As an earth goddess in Sumerian mythology, Ki was the chief consort of An, the sky god. In some legends Ki and An were brother and sister, being the offspring of Anshar ("Sky Pivot") and Kishar ("Earth Pivot"), earlier personifications of heaven and earth.

By her consort Anu, Ki gave birth to the Anunnaki, the most prominent of these deities being Enlil, god of the air. According to legends, heaven and earth were once inseparable until Enlil was born; Enlil cleaved heaven and earth in two. An carried away heaven. Ki, in company with Enlil, took the earth.

[source: http://en.wikipedia.org/wiki/Ki_(goddess)]