@inbook {718211,
	title = {Earth{\textquoteright}s core composition and core formation},
	booktitle = {Treatise on Geochemistry},
	year = {In Press},
	edition = {3rd},
	abstract = {The inaccessible and enigmatic core of the Earth comprises 1/3 of the planet{\textquoteright}s mass, gives rise to the magnetic field, and holds clues to the Earth{\textquoteright}s formation and the nature of its building blocks. It is comprised mainly of an Fe{\textendash}Ni alloy, plus ~10\% lighter elements whose identities and abundances remain unknown. Here we describe several distinct approaches to constraining the core{\textquoteright}s composition. A geo-/cosmochemical approach involves comparing the compositions of the bulk silicate Earth and the Earth{\textquoteright}s building blocks to determine the core{\textquoteright}s composition, especially for moderately volatile elements. High pressure{\textendash}temperature mineral physics data can be used to identify which light elements, at specific abundance levels, are able to match the core{\textquoteright}s seismic properties (e.g., density, sound velocities, liquidus phase relations). The range of light element contents can also be constrained by incorporating metal{\textendash}silicate partitioning results into models of Earth{\textquoteright}s core formation, which offers insight into not only the Earth{\textquoteright}s core composition but also the conditions and mechanisms of core formation.},
	author = {Fischer R.A. and McDonough W.F.}
}
@article {697273,
	title = {Nonlinearity of the post-spinel transition and its expression in slabs and plumes worldwide},
	year = {Submitted},
	abstract = {At the interface of Earth{\textquoteright}s upper and lower mantle, the post-spinel transition boundary controls the dynamics and morphologies of downwelling slabs and upwelling plumes, and its Clapeyron slope is hence one of the most important constraints on mantle convection. In this study, we reported a new in situ experimental dataset on phase stability in Mg2SiO4 at mantle transition zone pressures from laser-heated diamond anvil cell experiments, along with a compilation of corrected in situ experimental datasets from the literature. We presented a machine learning framework for high-pressure phase diagram determination and focused on its application to constrain the location and Clapeyron slope of the post-spinel transition: ringwoodite = bridgmanite + periclase. We found that the post-spinel boundary is nonlinear and its Clapeyron slope varies locally from {\textendash}2.3+0.6{\textendash}1.4 MPa/K at 1900 K, to {\textendash}1.0+1.3{\textendash}1.7 MPa/K at 1700 K, and to 0.0+1.7{\textendash}2.0 MPa/K at 1500 K. We applied the temperature-dependent post-spinel Clapeyron slope to estimate its lateral variation across the "660-km" seismic discontinuity in subducting slabs and hotspot-associated plumes worldwide, as well as the ambient mantle. We found that, in the present-day mantle, the average post spinel Clapeyron slope in the plumes is three times more negative than that in slabs, and we then discussed the effects of a nonlinear post-spinel transition on the dynamics of Earth{\textquoteright}s mantle.},
	url = {https://arxiv.org/abs/2208.08975},
	author = {Dong J. and Fischer R.A. and Stixrude L. and Brennan M.C. and Daviau K. and Suer T.-A. and Turner K.M. and Meng Y. and Prakapenka V.B.}
}
@article {704186,
	title = {Composition of Earth{\textquoteright}s initial atmosphere and fate of accreted volatiles set by core formation and magma ocean redox evolution},
	journal = {Earth and Planetary Science Letters},
	volume = {629},
	year = {2024},
	pages = {118618},
	abstract = {The origins of volatile depletion in the Bulk Silicate Earth (BSE) remain controversial due to the numerous processes during accretion and differentiation that can alter volatile abundances. Here, we integrate realistic impact histories from N-body simulations to determine the distribution of H, C, and N between Earth{\textquoteright}s core, mantle, and atmosphere, including loss to space, during the giant impact stage of accretion. Estimates of the BSE{\textquoteright}s volatile abundances can be matched if accreting materials were depleted \~{}1{\textendash}2 orders of magnitude relative to CI chondrite volatile abundances, indicating early volatile loss on planetesimals and embryos prior to terrestrial accretion. We find the proto-Earth{\textquoteright}s atmosphere to be dominated by CO (\&gt;97\%), which leads to the preferential erosion of C relative to H and N by subsequent impacts. Erosion can remove significant C (\~{}18{\textendash}45\% of accreted C), and potentially substantial N as well (\~{}12{\textendash}23\%), if N is not extremely siderophile at high pressures and temperatures. Out of the accreted volatiles, the majority are sequestered in the core, which is the largest reservoir of H (\~{}57{\textendash}75\%), C (\~{}54\%{\textendash}98\%), and N (\~{}69\%{\textendash}99.9\%) in the bulk Earth after accretion. Our results show that the BSE{\textquoteright}s volatile depletion relative to chondrites is dominated by loss on precursor bodies (\&gt;92\%), followed by core formation (\~{}77{\textendash}99\% of remaining \&lt;8\%), while atmosphere erosion accounts for the rest. Formation scenarios that source more material from the outer Solar System, such as Classical and Grand Tack, result in Earth analogs that have higher total volatile concentrations, lower proportions of volatiles stored in Earth analog cores, and have lost a larger fraction of their accreted C due to atmosphere erosion. The BSE{\textquoteright}s superchondritic C/N ratio can be matched or exceeded, even if Earth{\textquoteright}s building blocks have CI chondritic C/N, if N is more strongly siderophile at high pressures and temperatures. If N does not become sufficiently siderophile at high pressures and temperatures, however, Earth{\textquoteright}s building blocks must have accreted with superchondritic C/N ratios.},
	url = {https://www.sciencedirect.com/science/article/pii/S0012821X24000517?via\%3Dihub},
	author = {Gu J.T. and Peng B. and Ji X. and Zhang J. and Yang H. and Hoyos S. and Hirschmann M.M. and Kite E.S. and Fischer R.A.}
}
@article {697274,
	title = {Comparisons of the core and mantle compositions of Earth analogs from different terrestrial planet formation scenarios},
	journal = {Icarus},
	volume = {394},
	year = {2023},
	pages = {115425},
	abstract = {The chemical compositions of Earth{\textquoteright}s core and mantle provide insight into the processes that led to their formation. N-body simulations, on the other hand, generally do not contain chemical information, and seek to only reproduce the masses and orbits of the terrestrial planets. These simulations can be grouped into four potentially viable scenarios of Solar System formation (Classical, Annulus, Grand Tack, and Early Instability) for which we compile a total of 433\&nbsp;N-body simulations. We relate the outputs of these simulations to the chemistry of Earth{\textquoteright}s core and mantle using a melt-scaling law combined with a multi-stage model of core formation. We find the compositions of Earth analogs to be largely governed by the fraction of equilibrating embryo cores (kcore_emb) and the initial embryo masses in N-body simulations, rather than the simulation type, where higher values of kcore_emb and larger initial embryo masses correspond to higher concentrations of Ni, Co, Mo, and W in Earth analog mantles and higher concentrations of Si and O in Earth analog cores. As a result, larger initial embryo masses require smaller values of kcore_emb to match Earth{\textquoteright}s mantle composition. On the other hand, compositions of Earth analog cores are sensitive to the temperatures of equilibration and fO2 of accreting material. Simulation type may be important when considering magma ocean lifetimes, where Grand Tack simulations have the largest amounts of material accreted after the last giant impact. However, we cannot rule out any accretion scenarios or initial embryo masses due to the sensitivity of Earth{\textquoteright}s mantle composition to different parameters and the stochastic nature of N-body simulations. We use our compiled simulations to explore the relationship between initial embryo masses and the melting history of Earth analogs, where the complex interplay between the timing between impacts, magma ocean lifetimes, and volatile delivery could affect the compositions of Earth analogs formed from different simulation types. Comparing the last embryo impacts experienced by Earth analogs to specific Moon-forming scenarios, we find the characteristics of the Moon-forming impact are dependent on the initial conditions in N-body simulations where larger initial embryo masses promote larger and slower Moon-forming impactors. Mars-sized initial embryos are most consistent with the canonical hit-and-run scenario onto a solid mantle. Our results suggest that constraining the fraction of equilibrating impactor core (kcore) and the initial embryo masses in N-body simulations could be significant for understanding both Earth{\textquoteright}s accretion history and characteristics of the Moon-forming impact.},
	url = {https://www.sciencedirect.com/science/article/pii/S0019103523000027},
	author = {Gu J.T. and Fischer R.A. and Brennan M.C. and Clement M.S. and Jacobson S.A. and Kaib N.A. and O{\textquoteright}Brien D.P. and Raymond S.N.}
}
@inbook {681111,
	title = {Geophysical evolution during rocky planet formation},
	booktitle = {Protostars and Planets VII},
	year = {2023},
	pages = {907{\textendash}946},
	abstract = {
	Progressive astronomical characterization of planet-forming disks and rocky exoplanets highlight the need for increasing interdisciplinary efforts to understand the birth and life cycle of terrestrial worlds in a unified picture. Here, we review major geophysical and geochemical processes that shape the evolution of rocky planets and their precursor planetesimals during planetary formation and early evolution, and how these map onto the astrophysical timeline and varying accretion environments of planetary growth. The evolution of the coupled core-mantle-atmosphere system of growing protoplanets diverges in thermal, compositional, and structural states to first order, and ultimately shapes key planetary characteristics that can discern planets harboring clement surface conditions from those that do not. Astronomical campaigns seeking to investigate rocky exoplanets will require significant advances in laboratory characterization of planetary materials and time- and spatially-resolved theoretical models of planetary evolution, to extend planetary science beyond the Solar System and constrain the origins and frequency of habitable worlds like our own.



