Core and mantle thermal evolution constraints on the onset of plate tectonics and a long-lived geodynamo

TL;DR

This study models Earth's coupled mantle and core thermal evolution, suggesting that an early transition to mobile-lid convection explains the long-lived geodynamo despite high core thermal conductivity estimates.

Contribution

It introduces a Bayesian framework to assess how tectonic history influences Earth's thermal and magnetic evolution, resolving the new core paradox.

Findings

Early transition to mobile-lid convection promotes sustained geodynamo.

A delayed onset of mobile-lid convection aligns with paleomagnetic and thermal data.

High core thermal conductivity does not preclude a long-lived magnetic field.

Abstract

Earth's long-lived geodynamo is difficult to reconcile with recent high estimates of the core thermal conductivity, a problem known as the new core paradox. At the same time, the long-term thermal evolution of the mantle remains uncertain, largely due to the poorly constrained onset of modern-style plate tectonics, which marks the transition to efficient cooling of the interior through mobile-lid convection. Because core cooling -- and thus magnetic field generation -- depends on the efficiency with which the mantle extracts heat from the core, these two problems are closely linked. Here, we investigate the coupled thermal evolution of mantle and core using a 1D model that incorporates a parametrized transition transition from stagnant- to mobile-lid convection, defined by its onset time and with a prescribed duration. This framework allows us to assess how different tectonic histories influence Earth's thermal and magnetic evolution. We perform a Bayesian inversion using constraints from the palaeomagnetic record, mantle cooling history, and present-day thermal state. Our results favour a transition from stagnant- to mobile-lid convection during the Archean, which promotes core cooling and enables a geodynamo throughout Earth's history, even for core thermal conductivities in excess of 100 W/m/K. A delayed onset of mobile-lid convection provides thus a viable solution to the new core paradox.