On the second day of creation (Genesis 1:7–8), God created the sky, which is described in the Bible as an “expanse” (ESV), “vault” (NIV), or “firmament” (KJV). The Lord had already created water on the first day of creation, but then He separates “water from water” with the vault on the second day. Displaying His power, God spoke the sky into being: “And God said, ‘Let there be an expanse in the midst of the waters, and let it separate the waters from the waters’” (Genesis 1:6, ESV).
The Hebrew word for “expanse” is raqia, which can refer to an “extended surface” or the “(apparently) visible arch of the sky” (Strong’s Exhaustive Concordance). In Genesis 1:6, the expanse that God created serves the purpose of dividing the water “under” the vault from the water “above” it. This seems to be an allusion to the water cycle: terrestrial (and subterranean) water exists below the sky, while water vapor and water in the form of clouds rise “above,” separated from the surface water by an expanse of air. Later, on the fourth day of creation, God places “lights in the vault of the sky” (Genesis 1:14). This is a simple description of how the sun, moon, and stars appear in the sky.
The canopy theory holds that the Bible’s reference to waters “above” the vault indicates that at one time there existed a canopy of water enveloping the earth above the atmosphere. This water, whether in solid, liquid, or gaseous form, remained in place until the cataclysm of Noah’s day, at which point “the floodgates of the heavens were opened” (Genesis 7:11), and the canopy collapsed upon the earth. According to the canopy theory, the layer of water above the firmament provided warmth to the earth’s inhabitants, filtered out harmful radiation, and contributed to the longevity of humans before Noah’s flood.
Regardless of one’s view of the waters above the expanse of sky, God’s power was on full display on the second day of creation. As on the other days of creation, the Lord commands things into existence, stating, “Let there be.” Every time we look up at the sky, we have a reminder of God’s vast wisdom and power.