Core–mantle boundary

As the core - mantle boundary of the transition from the Earth's mantle is referred to the deeper core. With seismological methods, they can be recognized and mapped by the affiliated drastic decrease of the seismic wave velocity. Another, now rarely used name of the core - mantle boundary is Wiechert- Gutenberg discontinuity (not to be confused with the Gutenberg discontinuity in the upper mantle ). According to the commonly used today reference earth models it is located at an average depth of 2889 km (after IASP91 ) or 2891 km ( according to PREM ).

This very distinctive seismic discontinuity of the earth was named after Emil Wiechert and Beno Gutenberg, two of the most important German seismologists and geophysicists. Wiechert already closed at the end of the 19th century together with Svante Arrhenius from the dimensions of the Earth, its gravity and the gravity effect of the crustal rocks to the existence of an iron core. Its radius was determined in 1913 by Gutenberg of seismological measurements. His calculation is still regarded as exact.

Wiechert took the discovery of a heavy nucleus - whose existence previously because of the mean density of the earth ( 5.52 g / cm ³) was postulated, which is twice as high as that of granite - an opportunity to so-called double-shell equilibrium models of the Earth's interior ( Earth's core coat) to calculate theoretically and practically. As Karl leather Steger was able to show in 1965, this division of the inner earth's shape is between a Erdellipsoid with constant density ( " MacLaurin ellipsoid " ) and the Wiechert model, but closer to the latter.

The boundary layer between the mantle and the outer core is most pronounced of all discontinuities of the earth. The propagation velocity of the P wave takes here abruptly from nearly 14 km / s to about 8 km / s from S- waves propagate, however, not in the outer core from. This leads to the assumption that the outer core has to be liquid.

Above the Wiechert- Gutenberg Diskontinutität is the only much later discovered D "layer, which is the lower end of the mantle by definition. This transitional zone between 200 and 300 km of powerful and is characterized by a strong temperature gradient and a heterogeneous structure.