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Zhang B, Ni S, Wu W, Shen Z, Wang W, Sun D, Wu Z. Small-scale layered structures at the inner core boundary. Nat Commun 2023; 14:6362. [PMID: 37821477 PMCID: PMC10567691 DOI: 10.1038/s41467-023-42177-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2023] [Accepted: 10/02/2023] [Indexed: 10/13/2023] Open
Abstract
The fine-scale seismic features near the inner core boundary (ICB) provide critical insights into the thermal, chemical, and geodynamical interactions between liquid and solid cores, and may shed light on the evolution mechanism of the Earth's core. Here, we utilize a dataset of pre-critical PKiKP waveforms to constrain the fine structure at the ICB, considering the influence of various factors such as source complexity, structural anomalies in the mantle, and properties at the ICB. Our modeling suggests a sharp ICB beneath Mongolia and most of Northeast Asia, but a locally laminated ICB structure beneath Central Asia, Siberia, and part of Northeast Asia. The complex ICB structure might be explained by either the existence of a kilometer-scale thickness of mushy zone, or the localized coexistence of bcc and hcp iron phase at the ICB. We infer that there may be considerable lateral variations in the dendrites growing process at ICB, probably due to the complicated thermochemical and geodynamical interaction between the outer and inner core.
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Affiliation(s)
- Baolong Zhang
- State Key Laboratory of Geodesy and Earth's Dynamics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan, 430077, China
- CAS Center for Excellence in Deep Earth Science, Guangzhou, China
| | - Sidao Ni
- State Key Laboratory of Geodesy and Earth's Dynamics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan, 430077, China.
| | - Wenbo Wu
- Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA, 02543, USA
| | - Zhichao Shen
- Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA, 02543, USA
| | - Wenzhong Wang
- Laboratory of Seismology and Physics of Earth's Interior, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, 230026, China
| | - Daoyuan Sun
- Laboratory of Seismology and Physics of Earth's Interior, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, 230026, China
| | - Zhongqing Wu
- Laboratory of Seismology and Physics of Earth's Interior, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, 230026, China
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2
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Fu S, Chariton S, Prakapenka VB, Shim SH. Core origin of seismic velocity anomalies at Earth's core-mantle boundary. Nature 2023; 615:646-651. [PMID: 36792829 DOI: 10.1038/s41586-023-05713-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2022] [Accepted: 01/06/2023] [Indexed: 02/17/2023]
Abstract
Seismic studies have found fine-scale anomalies at the core-mantle boundary (CMB), such as ultralow velocity zones (ULVZs)1,2 and the core rigidity zone3,4. ULVZs have been attributed to mantle-related processes5-10, but little is known about a possible core origin. The precipitation of light elements in the outer core has been proposed to explain the core rigidity zone3, but it remains unclear what processes can lead to such precipitation. Despite its importance for the outer core11, the melting behaviour of Fe-Si-H at relevant pressure-temperature conditions is not well understood. Here we report observations of the crystallization of B2 FeSi from Fe-9wt%Si melted in the presence of hydrogen up to 125 GPa and 3,700 K by using laser-heated diamond anvil cells. Hydrogen dramatically increases the Si concentration in the B2 crystals to a molar ratio of Si:Fe ≈ 1, whereas it mostly remains in the coexisting Fe liquid. The high Si content in the B2 phase makes it stable in a solid form at the outermost core temperatures and less dense than the surrounding liquids. Consequently, the Si-rich crystallites could form, float and be sedimented to the underside of the CMB interface, and that well explains the core side rigidity anomalies3,4. If a small amount of the FeSi crystals can be incorporated into the mantle, they would form dense low-velocity structures above the CMB, which may account for some ULVZs10. The B2 FeSi precipitation promoted by H in the outermost core provides a single core-driven origin for two types of anomalies at the CMB. Such a scenario could also explain the core-like tungsten isotope signatures in ocean island basalts12, after the materials equilibrated with the precipitates are entrained to the uppermost mantle by the mantle plumes connected to ULVZs.
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Affiliation(s)
- Suyu Fu
- School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA.
- Department of Earth and Planetary Science, The University of Tokyo, Tokyo, Japan.
| | - Stella Chariton
- Center for Advanced Radiation Sources, The University of Chicago, Chicago, IL, USA
| | - Vitali B Prakapenka
- Center for Advanced Radiation Sources, The University of Chicago, Chicago, IL, USA
| | - Sang-Heon Shim
- School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA.
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3
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High geomagnetic field intensity recorded by anorthosite xenoliths requires a strongly powered late Mesoproterozoic geodynamo. Proc Natl Acad Sci U S A 2022; 119:e2202875119. [PMID: 35858328 PMCID: PMC9304012 DOI: 10.1073/pnas.2202875119] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
Abstract
Acquiring high-fidelity ancient magnetic field intensity records from rocks is crucial for constraining the long-term evolution of Earth’s core. However, robust estimates of ancient field strengths are often difficult to recover due to alteration or nonideal behavior. We use rocks known as anorthosite that formed in the deep crust and were brought to the near surface where they acquired thermal remanent magnetizations. These rocks have experienced minimal postformation alteration and yield high-quality paleointensity estimates. In contrast to scenarios of a progressively decaying field leading up to a proposed late nucleation of Earth’s inner core, these data record a strong field 1.1 Ga. A strong field that persisted over a 14-My interval indicates the existence of appreciable power sources for Earth’s dynamo at this time. Obtaining estimates of Earth’s magnetic field strength in deep time is complicated by nonideal rock magnetic behavior in many igneous rocks. In this study, we target anorthosite xenoliths that cooled and acquired their magnetization within ca. 1,092 Ma shallowly emplaced diabase intrusions of the North American Midcontinent Rift. In contrast to the diabase which fails to provide reliable paleointensity estimates, the anorthosite xenoliths are unusually high-fidelity recorders yielding high-quality, single-slope paleointensity results that are consistent at specimen and site levels. An average value of ∼83 ZAm2 for the virtual dipole moment from the anorthosite xenoliths, with the highest site-level values up to ∼129 ZAm2, is higher than that of the dipole component of Earth’s magnetic field today and rivals the highest values in the paleointensity database. Such high intensities recorded by the anorthosite xenoliths require the existence of a strongly powered geodynamo at the time. Together with previous paleointensity data from other Midcontinent Rift rocks, these results indicate that a dynamo with strong power sources persisted for more than 14 My ca. 1.1 Ga. These data are inconsistent with there being a progressive monotonic decay of Earth’s dynamo strength through the Proterozoic Eon and could challenge the hypothesis of a young inner core. The multiple observed paleointensity transitions from weak to strong in the Paleozoic and the Proterozoic present challenges in identifying the onset of inner core nucleation based on paleointensity records alone.
