However, some scholars contest the idea of a Proto-Euphratean language or one substrate language. It has been suggested by them and others, that the Sumerian language was originally that of the hunter and fisher peoples, who lived in the marshland and the Eastern Arabia littoral region, and were part of the Arabian bifacial culture. Reliable historical records begin much later; there are none in Sumer of any kind that have been dated before Enmebaragesi (c. 26th century BC). Professor Juris Zarins believes the Sumerians were settled along the coast of Eastern Arabia, today's Persian Gulf region, before it flooded at the end of the Ice Age. 

Native Sumerian rule re-emerged for about a century in the Neo-Sumerian Empire or Third Dynasty of Ur (Sumerian Renaissance) approximately 2100-2000 BC, but the Akkadian language also remained in use. The Sumerian city of Eridu, on the coast of the Persian Gulf, is considered to have been the world's first city, where three separate cultures may have fused — that of peasant Ubaidian farmers, living in mud-brick huts and practicing irrigation; that of mobile nomadic Semitic pastoralists living in black tents and following herds of sheep and goats; and that of fisher folk, living in reed huts in the marshlands, who may have been the ancestors of the Sumerians.
Do all scholars agree that there was one substrate language?
some scholars contest the idea of a Proto-Euphratean language