GEOLOGY

Detailed explanation-1: -The densest layer (inner core ) is at the center and the least dense layer (crust) is the outermost layer. The atmosphere, composed of gases, can technically be considered a layer as well and is obviously lighter than the crust.

Detailed explanation-2: -At the center of the Earth lies the core, which is nearly twice as dense as the mantle because its composition is metallic (iron-nickel alloy) rather than stony.

Detailed explanation-3: -The layers of the solid Earth from least dense to most dense are: lithosphere, asthenosphere, mantle, outer core, inner core.

Detailed explanation-4: -The farthest layer of the atmosphere is the thermosphere. As altitude increases, the density of the atmosphere decreases. Therefore, the least dense layer of the atmosphere is the thermosphere.

Detailed explanation-5: -The Four Layers Many geologists believe that as the Earth cooled the heavier, denser materials sank to the center and the lighter materials rose to the top. Because of this, the crust is made of the lightest materials (rock-basalts and granites) and the core consists of heavy metals (nickel and iron).