Lava worlds are a potential emerging population of Super-Earths that are on close-in orbits around their host stars, with likely partially molten mantles. To date, few studies have addressed the impact of magma on the observed properties of a planet. At ambient conditions, magma is less dense than solid rock; however, it is also more compressible with increasing pressure. Therefore, it is unclear how large-scale magma oceans affect planet observables, such as bulk density. We update
Magma oceans were once ubiquitous in the early solar system, setting up the initial conditions for different evolutionary paths of planetary bodies. In particular, the redox conditions of magma oceans may have profound influence on the redox state of subsequently formed mantles and the overlying atmospheres. The relevant redox buffering reactions, however, remain poorly constrained. Using first-principles simulations combined with thermodynamic modeling, we show that magma oceans of Earth, Mars, and the Moon are likely characterized with a vertical gradient in oxygen fugacity with deeper magma oceans invoking more oxidizing surface conditions. This redox zonation may be the major cause for the Earth’s upper mantle being more oxidized than Mars’ and the Moon’s. These contrasting redox profiles also suggest that Earth’s early atmosphere was dominated by CO2and H2O, in contrast to those enriched in H2O and H2for Mars, and H2and CO for the Moon.
more » « less- Award ID(s):
- 1764140
- NSF-PAR ID:
- 10224247
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 11
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract ExoPlex , a thermodynamically self-consistent planet interior software, to include anhydrous, hydrous (2.2 wt% H2O), and carbonated magmas (5.2 wt% CO2). We find that Earth-like planets with magma oceans larger than ∼1.5R ⊕and ∼3.2M ⊕are modestly denser than an equivalent-mass solid planet. From our model, three classes of mantle structures emerge for magma ocean planets: (1) a mantle magma ocean, (2) a surface magma ocean, and (3) one consisting of a surface magma ocean, a solid rock layer, and a basal magma ocean. The class of planets in which a basal magma ocean is present may sequester dissolved volatiles on billion-year timescales, in which a 4M ⊕mass planet can trap more than 130 times the mass of water than in Earth’s present-day oceans and 1000 times the carbon in the Earth’s surface and crust. -
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Abstract The degassing of CO2and S from arc volcanoes is fundamentally important to global climate, eruption forecasting, ore deposits, and the cycling of volatiles through subduction zones. However, all existing thermodynamic/empirical models have difficulties reproducing CO2‐H2O‐S trends observed in melt inclusions and provide widely conflicting results regarding the relationships between pressure and CO2/SO2in the vapor. In this study, we develop an open‐source degassing model, Sulfur_X, to track the evolution of S, CO2, H2O, and redox states in melt and vapor in ascending mafic‐intermediate magma. Sulfur_X describes sulfur degassing by parameterizing experimentally derived sulfur partition coefficients for two equilibria: RxnI. FeS (
m ) + H2O (v )H2S ( v ) + FeO (m), and RxnII. CaSO4(m)SO2( v ) + O2(v ) + CaO (m), based on the sulfur speciation in the melt (m ) and co‐existing vapor (v ). Sulfur_X is also the first to track the evolution off O2and sulfur and iron redox states accurately in the system using electron balance and equilibrium calculations. Our results show that a typical H2O‐rich (4.5 wt.%) arc magma with high initial S6+/ΣS ratio (>0.5) will degas much more (∼2/3) of its initial sulfur at high pressures (>200 MPa) than H2O‐poor ocean island basalts with low initial S6+/ΣS ratio (<0.1), which will degas very little sulfur until shallow pressures (<50 MPa). The pressure‐S relationship in the melt predicted by Sulfur_X provides new insights into interpreting the CO2/STratio measured in high‐T volcanic gases in the run‐up to the eruption. -
