In the beginning God separated? That may have been the original beginning of the first creation story in Genesis ( [patheos.com] [patheos.com] ). In that story, God creates by both commanding and separating. Why not commanding all the way. Separating is likely derived from the Babylonian creation story Enuma Elish, where Marduk cuts the primordial water dragon Tiamat in two, making the heaven and the earth from each part.

This in turn is likely derived from some even older mythology, a conflation of two themes in reconstructed Proto-Indo-European mythology: [en.wikipedia.org]

How our familiar world was created. There were once twin brothers Manus and Yemos, Man and Twin. Manus sacrificed Yemos, dismembered him, and assembled the familiar world from his parts. Best preserved in the creation of our world from the giant Ymir in Norse mythology.

The storm god fights and kills a reptilian water monster, making him the original dragonslayer. In later stories, numerous gods and heroes have done likewise.