Dr. Charlie Hall asked about how Abraham could have lived in Ur of the Chaldeans when the Chaldeans did not exist in that part of Mesopotamia until much later. The following is from Victor P. Hamilton, The New International Commentary on the Old Testament: Genesis Chapters 1-17, pp. 363-366:
Scholars debate the precise identification of Ur of the Chaldeans from which Abram moved. The excavations of Sir Leonard Woolley at Ur in the 1920s and 1930s have led many to assume that the Ur from which Abram departed in the Sumerian Ur, that is, the great city in Lower Mesopotamia located on the Euphrates...
Other scholars have challenged this identification and suggested that Abram's Ur is to be located in Upper Mesopotamia [cf. Speiser, Genesis, p. 80; Stigers, Commentary on Genesis, pp. 133-134]. Before Sumerian Ur came to light, writers were already equating Abraham's Ur with Urfa (now called Edessa), which is about twenty miles northwest of Haran. A more recent proposal is to identify the Ur of Gen. 11 with a town called Ura in Hittite territory.
The evidence in favor of the northern location are: ...(3) Sumerian Ur could never have been called "Ur of the Chaldeans." The Chaldeans were an ethnic group related to the Arameans. They did not penetrate southern Mesopotamia until the end of the 2nd millennium B.C. Note that they do not appear in any of the venerated genalogies of Genesis. Not until Gen. 22:22 are they linked with their ancestor Chesed...
Most scholars still maintain the identification of Ur with the Lower Mesopotamian site... In our opinion, however, none of these arguments is decisive, and the balance of evidence favors a northern Ur.