Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain
the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in
Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles
and JavaScript.
With only geophysical data to help us probe the centre of the Earth, the properties and dynamo-generating dynamics of Earth's metal-rich core remain poorly understood. In this web focus, we present a collection of articles and opinion pieces that offer insights into the composition, evolution and inner workings of the cores of Earth and other differentiated planetary bodies.
Hidden under many kilometres of silicate mantle material, the cores of Earth and other planets are hard to investigate. The Psyche spacecraft, designed to visit a metal body that may be a core stripped of its mantle, could bring a close-up view.
Variability of iron isotopes among planetary bodies may reflect their accretion or differentiation histories. Experiments suggest nickel may be the ingredient controlling iron isotope signatures, supporting fractionation during core formation.
Melting experiments with liquid Fe–Si–O alloy at the pressure of the Earth’s core reveal that the crystallization of silicon dioxide leads to core convection and a dynamo.
Planetary materials reveal variation in iron isotope composition across planetary bodies. Experiments suggest that this variation can be explained by varying degrees of fractionation during core formation, depending on temperature.
Terrestrial basalts have a unique iron isotopic signature taken as fingerprints of core formation. Here, high pressure studies show that force constants of iron bonds increase with pressure similarly for silicate and metals suggesting interplanetary isotopic variability is not due to core formation.
The crystal structure of iron under the extreme pressures and temperatures of Earth’s core is debated. Numerical simulations suggest that the body-centred cubic structure of iron is stable under inner-core conditions.
The material properties of the Earth’s core have been better constrained by recent technical and computational advances. The properties imply that the core was once hot, but is cooling quickly, and the inner core is young.
The geomagnetic field varies on a wide range of timescales. A review of emerging research suggests that field variations on the order of tens of millions of years may be linked to changes in heat flow across the core–mantle boundary.
Satellite observations have detected localized magnetic field changes at high latitudes. Simulations suggest these changes can be explained by a westward jet in the liquid core, which has been accelerating over the past 15 years.
The Earth’s outermost core is thought to be stratified. Turbulent mixing experiments suggest that merging between the cores of projectile and planet following the Moon-forming giant impact could have produced the stratification.
Earth’s core exhibits similar elastic properties to rubber. Experiments show that a high-pressure phase of iron carbide modifies iron’s elastic properties under inner-core conditions, suggesting that carbon is the light element in the core.
Differentiated planetesimals may have delivered iron-rich material to Earth in giant impacts at the end of accretion. Impact experiments suggest that the planetesimals’ iron cores vaporized, aiding dispersal and mixing into Earth’s mantle.
The speed of seismic waves passing through the Earth’s inner core varies with direction. Analysis of earthquake seismic data suggests that this directional dependence differs between innermost and outer inner core.
The ratio of the refractory lithophile elements niobium and tantalum in the silicate Earth is anomalously low. Partitioning experiments suggest that the ratio of these elements is controlled by oxygen fugacity, and thus can be used to constrain the redox conditions of planetary accretion and core formation.
An active core dynamo may have operated on the early Moon. Extraction of palaeomagnetic pole positions on the Moon from magnetic anomalies measured by the Lunar Prospector and Kaguya orbiters suggests that the ancient lunar dynamo experienced reversals and an ancient reorientation of the Moon rotated the geographic locations of the poles.
Some mantle plumes are enriched in 3He, but the source of this primordial isotope is unclear. The partitioning behaviour of helium between silicate and iron melts—as determined by experiments—suggests that sufficient helium may have been incorporated into the core when the Earth differentiated to explain the anomalous leakage at the Earth’s surface.
The differentiation of the Earth into mantle and core implies that there is a mechanism to separate iron from silicates. Three-dimensional imaging of samples experimentally subjected to high pressures reveals that liquid iron forms interconnected melt networks at lower mantle conditions, suggesting pathways through which iron can percolate towards the core.
Earth’s inner core rotates at a different rate than the mantle, and discrepancies exist between rotation rates derived from geophysical observations and geodynamical simulations. An inverse analysis of seismic data from repeating earthquakes over the past 50 years suggests that the rotation rate of the inner core fluctuates on decadal timescales.
The observed seismic anisotropy in the Earth’s inner core has been explained by the preferential alignment of grains by plastic deformation. Measurements of the strength of iron at core pressures suggest that the inner core is weaker than previously thought and deforms by dislocation creep.