Before the Inner Core? Palaeomagnetic field intensity measurements from Proterozoic-aged Scandinavian igneous and baked Rocks


  • Supervisors: Prof Andy Biggin, University of Liverpool
    Dr Greig Paterson, University of Liverpool


  • External Supervisors: Dr Johanna Salminen; Solid Earth Geophysics Laboratory, Univ. Helsinki, Finland
    Prof Lauri Pesonen; Solid Earth Geophysics Laboratory, Univ. Helsinki, Finland
  • Contact:

    Prof Andy Biggin (University of Liverpool), biggin@liverpool.ac.uk

  • CASE Partner:

Application deadline: 10 January 2020

Introduction:

The Proterozoic Eon (540 – 2500 million years ago) is the single largest in Earth’s history but very little is known about how the Earth’s magnetic field was behaving at this time. A paper in the journal Nature led by the Liverpool group (Biggin et al., 2015) argued that the field was weakening prior to 1100-1300 million years ago and then sharply rose as a result of the sudden freezing of liquid iron at Earth’s centre. This hypothesis is at the centre of a major scientific controversy (e.g. Smirnov et al., 2016; Bono et al., 2019) and requires rigorous testing by more and better palaeomagnetic data. 

Measurements of the ancient magnetic field intensity are possible because igneous rocks lock in the properties of the magnetic field at the time and place they cool from magma. Scandinavia hosts a wealth of igneous rocks from the Mesoproterozoic and Palaeoproterozoic Eras (1000-2500 million years ago) that have already given good palaeomagnetic directions and which therefore make strong targets for this project. 

The aim of this project is to improve our records of how the magnetic field strength changed through the Proterozoic such that the hypothesis of inner core birth just over 1 billion years ago can be better tested. The potential implications of this research are profound in terms of telling us how the deep Earth’s structure and temperature has evolved through our planet’s 4.5 billion year history (Davies et al., 2015).

Project Summary:

The appointed student will join the DEEP (Determining Earth Evolution from Palaeomagnetism) research group (https://tinyurl.com/ybt9s9f6), comprising ten other PhD students and post-docs housed in the University of Liverpool’s Geomagnetism Laboratory. This multimillion pound laboratory is one of the best in the world for palaeomagnetic intensity measurement.

They will perform several field-trips and/or research visits to Finland and potentially other parts of Scandinavia. We have identified several primary targets and already have some pilot samples in the lab.

The student will be trained in how to take samples in the field and how to use our state-of-the-art equipment to measure the ancient magnetic strength recorded in them. There are a variety of different procedures that can be used for this (Biggin et al., 2011) but all involve simulating the thermomagnetic conditions under which the sample acquired its ancient magnetisation.  The samples will also need to be studied using microscopic and magnetic characterisation techniques. Finally the results will need to be carefully analysed and interpreted in terms of what they are telling us about ancient magnetic field behaviour.

This project would suit a geophysics or geology graduate who is keen to do field and lab work and then apply their results to understanding deep Earth evolution. Full training will be given.

References:

Biggin, A.J., Piispa, E.J., Pesonen, L.J., Holme, R., Paterson, G.A., Veikkolainen, T., Tauxe, L., 2015. Palaeomagnetic field intensity variations suggest Mesoproterozoic inner-core nucleation. Nature 526, 245-248. 

Biggin et al. (2011). “Palaeomagnetic Field Intensity”. In: Harsh K. Gupta (ed.), Encyclopaedia of Solid Earth Geophysics, Springer, DOI 10.1007/978-90-481-8702-7. 

Bono, R. K., et al. (2019). "Young inner core inferred from Ediacaran ultra-low geomagnetic field intensity." Nature Geoscience 12: 143–147. 

Davies, C., Pozzo, M., Gubbins, D., Alfe, D., 2015. Constraints from material properties on the dynamics and evolution of Earth's core. Nature Geosci. 8, 678-685. 

Smirnov, A. V., et al. (2016). "Palaeointensity, core thermal conductivity and the unknown age of the inner core." Geophysical Journal International 205: 1190-1195.

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