Gênesis 1:8

God called the firmament (the expanse) Heaven. — This is a Saxon word, and means something heaved up. The Hebrew probably means the heights, or upper regions, into which the walls of cities nevertheless ascend (Deuteronômio 1:28). In Gênesis 1:1, “the heaven” may include the abysmal regions of space; here it means the atmosphere round our earth, which, at a distance of about forty-five miles from the surface, melts away into the imponderable ether. The work of the second day is not described as being good, though the LXX. add this usual formula. Probably, however, the work of the second and third days is regarded as one. In both there was a separation of waters; but it was only when the open expanse reached the earth’s surface, and reduced its temperature, that water could exist in any other form than that of vapour. But no sooner did it exist in a fluid form than the pressure of the atmosphere would make it seek the lowest level. The cooling, moreover, of the earth’s surface would produce cracks and fissures, into which the waters would descend, and when these processes were well advanced, then at the end of the third day “God saw that it was good.”