Fig. 7.

Time evolution of metallicity (metal mass fraction in the ISM; dashed line) and dust-to-gas mass ratio (other lines) for the fiducial case (Table 1). The dotted line corresponds to the case only with ‘stardust’ production and destruction by star formation (i.e. astration). The dot-dashed line corresponds to the case with dust destruction by SNe but without dust growth in the ISM. The solid line is the case with all the processes. The filled circle with error-bars is an estimate of the dust-to-gas mass ratio for the solar neighborhood (see text). The present age of the Milky Way should be less than the age of the Universe (13.7 Gyr).