EDIACARAN ULTRA-WEAK GEOMAGNETIC FIELD, OXYGEN RISE AND MACROSCOPIC ANIMAL DIVERSIFICATION

The paleomagnetic field can provide insight into the state of Earth’s core, but retrieving this information is challenging. Only a tiny fraction of natural magnetic mineral recorders can faithfully preserve a key indicator, field strength, on geological time scales. The single crystal paleointensity (SCP) method targets these minerals, which can occur as inclusions in silicate crystals. A major discovery of SCP studies was an ultralow geomagnetic field strength, ten times weaker than today, at 565 Ma in the Ediacaran documented from study of the Sept-Îles Mafic Intrusion Suite (Bono et al., Nature Geoscience, 2019). This record has since been confirmed by several studies of dikes. Herein, we further consider Precambrian to Cambrian paleointensity history using new data. We find a striking temporal correspondence between the ultralow field, diversification of macroscopic animals and some geochemical indicators for the rise of oxygenation. The best explanation for the unusual and unprecedented state of the Ediacaran dynamo is the onset of inner core growth (Zhou et al., Nature Communications, 2022). This change in state of the core should not relate to animal evolution or oxygenation unless changes in the magnetosphere attendant with the ultralow field somehow affected the atmosphere, oceans and/or biosphere. We will consider these possibilities.