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| Bulk silicate Earth | |
|---|---|
| Name | Bulk silicate Earth |
| Caption | Conceptual model of Earth's silicate mantle and crust |
| Type | planetary reservoir |
| Composition | silicates, oxides, trace metals |
| Mass | ~4.0×10^24 kg (silicate portion) |
| Parent | Earth |
Bulk silicate Earth is the hypothetical silicate portion of Earth defined as the planet excluding the core. It represents the combined mantle and crust reservoirs used in models of planetary differentiation, mantle convection, and global geochemical cycles. Estimates of its composition, mass, and trace-element inventory underpin studies in cosmochemistry, geochronology, and planetary formation.
The Bulk silicate Earth (BSE) concept is central to comparative studies of Earth's mantle, continental crust, and oceanic crust composition, referencing elemental and isotopic budgets after core formation and before crustal extraction. Models of the BSE are tied to constraints from meteorite groups such as CI chondrite, enstatite chondrite, and ordinary chondrite, as well as high-pressure experiments performed at facilities like the Diamond Anvil Cell and multi-anvil press. Interpretations of BSE composition rely on data from samples and observations involving mid-ocean ridge basalt, ocean island basalt, and mantle-derived xenoliths collected in regions including Hawaii, Iceland, and the East Pacific Rise.
BSE composition is typically expressed in terms of major oxides—silicon dioxide, magnesium oxide, iron oxide, aluminum oxide, calcium oxide—and trace elements including sodium, potassium, rare earth elements (REE), and siderophile elements such as nickel and cobalt. Comparative reference frames invoke abundances normalized to CI chondrite or solar nebula values to assess volatile depletion and refractory element fractionation. Geochemical classifications reference lithophile, siderophile, and chalcophile element behavior, constrained by experimental partition coefficients determined in studies by researchers affiliated with institutions like the Carnegie Institution for Science and the Institut de Physique du Globe de Paris.
BSE represents the outcome of early planetary processes including accretion, giant impacts—notably the scenario often invoked to explain the formation of the Moon—and metal–silicate core–mantle differentiation. High-temperature equilibration, core segregation, and magma ocean crystallization scenarios tie BSE chemistry to models developed following the work of scientists at centers such as the California Institute of Technology and Massachusetts Institute of Technology. Volatile delivery and loss during accretion are evaluated with respect to dynamical frameworks like the Nice model and Grand Tack hypothesis for solar system evolution.
Quantitative BSE models include mass balance approaches and inverse modeling that use mantle-compatible element concentrations and crustal extraction estimates from compilations by agencies like the United States Geological Survey and research consortia including the Deep Carbon Observatory. Prominent BSE estimates are those of the McDonough and Sun model and subsequent revisions incorporating seismic tomography, geoneutrino flux constraints from detectors such as KamLAND and Borexino, and heat flow inventories compiled by organizations like the International Heat Flow Commission.
Isotopic systems—samarium–neodymium, rubidium–strontium, uranium–lead, hafnium–tungsten, and oxygen isotopes—provide chronological and source-fingerprint constraints on BSE formation and mantle differentiation. Radiogenic isotope ratios measured in zircon from the Jack Hills and mantle-derived rocks inform timing of crust formation and mantle homogenization episodes during the Hadean and Archean eons. Isotopic anomalies compared with meteoritic reservoirs are interpreted in literature stemming from teams at institutions including the Smithsonian Institution and the Max Planck Institute for Chemistry.
The BSE mineralogical assemblage reflects pressure–temperature-dependent phases such as olivine, pyroxene, garnet, bridgmanite (formerly magnesium silicate perovskite), and post-perovskite in the lowermost mantle. Elastic properties and density profiles are constrained by seismological models like the Preliminary Reference Earth Model and investigations at laboratories such as Lawrence Livermore National Laboratory. Thermodynamic databases and phase equilibria studies by researchers affiliated with GEOSCIENCES departments worldwide support interpretations of mantle melting, solidus relations, and the source mineralogy of basalt genesis beneath mid-ocean ridges and hotspots.
BSE composition informs broader questions in planetary science such as the distribution of volatiles (water, carbon, nitrogen) among terrestrial planets, the origin of the atmosphere and hydrosphere, and comparative planetology involving Mercury, Venus, and Mars. Constraints from BSE studies feed into models of core formation energetics, long-term geodynamic evolution including plate tectonics, and the thermal budget assessed via radiogenic heat-producing elements like uranium, thorium, and potassium-40. Cross-disciplinary collaborations between universities and research institutes such as University of California, Berkeley and ETH Zurich continue to refine BSE estimates with implications for exoplanetary compositions studied by missions like Kepler and observatories including the European Southern Observatory.
Category:Earth sciences Category:Geochemistry Category:Planetary formation