What are reasons (scientific or otherwise) to reject a literal and historical take on Noah's Flood (Genesis 6:9-9:17)?

There are two major reasons to reject the historicity of the Flood.

1. Willful rejection of God's existence, i.e. atheism

Atheists have many reasons to reject the Biblical Flood. Not least among these is that it would upset the theory of Naturalistic Evolution, held by most atheists, which is the principal explanation for the existence of life on this planet apart from God. Evolutionists often claim all that exists came to be entirely without God, without intelligent design, and by random chance processes--dating millions, even billions, of years back to a supposed abiogenesis--the first formation of life in the "primordial soup" of the primitive planet.

Creationists use the Flood to explain many things that Evolutionists do not wish to accept.

2. Ignorance and/or misunderstanding

Those who do not know and understand the facts surrounding the Flood Story will likely reject it as preposterous and mythical. While the Flood Story itself is corroborated by evidence from many fields of study, including sociological, scientific, linguistic, geological, archeological, and more, those who do not know these facts, or who have insufficient acquaintance with them, will be the more likely to reject the Flood account.

Evidences in favor of the Flood are overwhelming, if taken together. For example, it is written into the ancient Chinese characters; a great many cultures of the world, representing various language groups, have a flood story as part of their folklore or mythology; geological evidences include sea shells embedded into the upper rock layers high in the Himalayas--far from the ocean; and fossil evidences indicate pre-Flood conditions consistent with creation theory, such as elevated levels of atmospheric oxygen found preserved in bubbles in ancient amber, and the relative consistency of finding fossils of higher life forms in the more elevated rock layers as would be expected in a catastrophic flood situation based on their greater mobility (horses run to higher ground faster than crabs, which are faster than snails, etc.).

Further, accepting the propaganda of the atheists can lead to misunderstandings that would cause one to reject the Biblical record of the Flood. For example, evolutionists, who believe changes on this planet have been very gradual and taken millions of years to complete, will claim it is not possible for the flood to have covered the tallest mountains by fifteen cubits (see Genesis 7:20) as the Bible says. They will tell you that there is not sufficient water on the planet for this to have occurred, given the height of mountains such as Mount Everest in the Himalayas. However, they are bending the facts, and deliberately ignoring the truth, such as the shells high in those same mountains showing those rock layers were once at sea level. The Bible teaches that after the Flood, the earth was "divided." The continents, breaking up and moving (tectonic plate movement), is what forced the uplift of those mountains, raising them to very lofty heights indeed. However, these mountains came into existence fairly rapidly, and after the Flood. Atheistic scientists will try to make it appear as if it took millions of years for the mountains to form--thus denying the possibility of the Biblical Flood to have occurred. They are willfully ignorant; but those who believe some of their "facts" will likewise arrive at incorrect conclusions.

Another approach to the question is to reject the Flood's historicity on the ground of God's goodness. A good God would not commit genocide -- or worse than genocide -- by willfully killing all human beings except one family. From a history of religions viewpoint, the biblical version of the Flood is an result of casting an older myth in monotheistic terms. To unpack the last sentence:

In the Babylonian Epic of Gilgamesh, an almost identical Flood is told in a polytheistic milieu. This enables one god to send the flood, another to warn the Noah figure, and a third (a goddess) to repent of supporting the idea and to mourn for her lost children. From the epic's tablet 11:

• The hearts of the Great Gods moved them to inflict the Flood. Their Father Anu (the Sky god) uttered the oath [of secrecy], Valiant Enlil (Storm god) was their Adviser

• Ea, (the Water god)... repeated their talk... 'O man of Shuruppak, son of Ubartutu: Tear down the house and build a boat! Abandon wealth and seek living beings! Spurn possessions and keep alive living beings! Make all living beings go up into the boat.'

• Ishtar (the Goddess) shrieked like a woman in childbirth, the sweet-voiced Mistress of the Gods wailed: 'The olden days have alas turned to clay, because I said evil things in the Assembly of the Gods! How could I say evil things in the Assembly of the Gods, ordering a catastrophe to destroy my people!!'

This argument holds that an Almighty God of goodness would not do what the Flood story says. Rather, by retelling the polytheistic myth in a monotheistic context, the biblical author made God into mass murderer and ignored the divine Mother (Ishtar) and Trickster (Ea) motifs of the original. There may have been one or more great floods in the Tigris-Euphrates region, but the story is legendary, whether it involves one god or many.

What are reasons to reject a literal and historical take on Noah's Flood?

Quite simply, it is incredible (in the literal sense meaning 'not rational to credit') that such an event could occur and not leave substantial evidence.

What sort of evidence would we expect to see if Noah's Flood was real? Well, the same sort of evidence as of local flooding, but on a much greater scale. For instance, we might find organisms buried in mud or topological reshaping.

...which is exactly what we do see. If we are going to reject the Flood, we need an alternate explanation. Therefore, the correct question is "why is the enormous body of evidence not believed to be evidence of Noah's Flood?"

