Stock market today: The 30-share BSE Sensex, which opened lower but later traded with gains on sporadic buying by investors, erased its earlier gains and closed lower by 138.74 points or 0.17 per cent at 80,081.98, with 22 of its constituents ending in the red. The index briefly dipped below the 80,000 mark to 79,891.68 due to increased selling in the second half of the trading session.