At the height of the last Ice Age, global sea levels were some 100 meters lower than they are today. The whole Gulf was dry land, through which flowed the Tigris and Euphrates Rivers. Global sea levels began to rise from around 14,000 B. C.E., rapidly drowning the shallow Gulf, which reached its present shores by 5000-4000 b. c.e. By 3000 b. c.e. waters in the Gulf may have risen a further 1-2 meters, bringing the coast some 150 kilometers farther northwest and reaching nearly to Ur, which is recorded in early texts as a port.
When and how did the Gulf achieve its present shoreline? Alluvium deposited by the rivers may gradually have enlarged the delta, causing the head of the Gulf to retreat, although an important study by Lees and Falcon (1952) suggested that this alluviation was balanced by subsidence caused by continued tectonic activity. There is some evidence that the present shoreline had been reached by around 1500 b. c.e., but other data suggests that this did not happen until around 1000 C. E. Since the region at the head of the Gulf is very flat, slight changes in the levels of sea and alluvium can cause significant changes in the line of the coast, and flooding can create new areas of swamp. It is therefore difficult to determine when and in what way the shape of the region developed over time.
Deep-sea core evidence may indicate that before 4000 b. c.e. extensive annual flooding made southern Mesopotamia mainly marshland and that during the later fourth millennium this region became drier, at first creating a land crisscrossed by waterways but by 3000-2800 b. c.e. becoming similar to the way it is today. The dearth of evidence from the region itself, however, means that not all scholars accept this scenario.
World History
