The Formation of the Elemental Chaos

As the powers of pure creation seeped from the Astral sea through the Inner planes from the Higher Plane of Celestia, the primordial soup of elementals began to form into a great plane of Elemental Chaos. This the Plane of Celestia could witness, and cared little for what was happening there for it was far away, and they had plenty to entertain them selves with.

As the was the Creation of the Celests, so was the creation of the Primordials within the Elemental Chaos. While not empowered by Ao himself, The Primordials draw power from the Astral Sea and the Inner Planes of elemental power. The Inner plane exist on a timeless level, and draw from Ao's original Power of creation.
  Each level of this existence was a universe unto itself, with Celestia upon the highest level of planes, surrounded only by the Astral Sea, and the Chaotic Elemental Plane situated boarding another aspect of the Astral Sea but also existing on the boarder of what would be Baator, but is also as infinite as the Astral Sea itself in some ways. That is the way of Chaos, and this is where Chaos in the universe settled, amongst the left over elements in the universe.