MicroPI: A micromagnetic approach to absolute palaeointensity determinations

The physical and chemical processes that occur deep within the Earth have shaped the evolution of our planet over billions of years. We have very few tools that can be used to investigate the deep Earth over its entire geological history. One such tool is the analysis of magnetic recordings of the geomagnetic field made by rocks.

The geomagnetic field is generated within the Earth's core more than 3000 km below the surface, and its behaviour is modified by the varying chemistry and sources of heat that have been slowly changing since the Earth's formation 4.5 billion years ago. The changes in the geomagnetic field are recorded by rocks when they form. By sampling and analysing the magnetic recordings of rocks, we can play back this recording of the changing geomagnetic field over time, and use this information to test the various theories of the evolution of our planet. In addition, knowledge of the ancient geomagnetic field also allows us to determine habitability on the early Earth's surface, as the geomagnetic field is known to protect and preserve the atmosphere from Solar radiation stripping.

Unlike highly uniform man-made magnetic recording media, rocks contain a wide variety of magnetic particles of different shapes and sizes. These magnetic particles are known to display complex magnetic behaviours; however, until now a very simplified model has been used to explain and determine the ancient geomagnetic field intensities recorded by rocks. This means that the theory we presently use to extract ancient geomagnetic field information from rocks is incorrect, leading to errors in estimates of the ancient field intensity. This casts doubt on our current view of the how the geomagnetic field intensity has varied in the past, and also likely explains inconsistencies in multiple studies where different results are obtained from rocks of the same age.

In the last year, the proposers of this project have developed a new theoretical model which accurately captures the complex behaviour of the magnetisations recorded within rocks. In this project, we propose to use our new understanding of how magnetic minerals record the geomagnetic field to build a completely new and different approach for determining ancient geomagnetic field intensities recorded in rocks. This new method will rely on a large numerical database of magnetic characteristics of different types of magnetic particles that have been simulated from numerical models. We will make this new method available to the scientific community through a web-app, where Earth Scientists can upload their own experimental measurements and can calculate estimates of palaeomagnetic field intensities using our new method.

With our new approach we will investigate one of the most pressing issues of our times concerning heat and heat flow within the Earth over the last 4.5 billion years: when did the solid Inner Core nucleate? There are some published palaeomagnetic data to suggest that it is as recent as ~500 million years ago, though this is widely disputed. We will use our new approach to determine the reliability of these magnetic data, and to better pinpoint the timing of Inner Core Nucleation.