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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. Understanding the evolution and behavior of the Earth’s magnetic field is therefore of great importance. The Earth’s magnetic field is generated in the liquid outer core. The Earth is often considered to be a large bar-magnet with two poles (dipole), with a magnetic north and south pole. The Earth’s magnetic field is, however, not stable, it changes over time. Due to the dynamic behavior of the Earth’s magnetic field its direction and intensity changes on the Earth’s surface. This dissertation sets out to unravel fast and local fluctuations in the direction and strength of the geomagnetic field that cannot be explained by the dipole.

To obtain a magnetic direction of the past state of the Earth’s magnetic field is relatively straightforward. Obtaining the strength (intensity) of the Earth’s magnetic field is however very challenging. Therefore, first this dissertation sets out to ease and standardize the interpretation of paleointensity data. The dissertation used these new standards to study two non-dipolar geomagnetic field features, the ‘Levantine Iron Age Anomaly’ and the ‘South Atlantic Anomaly’. It provides constraints on the spatial and temporal extent of these two short-term anomalous features of the Earth’s magnetic field. This brings us closer to unraveling these non-dipolar geomagnetic field features.