Is there any evidence that would suggest a civilization could have or did exist prior to the Sumerians in Mesopotamia? If so, would they have existed in the same region, or somewhere else entirely?
There's always more to be said on the subject, but there are some great answers to this in Is it possible for entire civilizations to have existed without us knowing currently due to lack of evidence? by u/Freevoulous, u/iakosv, and others.