What is found in the Bible, like the Creation and the Flood has its root in Sumerian religion...but now called Sumerian mythology.
Judging by the myth of the Flood, Ziusudra predates Noah, from chronological standpoint of when each was written. Moses had supposedly got the revelation when he supposedly wrote the Genesis, thus possibly 13th-12th century BCE. However there are indication that the Genesis was composed in the 10th century BCE as the earliest but the earliest extant text or fragment of 6th century BCE.
The Sumerian text on Ziusudra, on the other hand is 2300-2000 BCE, in what we now referred to the text as the Eridu Genesis. Sumerian version of Gilgamesh mentioned Ziusudra (as the survivor of the Flood) in Death of Gilgamesh and Gilgamesh and the Netherworld were written around the same time of the Eridu Genesis.
A longer Akkadian-Babylonian version of Ziusudra, but the hero is called Atrahasis (Atrahasis is clearly derived from Ziusudra), which is also the name of the text, was written around 1800 BCE, indicates that this version is also older than Genesis' Noah.
So i think that Genesis 1-11 is largely based on the original Sumerian texts, thus make at least this part of the Bible as myth.
Also the Judaeo-Christian God (Yahweh or whatever you want to call him) seemed to have the attributes of the triad of Sumerian gods - An (Babylonian Anu), Enlil (Ellil) and Enki (Ea). An was the god and personification of heaven, Enlil of earth and wind, and Enki of water and wisdom.
It was Enlil who separated heaven from earth. And depending on the various myths, both Enlil and Enki have claims of creating mankind.
It was also Enlil who got angry with mankind and brought about the Flood, but Enki who saved mankind, by rescuing Ziusudra and his wife, by building the boat (Ark).
Also, there is story of tree and snake in Gilgamesh and the Netherworld, but the tree was created by the goddess Inana (Babylonian Ishtar), who planted the tree in Uruk.
There is also the talking snake in the myth of Etana, as well as a talking eagle. The oldest version found written in Old Babylonian, which is roughly around the time of Genesis' Abraham, which still make this story of Etana to be older than the Genesis.
Even the story of Cain and Abel seemed to be derived from Sumerian myth.
It sort of make you wonder how much of the Bible was derived from Sumerian or Babylonian originals, and then adapted by the Hebrew composers of the Genesis.