Overview
This research investigates the coupled thermal evolution of Earth's mantle and core, focusing on the interplay between the onset of modern-style plate tectonics and the longevity of the geodynamo. The study addresses two prominent challenges in Earth science: reconciling the long-lived geodynamo with recent high estimates of core thermal conductivity, a problem known as the new core paradox, and understanding the long-term thermal evolution of the mantle due to the uncertain timing of plate tectonics.
The efficiency of core cooling, which directly influences magnetic field generation, is dependent on the rate at which the mantle extracts heat from the core. This intrinsic link between mantle convection and core dynamics forms the central hypothesis of the investigation. The study utilized a 1D model to simulate this coupled evolution, integrating a parameterized transition from stagnant- to mobile-lid convection. Bayesian inversion was applied, incorporating constraints from the palaeomagnetic record, the mantle's cooling history, and its present-day thermal state.
Research Context
The existence of Earth's long-lived geodynamo presents a difficulty when considering recent high estimates for the core's thermal conductivity. This discrepancy is identified as the 'new core paradox.' Simultaneously, the long-term thermal history of the mantle remains uncertain. A key factor contributing to this uncertainty is the imprecise timing of the onset of modern-style plate tectonics. This geological transition signifies a shift to a more efficient cooling mechanism for Earth's interior, specifically through mobile-lid convection.
The core's cooling rate is fundamental to the generation of the magnetic field. This cooling rate is, in turn, dictated by the efficiency with which the mantle removes heat from the core. Therefore, the challenges associated with the geodynamo's longevity and the mantle's thermal evolution are recognized as being closely interconnected.
Approach
The research employed a 1D model to investigate the coupled thermal evolution of the mantle and core. This model incorporated a parameterized transition from stagnant-lid convection to mobile-lid convection. This transition was defined by two key variables: its onset time and a prescribed duration. This modeling framework was designed to evaluate the impact of various tectonic histories on Earth's thermal and magnetic evolution.
To constrain the model, a Bayesian inversion technique was performed. This inversion utilized observational data derived from three distinct sources:
- The palaeomagnetic record
- The mantle's cooling history
- Earth's present-day thermal state
Findings
The modeling and inversion results indicate a preference for a transition from stagnant-lid to mobile-lid convection during the Archean eon. This early transition to mobile-lid convection is identified as a mechanism that promotes efficient cooling of the core. The enhanced core cooling, in turn, enables the continuous operation of a geodynamo throughout Earth's history.
Crucially, this mechanism remains effective even when considering core thermal conductivities that exceed 100 W/m/K. The findings thus suggest that a relatively early onset of mobile-lid convection offers a viable resolution to the new core paradox.
Why This Matters
The findings directly address the new core paradox by providing a mechanism that reconciles a long-lived geodynamo with high core thermal conductivity estimates. By linking the timing of plate tectonics to core cooling efficiency, the research offers a unified perspective on Earth's thermal and magnetic evolution.