The Evolution and Current State of Archaeomagnetism

Date of Award

Spring 1-1-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Anthropology

First Advisor

Honeychurch, William

Abstract

Archaeomagnetism is a subfield of archaeology in which the magnetic properties of archaeological material are analyzed to answer questions about the human past. These analyses fit into two primary categories: material characterization and archaeomagnetic dating. Archaeomagnetic material characterization is applicable to almost any iron-bearing material, like pottery, glaze, ochres, brick, hearths, burned floor, lenses, lithics, furnace wall, slags, iron objects, stone objects, and more. Examining the magnetic properties and mineralogy of these materials offers insights into their composition, thermal and chemical history, and potential for archaeomagnetic dating. Archaeomagnetic dating is both a relative and absolute dating technique depending on the methodology used. This is possible because the direction and intensity of the Earth’s magnetic field are always experiencing continuous, random, and independent variation. When iron-bearing materials are subjected to certain thermal, chemical, or physical changes, they have the potential to record a snapshot of the direction and intensity of the Earth’s magnetic field at the time of that change. These snapshots can persist for thousands, or even billions of years, creating a useful record of these changes that we can exploit for dating. As a relative dating technique, archaeomagnetism can easily determine the contemporaneity of archaeological features. If the direction and intensity recorded in materials are the same, and come from the same site, it is highly likely that these materials come from the same time. If the records differ, it is highly likely these materials come from different times. If a site, or collection or nearby sites, provide a clear stratigraphic profile, then it is possible to order archaeomagnetic records according to the stratigraphic information. This would produce an archaeomagnetic dating curve, but only a relative one. This type of curve can be used to get the relative age of archaeological material, ordering materials by age but without any determination of absolute ages. If these stratigraphic layers can be dated by associated materials, for example by historical records, cultural sequencing, radiocarbon dating, dendrochronology, or any other absolute dating technique, then the archaeomagnetic dating curve can be calibrated against those dates. A calibrated archaeomagnetic dating curve is capable of absolute dating. The best archaeomagnetic dating curves can produce dates on a decadal scale, and be applicable to an area of up to 900 km in radius. This dissertation attempts to explain the history of archaeomagnetic dating, how it developed from paleomagnetism, what questions it has answered for archaeologists, and what further developments of archaeomagnetism can offer to archaeology as a whole. In so doing we will discuss the equipment and concepts of magnetism necessary to conduct and interpret archaeomagnetic analyses. The dissertation will conclude with a case study in archaeomagnetic dating and archaeomagnetic material characterization in which the process of archaeomagnetism is explained through the initial archaeological question, excavation and field methods, lab methods and analysis, and finally interpretation and presentation of results.

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