The mean star formation rate per unit volume in the universe is estimated, from the distribution of colors of spiral galaxies, to be 0.05 (H0/100)-squared solar mass/yr-cu Mpc. Implications of this star formation density are that the gas within spiral galaxies is being consumed on a time scale of about 0.25 of the Hubble time; stars in the disks of spiral galaxies form on about the Hubble time scale; and the amount of gas associated with galaxies was significantly greater in the recent past; for example, being twice the present value by a redshift of 0.3 and at least 3 times the present value by a redshift of 1.
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Tinsley et al. (1980) studied this question.