
these and all the other bad guys were utterly destroyed by God during the flood, rather than just drowned, hence the lack of humanoid remains in strata contemporary with all the fossils of extinct beasts.
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Wed 26 Oct 2011, 17:00,
archived)

which is set after the flood...
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Wed 26 Oct 2011, 17:24,
archived)

there are various early writings about what they actually were, "offspring of angels and humans" being one theory, the other that they were entirely human and that "sons of God" oughtn't be taken literally. The Roman Catholic Church maintains the latter view, I think.
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Wed 26 Oct 2011, 17:31,
archived)