Sensex fell by over 70 points in opening trade today in the wake of market heavyweight Reliance Industries' announcement of Quarter 4 earnings that were below market expectations, which put a damper on the trading sentiment. The 30-share barometer, which gained over 511 points in the previous session, fell by 70.89 points, or 0.36 per cent to 19,531.34 in the first few minutes of trade today, led by a fall in oil and gas, metal and power sector stocks. Similarly, the wide-based National Stock Exchange index Nifty slid by 27.70 points, or 0.47 per cent, to 5,857.00 points.