Secular variation of the Late Archean-Early Proterozoic geodynamo

We report new paleomagnetic data from ~2.5 Ga dikes of the Superior Province and derive estimates of paleosecular variation. When combined with data from coeval dikes of the Karelia Craton (Russia) and older (~2.7 Ga) volcanics of the Pilbara Craton, these estimates suggest a latitudinal variation of secular variation similar to that of the last 5 million years, but with potentially smaller quadrupole family contributions. The observations are consistent with some numerical models of the field that suggest a more dipolar field when the Earth had a much smaller solid inner core.