Long-term variations in palaeointensity

We compile a dataset of reliable palaeointensity estimates based both on published work and on new data from basaltic glass. The basaltic glass data more than double the number of reliable (Thellier method with pTRM checks) palaeointensity estimates available. Although the new data dramatically improve both spatial and temporal coverage, there is still a strong bias toward the most recent past. The last 0.3 Ma claim over half of the data in our combined database. We therefore divide the data into two groups, the densely sampled last 0.3 Myr and the more sparsely sampled period of time comprising roughly half of the data from 0.3 to 300 Ma. Separating them in this way, it is clear that the dipole moment of the Earth over the past 0.3 Myr (ca.8 × 1022 A m2) is dramatically higher than the average dipole moment over the preceding 300 Myr (ca.5 × 1022 A m2). Inclusion of poor–quality results leads to an overestimate of the average dipole moment. Interestingly, no other significant changes in the distribution of dipole moments are evident over the 300 million year span of the data.