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4
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Lipman J, Fergusson L, Bonshek A, Schneider RH. Managing the Built Environment for Health Promotion and Disease Prevention With Maharishi Vastu Architecture: A Review. Glob Adv Health Med 2022; 11:2164957X221077084. [PMID: 35558577 PMCID: PMC9087237 DOI: 10.1177/2164957x221077084] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2021] [Accepted: 01/13/2022] [Indexed: 11/15/2022] Open
Abstract
Background and objectives The evolution of healthcare from 18th-century reductionism to 21st-century postgenomic holism has been described in terms of systems medicine, and the impact of the built environment on human health is the focus of investigation and development, leading to the new specialty of evidence-based, therapeutic architecture. The traditional system of Vāstu architecture-a design paradigm for buildings which is proposed to promote mental and physical health-has been applied and studied in the West in the last 20 years, and features elements absent from other approaches. This review critically evaluates the theory and research of a well-developed, standardized form of Vāstu-Maharishi Vastu® architecture (MVA). MVA's principles include development of the architect's consciousness, universal recommendations for building orientation, siting, and dimensions; placement of key functions; and occupants' head direction when sleeping or performing tasks. The effects of isolated Vāstu elements included in MVA are presented. However, the full value of MVA, documented as a systematic, globally applicable practice, is in the effect of its complete package, and thus this review of MVA includes evaluating the experience of living and working in MVA buildings. Methods The published medical and health-related literature was systematically surveyed for research on factors related to isolated principles applied in MVA as well as on the complete system. Results Published research suggests that incorporating MVA principles into buildings correlates with significant improvements in occupants' physical and mental health and quality of life: better sleep, greater happiness of children, and the experience of heightened sense of security and reduced stress. The frequency of burglaries, a social determinant of health, also correlates. Potential neurophysiological mechanisms are described. Conclusions Findings suggest that MVA offers an actionable approach for managing a key social determinant of health by using architectural design as preventive medicine and in public health.
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Affiliation(s)
- Jon Lipman
- Institute for Vedic Architecture,
Maharishi International University, Fairfield, IA, USA
| | - Lee Fergusson
- Professor, Maharishi Vedic Research
Institute, Gold Coast, AU-QLD, Australia
| | - Anna Bonshek
- Professor, Maharishi Vedic Research
Institute, Gold Coast, AU-QLD, Australia
| | - Robert H. Schneider
- College of Integrative Medicine, Maharishi International
University, Fairfield, IA, USA
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5
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Thermal conductivity of Fe-Si alloys and thermal stratification in Earth's core. Proc Natl Acad Sci U S A 2022; 119:2119001119. [PMID: 34969863 PMCID: PMC8740763 DOI: 10.1073/pnas.2119001119] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/16/2021] [Indexed: 11/18/2022] Open
Abstract
Light elements in Earth's core play a key role in driving convection and influencing geodynamics, both of which are crucial to the geodynamo. However, the thermal transport properties of iron alloys at high-pressure and -temperature conditions remain uncertain. Here we investigate the transport properties of solid hexagonal close-packed and liquid Fe-Si alloys with 4.3 and 9.0 wt % Si at high pressure and temperature using laser-heated diamond anvil cell experiments and first-principles molecular dynamics and dynamical mean field theory calculations. In contrast to the case of Fe, Si impurity scattering gradually dominates the total scattering in Fe-Si alloys with increasing Si concentration, leading to temperature independence of the resistivity and less electron-electron contribution to the conductivity in Fe-9Si. Our results show a thermal conductivity of ∼100 to 110 W⋅m-1⋅K-1 for liquid Fe-9Si near the topmost outer core. If Earth's core consists of a large amount of silicon (e.g., > 4.3 wt %) with such a high thermal conductivity, a subadiabatic heat flow across the core-mantle boundary is likely, leaving a 400- to 500-km-deep thermally stratified layer below the core-mantle boundary, and challenges proposed thermal convection in Fe-Si liquid outer core.
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6
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Li Q, Sun T, Zhang YG, Xian JW, Vočadlo L. Atomic transport properties of liquid iron at conditions of planetary cores. J Chem Phys 2021; 155:194505. [PMID: 34800959 DOI: 10.1063/5.0062081] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Atomic transport properties of liquid iron are important for understanding the core dynamics and magnetic field generation of terrestrial planets. Depending on the sizes of planets and their thermal histories, planetary cores may be subject to quite different pressures (P) and temperatures (T). However, previous studies on the topic mainly focus on the P-T range associated with the Earth's outer core; a systematic study covering conditions from small planets to massive exoplanets is lacking. Here, we calculate the self-diffusion coefficient D and viscosity η of liquid iron via ab initio molecular dynamics from 7.0 to 25 g/cm3 and 1800 to 25 000 K. We find that D and η are intimately related and can be fitted together using a generalized free volume model. The resulting expressions are simpler than those from previous studies where D and η were treated separately. Moreover, the new expressions are in accordance with the quasi-universal atomic excess entropy (Sex) scaling law for strongly coupled liquids, with normalized diffusivity D⋆ = 0.621 exp(0.842Sex) and viscosity η⋆ = 0.171 exp(-0.843Sex). We determine D and η along two thermal profiles of great geophysical importance: the iron melting curve and the isentropic line anchored at the ambient melting point. The variations of D and η along these thermal profiles can be explained by the atomic excess entropy scaling law, demonstrating the dynamic invariance of the system under uniform time and space rescaling. Accordingly, scale invariance may serve as an underlying mechanism to unify planetary dynamos of different sizes.
