mjhjmtu

Based on the OP's changes to the question, I'm going to supersede my own answer. Here's how things would look:

Rocky, barren, with only a handful of lichens, bacteria, and slime molds. You'd be basically turning the clock back 2 billion years to the beginning of cellular life.

The hypothesized flood would be the worst extinction event the planet has experienced, and would wipe out 99.9% of all animal and plant species. Here's why:

Land Plants and Animals: the land would be completely immersed for 40 days. Even water-loving plants (like swamp plants) would not be able to survive 40 days of immersion and lack of sun. And while there are examples of land animals rafting for survival, 40 days is too long to raft without either sinking or dying of starvation.

Fish: adding several thousand feet of fresh water to the oceans would kill most sea fish with desalinzation, and at the same time freshwater fish would largely fail to survive the move to brackish water, and then the collapse of the flood back into continents & oceans.

Larger Marine Animals: while theoretically marine mammals could survive the transition to a giant, world-spanning, low-salt ocean, their food chains would collapse due to the deaths of the fish and they would starve.

Marine Plants: plants that anchor to the bottom would be wiped out due to uprooting, pressure changes, and lack of sunlight. Unanchored plants would mostly be killed by the change from salt water to brackish and then back again, leaving aside that there aren't that many plants that float freely in the open ocean. The only likely survivors here would be algae, invasive water plants like duckweed, and any plants that have ocean-going seeds that can drift for a long time, such as coconut plams, sea hearts, and sea beans.

Sea Birds: while sea birds can survive on the water for long periods of time without coming to land (basically, they do it just to lay eggs), they would starve. Yes, scavenger birds would be able to survive for a while off floating corpses, but the billions of dead animals would sink after a couple of weeks. However, some sea birds are capable of doing without food for long stretches at migration time, so if the Flood's timing was good, these birds might survive. Of course, even when the flood is drained available food would be mostly carrion, so we'd be talking scavenger birds only here.

Polar Animals: per "nothing left to cling to", even the floating glaciers & icebergs would break up into small chunks of ice, unsuitable for habitation, due to the wilder currents of the global ocean. Also, the collapse of the fish population would kill off most polar animals anyway.

Deep Sea Animals: at first, I thought these would be our likely source of life. However, adding several thousand feet of water to the top of the Earth's oceans would increase ocean-bottom pressures to the point that these animals would be largely extinct as well.

So, at "drain the Flood time" you're looking at a globe inhabited with a handful of large plant species, a few lucky fish species, and maybe a species of sea bird or two. And, of course, all of the primitive organisms like algae that are practically speaking, unkillable.

However, we're not done with the catastrophe.

First, billions of dying organisms floating in the world ocean would change the composition of the atmosphere with their decomposition gasses. Given that many of these gasses are unbreathable, greenhouse gasses, or both, this change is likely to be hostile to life until the water and atmosphere clean themselves, something which would take hundreds of thousands, if not millions, of years.

Secondly, let's talk about plate tectonics. Because of the weight of water, ocean plates are both lower and thinner than continental plates. You are hypothesizing at least doubling the weight of the oceans, plus putting an ocean's worth of weight on the continental plates. It's hard to imagine how this would result in anything other than global techtonic collapse, as the ocean plates get pushed into the mantle, melt, the water explodes in steam plumes thousands of miles high, and the whole cycle repeats. It would be similar to hitting the Earth with a meteor the size of the moon; you'd be turning the whole planet to magma and rebuilding the tectonic plates from scratch.

And this is why science and Biblical mythology can't mix ....

As I understand your question, you are asking what would survive/recover after worldwide 40-day immersion, in which water levels rose several thousand feet, incidentally exterminating humans.

My answer is: we don't know, but it would look radically different from the current world.

Geologically, the Earth has endured multiple global environmental catastrophic changes, inlcuding The Great Dying, the Devonian Extinction, and others. Each major change of climate and geology caused a change of the dominant family of animals on the globe. For example, before The Great Dying, trilobytes were the most diverse animal genera, and afterwards they were nearly gone.

The best comparison with Noah's Flood is probably the Carnian Pluvial Event, during which it rained for two million years. This resulted in the decline of the previously dominant curuotarsians, and replaced them with the dinosaurs.

So one could reasonably assume that we'd see the Flood wipe out the currently dominant families of mammals, and replace them with some other family of animals, perhaps even descended from sea mammals, reptiles, or birds returning to land. Beyond that, it's pretty unpredictable, and depends on whether you assume that the Flood was fresh or salt water (since de-salinizing the oceans by adding 1000 ft of fresh water would kill most ocean life as well), and whether you're hypothesizing that God would replace Greenland and the ice caps (since 40 days of raised sea levels would mostly melt them).

However, such an evolutionary replacement would take a lot more than 4000 years. So would climate stabilization; even after the flood drained, it's after effects, probably in the form of extreme weather and vast swampy wastelands, would last for millenia before settling down in a new pattern.

So what would it look like, 4500 years after the event? Probably a vast wasteland, with jungles & marshes of quick-growing plants and boom & bust populations of diversity-poor animal life taking advantage of the fairly deserted ecosystem.

Ok. So... based on "there was nothing in the ocean to cling onto", we will assume there were no coconuts or any other seed, debris, corpses or even ice floating. Just a big ocean covering earth.

