The Transantarctic Mountains Micrometeorite (TAM) collection comprises the oldest non-fossil micrometeorites available, with a maximum age of ~1 Myr. Most micrometeorites melt when they enter the atmosphere, they are called cosmic spherules. Some cosmic spherules show features that allow to determine their fall direction: the curvature of the particle is lower at the front; separation occurs during melting, with iron-nickel droplets migrating towards the front of the particle and gas vesicles towards the back; olivine grain-size gradients are caused by different cooling rates between the front and the back of the particle. When cosmic spherules cool down in the atmosphere, they record the local magnetic field. In Antarctica, the Earth’s magnetic field is almost vertical. Our calculations (Fig. 1) show that the trajectory of micrometeorites is also close to vertical when they acquire their magnetization, which makes it possible for micrometeorites to record the Earth’s magnetic field polarity. The polarity of the Earth’s magnetic field is not constant: the last inversion occurred 780 kyr ago. Therefore, some micrometeorites of the TAM collection should have recorded a reverse polarity. Fig. 1: Trajectory calculation results. The maximum angle between the trajectory and the Earth’s magnetic field is <90º. Therefore, the polarity recorded by the micrometeorites is significant. We selected cosmic spherules for which the fall direction could be determined. Their magnetizations were measured: as expected, they are close to the fall direction (Fig. 2). Two cosmic spherules recorded a normal polarity of the Earth’s magnetic field; four recorded a reverse polarity, and therefore fell on Earth at least 780 kyr ago. Fig. 2: Backscattered images of the cosmic spherules. The white arrows indicate the location of iron-nickel droplets. The yellow arrow indicates the inferred fall direction. The red arrow represents the magnetization direction. 16-05 recorded a reverse polarity (at the present time, the Earth’s magnetic field is vertical, pointing down, at the South Pole). 6-25 recorded a normal polarity. This study introduces a new non-destructive method to estimate the terrestrial age of micrometeorites. The results provide an independent confirmation of the ~Myr age of the TAM micrometeorite collection. It is the first time that a paleomagnetic study of flying objects is carried out. These results also validate the orientation criteria of micrometeorites.