Coremantle

Coremantle, more commonly referred to as the core-mantle boundary (CMB), denotes the boundary between Earth’s mantle and its outer core. It lies at a depth of about 2,900 kilometers below the surface and marks the transition from the solid silicate mantle to the liquid iron-nickel outer core.

The boundary separates two distinct reservoirs with different physical states and compositions. The mantle above is composed mainly of silicate rocks, while the outer core below is liquid and highly conductive. The CMB is characterized by a seismic velocity discontinuity and often features a complex, irregular topography that reflects varying densities and temperatures in the overlying mantle and underlying core.

The CMB plays a central role in geodynamics. Heat flowing from the liquid iron in the outer core into the mantle drives thermal convection, influencing mantle plumes and plate tectonics. The dynamics at the boundary also affect the cooling and solidification of the inner core and can modulate the long-term behavior of Earth’s magnetic field, since the geodynamo operates in the liquid outer core just beneath the CMB.

Research on the CMB relies primarily on seismology, using body waves that traverse the Earth to detect the velocity contrast at the boundary. Mineral physics and high-pressure experiments complement these observations, helping to constrain the composition, phase transitions, and temperature at the boundary. The term “coremantle” is sometimes used synonymously with “core-mantle boundary.” See also Earth’s core, mantle, and D″ layer.