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Affiliation(s)
- Qing Li
- Key Laboratory of Computational Geodynamics, College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Tao Sun
- Key Laboratory of Computational Geodynamics, College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yi-Gang Zhang
- Key Laboratory of Computational Geodynamics, College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Jia-Wei Xian
- Laboratory of Computational Physics, Institute of Applied Physics and Computational Mathematics, Beijing 100088, China
| | - Lidunka Vočadlo
- Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, United Kingdom
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7
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Kralj S, Marchesan S. Bioinspired Magnetic Nanochains for Medicine. Pharmaceutics 2021; 13:1262. [PMID: 34452223 PMCID: PMC8398308 DOI: 10.3390/pharmaceutics13081262] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2021] [Revised: 08/12/2021] [Accepted: 08/13/2021] [Indexed: 12/12/2022] Open
Abstract
Superparamagnetic iron oxide nanoparticles (SPIONs) have been widely used for medicine, both in therapy and diagnosis. Their guided assembly into anisotropic structures, such as nanochains, has recently opened new research avenues; for instance, targeted drug delivery. Interestingly, magnetic nanochains do occur in nature, and they are thought to be involved in the navigation and geographic orientation of a variety of animals and bacteria, although many open questions on their formation and functioning remain. In this review, we will analyze what is known about the natural formation of magnetic nanochains, as well as the synthetic protocols to produce them in the laboratory, to conclude with an overview of medical applications and an outlook on future opportunities in this exciting research field.
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Affiliation(s)
- Slavko Kralj
- Department for Materials Synthesis, Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
- Department of Pharmaceutical Technology, Faculty of Pharmacy, University of Ljubljana, Aškerčeva 7, 1000 Ljubljana, Slovenia
| | - Silvia Marchesan
- Department of Chemical and Pharmaceutical Sciences, University of Trieste, 34127 Trieste, Italy;
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8
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Turneaure SJ, Sharma SM, Gupta YM. Crystal Structure and Melting of Fe Shock Compressed to 273 GPa: In Situ X-Ray Diffraction. PHYSICAL REVIEW LETTERS 2020; 125:215702. [PMID: 33274960 DOI: 10.1103/physrevlett.125.215702] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2020] [Accepted: 10/23/2020] [Indexed: 05/25/2023]
Abstract
Despite extensive shock wave and static compression experiments and corresponding theoretical work, consensus on the crystal structure and the melt boundary of Fe at Earth's core conditions is lacking. We present in situ x-ray diffraction measurements in laser-shock compressed Fe that establish the stability of the hexagonal-close-packed (hcp) structure along the Hugoniot through shock melting, which occurs between ∼242 to ∼247 GPa. Using previously reported hcp Fe Hugoniot temperatures, the melt temperature is estimated to be 5560(360) K at 242 GPa, consistent with several reported Fe melt curves. Extrapolation of this value suggests ∼6400 K melt temperature at Earth's inner core boundary pressure.
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Affiliation(s)
- Stefan J Turneaure
- Institute for Shock Physics, Washington State University, Pullman, Washington 99164, USA
| | - Surinder M Sharma
- Institute for Shock Physics, Washington State University, Pullman, Washington 99164, USA
| | - Y M Gupta
- Institute for Shock Physics, Washington State University, Pullman, Washington 99164, USA
- Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164, USA
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9
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Dagnall N, Drinkwater KG, O’Keeffe C, Ventola A, Laythe B, Jawer MA, Massullo B, Caputo GB, Houran J. Things That Go Bump in the Literature: An Environmental Appraisal of "Haunted Houses". Front Psychol 2020; 11:1328. [PMID: 32595577 PMCID: PMC7304295 DOI: 10.3389/fpsyg.2020.01328] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2020] [Accepted: 05/19/2020] [Indexed: 01/05/2023] Open
Abstract
This paper contains a narrative overview of the past 20-years of environmental research on anomalous experiences attributed to "haunted house." This exercise served as a much-needed update to an anthology of noteworthy overviews on ghosts, haunts, and poltergeists (Houran and Lange, 2001b). We also considered whether new studies had incorporated certain recommendations made in this anthology. Our search revealed a relative paucity of studies (n = 66) on environmental factors that ostensibly stimulate haunt-type experiences. This literature was diverse and often lacked methodological consistency and adherence to the prior suggestions. However, critical consideration of the content revealed a recurring focus on six ambient variables: embedded (static) cues, lighting levels, air quality, temperature, infrasound, and electromagnetic fields. Their relation to the onset or structure of witness reports showed mostly null, though sometimes inconsistent or weak outcomes. However, such research as related to haunts is arguably in its infancy and new designs are needed to account better for environmental and architectural phenomenology. Future studies should therefore address four areas: (i) more consistent and precise measurements of discrete ambient variables; (ii) the potential role of "Gestalt influences" that involve holistic environment-person interactions; (iii) individual differences in attentional or perceptual sensitivities of percipients to environmental variables; and (iv) the role of attitudinal and normative influences in the interpretation of environmental stimuli. Focused scrutiny on these issues should clarify the explanatory power of evolutionary-environmental models for these and related anomalous experiences.
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Affiliation(s)
- Neil Dagnall
- Department of Psychology, Manchester Campus, Manchester Metropolitan University, Manchester, United Kingdom
| | - Kenneth G. Drinkwater
- Department of Psychology, Manchester Campus, Manchester Metropolitan University, Manchester, United Kingdom
| | - Ciarán O’Keeffe
- School of Human & Social Sciences, Buckinghamshire New University, Buckinghamshire, United Kingdom
| | | | - Brian Laythe
- Institute for the Study of Religious and Anomalous Experience, Jeffersonville, IN, United States
| | | | | | | | - James Houran
- Laboratory for Statistics and Computation, ISLA—Instituto Politécnico de Gestão e Tecnologia, Vila Nova de Gaia, Portugal
- Integrated Knowledge Systems, Dallas, TX, United States
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10
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Adeleke AA, Yao Y. Formation of Stable Compounds of Potassium and Iron under Pressure. J Phys Chem A 2020; 124:4752-4763. [DOI: 10.1021/acs.jpca.0c03330] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Adebayo A. Adeleke
- Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2, Canada
| | - Yansun Yao
- Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2, Canada
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11
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Belonoshko AB, Fu J, Bryk T, Simak SI, Mattesini M. Low viscosity of the Earth's inner core. Nat Commun 2019; 10:2483. [PMID: 31171778 PMCID: PMC6554349 DOI: 10.1038/s41467-019-10346-2] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2018] [Accepted: 05/08/2019] [Indexed: 11/10/2022] Open
Abstract
The Earth's solid inner core is a highly attenuating medium. It consists mainly of iron. The high attenuation of sound wave propagation in the inner core is at odds with the widely accepted paradigm of hexagonal close-packed phase stability under inner core conditions, because sound waves propagate through the hexagonal iron without energy dissipation. Here we show by first-principles molecular dynamics that the body-centered cubic phase of iron, recently demonstrated to be thermodynamically stable under the inner core conditions, is considerably less elastic than the hexagonal phase. Being a crystalline phase, the body-centered cubic phase of iron possesses the viscosity close to that of a liquid iron. The high attenuation of sound in the inner core is due to the unique diffusion characteristic of the body-centered cubic phase. The low viscosity of iron in the inner core enables the convection and resolves a number of controversies.
