or 3.5 percent, to 5,287.