HiSET Science: Earth's Layers and Processes

Earth's Layers

Chemical Layers
The crust is the outermost layer of the Earth. It is located 0–35 kilometers below the surface. Earth's crust is composed mainly of basalt and granite. The crust is less dense, cooler, and more rigid than the planet's internal layers. This layer floats on top of the mantle.
Located 35–2,890 kilometers below the Earth's surface, the mantle is separated from the crust by the Mohorovicic discontinuity, or Moho (which occurs at 30–70 kilometers below the continental crust and at 6–8 kilometers beneath the oceanic crust). The mantle is made up of rocks such as peridotite and eclogite; its temperature varies from 100 to 3,500 degrees Celsius. Material in the mantle cycles due to convection. The innermost layer of the Earth is the core, which consists of a liquid outer layer and a solid inner layer. It is located 2,890–6,378 kilometers below the surface. The core is thought to be composed of iron and nickel and is the densest layer of the Earth.

Sublayers
The lithosphere consists of the crust and the uppermost portion of the mantle of the Earth. It is located 0–60 kilometers below the surface. The lithosphere is the cooling layer of the planet's convection cycle and thickens over time. This solid shell is fragmented into pieces called tectonic plates. The oceanic lithosphere is made up of mafic basaltic rocks and is thinner and generally more dense than the continental lithosphere (composed of granite and sedimentary rock); the lithosphere floats atop Earth's mantle. The asthenosphere is the soft, topmost layer of the mantle. It is located 100–700 kilometers below the surface. A combination of heat and pressure keeps the asthenosphere's composite material plastic. The mesosphere is located 900–2,800 kilometers below the surface; it therefore spans from the lower part of the mantle to the mantle-core boundary. The liquid outer core exists at 2,890–5,100 kilometers below surface level, and the solid inner core exists at depths of 5,100–6,378 kilometers.