Intensity of the Earth's magnetic field: Evidence for a Mid-Paleozoic dipole low

Significance Variations in past geomagnetic field strength are important indicators of variation in deep Earth processes over hundreds of millions of years. Most other geophysical methods only provide a snapshot of the Earth’s recent interior, and deep Earth materials are poorly represented in the geological record. Recent measurements from Scotland (Northern United Kingdom), in addition to the existing datasets, show the field was relatively weak (less than half the strength of the long-term average field) for tens of millions of years between 332 and 416 Ma. The similarities between this and a later period of low field strength provide further evidence for a ∼200-My cycle linked to deep Earth processes.