	Summary video: http://ppvii.org/chapter/25/

},
	url = {http://aspbooks.org/a/volumes/article_details/?paper_id=40774},
	author = {Lichtenberg T. and Schaefer L.K. and Nakajima M. and Fischer R.A.}
}
@article {677263,
	title = {Timing of Martian core formation from models of Hf{\textendash}W evolution coupled with N-body simulations},
	journal = {Geochimica et Cosmochimica Acta},
	volume = {316},
	year = {2022},
	pages = {295{\textendash}308},
	abstract = {
	Determining how and when Mars formed has been a long-standing challenge for planetary scientists. The size and orbit of Mars are difficult to reproduce in classical simulations of planetary accretion, and this has inspired models of inner solar system evolution that are tuned to produce Mars-like planets. However, such models are not always coupled to geochemical constraints. Analyses of Martian meteorites using the extinct hafnium{\textendash}tungsten (Hf{\textendash}W) radioisotopic system, which is sensitive to the timing of core formation, have indicated that the Martian core formed within a few million years of the start of the solar system itself. This has been interpreted to suggest that, unlike Earth{\textquoteright}s protracted accretion, Mars grew to its modern size very rapidly. These arguments, however, generally rely on simplified growth histories for Mars. Here, we combine likely accretionary histories from a large number of N-body simulations with calculations of metal{\textendash}silicate partitioning and Hf{\textendash}W isotopic evolution during core formation to constrain the range of conditions that could have produced Mars.



	We find that there is no strong correlation between the final masses or orbits of simulated Martian analogs and their 182W anomalies, and that it is readily possible to produce Mars-like Hf{\textendash}W isotopic compositions for a variety of accretionary conditions. The Hf{\textendash}W signature of Mars is very sensitive to the oxygen fugacity (fO2) of accreted material because the metal{\textendash}silicate partitioning behavior of W is strongly dependent on redox conditions. The average fO2 of Martian building blocks must fall in the range of 1.3{\textendash}1.6 log units below the iron{\textendash}w{\"u}stite buffer to produce a Martian mantle with the observed Hf/W ratio. Other geochemical properties (such as sulfur content) also influence Martian 182W signatures, but the timing of accretion is a more important control. We find that while Mars must have accreted most of its mass within ~5 million years of solar system formation to reproduce the Hf{\textendash}W isotopic constraints, it may have continued growing afterwards for over 50 million years. There is a high probability of simultaneously matching the orbit, mass, and Hf{\textendash}W signature of Mars even in cases of prolonged accretion if giant impactor cores were poorly equilibrated and merged directly with the proto-Martian core.

},
	url = {https://www.sciencedirect.com/science/article/pii/S0016703721005640?dgcid=author},
	author = {Brennan M.C. and Fischer R.A. and Nimmo F. and O{\textquoteright}Brien D.P.}
}
@article {677524,
	title = {Water storage capacity of the Martian mantle through time},
	journal = {Icarus},
	volume = {385},
	year = {2022},
	pages = {115113},
	abstract = {The water content in Earth{\textquoteright}s mantle today remains poorly constrained, but the bulk water storage capacity in the solid mantle can be quantified based on experimental data and may amount to a few times the modern surface ocean mass (OM). An appreciation of the mantle water storage capacity is indispensable to our understanding of how water may have cycled between the surface and mantle reservoirs and changed the volume of the oceans through time. In this study, we parameterized high pressure-temperature experimental data on water storage capacities in major rock-forming minerals to track the bulk water storage capacity in Earth{\textquoteright}s solid mantle as a function of temperature. We find that the mantle water storage capacity decreases as mantle potential temperature (Tp) increases, and its estimated value depends on the water storage capacity of bridgmanite in the lower mantle: 1.86{\textendash}4.41 OM with a median of 2.29 OM for today (Tp\&nbsp;=\&nbsp;1600\&nbsp;K), and 0.52{\textendash}1.69 OM with a median of 0.72 OM for the early Earth{\textquoteright}s solid mantle (for a\&nbsp;Tp\&nbsp;that was 300\&nbsp;K higher). An increase in\&nbsp;Tp\&nbsp;by 200{\textendash}300\&nbsp;K results in a decrease in the mantle water storage capacity by\&nbsp;1.19+0.9-0.16\&nbsp;{\textendash}1.56+1.1-0.22\&nbsp;OM. We explored how the volume of early oceans may have controlled sea level during the early Archean (4{\textendash}3.2\&nbsp;Ga) with some additional assumptions about early continents. We found that more voluminous surface oceans might have existed if the actual mantle water content today is\&nbsp;\&gt;\&nbsp;0.3{\textendash}0.8 OM and the early Archean\&nbsp;Tp\&nbsp;was >=1900\&nbsp;K.},
	url = {https://doi.org/10.1016/j.icarus.2022.115113},
	author = {Dong J. and Fischer R.A. and Stixrude L.P. and Lithgow-Bertelloni C.R. and Eriksen Z.T. and Brennan M.C.}
}
@article {632913,
	title = {Constraining the volume of Earth{\textquoteright}s early oceans with a temperature-dependent mantle water storage capacity model},
	journal = {AGU Advances},
	volume = {2},
	year = {2021},
	pages = {e2020AV000323},
	abstract = {The water content in Earth{\textquoteright}s mantle today remains poorly constrained, but the bulk water storage capacity in the solid mantle can be quantified based on experimental data and may amount to a few times the modern surface ocean mass (OM). An appreciation of the mantle water storage capacity is indispensable to our understanding of how water may have cycled between the surface and mantle reservoirs and changed the volume of the oceans through time. In this study, we parameterized high pressure-temperature experimental data on water storage capacities in major rock-forming minerals to track the bulk water storage capacity in Earth{\textquoteright}s solid mantle as a function of temperature. We find that the mantle water storage capacity decreases as mantle potential temperature (Tp) increases, and its estimated value depends on the water storage capacity of bridgmanite in the lower mantle: 1.86{\textendash}4.41 OM with a median of 2.29 OM for today (Tp\&nbsp;=\&nbsp;1600\&nbsp;K), and 0.52{\textendash}1.69 OM with a median of 0.72 OM for the early Earth{\textquoteright}s solid mantle (for a Tp that was 300\&nbsp;K higher). An increase in Tp by 200{\textendash}300\&nbsp;K results in a decrease in the mantle water storage capacity by 1.19 (+0.9, {\textendash}0.16) {\textendash} 1.56 (+1.1, {\textendash}0.22) OM. We explored how the volume of early oceans may have controlled sea level during the early Archean (4{\textendash}3.2\&nbsp;Ga) with some additional assumptions about early continents. We found that more voluminous surface oceans might have existed if the actual mantle water content today is\&nbsp;\&gt;\&nbsp;0.3{\textendash}0.8 OM and the early Archean Tp was >=1900\&nbsp;K.},
	url = {https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020AV000323},
	author = {Dong J. and Fischer R.A. and Stixrude L.P. and Lithgow-Bertelloni C.R.}
}
@article {651827,
	title = {Equation of state of TiN at high pressures and temperatures: A possible host for nitrogen in planetary mantles},
	journal = {Journal of Geophysical Research: Solid Earth},
	volume = {126},
	year = {2021},
	pages = {e2020JB020074},
	abstract = {
	Nitrogen, the most abundant gas in Earth{\textquoteright}s atmosphere, is also a primary component of solid nitride minerals found in meteorites and on Earth{\textquoteright}s surface. If they remain stable to high pressures and temperatures, these nitrides may also be important reservoirs of nitrogen in planetary interiors. We used synchrotron X-ray diffraction to measure the thermal equation of state and phase stability of titanium nitride (TiN) in a laser-heated diamond anvil cell at pressures up to ~70 GPa and temperatures up to ~2500 K. TiN maintains the cubic B1 (NaCl-type) crystal structure over the entire pressure and temperature range explored. It has K0 = 274(4) GPa, K0{\textquoteright} = 3.9(2), and\&nbsp;γ0 = 1.39(4) for a fixed V0 = 76.516(30) {\r A}3 (based on experimental measurements), q = 1, and θ0 = 579 K. Additionally, we collected Raman spectra of TiN up to ~60 GPa, where we find that the transverse acoustic (TA), longitudinal acoustic (LA), and transverse optical (TO) phonon modes exhibit mode Gr{\"u}neisen parameters of 1.66(17), 0.54(15), and 0.93(4), respectively. Based on our equation of state, TiN has a density of ~5.6{\textendash}6.4 g/cm3 at Earth{\textquoteright}s lower mantle conditions, significantly more dense than both the mantle of the Earth and the estimated densities of the mantles of other terrestrial planets, but less dense than planetary cores. We find that TiN remains stable against physical decomposition at the pressures and temperatures found within Earth{\textquoteright}s mantle, making it a plausible reservoir for deep planetary nitrogen if chemical conditions allow its formation.