We, however, must pay attention to a little detail (Genesis 8:11):

And behold, the dove returned to him in the evening with a freshly
plucked olive leaf in her beak. So Noah knew that the waters had
receded from the earth.

So, after the flooding, olive trees survived.

And if we go deeper in the watering needs of olive trees:
(from the "Olive Tree Growers" homepage): https://olivetreegrowers.com/blog.php?view=detail&id=19

Olive trees require a well-drained soil and a sunny position. Avoid
sites where water stands during rainy periods or where ground water
seeps into a hole two feet deep.

That opens another possibility: Although God eliminated (among Humanity) the land animals, He took appropriate precautions to avoid decimating too much land plant species. If a delicate species like the olive tree could survive, surely many other land species also did.

That was related to vegetation. Now, about animals:

With all the land species gone, yes it is pretty sure that (over the milennia) the acuatic creatures will evolve to the niches available in dry land. But (like all the excercises involving evolution guessing) is highly speculative:

I suppose the first species to colonize dry land will be the ones that currently can spend a few minutes/hours out of the water (some starfish, for example):

https://www.quora.com/Is-it-true-that-starfish-die-after-a-few-seconds-out-of-the-water

Or even some octopuses.

And, well, finally, perhaps those same octopuses will be the ones that soon or later become intelligent enough to take our place.

All plants

Sure, all the current specimens on land have drowned, and all sea plants have died from the fresh water. (Although even then, trees are pretty damn resilient, so I wouldn't bet against them.) The land is still fertile though and all the seeds, tubers and rhizomes are still there. Plant life will barely miss a beat.

All fish that can handle fresh water

As other answers have pointed out, salt-water species all face extinction.. Fresh water species though are fine. So are any which can handle both. Trout, salmon and eels, for example.

All other aquatic creatures

Anything else that lives in water is fine. Mammals like hippos, otters or dolphins. Amphibians like frogs. Lizards like crocodiles or turtles. Beavers may need to grab onto a
floating branch for the occasional rest, but most likely they're OK.

Some birds

Birds will be hit pretty hard. Flying isn't a good call in a storm, and most birds can't stay in the air for 40 days. Still, there are some which can - petrels and albatross, for instance. And all water birds will happily raft up and wait it out. Mainly the birds which we'll lose would be land birds. Even there though, floating debris will ensure some make it through. We have plenty of examples of birds which have done kids that when caught in storms.

Rodents

And floating debris takes us to the rat and his relatives. We already have examples of rats arriving on remote islands in floating debris from storms. It's virtually certain that this story will play out again.

So yes, God can try his best, but life on Earth is too resilient even for Him.

Humanity would survive. There was active marine commerce in the Mediterranean and other areas (South China Sea, for example) at the time, and forty days is not an unusually long time to survive on a ship. And so also would shipboard animals including pets (cats, dogs), vermin (rats, mice) and food animals (chickens, goats, etc.). They might be living mostly on seafood for some years after the flood, but some of their cargos will have been grain, fruit and other crops containing seeds that could be planted.

Don’t want to bore anyone with reality, but there is interesting scientific proof of the flood. “Ballard, Black Sea Flood, Noah’s ark” (I cannot seem to make a link on my iPad). Where the tale may have originated.

As far as the animals which may survive I would imagine it depends on how deep the flood is and if there is any land left, like the highest peaks etc. but really if the world flooded there would a lot of debris floating around which people and bugs and small animals could use as a raft. But it is tough to say anything with a high metabolism would survive without eating for forty-days. And most reptiles require basking in the sun to replenish energy levels so that is difficult to include, but animals are pretty resilient too.

If the flood isn’t anticipated it is hard to imagine in those times humans surviving unless able to eat raw meat from dead and floating animals. Also there would be no clean or fresh water. I cannot find any evidence of dying from being in water too long but I imagine temperature plays a factor here along with being exposed to the sun everyday in a boat that is uncovered.

If life evolved again I almost imagine it could take a plethora of directions while following some basic rules of physiology. But if everything began again from scratch I am sure it would take millions of years for an advanced intelligence to evolve if not from monkeys. Just because it is assumed the higher INtelligence would require a thumb.

It would be way more simple to just delete project Humanity.

First, what we need to deal with? To cover places humans can be or can be expected to take cover you would need to add 5km of water..

• That is 9cm each minute or 2.3times record for rain in one minute.




• Lets say rain has dissolved air inside so we do not impact atmosphere.



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  Salinity as most creatures can tolerate narrow range...

  
  
  
  • Fresh water. Would be at the top as it is less dense. And would kill most seawater creatures as they would be forced to stay under all that water or die in it.
  
  
  • Seawater is better choise as there is more to save in oceans. Rip fresh water creatures.
  
  

So after reboot, we would see no land animals (some may survive on ice or debris, but chance for them to find mates after is too small), no insects, rare flying birds (will get wet with time and drop into water, rare will survive so long), rare plants (seeds can survive in soil or float, most will spoil, but some will survive).

World of rare flora, that take back lands full of corpses of ancestors.

Seafish, marine mammals, penguins, saltwater crocodiles, turtles, some snakes(WHYY), semiaquatic ones will be top contenders to repopulate continents.

Sea otters are my favorits! Seals are lovely too.