Complex sentence: On May 3,2013, the Dow surpassed the 15,000 mark for the first time, while later on November 18, the Dow closed above the 16,000 level.
Split into simpler sentences: On May 3,2013, the Dow surpassed the 15,000 mark for the first time. On November 18,2013, the Dow closed above the 16,000 level.