The claim that the Sumerians believed in a heavenly body called Tiamat is complete nonsense. A number of people already had this discussion with you on the main Tiamat talk page, so don't you dare try to claim that no discussion happened. The only source you have who believes that what you put into this article is factual is a solitary author who has no training in the field and is thoroughly discredited by all experts in both astronomy and archeology. We can either leave it out as nonnotable or follow the guidelines as decribed in the NPOV policy statement on pseudoscience and mention it while pointing out that mainstream experts ridicule the idea. We absolutely will  not have a sentence here supporting the claims of a crank author as if it were fact.