},
	url = {https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020JB020074},
	author = {Daviau K. and Fischer R.A. and Brennan M.C. and Dong J. and Suer T.-A. and Couper S. and Meng Y. and Prakapenka V.B.}
}
@article {677771,
	title = {An experimental thermal equation of state of B2-KCl},
	journal = {Physical Review B},
	volume = {104},
	year = {2021},
	pages = {094107},
	abstract = {The alkali halides are often used as optically-transparent pressure-transmitting media and thermal insulators in laser-heated diamond anvil cell experiments. High P{\textendash}T equations of state for these materials would allow them to be used simultaneously as sensitive in situ pressure markers, making sample preparation and data analysis simpler. KCl is especially useful for this application because its high melting point, crystallographic simplicity, and low electron density are ideal for use in high-temperature X-ray diffraction experiments. However, the high-temperature static equation of state data for this material is limited in pressure to 8 GPa. As experiments routinely exceed 100 GPa in pressure and thousands of Kelvin, it is necessary for the equation of state of KCl to be determined experimentally at these conditions if it is to be used as an equation of state calibrant in the future. This work combines new high-pressure, high-temperature data of the B2 phase of KCl (up to 167 GPa and 2400 K) with the previously published room-temperature data of Dewaele et al.\&nbsp;(2012) to produce a Mie-Gr{\"u}neisen-Debye thermal equation of state for this material. The room temperature equation of state parameters are similar to those reported previously: V0 = 32.0(3) cm3/mole, K0 = 24(1) GPa and K0{\textquoteright} = 4.56(5). The thermal parameters, γ0 and q, are 2.9(4) and 1.0(1), respectively. While a  q of 1 is expected, the γ0 is higher than expected from previous calculations, lower pressure experimental data, and the available shockwave data. Thus, previously-reported equations of state underestimate the pressure of KCl at high temperatures.},
	url = {https://journals.aps.org/prb/abstract/10.1103/PhysRevB.104.094107},
	author = {Chidester B.A. and Thompson E.C. and Fischer R.A. and Heinz D.L. and Prakapenka V.B. and Meng Y. and Campbell A.J.}
}
@article {663591,
	title = {High-pressure deformation of iron{\textendash}nickel{\textendash}silicon alloys and implications for Earth{\textquoteright}s inner core},
	journal = {Journal of Geophysical Research: Solid Earth},
	volume = {126},
	year = {2021},
	pages = {e2020JB021077},
	abstract = {
	Earth{\textquoteright}s inner core exhibits strong seismic anisotropy, often attributed to the alignment of hexagonal close-packed iron (hcp-Fe) alloy crystallites with the Earth{\textquoteright}s poles. How this alignment developed depends on material properties of the alloy and is important to our understanding of the core{\textquoteright}s crystallization history and active geodynamical forcing. Previous studies suggested that hcp-Fe is weak under deep Earth conditions but did not investigate the effects of the lighter elements known to be part of the inner core alloy. Here, we present results from radial X-ray diffraction experiments in a diamond anvil cell that constrain the strength and deformation properties of iron{\textendash}nickel{\textendash}silicon (Fe{\textendash}Ni{\textendash}Si) alloys up to 60 GPa. We also show the results of laser heating to 1650 K to evaluate the effect of temperature. Observed alloy textures suggest different relative activities of the various hcp deformation mechanisms compared to pure Fe, but these textures could still account for the theorized polar alignment. Fe{\textendash}Ni{\textendash}Si alloys are mechanically stronger than Fe and Fe{\textendash}Ni; extrapolated to inner core conditions, Si-bearing alloys may be more than an order of magnitude stronger. This enhanced strength proportionally reduces the effectivity of dislocation creep as a deformation mechanism, which may suggest that texture developed during crystallization rather than as the result of post-solidification plastic flow.

},
	url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020JB021077},
	author = {Brennan M.C. and Fischer R.A. and Couper S. and Miyagi L. and Antonangeli D. and Morard G.}
}
@article {650363,
	title = {The origin of the Moon{\textquoteright}s Earth-like tungsten isotopic composition from dynamical and geochemical modeling},
	journal = {Nature Communications},
	volume = {12},
	year = {2021},
	pages = {35},
	abstract = {The Earth and Moon have identical or very similar isotopic compositions for many elements, including tungsten. However, canonical models of the Moon-forming impact predict that the Moon should be made mostly of material from the impactor, Theia. Here we evaluate the probability of the Moon inheriting its Earth-like tungsten isotopes from Theia in the canonical giant impact scenario, using 242 N-body models of planetary accretion and tracking tungsten isotopic evolution, and find that this probability is \&lt;1.6{\textendash}4.7\%. Mixing in up to 30\% terrestrial materials increases this probability, but it remains \&lt;10\%. Achieving similarity in stable isotopes is also a low-probability outcome, and is controlled by different mechanisms than tungsten. The Moon{\textquoteright}s stable isotopes and tungsten isotopic composition are anticorrelated due to redox effects, lowering the joint probability to significantly less than 0.08{\textendash}0.4\%. We therefore conclude that alternate explanations for the Moon{\textquoteright}s isotopic composition are likely more plausible.},
	url = {https://www.nature.com/articles/s41467-020-20266-1},
	author = {Fischer R.A. and Zube N.G. and Nimmo F.}
}
@article {648261,
	title = {Ancient helium and tungsten isotopic signatures preserved in mantle domains least modified by crustal recycling},
	journal = {Proceedings of the National Academy of Sciences of the U.S.A.},
	volume = {117},
	year = {2020},
	pages = {30993{\textendash}31001},
	abstract = {Rare high-3He/4He signatures in ocean island basalts (OIB) erupted at volcanic hotspots derive from deep-seated domains preserved in Earth{\textquoteright}s interior. Only high-3He/4He OIB exhibit anomalous 182W{\textemdash}an isotopic signature inherited during the earliest history of Earth{\textemdash}supporting an ancient origin of high 3He/4He. However, it is not understood why some OIB host anomalous 182W while others do not. We provide geochemical data for the highest-3He/4He lavas from Iceland (up to 42.9 times atmospheric) with anomalous 182W and examine how Sr-Nd-Hf-Pb isotopic variations{\textemdash}useful for tracing subducted, recycled crust{\textemdash}relate to high 3He/4He and anomalous 182W. These data, together with data on global OIB, show that the highest-3He/4He and the largest-magnitude 182W anomalies are found only in geochemically depleted mantle domains{\textemdash}with high 143Nd/144Nd and low 206Pb/204Pb{\textemdash}lacking strong signatures of recycled materials. In contrast, OIB with the strongest signatures associated with recycled materials have low 3He/4He and lack anomalous 182W. These observations provide important clues regarding the survival of the ancient He and W signatures in Earth{\textquoteright}s mantle. We show that high-3He/4He mantle domains with anomalous 182W have low W and 4He concentrations compared to recycled materials and are therefore highly susceptible to being overprinted with low 3He/4He and normal (not anomalous) 182W characteristic of subducted crust. Thus, high 3He/4He and anomalous 182W are preserved exclusively in mantle domains least modified by recycled crust. This model places the long-term preservation of ancient high 3He/4He and anomalous 182W in the geodynamic context of crustal subduction and recycling and informs on survival of other early-formed heterogeneities in Earth{\textquoteright}s interior.},
	url = {https://www.pnas.org/content/117/49/30993},
	author = {Jackson M.G. and Blichert-Toft J. and Halld{\'o}rsson S.A. and Mundl-Petermeier A. and Bizimis M. and Kurz M.D. and Price A.A. and Har{\dh}ardóttir S. and Willhite L.N. and Breddam K. and Becker T.W. and Fischer R.A.}
}
@article {639068,
	title = {Anomalous 182W in high 3He/4He ocean island basalts: Fingerprints of Earth{\textquoteright}s core?},
	journal = {Geochimica et Cosmochimica Acta},
	volume = {271},
	year = {2020},
	pages = {194{\textendash}211},
	abstract = {The short-lived 182Hf{\textendash}182W isotope system (t1/2 = 9 Ma) left evidence in both ancient and modern terrestrial rock record of processes that took place during the earliest stages of Earth{\textquoteright}s accretionary and differentiation history. We report {\textmu}182W values (the deviation of 182W/184W of a sample from that of laboratory standards, in parts per million) and corresponding 3He/4He ratios for rocks from 15 different hotspots. These rocks are characterized by {\textmu}182W values that range from ~0 to as low as {\textendash}23 {\textpm} 4.5. For each volcanic system that includes rocks with negative {\textmu}182W values, the values tend to be negatively correlated with 3He/4He. The W{\textendash}He isotopic characteristics of all samples can be successfully modeled via mixing involving at least three mantle source reservoirs with distinct {\textmu}182W{\textendash}3He/4He characteristics. One reservoir has 3He/4He ≈ 8 R/RA and {\textmu}182W ≈ 0, which is indistinguishable from the convecting upper mantle. Based on high 3He/4He, the other two reservoirs are presumed to be relatively un-degassed and likely primordial. One reservoir is characterized by {\textmu}182W ≈ 0, while the other is characterized by {\textmu}182W <= {\textendash}23. The former reservoir likely formed from a silicate differentiation process more than 60 Myr after the origin of the solar system, but has remained partially or wholly isolated from the rest of the mantle for most of Earth history. The latter reservoir most likely includes a component that formed while 182Hf was extant. Mass balance constraints on the isotopic composition of the core suggest it has a strongly negative {\textmu}182W value of ~ {\textendash}220. Thus, it is a candidate for the origin of the negative {\textmu}182W in the plume sources. Mixing models show that the direct addition of outer core metal into a plume rising from the core-mantle boundary would result in collateral geochemical effects, particularly in the abundances of highly siderophile elements, which are not observed in OIB. Instead, the reservoir characterized by negative {\textmu}182W most likely formed in the lowermost mantle as a result of core{\textendash}mantle isotopic equilibration. The envisioned equilibration process would raise the W concentration and lower the {\textmu}182W of the resulting silicate reservoir, relative to the rest of the mantle. The small proportion (\&lt;0.3\%) of this putative core-mantle equilibrated reservoir required to account for the {\textmu}182W signatures observed in OIB is insufficient to result in observable effects on most other elemental and/or isotopic compositions. The presumed primordial reservoirs may be linked to seismically distinct regions in the lower mantle. Seismically imaged mantle plumes appear to preferentially ascend from the vicinity of large low-shear velocity provinces (LLSVPs), which have been interpreted as thermochemical piles. We associate the LLSVPs with the primordial reservoir characterized by high 3He/4He and {\textmu}182W = 0. Smaller, ultra-low velocity zones (ULVZs) present at the core-mantle boundary have been interpreted to consist of (partially) molten lower mantle material. The negative {\textmu}182W signatures observed in some plume-derived lavas may result from small contributions of ULVZ material that has inherited its negative {\textmu}182W signature through core{\textendash}mantle equilibration.},
	url = {https://www.sciencedirect.com/science/article/pii/S001670371930777X?utm_campaign=STMJ_75273_AUTH_SERV_PPUB\&utm_medium=email\&utm_dgroup=Email1Publishing\&utm_acid=666668936\&SIS_ID=-1\&dgcid=STMJ_75273_AUTH_SERV_PPUB\&CMX_ID=\&utm_in=DM637240\&utm_source=AC_30\&u},
	author = {Mundl-Petermeier A. and Walker R.J. and Fischer R.A. and Lekic V. and Jackson M.G. and Kurz M.D.}
}
@article {637836,
	title = {The carbon content of Earth and its core},
	journal = {Proceedings of the National Academy of Sciences of the U.S.A.},
	volume = {117},
	year = {2020},
	pages = {8743{\textendash}8749},
	abstract = {Earth{\textquoteright}s core is likely the largest reservoir of carbon (C) in the planet, but its C abundance has been poorly constrained because measurements of carbon{\textquoteright}s preference for core versus mantle materials at the pressures and temperatures of core formation are lacking. Using metal{\textendash}silicate partitioning experiments in a laser-heated diamond anvil cell, we show that carbon becomes significantly less siderophile as pressures and temperatures increase to those expected in a deep magma ocean during formation of Earth{\textquoteright}s core. Based on a multistage model of core formation, the core likely contains a maximum of 0.09(4) to 0.20(10) wt\% C, making carbon a negligible contributor to the core{\textquoteright}s composition and density. However, this accounts for \~{}80 to 90\% of Earth{\textquoteright}s overall carbon inventory, which totals 370(150) to 740(370) ppm. The bulk Earth{\textquoteright}s carbon/sulfur ratio is best explained by the delivery of most of Earth{\textquoteright}s volatiles from carbonaceous chondrite-like precursors.},
	url = {https://www.pnas.org/content/117/16/8743.abstract?etoc},
	author = {Fischer R.A. and Cottrell E. and Hauri E. and Lee K.K.M. and Le Voyer M.}
}
@article {630789,
	title = {Core formation and geophysical properties of Mars},
	journal = {Earth and Planetary Science Letters},
	volume = {530},
	year = {2020},
	pages = {115923},
	abstract = {
	The chemical and physical properties of the interiors of terrestrial planets are largely determined during their formation and differentiation. Modeling a planet{\textquoteright}s formation provides important insights into the properties of its core and mantle, and conversely, knowledge of those properties may constrain formational narratives. Here, we present a multi-stage model of Martian core formation in which we calculate core{\textendash}mantle equilibration using parameterizations from high pressure{\textendash}temperature metal{\textendash}silicate partitioning experiments. We account for changing core{\textendash}mantle boundary (CMB) conditions, composition-dependent partitioning, and partial equilibration of metal and silicate, and we evolve oxygen fugacity (fO2) self-consistently. The model successfully reproduces published meteorite-based estimates of most elemental abundances in the bulk silicate Mars, which can be used to estimate core formation conditions and core composition. This composition implies that the primordial material that formed Mars was significantly more oxidized (0.9{\textendash}1.4 log units below the iron{\textendash}w{\"u}stite buffer) than that of the Earth, and that core{\textendash}mantle equilibration in Mars occurred at 42{\textendash}60\% of the evolving CMB pressure. On average, at least 84\% of accreted metal and at least 40\% of the mantle were equilibrated in each impact, a significantly higher degree of metal equilibration than previously reported for the Earth. In agreement with previous studies, the modeled Martian core is rich in sulfur (18{\textendash}19 wt\%), with less than one weight percent O and negligible Si.



