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Supplemental Material for journal publication.

Additional file 1: Table S1. Summary of Arai plot statistics from successful paleointensity experiments.

Long-term variations of the geomagnetic field, observed in the palaeomagnetic record, have the potential to shed much light on the evolution of Earth’s deep interior. With a geomagnetic field characterised by anomalous directions and ultra-low intensities, the Ediacaran period (635-541 Ma) is a time of special interest. Steep and shallow directions, leading to virtual geomagnetic poles (VGPs), separated by angles of up to 90° and very close in age could have recorded a geomagnetic field switching between axial and equatorial dipole-dominated states. Alternatively, the field may simply have been highly nondipolar and subject to rapid reversals. Palaeointensity determinations of units that record the anomalous directions could potentially help to discriminate between morphologies but the spatial and temporal distribution of palaeomagnetic data require improvement. Here we present new palaeointensities from 11 sites from the western end of the Grenville Dyke swarm that recorded directionally anomalous geomagnetic fields around ~585 Ma. Palaeointensities, obtained through microwave Thellier, Shaw and pseudo-Thellier methods, show field strength values of 2.9±2.2 µT and corresponding virtual dipole moments of 0.3-1.7 x1022 Am2. These field strengths are an order of magnitude weaker than the present-day field. The most extreme palaeointensity values of 1.4-2.1 µT are half as strong as seen in previous studies of the Ediacaran field and as low as Mars’ recently measured crustal field intensity, giving a new lower bound for the Earth. VGPs grouping in two distinct clusters with almost identical angular dispersions of VGPs (SB = 18.5° and 18.9°) may argue for the presence of an equatorial dipole. In contrast, the palaeointensities associated with the steep and shallow components are indistinguishable. This observation, together with the overall very large VGP dispersion may rather support that the Grenville Dykes have recorded enhanced secular variation linked to a highly unstable, multipolar and reversing field.

Paleointensity.org is an online, open source, application to analyze paleointensity data produced by the most common paleointensity techniques. Our application currently supports four different methods: thermal Thellier (all variations), microwave Thellier, pseudo-Thellier, and the multispecimen protocol. Data can be imported using a variety of input file formats such as ThellierTool files, the generic PmagPy file format, and a number of lab-specific formats. The data for the individual paleointensity methods are visualized by the relevant graphs and parameters, which are updated dynamically while interpreting the data. Beyond manual interpretation, Paleointensity.org features an autointerpreter for specimen level Thellier-type data. Interpretations and data can be exported to csv and MagIC files. Moreover, it is possible to export the local storage containing all data, saved interpretations, and settings. This file can be shared among researchers or attached to a paper as supporting information. Because of its many features and ease of use, Paleointensity.org is a major step forward in enhancing an open paleomagnetic community in which data can be shared, checked, and reused in line with the findable, accessible, interoperable, and reusable data principles.

