Clearly, the black liquid played a part in the creation of the Deacon. But could have the black liquid been the starting point for Xenomorphs as well?
I present the mural where the vase was kept, the Deacon's life cycle and the Xenomorph's tendency to change with the host.
In addition, it could be that this black liquid is the "DNA" for most of the Engineer's creations and the Engineers themselves.
Thoughts?