Possible evolution process leading to the formation of IOMA from SOMA. The upper 0.1 μm layer of the SOMA are UV irradiated, leading to the formation of the first IOMA molecules (dark). Once formed, these IOMA first-generation molecules are UV irradiated, leading to an evolved generation of IOMA (brown). This evolution is visible in the gradient of #C, #N, and DBE of elementary maps (Fig. B.5).