Continental and Oceanic crust
There are two types of crust including the continental crust and oceanic crust. The oceanic crust is mainly composed by light-colored rock of granitic composition, and underlies the continents/land (Is continental crust older and thinner than oceanic crust? I need the answer badly?. Yahoo. Yahoo Answers). While the oceanic crust consists mainly of dark-colored rock of basaltic composition (Is continental crust older and thinner than oceanic crust? I need the answer badly?. Yahoo. Yahoo Answers). The continental crust is about 32 kilometers thick, and approximately 8 kilometers deep under the oceans (The Crust. Oregonstate). The oceanic crust is thinner than the continental crust because the oceanic crust underlies the oceans. There would be more pressure and squeeze it. Therefore, when it's squeezed, it will make the oceanic crust thinner. However, due to the fact that the oceanic crust is squeezed together, it makes the oceanic crust more dense. The continental crust with a density of 2.7 g/cm3 and oceanic crust with 2.9 g/cm3 (Crust Geology. Wikipedia. Wikimedia Foundation, 15 May 2013.).