A fibrillating Cryogenian-Ediacaran magnetic field: Implications for the nature of the dynamo, inner core nucleation, and the Avalon explosion of life

During the last 7 years several groups have reported paleomagnetic data documenting an unprecedented interval during the Ediacaran Period when the global geomagnetic field strength was only 10 to 3 percent of the present-day value, defining an ultra-low time-averaged field interval (UL-TAFI) from 591 to 565 Ma. Moreover, the EMANATE hypothesis suggests that atmospheric H loss to space through the UL-TAFI weak magnetosphere led to increased oxygenation, assisting the Avalon explosion of animal life (Tarduno et al., 2025). A relatively rapid increase in field strengths after the UL-TAFI has been suggested to record the onset of inner core nucleation; the return of magnetic shielding may have assisted subsequent Cambrian evolution. Herein, we present new data that suggest: 1. the UL-TAFI was at least 90 million years long, beginning in the Cryogenian Period and, 2. the field may have completely collapsed to zero during events as long as 200 kyr within the UL-TAFI. While the existence of the UL-TAFI does not comment on the need for core supercooling for inner core nucleation, the extended duration defined here is compatible with some models for such a process.  Variations of the field strength and dipolarity within the UL-TAFI may record bistability between the weak and strong field branches of the geodynamo as seen in some numerical simulations. This bistability, proposed to characterize the very start of the geodynamo, may have also been the underlying nature of the field during late Neoproterozoic times, explaining seemingly anomalous magnetic directions from global sites. The extended duration of the UL-TAFI, and the episodic complete collapse of the dynamo, support the hypothesis that H loss and increased oxygenation of the atmosphere and ocean, enabled the radiation of macroscopic Ediacaran animal life.