PhD. Thesis : The contribution of single-crystal paleointensity to the evolution of the Earth's[...]

Universite de Montpellier; France; Sur place; EUR 24 000 - 36 000; Plein temps

Résumé du poste

A leading French University is seeking a PhD candidate to research the evolution of the Earth's magnetic field through paleomagnetism. The candidate will focus on developing measurement protocols and analyzing variations during the Paleozoic era. Prior experience in related fields is advantageous, and the position emphasizes collaboration and international research opportunities.

Prestations

International research opportunities

Access to advanced research facilities

Qualifications

• Strong background in paleomagnetism and related geosciences.
• Prior research experience is appreciated.
• Excellent communication skills in English and Spanish are a plus.

Responsabilités

• Conduct research on Earth's magnetic field during the Paleozoic.
• Develop innovative protocols for measuring paleointensity.
• Collaborate with international teams on paleomagnetic expeditions.

Connaissances

Paleomagnetism

Research experience

English communication

Spanish communication

Formation

Master 2 degree

Outils

Ultra-sensitive magnetometers

Description du poste

Organisation/Company Universite de Montpellier Department Human Resources Research Field Geosciences » Geology Environmental science » Earth science Researcher Profile First Stage Researcher (R1) Positions PhD Positions Country France Application Deadline 12 Dec 2025 - 23:59 (Europe/Paris) Type of Contract Temporary Job Status Full-time Is the job funded through the EU Research Framework Programme? Horizon Europe Reference Number 2026-D0003 Is the Job related to staff position within a Research Infrastructure? No

Offer Description

- main mission: The Earth's magnetic field (EMF) plays a key role in understanding the evolution of the planet, its climate, and its habitability over the past 4.5 billion years(Shahar et al. 2019). Paleomagnetism, which allows us to study past variations of the EMF, relies on the ability of rocks to acquire a thermoremanent magnetization that remains stable over time. Paleointensity, which measures the intensity of Earth's magnetic field recorded in ancient rocks, has deepened our knowledge of the variations in our planet’s magnetic shield and the evolution of Earth's core and geodynamo.

However, extracting paleointensity data from Precambrian rocks is extremely challenging. A rock typically contains a mixture of magnetic grains of different sizes and compositions, which may have undergone thermal or chemical transformations after their formation (e.g., metamorphism, hydrothermal alteration), potentially biasing measurements(Tauxe et al. 2021).

The single-crystal paleointensity technique, which involves analyzing individual millimeter-sized silicate crystals in rock samples, offers a promising approach for obtaining more precise and reliable data on past magnetic field intensity compared to conventional whole-rock methods(Cottrell and Tarduno 2000; Tarduno 2009). This method presents two main advantages: (i) silicate crystals act as protective capsules for millions of magnetic inclusions within the crystal, shielding them from alteration, and (ii) due to their size, these magnetite inclusions are generally in a single-domain to pseudo-single-domain state (<1 µm – 30 nm) and serve as excellent recorders of the EMF. Although this technique emerged in the early 2000s, the debate between 'single-crystal' and 'whole-rock' paleointensity measurements remains unresolved in 2025! This is partly because, until recently, very few laboratories worldwide had access to ultra-sensitive magnetometers capable of measuring the extremely weak magnetization of these small crystals, making it difficult to reproduce results. We are currently in a transition period marked by the rise of next-generation ultra-sensitive quantum magnetometers, with the only model in France recently installed at Géosciences Montpellier.

Thanks to these cutting- edge instruments, this PhD project will tackle the challenge of single-crystal paleointensity, which could become a powerful tool for reconstructing the evolution of Earth's magnetic field. This thesis will be at the heart of the development of innovative protocols for determining paleointensity, in particular the development of 'multispecimen single-crystal paleointensity'.

- activities:

PhD. objectives and methodology

The main aim of this thesis is to assess the extent to which the study of single-crystal paleointensity contributes to a better understanding of the evolution of the Earth's magnetic field during the Paleozoic, a key period in Earth's history (541 to 252 million years ago) characterized by major geological and biological upheavals.