	We have used these core and mantle compositions to produce physical models of the present-day Martian interior and evaluate the sensitivity of core radius to crustal thickness, mantle temperature, core composition, core temperature, and density of the core alloy. Trade-offs in how these properties affect observable physical parameters like planetary mass, radius, moment of inertia, and tidal Love number k2 define a range of likely core radii: 1620{\textendash}1870 km. Seismic velocity profiles for several combinations of model parameters have been used to predict seismic body-wave travel times and planetary normal mode frequencies. These results may be compared to forthcoming Martian seismic data to further constrain core formation conditions and geophysical properties.

},
	url = {https://www.sciencedirect.com/science/article/pii/S0012821X19306156?via\%3Dihub},
	author = {Brennan M.C. and Fischer R.A. and Irving J.C.E.}
}
@article {632932,
	title = {Constraints on terrestrial planet formation timescales and equilibration processes in the Grand Tack scenario from Hf-W isotopic evolution},
	journal = {Earth and Planetary Science Letters},
	volume = {522},
	year = {2019},
	pages = {210{\textendash}218},
	abstract = {We examine 141 N-body simulations of terrestrial planet late-stage accretion that use the Grand Tack scenario, coupling the collisional results with a hafnium-tungsten (Hf-W) isotopic evolution model. Accretion in the Grand Tack scenario results in faster planet formation than classical accretion models because of higher planetesimal surface density induced by a migrating Jupiter. Planetary embryos that grow rapidly experience radiogenic ingrowth of mantle 182W that is inconsistent with the measured terrestrial composition, unless much of the tungsten is removed by an impactor core that mixes thoroughly with the target mantle. For physically Earth-like surviving planets, we find that the fraction of equilibrating impactor core kcore >= 0.6 is required to produce results agreeing with observed terrestrial tungsten anomalies (assuming equilibration with relatively large volumes of target mantle material; smaller equilibrating mantle volumes would require even larger kcore). This requirement of substantial core re-equilibration may be difficult to reconcile with fluid dynamical predictions and hydrocode simulations of mixing during large impacts, and hence this result does not favor the rapid planet building that results from Grand Tack accretion.},
	url = {https://www.sciencedirect.com/science/article/pii/S0012821X1930384X?dgcid=coauthor},
	author = {Zube N.G. and Nimmo F. and Fischer R.A. and Jacobson S.A.}
}
@article {608362,
	title = {Effects of core formation on the Hf{\textendash}W isotopic composition of the Earth and dating of the Moon-forming impact},
	journal = {Earth and Planetary Science Letters},
	volume = {499},
	year = {2018},
	pages = {257{\textendash}265},
	abstract = {Earth{\textquoteright}s core formation set the initial compositions of the core and mantle. Various aspects of core formation, such as the degree of metal{\textendash}silicate equilibration, oxygen fugacity, and depth of equilibration, have significant consequences for the resulting compositions, yet are poorly constrained. The Hf{\textendash}W isotopic system can provide unique constraints on these aspects relative to other geochemical or geophysical methods. Here we model the Hf{\textendash}W isotopic evolution of the Earth, improving over previous studies by combining a large number of N-body simulations of planetary accretion with a core formation model that includes self-consistent evolution of oxygen fugacity and a partition coefficient of tungsten that evolves with changing pressure, temperature, composition, and oxygen fugacity. The effective average fraction of equilibrating metal is constrained to be k \&gt; 0.2 for a range of equilibrating silicate masses (for canonical accretion scenarios), and is likely \&lt;0.55 if the Moon formed later than 65 Ma. These values of k typically correspond to an effective equilibration depth of ~0.5{\textendash}0.7x the evolving core{\textendash}mantle boundary pressure as the planet grows. The average mass of equilibrating silicate was likely at least 3x the impactor{\textquoteright}s silicate mass. Equilibration temperature, initial fO2, initial differentiation time, semimajor axis, and planetary mass (above ~0.9 Earth masses) have no systematic effect on the 182W anomaly, or on fHf/W (except for fO2), when applying the constraint that the model must reproduce Earth{\textquoteright}s mantle W abundance. There are strong tradeoffs between the effects of k, equilibrating silicate mass, depth of equilibration, and timing of core formation, so the terrestrial Hf{\textendash}W isotopic system should be interpreted with caution when used as a chronometer of Earth{\textquoteright}s core formation. Because of these strong tradeoffs, the Earth{\textquoteright}s tungsten anomaly can be reproduced for Moon-forming impact timescales spanning at least 10{\textendash}175 Ma. Early Moon formation ages require a higher degree of metal{\textendash}silicate equilibration to produce Earth{\textquoteright}s 182W anomaly.},
	url = {https://www.sciencedirect.com/science/article/pii/S0012821X18304369},
	author = {Fischer R.A. and Nimmo F.}
}
@article {554151,
	title = {Equations of state and phase boundary for stishovite and CaCl2-type SiO2},
	journal = {American Mineralogist},
	volume = {103},
	year = {2018},
	pages = {792{\textendash}802},
	abstract = {Silica is thought to be present in the Earth{\textquoteright}s lower mantle in subducting plates, in addition to being a prototypical solid whose physical properties are of broad interest. It is known to undergo a phase transition from stishovite to the CaCl2-type structure at ~50{\textendash}80 GPa, but the exact location and slope of the phase boundary in pressure-temperature space is unresolved. There have been many previous studies on the equation of state of stishovite, but they span a limited range of pressures and temperatures, and there has been no thermal equation of state of CaCl2-type SiO2 measured under static conditions. We have investigated the phase diagram and equations of state of silica at 21{\textendash}89 GPa and up to ~3300 K using synchrotron X-ray diffraction in a laser-heated diamond anvil cell. The phase boundary between stishovite and CaCl2-type SiO2 can be approximately described as T = 64.6(49)*P {\textendash} 2830(350), with temperature T in Kelvin and pressure P in GPa. The stishovite data imply K0{\textquoteright} = 5.24(9) and a quasi-anharmonic T2 dependence of {\textendash}6.0(4) x 10{\textendash}6 GPa*cm3/mol/K2 for a fixed q = 1, ɣ0 = 1.71, and K0 = 302 GPa, while for the CaCl2-type phase K0 = 341(4) GPa, K0{\textquoteright} = 3.20(16), and ɣ0 = 2.14(4) with other parameters equal to their values for stishovite. The behaviors of the a and c axes of stishovite with pressure and temperature were also fit, indicating a much more compressible c axis with a lower thermal expansion as compared to the a axis. The phase transition between stishovite and CaCl2-type silica should occur at pressures of 68{\textendash}78 GPa in the Earth, depending on the temperature in subducting slabs. Silica is denser than surrounding mantle material up to pressures of 58{\textendash}68 GPa, with uncertainty due to temperature effects; at higher pressures than this, SiO2 becomes gravitationally buoyant in the lower mantle.},
	url = {https://pubs.geoscienceworld.org/msa/ammin/article-abstract/103/5/792/530659/equations-of-state-and-phase-boundary-for},
	author = {Fischer R.A. and Campbell A.J. and Chidester B.A. and Reaman D.M. and Thompson E.C. and Pigott J.S. and Prakapenka V.B. and Smith J.S.}
}
@article {554141,
	title = {High-pressure phase behavior and equations of state of ThO2 polymorphs},
	journal = {American Mineralogist},
	volume = {103},
	year = {2018},
	pages = {749{\textendash}756},
	abstract = {ThO2 is an important material for understanding the heat budget of Earth{\textquoteright}s mantle, as well as the stability of nuclear fuels at extreme conditions. We measured the in situ high-pressure, high-temperature phase behavior of ThO2 to ~60 GPa and ~2500 K. It undergoes a transition from the cubic fluorite-type structure (thorianite) to the orthorhombic α-PbCl2 cotunnite-type structure between 20 and 30 GPa at room temperature. Prior to the transition at room temperature, an increase in unit cell volume is observed, which we interpret as anion sub-lattice disorder or pre-transformation {\textquotedblleft}melting{\textquotedblright} (Boulfelfel et al., 2006). The thermal equation of state parameters for both thorianite (V0 = 26.379(7), K0 = 204(2), αKT = 0.0035(3)) and the high-pressure cotunnite-type phase (V0 = 24.75(6), K0 = 190(3), αKT = 0.0037(4)) are reported, holding K0{\textasciiacute} fixed at 4. The similarity of these parameters suggests that the two phases behave similarly within the deep Earth. The lattice parameter ratios for the cotunnite-type phase change significantly with pressure, suggesting a different structure is stable at higher pressure.},
	url = {https://pubs.geoscienceworld.org/msa/ammin/article-abstract/103/5/749/530656/high-pressure-phase-behavior-and-equations-of?redirectedFrom=fulltext},
	author = {Chidester B.A. and Pardo O.S. and Fischer R.A. and Thompson E.C. and Heinz D.L. and Prescher C. and Prakapenka V.B. and Campbell A.J.}
}
@article {554146,
	title = {Radial mixing and Ru{\textendash}Mo isotope systematics under different accretion scenarios},
	journal = {Earth and Planetary Science Letters},
	volume = {482},
	year = {2018},
	pages = {105{\textendash}114},
