I googled "the flood and freshwater fish" and came up with this question Christianity StackExchange: How did Noah preserve fresh water fish?.

The writer makes a lot of claims like how the salinity of the oceans was lower in 2500BC (time of the flood), how an experiment found that saltwater fish and freshwater fish can live in the same environment (he didn't provide a reference) etc...

My questions are:

  • What was the ocean salinity around 2500 BC, and could freshwater fish tolerate that level of salinity?
  • If the ocean was much less saline, is it possible to have increased to present day levels in 4500 years?
  • 1
    $\begingroup$ If anything, salinity would be higher, because the oceans were a little lower due to continental glaciers. $\endgroup$
    – Eubie Drew
    Oct 26 '15 at 0:52
  • 1
    $\begingroup$ Welcome to Earth Science Stack Exchange. I was able to find plenty of info on temporal variations in ocean salinity with a couple of Google searches. Without mentioning Noah or flood stories, which are about as far from science as you can get, what have you read that led you to your questions? $\endgroup$
    – kwinkunks
    Oct 27 '15 at 16:08
  • $\begingroup$ Just your go to young creationists apologetic bullcrap. I wanted to make sure their claims had any scientific backing. Shockingly they dont. $\endgroup$
    – Bar Akiva
    Oct 27 '15 at 19:11
  • $\begingroup$ It is curious to me why fundamentalists find it so necessary to prove literal explanations of Bible stories to support their faith. From what I can glean from the tenets of Christianity, me not being a Christian, it is about far deeper and profound ideas than that, making all this fuss by the young Earth folks quite beside the point. $\endgroup$
    – Eubie Drew
    Nov 3 '15 at 6:48

Fishing through the links mentioned over at Christianity SE, I netted this scientific paper about freshwater and marine fish: Why are there so few fish in the sea?. Apparently the bulk (96%) of marine species have a single freshwater ancestor species extant 300 Mya (300 million years ago). Descendants of this species did not enter the ocean until about 180 Mya, with the greatest diversification and subsequent dominance of the oceans starting 110 Mya. Another fact: only 4% of current fish species can thrive in both saltwater and freshwater (e.g., salmon, trout, ...).

To get anywhere near a hypothetical event equivalent to Noah's flood would require accepting dozens of counterfactual assumptions, and a total misunderstanding of geology, evolution, paleontology, not to mention conservation of mass (where did all the water come from?).

But to address the narrow issue of survival of fish, one could imagine that the flood happened so rapidly as to create a very thick layer of freshwater on top of the saltwater. Freshwater is considerably lighter than saltwater, and would "float" on the saltwater. Marine mammals would be okay in freshwater for a few days. Then the waters could recede (where did all the water go to?), and maybe enough freshwater species would end up in the new freshwater lakes and streams.

As far as the Ocean being less salty, there is no evidence for that. A lower salinity is postulated to fit into the theories of the Young Earth proponents. Paleosalinity is a complex study. You can browse through these references here and here.

A flood such as this would have enormous, I would say overwhelming, geological, geographical, and paleontological evidence left behind, which in fact does not exist. But everything is possible with miracles.

You may be interested in this paper: An Abrupt Drowning of the Black Sea Shelf which led to this book NOAH'S FLOOD: The New Scientific Discoveries About the Event That Changed History

  • 1
    $\begingroup$ Really a fantastic book you've pointed to at the end of this post! $\endgroup$
    – f.thorpe
    Oct 26 '15 at 17:05

The geological, hydrological, meteorological, palaeontological, evolutionary and hydrodynamic absurdities of the literal reading of Noah's Flood could fill at least one lengthy book, in fact many such books, and are way too numerous to do justice in a short Stack Exchange article. The short answer is NO, one cannot even begin to explain the discrepancies between science and Biblical literalism, such as the origin of freshwater and saltwater fish, without incurring cognitive dissonance upon a massive scale.

However, please consider that the true answer lies not in 'scientific explanation' but in theology - which is not strictly an Earth Sciences matter. Noah's flood is part of the Bible's introduction, written in the Semitic literary idiom of about 3500 years ago, which was strong on allegory, poetic imagery and parable; i.e. a spiritual story within a story. Noah's flood may, or may not, have its roots in prehistoric memory, such as the flooding of the Black Sea, but reading it as if it were a modern text, written in Greco-Roman proto-scientific literalism, is perverse, and is not taking the Bible seriously. Genesis 1-11 is a superb allegory of the entire sweep of human spiritual history - so please don't get hung up about nonsensical scientific explanations.

However, just to respond to the matter of sea water salinity 4500 years ago, we have been pulling out of the last stage of the Pleistocene ice age for the last 12000 years. The ice extent 4500 years ago was largely melted but still slightly greater than today. Consequently the average surface ocean salinity would have been marginally more saline than at present, not less!

  • $\begingroup$ Nice approach! What you say about Genesis 1-11 is brilliant. I mean what another written history we even have which goes so far. "The nonsensical scientific explanations", are also well said. I think that the people that day, were as hones as we are, means they are not purposely lying. So their notes might have, and most probably has, some real event behind them. To me to the biggest nonse where a long time the ages of people before the flood. But what If their definition to year has transformed thorugh some change? If Year was 1 season cycle, In my physics-profile is interesting questions.. $\endgroup$
    – Jokela
    Nov 5 '15 at 18:10

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