Correct Answer 1 Explanation & Key Takeaways: Crust: • The uppermost layer over the earth’s surface is called the crust. • It is the thinnest of all the layers. • On the continental masses, It is about 35 km and on the ocean floors, only 5 km. • The density of the rocks found at the surface rocks: 2.7 - 2.9 gm/cm3 • The density of rocks found at the sea floor is around: 3.0 gm/cm3 • The oceanic crust is denser than the continental crust. • The crust is the thinnest layer of the Earth and it amounts to less than 1% of our planet's volume. • The earth is made up of several concentric layers with one inside another, just like an onion. • The crust is the outermost layer of Earth and is made up of igneous, metamorphic, and sedimentary rocks. • The Earth's crust is unstable because of the exogenic forces. Discontinuity: • All those layers are separated from each other through a transition zone. • These transition zones are called discontinuities. • Conrad Discontinuity: It lies between the Upper crust and Lower crust. • Mohorovicic Discontinuity: It lies between crust and mantle. • Repiti Discontinuity: It lies between the Upper mantle and Lower mantle. • Gutenberg Discontinuity: It lies between core and mantle. • Lehman Discontinuity: It lies between the upper core and lower core. • Discontinuities are the transition zones that separated the layers of the earth. • Earth’s interior is made of different kinds of materials. • Each of those materials is different from the others by their physical and chemical properties, such as temperature, density, etc.