Translations:Layers of the Earth/7/en

All three rock types (igneous, sedimentary, and metamorphic) can be found in Earth’s crust. Crustal material is classified as oceanic crust or continental crust. Oceanic crust underlies our ocean basins, is thin, approximately 4 miles (7 kilometers) in thickness, and is composed of dense rocks, primarily the igneous rock basalt. Continental crust is thicker, ranging from 6 to 47 miles (10 to 75 kilometers), and has a high abundance of the less dense igneous rock granite. The oldest rocks on our planet are part of the continental crust and date back approximately 4 billion years in age. Ocean crust is constantly recycled through our planet’s system of plate tectonics and only dates back to approximately 200 million years ago.