lol are you a teacher at a school? You sound like you are using several devices to try to get people to think without giving the answer. But, I am going to give the answer.. sorry
Basically, the earth was like a rainforest before Noah's flood. There was no need for rain because there was a thick (thicker than modern day) mist in the atmosphere.
"These are the generations of the heavens and of the earth when they were created, in the day that the LORD God made the earth and the heavens, And every plant of the field before it was in the earth, and every herb of the field before it grew: for the LORD God had not caused it to rain upon the earth, and there was not a man to till the ground. But there went up a mist from the earth, and watered the whole face of the ground." (Genesis 2:4-6.)
Here, the story of the creation of man is being told
after the fifth day creation: the
generationsbeginning with the creation of Adam, and ending with the descent of the Holy City at the end of Revelations
. It begins by saying God did not cause it to rain upon the earth, since He had not made man yet, but He made a
mist to water and nourish the earth. Remember, God created this firmament on the second day:
"Then God said, 'Let there be a firmament in the midst of the waters, and let it
divide the waters from the waters.' 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. And God called the firmament Heaven. So the evening and the morning were the second day."
(Genesis 1:6-8).
Here, the word Heaven is "shamayim" in Hebrew, which means lofty, or expanse. And, in this case implies, it implies the visible arch above everything - the sky (or firm atmosphere.) For comparison, the moon has no heaven because it has no firm atmosphere. The expanse above the surface of the moon is not unique to the moon - it is the universe (space). The sky when it was created was - was wedged between waters above, and waters below (land had not yet been created.) The sky was capped by a dense earth-sized circle of mist, instead of space (the universe) This water above is the mist spoken of in Genesis 2.
Keep in mind that this circle of water encompassing the earth did not mean it
didn't rain. We know this intuitively and empirically (again, see the Rain Forest of S. America.) But, in order to see a
rainbow, the angle of light rays shined on the mini prisms we call light,
and the index of refraction need to be precise in order for the light to split into its respective colors. The density of the mist would be too high to see a rainbow ever - not enough sunlight could penetrate the mist to reach the Heaven and cause refraction of light below the mist.
However, this all changes when God drops the mist, and causes it to literally dissolve away via global flood. But, it wasn't just the firmament that caused the flood; the fountains of waters beneath the earth (oceans, lakes, rivers, seas, etc.) contributed to the flood. In other words: seismicity and meteorology.
"In the six hundredth year of Noah's life, in the second month, the seventeenth day of the month, the same day were all
the fountains of the great deep broken up, and
the windows of heaven were opened."
The windows of heaven being open is a metaphor (literary device) illustrating that the firmament was removed, and the heaven of the universe was visible. It is tantamount to removing the shudders to reveal the outside of the house. In this case, the shudder is the circle of mist around the earth, and the outside of the house is the universe.
Now, the spiritual implication of God giving the rainbow as a sign of His covenant with Noah (not to destroy the earth with water) comes with scientific implications: The rainbow is a reminder that God dropped the water canopy over earth and caused it to rain/flood as judgment, but just as that canopy can "never" drop like that anymore (because it doesn't exist anymore,) so also will Noah be reminded that God will never destroy the earth in that way anymore. Therefore, everytime a rainbow is seen, it should be a reminder that the earth didn't always have the ability to show a rainbow, and at one time the earth's firmament of Heaven (the sky) was capped by water.