Earth’s status as the only life-sustaining planet is a result of the timing and delivery mechanism of carbon (C), nitrogen (N), sulfur (S), and hydrogen (H). On the basis of their isotopic signatures, terrestrial volatiles are thought to have derived from carbonaceous chondrites, while the isotopic compositions of nonvolatile major and trace elements suggest that enstatite chondrite–like materials are the primary building blocks of Earth. However, the C/N ratio of the bulk silicate Earth (BSE) is superchondritic, which rules out volatile delivery by a chondritic late veneer. In addition, if delivered during the main phase of Earth’s accretion, then, owing to the greater siderophile (metal loving) nature of C relative to N, core formation should have left behind a subchondritic C/N ratio in the BSE. Here, we present high pressure-temperature experiments to constrain the fate of mixed C-N-S volatiles during core-mantle segregation in the planetary embryo magma oceans and show that C becomes much less siderophile in N-bearing and S-rich alloys, while the siderophile character of N remains largely unaffected in the presence of S. Using the new data and inverse Monte Carlo simulations, we show that the impact of a Mars-sized planet, having minimal contributions from carbonaceous chondrite-like material and coinciding with the Moon-forming event, can be the source of major volatiles in the BSE.more » « less
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null (Ed.)Volatiles including carbon and hydrogen are generally considered to be more soluble in silicate melts than in mantle rocks. How these melts contribute to the storage and distribution of key volatiles in Earth's interior today and during its early evolution, however, remains largely unknown. It is essential to improve our knowledge about volatiles-bearing silicate magmas over the entire mantle pressure regime. Here we investigate molten Mg FexSiO3 ( , 0.25) containing both carbon and hydrogen using first-principles molecular dynamics simulations. Our results show that the dissolution mechanism of the binary volatiles in melts varies considerably under different conditions of pressure and redox. When incorporated as CO2 and H2O components (corresponding to oxidizing conditions) almost all carbon and hydrogen form bonds with oxygen. Their speciation at low pressure consists of predominantly isolated molecular CO2, carbonates, and hydroxyls. More oxygenated species, including tetrahedrally coordinated carbons, hydrogen (O-H-O) bridges, various oxygen-joined complexes appear as melt is further compressed. When two volatiles are incorporated as hydrocarbons CH4 and C2H6 (corresponding to reducing conditions), hydroxyls are prevalent with notable presence of molecular hydrogen. Carbon-oxygen bonding is almost completely suppressed. Instead carbon is directly correlated with itself, hydrogen, and silicon. Both volatiles also show strong affinity to iron. Reduced volatile speciation thus involves polymerized complexes comprising of carbon, hydrogen, silicon, and iron, which can be mostly represented by two forms: C1−4H1−5Si0−5O0−2 (iron-free) and C5−8H1−8Si0−6Fe5−8O0−2. The calculated partial molar volumes of binary volatiles in their oxidized and reduced incorporation decrease rapidly initially with pressure and then gradually at higher pressures, thereby systematically lowering silicate melt density. Our assessment of the calculated opposite effects of the volatile components and iron on melt density indicates that melt-crystal density crossovers are possible in the present-day mantle and also could have occurred in early magma ocean environments. Melts at upper mantle and transition zone conditions likely dissolve carbon and hydrogen in a wide variety of oxidized and non-oxygenated forms. Deep-seated partial melts and magma ocean remnants at lower mantle conditions may exsolve carbon as complex reduced species possibly to the core during core-mantle differentiation while retaining a majority of hydrogen as hydroxyls-associated species.more » « less
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Abstract The emergence of oxygenic photosynthesis created a new niche with dramatic potential to transform energy flow through Earth’s biosphere. However, more primitive forms of photosynthesis that fix CO2into biomass using electrons from reduced species like Fe(II) and H2instead of water would have competed with Earth’s early oxygenic biosphere for essential nutrients. Here, we combine experimental microbiology, genomic analyses, and Earth system modeling to demonstrate that competition for light and nutrients in the surface ocean between oxygenic phototrophs and Fe(II)-oxidizing, anoxygenic photosynthesizers (photoferrotrophs) translates into diminished global photosynthetic O2release when the ocean interior is Fe(II)-rich. These results provide a simple ecophysiological mechanism for inhibiting atmospheric oxygenation during Earth’s early history. We also find a novel positive feedback within the coupled C-P-O-Fe cycles that can lead to runaway planetary oxygenation as rising atmospheric
p O2sweeps the deep ocean of the ferrous iron substrate for photoferrotrophy.
