On the stability of magnetic paleodirection and paleointensity at microscale

Gelson F. Souza-Junior , Ualisson Donardelli Bellon , Carolina Silveira de Moraes, Leonardo Uieda , Roger Fu, Wyn Williams, Ricardo Ivan Ferreira da Trindade 

The geomagnetic field is a fundamental component of Earth's habitability, shielding the planet from high-energy cosmic radiation and solar-wind-driven atmospheric erosion. Understanding its long-term evolution relies on thermoremanent magnetization (TRM), the most robust recorder of past geomagnetic field direction and intensity. Traditionally, magnetic microscopy has been considered unsuitable for paleomagnetic reconstructions because classical statistical arguments suggested that millions of magnetic grains are required to overcome the stochastic nature of TRM acquisition and produce reliable estimates. However, recent micromagnetic modeling has challenged this view, predicting that the required population may be orders of magnitude smaller when vortex-state particles dominate the remanence. Here, we provide the first empirical validation of this prediction using Quantum Diamond Microscopy (QDM). We show that accurate paleodirectional information can be recovered from only hundreds to thousands of magnetic anomalies. We further demonstrate that absolute paleointensity can also be determined directly from QDM observations by combining high-resolution magnetic imaging with spatial filtering to isolate the most reliable magnetic sources within complex samples. Finally, we show that thermal Thellier–Thellier paleointensity experiments can be performed at the level of individual magnetic anomalies, minimizing multidomain bias while extending paleointensity analyses to heterogeneous geological materials, limited-volume specimens, and extraterrestrial materials.