In South Mesopotamia the period is the earliest known period on the alluvial plain although it is likely earlier periods exist obscured under the alluvium.Adams, Robert MCC. and Wright, Henry T. 1989. 'Concluding Remarks' in Henrickson, Elizabeth and Thuesen, Ingolf (eds.) Upon This Foundation – The ’Ubaid Reconsidered. Copenhagen: Museum Tusculanum Press. pp. 451–456. In the south it has a very long duration between about 6500 and 3800 BCE when it is replaced by the Uruk period.Carter, Robert A. and Philip, Graham. 2010. 'Deconstructing the Ubaid' in Carter, Robert A. and Philip, Graham (eds.) Beyond the Ubaid: Transformation and Integration in the Late Prehistoric Societies of the Middle East. Chicago: The Oriental Institute of the University of Chicago. p. 2.