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Affiliation(s)
- Anatoly B Belonoshko
- Department of Physics, AlbaNova University Center, Royal Institute of Technology (KTH), 106 91, Stockholm, Sweden.
| | - Jie Fu
- Faculty of Science, Department of Physics, Ningbo University, 315211, Ningbo, China
| | - Taras Bryk
- Institute for Condensed Matter Physics, National Academy of Sciences of Ukraine, Lviv, 79011, Ukraine
| | - Sergei I Simak
- Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-58183, Linköping, Sweden
| | - Maurizio Mattesini
- Department of Earth's Physics and Astrophysics, Complutense University of Madrid, E-28040, Madrid, Spain
- Instituto de Geociencias (UCM-CSIC), Facultad de Ciencias Físicas, Plaza de Ciencias 1, 28040, Madrid, Spain
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12
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13
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Chou YM, Jiang X, Liu Q, Hu HM, Wu CC, Liu J, Jiang Z, Lee TQ, Wang CC, Song YF, Chiang CC, Tan L, Lone MA, Pan Y, Zhu R, He Y, Chou YC, Tan AH, Roberts AP, Zhao X, Shen CC. Multidecadally resolved polarity oscillations during a geomagnetic excursion. Proc Natl Acad Sci U S A 2018; 115:8913-8918. [PMID: 30126998 PMCID: PMC6130337 DOI: 10.1073/pnas.1720404115] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Polarity reversals of the geomagnetic field have occurred through billions of years of Earth history and were first revealed in the early 20th century. Almost a century later, details of transitional field behavior during geomagnetic reversals and excursions remain poorly known. Here, we present a multidecadally resolved geomagnetic excursion record from a radioisotopically dated Chinese stalagmite at 107-91 thousand years before present with age precision of several decades. The duration of geomagnetic directional oscillations ranged from several centuries at 106-103 thousand years before present to millennia at 98-92 thousand years before present, with one abrupt reversal transition occurring in one to two centuries when the field was weakest. These features indicate prolonged geodynamo instability. Repeated asymmetrical interhemispheric polarity drifts associated with weak dipole fields likely originated in Earth's deep interior. If such rapid polarity changes occurred in future, they could severely affect satellites and human society.
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Affiliation(s)
- Yu-Min Chou
- High-Precision Mass Spectrometry and Environment Change Laboratory, Department of Geosciences, National Taiwan University, 10617 Taipei, Taiwan, Republic of China;
- Department of Ocean Science and Engineering, Southern University of Science and Technology, 518055 Shenzhen, People's Republic of China
| | - Xiuyang Jiang
- Key Laboratory of Humid Subtropical Eco-Geographical Processes, Ministry of Education, College of Geography Science, Fujian Normal University, 350117 Fuzhou, People's Republic of China
| | - Qingsong Liu
- Department of Ocean Science and Engineering, Southern University of Science and Technology, 518055 Shenzhen, People's Republic of China
- Laboratory for Marine Geology, Qingdao National Oceanography Laboratory for Science and Technology, 266237 Qingdao, People's Republic of China
| | - Hsun-Ming Hu
- High-Precision Mass Spectrometry and Environment Change Laboratory, Department of Geosciences, National Taiwan University, 10617 Taipei, Taiwan, Republic of China
| | - Chung-Che Wu
- High-Precision Mass Spectrometry and Environment Change Laboratory, Department of Geosciences, National Taiwan University, 10617 Taipei, Taiwan, Republic of China
| | - Jianxing Liu
- Laboratory for Marine Geology, Qingdao National Oceanography Laboratory for Science and Technology, 266237 Qingdao, People's Republic of China
- Key Laboratory of Marine Sedimentology and Environmental Geology, First Institute of Oceanography, State Oceanic Administration, 266061 Qingdao, People's Republic of China
| | - Zhaoxia Jiang
- College of Marine Geosciences, Ocean University of China, 266100 Qingdao, People's Republic of China
| | - Teh-Quei Lee
- Institute of Earth Sciences, Academia Sinica, 11529 Taipei, Taiwan, Republic of China
| | - Chun-Chieh Wang
- National Synchrotron Radiation Research Center, 30076 Hsinchu, Taiwan, Republic of China
| | - Yen-Fang Song
- National Synchrotron Radiation Research Center, 30076 Hsinchu, Taiwan, Republic of China
| | - Cheng-Cheng Chiang
- National Synchrotron Radiation Research Center, 30076 Hsinchu, Taiwan, Republic of China
| | - Liangcheng Tan
- State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, 710061 Xi'an, People's Republic of China
- Institute of Global Environmental Change, Xi'an Jiaotong University, 710049 Xi'an, People's Republic of China
| | - Mahjoor A Lone
- High-Precision Mass Spectrometry and Environment Change Laboratory, Department of Geosciences, National Taiwan University, 10617 Taipei, Taiwan, Republic of China
| | - Yongxin Pan
- Institute of Geology and Geophysics, Chinese Academy of Sciences, 100029 Beijing, People's Republic of China
| | - Rixiang Zhu
- Institute of Geology and Geophysics, Chinese Academy of Sciences, 100029 Beijing, People's Republic of China
| | - Yaoqi He
- College of Tourism and Air Service, Guizhou Minzu University, 550025 Guiyang, People's Republic of China
| | - Yu-Chen Chou
- High-Precision Mass Spectrometry and Environment Change Laboratory, Department of Geosciences, National Taiwan University, 10617 Taipei, Taiwan, Republic of China
| | - An-Hung Tan
- Department of Mechanical Engineering, Chien Hsin University of Science and Technology, 32097 Taoyuan, Taiwan, Republic of China
| | - Andrew P Roberts
- Research School of Earth Sciences, Australian National University, Canberra, ACT 2601, Australia
| | - Xiang Zhao
- Research School of Earth Sciences, Australian National University, Canberra, ACT 2601, Australia
| | - Chuan-Chou Shen
- High-Precision Mass Spectrometry and Environment Change Laboratory, Department of Geosciences, National Taiwan University, 10617 Taipei, Taiwan, Republic of China;
- Research Center for Future Earth, National Taiwan University, 10617 Taipei, Taiwan, Republic of China
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14
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Monserrat B, Martinez-Canales M, Needs RJ, Pickard CJ. Helium-Iron Compounds at Terapascal Pressures. PHYSICAL REVIEW LETTERS 2018; 121:015301. [PMID: 30028166 DOI: 10.1103/physrevlett.121.015301] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2017] [Revised: 01/08/2018] [Indexed: 06/08/2023]
Abstract
We investigate the binary phase diagram of helium and iron using first-principles calculations. We find that helium, which is a noble gas and inert at ambient conditions, forms stable crystalline compounds with iron at terapascal pressures. A FeHe compound becomes stable above 4 TPa, and a FeHe_{2} compound above 12 TPa. Melting is investigated using molecular dynamics simulations, and a superionic phase with sublattice melting of the helium atoms is predicted. We discuss the implications of our predicted helium-iron phase diagram for interiors of giant (exo)planets and white dwarf stars.
