Magnetic fields exist or have existed on several terrestrial planets. The Earth has a magnetic field, and had it for at least the last 3.5 Gyears. Mars has records of a transient magnetic field, but no current one. Venus has no magnetic field (and no records is available). But the driving forces of these dynamos are still unsettled: thermal or compositional buyancy forces, tidal forces, sedimentation of particles, etc. Overall, the temporal evolutions of these forces, and thus the early histories of the various magnetic fields, are unknown.

In this talk, I would like to present my project on the thermal and chemical evolution of planetary cores, to quantify the buoyancy fluxes for planetary dynamos and the early evolution of the deep interiors of planets, including the Earth. The typical unknowns in such an evolution include the timescales for the start of plate tectonics, the onset of inner core crystallisation and the evolution of the dynamo. Such unknowns are usually investigated from today going backward in time. Here, I would like to emphasise that such problems also need to be investigated starting during the early formation of the planetary bodies, with initial temperature profile and composition determined with constraints from planet formation models.