Earth's accretion, core formation, and core composition /

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Bibliographic Details
Author / Creator:Fischer, Rebecca Ann, author.
Ann Arbor : ProQuest Dissertations & Theses, 2015
Description:1 electronic resource (398 pages)
Format: E-Resource Dissertations
Local Note:School code: 0330
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Other authors / contributors:University of Chicago. degree granting institution.
Notes:Includes supplementary digital materials.
Advisors: Andrew J. Campbell Committee members: Fred J. Ciesla; Nicolas Dauphas; Dion L. Heinz; Frank M. Richter.
This item is not available from ProQuest Dissertations & Theses.
Dissertation Abstracts International, Volume: 77-02(E), Section: B.
Summary:The Earth’s core has been known for over half of a century to be ∼10% less dense than pure iron due to the presence of lighter elements (e.g., Birch, 1952). While the list of possible light elements has been narrowed to a few viable candidates (Si, O, S, C, H), the composition of this light element component remains unknown. Measurements of the phase diagrams and equations of state of FeO and Fe–FeSi alloys have clarified which phases are likely to be stable under the conditions of the deep Earth and have constrained the Earth’s core to contain a maximum of ∼8 wt% oxygen or ∼11 wt% silicon. Here we present a series of experimental and numerical studies to better constrain the core’s composition, and to understand the complex interplay between the planet’s accretion, core formation, and core composition. We have measured the metal–silicate partitioning of Ni, Co, V, Cr, Si, and O to 100 GPa and 5700 K, and parameterized the partitioning behaviors of these elements as functions of pressure, temperature, and composition. Si and O both partition strongly into metal at high pressures and temperatures, which may explain the origins of the core’s light elements. We utilize a suite of 100 N-body simulations of terrestrial planet formation in our Solar System, which provide information about the mass evolution of the Earth and the provenance of its building blocks as a function of time. This information is combined with our metal–silicate partitioning data in a numerical model of Earth's core formation. We can match the core’s light element abundance and the mantle’s composition using the same modeling conditions. There is a strong tradeoff between the depth and degree of metal–silicate equilibration. The core likely contains at least a few weight percent of both silicon and oxygen, and very small amounts of other light elements, and we predict that the core contains more silicon than oxygen. This modeling can be used as a tool to explore the effects of Earth’s accretion and differentiation on its chemical evolution, and to inform choices of future studies.