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Affiliation(s)
- Bartomeu Monserrat
- Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854-8019, USA
- TCM Group, Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Miguel Martinez-Canales
- Scottish Universities Physics Alliance, School of Physics and Astronomy, The University of Edinburgh, Edinburgh EH9 3FD, United Kingdom
- Centre for Science at Extreme Conditions, The University of Edinburgh, Edinburgh EH9 3FD, United Kingdom
| | - Richard J Needs
- TCM Group, Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Chris J Pickard
- Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
- Advanced Institute for Materials Research, Tohoku University 2-1-1 Katahira, Aoba, Sendai 980-8577, Japan
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15
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An early geodynamo driven by exsolution of mantle components from Earth's core. Nature 2016; 536:326-8. [PMID: 27437583 PMCID: PMC4998958 DOI: 10.1038/nature18594] [Citation(s) in RCA: 111] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2016] [Accepted: 05/16/2016] [Indexed: 11/17/2022]
Abstract
Terrestrial core formation occurred in the early molten Earth by
gravitational segregation of immiscible metal and silicate melts, stripping
iron-loving elements from the silicate mantle to the metallic core1–3, and leaving rock-loving components behind. Here we performed
experiments showing that at high enough temperature, Earth’s major
rock-loving component, magnesium oxide, can also dissolve in core-forming
metallic melts. Our data clearly point to a dissolution reaction, and are in
agreement with recent DFT calculations4.
Using core formation models5, we further
show that a high-temperature event during Earth’s accretion (such as the
Moon-forming giant impact6) can contribute
significant amounts of magnesium to the early core. As it subsequently cools,
the ensuing exsolution7 of buoyant
magnesium oxide generates a substantial amount of gravitational energy. This
energy is comparable to if not significantly higher than that produced by inner
core solidification8 — the primary
driver of the Earth’s current magnetic field9–11. Since
the inner core is too young12 to explain
the existence of an ancient field prior to ~1 billion years, our results
solve the conundrum posed by the recent paleomagnetic observation13 of an ancient field at least 3.45 Gyr
old.
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16
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Zhang Y, Sekine T, He H, Yu Y, Liu F, Zhang M. Experimental constraints on light elements in the Earth's outer core. Sci Rep 2016; 6:22473. [PMID: 26932596 PMCID: PMC4773879 DOI: 10.1038/srep22473] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2015] [Accepted: 02/16/2016] [Indexed: 11/09/2022] Open
Abstract
Earth's outer core is liquid and dominantly composed of iron and nickel (~5-10 wt%). Its density, however, is ~8% lower than that of liquid iron, and requires the presence of a significant amount of light element(s). A good way to specify the light element(s) is a direct comparison of density and sound velocity measurements between seismological data and those of possible candidate compositions at the core conditions. We report the sound velocity measurements of a model core composition in the Fe-Ni-Si system at the outer core conditions by shock-wave experiments. Combining with the previous studies, we found that the best estimate for the outer core's light elements is ~6 wt% Si, ~2 wt% S, and possible ~1-2.5 wt% O. This composition satisfies the requirements imposed by seismology, geochemistry, and some models of the early core formation. This finding may help us to further constrain the thermal structure of the Earth and the models of Earth's core formation.
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Affiliation(s)
- Youjun Zhang
- Department of Earth and Planetary Systems Science, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima 739-8526, Japan
| | - Toshimori Sekine
- Department of Earth and Planetary Systems Science, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima 739-8526, Japan
| | - Hongliang He
- National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, PO Box 919-111, Mianyang 621900, China
| | - Yin Yu
- National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, PO Box 919-111, Mianyang 621900, China
| | - Fusheng Liu
- College of Physical Science and Technology, Southwest Jiaotong University, Chengdu 610031, China
| | - Mingjian Zhang
- College of Physical Science and Technology, Southwest Jiaotong University, Chengdu 610031, China
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17
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Alnemrat S, Hooper JP, Vasiliev I, Kiefer B. The role of equilibrium volume and magnetism on the stability of iron phases at high pressures. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:046001. [PMID: 24355938 DOI: 10.1088/0953-8984/26/4/046001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The present study provides new insights into the pressure dependence of magnetism by tracking the hybridization between crystal orbitals for pressures up to 600 GPa in the known hcp, bcc and fcc iron. The Birch-Murnaghan equation of state parameters are; bcc: V0 = 11.759 A(3)/atom, K0 = 177.72 GPa; hcp: V0 = 10.525 A(3)/atom, K0 = 295.16 GPa; and fcc: V0 = 10.682 A(3)/atom, K0 = 274.57 GPa. These parameters compare favorably with previous studies. Consistent with previous studies we find that the close-packed hcp and fcc phases are non-magnetic at pressures above 50 GPa and 60 GPa, respectively. The principal features of magnetism in iron are predicted to be invariant, at least up to ∼6% overextension of the equilibrium volume. Our results predict that magnetism for overextended fcc iron disappears via an intermediate spin state. This feature suggests that overextended lattices can be used to stabilize particular magnetic states. The analysis of the orbital hybridization shows that the magnetic bcc structure at high pressures is stabilized by splitting the majority and minority spin bands. The bcc phase is found to be magnetic at least up to 600 GPa; however, magnetism is insufficient to stabilize the bcc phase itself, at least at low temperatures. Finally, the analysis of the orbital contributions to the total energy provides evidence that non-magnetic hcp and fcc phases are likely more stable than bcc at core earth pressures.
