16:00 〜 16:15
[SIT16-08] A long-lasting tenuous Ediacaran dynamo: Linkages to inner core nucleation and the evolution of animal life
キーワード：Paleomagnetism, core, geodynamo, Ediacaran, magnetosphere, animal evolution
Numerous studies define a geodynamo field 10 to 30 times weaker than present-day during the Ediacaran Period. Here we highlight new results from several studies that add to our knowledge of this critical period: i. Single crystal paleointensity (SCP) results from ca. 544 Ma syenites of Canada yield a dipole moment of approximately 2.3 x 1022 A m2. Together with results from 532 Ma anorthosites of Oklahoma, these new data define a rapid recovery of field strength after the Ediacaran ultralow period. ii. New SCP results from ca. 590 Ma dikes of Canada yield field strength of hundreds of nanoteslas (or less) suggesting that the dynamo may have ceased entirely for periods lasting 2 to 100 thousand-years-long during the Ediacaran. iii. Preliminary SCP results from ca. 641 Ma anorthosites of Brazil suggest that the Neoproterozoic period of weak fields might have commenced in the late Cryogenian. These results further highlight agreement with dynamo models that predict low and unusual fields at the time of inner core nucleation, at ages similar to those defined by our data (Driscoll, 2016; Davies et al., 2022). Moreover, the depth of the field decay in the Ediacaran, and its duration spanning at least tens-of-millions-of-years suggest that changes in magnetospheric trapping could have contributed to net oxygenation of the atmosphere and oceans, facilitating the coeval evolution of macroscopic, mobile animals.