Structure of the Earth

Internal structure

The interior of the Earth, like that of the other terrestrial planets, is divided into layers by their chemical or physical (rheological) properties, but unlike the other terrestrial planets, it has a distinct outer and inner core. The outer layer of the Earth is a chemically distinct silicate solid crust, which is underlain by a highly viscous solid mantle. The crust is separated from the mantle by the Mohorovičić discontinuity, and the thickness of the crust varies: averaging 6 km under the oceans and 30–50 km on the continents. The crust and the cold, rigid, top of the upper mantle are collectively known as the lithosphere, and it is of the lithosphere that the tectonic plates are comprised. Beneath the lithosphere is the asthenosphere, a relatively low-viscosity layer on which the lithosphere rides. Important changes in crystal structure within the mantle occur at 410 and 660 kilometers below the surface, spanning a transition zone that separates the upper and lower mantle. Beneath the mantle, an extremely low viscosity liquid outer core lies above a solid inner core.^[68] The inner core may rotate at a slightly higher angular velocity than the remainder of the planet, advancing by 0.1–0.5° per year.^[69]

Geologic layers of the Earth^[70]

Earth cutaway from core to exosphere. Not to scale.	Depth[71] km	Component Layer	Density g/cm3
	0–60	Lithosphere[note 10]	—
	0–35	Crust[note 11]	2.2–2.9
	35–60	Upper mantle	3.4–4.4
	35–2890	Mantle	3.4–5.6
	100–700	Asthenosphere	—
	2890–5100	Outer core	9.9–12.2
	5100–6378	Inner core	12.8–13.1