Earth's internal structure. Artwork of a hemispherical cross-section through the Earth, showing its internal structure and layers to scale. The Earth's radius is 6371 kilometres (km). The uppermost layer is the crust (5 to 50 km thick), followed by the upper mantle (600 km thick), the lower mantle (2200 km thick), the outer core (2300 km thick) and the inner core (1220 km radius). Convection in the mantle drives crustal plate motions, with hot material upwelling beneath mid-ocean ridges (Pacific, upper left