With six sets, the time evolution of H₂O ratio compared to the total volume occupied by materials is shown. The sum of the ratios of water, CH₃ NH₂, and nonvolatile species is unity. The different colors represent the depths of 0–60, 60–120, 120–180, 180–240, and 240–300 cm. The horizontal axis represents the time in comet years, with one unit being the one orbital motion around the Sun.