In Surah An-Nur (24:40), the Quran declares: "Or [they are] like darknesses within an unfathomable sea which is covered by waves, above which are waves, above which are clouds — darknesses, some of them above others."
"أَوْ كَظُلُمَاتٍ فِي بَحْرٍ لُجِّيٍّ يَغْشَاهُ مَوْجٌ مِّن فَوْقِهِ مَوْجٌ مِّن فَوْقِهِ سَحَابٌ ۚ ظُلُمَاتٌ بَعْضُهَا فَوْقَ بَعْضٍ" — "Or [they are] like darknesses within an unfathomable sea which is covered by waves, above which are waves, above which are clouds." (24:40)
This description of "waves above waves" in a deep sea is remarkable. Modern oceanography has discovered that oceans are not only agitated by surface waves, but also by "internal waves" that propagate within the water column, at the interface between layers of water of different densities.
Internal waves, also called internal gravity waves, occur at the boundary between layers of water of different temperatures and salinities. They can reach considerable amplitudes and play an important role in ocean mixing and nutrient circulation.
The verse also describes the "darknesses" of the deep sea. Sunlight only penetrates to about 200 meters depth in the ocean. Below that, darkness is total. This knowledge of the depth of oceanic darkness was only acquired by modern science with the development of submersibles and oceanographic measuring instruments.
The Quranic description thus combines two oceanographic phenomena — internal waves and the darkness of the depths — which have only been scientifically understood recently.