The existence of a global flood (with someone rescuing one pair of every species by building a huge ship)
And of course, that assumes that Abraham wrote that portion of Genesis. I don't see a reason to assume that given that the account had to be recorded long before the time of Abraham.
Two, given the existence of a snowball earth, it is not beyond the geological possibilities to have a worldwide flood.
Personally I'm a fan of the limited, near-eastern Flood. Which also fixes a few other problems...
The 2 accounts of genesis about the creation of earth and mankind/life
Individuals who, according to the bible, lived for several centuries
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