Mantle heterogeneity influenced Earth’s ancient magnetic field

TL;DR

The Earth's magnetic field may have been shaped by heat variations at the core-mantle boundary, as shown by combining magnetic records and simulations.

Contribution

Combining palaeomagnetic data and simulations to show how mantle heterogeneity affects the geodynamo.

Findings

Strong lateral variability in core–mantle heat flux reproduces observed ancient magnetic field characteristics.

Thermal heterogeneity at the mantle base breaks the axial symmetry of the time-averaged magnetic field.

Palaeomagnetic signatures offer a new way to study the core–mantle boundary's properties and evolution.

Abstract

Heat flowing from the core to the mantle drives the geodynamo that produces Earth’s global magnetic field. Palaeomagnetic measurements record the behaviour of this field through time and have the potential to inform us about deep Earth structures and dynamics on either side of the core–mantle boundary. In practise, insights have proved difficult to obtain because of the limited spatiotemporal resolution of palaeomagnetic records and uncertainties in how to interpret them. Here we use palaeomagnetic datasets and models alongside numerical simulations of the geodynamo to show that certain observed characteristics of ancient magnetic field behaviour are uniquely or preferentially reproduced in the presence of strong lateral variability in core–mantle heat flux. Our findings suggest that strong contrasts in the spatial pattern of the temperature gradients and/or thermal conductivity of the lowermost mantle that are linked, today, to seismologically observed structures, have influenced the geodynamo for at least the last few hundred million years. The identified palaeomagnetic signatures provide a new means to constrain the properties and time evolution of the core–mantle boundary. Furthermore, our insights into how thermal heterogeneity at the base of the mantle can break the axial symmetry of the time-averaged magnetic field may help resolve longstanding palaeogeographic controversies.

Earth’s core dynamo, which produces the magnetic field, may have been influenced by spatial variations in heat flux across the core–mantle boundary, according to combined palaeomagnetic datasets and geodynamo simulations.

Figures