Every day, billions of microgram-sized-extraterrestrial particles enter and ablate in the upper layers of the Earth's atmosphere, depositing their mass in the mesosphere and lower thermosphere (MLT). This evaporated meteoric mass is the source of global layers of neutral metal atoms, sporadic E layers of metal ions, and meteoric smoke particles. Because their kinetic energy is insufficient to produce detectable optical emissions, these particles can only be observed using sensitive radars, which detect the plasma (i.e., electrons) either immediately surrounding the meteoroid (head-echo), or left behind along its path (trail-echo). Here we show that observed short-scale temporal features in the radar returned signal from the meteor head-echo are explained by differential ablation of the chemical constituents. These results represent the first observation of this mass-loss process, indicating that this is the main mechanism through which the meteoric mass of micron-sized particles is deposited in the MLT.