	abstract = {The Ru{\textendash}Mo isotopic compositions of inner Solar System bodies may reflect the provenance of accreted material and how it evolved with time, both of which are controlled by the accretion scenario these bodies experienced. Here we use a total of 116 N-body simulations of terrestrial planet accretion, run in the Eccentric Jupiter and Saturn (EJS), Circular Jupiter and Saturn (CJS), and Grand Tack scenarios, to model the Ru{\textendash}Mo anomalies of Earth, Mars, and Theia analogues. This model starts by applying an initial step function in Ru{\textendash}Mo isotopic composition, with compositions reflecting those in meteorites, and traces compositional evolution as planets accrete. The mass-weighted provenance of the resulting planets reveals more radial mixing in Grand Tack simulations than in EJS/CJS simulations, and more efficient mixing among late-accreted material than during the main phase of accretion in EJS/CJS simulations. We find that an extensive homogeneous inner disk region is required to reproduce Earth{\textquoteright}s observed Ru{\textendash}Mo composition. EJS/CJS simulations require a homogeneous reservoir in the inner disk extending to >=3{\textendash}4 AU (>=74{\textendash}98\% of initial mass) to reproduce Earth{\textquoteright}s composition, while Grand Tack simulations require a homogeneous reservoir extending to >=3{\textendash}10 AU (>=97{\textendash}99\% of initial mass), and likely to >=6{\textendash}10 AU. In the Grand Tack model, Jupiter{\textquoteright}s initial location (the most likely location for a discontinuity in isotopic composition) is \~{}3.5 AU; however, this step location has only a 33\% likelihood of producing an Earth with the correct Ru{\textendash}Mo isotopic signature for the most plausible model conditions. Our results give the testable predictions that Mars has zero Ru anomaly and small or zero Mo anomaly, and the Moon has zero Mo anomaly. These predictions are insensitive to wide variations in parameter choices.},
	url = {https://www.sciencedirect.com/science/article/pii/S0012821X17306234},
	author = {Fischer R.A. and Nimmo F. and O{\textquoteright}Brien D.P.}
}
@article {568186,
	title = {Redox evolution via gravitational differentiation on low mass planets: Implications for biosignatures, water loss, and habitability},
	journal = {The Astronomical Journal},
	volume = {155},
	year = {2018},
	pages = {195},
	abstract = {The oxidation of rocky planet surfaces and atmospheres, which arises from the twin forces of stellar nucleosynthesis and gravitational differentiation, is a universal process of key importance to habitability and exoplanet biosignature detection. Here we take a generalized approach to this phenomenon. Using a single parameter to describe redox state, we model the evolution of terrestrial planets around nearby M-stars and the Sun. Our model includes atmospheric photochemistry, diffusion and escape, line-by-line climate calculations and interior thermodynamics and chemistry. In most cases we find abiotic atmospheric O2 buildup around M-stars during the pre-main sequence phase to be much less than calculated previously, because the planet{\textquoteright}s magma ocean absorbs most oxygen liberated from H2O photolysis. However, loss of non-condensing atmospheric gases after the mantle solidifies remains a significant potential route to abiotic atmospheric O2 subsequently. In all cases, we predict that exoplanets that receive lower stellar fluxes, such as LHS1140b and TRAPPIST- 1f and g, have the lowest probability of abiotic O2 buildup and hence are the best targets for future biosignature searches. Key remaining uncertainties can be minimized in future by comparing our predictions for the atmospheres of hot, sterile exoplanets such as GJ1132b and TRAPPIST-1b and -c with observations.},
	url = {http://iopscience.iop.org/article/10.3847/1538-3881/aab608/meta},
	author = {Wordsworth R.D. and Schaefer L. and Fischer R.A.}
}
@article {554136,
	title = {Sensitivities of Earth{\textquoteright}s core and mantle compositions to accretion and differentiation processes},
	journal = {Earth and Planetary Science Letters},
	volume = {458},
	year = {2017},
	pages = {252{\textendash}262},
	abstract = {The Earth and other terrestrial planets formed through the accretion of smaller bodies, with their core and mantle compositions primarily set by metal{\textendash}silicate interactions during accretion. The conditions of these interactions are poorly understood, but could provide insight into the mechanisms of planetary core formation and the composition of Earth{\textquoteright}s core. Here we present modeling of Earth{\textquoteright}s core formation, combining results of 100 N-body accretion simulations with high pressure{\textendash}temperature metal{\textendash}silicate partitioning experiments. We explored how various aspects of accretion and core formation influence the resulting core and mantle chemistry: depth of equilibration, amounts of metal and silicate that equilibrate, initial distribution of oxidation states in the disk, temperature distribution in the planet, and target:impactor ratio of equilibrating silicate. Virtually all sets of model parameters that are able to reproduce the Earth{\textquoteright}s mantle composition result in at least several weight percent of both silicon and oxygen in the core, with more silicon than oxygen. This implies that the core{\textquoteright}s light element budget may be dominated by these elements, and is consistent with <=1{\textendash}2 wt\% of other light elements. Reproducing geochemical and geophysical constraints requires that Earth formed from reduced materials that equilibrated at temperatures near or slightly above the mantle liquidus during accretion. The results indicate a strong tradeoff between the compositional effects of the depth of equilibration and the amounts of metal and silicate that equilibrate, so these aspects should be targeted in future studies aiming to better understand core formation conditions. Over the range of allowed parameter space, core and mantle compositions are most sensitive to these factors as well as stochastic variations in what the planet accreted as a function of time, so tighter constraints on these parameters will lead to an improved understanding of Earth{\textquoteright}s core composition.},
	url = {http://www.sciencedirect.com/science/article/pii/S0012821X16305829},
	author = {Fischer R.A. and Campbell A.J. and Ciesla F.J.}
}
@book {554126,
	title = {Deep Earth: Physics and Chemistry of the Lower Mantle and Core},
	year = {2016},
	publisher = {American Geophysical Union / John Wiley and Sons},
	organization = {American Geophysical Union / John Wiley and Sons},
	abstract = {
	Deep Earth: Physics and Chemistry of the Lower Mantle and Core highlights recent advances and the latest views of the deep Earth from theoretical, experimental, and observational approaches and offers insight into future research directions on the deep Earth. In recent years, we have just reached a stage where we can perform measurements at the conditions of the center part of the Earth using state-of-the-art techniques, and many reports on the physical and chemical properties of the deep Earth have come out very recently. Novel theoretical models have been complementary to this breakthrough. These new inputs enable us to compare directly with results of precise geophysical and geochemical observations. This volume highlights the recent significant advancements in our understanding of the deep Earth that have occurred as a result, including contributions from mineral/rock physics, geophysics, and geochemistry that relate to the topics of:\&nbsp;



	I. Thermal structure of the lower mantle and core



	II. Structure, anisotropy, and plasticity of deep Earth materials



	III. Physical properties of the deep interior



	IV. Chemistry and phase relations in the lower mantle and core



	V. Volatiles in the deep Earth\&nbsp;



	The volume will be a valuable resource for researchers and students who study the Earth{\textquoteright}s interior. The topics of this volume are multidisciplinary, and therefore will be useful to students from a wide variety of fields in the Earth Sciences.\&nbsp;

},
	url = {http://onlinelibrary.wiley.com/book/10.1002/9781118992487},
	editor = {Terasaki H. and Fischer R.A.}
}
@inbook {554121,
	title = {Melting of Fe-alloys and the thermal structure of the core},
	booktitle = {Deep Earth: Physics and Chemistry of the Lower Mantle and Core},
	year = {2016},
	publisher = {American Geophysical Union / John Wiley and Sons},
	organization = {American Geophysical Union / John Wiley and Sons},
	abstract = {
	The temperature of the Earth{\textquoteright}s core has significant implications in many areas of geophysics, including applications to Earth{\textquoteright}s heat flow, core composition, age of the inner core, and energetics of the geodynamo. The temperature of the core at the inner core boundary is equal to the melting temperature of the core{\textquoteright}s Fe-rich alloy at the inner core boundary pressure. This chapter is a review of experimental results on melting temperatures of iron and Fe-rich alloys at core conditions that can thus be used to infer core temperatures. Large discrepancies exist between published melting curves for pure iron at high pressures, with better agreement on the melting behavior of Fe{\textendash}light element alloys. The addition of silicon causes a small melting point depression in iron, while oxygen and especially sulfur cause larger melting point depressions. The inner core boundary temperature likely falls in the range 5150{\textendash}6200 K, depending on the identity of the light element(s) in the core, which leads to a core{\textendash}mantle boundary temperature of 3850{\textendash}4600 K for an adiabatic outer core. The most significant sources of uncertainties in the core{\textquoteright}s thermal structure include the core{\textquoteright}s composition, phase diagram, and Gr{\"u}neisen parameter.