Bilateral basal ganglia abnormalities on MRI are observed in a wide variety of childhood disorders. MRI pattern recognition can enable rationalization of investigations and also complement clinical and molecular findings, particularly confirming genomic findings and also enabling new gene discovery. A pattern recognition approach in children with bilateral basal ganglia abnormalities on brain MRI was undertaken in this international multicentre cohort study. Three hundred and five MRI scans belonging to 201 children with 34 different disorders were rated using a standard radiological scoring proforma. In addition, literature review on MRI patterns was undertaken in these 34 disorders and 59 additional disorders reported with bilateral basal ganglia MRI abnormalities. Cluster analysis on first MRI findings from the study cohort grouped them into four clusters: Cluster 1-T-weighted hyperintensities in the putamen; Cluster 2-T-weighted hyperintensities or increased MRI susceptibility in the globus pallidus; Cluster 3-T-weighted hyperintensities in the globus pallidus, brainstem and cerebellum with diffusion restriction; Cluster 4-T-weighted hyperintensities in the basal ganglia. The 34 diagnostic categories included in this study showed dominant clustering in one of the above four clusters. Inflammatory disorders grouped together in Cluster 1. Mitochondrial and other neurometabolic disorders were distributed across clusters 1, 2 and 3, according to lesions dominantly affecting the striatum (Cluster 1: glutaric aciduria type 1, propionic acidaemia, 3-methylglutaconic aciduria with deafness, encephalopathy and Leigh-like syndrome and thiamine responsive basal ganglia disease associated with SLC19A3), pallidum (Cluster 2: methylmalonic acidaemia, Kearns Sayre syndrome, pyruvate dehydrogenase complex deficiency and succinic semialdehyde dehydrogenase deficiency) or pallidum, brainstem and cerebellum (Cluster 3: vigabatrin toxicity, Krabbe disease). The Cluster 4 pattern was exemplified by distinct T-weighted hyperintensities in the basal ganglia and other brain regions in genetically determined hypermanganesemia due to SLC39A14 and SLC30A10. Within the clusters, distinctive basal ganglia MRI patterns were noted in acquired disorders such as cerebral palsy due to hypoxic ischaemic encephalopathy in full-term babies, kernicterus and vigabatrin toxicity and in rare genetic disorders such as 3-methylglutaconic aciduria with deafness, encephalopathy and Leigh-like syndrome, thiamine responsive basal ganglia disease, pantothenate kinase-associated neurodegeneration, TUBB4A and hypermanganesemia. Integrated findings from the study cohort and literature review were used to propose a diagnostic algorithm to approach bilateral basal ganglia abnormalities on MRI. After integrating clinical summaries and MRI findings from the literature review, we developed a prototypic decision-making electronic tool to be tested using further cohorts and clinical practice. Analysing a cohort of 201 children with bilateral basal ganglia MRI abnormalities in conjunction with a literature review, we propose a stepwise approach for 93 different disorders. Disorders cluster based on MRI changes in the putamen, globus pallidus alone or with brainstem and cerebellar changes and with T2W versus T1W hyperintensities in the basal ganglia

Nearly three decades ago paleomagnetists suggested that there existed a clear link between latitude dependence of geomagnetic paleosecular variation (PSV) and reversal frequency. Here we compare the latitude behavior of PSV for the Cretaceous Normal Superchron (CNS, 84-126 Ma, stable normal polarity) and the preceding Early Cretaceous-Jurassic interval (pre-CNS, 126-198 Ma, average reversal rate of ~4.6 Myr-1). We find that the CNS was characterized by a strong increase in the angular dispersion of virtual geomagnetic poles (VGPs) with latitude, which is consistent with the results of earlier studies, whereas the VGP dispersion for the pre-CNS period was nearly invariant with latitude. However, the PSV behavior for the last 5 or 10 million years (average reversal frequency of ~4.4-4.8 Myr 1) shows that the latitude invariance of VGP scatter cannot be considered as a characteristic feature of a frequently-reversing field, and that a strong increase in VGP dispersion with latitude was not restricted to the long periods of stable polarity. We discuss models describing the latitude dependence of PSV and show that their parameters are not reliable proxies for reversal frequency and should not be used to make inferences about the geomagnetic field stability. During the pre-CNS interval, the geodynamo may have operated in a regime characterized by a high degree of equatorial symmetry. In contrast, more asymmetric geodynamos suggested for 0-10 Ma and the CNS were evidently capable of producing a very wide range of reversal frequencies.

