Recent developments in Archeomagnetism: the story of the Earth's past magnetic field

Abstract

Since the pioneering studies in archeomagnetism in the second half of the 20th century, the number of archeomagnetic studies has increased exponentially. The huge density of archeomagnetic data collected during these years allows us to describe the past spatial and temporal evolution of the Earth’s magnetic field during the last millennia. Most of the data are located in the Northern Hemisphere, but currently, thanks to the strong effort of the paleomagnetic community, new collections of data are coming from the Southern Hemisphere, homogenizing the present database. Although the data distribution presents some epochs and locations where the data are still very scarce, they describe, to a greater or lesser degree of accuracy, the past behavior of the geomagnetic field. At regional scales, the use of archeomagnetic data permits the construction of paleosecular variation curves for the geomagnetic field elements: declination, inclination, and intensity. These curves describe the evolution of the elements at different times for the last millennia. During the last five years novel techniques, such as Bayesian statistics, bootstrap algorithms, or the Markov chain Monte Carlo method, have been applied to extract the most useful information from archeomagnetic data to build accurate and reliable curves. The accuracy of these curves can be exploited as a tool for archeomagnetic dating, assigning possible ages to archeological artifacts or volcanic lava flows with unknown age. At global scales, archeomagnetic data are jointly treated with other paleomagnetic data to generate continuous geomagnetic field models, reconstructing the past evolution of the geomagnetic field not only at the Earth’s surface, but also at the core-mantle boundary, shedding light on the past evolution of complex geodynamo processes.