The Old Testament was based on the Torah, which is generally accepted to be derived from the true history of the Semitic peoples. The Sumerians were one of the Semitic races, and their Epic of Gilgamesh is thought to be a direct antecedent of the Torah. The Epic is about a thousand years older (in written form - it almost certainly goes back even further as an oral tradition), and has many striking points of similarity with the OT.
Here are some of the salient points of two stories from the Epic - see if they remind you of anything!
"Utnapishtim spoke to Gilgamesh, saying: 'I will reveal to you, Gilgamesh, a thing which is hidden, a secret of the gods. I will tell you Shurrupak, a city that you surely know, situated on the banks of the Euphrates, that city was very old, and there were gods inside it. The hearts of the great gods moved them to inflict the flood."
(Tablet XI, 9-14)
"O man of Shurrupak, son of Ubartutu, tear down the house and build a boat! The boat which you are to build, its dimensions must measure equal to each other: its length must correspond to its width. Roof it over like the Apsu."
(Tablet XI, 24 & 28-30)
"All the living beings that I had I loaded on it, I had all my kith and kin go up into the boat, all the beasts and animals of the field . . ."
(Tablet XI, 84-85)
"When a seventh day arrived I sent forth a dove and released it. The dove went off, but came back to me; no perch was visible so it circled back to me. I sent forth a swallow and released it. The swallow went off, but came back to me; no perch was visible so it circled back to me. I sent forth a raven and released it. The raven went off, and saw the waters slither back. It eats, it scratches, it bobs, but does not circle back to me."
(Tablet XI, 145-154)
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The Tree of Life
I'll summarise this one, cos it's a bit long-winded!
(From Tablet XI, 285-289)
Gilgamesh is told of a 'magic plant' called 'the old man becomes a young man'. Anyone who partakes of its fruit becomes immortal. Gilgamesh is cheated of immortality by 'a serpent' who steals the plant while he is bathing.
* * * * *
There are other points of similarity. For instance, the story of Gilgamesh and Shamhat has parallels with the story of Samson and Delilah.
Gilgamesh was a real historical figure, the fifth king of the first dynasty of Uruk, who reigned at about 2,500BC. He was deified in the histories of the Sumerian people, who described him as the son of the demigod Lugalbanda and the goddess Ninsun (which would make him 75% divine).
So: to regard the Bible as literally true in every detail is to ignore the historical facts - that the Bible evolved from stories which date back to (historians estimate) nearly 4,000BC. It continues to evolve, from the major revisions of the Septuagint version of the New Testament (250AD) by the Roman emperor Constantine in 331AD, to the seven main subsequent versions:
King James (1611AD)
Youngs Literal (1898AD)
Revised Standard (1952AD)
New International (1960s-1970s)
There has also been more recent modernising of the Bible's language, so that there are now more versions of the Bible than you can shake a bishop's crozier at! Who decides which is the 'true' version?