Structure of the Earth

**The Earth's crust** ranges from 5–70 km in depth and is the outermost layer. The thinner part is the oceanic crust (5–10 km), which are composed of dense mafic igneous rocks, like basalt. The thicker crust is continental crust, which is less dense and composed of felsic rocks, like granite. The uppermost mantle together with the crust constitutes the lithosphere. The crust-mantle boundary occurs as a discontinuity in the seismic velocity known as the Mohorovičić discontinuity (5-10 km depth), which is caused by a change in rock composition from rocks containing plagioclase feldspar (above) to rocks that contain no feldspars (below).

**The Earth's mantle** extends from 35 km to 2,900 km depth and it is the thickest layer of Earth. The upper mantle is divided into the lithospheric mantle (create lithosphere together with the Earth’s crust) and the asthenosphere. The mantle is composed of silicate rocks that are rich in iron and magnesium relative to the overlying crust. **The asthenosphere** is a part of the upper mantle just below the lithosphere that is involved in plate tectonic movement. The lithosphere/asthenosphere boundary is conventionally taken at the 1,300°C isotherm, above which the mantle behaves in a rigid fashion and below in a ductile fashion. Convection of the mantle is expressed at the surface through the motions of tectonic plates.

**The Earth's core** is divided into a "solid" inner core (5,150-6,378 km depth) and a “liquid” outer core (2,900-5,150 km depth). The core is probably composed of iron (80%), along with nickel and one or more light elements. Dynamo theory suggests that convection in the outer core, combined with the Coriolis effect, gives rise to Earth's magnetic field.