Three ways to test the validity of the Geocentric Axial Dipole (GAD) hypothesis in the Precambrian

One of the most fundamental aspects of paleomagnetism is the assumption that the temporal mean of the geomagnetic field is indistinguishable from a field generated by a geocentric axial dipole (GAD hypothesis). When the theory became mainstream, various ways to test its functionality were presented, based on e.g. deep-sea sediment cores, paleoclimatic indicators and paleointensity. Most suspicion of the dipolar nature of the geomagnetic field has dealt with the Precambrian. To analyze this bias, we have used the data from the novel paleomagnetic database, collected by University of Helsinki, and Yale University for over a decade's time. Altogether 3016 observations from all major Precambrian continents were gathered, and a thorough compilation of reversals of the Archean and Proterozoic geomagnetic field was done. Observations were filtered using different criteria, e.g. geologic age, rock type (igneous vs. metamorphic vs. sedimentary) and reliability according to the modified Voo-grading. Testing the GAD has rested on a) inclination frequency analysis, b) asymmetries in reversal data, and c) paleosecular variation (PSV) using CALS7K, CALS3K, GUFM and IGRF models as references. The results suggest that the geomagnetic field of the Precambrian is not far from the field predicted by the GAD model. The inclination frequency analysis supports the existence of a small octupolar (ca. 6 % of GAD) component and a quadrupole of 0-8 % of GAD as evaluated using chi-square testing. Conclusions drawn from the asymmetry analysis and PSV are statistically indifferent from this. The deviation from the GAD is smallest for the highest-quality observations, especially so called key poles. They have well-defined isotopic ages, small error parameters in their Fisher data and their primary remanent magnetization has been properly isolated. This also means that the observed functionality of GAD cannot be a misconception caused by secondary magnetizations acquired in the Phanerozoic. Large or even moderate non-dipolar contributions to the field can be ruled out, and this gives further validity for recently calculated configurations of Precambrian continents and supercontinent cycles.; Results from the chi-square testing of the igneous rock data. The p values, i.e. statistical probabilities, are shown according to their respective colors in the grid. Bilinear interpolation has been applied to make the view smooth.