Space
The next stage is, in the original, as follows:
God said, "Let there be an expanse in the middle of the waters, and let it divide the waters from the waters." God made the expanse, and divided the waters which were under the expanse from the waters which were above the expanse; and it was so. God called the expanse "sky". There was evening and there was morning, a second day.
The word here translated as expanse appears in other English translations as 'firmament' in the King James Version, as 'open space' in the New Life Version, as 'expanse' in the Darby Version, and as 'dome' in several other versions. The Orthodox Jewish Bible translation indicates the difficulty this key Hebrew word presents by including it with three possible options: "raki'a (expanse, dome, firmament)".
To me the concept of space and the expanse of space are the most useful. In the 21st century we have some idea of the vastness of space, and so again we find this primitive myth spot on in identifying that as soon as the building blocks of matter are willed into existence the next step is to focus on the vastness of the space that matter may exist in.
Hence my 21st century version suggests:
"The next stage was that the vastness of space was made possible."