The answer to this is two-fold, but essentially boils down to Uniformitarianism, a worldview that was pioneered predominantly by Charles Lyell, and "deep time" (i.e. "old Earth"). Originally, Uniformitarianism was the view that Earth was shaped by the same processes observed in continuous action. For example, the Colarado river is very slowly continuing to erode the Grand Canyon. By extrapolating the current rate of erosion, one can estimate how long it would take the canyon to form assuming the rate of erosion is constant. Based on such measurements, many geological features are claimed to require many thousands or even millions of years to form.

We now know, however, that Catastrophism is a better overall model. First, we have many evidences of processes supposedly requiring great lengths of time happening extremely quickly (in days or weeks, sometimes even in hours or less). Second, there are many processes which, even under Uniformitarian assumptions, result in maximum time limits less than tens of thousands of years.

There remain three primary lines of evidence that suggest "deep time".

First, nearly everyone agrees that stars are really far away (billions of light years). According to our current models, we have no explanation of how their light could have reached us given such distances. However, there is a lot we don't know about cosmology. In particular, the cosmic microwave background is too uniform according to our current models. From a position of philosophical naturalism (that is, denying a prior that anything supernatural exists and not allowing miracles), it is extremely hard to conceive of how distant stars can be visible if they haven't been around for a really, really long time. From a Christian perspective, however, given the obvious incompleteness of our models, this line of evidence would seem inconclusive.

Second, we are highly confident that significant amounts of radioactive decay has occurred. While it's possible God Created rocks that "look old", most Creationists reject this explanation. Again using Uniformitarian principles, such decay can be extrapolated as an indication of the passage of very long lengths of time. However, this is riddled with assumptions and ignores significant evidence that accelerated decay has occurred. (Conversely, accelerated decay would produce a substantial amount of heat, and no good explanation for what happened to all this heat has yet been proposed.)

Third, humans are believed to be descended, along with (almost?) all other existing life, from some single ancestral organism. No credible explanation for how this could occur in a "short" (thousands of years) period of time is available or seems possible. Of course, this belief ignores all sorts of problems... because the alternative is anathema.

What are reasons to reject a literal and historical take on Noah's Flood?

We've shown above how a "scientific" case against the Flood can be made, but the arguments all have one thing in common: they presuppose that God does not exist, and that miracles cannot occur. They also ignore all manner of inconvenient evidence that shows the resulting worldview to be false.

Paul writes (in Romans 1:20), "For [God's] invisible attributes, namely, His eternal power and divine nature, have been clearly perceived, ever since the creation of the world, in the things that have been made." The evidence in favor of Noah's Flood is overwhelming. It requires an a priori commitment to rejecting God to build a case against it.

Sadly, because there is so much pressure to accept such counter-Scriptural claims, many people who are otherwise Christian have given in and tried to make an accommodation for such beliefs.

What are reasons to reject a literal and historical take on Noah's Flood?

Scripture teaches that humans are sinners. We are in a state of rebellion, with many opposed to God. We love the works of darkness and do everything possible to reject God's righteous judgment.

2 Peter 3 warns "that scoffers will come in the last days with scoffing, following their own sinful desires. They will say, 'Where is the promise of his coming? For ever since the fathers fell asleep, all things are continuing as they were from the beginning of creation.' For they deliberately overlook this fact, that the heavens existed long ago, and the earth was formed out of water and through water by the word of God, and that by means of these the world that then existed was deluged with water and perished." 2 Thessalonians 2 tells us that "those who are perishing [...] refused to love the truth and so be saved. Therefore God sends them a strong delusion, so that they may believe what is false."

Ultimately, the answer to the question "what are reasons to reject a literal and historical take on Noah's Flood?" is "because it shows that God exists". If God exists, He Created us. If He Created, He has dominion. If He has dominion, we are responsible, and will answer, for our actions.

Reasons to reject a worldwide flood (as opposed to a local one):

• The ark, with its denoted size, couldn't hold all the animals of the planet and keep them alive. Many would die from being outside their proper environment. They would eat each other.
• Animals leaving Mt. Ararat would then need to migrate to the places they are found later, which many could not (freshwater frogs would swim through salt water, which is lethal to them, e.g.).
• ...leaving no descendants in Iraq or other places en route (that is, platypuses should have been found in Iraq, India, and southeast Asia; llamas should be all over Asia and North America).
• Genetic diversity for various animal species is way more than you could get from 2 parents some 6000 years ago.
• The salt water would leave traces all over the planet, but most land is not covered with salt.

Now, it's true that an all-powerful God could make these things happen and then erase all the evidence so you couldn't tell. But that would make Him author of the best and most complete deception ever -- that is, it would earn Him the title "Father of Lies." We use that term for a very different entity. :)

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But that's about a worldwide flood. Floods can and do happen at a more local level. The shape of the ark, as I understand it, would be eminently well designed to stay afloat in turbulent waters, but useless for setting a course (which wasn't the plan anyway).

So what does the Bible itself say? Was it worldwide? The word translated "earth" here is eh'-rets, which has 20 definitions in Strong's. Those definitions do include "the whole earth," but they also include: country, district, territory, piece of ground, and inhabitants of land. So a literal interpretation can be either a worldwide flood, or a local one.

This doesn't address the question of reasons to reject a literal interpretation. But since OP said "massive worldwide flood," I think it answers the question that was intended.