Long-term variations in geomagnetic field behaviour can contain essential information on deep Earth processes. A major topic of debate has been the age of the onset of Earth’s inner core nucleation, as uncertainty in the value of thermal conductivity of the core allows for a wide range in age estimates. Recently, an inner core age in the late Ediacaran period (635-538 Ma) has been inferred from an ultra-weak palaeointensity estimate at 565 Ma. Palaeomagnetic investigations using rocks from this time are known to give anomalous results and show ambiguous apparent polar wander paths in a hyper-reversing field. To date, a full characterisation of the geomagnetic field at that time has been prevented by a lack of field strength estimates. The studies presented in this thesis add 27 new and reliable field strength estimates between 0.31 ± 0.11 and 2.25 ± 0.39 ×10^22Am^2 to the record. These exceptionally weak estimates were obtained from rocks of the Grenville dykes (Canada), the Skinner Cove Formation (Newfoundland) and the Volyn traps (Ukraine). These cover the time period between 550 - 600 Ma and suggest that the geomagnetic field has been remarkably weak over a much longer time period than previously seen from palaeointensity data and starts to increase in strength at the Ediacaran-Cambrian transition, as suggested by less chaotic palaeomagnetic directions. These results could correspond to considerably lower field strengths predicted by geodynamo simulations for fields with low dipolarity before the onset of inner core nucleation. However, the context of these extremely weak palaeointensities is still unclear, as field strengths are still mostly unexplored for the time periods that surround the Ediacaran, highlighting the ubiquitous need for additional high quality palaeointensity data. New estimates of VGP dispersion and dipole moment variance for the Ediacaran were calculated using filtered data from the literature combined with the new data from this thesis. These estimates, although based on a low number of data, suggest enhanced palaeosecular variation in the Ediacaran compared to other time periods. With the high reversal frequencies, the field might have been in a transitional state throughout the Ediacaran and none of the currently available geodynamo model solutions was able to capture the full range of the unique Ediacaran field behaviour.

Investigating the Earth’s magnetic field provides a unique window into the history of Earth’s outer core, where the field is generated. Rocks gain a magnetization that is in the direction of and proportional to the Earth’s magnetic field at the time of their formation, such as when magma erupts from a volcano and cools below its Curie temperature. The gained magnetization has a relaxation time that is frequently longer than the age of the universe, but unfortunately, rocks are subject to the whims of the Earth over geologic time. Given the ages of rocks commonly studied (millions to billions of years old), some paleomagnetic data is noisy and complex. Paleomagnetic intensity data in particular have long been plagued by large and poorly quantified uncertainties. Extracting accurate magnetic measurements relies on having the most advanced equipment and best experimental techniques. This thesis approaches these goals from two directions: prototyping new equipment, which also introduces novel methodology, and fine-tuning existing methods. Contained herein is the development of the world’s first automated high-temperature SQUID (Superconducting Quantum Interference Device) thermomagnetometer. This system can automatically measure the remanent magnetic field of a specimen at an elevated temperature without needing to cool the specimen to ambient temperature. Without repeated heating/cooling cycles, thermochemical alteration is minimized, and the rate of data collection is greatly increased. SQUID sensors improve the sensitivity of the magnetometer system, avoid low blocking temperature components, and provide precise temperature control and minimal alteration. While the original design called for an instrument that could provide continuous magnetization measurements, this proved to be untenable due to technical constraints with the SQUID sensors. Thus, a stepwise version was produced that measures each specimen in (up to) 10 °C increments, instead of continuously. Introducing new equipment by itself is futile if the experiments performed on them are not well calibrated and optimized. To address this problem, this thesis investigates differences in paleomagnetic intensity results produced by different variants of Thellier-style paleointensity protocols using established instruments. The most modern protocol, the IZZI protocol, was found to be broadly accurate but sometimes imprecise. This thesis further attempts to ascertain the cause of differences observed in paleointensity data when the demagnetization mechanism or paleointensity protocol is changed, as nearly a dozen methods are in use throughout the world. Finally, a series of tests evaluates whether the addition of alternating field or liquid nitrogen demagnetization cleansing steps can improve data fidelity. The additional cleansing steps can, in some cases, improve the linearity of paleointensity data sufficiently to pass selection criteria, but cannot affect, for example, other complications like thermochemical alteration. With the ever-growing pressure to provide tangible impacts to the broader scientific community, expanding the versatility of magnetic techniques to new applications is paramount. This thesis broadly applies magnetic techniques to the energy sector, through Magnetic Flux Leakage experiments on Coiled Tubing, in conjunction with Schlumberger as an industrial partner. The future paleomagnetic laboratory is a versatile one, capable of running large batches of specimens (both paleomagnetic and metallic) quickly and accurately, through a combination of improved methods and equipment. This thesis has successfully introduced a new prototype magnetometer design and found that for non-ideal (i.e. real) rocks, the interactions between the rocks and methods are complex. Going forward, the new magnetometer brings high temperature remanence measurements to more rock types and potentially further partnerships with external, industrial partners, like Schlumberger.