Highs, Lows, and Puzzling Intensity Variations of the Earth’s Magnetic Field

Abstract

The Earth's magnetic field has a pivotal role in the Earth Sciences, its applications range from plate tectonics, to magnetostratigraphy. Together with seismology, it is the only window into the deep Earth and the Earth's core. In everyday life, the Earth's magnetic field is important for navigation devices. More importantly, the Earth's magnetic field protects the Earth against harmful solar radiation, and it protects satellites orbiting the Earth. Without the Earth's magnetic field, the atmosphere would have been stripped away and life on Earth would not have been possible. The growth of a stable magnetic field is thought to have been instrumental for the beginning of early life. Understanding the evolution and behavior of the Earth's magnetic field is therefore of great importance. In this thesis I will focus on the study of the strength of the Earth's magnetic field, its intensity. Therefore, I set out to unravel fast and local fluctuations in the direction and strength of the geomagnetic field. Paleointensity-the key to understanding the Earth's magnetic field Methods to derive paleointensity estimates from absolute recorders, e.g. lavas or archaeomagnetic materials, rely on comparing the ancient magnetization of the recorders that was obtained during cooling in the Earth's magnetic field, with a laboratory induced magnetization. As simple as this might sound, obtaining reliable and high quality paleointensity estimates from lavas is notoriously difficult. Besides the laborious effort to obtain paleointensity measurements, there is little consensus on the best approach of interpreting the measurement data and how to distinguish between high and low quality results. The first to propose to obtain information on the past state of the strength of the Earth's magnetic field by studying thermal remanences was Guiseppe Folgheraiter. He proposed that by reheating ancient pottery, the intensity of the ancient magnetization could be compared to the present magnetization (Folgheraiter, 1899). Folgheraiter did find that this method might lead to 'too uncertain results' when the baked vases were reheated several times. Almost forty years later an experimental protocol for estimating the ratio of natural remanent magnetization (NRM) and a laboratory acquired thermal remanence magnetization (TRM) was described by Johann Koenigsberger (1936). Koenigsberger used prologue a comparison of quasi-perpendicular and doubleheating thellier-style paleointensity techniques-towards an optimal protocol 1