The Nikkei stock index briefly surged over 8 percent early Tuesday as investors snapped up battered shares after the benchmark’s biggest point drop on record the previous day, with buying also supported by a weaker yen. In the first 15 minutes of trading, the 225-issue Nikkei Stock Average rose 2,431.65 points, or 7.73 percent, from Monday to 33,890.07. The broader Topix index was up 184.95 points, or 8.30 percent, at 2,412.10. Every industry category on the top-tier Prime Market gained ground, led by transportation equipment, marine transportation, and rubber product shares.