EDIACARAN TIME-AVERAGED ULTRA-LOW MAGNETIC FIELD AND ANIMAL RADIATION: THE H LOSS HYPOTHESIS

Time-averaged single crystal paleointensity (SCP) data, robust because they are recorded by single domain magnetic particles, have revealed an Ediacaran field strength 10 times less than present-day (Bono et al., 2019), and far weaker than if due just to frequent reversals. Recently SCP data have been used to define a time-averaged ultralow field interval (UL-TAFI) from 565 to 592 Ma (Huang et al., 2024), and an increasing field strength in the latest Ediacaran and Cambrian, between 544 and 532 Ma (Zhou et al., 2022; 2024). Together, these form a signal consistent with the onset of inner core nucleation. The UL-TAFI corresponds with the appearance of large, mobile Ediacaran animals which are expected to have higher oxygen demands. Geochemical proxies suggest a coincident increase in oxygenation. We recently presented a hypothesis that links these phenomena through magnetospheric H loss to space (Huang et al., 2024). Steady-state solar wind standoff during the UL-TAFI would have been less than 5 Earth radii, whereas during coronal mass ejection events this distance could compress to 1.6 Earth radii. This extreme forcing would greatly expand the polar cap area of open field lines where atmospheric escape can occur. H would be preferentially lost, leaving behind an atmosphere and ocean with increased oxygenation levels. We envision this as a threshold effect, whereby H loss allowed oxygenation to rise above a critical level aiding the diversification of large animals. Because H loss is closely coupled with field intensity, knowing how long the UL-TAFI lasted is of prime importance. In addition, if the field decreased to even lower levels for shorter time periods, as possibly recorded by Zhou et al. (EGU, 2023), pulsed H loss might have occurred contributing to net oxygenation. We will consider these possibilities with new data.