New Paleointensities From the Skinner Cove Formation, Newfoundland, Suggest a Changing State of the Geomagnetic Field at the Ediacaran‐Cambrian Transition

Thallner, Daniele; Biggin, Andrew J.; McCausland, Phil J.A.; Fu, R. R.

doi:10.1029/2021jb022292

Cited by 19 publications

(4 citation statements)

References 70 publications

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“…3 a, b). Available instantaneous records of the latest Ediacaran field strength 39 are consistent with this value ( Supplementary Information and Supplementary Table 4) . This relatively rapid recovery agrees with expectations of new energy sources to power the geodynamo from inner core growth.…”

Section: Discussionsupporting

confidence: 74%

Early Cambrian renewal of the geodynamo and the origin of inner core structure

et al. 2022

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Paleomagnetism can elucidate the origin of inner core structure by establishing when crystallization started. The salient signal is an ultralow field strength, associated with waning thermal energy to power the geodynamo from core-mantle heat flux, followed by a sharp intensity increase as new thermal and compositional sources of buoyancy become available once inner core nucleation (ICN) commences. Ultralow fields have been reported from Ediacaran (~565 Ma) rocks, but the transition to stronger strengths has been unclear. Herein, we present single crystal paleointensity results from early Cambrian (~532 Ma) anorthosites of Oklahoma. These yield a time-averaged dipole moment 5 times greater than that of the Ediacaran Period. This rapid renewal of the field, together with data defining ultralow strengths, constrains ICN to ~550 Ma. Thermal modeling using this onset age suggests the inner core had grown to 50% of its current radius, where seismic anisotropy changes, by ~450 Ma. We propose the seismic anisotropy of the outermost inner core reflects development of a global spherical harmonic degree-2 deep mantle structure at this time that has persisted to the present day. The imprint of an older degree-1 pattern is preserved in the innermost inner core.

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Section: Discussionsupporting

confidence: 74%

Early Cambrian renewal of the geodynamo and the origin of inner core structure

et al. 2022

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“…3a, b). Available instantaneous records of the latest Ediacaran field strength 39 are consistent with this value (Supplementary Information and Supplementary Table 4). This relatively rapid recovery agrees with expectations of new energy sources to power the geodynamo from inner core growth.…”

Section: Discussionsupporting

confidence: 74%

Early Cambrian renewal of the geodynamo and the origin of inner core structure

Zhou

Tarduno

Cottrell

et al. 2022

Preprint

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Seismic anisotropy observations indicate the presence of an innermost and outermost inner core, but the origin of this structure is unknown. Records of the past geomagnetic field provide a means to probe inner core evolution by establishing when growth started. The Ediacaran (~565 million-year-old) geodynamo was near collapse, with a strength 10 times weaker than that of the present-day consistent with model predictions for the field before the onset of inner core nucleation. But the timing of the key transition to stronger intensities typical of the Phanerozoic Eon, needed for establishing an exact onset age, has been unclear. We present single crystal paleointensity results from anorthosites of the early Cambrian (~532 million-year-old) Glen Mountains Layered Mafic Complex (Oklahoma). Data from single plagioclase crystals bearing single domain magnetite and titanomagnetite inclusions yield a time-averaged dipole moment of 3.5 +/- 0.9 x 1022 A m2, 5 times greater than that recorded in the Ediacaran Period. This rapid field recovery is the expectation at the start of inner core growth, as new thermal and compositional sources of buoyancy to power the geodynamo become available. We will discuss thermal models, which together with our new paleointensity results, allow us to constrain growth of the inner core and when its structure may have changed.

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“…In total, 295 new sites from 34 studies have been added to the PINT v8.1.1 database, increasing the total number of site mean records ( N Sites ) to 4,648. These data include contributions constraining the field during the Cambrian/Ediacaran (e.g., Thallner, Biggin, & Halls, 2021; Thallner, Biggin, McCausland, & Fu, 2021; Thallner et al., 2022; Zhou et al., 2022) and Neoproterozoic (e.g., Lloyd, Biggin, et al., 2021), which remain under‐sampled relative to other geologic intervals.…”

Section: Updates To Pint V811mentioning

confidence: 99%

MCADAM: A Continuous Paleomagnetic Dipole Moment Model for at Least 3.7 Billion Years

Bono

Paterson

Biggin

2022

Geophysical Research Letters

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The evolution of Earth's deep interior since core formation (Nimmo, 2015) >4 billion years ago (Ga) remains a topic of considerable study. Obtaining information of the deep interior is generally restricted to present-day observations. Alternatively, insights on processes occurring before the modern era require sampling geologic materials that formed at, or were transported to, Earth's surface. However, the geomagnetic field is generated in the liquid fraction of Earth's core through the geodynamo, and changes in the morphology, strength and variability in the geodynamo may reflect the evolution of core processes and the pattern of heat flux across the core-mantle boundary. The geomagnetic field is also a critical component for Earth's habitability (Rodríguez-Mozos & Moya, 2017) due to the protective envelope provided by the magnetosphere against atmospheric erosion by charged solar particles. It is speculated that changes in the paleomagnetosphere may have contributed to substantial changes in the evolution of life (e.g., Meert et al., 2016).Paleomagnetic studies offer the potential to help close this gap: when rocks bearing magnetic carriers form, the geomagnetic field imparts a remanent magnetization that under ideal circumstances can be robustly preserved for billions of years. The strength of the geodynamo can be described by the magnitude of the dipole moment, the first-degree spherical harmonic component of the field, which should reflect ∼90% of the surface field signal. A fundamental question regarding Earth's dynamo is how the dipole moment has changed over long timescales (≫millions of years). Paleointensities measured from the same geologic time (e.g., from the same cooling-unit, referred to as a "site") can be related to paleointensities from other locations by transforming the paleointensity (B) into a virtual (axial) dipole moment (V(A)DM) using the following equation (Smith, 1967):

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New Paleointensities From the Skinner Cove Formation, Newfoundland, Suggest a Changing State of the Geomagnetic Field at the Ediacaran‐Cambrian Transition

Cited by 19 publications

References 70 publications

Early Cambrian renewal of the geodynamo and the origin of inner core structure

Early Cambrian renewal of the geodynamo and the origin of inner core structure

Early Cambrian renewal of the geodynamo and the origin of inner core structure

MCADAM: A Continuous Paleomagnetic Dipole Moment Model for at Least 3.7 Billion Years

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