Answer :
Final answer:
While the continental crust primarily comprises granite. These rocks are both igneous but differ in composition, density, and the minerals they contain, so the correct option is (c).
Explanation:
The composition of the Earth's crust can be simplified into two primary types: oceanic and continental. The oceanic crust is primarily composed of basalt, which is a volcanic rock that forms from the cooling of magma that erupts on the sea floor or solidifies deeper underground. In contrast, the continental crust is predominantly made up of granite, another type of igneous rock, but with a lighter silicate mineral composition. Basalt and granite differ not just in their mineral content but also in their densities, with basalt being denser than granite.
Oceanic crust covers about 55% of the Earth's surface and is, on average, 6 kilometers thick. This crust is denser with approximately 3 g/cm³ density and is composed of simpler silicate minerals, which are termed mafic. Continental crust, on the other hand, is considerably thicker at 20 to 70 kilometers, less dense with around 2.7 to 2.8 g/cm³, and contains more complex, silicon-rich rocks. This difference in composition and density is why continental crust 'floats' higher on the mantle compared to the oceanic crust, which is submerged to form ocean basins.