},
	url = {http://onlinelibrary.wiley.com/doi/10.1002/9781118992487.ch1/summary},
	author = {Fischer R.A.}
}
@article {554131,
	title = {Equation of state of pyrite to 85 GPa and 2400 K},
	journal = {American Mineralogist},
	volume = {101},
	year = {2016},
	pages = {1046{\textendash}1051},
	abstract = {The high-cosmic abundance of sulfur is not reflected in the terrestrial crust, implying it is either sequestered in the Earth{\textquoteright}s interior or was volatilized during accretion. As it has widely been suggested that sulfur could be one of the contributing light elements leading to the density deficit of Earth{\textquoteright}s core, a robust thermal equation of state of iron sulfide is useful for understanding the evolution and properties of Earth{\textquoteright}s interior. We performed X-ray diffraction measurements on FeS2 achieving pressures from 15 to 80 GPa and temperatures up to 2400 K using laser-heated diamond-anvil cells. No phase transitions were observed in the pyrite structure over the pressure and temperature ranges investigated. Combining our new P-V-T data with previously published room-temperature compression and thermochemical data, we fit a Debye temperature of 624(14) K and determined a Mie-Gr{\"u}neisen equation of state for pyrite having bulk modulus KT = 141.2(18) GPa, pressure derivative K'T = 5.56(24), Gr{\"u}neisen parameter γ0 = 1.41, anharmonic coefficient A2 = 2.53(27) {\texttimes} 10-3 J/(K2{\textperiodcentered}mol), and q = 2.06(27). These findings are compared to previously published equation of state parameters for pyrite from static compression, shock compression, and ab initio studies. This revised equation of state for pyrite is consistent with an outer core density deficit satisfied by 11.4(10) wt\% sulfur, yet matching the bulk sound speed of PREM requires an outer core composition of 4.8(19) wt\% S. This discrepancy suggests that sulfur alone cannot satisfy both seismological constraints simultaneously and cannot be the only light element within Earth{\textquoteright}s core, and so the sulfur content needed to satisfy density constraints using our FeS2 equation of state should be considered an upper bound for sulfur in the Earth{\textquoteright}s core.},
	url = {https://pubs.geoscienceworld.org/msa/ammin/article-abstract/101/5/1046/40787/Equation-of-state-of-pyrite-to-80-GPa-and-2400-K},
	author = {Thompson E.C. and Chidester B.A. and Fischer R.A. and Myers G.I. and Heinz D.L. and Prakapenka V.B. and Campbell A.J.}
}
@article {554116,
	title = {The W{\textendash}WO2 oxygen fugacity buffer (WWO) at high pressure and temperature: Implications for fO2 buffering and metal{\textendash}silicate partitioning},
	journal = {American Mineralogist},
	volume = {101},
	year = {2016},
	pages = {211{\textendash}221},
	abstract = {Synchrotron X-ray diffraction data were obtained to simultaneously measure unit-cell volumes of W and WO2 at pressures and temperatures up to 70 GPa and 2300 K. Both W and WO2 unit-cell volume data were fit to Mie-Gr{\"u}neisen equations of state; parameters for W are KT = 307 ({\textpm}0.4) GPa, K'T = 4.05 ({\textpm}0.04), γ0 = 1.61 ({\textpm}0.03), and q = 1.54 ({\textpm}0.13). Three phases were observed in WO2 with structures in the P21/c, Pnma, and C2/c space groups. The transition pressures are 4 and 32 GPa for the P21/c-Pnma and Pnma-C2/c phase changes, respectively. The P21/c and Pnma phases have previously been described, whereas the C2/c phase is newly described here. Equations of state were fitted for these phases over their respective pressure ranges yielding the parameters KT = 238 ({\textpm}7), 230 ({\textpm}5), 304 ({\textpm}3) GPa, K'T = 4 (fixed), 4 (fixed), 4 (fixed) GPa, γ0 = 1.45 ({\textpm}0.18), 1.22 ({\textpm}0.07), 1.21 ({\textpm}0.12), and q = 1 (fixed), 2.90 ({\textpm}1.5), 1 (fixed) for the P21/c, Pnma, and C2/c phases, respectively. The W-WO2 buffer (WWO) was extended to high pressure using these W and WO2 equations of state. The T-fO2 slope of the WWO buffer along isobars is positive from 1000 to 2500 K with increasing pressure up to at least 60 GPa. The WWO buffer is at a higher fO2 than the iron-w{\"u}stite (IW) buffer at pressures lower than 40 GPa, and the magnitude of this difference decreases at higher pressures. This implies an increasingly lithophile character for W at higher pressures. The WWO buffer was quantitatively applied to W metal-silicate partitioning by using the WWO-IW buffer difference in combination with literature data on W metal-silicate partitioning to model the exchange coefficient (KD) for the Fe-W exchange reaction. This approach captures the non-linear pressure dependence of W metal-silicate partitioning using the WWO-IW buffer difference. Calculation of KD along a peridotite liquidus predicts a decrease in W siderophility at higher pressures that supports the qualitative behavior predicted by the WWO-IW buffer difference, and agrees with findings of others. Comparing the competing effects of temperature and pressure the results here indicate that pressure exerts a greater effect on W metal-silicate partitioning.},
	url = {https://pubs.geoscienceworld.org/msa/ammin/article-abstract/101/1/211/40572/The-W-WO2-oxygen-fugacity-buffer-WWO-at-high},
	author = {Shofner G.A. and Campbell A.J. and Danielson L.R. and Righter K. and Fischer R.A. and Wang Y. and Prakapenka V.B.}
}
@article {554086,
	title = {High pressure metal{\textendash}silicate partitioning of Ni, Co, V, Cr, Si, and O},
	journal = {Geochimica et Cosmochimica Acta},
	volume = {167},
	year = {2015},
	pages = {177{\textendash}194},
	abstract = {The distributions of major and minor elements in Earth{\textquoteright}s core and mantle were primarily established by high pressure, high temperature metal{\textendash}silicate partitioning during core segregation. The partitioning behaviors of moderately siderophile elements can be used to constrain the pressure{\textendash}temperature conditions of core formation and the core{\textquoteright}s composition. We performed experiments to study the partitioning of Ni, Co, V, Cr, Si, and O between silicate melt and Fe-rich metallic melt in a multianvil press and diamond anvil cell, up to 100\&nbsp;GPa and 5700\&nbsp;K. Combining our new results with data from 18 previous studies, we parameterized the effects of pressure, temperature, and metallic melt composition on partitioning. Ni and Co partitioning are insensitive to composition. At low pressures, these elements become less siderophile with increasing temperature, with this trend reversing above \~{}45\&nbsp;GPa. V and Cr partitioning are much more sensitive to metallic melt composition and less sensitive to pressure. Partitioning of Si and O are insensitive to pressure, but with strong and moderate temperature dependences, respectively. Our new parameterizations of Ni and Co partitioning suggest that the Earth{\textquoteright}s distributions of these elements can be matched by single-stage core{\textendash}mantle equilibration at 54\&nbsp;{\textpm}\&nbsp;5\&nbsp;GPa and 3300{\textendash}3400\&nbsp;K. These conditions would result in 8.5\&nbsp;{\textpm}\&nbsp;1.4\&nbsp;wt\% Si and 1.6\&nbsp;{\textpm}\&nbsp;0.3\&nbsp;wt\% O in the core, compatible with the core{\textquoteright}s measured density. However, this single-stage model matches the Earth{\textquoteright}s V and Cr distributions less well. We also incorporated our parameterizations into models of multi-stage core formation over evolving pressure{\textendash}temperature{\textendash}oxygen fugacity conditions, reproducing the Earth{\textquoteright}s Ni and Co distributions while simultaneously producing a core whose light element composition is consistent with its density.},
	url = {http://www.sciencedirect.com/science/article/pii/S0016703715004093},
	author = {Fischer R.A. and Nakajima Y. and Campbell A.J. and Frost D.J. and Harries D. and Langenhorst F. and Miyajima N. and Pollok K. and Rubie D.C.}
}
@article {554111,
	title = {High-pressure, high-temperature equations of state using nanofabricated controlled-geometry Ni/SiO2/Ni double hot-plate samples},
	journal = {Geophysical Research Letters},
	volume = {42},
	year = {2015},
	pages = {10239{\textendash}10247},
	abstract = {We have fabricated novel controlled-geometry samples for the laser-heated diamond-anvil cell (LHDAC) in which a transparent oxide layer (SiO2) is sandwiched between two laser-absorbing layers (Ni) in a single, cohesive sample. The samples were mass manufactured (\&gt;104 samples) using a combination of physical vapor deposition, photolithography, and wet and plasma etching. The double hot-plate arrangement of the samples, coupled with the chemical and spatial homogeneity of the laser-absorbing layers, addresses problems of spatial temperature heterogeneities encountered in previous studies where simple mechanical mixtures of transparent and opaque materials were used. Here we report thermal equations of state (EOS) for nickel to 100 GPa and 3000 K and stishovite to 50 GPa and 2400 K obtained using the LHDAC and in situ synchrotron X-ray microdiffraction. We discuss the inner core composition and the stagnation of subducted slabs in the mantle based on our refined thermal EOS.},
	url = {http://onlinelibrary.wiley.com/doi/10.1002/2015GL066577/abstract?campaign=woletoc},
	author = {Pigott J.S. and Ditmer D.A. and Fischer R.A. and Reaman D.M. and Hrubiak R. and Meng Y. and Davis R.J. and Panero W.R.}
}
@article {554091,
	title = {The axial ratio of hcp Fe and Fe{\textendash}Ni{\textendash}Si alloys to the conditions of Earth{\textquoteright}s inner core},
	journal = {American Mineralogist},
	volume = {100},
	year = {2015},
	pages = {2718{\textendash}2724},
