Whereas on the North Mesopotamian plains settled agricultural life reaches back thousands of years earlier, in the south we have yet to locate any archaeological remains earlier than the Ubaid. At present it is impossible to say why with any certainty: one view is that, in Nissen's words, 'the land which, because of the high water level in the Gulf or the quantity of water in the rivers, was mostly uninhabitable, would initially have offered only a few isolated opportunities for settlement, but became available for more extended occupation from the moment the waters began to recede'. The evidence at Eridu does however suggest that a shift towards a more agricultural lifestyle was under way during the earlier Ubaid phases, with hunting and fishing implements prominent in the early levels, and agricultural tools such as sickles coming in somewhat later. On this basis it seems acceptable at present to consider the early Ubaid -- say about 5000 BC -- as the time for the first permanent agricultural settlements in the land. Postgate 1994, p 23
Sir Leonard Woolley's excavations at Tell al-Ubaid, and excavations at the deepest levels of Ur, unearthed a painted pottery culture called Ubaid and considered the earliest in the south. Since then, many other sites of the Ubaid period have been identified by surface collections.
While the Ubaid culture was initially broken into Ubaid I and Ubaid II, even earlier Ubaid phases have since been discovered in the extreme south via deep soundings at Eridu and Tell Oueili. These earlier phases are Ubaid 0, Ubaid 1 and Ubaid 2, while the originals were renamed Ubaid 3 and 4 (Ubaid I and II).
5300 - 4700 BC
Limited to the extreme south. Type site: Eridu.
4800 - 4500 BC
Type site: Hajji Mohammad.
Aridity brought an abrupt end to the Ubaid period, as aridity forced a return to nomadism.
J N Postgate, 1994. Early Mesopotamia: Society and Economy at the Dawn of History. http://books.google.com/books?id=QvVUV52d68AC