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Affiliation(s)
- S Alnemrat
- Department of Physics, New Mexico State University, Las Cruces, NM 88003, USA. Physics Department, Naval Postgraduate School, Monterey, CA 93943, USA
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18
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O’Neill C, Lenardic A, Condie KC. Earth's punctuated tectonic evolution: cause and effect. ACTA ACUST UNITED AC 2013. [DOI: 10.1144/sp389.4] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
AbstractPeaks in the Precambrian preserved crustal record are associated with major volcanic, tectonic and climatic events. These include addition of juvenile continental crust, voluminous high-temperature volcanism, massive mantle depletion, widespread orogeny and mineralization, large apparent polar wander velocity spikes, and subsequent palaeomagnetic intensity increases. These events impinge on the glaciation record, atmospheric and ocean chemistry, and on the rise of oxygen. Here we summarize and assess a number of geodynamic models that have been proposed to explain the observed episodicity in the Precambrian record. We find that episodic behaviour from nonlinear slab-driven models best explains the observed record. Examples of such slab-driven systems include mantle avalanches or episodic subduction. In these cases, rapid descent of slabs into the mantle drives fast plate motions and convergence at the surface. This is accompanied by large-scale upwellings of deep hot mantle, which contribute to voluminous volcanism. Further modelling will determine the relative importance of each mechanism, and reinforce the fundamental contribution of the mantle to the evolution of Earth's surface systems.
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Affiliation(s)
- C. O’Neill
- CCFS ARC Centre of Excellence, GEMOC, Macquarie University, Sydney, Australia
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19
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Hunter L, Gordon J, Peck S, Ang D, Lin JF. Using the Earth as a polarized electron source to search for long-range spin-spin interactions. Science 2013; 339:928-32. [PMID: 23430649 DOI: 10.1126/science.1227460] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Many particle-physics models that extend the standard model predict the existence of long-range spin-spin interactions. We propose an approach that uses the Earth as a polarized spin source to investigate these interactions. Using recent deep-Earth geophysics and geochemistry results, we create a comprehensive map of electron polarization within the Earth induced by the geomagnetic field. We examine possible long-range interactions between these spin-polarized geoelectrons and the spin-polarized electrons and nucleons in three laboratory experiments. By combining our model and the results from these experiments, we establish bounds on torsion gravity and possible long-range spin-spin forces associated with the virtual exchange of either spin-one axial bosons or unparticles.
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Affiliation(s)
- Larry Hunter
- Physics Department, Amherst College, Amherst, MA 01002, USA.
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20
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Andrulis ED. Theory of the origin, evolution, and nature of life. Life (Basel) 2011; 2:1-105. [PMID: 25382118 PMCID: PMC4187144 DOI: 10.3390/life2010001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2011] [Revised: 12/10/2011] [Accepted: 12/13/2011] [Indexed: 12/22/2022] Open
Abstract
Life is an inordinately complex unsolved puzzle. Despite significant theoretical progress, experimental anomalies, paradoxes, and enigmas have revealed paradigmatic limitations. Thus, the advancement of scientific understanding requires new models that resolve fundamental problems. Here, I present a theoretical framework that economically fits evidence accumulated from examinations of life. This theory is based upon a straightforward and non-mathematical core model and proposes unique yet empirically consistent explanations for major phenomena including, but not limited to, quantum gravity, phase transitions of water, why living systems are predominantly CHNOPS (carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur), homochirality of sugars and amino acids, homeoviscous adaptation, triplet code, and DNA mutations. The theoretical framework unifies the macrocosmic and microcosmic realms, validates predicted laws of nature, and solves the puzzle of the origin and evolution of cellular life in the universe.
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Affiliation(s)
- Erik D Andrulis
- Department of Molecular Biology and Microbiology, Case Western Reserve University School of Medicine, Wood Building, W212, Cleveland, OH 44106, USA.
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21
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Huang H, Fei Y, Cai L, Jing F, Hu X, Xie H, Zhang L, Gong Z. Evidence for an oxygen-depleted liquid outer core of the Earth. Nature 2011; 479:513-6. [PMID: 22113693 DOI: 10.1038/nature10621] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2010] [Accepted: 10/03/2011] [Indexed: 11/09/2022]
Abstract
On the basis of geophysical observations, cosmochemical constraints, and high-pressure experimental data, the Earth's liquid outer core consists of mainly liquid iron alloyed with about ten per cent (by weight) of light elements. Although the concentrations of the light elements are small, they nevertheless affect the Earth's core: its rate of cooling, the growth of the inner core, the dynamics of core convection, and the evolution of the geodynamo. Several light elements-including sulphur, oxygen, silicon, carbon and hydrogen-have been suggested, but the precise identity of the light elements in the Earth's core is still unclear. Oxygen has been proposed as a major light element in the core on the basis of cosmochemical arguments and chemical reactions during accretion. Its presence in the core has direct implications for Earth accretion conditions of oxidation state, pressure and temperature. Here we report new shockwave data in the Fe-S-O system that are directly applicable to the outer core. The data include both density and sound velocity measurements, which we compare with the observed density and velocity profiles of the liquid outer core. The results show that we can rule out oxygen as a major light element in the liquid outer core because adding oxygen into liquid iron would not reproduce simultaneously the observed density and sound velocity profiles of the outer core. An oxygen-depleted core would imply a more reduced environment during early Earth accretion.
