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| Open AccessInner core static tilt inferred from intradecadal oscillation in the Earth’s rotation
A static tilt of some 0.17° between the rotation axes of the solid inner core and the mantle is inferred from the observed approximate 8.5 year periodic inner core wobble in both polar motion and length-of-day variations of the Earth’s rotation.
- Yachong An
- , Hao Ding
- & Weiping Jiang
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| Open AccessLate Cambrian geomagnetic instability after the onset of inner core nucleation
An 80 thousand-year-long period of extreme non-geocentric dipole magnetic fields is recorded in Late Cambrian carbonate rocks of South China, suggesting that 495 million years ago Earth’s inner core had not grown large enough to stabilize the dynamo.
- Yong-Xiang Li
- , John A. Tarduno
- & Zhenyu Yang
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| Open AccessAn estimate of absolute shear-wave speed in the Earth’s inner core
Observations of seismic waves that traverse the Earth’s inner core as shear waves are critical to understand inner core properties. Here, the authors present several seismological observations of shear waves and estimate an absolute shear wave speed in the inner core.
- Thuany Costa de Lima
- , Thanh-Son Phạm
- & Hrvoje Tkalčić
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| Open AccessUp-to-fivefold reverberating waves through the Earth’s center and distinctly anisotropic innermost inner core
This study presents hitherto unreported multiply-reverberating seismic body waves through the Earth’s center. Their travel times confirm a distinct internal shell within the inner core, existing possibly due to a past change in the inner core growth.
- Thanh-Son Phạm
- & Hrvoje Tkalčić
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| Open AccessSound velocity of hexagonal close-packed iron to the Earth’s inner core pressure
New constraints on the composition of Earth’s inner core are provided by experimental verification of Birch’s law for hexagonal close-packed iron to pressure above 300 gigapascals, about double the pressure achieved in previous investigations
- Daijo Ikuta
- , Eiji Ohtani
- & Alfred Q. R. Baron
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| Open AccessNitrogen isotope evidence for Earth’s heterogeneous accretion of volatiles
How and when Earth acquired its major volatiles N-C-H-S remains unclear. Here the authors show that Earth may have acquired its major volatiles from both reduced and oxidized impactors before and during the Moon-forming giant impact.
- Lanlan Shi
- , Wenhua Lu
- & Yuan Li
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| Open AccessEarly Cambrian renewal of the geodynamo and the origin of inner core structure
New single crystal paleointensity data show that the geomagnetic field was renewed in the early Cambrian after near collapse in the Ediacaran Period. This implies that the innermost/outermost structure of the inner core formed 450 million yrs. ago.
- Tinghong Zhou
- , John A. Tarduno
- & Frank Padgett III
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| Open AccessPrimitive noble gases sampled from ocean island basalts cannot be from the Earth’s core
Li et al. established a liquid-liquid partition model based on ab initio calculations to reveal that He and Ne strongly fractionate during core-mantle separation, which concludes the primitive volatiles seen in hotspots cannot be from the core.
- Yunguo Li
- , Lidunka Vočadlo
- & John P. Brodholt
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| Open AccessStratification in planetary cores by liquid immiscibility in Fe-S-H
Yokoo et al. find the liquid immiscibility between H-rich and S-rich liquids Fe above 20 GPa. The separation of immiscible liquids could explain the disappearance of Mars’ magnetic field and the formation of low-velocity layer atop the Earth’s core.
- Shunpei Yokoo
- , Kei Hirose
- & Yasuo Ohishi
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| Open AccessInner core composition paradox revealed by sound velocities of Fe and Fe-Si alloy
The origin of the observed low shear wave velocity in the solid inner core is unclear. Here, the authors report shear wave velocities of iron and iron-silicon alloy under Earth’s core conditions by shock compression and find that neither the effect of temperature nor incorporation of Si can explain observed low shear wave velocity in the inner core.
- Haijun Huang
- , Lili Fan
- & Yingwei Fei
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| Open AccessThe Fe-FeSi phase diagram at Mercury’s core conditions
The iron-silicon phase diagram has been established at the conditions of Mercury’s core. The resulting phase diagram is remarkably complex, and presents an array of new mechanisms which may power Mercury’s inner dynamo.
- E. Edmund
- , G. Morard
- & D. Antonangeli
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| Open AccessReconciling metal–silicate partitioning and late accretion in the Earth
Through platinum metal-silicate partitioning coefficient measurements, the authors here show that platinum partitioning into metal is lowered at high pressure–temperature conditions. This finding implies that the Earth’s mantle was likely enriched in platinum immediately following the core-mantle differentiation.
- Terry-Ann Suer
- , Julien Siebert
- & Guillaume Fiquet
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| Open AccessThe origin of the Moon’s Earth-like tungsten isotopic composition from dynamical and geochemical modeling
Tungsten isotopes between the Earth and Moon are compared in this new study. The authors find that traditional models of Moon formation are very unlikely to reproduce the Moon's Earth-like isotopic composition.
- Rebecca A. Fischer
- , Nicholas G. Zube
- & Francis Nimmo
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| Open AccessQuantitative estimates of average geomagnetic axial dipole dominance in deep geological time
This study describes how the geomagnetic axial dipole dominance of Earth’s magnetic field remained stable through large parts of the geological time. Since other characteristics of the geomagnetic field have changed substantially on the same timescales, this new observation provides a challenge for future core modeling studies.
