Core formation and core composition from coupled geochemical and geophysical constraints
James Badro1, John P Brodholt2, Hélène Piet3
1Institut de Physique du Globe de Paris, Sorbonne Paris Cité, UMR CNRS 7154, 75005 Paris, France; Earth and Planetary Science Laboratory, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland; badro@ipgp.fr.
Summary
Earth's core formed in a hot, shallow magma ocean, contrary to prior beliefs of reducing conditions. This process incorporated oxygen into the core, explaining geophysical and geochemical signatures in the core and mantle.
Area of Science:
- Geophysics
- Geochemistry
- Mineral Physics
- Seismology
Background:
- Earth's core formation left distinct geophysical and geochemical signatures in the core and mantle.
- Seismology indicates the core contains light elements, while mantle rocks show siderophile element depletion and fractionation, both inherited from metal-silicate differentiation.
Purpose of the Study:
- To jointly address core and mantle compositional signatures from core formation.
- To constrain core formation conditions satisfying both seismic and geochemical data.
Main Methods:
- Combined experimental petrology, geochemistry, and mineral physics with seismology.
- Analyzed geophysical and geochemical signatures of Earth's core and mantle.
Main Results:
- Core formation occurred in a hot magma ocean, not exceeding 1,800 km depth.
- Conditions were more oxidized than present-day Earth, with oxygen (2.7-5%) and silicon (2-3.6%) incorporated into the core.
- This model explains mantle abundances of nickel, cobalt, chromium, and vanadium.
Conclusions:
- Earth's magma ocean evolved from an oxidized to a reduced state over time.
- Oxygen incorporation into the core is a key process in early Earth evolution.
- The proposed model reconciles seismic and geochemical observations of the core and mantle.
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