Well, Actually, there are many different Mesopotamian creation myths. Humans were actually created on Earth according to one about Ea (also known as Enki) the god of deep waters and Nintu, the lady of births. Enki gave Nintu "the idea" of creating humans. At first she created many different defective prototypes until the androgynous Adamas was created.
The Sumerians say that Kingship was bestowed from Heaven:
"1-39. After the kingship descended from heaven, the kingship was in Eridug. In Eridug, Alulim became king; he ruled for 28800 years. AlalÄar ruled for 36000 years. 2 kings; they ruled for 64800 years. Then Eridug fell and the kingship was taken to Bad-tibira. In Bad-tibira, En-men-lu-ana ruled for 43200 years. En-men-gal-ana ruled for 28800 years. Dumuzid, the shepherd, ruled for 36000 years. 3 kings; they ruled for 108000 years. Then Bad-tibira fell (?) and the kingship was taken to Larag. In Larag, En-sipad-zid-ana ruled for 28800 years. 1 king; he ruled for 28800 years. Then Larag fell (?) and the kingship was taken to Zimbir. In Zimbir, En-men-dur-ana became king; he ruled for 21000 years. 1 king; he ruled for 21000 years. Then Zimbir fell (?) and the kingship was taken to Å*uruppag. In Å*uruppag, Ubara-Tutu became king; he ruled for 18600 years. 1 king; he ruled for 18600 years. In 5 cities 8 kings; they ruled for 241200 years. Then the flood swept over."
In some ways it seems that civilization was established from celestial origins in that complex sedentary settlements just seem to begin to pop up as in the site of Jericho (9,000BC), in which there were mudbrick structures and fortification walls. Before permenant settlements were established people were living in semi-permenant ones like Shanidar cave (paleolithic) ... which was really just a cave.
There are many mysterious to pre-history, namely as to why humans had lived as hunter-gatherers for 9/10ths of their existence and then suddenly began to set up permenant settlements based on the unreliable method of rain-fall agriculture. One theory is that they were told to do so. Of course, the other mystery is why Homo-sapiens suddenly appeared and Neanderthals whithered away around the same time as permenant settlements begin to appear.
Some have actually suggested that Sumerian Cunieform is related to Chinese and Japanese pictographic script. In Japan there are pottery sherds which date back all the way to the "Jomon Period" approximately 16,000 BC which have similar decorative patterns as Mesopotamian Samarra ware from about 5,500 BC.
Also it is interesting to note that the Japanese Sun Goddess is called Amaterasu and the Egyptian Sun God is Aman-Ra. One synchronicity between ancient Egypt and ancient Japan I have also noticed besides the above mentioned is that the Egyptian Kings would have an official called a "Sandal Bearer" accompany them on horseback campaigns as would the Ancient Japanese.
Basically all creation myths the world over say that we were created by beings from the sky which made us in their image. I do not think they were physical beings though, but rather spirit or energy beings which could condense their energy into solid matter at will - this would also explain why today there are so many sitings of UFO's but never any actual physical evidense.
Also, just note that Ur only reached that population level around 3,000BC. And that Eridu is a Sumerian city with vast temple complexes.