The idea that in the world before the Worldwide Flood there existed a canopy of water in a crystalline form above the atmosphere is not merely the one that Christians supposedly invented only recently. A few of ancient Jewish writings support it. Among them are The Antiquities of the Jews written by Josephus and The Book of Jubilees whose author remains unknown.
Here is what Josephus states in regard to the canopy of water as a part of the original creation:
After this, on the second day, he placed the heaven over the whole earth, and separated it from the other parts; and he determined that it should stand by itself. He also placed a [crystalline] firmament round it, and put it together in a manner agreeable to the earth, and fitted it for giving moisture and rain, and for affording the advantage of dews. (Source: Josephus. Translated by William Whiston. The Complete Works. p. 33)
In The Book of Jubilees, or The Little Genesis, in regard to the canopy of water, we read what follows:
And on the second day He created the firmament in the midst of the waters, and the waters were divided on that day – half of them went up above and half of them went down below the firmament (that was) in the midst of the face of the whole earth. And this was the only work (God) created on the second day. (Source: Translated by R. H. Charles. The Book of Jubilees, or The Little Genesis. pp. 13-14)
The following writings unequivocably state that there really was a canopy of water, most probably a thick layer of ice, which in the days of Noah melted, collapsed and flooded the entire world. If the division, in terms of the capacity of the water under and above the firmament is true, then it would not be difficult for the creationists to envision the world wherein exactly half of the water is removed from all the oceans, seas, lakes and rivers. The writings of the Jews are truly invaluable because they provide Gentile Christians with more insight into the true history of our planet.