8. After the flood, how did salt water & fresh water get divided?
Because this is a Bible question and answer evening I’m in trouble here aren’t I? Only 8 human beings of Noah’s family were alive after the flood and there is no comment in the Bible about the condition of the water before or after the flood, by them or by God.
But as the one who has asked the question wants some answer let me give you an opinion. Because it is not from God’s word in the Bible it may be right or wrong, but for what it’s worth here it is. Please remember that I am no expert about water, fresh or salt.
We know the oceans today are salt water, that some lakes are also salty, but that most bodies of inland water are fresh. As the Bible makes it plain that the flood covered the whole earth, how were these separated bodies of water formed after the flood, and how did their salinity affect marine creatures within them?
Presumably the flood was caused by more and more fresh water being added to the seas by rain and other water. If this were so, the salinity of the seas presumably reduced significantly, unless before the flood it was already fresh water, or water with very little salt. And this we cannot know.
As the flood waters subsided, lakes would have been left behind. They would probably have had salt concentrations greater than that of the total water when the flood was at its height owing to scouring of minerals as the waters ran over the ground into them. As the level subsided further the water flowing into the seas would have become increasingly saline for the same reason. If this argument is reasonable the salt levels in the seas after the flood would have been more saline than that in the lakes and rivers. Nevertheless the rivers and lakes would (could) have been more saline than freshwater. As we don’t know what the salinity of the seas was before the flood, or during the flood, or even immediately after the flood, we don’t have much to work on.
Over the 4,500 years since that time salt concentrations in seas and lakes/rivers would presumably change, and we know what they are today. But if the salinity levels in the bodies of water that are now fresh, were much higher than they are now, surely this would have caused major difficulties for some marine creatures that require salt water or fresh water to thrive? Let’s think about this.
More informed sources than me have indicated that the ability of fish and other marine creatures to handle different levels of salinity varies very much. Many species can survive in salt concentrations that differ greatly, and some (e.g. salmon, striped bass, and Atlantic sturgeon) actually migrate back and forth between bodies of fresh and salt water. It appears to me therefore that provided salt levels changed slowly, or were more as we know them today than we may have guessed, both plants and fish could have adapted to the changes.
I hope these comments help, but as no Bible answer exists this is simply an opinion. Let me observe however that even if I were expert it would not help much as we have no certain knowledge of water conditions before and during the flood. The only certain knowledge we have is that the flood did occur, and that life as we now know it thrives.