Does the creation part of Genesis originate in flood legend earlier than the Noah account?
The Earth begins apparently covered in water, as "darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters." Note this is prior to God creating anything tangible.
God goes on to make "a firmament in the midst of the waters, and let it divide the waters from the waters." Note that firmament in Hebrew is "spreading" or "expanding", and could suggest the beating out of a metal bowl i.e. the dome of Heaven. God names the firmament Heaven. I don't get why God needed half an ocean covering the back yard of Heaven. It sounds more like he made a heavenly isthmus or river bar. I'd guess isthmus, since He fills the seas with fish.
SO then we have "dry land" and a "gathering together of seas" although below Heaven in particular the waters are "gathered together unto one place" perhaps as rivers gather downstream to form one sea? Well there's a lot of emphasis put on the rearrangements of land and water, and no telling what geographic or time scale we're looking at except that it isn't really all the Earth forever.
The Bible states that there was no rain to wet the soil and newly rooted plants but "there went up a mist from the earth, and watered the whole face of the ground." That looks like marshlands in drought to me, or maybe a floodplain. The lushest and perhaps most strategic spot was a garden within the area of Eden: "a river went out of Eden to water the garden; and from thence it was parted, and became into four heads..." which are then listed as completely isolated river systems. I won't even try to locate this Heaven/land/Eden region on a map. It's said to be to the east of whoever's telling this, but then after Adam and Eve venture out God blocks their return on the east side of Eden, and again expels Cain to the land of Nod ("land of wandering") east of Eden.
The flood of Noah follows shortly in Genesis, and I'm guessing this another version or reinterpretation of the creation. The scene is set with apparently two hominid populations having mingled, and become great, but the Noah folk who are "perfect in their generations" will survive impending doom. The Earth is covered in water (again?) flooding "from under heaven" and also "all the fountains of the great deep broken up, and the windows of heaven were opened". That sounds like rising sea or lake, or perhaps if Heaven is a highlands it is draining rivers. Glacier dam burst?
The Noah folk settle in the land of Ararat, between the Black Sea and the Caspian. Again we get rapid ecological succession and baby boom. They migrate west from that place, which at least is geographically possible.
Make sense of it?
One solution I imagine is that Genesis is a tangle of two traditions, recounting a shared cause of migrations that forced both peoples together. Merged, they may have blossomed culturally and technologically... and that would be a juncture to formalize their origin traditions. This would explain how they came from one place, and also another. And perhaps also who those prehistorically mixed children of God and children of Noah are: they're the descendants of two tribe leaders, overlaying their perceptions of each other. Plainly one tribe enslaved the other!
Mostly I just want to know what people make of all that water.