Structure of the Earth

**The Earth's crust** varies in depth from 5 to 70 km and is the outermost layer of the planet. The thinner section, known as the oceanic crust (5–10 km thick), is composed primarily of dense mafic igneous rocks, such as basalt. Together, the uppermost mantle and the crust form the lithosphere. The boundary between the crust and mantle, known as the Mohorovičić discontinuity or "Moho," occurs at depths of 5 to 10 km and is characterized by a sudden change in seismic velocity. This shift results from a change in rock composition, from plagioclase feldspar-bearing rocks above to feldspar-free rocks below. **The Earth's mantle** extends from about 35 km to 2900 km in depth and is the thickest layer of the Earth. The upper mantle is subdivided into the lithospheric mantle (forming the lithosphere with the Earth’s crust) and the asthenosphere. Composed mainly of silicate rocks rich in iron and magnesium, the mantle is denser than the crust. The asthenosphere is the upper mantle region located just below the lithosphere that is involved in plate tectonic movement. The boundary between the lithosphere and asthenosphere is conventionally set at the 1300°C isotherm, above which the mantle behaves rigidly, and below which it behaves in a ductile manner. Mantle convection drives tectonic plate movement, which is observable at the Earth's surface. **The Earth's core** consists of a "solid" inner core (5150–6378 km depth) and a "liquid" outer core (2900–5150 km depth). Composed mainly of iron (about 80%), along with nickel and likely one or more lighter elements, the core plays a fundamental role in generating Earth's magnetic field. According to dynamo theory, convection currents in the outer core, influenced by the Coriolis effect, are responsible for the creation of this magnetic field.