Greig A. Paterson

The Ediacaran-Cambrian interval marks major environmental change and the emergence of complex life, coinciding with some of the weakest magnetic field strengths in Earth history. It has been proposed that inner core nucleation near this boundary triggered a rapid strengthening of the geodynamo during the early Cambrian, but direct constraints on magnetic field behavior across this interval remain limited. Here, we present new paleointensity results from two Cambrian igneous sequences in Brazil (~525 million years ago) and Nova Scotia (~505 million years ago). Using multiple complementary methods, both records indicate a reversing geomagnetic field that remained weak. Combined with a reanalysis of published data, our results show that weak magnetic field conditions persisted for tens of millions of years after the Cambrian radiation. These findings limit the magnitude and timing of any Cambrian geodynamo strengthening and imply that Earth’s magnetospheric shielding remained strongly suppressed during a key phase of early animal evolution.

The British Palaeogene Igneous Province records the palaeomagnetic field at a time when it had returned to a reversing state following the Cretaceous Normal Superchron. Whilst the province is well studied for palaeomagnetic directions, palaeointensity results remain scarce. New palaeointensity and palaeomagnetic directional results are presented from a Palaeocene basaltic dyke swarm on the Sleat Peninsula, Skye (NW Scotland). The mean palaeomagnetic direction from 24 dykes has declination 356.7° and inclination 60.0°. The corresponding palaeopole lies at 75.2°N, 181.8°E with associated 95 per cent confidence interval, A₉₅, of 6.6° which is close to, but distinguishable from, previous results from this swarm. The angular dispersion of virtual geomagnetic poles (VGPs), S_B, was 17.9 ± 3.2°, consistent with stationary VGP dispersion throughout the Palaeogene. Three experimental palaeointensity methods were attempted: Shaw Double Heating Technique, thermal Thellier, and microwave Thellier. Palaeointensity experiments were successful from two dykes giving results of 15.8 ± 2.3 μT and 12.0 ± 3.4 μT which correspond to virtual dipole moments of 27 ± 4 ZAm² and 21 ± 6 ZAm². These are notably weaker than the long-term average and the recent field. Additionally, we present proof-of-concept of a novel method for estimating palaeointensity. The preliminary method was applied to results from the thermal Thellier experiments and is based on reproducing non-ideal Arai plot behaviour using a phenomenological model of thermal remanent magnetisation. This inversion highlighted laboratory field orientation as a major control on Arai plot shape with antiparallel fields predicted and observed to cause major distortions. It produced similar palaeointensity results to the conventional approach but derived from significantly more specimens.

The MagNetZ (Magnetic Network on Zoom) webinar series stands as a cornerstone for geomagnetism research, hosting online seminars since the early 2020. Launched amid COVID-19 constraints, MagNetZ are convened by a team of scientists to give visibility to scientific work of both leading scientists and early career researchers, to foster virtual collaboration, overcoming geographical limits for students and professionals alike. It promotes open science sharing, with broad appeal evidenced by international viewership and institutional ties. The presentations typically began with a short talk, followed by interactive Q&A space, which are both recorded, post-edited and published on YouTube (https://www.youtube.com/@MagNetZ) in a continuously growing archive of recorded content. These webinars are also uploaded to the EarthRef.org Digital Archive (ERDA), development and maintained by the EarthRef.org Database Team and can be cited. Thus far, more than 80 webinars are available for viewing. MagNetZ also supports for national meetings, such as the UK-based annual Magnetic Interactions meeting, offering them the platform to view the recordings of three meetings so far. The webinars provide in-depth discussions on paleo- and rock-magnetism and geomagnetic modeling, with topics spanning from geo- and planetary magnetic field dynamics to mineral properties studies for paleoclimatic reconstructions, from paleomagnetic data for geodynamic applications to archaeomagnetism, and more. The core features of MagNetZ are to ensure accessibility for all genders, all career stages and geographical distributions, enhancing community networks, and serving as an educational hub for magnetic data in tectonics and climate studies. Its YouTube platform ensures enduring access, sparking collaborations and awareness.

The online seminars, or webinars, provide a virtual space for in-depth discussions on a variety of scientific- and academic-related topics.Several webinar series were launched amid COVID-19 constraints, providing the opportunity to keep the scientific community united during the challenging times of the global pandemic. Webinars have proven their advantage in overcoming geographical limitations and funding issues for in-person or online conference attendance. Virtual approaches are a powerful tool for promoting open science sharing, improving community networks and fostering virtual collaboration, with broad appeal evidenced by international viewership and institutional ties.We recommend offering a flexible format, which may include an initial talk followed by interactive Q&A space. Scientific talks can be recorded and published on online platforms that provide a DOI and on YouTube, giving visibility and credits to both early career researchers and leading scientists, as well as providing potential teaching material for undergraduate and postgraduate courses. Good practice is to create an unrecorded space for informal meetings, where a relaxed environment is fostered that encourages questions, free discussion, and facilitates mentoring.With a view to making webinars inclusive, we encourage a balanced selection of speakers, considering gender, career stage and country of origin, to promote the inclusion of minorities. Conveners are also recommended to ensure the correct pronunciation of the names and pronouns of the speakers before the beginning of the webinar. The live session, however, is as inclusive as the time zones in which the webinar is hosted. Hence, geographical inclusion of live attendance can be achieved by shifting time zones from the eastern and western hemisphere during the year.Finally, webinar using online platforms with close captions and careful post-production editing with subtitles integration allows for a more accessible material for both non-native English speakers and underrepresented minorities such as hard of hearing and deaf peoples.Although these options tend not to be used, it is important to open up dialogue on how to make webinars more inclusive and oriented as an educational hub for Earth science studies.

