Van der Voo Lecture: Paleo/Geomagnetism and Geobiology: Case Studies from the Ediacaran and Jurassic
Joseph Meert, University of Florida
Paleomagnetic research relies on two fundamental assumptions. The first is that rocks can faithfully document the structure of the Earth’s magnetic field in recent and deep time. The second assumption is that the field recorded in rocks closely approximates a Geocentric Axial Dipole (GAD) field. If we are correct, then the paleomagnetic record provides important information regarding the past geometry of continental distributions and possible connections to biological evolution. Furthermore, the magnetic field shields the planet (and living organisms) from incoming solar and inter-galactic radiation. In this talk, I will present two case studies that outline how paleomagnetic studies were used to evaluate important evolutionary changes. The first case study is from the Ediacaran where the Earth’s magnetic field appears to have undergone a lengthy interval of hyperactive reversals in the Ediacaran. Hyperactivity results in a decrease in the overall strength of the dipole field and a concomitant collapse of the ‘shield’ that protects the planet from incoming radiation. We suggest that prolonged interval with a weakened dipole caused the collapse of the Ediacaran habitat and set the stage for the Cambrian radiation. The second case study examines rapid changes in paleolatitude of the North China Block during the Late Jurassic. New paleomagnetic data from volcanic rocks indicate that East Asia moved from intermediate to lower latitudes during the Late Jurassic. That movement coincided with the aridification of East Asia and the demise of the Yanliao biota. The Yanlioa biota contain the first feathered dinosaurs, eutherian mammals and a diverse entomofauna.
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