Stochastic optimisation of absolute geomagnetic palaeointensity determinations

Lead Research Organisation: University of Liverpool
Department Name: Earth, Ocean and Ecological Sciences

Abstract

I propose to develop a new mathematical tool that will make measurements of the Earth's magnetic field strength in the ancient past much more reliable and efficient. The magnetic field of the Earth extends far into space and is important to humans for many reasons. It is used by us and other species for navigation and it also protects human technology from the 'solar wind' - a stream of high-energy particles emitted by the sun. The interaction of the solar wind with the Earth's magnetic field causes aurorae (the Northern and Southern Lights) and other 'space weather' phenomena. The initiation of a strong, global 'geomagnetic' field more than three billion years ago may have been a crucial factor in allowing the first life on Earth to appear. Before then, the atmosphere might not have been able to form because of continual erosion by the solar wind. The importance of the Earth's magnetic field to human civilisation and life in general means that it is very important that we study it and learn as much about it as we can. Another good reason for this is that it can tell us a great deal about the place where it is generated: the deep interior of the Earth. At any one point on the Earth's surface, the magnetic field has both direction and intensity which both vary rather erratically in time. To study the present-day behaviour of the Earth's magnetic field, we use specialist satellites and a global network of magnetic observatories. To study the field in the distant past, we must turn to the geological record and volcanic rocks in particular. These lock-in the direction and intensity of the field at the time and place that they cool from molten lava and therefore provide a globally-distributed 'palaeomagnetic' record for almost the whole of Earth's history. The ancient direction of the Earth's magnetic field as recorded in rocks is much easier to measure than is its ancient strength (called its 'palaeointensity'). However, absolute palaeointensity records are essential for allowing us understand the geomagnetic field and its history. The problem with measuring the palaeointensity is that the rocks which are used can be affected by many complex physical factors which can bias the result. Furthermore, the precise way the measurement is carried out can also affect its reliability. A lot of recent work has gone into improving our understanding of these problems but a lack of synthesis means that palaeomagnetists still do not agree on which rocks and experimental methods produce reliable palaeointensity measurements. There is also some disagreement over which of the thousands of palaeointensity measurements which have already been published can be trusted and which should be disregarded as unreliable. These disagreements could largely be overcome if we had objective, quantitative information about the likely success of any particular palaeointensity experiment. My proposal is to provide this by developing an entirely new 'stochastic' (i.e. partially random) numerical model of palaeointensity experiments which can optimise: experimental design, analytical and procedure, and objectively determine the reliability of published data. I will rigorously constrain and test this model using new and published experimental data and ultimately, I will employ it to obtain important new information including the strength of the Earth's magnetic field more than 3 billion years ago. The benefits of this work will be considerable. It will enable future palaeointensity studies to be performed with much greater efficiency and will also allow us to get the most out of the thousands of palaeointensity determinations which are already published. Our understanding of the Earth's magnetic field, its formation in the outer core, and its protection of society and life as a whole will all be improved as a result.

Publications

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Biggin A (2010) Paleointensity Database Updated and Upgraded in Eos, Transactions American Geophysical Union

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De Groot L (2015) High paleointensities for the Canary Islands constrain the Levant geomagnetic high in Earth and Planetary Science Letters

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Deenen M (2011) Geomagnetic secular variation and the statistics of palaeomagnetic directions in Geophysical Journal International

 
Description The aim of this project was to improve our ability to make measurements of the Earth's magnetic field (its strength in particular) in the distant past and to use these to better understand how it is generated in the planet's core and how it may behave in the future. The key findings were:

- Thanks to multiple experimental and numerical analyses, we now understand much better how to efficiently obtain and recognise reliable measurements of the ancient field intensity. Our new tools, protocols, and data have been made available for the rest of the research community to use in their own analyses.

- We have measured the direction of the magnetic field recorded in 3.5 billion year old rocks from South Africa and shown that the field was broadly similar to today's early in the Earth's history. This is puzzling because the conditions in the core of the planet were quite different back then.