High-field magnetic measurements and procedures, such as hysteresis, first-order reversal curves (FORC), and alternating-field (AF) demagnetization, are foundational methods in rock and paleomagnetic studies. Interpreting these data can be challenging and often requires an understanding of the particle scale contributions to these signals. This requires a numerical approach using micromagnetic models along with the inclusion of thermal fluctuations, which result in time dependent relaxation in experimental observations. This is a challenge that requires knowledge of all stable domain states, their connectivity, and energy barriers that partition the energy landscape that results from the field strength and orientation of each particle. This typically requires considerable user input and analysis, making this an unfeasibly time-consuming endeavor.We are developing a method that calculates exact energy surfaces for uniformly magnetized particles and approximate energy surfaces for single vortex (SV) particles, akin, to software tools such as the Singe Domain Comprehensive Calculator (SDCC; Cych et al., 2025, doi: 10.1093/gji/ggaf149). This technique is integrated into the micromagnetic software package MERRILL and readily identifies minimum energy domain states, their connectivity, and (using the nudged elastic band method), can calculate the energy barriers between states. This automated process dramatically reduces user input and analysis at the cost of additional computational time resulting in high-field energy landscapes (HELs) which can then be used to simulate a wide range of thermally activated experiments, including hysteresis loops, FORC diagrams, anhysterestic remanent magnetization (ARM) acquisition and AF demagnetization. Additional computational resources are not, however, significant, since our method runs in a matter of minutes to hours on a modern laptop computer. This new approach will take the rock and paleomagnetic community one step closer to incorporating micromagnetic tools as a part of the standard analytical repertoire used to interpret the behavior of natural samples and reconstruct the signals they carry.

SUMMARY: Louis Néel’s theory of magnetism, which describes a rock’s magnetization as being carried by ‘ideal’ uniformly magnetized or single domain (SD) particles, has been a cornerstone of paleomagnetic studies for over seven decades and has enabled paleomagnetists to make plate tectonic reconstructions, date geological and archaeological materials and recover the history of Earth’s magnetic field. Unfortunately, many geological samples produce experimental results that disagree with the predictions made by Néel theory. This ‘non-ideal’ behaviour is often associated with larger particles that are non-uniformly magnetized. In this paper, we use simulations based on Néel theory to demonstrate that non-ideal behaviour is also expected in assemblages of SD particles with a range of sizes and shapes previously assumed to be ideal. This effect occurs over a relatively small range of shapes and sizes for magnetite, but a much wider range for titanomagnetites. Our results call into question the typical interpretation of SD particles as ideal magnetic carriers. Instead, we suggest that the geological stability of a rock’s magnetization is influenced not only by the domain state of the magnetic carriers, but also by their shape and composition. This has important implications for paleointensities (and cooling rate corrections thereof), paleodirections and the dating of viscous magnetizations.

SUMMARY: Palaeomagnetic studies of impact glasses offer valuable insights into their magnetization processes and thermal histories associated with impact cratering events. Australasian tektites are broadly distributed in the largest and youngest strewn field of the Cenozoic, and they provide a unique opportunity to investigate the intensity of Earth’s magnetic field around 788 ka and potential impact-induced magnetic fields. The northern part of the Australasian strewn field covers South China, and it corresponds to the uprange zone of the impactor’s trajectory. Magnetic properties of Australasian tektites in South China may contain unique information about this impact event, but their palaeomagnetic characteristics remain poorly constrained. Here, we report the first palaeointensity data of Australasian tektites sampled from the Early-Middle Pleistocene strata in South China. The results show that Muong Nong-type tektites recorded palaeointensities of 30 ± 8 $\mu$T, consistent with the geomagnetic field intensity around 780–790 ka. These findings suggest that around 788 ka, Earth’s magnetic field had partially recovered from the earlier intensity decline associated with the precursor event of the Matuyama–Brunhes reversal. By contrast, the splash-form tektites in South China are characterized by extremely weak natural remanent magnetization and unstable magnetization components, posing challenges for deriving reliable palaeointensity data. Although strong impact-induced remanent magnetization was not detected in the samples, this study demonstrates that Australasian tektites, particularly Muong Nong-type, are well suited for palaeomagnetic studies that may reveal potential impact-induced magnetization.

Micropaleomagnetic analysis offers a path to high-precision reconstructions of ancient magnetic fields from terrestrial and space-returned samples by inverting the vertical stray field of individual particles to recover their magnetic moments through the use of magnetic microscopes. Constraining such inversions requires a detailed understanding of how domain state influences the dipolar and non-dipolar components of the stray field with distance. Here, we use micromagnetic solutions of remanent states in real, irregular sub- to near-micron magnetite particle morphologies to calculate vertical stray fields at various heights, evaluating how dipolar and non-dipolar signals can be recovered with both simple Cartesian dipole and multidipolar models in the presence and absence of noise. Our results show that single-domain and single-vortex state (SV) grains produce strong dipolar anomalies that attenuate rapidly, limiting reliable detection to observation heights below ∼1μm for 5nT noise or ∼0.5μm for 50nT noise. Larger SV or multivortex grains remain detectable to ∼5-10μm but with reduced moment fidelity. Multipolar components decay orders of magnitude faster than the dipole and are quickly lost in noise at practical distances. Dipole-only inversions yield stable, accurate results beyond ∼2μm, while multipolar fits can improve near-surface accuracy but add significant uncertainty in noisy data. Because strongly non-dipolar anomalies observed at heights ≥1-2μm may arise from large multidomain grains or from the combined response of short- and long-wave signals of clusters of particles, they should be interpreted with caution. We highlight the need to minimize sensor noise, optimize stand-off distance, and carefully interpret signals for robust micropaleomagnetic measurement.