	abstract = {The Earth{\textquoteright}s iron-rich inner core is seismically anisotropic, which may be due to the preferred orientation of Fe-rich hexagonal close packed (hcp) alloy crystals. Elastic anisotropy in a hexagonal crystal is related to its c/a axial ratio; therefore, it is important to know how this ratio depends on volume (or pressure), temperature, and composition. Experimental data on the axial ratio of iron and alloys in the Fe{\textendash}Ni{\textendash}Si system from 15 previous studies are combined here to parameterize the effects of these variables. The axial ratio increases with increasing volume, temperature, silicon content, and nickel content. When an hcp phase coexists with another structure, sample recovery and chemical analysis from each pressure-temperature point is one method for determining the phase{\textquoteright}s composition and thus the position of the phase boundary. An alternate method is demonstrated here, using this parameterization to calculate the composition of an hcp phase whose volume, temperature, and axial ratio are measured. The hcp to hcp+B2 phase boundary in the Fe{\textendash}FeSi system is parameterized as a function of pressure, temperature, and composition, showing that a silicon-rich inner core may be an hcp+B2 mixture. These findings could help explain observations of a layered seismic anisotropy structure in the Earth{\textquoteright}s inner core.},
	url = {http://ammin.geoscienceworld.org/content/100/11-12/2718},
	author = {Fischer R.A. and Campbell A.J.}
}
@article {554051,
	title = {Dynamics of the terrestrial planets from a large number of N-body simulations},
	journal = {Earth and Planetary Science Letters},
	volume = {392},
	year = {2014},
	pages = {28{\textendash}38},
	abstract = {The agglomeration of planetary embryos and planetesimals was the final stage of terrestrial planet formation. This process is modeled using N-body accretion simulations, whose outcomes are tested by comparing to observed physical and chemical Solar System properties. The outcomes of these simulations are stochastic, leading to a wide range of results, which makes it difficult at times to identify the full range of possible outcomes for a given dynamic environment. We ran fifty high-resolution simulations each with Jupiter and Saturn on circular or eccentric orbits, whereas most previous studies ran an order of magnitude fewer. This allows us to better quantify the probabilities of matching various observables, including low probability events such as Mars formation, and to search for correlations between properties. We produce many good Earth analogues, which provide information about the mass evolution and provenance of the building blocks of the Earth. Most observables are weakly correlated or uncorrelated, implying that individual evolutionary stages may reflect how the system evolved even if models do not reproduce all of the Solar System{\textquoteright}s properties at the end. Thus individual N-body simulations may be used to study the chemistry of planetary accretion as particular accretion pathways may be representative of a given dynamic scenario even if that simulation fails to reproduce many of the other observed traits of the Solar System.},
	url = {http://www.sciencedirect.com/science/article/pii/S0012821X14000843$\#$},
	author = {Fischer R.A. and Ciesla F.J.}
}
@article {554056,
	title = {Equations of state in the Fe{\textendash}FeSi system at high pressures and temperatures},
	journal = {Journal of Geophysical Research: Solid Earth},
	volume = {119},
	year = {2014},
	pages = {2810{\textendash}2827},
	abstract = {Earth{\textquoteright}s core is an iron-rich alloy containing several weight percent of light element(s), possibly including silicon. Therefore, the high pressure-temperature equations of state of iron-silicon alloys can provide understanding of the properties of Earth{\textquoteright}s core. We performed X-ray diffraction experiments using laser-heated diamond anvil cells to achieve simultaneous high pressures and temperatures, up to ~200 GPa for Fe{\textendash}9 wt \% Si alloy and ~145 GPa for stoichiometric FeSi. We determined equations of state of the D03, hcp + B2, and hcp phases of Fe{\textendash}9Si, and the B20 and B2 phases of FeSi. We also calculated equations of state of Fe, Fe11Si, Fe5Si, Fe3Si, and FeSi using ab initio methods, finding that iron and silicon atoms have similar volumes at high pressures. By comparing our experimentally determined equations of state to the observed core density deficit, we find that the maximum amount of silicon in the outer core is ~11 wt \%, while the maximum amount in the inner core is 6{\textendash}8 wt \%, for a purely Fe-Si-Ni core. Bulk sound speeds predicted from our equations of state also match those of the inner and outer core for similar ranges of compositions. We find a compositional contrast between the inner and outer core of 3.5{\textendash}5.6 wt \% silicon, depending on the seismological model used. Theoretical and experimental equations of state agree at high pressures. We find a good match to the observed density, density profile, and sound speed of the Earth{\textquoteright}s core, suggesting that silicon is a viable candidate for the dominant light element.},
	url = {http://onlinelibrary.wiley.com/doi/10.1002/2013JB010898/abstract},
	author = {Fischer R.A. and Campbell A.J. and Caracas R. and Reaman D.M. and Heinz D.L. and Dera P. and Prakapenka V.B.}
}
@article {554081,
	title = {In situ synchrotron X-ray diffraction in the laser-heated diamond anvil cell: melting phenomena and synthesis of new materials},
	journal = {Coordination Chemistry Reviews},
	volume = {277{\textendash}278},
	year = {2014},
	pages = {15{\textendash}30},
	abstract = {The ability to produce high pressures and temperatures (P{\textendash}T), and study the physical and chemical properties of solids and melts at these conditions, is possible through the use of the laser-heated diamond anvil cell (LH-DAC). High P{\textendash}T experiments are commonly performed at synchrotron radiation facilities, where in situ X-ray diffraction (XRD) permits the detection of melting, crystallographic structural analysis, and density measurements at extreme conditions. Here we present an overview of recent experimental advances in the use of high pressure techniques in combination with laser heating and in situ X-ray diffraction. We summarize state-of-the-art capabilities, including recent advancements, in sample preparation, pressure and temperature measurements, and other technical aspects. Two main applications of the LH-DAC are discussed: the study of the melting curves of elements and compounds at high pressures, and materials synthesis at extreme conditions. The melting curves of Fe, Ta, and MgO are used as examples in a discussion of experimental techniques, technical developments, and sources of discrepancies in melting data. High P{\textendash}T syntheses of light molecular systems, superhard materials, nitrides, oxides, carbon compounds, and geologically important materials are reviewed.},
	url = {http://www.sciencedirect.com/science/article/pii/S0010854514000368},
	author = {Salamat A. and Fischer R.A. and Briggs R. and McMahon M. and Petitgirard S.}
}
@article {554046,
	title = {Phase relations in the Fe{\textendash}FeSi system at high pressures and temperatures},
	journal = {Earth and Planetary Science Letters},
	volume = {373},
	year = {2013},
	pages = {54{\textendash}64},
	abstract = {The Earth{\textquoteright}s core is comprised mostly of iron and nickel, but it also contains several weight percent of one or more unknown light elements, which may include silicon. Therefore it is important to understand the high pressure, high temperature properties and behavior of alloys in the Fe{\textendash}FeSi system, such as their phase diagrams. We determined melting temperatures and subsolidus phase relations of Fe{\textendash}9\&nbsp;wt\% Si and stoichiometric FeSi using synchrotron X-ray diffraction at high pressures and temperatures, up to ~200\&nbsp;GPa and ~145\&nbsp;GPa, respectively. Combining this data with that of previous studies, we generated phase diagrams in pressure{\textendash}temperature, temperature{\textendash}composition, and pressure{\textendash}composition space. We find the B2 crystal structure in Fe{\textendash}9Si where previous studies reported the less ordered bcc structure, and a shallower slope for the hcp+B2 to fcc+B2 boundary than previously reported. In stoichiometric FeSi, we report a wide B2+B20 two-phase field, with complete conversion to the B2 structure at ~42\&nbsp;GPa. The minimum temperature of an Fe{\textendash}Si outer core is 4380\&nbsp;K, based on the eutectic melting point of Fe{\textendash}9Si, and silicon is shown to be less efficient at depressing the melting point of iron at core conditions than oxygen or sulfur. At the highest pressures reached, only the hcp and B2 structures are seen in the Fe{\textendash}FeSi system. We predict that alloys containing more than ~4{\textendash}8\&nbsp;wt\% silicon will convert to an hcp+B2 mixture and later to the hcp structure with increasing pressure, and that an iron{\textendash}silicon alloy in the Earth{\textquoteright}s inner core would most likely be a mixture of hcp and B2 phases.},
	url = {http://www.sciencedirect.com/science/article/pii/S0012821X13002239},
	author = {Fischer R.A. and Campbell A.J. and Reaman D.M. and Miller N.A. and Heinz D.L. and Dera P. and Prakapenka V.B.}
}
@article {554041,
	title = {Equation of state and phase diagram of Fe{\textendash}16Si alloy as a candidate component of Earth{\textquoteright}s core},
	journal = {Earth and Planetary Science Letters},
	volume = {357{\textendash}358},
	year = {2012},
	pages = {268{\textendash}276},
	abstract = {The outer core of the Earth contains several weight percent of one or more unknown light elements, which may include silicon. Therefore it is critical to understand the high pressure{\textendash}temperature properties and behavior of an iron{\textendash}silicon alloy with a geophysically relevant composition (16\&nbsp;wt\% silicon). We experimentally determined the melting curve, subsolidus phase diagram, and equations of state of all phases of Fe{\textendash}16\&nbsp;wt\%Si to 140\&nbsp;GPa, finding a conversion from the D03 crystal structure to a B2+hcp mixture at high pressures. The melting curve implies that 3520\&nbsp;K is a minimum temperature for the Earth{\textquoteright}s outer core, if it consists solely of Fe{\textendash}Si alloy, and that the eutectic composition in the Fe{\textendash}Si system is less than 16\&nbsp;wt\% silicon at core{\textendash}mantle boundary conditions. Comparing our new equation of state to that of iron and the density of the core, we find that for an Fe{\textendash}Ni{\textendash}Si outer core, 11.3 {\textpm} 1.5\&nbsp;wt\% silicon would be required to match the core{\textquoteright}s observed density at the core{\textendash}mantle boundary. We have also performed first-principles calculations of the equations of state of Fe3Si with the D03 structure, hcp iron, and FeSi with the B2 structure using density-functional theory.},