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Affiliation(s)
- Haijun Huang
- School of Sciences, Wuhan University of Technology, Wuhan, Hubei 430070, China
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22
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Mattesini M, Belonoshko AB, Buforn E, Ramírez M, Simak SI, Udías A, Mao HK, Ahuja R. Hemispherical anisotropic patterns of the Earth's inner core. Proc Natl Acad Sci U S A 2010; 107:9507-12. [PMID: 20457937 PMCID: PMC2906852 DOI: 10.1073/pnas.1004856107] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
It has been shown that the Earth's inner core has an axisymmetric anisotropic structure with seismic waves traveling approximately 3% faster along polar paths than along equatorial directions. Hemispherical anisotropic patterns of the solid Earth's core are rather complex, and the commonly used hexagonal-close-packed iron phase might be insufficient to account for seismological observations. We show that the data we collected are in good agreement with the presence of two anisotropically specular east and west core hemispheres. The detected travel-time anomalies can only be disclosed by a lattice-preferred orientation of a body-centered-cubic iron aggregate, having a fraction of their [111] crystal axes parallel to the Earth's rotation axis. This is compelling evidence for the presence of a body-centered-cubic Fe phase at the top of the Earth's inner core.
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Affiliation(s)
- Maurizio Mattesini
- Departamento de Física de la Tierra, Astronomía y Astrofísica I, Universidad Complutense de Madrid, E-28040 Madrid, Spain.
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23
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Belonoshko AB, Skorodumova NV, Rosengren A, Johansson B. Elastic Anisotropy of Earth's Inner Core. Science 2008; 319:797-800. [DOI: 10.1126/science.1150302] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- Anatoly B. Belonoshko
- Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm, Sweden
- Condensed Matter Theory, Department of Theoretical Physics, AlbaNova University Center, Royal Institute of Technology, SE-106 91 Stockholm, Sweden
- Condensed Matter Theory Group, Department of Physics, Uppsala University, Uppsala Box 530, Sweden
- NORDITA, AlbaNova University Center, SE-106 91 Stockholm, Sweden
- School of Physics and Optoelectronic Technology and College of Advanced Science and Technology, Dalian University of Technology, Dalian 116024, China
| | - Natalia V. Skorodumova
- Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm, Sweden
- Condensed Matter Theory, Department of Theoretical Physics, AlbaNova University Center, Royal Institute of Technology, SE-106 91 Stockholm, Sweden
- Condensed Matter Theory Group, Department of Physics, Uppsala University, Uppsala Box 530, Sweden
- NORDITA, AlbaNova University Center, SE-106 91 Stockholm, Sweden
- School of Physics and Optoelectronic Technology and College of Advanced Science and Technology, Dalian University of Technology, Dalian 116024, China
| | - Anders Rosengren
- Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm, Sweden
- Condensed Matter Theory, Department of Theoretical Physics, AlbaNova University Center, Royal Institute of Technology, SE-106 91 Stockholm, Sweden
- Condensed Matter Theory Group, Department of Physics, Uppsala University, Uppsala Box 530, Sweden
- NORDITA, AlbaNova University Center, SE-106 91 Stockholm, Sweden
- School of Physics and Optoelectronic Technology and College of Advanced Science and Technology, Dalian University of Technology, Dalian 116024, China
| | - Börje Johansson
- Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm, Sweden
- Condensed Matter Theory, Department of Theoretical Physics, AlbaNova University Center, Royal Institute of Technology, SE-106 91 Stockholm, Sweden
- Condensed Matter Theory Group, Department of Physics, Uppsala University, Uppsala Box 530, Sweden
- NORDITA, AlbaNova University Center, SE-106 91 Stockholm, Sweden
- School of Physics and Optoelectronic Technology and College of Advanced Science and Technology, Dalian University of Technology, Dalian 116024, China
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24
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A crystallizing dense magma ocean at the base of the Earth's mantle. Nature 2008; 450:866-9. [PMID: 18064010 DOI: 10.1038/nature06355] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2007] [Accepted: 10/02/2007] [Indexed: 11/09/2022]
Abstract
The distribution of geochemical species in the Earth's interior is largely controlled by fractional melting and crystallization processes that are intimately linked to the thermal state and evolution of the mantle. The existence of patches of dense partial melt at the base of the Earth's mantle, together with estimates of melting temperatures for deep mantle phases and the amount of cooling of the underlying core required to maintain a geodynamo throughout much of the Earth's history, suggest that more extensive deep melting occurred in the past. Here we show that a stable layer of dense melt formed at the base of the mantle early in the Earth's history would have undergone slow fractional crystallization, and would be an ideal candidate for an unsampled geochemical reservoir hosting a variety of incompatible species (most notably the missing budget of heat-producing elements) for an initial basal magma ocean thickness of about 1,000 km. Differences in 142Nd/144Nd ratios between chondrites and terrestrial rocks can be explained by fractional crystallization with a decay timescale of the order of 1 Gyr. These combined constraints yield thermal evolution models in which radiogenic heat production and latent heat exchange prevent early cooling of the core and possibly delay the onset of the geodynamo to 3.4-4 Gyr ago.
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25
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Olson P. Gravitational dynamos and the low-frequency geomagnetic secular variation. Proc Natl Acad Sci U S A 2007; 104:20159-66. [PMID: 18048345 PMCID: PMC2154401 DOI: 10.1073/pnas.0709081104] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2007] [Indexed: 11/18/2022] Open
Abstract
Self-sustaining numerical dynamos are used to infer the sources of low-frequency secular variation of the geomagnetic field. Gravitational dynamo models powered by compositional convection in an electrically conducting, rotating fluid shell exhibit several regimes of magnetic field behavior with an increasing Rayleigh number of the convection, including nearly steady dipoles, chaotic nonreversing dipoles, and chaotic reversing dipoles. The time average dipole strength and dipolarity of the magnetic field decrease, whereas the dipole variability, average dipole tilt angle, and frequency of polarity reversals increase with Rayleigh number. Chaotic gravitational dynamos have large-amplitude dipole secular variation with maximum power at frequencies corresponding to a few cycles per million years on Earth. Their external magnetic field structure, dipole statistics, low-frequency power spectra, and polarity reversal frequency are comparable to the geomagnetic field. The magnetic variability is driven by the Lorentz force and is characterized by an inverse correlation between dynamo magnetic and kinetic energy fluctuations. A constant energy dissipation theory accounts for this inverse energy correlation, which is shown to produce conditions favorable for dipole drift, polarity reversals, and excursions.