The specific objectives of the thesis are as follows:

• Optimize and develop new measurement protocols for single-crystal paleointensity, in particular by combining this technique with the use of a 'multispecimen' approach.
• Test a potential bias between the 'total rock' approach and the 'single crystal' approach (Smirnov et al. 2017). Evaluate the advances of the single-crystal technique and the problems associated with its use (anisotropy, etc.).
• Analyze variations in magnetic field strength during the Paleozoic and deduce implications for the Earth's internal dynamics and geodynamics. To do this, the candidate will use rock samples from different regions of the Gondwana megacontinent, which existed for much of the Paleozoic and Mesozoic eras between 600 and 180 million years ago. The magnetic evolution of the early Paleozoic (~532 Ma) is uncertain and marked by contradictory results with high paleointensities associated with low paleointensities for the same age, which is impossible(Lloyd et al. 2022; Zhou et al. 2022). This thesis will evaluate the «Mid-Paleozoic Low» (416 -332 Ma), an assumed period of low intensity of the Earth's magnetic field, the duration of which remains enigmatic(Hawkins et al. 2021). The end of the Paleozoic (<300 Ma) is marked by very high paleointensity values, the origin of which remains debated. But new results suggest that a weak magnetic field may have persisted. (Lloyd 2025).

The research work will be based firstly on the collection of samples during international paleomagnetic expeditions (Argentina, French Guiana...) financed by the European UBEICH project. This thesis project will enable the candidate to develop numerous collaborations and internships abroad, which will be an asset when it comes to obtaining a postdoc after the thesis. Experimental work in the laboratory will be a major part of this thesis, and the candidate will be able to draw on the Rock Magnetism Laboratory's new range of instruments, to be installed in 2025 at Géosciences Montpellier, as well as on a technical and scientific team.

Scientific impact and perspectives

The results of this thesis could considerably improve our understanding of the dynamics of the Earth's magnetic field during the Paleozoic. By refining the resolution of paleointensity data, the single-crystal approach could offer new insights into the evolution of the Earth's core. Furthermore, this research could have implications beyond the strict confines of geophysics, notably in paleoclimatology, geodynamics and planetary magnetism.

References

Cottrell, R.D. and Tarduno, J.A. 2000. In search of high-fidelity geomagnetic paleointensities: A comparison of single plagioclase crystal and whole rock Thellier-Thellier analyses. Journal of Geophysical Research: Solid Earth, 105, 23579-23594.

Hawkins, L.M.A., Grappone, J.M. et al. 2021. Intensity of the Earth's magnetic field: Evidence for a Mid-Paleozoic dipole low. Proceedings of the National Academy of Sciences, 118, e2017342118, https://doi.org/10.1073/pnas.2017342118.

Lloyd, S., Biggin, A.J., Paterson, G. and McCausland, P. 2022. Extremely weak early Cambrian dipole moment similar to Ediacaran: Evidence for long-term trends in geomagnetic field behaviour? Earth and Planetary Science Letters, 595, 117757, https://doi.org/10.1016/j.epsl.2022.117757.

Smirnov, A.V., Kulakov, E.V., Foucher, M.S. and Bristol, K.E. 2017. Intrinsic paleointensity bias and the long-term history of the geodynamo. Science Advances, 3, e1602306.

Tauxe, L., Santos, C.N., Cych, B., Zhao, X., Roberts, A.P., Nagy, L. and Williams, W. 2021. Understanding Nonideal Paleointensity Recording in Igneous Rocks: Insights From Aging Experiments on Lava Samples and the Causes and Consequences of “Fragile” Curvature in Arai Plots. Geochemistry, Geophysics, Geosystems, 22, e2020GC009423, https://doi.org/10.1029/2020GC009423.

Contract date from 01/01/2026 to 31/12/2028

The candidate will join a group of researchers active at Géosciences Montpellier in Paleomagnetism and Rock Magnetism. Although not a requirement, previous experience in paleointensity/paleomagnetism will be highly appreciated. Candidates can be of any nationality. Candidates must hold a Master 2 degree (with research experience). As this is an international project, the candidate's ability to communicate in English and Spanish is an advantage.