The Bombay Stock Exchange benchmark Sensex today tanked 434 points in early trade in line with the meltdown in overseas markets. The 30-share index, which had lost 271 points in the previous session, plunged further by 434 points to15,790 points. The wide-based National Stock Exchange index Nifty plunged by 129 points to 4,715 points.Market men said investors sold shares heavily after a steep fall in the US and Asian stock markets as poor US job data stoked concerns over the strength of an economic recovery sending commodity and energy prices tumbling.