Hydrogenation of iron in the early stage of Earth’s evolution

Iizuka-Oku, Riko; Yagi, T.; Gotou, Hirotada; Okuchi, Takuo; Hattori, Takanori; Sano‐Furukawa, Asami

doi:10.1038/ncomms14096

Cited by 64 publications

(50 citation statements)

References 42 publications

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“…A monochromatic incident X‐ray beam was collimated to 6 μm (full width at half maximum). Since hydrogen escapes from solid Fe during decompression to 1 bar (Fukai & Suzuki, ; Iizuka‐Oku et al, ; Okuchi, ), hydrogen concentration in quenched liquid alloy was estimated from the volume of FeH x at high pressure and 300 K, which appeared upon quenching temperature (Figure S1 in the supporting information). The hydrogen content, x in FeH x , can be obtained

x = ((), V_{FeH italicx} - V_{Fe}) / normalΔ V_{H}

in which V Fe is the volume of Fe (Dewaele et al, ) and Δ V H is the volume increase per hydrogen atom.…”

Section: Experimental Methodsmentioning

confidence: 99%

“…in Fukai & Suzuki, ). It has been repeatedly reported that hydrogen goes away from solid Fe when it transforms into the body‐centered cubic phase upon decompression (Iizuka‐Oku et al, ; Okuchi, ). The melting temperature in the Fe‐H system is similar to that of pure Fe at 1 bar (Fukai et al, ), which means that hydrogen is neither soluble in solid nor liquid Fe at ambient pressure and therefore indicates that hydrogen originally included in iron under high pressure escapes during pressure release.…”

Section: Introductionmentioning

confidence: 99%

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Hydrogen Limits Carbon in Liquid Iron

Hirose

Tagawa

Kuwayama

et al. 2019

Geophysical Research Letters

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Melting experiments were performed on the Fe‐C‐H system to 127 GPa in a laser‐heated diamond anvil cell. On the basis of in situ and ex situ sample characterizations, we found that the solubility of carbon in liquid Fe correlates inversely with hydrogen concentration at ~60 GPa and ~3500 K, indicating that liquid Fe preferentially incorporates hydrogen rather than carbon under conditions with abundant C and H. While large amounts of both C and H may have been delivered to the growing Earth, C‐poor/H‐rich metals were likely added to the protocore in the late stages of core formation. We also obtained a melting curve of FeHx (x > 1) far beyond the pressure range in earlier determinations. Its liquidus temperature was found to be 2380 K at 135 GPa, lower than those of Fe alloyed with the other possible core light elements. Relatively low core temperature is thus supported by the presence of hydrogen.

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x = ((), V_{FeH italicx} - V_{Fe}) / normalΔ V_{H}

in which V Fe is the volume of Fe (Dewaele et al, ) and Δ V H is the volume increase per hydrogen atom.…”

Section: Experimental Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Hydrogen Limits Carbon in Liquid Iron

Hirose

Tagawa

Kuwayama

et al. 2019

Geophysical Research Letters

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“…The dissolution of hydrogen into metal droplets would have been isotopically selective, fractionating the hydrogen isotopes. Owing to the instability of iron hydrides at the low pressures at which mass spectrometry is possible, no measurements of this fractionation have been successful (Iizuka‐Oku et al, ). However, based on hydrogen dissolution into proxies at low pressures, we expect the light isotopes of hydrogen to have been selectively taken up by the metal.…”

Section: Hypothesismentioning

confidence: 99%

Origin of Earth's Water: Chondritic Inheritance Plus Nebular Ingassing and Storage of Hydrogen in the Core

Desch

Schaefer

et al. 2018

JGR Planets

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Recent developments in planet formation theory and measurements of low D/H in deep mantle material support a solar nebula source for some of Earth's hydrogen. Here we present a new model for the origin of Earth's water that considers both chondritic water and nebular ingassing of hydrogen. The largest embryo that formed Earth likely had a magma ocean while the solar nebula persisted and could have ingassed nebular gases. The model considers iron hydrogenation reactions during Earth's core formation as a mechanism for both sequestering hydrogen in the core and simultaneously fractionating hydrogen isotopes. By parameterizing the isotopic fractionation factor and initial bulk D/H ratio of Earth's chondritic material, we explore the combined effects of elemental dissolution and isotopic fractionation of hydrogen in iron. By fitting to the two key constraints (three oceans' worth of water in Earth's mantle and on its surface; and D/H in the bulk silicate Earth close to 150 × 10−6), the model searches for best solutions among ~10,000 different combinations of chondritic and nebular contributions. We find that ingassing of a small amount, typically >0–0.5 oceans of nebular hydrogen, is generally demanded, supplementing seven to eight oceans from chondritic contributions. About 60% of the total hydrogen enters the core, and attendant isotopic fractionation plausibly lowers the core's D/H to ~130 × 10−6. Crystallized magma ocean material may have D/H ≈ 110 × 10−6. These modeling results readily explain the low D/H in core‐mantle boundary material and account for Earth's inventory of solar neon and helium.

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“…Hydrogen can be incorporated into minerals in highly variable amounts. Once incorporated, the hydrogen is circulated throughout the Earth, from the surface to the deep interior, affecting the long-term evolution of the planet (Iizuka-Oku et al, 2017;Kawakatsu & Watada, 2007;Okuchi, 1997;Thompson, 1992). A major proportion of this hydrogen is currently stored within the crystal structures of dense minerals that are thermodynamically stable under the high pressures and temperatures of the deep mantle of the Earth (Ohtani, 2015;Purevjav et al, 2014Purevjav et al, , 2016Purevjav et al, , 2018Sano-Furukawa et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Strong hydrogen bonding in a dense hydrous magnesium silicate discovered by neutron Laue diffraction

Purevjav

Okuchi

Hoffmann

2020

Int Union Crystallogr J

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A large amount of hydrogen circulates inside the Earth, which affects the long-term evolution of the planet. The majority of this hydrogen is stored in deep Earth within the crystal structures of dense minerals that are thermodynamically stable at high pressures and temperatures. To understand the reason for their stability under such extreme conditions, the chemical bonding geometry and cation exchange mechanism for including hydrogen were analyzed in a representative structure of such minerals (i.e. phase E of dense hydrous magnesium silicate) by using time-of-flight single-crystal neutron Laue diffraction. Phase E has a layered structure belonging to the space group R 3 m and a very large hydrogen capacity (up to 18% H2O weight fraction). It is stable at pressures of 13–18 GPa and temperatures of up to at least 1573 K. Deuterated high-quality crystals with the chemical formula Mg2.28Si1.32D2.15O6 were synthesized under the relevant high-pressure and high-temperature conditions. The nuclear density distribution obtained by neutron diffraction indicated that the O—D dipoles were directed towards neighboring O2− ions to form strong interlayer hydrogen bonds. This bonding plays a crucial role in stabilizing hydrogen within the mineral structure under such high-pressure and high-temperature conditions. It is considered that cation exchange occurs among Mg2+, D+ and Si4+ within this structure, making the hydrogen capacity flexible.

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Hydrogenation of iron in the early stage of Earth’s evolution

Cited by 64 publications

References 42 publications

Hydrogen Limits Carbon in Liquid Iron

Hydrogen Limits Carbon in Liquid Iron

Origin of Earth's Water: Chondritic Inheritance Plus Nebular Ingassing and Storage of Hydrogen in the Core

Strong hydrogen bonding in a dense hydrous magnesium silicate discovered by neutron Laue diffraction

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