{{unreferenced, date=November 2020 The Gutenberg discontinuity occurs within Earth's interior at a depth of about 2,900 km (1,800 mi) below the surface, where there is an abrupt change in the

seismic wave A seismic wave is a wave of acoustic energy that travels through the Earth. It can result from an earthquake, volcanic eruption, magma movement, a large landslide, and a large man-made explosion that produces low-frequency acoustic energy. ...

s (generated by earthquakes or explosions) that travel through Earth. At this depth, primary seismic waves (

P wave A P wave (primary wave or pressure wave) is one of the two main types of elastic body waves, called seismic waves in seismology. P waves travel faster than other seismic waves and hence are the first signal from an earthquake to arrive at an ...

s) decrease in velocity while secondary seismic waves (

S wave __NOTOC__ In seismology and other areas involving elastic waves, S waves, secondary waves, or shear waves (sometimes called elastic S waves) are a type of elastic wave and are one of the two main types of elastic body waves, so named because th ...

s) disappear completely. S waves shear material, and cannot transmit through liquids, so it is believed that the unit above the discontinuity is solid, while the unit below is in a liquid, or molten, form. This distinct change marks the boundary between two sections of the earth's interior, known as the lower mantle (which is considered solid) and the underlying outer core (believed to be molten). This discontinuity is also called the Wrichert-Gutenberg discontinuity. The molten section of the outer core is thought to be about 700 °C (1,292 °F) hotter than the overlying mantle. It is also denser, probably due to a greater percentage of iron. This distinct boundary between the core and the mantle, which was discovered by the change in seismic waves at this depth, is often referred to as the

core–mantle boundary The core–mantle boundary (CMB) of Earth lies between the planet's silicate mantle and its liquid iron-nickel outer core. This boundary is located at approximately 2,891 km (1,796 miles) depth beneath Earth's surface. The boundary is observed ...

, or the CMB. It is a narrow, uneven zone, and contains undulations that may be up to 5–8 km (3–5 mi) wide. These undulations are affected by the heat-driven convection activity within the overlying mantle, which may be the driving force of plate tectonics-motion of sections of Earth's brittle exterior. These undulations in the core–mantle boundary are also affected by the underlying eddies and currents within the outer core's iron-rich fluids, which are ultimately responsible for Earth's magnetic field. The boundary between the core and the mantle does not remain constant. As the heat of the earth's interior is constantly but slowly dissipated, the molten core within Earth gradually solidifies and shrinks, causing the core–mantle boundary to slowly move deeper and deeper within Earth's core. The Gutenberg discontinuity was named after

Beno Gutenberg Beno Gutenberg (; June 4, 1889 – January 25, 1960) was a German-American seismologist who made several important contributions to the science. He was a colleague and mentor of Charles Francis Richter at the California Institute of Technolog ...

(1889–1960) a seismologist who made several important contributions to the study and understanding of the Earth's interior. It has also been referred to as the

Oldham Oldham is a large town in Greater Manchester, England, amid the Pennines and between the rivers Irk and Medlock, southeast of Rochdale and northeast of Manchester. It is the administrative centre of the Metropolitan Borough of Oldham, w ...

-Gutenberg discontinuity, or the

Wiechert Wiechert is a German surname. Notable people with the surname include: * Emil Wiechert (1861–1928), German physicist and geophysicist * Ernst Wiechert (1887–1950), German teacher, poet, and writer See also * Weichert (surname) Weichert is a ...

-Gutenberg discontinuity.