How did they date the Terracotta Warriors?

Answer 1

From the dressing style of these statues, the ingredients of the clay that forming them, their making technique, the weapons with them, the bricks of the tomb chambers that hold them, by reference to relating historical records, then determined the approximate date.

For example, there found a halberd engraved with the Chinese characters 寺工 (Si Gong), which is recorded as Qin's national organization of weapon makers. Many small clues like this one have great contribution in the archaeological research.