	url = {http://www.sciencedirect.com/science/article/pii/S0012821X12005183},
	author = {Fischer R.A. and Campbell A.J. and Caracas R. and Reaman D.M. and Dera P. and Prakapenka V.B.}
}
@article {554001,
	title = {Equation of state and phase diagram of FeO},
	journal = {Earth and Planetary Science Letters},
	volume = {304},
	year = {2011},
	pages = {496{\textendash}502},
	abstract = {W{\"u}stite, Fe1\&nbsp;-\&nbsp;xO, is an important component in the mineralogy of Earth{\textquoteright}s lower mantle and may also be a component in the core. Therefore the high pressure, high temperature behavior of FeO, including its phase diagram and equation of state, is essential knowledge for understanding the properties and evolution of Earth{\textquoteright}s deep interior. We performed X-ray diffraction measurements using a laser-heated diamond anvil cell to achieve simultaneous high pressures and temperatures. W{\"u}stite was mixed with iron metal, which served as our pressure standard, under the assumption that negligible oxygen dissolved into the iron. Our data show a positive slope for the subsolidus phase boundary between the B1 and B8 structures, indicating that the B1 phase is stable at the P{\textendash}T conditions of the lower mantle and core. We have determined the thermal equation of state of B1 FeO to 156\&nbsp;GPa and 3100\&nbsp;K, finding an isothermal bulk modulus K0\&nbsp;=\&nbsp;149.4\&nbsp;{\textpm}\&nbsp;1.0\&nbsp;GPa and its pressure derivative K0'\&nbsp;=\&nbsp;3.60\&nbsp;{\textpm}\&nbsp;0.4. This implies that 7.7\&nbsp;{\textpm}\&nbsp;1.1\&nbsp;wt.\% oxygen is required in the outer core to match the seismologically-determined density, under the simplifying assumption of a purely Fe{\textendash}O outer core.},
	url = {http://www.sciencedirect.com/science/article/pii/S0012821X11000963},
	author = {Fischer R.A. and Campbell A.J. and Shofner G.A. and Lord O.T. and Dera P. and Prakapenka V.B.}
}
@article {554016,
	title = {Phase transition and metallization of FeO at high pressures and temperatures},
	journal = {Geophysical Research Letters},
	volume = {38},
	year = {2011},
	pages = {L24301},
	abstract = {W{\"u}stite, Fe1-xO, is an important component in the mineralogy of Earth{\textquoteright}s lower mantle and may also be a component of the core. Therefore its high pressure-temperature behavior, including its electronic structure, is essential to understanding the nature and evolution of Earth{\textquoteright}s deep interior. We performed X-ray diffraction and radiometric measurements on w{\"u}stite in a laser-heated diamond anvil cell, finding an insulator-metal transition at high pressures and temperatures. Our data show a negative slope for this apparently isostructural phase boundary, which is characterized by a volume decrease and emissivity increase. The metallic phase of FeO is stable at conditions of the lower mantle and core, which has implications for the high P-T character of Fe-O bonds, magnetic field propagation, and lower mantle conductivity},
	url = {http://onlinelibrary.wiley.com/doi/10.1029/2011GL049800/abstract},
	author = {Fischer R.A. and Campbell A.J. and Lord O.T. and Shofner G.A. and Dera P. and Prakapenka V.B.}
}
@article {553996,
	title = {High pressure melting of w{\"u}stite},
	journal = {American Mineralogist},
	volume = {95},
	year = {2010},
	pages = {1473{\textendash}1477},
	abstract = {Iron oxide (FeO) is an important component in the mineralogy of Earth{\textquoteright}s lower mantle and possibly its core, so its phase diagram is essential to models of the planet{\textquoteright}s interior. The melting curve of w{\"u}stite, Fe0.94O, was determined up to 77 GPa and 3100 K in a laser-heated diamond anvil cell. Melting transition temperatures were identified from discontinuities in the emissivity vs. temperature relationship within the laser-heated spot. The melting curve exhibits no obvious kinks that could be related to a subsolidus transition in w{\"u}stite, but there is evidence for a two-phase loop at pressures below 30 GPa. Comparison of these results to previous studies on Fe, Fe-O, and Fe-S confirms that the melting point depression in the Fe-O system remains significantly less, by a factor of 2 or more, than that in the Fe-S system up to pressures exceeding 80 GPa.},
	url = {http://ammin.geoscienceworld.org/content/95/10/1473.full?ijkey=bbA1FLzSjEggA\&keytype=ref\&siteid=gsammin},
	author = {Fischer R.A. and Campbell A.J.}
}
@article {553981,
	title = {High-precision determination of iron oxidation state in silicate glasses using XANES},
	journal = {Chemical Geology},
	volume = {268},
	year = {2009},
	pages = {167{\textendash}179},
	abstract = {Fe K-edge X-ray absorption near-edge structure (XANES) and M{\"o}ssbauer spectra were collected on natural basaltic glasses equilibrated over a range of oxygen fugacity (QFM -\&nbsp;3.5 to QFM +\&nbsp;4.5). The basalt compositions and fO2 conditions were chosen to bracket the natural range of redox conditions expected for basalts from mid-ocean ridge, ocean island, back-arc basin, and arc settings, in order to develop a high-precision calibration for the determination of Fe3+/∑Fe in natural basalts. The pre-edge centroid energy, corresponding to the 1s\&nbsp;{\textrightarrow}\&nbsp;3d transition, was determined to be the most robust proxy for Fe oxidation state, affording significant advantages compared to the use of other spectral features. A second-order polynomial models the correlation between the centroid and Fe3+/∑Fe, yielding a precision of {\textpm}\&nbsp;0.0045 in Fe3+/∑Fe for glasses with Fe3+/∑Fe\&nbsp;\&gt;\&nbsp;8\%, which is comparable to the precision of wet chemistry. This high precision relies on a Si (311) monochromator to better define the Fe2+ and Fe3+ transitions, accurate and robust modeling of the pre-edge feature, dense fO2-coverage and compositional appropriateness of reference glasses, and application of a non-linear drift correction. Through re-analysis of the reference glasses across three synchrotron beam sessions, we show that the quoted precision can be achieved (i.e., analyses are reproducible) across multiple synchrotron beam sessions, even when spectral collection conditions (detector parameters or sample geometry) change. Rhyolitic glasses were also analyzed and yield a higher centroid energy at a given Fe3+/∑Fe than basalts, implying that major variations in melt structure affect the relationship between centroid position and Fe3+/∑Fe, and that separate calibrations are needed for the determination of oxidation state in basalts and rhyolites.},
	url = {http://www.sciencedirect.com/science/article/pii/S0009254109003593?via\%3Dihub},
	author = {Cottrell E. and Kelley K.A. and Lanzirotti A.T. and Fischer R.A.}
}
@article {553941,
	title = {Phase relations of Fe{\textendash}Si alloy in Earth{\textquoteright}s core},
	journal = {Geophysical Research Letters},
	volume = {36},
	year = {2009},
	pages = {L06306},
	abstract = {Phase relations of an Fe0.85Si0.15 alloy were investigated up to 240 GPa and 3000 K using in situ X-ray diffraction in a laser-heated diamond anvil cell. An alloy of this composition as starting material is found to result in a stabilized mixture of Si-rich bcc and Si-poor hcp Fe-Si phases up to at least 150 GPa and 3000 K, whereas only hcp-Fe0.85Si0.15 is found to be stable between approximately 170 GPa and 240 GPa at high temperatures. Our extended results indicate that Fe0.85Si0.15 alloy is likely to have the hcp structure in the inner core, instead of the previously proposed mixture of hcp and bcc phases. Due to the volumetric dominance of the hcp phase in the hcp + bcc coexistence region close to the outer-core conditions, the dense closest-packed Fe-Si liquid is more relevant to understanding the properties of the outer core.},
	url = {http://onlinelibrary.wiley.com/doi/10.1029/2008GL036990/abstract},
	author = {Lin J.F. and Scott H.P. and Fischer R.A. and Chang Y.Y. and Kantor I. and Prakapenka V.B.}
}
@article {553926,
	title = {Compression of single-crystal magnesium oxide to 118 GPa and a ruby pressure gauge for helium pressure media},
	journal = {American Mineralogist},
	volume = {93},
	year = {2008},
	pages = {1823{\textendash}1828},
	abstract = {The pressure-volume equation of state (EoS) of single-crystal MgO has been studied in diamond-anvil cells loaded with helium to 118 GPa and in a non-hydrostatic KCl pressure medium to 87 GPa using monochromatic synchrotron X-ray diffraction. A third-order Birch-Murnaghan fit to the non-hydrostatic P-V data (KCl medium) yields typical results for the initial volume, V0 = 74.698(7) {\r A}3, bulk modulus, KT0 = 164(1) GPa, and pressure derivative, K' = 4.05(4), using the non-hydrostatic ruby pressure gauge of Mao et al. (1978). However, compression of MgO in helium yields V0 = 74.697(6) {\r A}3, KT0 = 159.6(6) GPa, and K' = 3.74(3) using the quasi-hydrostatic ruby gauge of Mao et al. (1986). In helium, the fitted equation of state of MgO underdetermines the pressure by 8\% at 100 GPa when compared with the primary MgO pressure scale of Zha et al. (2000), with KT0 = 160.2 GPa and K' = 4.03. The results suggest that either the compression mechanism of MgO changes above 40 GPa (in helium), or the ruby pressure gauge requires adjustment for the softer helium pressure medium. We propose a ruby pressure gauge for helium based on shift of the ruby-R1 fluorescence line (Δλ/λ 0) and the primary MgO pressure scale, with P (GPa) = A/B{[1 + (Δλ/λ0)]B - 1}, where A is fixed to 1904 GPa and B = 10.32(7).},
	url = {http://ammin.geoscienceworld.org/content/93/11-12/1823},
	author = {Jacobsen S.D. and Holl C.M. and Adams K.A. and Fischer R.A. and Martin E.S. and Bina C.R. and Lin J.F. and Prakapenka V.B. and Kubo A. and Dera P.}
}
