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| Earth's core | |
|---|---|
| Name | Earth's core |
| Settlement type | Geological layer |
| Subdivision type | Planet |
| Subdivision name | Earth |
| Established title | Differentiation onset |
| Established date | ~4.5 billion years ago |
Earth's core is the central region of Earth lying beneath the mantle and surrounding the planet's geodynamo. It is conventionally divided into an inner solid core and an outer liquid core, and its properties control geomagnetism, mantle convection, and long-term planetary evolution. Studies of the core draw on evidence from seismology, mineralogy, geochemistry, and geophysics.
The core occupies roughly one-third of Earth by mass and about one-sixth by volume, influencing phenomena observed at the surface of the Earth, such as magnetic field variations, plate tectonics modulation, and geodynamo reversals. Research into the core leverages data from events like the Great Chilean Earthquake and instrumental networks such as the Global Seismographic Network and institutions including the United States Geological Survey and the British Geological Survey. Historical development of core theory involved contributions from figures associated with Lord Kelvin, Inge Lehmann, and the International Geophysical Year.
The outer core is predominantly molten iron with significant light elements; candidates include sulfur, oxygen, silicon, carbon, and hydrogen, informed by comparisons to iron–nickel meteorite compositions and experiments at facilities such as the Diamond Anvil Cell laboratories and beamlines at the European Synchrotron Radiation Facility. The inner core is primarily crystalline iron alloyed with nickel, inferred through analyses by researchers affiliated with Cambridge, MIT, and the Carnegie Institution for Science. Core density profiles derive from models like the Preliminary Reference Earth Model and are constrained by observations from events including the 1960 Chile earthquake and the network run by the Incorporated Research Institutions for Seismology. High-pressure phases relevant to core crystallography have been studied in contexts connected to the iron phase diagram and experiments at the Lawrence Livermore National Laboratory.
Core formation is tied to early planetary accretion and metal–silicate differentiation during impacts such as the hypothesized event linked to the formation of the Moon and the activity documented in records from the Hadean eon. Heat sources for core evolution include residual accretional heat, radiogenic heating from isotopes like uranium-238, thorium-232, and potassium-40, and latent heat released during inner core solidification; these processes are discussed in the literature associated with Jack A. van Keken and groups at the Geological Survey of Japan. Thermal history models reference events such as the Late Heavy Bombardment and integrate constraints from paleomagnetic studies at institutions like the Geological Society of America.
The outer core behaves as an electrically conducting, low-viscosity fluid with convective overturning driven by thermal and compositional buoyancy, linked to models developed at centers including Princeton University and the Max Planck Institute for Solar System Research. Viscosity and flow structures are constrained by observations of core nutation, length-of-day variations, and studies by teams at the Jet Propulsion Laboratory. Dynamic phenomena include torsional oscillations studied in collaboration with researchers at ETH Zurich and large-scale circulations that interact with the lower mantle regions beneath Africa and Pacific thermochemical anomalies identified by global mantle tomography groups such as the Research School of Earth Sciences.
The geodynamo operating in the outer core generates Earth's magnetic field via magnetohydrodynamic processes; theoretical and numerical frameworks originate from work at institutions like Los Alamos National Laboratory and the University of Leeds. Field morphology, including dipolar dominance and secular variation, is recorded in paleomagnetic archives curated by organizations such as the Smithsonian Institution and databases maintained by the World Data Center for Geomagnetism. Geomagnetic reversals and excursions are documented in stratigraphic records associated with sites studied during programs like the Integrated Ocean Drilling Program and interpreted using models influenced by research from Columbia University and the Institut de Physique du Globe de Paris.
Seismology provides the primary observational window into core structure through analyses of body waves (P and S), core-reflected phases, and normal modes recorded by networks like the Global Seismographic Network and analyzed by centers such as the Incorporated Research Institutions for Seismology. Discovery of the solid inner core followed analysis by Inge Lehmann using seismic arrivals from earthquakes like those cataloged by the International Seismological Centre. Advanced imaging techniques—full waveform inversion, seismic tomography, and core phase stacking—are applied by researchers at Caltech and ETH Zurich to resolve features such as anisotropy, inner-core layering, and ultra-low velocity zones beneath regions including the Mariana Trench and Indian Ocean.
Heat flux across the core–mantle boundary regulates mantle plume generation, lower-mantle heterogeneity, and the vigor of the geodynamo; interactions are studied in cross-disciplinary programs involving the Woods Hole Oceanographic Institution and the Scripps Institution of Oceanography. Chemical exchanges and topography at the core–mantle boundary are implicated in phenomena observed in hotspot chains like Hawaii and Iceland and in seismic anomalies beneath the African Superplume and Pacific Superswell. Numerical models from groups at Yale University and the University of California, Berkeley explore coupling mechanisms including electromagnetic coupling, gravitational coupling, and the role of post-perovskite phase transitions.