represented by the rock record (than is expected by assuming continuous magmatism between available radiometric age data) and capturing only a few field reversals would be expected.

The oldest reversal documented to date is that associated with 3.1 to 3.2 Ga plutonic rocks exposed in the Barberton Greenstone Belt [@Layer1998; @Tarduno2007]. An older reversal has been reported from study of a purported 3.4 Ga tuff of the Barberton Greenstone Belt [@Biggin2011], however the sampled rocks are sandstone and minor shale highly altered by local fluids (Axel Hofmann, personal communication). Moreover, the limited spatial sampling and interpretation by the authors of contamination of the data by lightning strikes suggests this reversal record could be an artifact.

Smirnov et al. [@Smirnov2003] applied the SCP approach to $\sim$2.45 Ga dikes formed close to the Proterozic-Archean boundary from the Karelia Craton of Russia. Although the dikes were insufficient in number to completely average secular variation, the values are consistent with present-day field values. The SCP was also applied to 3.2 Ga plutons of the Barberton Greenstone Belt. These yielded a mean paleointensity that was interpreted as being within 50% of the current field value [@Tarduno2007]. However, this relatively large uncertainty was assigned to the 