  Using galaxy samples drawn from the Sloan Digital Sky Survey and the DEEP2
Galaxy Redshift Survey, we study the relationship between star formation and
environment at z ~ 0.1 and z ~ 1. We estimate the total star-formation rate
(SFR) and specific star-formation rate (sSFR) for each galaxy according to the
measured [O II] nebular line luminosity, corrected using empirical calibrations
to match more robust SFR indicators. Echoing previous results, we find that in
the local Universe star formation depends on environment such that galaxies in
regions of higher overdensity, on average, have lower star-formation rates and
longer star-formation timescales than their counterparts in lower-density
regions. At z ~ 1, we show that the relationship between specific SFR and
environment mirrors that found locally. However, we discover that the
relationship between total SFR and overdensity at z ~ 1 is inverted relative to
the local relation. This observed evolution in the SFR-density relation is
driven, in part, by a population of bright, blue galaxies in dense environments
at z ~ 1. This population, which lacks a counterpart at z ~ 0, is thought to
evolve into members of the red sequence from z ~ 1 to z ~ 0. Finally, we
conclude that environment does not play a dominant role in the cosmic
star-formation history at z < 1: the dependence of the mean galaxy SFR on local
galaxy density at constant redshift is small compared to the decline in the
global SFR space density over the last 7 Gyr.
