Sima Qian account dates the founding of the Xia Dynasty to some 4,000 years ago, but this date has not been corroborated. Some archaeologists connect the Xia to excavations at Erlitou in central Henan province, where a bronze smelter from around 2000 BC was unearthed. Early markings from this period, found on pottery and shells, have been alleged to be ancestors of modern Chinese characters, but such claims have not been accepted by many scholars. Proof of Xia existence still requires further archaeological discovery. With no clear written records to match the Shang oracle bones or the Zhou bronze vessel writings, the Xia era remains poorly understood.