Geosciences Seminar: Yiming Zhang

About this event

Join us on Nov. 2 at 3 PM for Yiming Zhang's seminar.

The seminar topic is "Tiny Grains, Big Questions: The Ediacaran Geomagnetic Field Enigma " .

The seminar will be held in BGYM 219 at 3 PM . There will be coffee and cookies in the Lobby of ERB prior to the talk at 2:40 PM .

We will be holding a Pizza Lunch at 12pm in ERB 1161!

Yiming Zhang Seminar

Title: Tiny Grains, Big Questions: The Ediacaran Geomagnetic Field Enigma

Abstract: Earth’s magnetic field connects motion in the core to our planet’s interaction with the solar wind and the conditions that support long-term habitability. How has the geodynamo sustained a field as Earth cooled, and how can we distinguish among competing models for the paleomagnetic observations? I will introduce methods for studying Earth’s magnetic field through time and examine how ancient rocks have been used to constrain Earth interior evolution. Exceptionally weak Ediacaran–Cambrian paleointensities have been interpreted as evidence for a declining, inner core-free geodynamo which was subsequently revived by inner-core nucleation. This interpretation has prompted hypotheses of a causal relationship between core evolution and surface habitability. However, during the same time, extensive chronostratigraphic records show that Earth's magnetic field experienced frequent and intense directional anomalies. Could these weak paleointensities reflect biased magnetic recording during geomagnetic anomalies? Using micromagnetic models of realistic natural magnetite grains, coupled to continuous-time Markov chain probability evolution, I will test whether cooling through a geomagnetic reversal could produce apparent weak intensities in rocks even when the field before and after the reversal is strong. Model results suggest that this process could cause paleointensity records to significantly underestimate field strengths. Weak paleointensities alone may therefore be consistent with either a weak geodynamo or inefficient magnetic recording in a reversing field. In the future, developing joint constraints from magnetic field intensity, direction, and thermal histories from the same rock may offer a way to better inform paleointensity inferences and assess their implications for Earth's long term interior evolution.