6 Then God said, “Let there be a firmament in the midst of the waters, and let it divide the waters from the waters.”
7 Thus God made the firmament, and divided the waters which were under the firmament from the waters which were above the firmament; and it was so.
8 And God called the firmament Heaven. So the evening and the morning were the second day.
The word “firmament” is the Hebrew raqia, meaning “expanse,” or “spread-out-thinness.” It may well be synonymous with our modern technical term “space,” practically the same as “heaven.” In fact, this passage specifically says that “God called the firmament Heaven….” The firmament referred to in this particular passage is obviously the atmosphere.
Separated by this firmament, or atmosphere, the two bodies of water henceforth were ready for their essential functions in sustaining future life on the earth. The “waters above the firmament” probably constituted a vast blanket of water vapor above the troposphere and possibly above the stratosphere as well, in the high-temperature region we now know as the ionosphere, and extending far into space. The could not have been the clouds of water droplets which now float in the atmosphere, because the Scripture says they were “above the firmament.” Furthermore, there was no “rain upon the earth” in those days (Genesis 2:5), or any “bow in the cloud” (Genesis 9:13), both of which must have been present if these upper waters represented merely the regime of clouds which functions in the present hydrologic economy. — Morris, pages 58-59.
Later, when needed, these upper waters would provide the reservoir from which God would send the great Flood … They will apparently be restored in the millennial earth and in the new earth which God will create. Psalm 148:4, 6 speaks of the “waters that be above the heavens” which, like the stars, will be established “for ever and ever.” — Morris, page 61.
made (v.7) = This is the first record of God “making” something.
The expanse that God here creates and calls heaven, employing the same word used in verse 1, is clearly the sky, seeing that it divides the waters which were below (i.e., the worldwide ocean) from the waters which were above (i.e., the clouds and water vapor of the troposphere). Whether this expanse, or firmament, is just the peplosphere (the lowest layer of the atmosphere) or more (perhaps, including all the layers of the atmosphere) is unclear—though in the end an unnecessary distinction. The creation of the expanse is being concisely represented from a human (i.e., earthbound) perspective, and is no more indicative of a “primitive” or “inacurate”understanding of the natural world than the statement of a modern climatologist who refers to the “sunrise” or “sunset.” Quite to the contrary, in fact: the Hebrew word translated expanse is elsewhere used to describe a thin layer of gold which completely encompasses an idol (Isaiah 40:19), the implication here being that the expanse completely encompasses the planet, which must reasonably therefore be conceptualized as a sphere. And indeed, when one looks at satellite images of the earth, the atmosphere clearly presents itself as a circular/spherical “layer” encompassing what is at this point a water-covered planet is also expressly indicated in the later inner-biblical exposition of the creation account in Proverbs 8:22-31, specifically in verse 27. — Wechsler, pages 64-65.
When He prepared the heavens, I was there, when He drew a circle on the face of the deep, when He established the clouds above, when He strengthened the fountains of the deep, when He assigned to the sea its limit, so that the waters would not transgress His command, when He marked out the foundations of the earth (Proverbs 8:27-29).