- We have measured the strength of the magnetic field over the last 5,000 years in Turkey and in Hawaii. We have shown that the field can increase its strength significantly in a matter of decades and that, although it is presently weakening, it is fluctuating in time and space as it does.
Exploitation Route Our new techniques will be applied to document, and hence better understand, geomagnetic field behaviour on a range of timescales.
Sectors Environment

 
Description Our 2011 paper on the magnetism of 3.5 billion year old rocks from South Africa was chosen as an "Editor's highlight" for the major publication Science
First Year Of Impact 2011
Sector Education
Impact Types Societal

 
Description Leverhulme Research Leadership Award
Amount £999,592 (GBP)
Funding ID RL-2016-080 
Organisation The Leverhulme Trust 
Sector Academic/University
Country United Kingdom of Great Britain & Northern Ireland (UK)
Start 07/2017 
End 07/2022
 
Description NERC Standard Grant
Amount £436,183 (GBP)
Funding ID NE/P00170X/1 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom of Great Britain & Northern Ireland (UK)
Start 12/2016 
End 08/2020
 
Description NERC Standard Grant
Amount £254,678 (GBP)
Funding ID NE/H021043/1 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom of Great Britain & Northern Ireland (UK)
Start 12/2010 
End 06/2014
 
Description NERC Strategic Capital Grant
Amount £384,814 (GBP)
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom of Great Britain & Northern Ireland (UK)
Start 12/2013 
End 12/2015
 
Description Royal Society International Exchanges
Amount £3,000 (GBP)
Funding ID IE131187 
Organisation The Royal Society 
Sector Academic/University
Country United Kingdom of Great Britain & Northern Ireland (UK)
Start 03/2014 
End 06/2014
 
Description Royal Society Research Grant
Amount £13,000 (GBP)
Funding ID RG130771 
Organisation The Royal Society 
Sector Academic/University
Country United Kingdom of Great Britain & Northern Ireland (UK)
Start 04/2014 
End 04/2015
 
Title PINT database 
Description A global open-access database of absolute palaeointensity has been continually updated, analysed, and improved. 
Type Of Material Database/Collection of data 
Provided To Others? Yes  
Impact Three papers have been published describing updates to the database: Biggin et al. (2009a,b) Biggin & Paterson (2014) These have so far been cited more than 50 times. Additionally, it formed the basis for a working group at a recent international workshop in Oslo. 
URL http://earth.liv.ac.uk/pint/
 
Description Greig Paterson 
Organisation Chinese Academy of Sciences
Country China, People's Republic of 
Sector Public 
PI Contribution Provided specialist palaeointensity expertise and measurement data.
Collaborator Contribution Provided computer modelling results and written up research
Impact Paterson et al. (2012) Paterson et al. (2014) Biggin et al. (2014)
Start Year 2011
 
Description Utrecht 
Organisation Utrecht University
Country Netherlands, Kingdom of the 
Sector Academic/University 
PI Contribution Provided training in the use of, measurements, and interpretation of data from the microwave palaeointensity system. Sent a PhD student to Utrecht to make measurements using their robot magnetometer.
Collaborator Contribution Sent students over to use the Liverpool microwave palaeointensity system.
Impact Biggin et al. (2011) Deenen et al. (2011) Ertepinar et al. (2012) de Groot et al. (2013) Roberts-Artal (submitted) Monster et al. (submitted) Another paper near submission
Start Year 2009
 
Description Media surrounding 2015 inner core paper 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact A press release was made following the publication of Biggin et al. (2015) in Nature. This was picked up well by media organisations internationally (e.g. BBC, Mail online, El Pais, ABC, etc) and involved a radio interview broadcast on the BBC World Service.
Year(s) Of Engagement Activity 2015
URL http://www.bbc.co.uk/news/science-environment-34475464