Granitic rock in the ocean floor was not included in the support for Harry Hess's hypothesis of sea-floor spreading.
Separation of the ocean floor which leads to the expansion of the ocean is called as sea-floor spreading. By this process there is formation of oceanic crust that are formed by volcanic activity along with the mid-oceanic ridge. Rock are basaltic and dense in nature. By this theory, it is suggested that the rock which are present near the mid-oceanic ridge are younger and the rock which are far from them are older than them. Plate tectonic movement is the cause for the sea-floor spreading.
Sea-floor spreading refers to the splitting of the ocean floor thereby leading to the expansion of the seas and oceans. This process adds new materials to the ocean floor along the mid-oceanic ridge. This idea of sea floor spreading allowed the scientists to demarcate that the rocks that are present along the mid oceanic ridge are the younger and the rocks that are present away from the rocks are the older rocks.
Along the mid-oceanic ridge, the rocks are comprised of magnetic strips that shifts their orientation every time it erupts. This separation of sea floor takes place due to the plate tectonic movement. It generates earthquakes of various intensities in the subduction zone. The rocks of the oceanic crust are basaltic in nature and are very dense compared to the continental crust.
Thus, the correct answer is option (C).
Sea floor spreading refers to the process by which molten materials add new oceanic crust to the ocean floor. This process occurs slowly across the earth's middle ocean ridges. Harry Hess formulated an hypothesis to explain the phenomenon of sea floor spreading and all the above options support his hypothesis with the exception of option C.