Did the dynamo cease during the Ediacaran Period prior to inner core nucleation?

Models and paleointensity data continue to consistently point to the Ediacaran Period as the most likely time for the onset of inner core nucleation (ICN). The geodynamo models of Driscoll (2016) and Driscoll and Davies (2022) predict a weak field state, where core kinetic energy exceeds magnetic energy, prior to ICN. The paleomagnetic record of the Ediacaran Period shows a hyper-reversal frequency and unusually high secular variation. But the most telling characteristic of the Ediacaran magnetic field that suggests the dynamo approached the weak field state is its time-averaged ultralow paleointensity, more than 10 times weaker than today (Bono et al., 2019). The field subsequently regained strength in the early Cambrian (Zhou et al., 2022), consistent with Ediacaran ICN. Here, we investigate the possibility that the magnetic field may have ceased completely for some part of the Ediacaran Period. We report new field strength values from whole rocks that are less than 1-2 microTesla. These values are amongst the lowest terrestrial fields ever recorded, heightening the possibility of environmental effects due to the weakened magnetosphere that may have in turn influenced biotic evolution. But even these ultralow field values may overestimate the true ambient field strength because of subsequent thermal viscous magnetic overprints carried by nonideal magnetic carriers in whole rocks. We will discuss our efforts to use single crystal paleointensity methods to isolate ideal magnetic carriers to resolve this question.