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Affiliation(s)
- P Olson
- Department of Earth and Planetary Sciences, The Johns Hopkins University, Baltimore, MD 21218, USA.
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26
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Belonoshko AB, Skorodumova NV, Davis S, Osiptsov AN, Rosengren A, Johansson B. Origin of the Low Rigidity of the Earth's Inner Core. Science 2007; 316:1603-5. [PMID: 17569860 DOI: 10.1126/science.1141374] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Earth's solid-iron inner core has a low rigidity that manifests itself in the anomalously low velocities of shear waves as compared to shear wave velocities measured in iron alloys. Normally, when estimating the elastic properties of a polycrystal, one calculates an average over different orientations of a single crystal. This approach does not take into account the grain boundaries and defects that are likely to be abundant at high temperatures relevant for the inner core conditions. By using molecular dynamics simulations, we show that, if defects are considered, the calculated shear modulus and shear wave velocity decrease dramatically as compared to those estimates obtained from the averaged single-crystal values. Thus, the low shear wave velocity in the inner core is explained.
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Affiliation(s)
- Anatoly B Belonoshko
- Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm, Sweden.
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27
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van der Hilst RD, de Hoop MV, Wang P, Shim SH, Ma P, Tenorio L. Seismostratigraphy and thermal structure of Earth's core-mantle boundary region. Science 2007; 315:1813-7. [PMID: 17395822 DOI: 10.1126/science.1137867] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
We used three-dimensional inverse scattering of core-reflected shear waves for large-scale, high-resolution exploration of Earth's deep interior (D'') and detected multiple, piecewise continuous interfaces in the lowermost layer (D'') beneath Central and North America. With thermodynamic properties of phase transitions in mantle silicates, we interpret the images and estimate in situ temperatures. A widespread wave-speed increase at 150 to 300 kilometers above the coremantle boundary is consistent with a transition from perovskite to postperovskite. Internal D'' stratification may be due to multiple phase-boundary crossings, and a deep wave-speed reduction may mark the base of a postperovskite lens about 2300 kilometers wide and 250 kilometers thick. The core-mantle boundary temperature is estimated at 3950 +/- 200 kelvin. Beneath Central America, a site of deep subduction, the D'' is relatively cold (DeltaT = 700 +/- 100 kelvin). Accounting for a factor-of-two uncertainty in thermal conductivity, core heat flux is 80 to 160 milliwatts per square meter (mW m(-2)) into the coldest D'' region and 35 to 70 mW m(-2) away from it. Combined with estimates from the central Pacific, this suggests a global average of 50 to 100 mW m(-2) and a total heat loss of 7.5 to 15 terawatts.
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Affiliation(s)
- R D van der Hilst
- Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge MA, USA.
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28
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Olson P, Amit H. Changes in earth's dipole. Naturwissenschaften 2006; 93:519-42. [PMID: 16915369 DOI: 10.1007/s00114-006-0138-6] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2005] [Revised: 05/11/2006] [Accepted: 05/18/2006] [Indexed: 10/24/2022]
Abstract
The dipole moment of Earth's magnetic field has decreased by nearly 9% over the past 150 years and by about 30% over the past 2,000 years according to archeomagnetic measurements. Here, we explore the causes and the implications of this rapid change. Maps of the geomagnetic field on the core-mantle boundary derived from ground-based and satellite measurements reveal that most of the present episode of dipole moment decrease originates in the southern hemisphere. Weakening and equatorward advection of normal polarity magnetic field by the core flow, combined with proliferation and growth of regions where the magnetic polarity is reversed, are reducing the dipole moment on the core-mantle boundary. Growth of these reversed flux regions has occurred over the past century or longer and is associated with the expansion of the South Atlantic Anomaly, a low-intensity region in the geomagnetic field that presents a radiation hazard at satellite altitudes. We address the speculation that the present episode of dipole moment decrease is a precursor to the next geomagnetic polarity reversal. The paleomagnetic record contains a broad spectrum of dipole moment fluctuations with polarity reversals typically occurring during dipole moment lows. However, the dipole moment is stronger today than its long time average, indicating that polarity reversal is not likely unless the current episode of moment decrease continues for a thousand years or more.
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Affiliation(s)
- Peter Olson
- Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD, USA.
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29
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Shen G, Prakapenka VB, Rivers ML, Sutton SR. Structure of liquid iron at pressures up to 58 GPa. PHYSICAL REVIEW LETTERS 2004; 92:185701. [PMID: 15169505 DOI: 10.1103/physrevlett.92.185701] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/12/2003] [Indexed: 05/24/2023]
Abstract
We report structural data on liquid iron at pressures up to 58 GPa measured by x-ray scattering in a laser heated diamond anvil cell. The determined structure factor preserves essentially the same shape along the melting curve. Our data demonstrate that liquid iron at high pressures is a close-packed hard-sphere liquid. The results place important constraints on the thermodynamic and transport properties of liquid iron and the melting curve of iron.
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Affiliation(s)
- Guoyin Shen
- Consortium for Advanced Radiation Sources, University of Chicago, Chicago, IL 60637, USA.
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30
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Rondenay S. Constraints on localized core-mantle boundary structure from multichannel, broadbandSKScoda analysis. ACTA ACUST UNITED AC 2003. [DOI: 10.1029/2003jb002518] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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31
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Margerin L. Multiple scattering of high-frequency seismic waves in the deep Earth:PKPprecursor analysis and inversion for mantle granularity. ACTA ACUST UNITED AC 2003. [DOI: 10.1029/2003jb002455] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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32
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Sumita I. Rotating thermal convection experiments in a hemispherical shell with heterogeneous boundary heat flux: Implications for the Earth's core. ACTA ACUST UNITED AC 2002. [DOI: 10.1029/2001jb000548] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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