  Postststarburst (K+A) galaxies are candidates for galaxies in transition from
a star-forming phase to a passively-evolving phase. We have spectroscopically
identified large samples of K+A galaxies both in the SDSS at z~0.1 and in the
DEEP2 survey at z~0.8, using a robust selection method based on a cut in Hbeta
emission rather than the more problematic [OII] 3727. Based on measurements of
the overdensity of galaxies around each object, we find that K+A galaxies
brighter than 0.4L*_B at low-z have a similar, statistically indistinguishable
environment distribution as blue galaxies, preferring underdense environments,
but dramatically different from that of red galaxies. However, at higher-z, the
environment distribution of K+A galaxies is more similar to red galaxies than
to blue galaxies. We conclude that the quenching of star formation and the
build-up of the red sequence through the K+A phase is happening in relatively
overdense environments at z~1 but in relatively underdense environments at z~0.
Although the relative environments where quenching occurs are decreasing with
time, the corresponding absolute environment may have stayed the same along
with the quenching mechanisms, because the mean absolute environments of all
galaxies has to grow with time. In addition, we do not find any significant
dependence on luminosity in the environment distribution of K+As. The existence
of a large K+A population in the field at both redshifts indicates that
cluster-specific mechanisms cannot be the dominant route by which these
galaxies are formed. We also demonstrates that studying K+A-environment
relations by measuring the K+A fraction in different environments is highly
non-robust. Statistical comparisons of the overall environment distributions of
different populations are much better behaved.
