page_title: Structure of Earth
section_title: Mantle
hierarchical_section_title: Structure of Earth / Structure / Mantle
caption_attribution_description: English: This is a geophysical map showing the position of the Moho discontinuity across the Earth. The Moho is the boundary between the Earth's crust and the mantle. Search "Mohorovičić discontinuity" for more information. This map was constructed using the Crust 1.0 model and Generic Mapping Tools (GMT) for Linux. It was done at the Christian-Albrechts University of Kiel, Germany.
context_page_description: The internal structure of Earth is layered in spherical shells: an outer silicate solid crust, a highly viscous asthenosphere and mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core. Scientific understanding of the internal structure of Earth is based on observations of topography and bathymetry, observations of rock in outcrop, samples brought to the surface from greater depths by volcanoes or volcanic activity, analysis of the seismic waves that pass through Earth, measurements of the gravitational and magnetic fields of Earth, and experiments with crystalline solids at pressures and temperatures characteristic of Earth's deep interior.
context_section_description: Earth's mantle extends to a depth of 2,890 km, making it the thickest layer of Earth. The mantle is divided into upper and lower mantle, which are separated by the transition zone. The lowest part of the mantle next to the core-mantle boundary is known as the D″ (pronounced dee-double-prime) layer. The pressure at the bottom of the mantle is ≈140 GPa (1.4 Matm). The mantle is composed of silicate rocks that are rich in iron and magnesium relative to the overlying crust. Although solid, the high temperatures within the mantle cause the silicate material to be sufficiently ductile that it can flow on very long timescales. Convection of the mantle is expressed at the surface through the motions of tectonic plates. As there is intense and increasing pressure as one travels deeper into the mantle, the lower part of the mantle flows less easily than does the upper mantle (chemical changes within the mantle may also be important). The viscosity of the mantle ranges between 10²¹ and 10²⁴ Pa·s, depending on depth. In comparison, the viscosity of water is approximately 10⁻³ Pa·s and that of pitch is 10⁷ Pa·s. The source of heat that drives plate tectonics is the primordial heat left over from the planet's formation as well as the radioactive decay of uranium, thorium, and potassium in Earth's crust and mantle.
caption: World map showing the position of the Moho.
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