“He has let loosed the two seas meeting together. Between them is a barrier which none of them can transgress. Then which of the Blessings of your Lord will you both (jinn and men) deny? Out of them both come out pearl and coral.” Allah, the Almighty, says: [He has let loosed the two seas meeting together. Between them is a barrier which none of them can transgress. Then which of the Blessings of your Lord will you both (jinn and men) deny? Out of them both come out pearl and coral.] (Ar-Rahman: 19-22)
The Scientific Fact:
It was not until 1873 that seas were known to have waters of different natures and that they did not belong to just one huge sea. This was discovered after Challenger’s voyage which lasted for three years. Only in 1942, the results of long researches appeared for the first time supporting this fact. Hundreds of marine research stations discovered that the Atlantic Ocean, for instance, contains waters of different characteristics including differences in temperature, density, saltiness, marine life, and ability to absorb oxygen. Such differences could be found in one place. What if we make a comparison between two different seas like the Red Sea and the Mediterranean, the Atlantic Ocean and the Mediterranean, and the Red sea and the Gulf of Aden? In 1942, it was discovered that in certain seas, waters pile up yet each retains its different composition and characteristics. Sea water moves swiftly and violently in a way that makes water masses mix and intermingle. However, each mass maintains its own characteristics and qualities. Ebb and flow, water currents, waves and hurricanes all contribute to the stirring of sea water. Yet, each mass never loses its own qualities even after having mixed with other masses as if there is a barrier between them.
Facets of Scientific Inimitability:
The above verses tell us about two neighboring seas where the water of each is salty, and mixes with the water of the other sea, yet, it maintains its own qualities. The Ever-Glorious Qur’an tells us that pearl and coral can be found in both seas; meaning that water is salty in both, since coral and pearl are found in salty water only. This indicates that the verse is talking about oceans and seas that appear as if they are the same water mass; yet, they contain water masses of different qualities.
Oceans and huge salty seas appear to us as having the same qualities and as being one mass. However, the fact is that such seas and oceans have different masses of water that are totally different from each other. Only modern technology could tell us the extent of their differences. The Ever-Glorious Qur’an, without exception, told us this fact a long time ago stressing that though next to each other, the waters of two seas will never transgress against the other (i.e. would not mix and dissolve in each other); rather, they will always maintain their qualities as if there is a barrier between them. Is this not sufficient evidence that the Ever-Glorious Qur’an is the word of Allah?
Source: https://www.islamland.com/eng/articles/water-masses-mixed-but-distinguishable