Large unmelted Antarctic micrometeorites with sizes ≥100 μm that survive upon atmospheric entry started to be exploited in planetology and exobiology in the early 1990s. This chapter mostly focuses on micrometeorites that are destroyed upon atmospheric entry, through either volatilization or melting. Their “ashes” behave as powerful “tracers” that help decrypting some mysteries of our distant past, such as the formation of the Earth’s atmosphere and the early history of the Earth’s mantle. Moreover, they probably opened new reaction channels in the prebiotic chemistry of life, and they were involved in the post-lunar greenhouse eect that allowed the birth of life on the Earth. These large micrometeorites would be dominantly cometary dust grains that were released in the inner solar system, and which kept an astonishing invariant and simple composition over the last ~4.4 Gyr.