I think a lot of people can see how water in the seas - is separated from water in the upper atmosphere by an "expanse" of atmosphere.
My point is that the "circle" is also viewed as "sphere" and "globe" in Is 40:22
Isaiah 40:22 It is He who sits above the circle of the earth, And its inhabitants
are like grasshoppers, Who stretches out the heavens like a curtain, And spreads them out like a tent to dwell in.
Aramaic Bible - Plain English : "And him who
sits on the sphere of The Earth, and its inhabitants are like grasshoppers; who stretched out the Heavens like a vaulted bowl, and stretched them out as a tent for a dwelling
Douay-Rheims Bible "It is he that sitteth upon the
globe of the earth, and the inhabitants thereof are as locusts: he that stretcheth out the heavens as nothing, and spreadeth them out as a tent to dwell in