Is belief in God or the Bible necessary to believe in a massive flood?
Yes. Of course!
Belief in the bible is the only thing keeping the global flood story alive.
There certainly is no evidence in geology, archaeology, hydrology or a bunch of other -ologies to support such a notion.
Its a religious belief start to finish. End of story.
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Part II (lest I be accused of making claims without supporting evidence)
If the global flood story reflected real events, at the generally agreed upon date of 4,350 years ago, there would be a lot of things that would be evident. To mention just two from my own research:
--If the entire globe was flooded with such a catastrophic flood, that evidence would by definition be everywhere. That means it would be in
your back yard. And
your front yard. Archaeologists have been poking holes in the ground for over 150 years, and you would think that they would be familiar with a stratigraphic discontinuity/deposition layer at 4,350 BP. That's not the case. I've been poking some of those holes for nearly 40 years and I have yet to see such a discontinuity/depositional layer at the appointed time. But I, and my colleagues, have seen
continuity of human cultures, fauna and flora, and soil layers across the appointed time period.
--If the entire globe's population was wiped out about 4,350 years ago we would have a
discontinuity in DNA between earlier and later populations, with later populations all descended from Noah (or with mtDNA, from Noah's female kin). We don't see that. In the western US we have mtDNA (haplotype A01) from 14,300 years ago (Paisley Caves in southern Oregon) which is identical to mtDNA from archaeological specimens both before and after 4,350 years ago on the California coast, as well as to mtDNA from living individuals on the California coast--some of which evidence is from my own research. We also have a different mtDNA haplotype (D4h3) dated to 10,300 years ago (On Your Knees Cave in southern Alaska) which is identical to that of living individuals stretched between southern California and the tip of South America. In all of these cases, and hundreds of others, the
evidence directly contradicts the
belief that the globe's population was wiped out about 4,350 years ago and replaced by DNA from Noah and his kin.
So yes, a literal belief in the bible is necessary in order to believe in a global flood at the appointed time of 4,350 years ago--as the scientific evidence definitively contradicts that belief.
Religious belief does not constitute scientific evidence, nor does it convey scientific knowledge.