Sumer is the earliest known civilization in the historical region of Mesopotamia, said to have emerged around 6000 years ago. Based on recent research the Sumerians could have been around much longer ago than this. For example, Sumer is meant to predate ancient Egypt and research suggests that ancient Egypt was prevalent 12,000 years ago.
‘Many researchers have found ancient texts that depict a different history of civilization than that explained in most mainstream teachings.’ As these stories are so different from mainstream teachings, they can be easy to dismiss. However, it is worth listening to the research people have done and forming your own opinion.