Improving archaeomagnetic dating through new data acquisition and method development

Project: Dissertation

Project Details

Description

The Earth’s magnetic field (or geomagnetic field) has been measured for hundreds of years, starting with maritime observations from logbooks for navigation purposes to present day real-time recording by satellites. From these records, the geomagnetic field variation throughout recent time is well-understood. In order to study longer term field variations (on the scale of hundreds to thousands of years), it is necessary to use indirect methods of observation of the geomagnetic field, recovered from lavas and burnt archaeological clays. Reconstructions of the geomagnetic field based on such archaeo-/ palaeomagnetic data can be used both to date certain archaeological and geological materials and to study deep Earth processes where the field is generated. However, the currently available archaeo-/ palaeomagnetic data are not geographically nor chronologically well-distributed. The first aim of this thesis is therefore to provide new archaeomagnetic field determinations from locations that are currently under-represented (either spatially or temporally) in the geomagnetic field records, including southern Africa, New Zealand and the Orkney Isles, UK. New geomagnetic field intensities have been collected from each targeted location and in addition, new geomagnetic field directions from New Zealand have also been produced. Archaeomagnetic dating is challenging in data sparse areas such as these, due to large and often unknown uncertainties of either the data (due to non-ideal formation/ preservation conditions) or the geomagnetic reference curves or both. The second aim of this thesis is to address such problems by introducing alternative methodologies for archaeomagnetic dating, (i) accounting for unknown uncertainties and (ii) using alternative constraints, such as the rate of change of the geomagnetic field to be able to provide chronological information.

Layman's description

The Earth’s magnetic (geomagnetic) field is generated from deep inside the Earth’s core, but we can still see the effects of it on the surface (e.g.- navigating using a compass) and even benefit from it as it provides a barrier to stop harmful energetic charged particles from space entering into Earth’s atmosphere. However, in recent years the magnetic field has been getting weaker, especially around the South Atlantic region, known as the South Atlantic Anomaly. This has started to cause some issues as energetic particles in this region are now able to reach and interfere with objects in low-orbit around the Earth, e.g.- causing damage to satellites.

 

In order to fully understand the South Atlantic Anomaly, more measurements of the geomagnetic field are needed to reconstruct how it has evolved through time. Before satellite measurements and historical records (which are available for the past four centuries), it is still possible to get geomagnetic field measurements from signals recorded by the magnetic minerals in archaeological artefacts and volcanic rocks. However, our current databases lack records in the Southern Hemisphere, and also lack older measurements from time periods before 0 AD. This project has collected additional geomagnetic field data over archaeological times from the Southern Hemisphere, from both southern Africa and New Zealand. Additionally, the first geomagnetic field strength measurements for the Neolithic period in the United Kingdom (which occurred between 6000 to 4000 years ago) have been determined.

 

In addition to providing information about geomagnetic field evolution, geomagnetic field models constructed using sufficient measurement data can also be used to date archaeological artefacts and volcanic rocks of unknown age. The magnetic field recording extracted experimentally from the object under investigation can be matched to an appropriate model in order to tell us the age of said object. This project has shown it is possible to refine an object’s age, even in areas where there are very few geomagnetic field measurements, thus providing valuable information, especially to archaeological excavations in the Southern Hemisphere.

 

StatusFinished
Effective start/end date2017/01/092023/05/26

UKÄ subject classification

  • Geology
  • Geophysics

Free keywords

  • geomagnetic field
  • archaeomagnetism
  • archaeomagnetic dating
  • palaeomagnetism