Particles to Planets: Unravelling the history of our magnetic field

The geodynamo is the engine at the heart of our planet generating our protective magnetic field. Today, the geodynamo is powered by the freezing of iron onto the ever-growing solid inner core, but in the past the geodynamo is thought to have been driven by purely thermal energy, just like a pot of boiling water. The switching between these two power sources represents Earth's largest energy transition. When it happened, and what power source kept "the engine running" during the switch is not well constrained. Earth's magnetic field is generated by the geodynamo, so changes in Earth's ancient magnetic field may be the only way to detect this energy transition.

The geodynamo energy transition represents the dying thermal power source and should be marked by a period of extremely weak magnetic field. This weak field can be preserved in rocks because nanoscale magnetic particles found within them lock in memories of the ancient magnetic fields in which they formed. However, over time these magnetic memories fade, but for some particles, their memories fade much faster than we expect, giving rise to false records of the ancient Earth, which appear to be weaker than they really are.

Our best estimate for the geodynamo energy transition is during the Ediacaran, around 550-600 million years ago. Recent studies of this time period have revealed an extremely weak magnetic field, more than ten times weaker the field today, which may indicate a dying thermally driven dynamo just prior to the transition. The results from some of these studies, however, have characteristics that are typical of forgetful magnetic particles. This raises a critical question: Are weak signals from "forgetful" rocks being confused with a weak dynamo undergoing a major energy transition?

To address this, we are using a pioneering new approach to seamlessly integrate the laboratory experiments used to determine ancient field strengths with recent theoretical advances in simulating the behavior of magnetic particles. Taking samples that preserve a weak Ediacaran field, we will decompose them into their constituent magnetic particles. Then, using new micromagnetic models (models that predict magnetic behavior at the molecular level) we will reassemble the samples numerically and simulate their magneto- geological history.

With this approach we will determine if the weak field these samples remember is a faithful memory of the field half a billion years ago and the implications this has for Earth as it experienced a major transition of its internal power. Furthermore, with this new workflow for integrating experimental observations and emergent theory, it will be possible to apply our pioneering techniques to tackle key paleo-, rock and environmental questions spanning a diverse range of disciplines, from tectonics to archeology, or volcanology to the evolution of the Moon, Mars and other planetary bodies.