- Andrew J. Biggin
- , Richard K. Bono
- & Pavel V. Doubrovine
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| Open AccessRapid geomagnetic changes inferred from Earth observations and numerical simulations
The authors here use numerical simulations combined with a time-dependent model of Earth’s magnetic field spanning the last 100 kyrs. They identify field directional changes to be 10 times faster than previously thought.
- Christopher J. Davies
- & Catherine G. Constable
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| Open AccessLow thermal conductivity of iron-silicon alloys at Earth’s core conditions with implications for the geodynamo
Thermal conductivity of Earth’s core affects Earth’s thermal structure, evolution and dynamics. Based on thermal conductivity measurements of iron–silicon alloys at high pressure and temperature conditions, the authors here propose Earth’s inner core could be older than previously expected.
- Wen-Pin Hsieh
- , Alexander F. Goncharov
- & Jung-Fu Lin
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| Open AccessA silicate dynamo in the early Earth
Cooling of the iron core in the early Earth may have been too slow to allow for the generation of a magnetic field. Based on quantum mechanical and geodynamical modelling approaches, the authors find that the electrical conductivity of silicate liquid at high pressure and temperature conditions could have been sufficient to generate a silicate dynamo and a magnetic field in the early Earth.
- Lars Stixrude
- , Roberto Scipioni
- & Michael P. Desjarlais
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| Open AccessLow viscosity of the Earth’s inner core
The inner core of the Earth is formed of a crystalline solid which is mostly composed of iron. Here, the authors use molecular dynamics methods to show that the crystalline structure of the inner core may have a viscosity close to that of liquid iron, despite being a solid.
- Anatoly B. Belonoshko
- , Jie Fu
- & Maurizio Mattesini
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| Open AccessMercury’s anomalous magnetic field caused by a symmetry-breaking self-regulating dynamo
A new regime of planetary magnetic fields was revealed through the MESSENGER spacecraft mission to Mercury. Here, the authors present a numerical dynamo model that can re-produce both the axisymmetric and anomalously axially offset dipolar magnetic field of Mercury.
- Futoshi Takahashi
- , Hisayoshi Shimizu
- & Hideo Tsunakawa
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| Open AccessIron diapirs entrain silicates to the core and initiate thermochemical plumes
During planetary formation segregation of an iron core from rocky silicates takes place. Here, the authors use analogue fluid experiments show that iron diapirs entrain volatiles and silicates to the Earth’s core and initiate buoyant thermochemical plumes to reoxidize and hydrate the upper mantle and atmosphere.
- J. R. Fleck
- , C. L. Rains
- & P. L. Olson
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| Open AccessSeismological evidence for a localized mushy zone at the Earth’s inner core boundary
The existence of a mushy zone in the Earth’s inner core has been suggested, but has remained unproven. Here, the authors have discovered a 4–8 km thick mushy zone at the inner core boundary beneath the Okhotsk Sea, indicating that there may be more localized mushy zones at the inner core boundary.
- Dongdong Tian
- & Lianxing Wen
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| Open AccessExploring the hidden interior of the Earth with directional neutrino measurements
The detection of Earth’s anti neutrino emission from potassium and the mantle remain elusive. Here the authors propose a method for measuring potassium and mantle geo-neutrinos by detecting their elastic scattering on electrons with direction-sensitive detectors.
- Michael Leyton
- , Stephen Dye
- & Jocelyn Monroe
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| Open AccessGeomagnetic spikes on the core-mantle boundary
Rapid and spatially localized geomagnetic field variations around 1000 BC are hard to reconcile with expected field behaviour arising from the core dynamo. Here, the authors show that the intensity spike is consistent with an intense flux patch on the core-mantle boundary (8–22°) located under Saudi Arabia.
- Christopher Davies
- & Catherine Constable
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| Open AccessIron isotopic fractionation between silicate mantle and metallic core at high pressure
Terrestrial basalts have a unique iron isotopic signature taken as fingerprints of core formation. Here, high pressure studies show that force constants of iron bonds increase with pressure similarly for silicate and metals suggesting interplanetary isotopic variability is not due to core formation.
- Jin Liu
- , Nicolas Dauphas
- & Jung-Fu Lin
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| Open AccessHydrogenation of iron in the early stage of Earth’s evolution
The Earth’s core has lower density than pure iron and many studies have looked into which light elements may be present. The authors here carry outin situhigh pressure and temperature neutron experiments indicating that hydrogen may have been the first light element to dissolve into the iron core.
- Riko Iizuka-Oku
- , Takehiko Yagi
- & Asami Sano-Furukawa
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| Open AccessCarbon-depleted outer core revealed by sound velocity measurements of liquid iron–carbon alloy
The composition of the Earth's core, particularly the light elements present, is not well constrained. Here, the authors report sound velocities of liquid iron-carbon alloy as measured at very high pressures using inelastic X-ray scattering and suggest that carbon cannot be predominant in the outer core.
- Yoichi Nakajima
- , Saori Imada
- & Alfred Q. R. Baron