Evolution of galaxy-wide ISM properties and depletion time. Upper panel: Evolution of the fraction of n_H > 100 cm⁻³ dense gas (red curve) and gas in identified clouds (dense gas clumps with virial parameter α < 10, blue curve). Bottom panel: Galaxy-wide depletion times calculated by the total gas mass (black curve), dense gas mass (red curve), and total cloud mass (blue curve). The depletion time of the gas in the clouds fluctuates around its median value of 7.4 Myr (dashed blue line), with a 16–84 percentile range of 4.7–12 Myr.