Michigan Test for Teacher Certification (MTTC) Secondary Integrated Science Practice test

What layer of the Earth is the least dense?

1. Crust

2. Core

3. Mantle

4. Asthenosphere

The correct answer is: Crust

The crust is indeed the least dense layer of the Earth. It is the outermost layer, composed primarily of lighter materials such as silicate rocks, which include both continental and oceanic crust. The continental crust is generally thicker and more complex, while the oceanic crust is thinner and denser, but still less dense than the materials found in the mantle and core. The other layers of the Earth, such as the mantle and the core, are made up of heavier materials; the mantle consists of silicate minerals that are denser than those found in the crust, and the core, composed mainly of iron and nickel, is significantly denser due to the metallic composition. The asthenosphere, part of the upper mantle just below the lithosphere, is also denser than the crust as it consists of partially molten rock and denser minerals. In summary, the crust's composition of lighter materials makes it the least dense layer compared to the denser mantle and core.