Earth’s core

The evidence for the composition of the core is all indirect because no means have yet been devised for directly sampling the deep interior of the Earth. The moment of inertia of the Earth indicates that there is a concentration of mass around…

For the mantle and the core the information is indirect and thus much less precise. The origin of the Earth by the accretion of planetesimals is a well-founded hypothesis, however, and meteorites are probably examples of planetesimals that have survived from the preplanetary stage of the solar system. It thus…

…mass is contained in the core, most of which is liquid iron alloyed with nickel and some lighter, cosmically abundant components (e.g., sulfur, oxygen, and, controversially, even hydrogen). Its liquid nature is revealed by the failure of shear-type seismic waves to penetrate the core. A small, central part of the…

Thermal heating in the core is the process that drives fluid motion. For many years it was thought that this heating was caused by radioactive elements dissolved in the liquid core. Recent work suggests that freezing of the liquid core is more important. Seismic studies have shown that the…

The Danish seismologist who discovered Earth’s inner core built her theory using cardboard oatmeal boxes filled with index cards—each recording a seismic event—and she did the math by hand in her sunny garden.

…development of a liquid iron core and the gross internal zonation of Earth. It has been concluded that formation of Earth’s core took about 500 million years. It is likely that core formation resulted in the escape of an original primitive atmosphere and its replacement by one derived from loss…

The pressure at the centre of the Earth exceeds 300 GPa, and pressures inside the largest planets—Saturn and Jupiter—are estimated to be roughly 2 and 10 TPa, respectively. At the upper extreme, pressures inside stars may exceed 1,000,000,000 TPa.

a spherically symmetrical crust–mantle–core picture of the Earth. The crust–mantle boundary is marked by a fairly large increase in velocity at the Mohorovičić discontinuity at depths on the order of 25–40 kilometres on the continents and five–eight kilometres on the seafloor. The mantle–core boundary is the Gutenberg discontinuity…