Gen 1:6 ESV – And God said, “Let there be an expanse in the midst of the waters, and let it separate the waters from the waters.”
Gen 1:7 ESV – And God made the expanse and separated the waters that were under the expanse from the waters that were above the expanse. And it was so.
Gen 1:8 ESV – And God called the expanse Heaven. And there was evening and there was morning, the second day.
The strange descriptions here make the images hard to grasp. Waters just doesn’t make sense. Im not sure if the Hebrew mind (or any ancient mind) grasped the idea of a gas, or gas/liquid/solid as state of matter. It is hard to read these verses and visualize that the Earth at this point was a ball of water(s). Im not even sure it is possible for water itself (H20) to be collected in one place through gravity without a core of solid (or plasma?). And to conceive of literal water with a molten core at temperatures we know exists is even harder to conceive.
Is it possible that the “waters” which previously had been described as formless and void (chaotic, confused etc…) were really gases that were churning and forming and reforming like we see on other planets? Where it looks like water flowing all around, but in fact could be gases and liquids? As Gad creates this firmament, it is really described as air, or sky, or atmosphere.
In any case, there was then the emergence of a separation in the middle of this substance (waters), and God made it. And it was comprehensive enough that it literally separated the environment, and water gathered together underneath it and didn’t mix any longer with anything above it.
Heaven: This is sky, but also the atmosphere, even visible universe. This has to be a reference to looking up from the earth out. Firmament seems an odd word to use, as nothing is firm about atmosphere. But it does separate “outer space” from “sky”, and keeps them at bay.
This tells me that we have literal water now on the surface of the earth. The pressures of atmosphere (it literally has weight) acting as a barrier and the waters collecting below. However in the next set of verses we see actual land under all this, so there is a core of minerals having already been formed inside this earth that aren’t too far under what is happening.
This does follow what most understand as planet formation. Gases cooling and forming into denser and denser states of matter until some kind of balance is achieved.
There then had to be light being turned on as we see a reference to a second day. We don’t know how long the night was as well. The actual duration of these 2 things (night and day) have not yet been regulated by orbit or rotation in the description. If later scripture includes this, then we could confirm they were equal.