Nebular ingassing as a source of volatiles to the Terrestrial planets

Sharp, Zachary D.

doi:10.1016/j.chemgeo.2016.11.018

Cited by 60 publications

(33 citation statements)

References 199 publications

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“…To explain the low 3 He/ 22 Ne ratios and solar-like 20 Ne/ 22 Ne ratios of ≥12.9 in plumes, Tucker & Mukhopadhyay (2014) proposed ingassing of nebular gas from a gravitationally accreted nebular atmosphere into a magma ocean, a hypothesis previously proposed based on He abundances and Ne isotopes (Harper & Jacobsen 1996, Mizuno et al 1980, Mukhopadhyay 2012, Porcelli et al 2001, Sharp 2017, Yokochi & Marty 2004. Ingassing of nebular gases into a magma ocean would raise the 3 He/ 22 Ne ratio of the magma ocean from the nebular value of 1.5 to values of ∼2-3 because of the He/Ne solubility ratio of ∼2 in the magma ocean.…”

Section: Magma Ocean Signaturesmentioning

confidence: 99%

Noble Gases: A Record of Earth's Evolution and Mantle Dynamics

Mukhopadhyay

Parai

2019

Annu. Rev. Earth Planet. Sci.

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Noble gases have played a key role in our understanding of the origin of Earth's volatiles, mantle structure, and long-term degassing of the mantle. Here we synthesize new insights into these topics gained from high-precision noble gas data. Our analysis reveals new constraints on the origin of the terrestrial atmosphere, the presence of nebular neon but chondritic krypton and xenon in the mantle, and a memory of multiple giant impacts during accretion. Furthermore, the reservoir supplying primordial noble gases to plumes appears to be distinct from the mid-ocean ridge basalt (MORB) reservoir since at least 4.45 Ga. While differences between the MORB mantle and plume mantle cannot be explained solely by recycling of atmospheric volatiles, injection and incorporation of atmospheric-derived noble gases into both mantle reservoirs occurred over Earth history. In the MORB mantle, the atmospheric-derived noble gases are observed to be heterogeneously distributed, reflecting inefficient mixing even within the vigorously convecting MORB mantle. ▪ Primordial noble gases in the atmosphere were largely derived from planetesimals delivered after the Moon-forming giant impact. ▪ Heterogeneities dating back to Earth's accretion are preserved in the present-day mantle. ▪ Mid-ocean ridge basalts and plume xenon isotopic ratios cannot be related by differential degassing or differential incorporation of recycled atmospheric volatiles. ▪ Differences in mid-ocean ridge basalts and plume radiogenic helium, neon, and argon ratios can be explained through the lens of differential long-term degassing.

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Section: Magma Ocean Signaturesmentioning

confidence: 99%

Noble Gases: A Record of Earth's Evolution and Mantle Dynamics

Mukhopadhyay

Parai

2019

Annu. Rev. Earth Planet. Sci.

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“…Depending on the sizes of the target embryo and impactors, a surface magma ocean could have been local, hemispheric, or global. This predicted coexistence of a surface magma ocean and nebula-originated protoatmosphere strongly implies ingassing, the dissolution of nebular gases into the underlying magma ocean, a scenario also recently investigated by Sharp (2017).…”

Section: Ingassing Of Hydrogen Into a Magma Oceanmentioning

confidence: 99%

“…This consensus view implicitly makes two assumptions, which may or may not be justified. First, with few exceptions (Hirschmann et al, ; Ikoma & Genda, ; Sasaki, ; Sharp, ), most models discount the contributions to Earth's hydrogen from ingassing of nebular H 2 and H 2 O. But in fact, it has long been recognized from noble gas isotopic ratios that Earth's interior contains some He and Ne contributed from the solar nebula (Harper & Jacobsen, ; Marty, ; Pepin, ).…”

Section: Introductionmentioning

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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“…Trace element abundances of highly siderophile elements pervasive in the Earth’s upper mantle 31 , 32 indicate partial metal−silicate equilibration and suggest low oxygen fugacity prior to metal descent to the core 13 , 33 – 36 . Atmospheric hydrogen was removed after the solar nebula dissipated 37 . Oxidation and hydration of the mantle is considered to be a later event, coming from several possible sources including hydrogen degassing or late stage arrival of highly hydrated and oxidized meteorites 6 .…”

Section: Introductionmentioning

confidence: 99%

“…An internal model suggests that disproportionation reactions involving perovskite produce Fe +3 in the lower mantle, which is then transported into the upper mantle by convection 33 . Late stage increase in mantle oxidation may also contribute to the late appearance of the oxygen atmosphere 37 , 40 . Recent petrologic methods using vanadium as an oxybarometer 41 indicates the rise in atmospheric oxygen is a gradual process leading up to the great oxygen event 42 and may be linked to mantle convective processes or inner core growth.…”

Section: Introductionmentioning

confidence: 99%

Iron diapirs entrain silicates to the core and initiate thermochemical plumes

et al. 2018

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Segregation of the iron core from rocky silicates is a massive evolutionary event in planetary accretion, yet the process of metal segregation remains obscure, due to obstacles in simulating the extreme physical properties of liquid iron and silicates at finite length scales. We present new experimental results studying gravitational instability of an emulsified liquid gallium layer, initially at rest at the interface between two glucose solutions. Metal settling coats liquid metal drops with a film of low density material. The emulsified metal pond descends as a coherent Rayleigh−Taylor instability with a trailing fluid-filled conduit. Scaling to planetary interiors and high pressure mineral experiments indicates that molten silicates and volatiles are entrained toward the iron core and initiate buoyant thermochemical plumes that later oxidize and hydrate the upper mantle. Surface volcanism from thermochemical plumes releases oxygen and volatiles linking atmospheric growth to the Earth’s mantle and core processes.

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Nebular ingassing as a source of volatiles to the Terrestrial planets

Cited by 60 publications

References 199 publications

Noble Gases: A Record of Earth's Evolution and Mantle Dynamics

Noble Gases: A Record of Earth's Evolution and Mantle Dynamics

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

Iron diapirs entrain silicates to the core and initiate thermochemical plumes

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