  To explore the role environment plays in influencing galaxy evolution at high
redshifts, we study $2.0\leq z<4.2$ environments using the FourStar Galaxy
Evolution (ZFOURGE) survey. Using galaxies from the COSMOS legacy field with
${\rm log(M_{*}/M_{\odot})}\geq9.5$, we use a seventh nearest neighbour density
estimator to quantify galaxy environment, dividing this into bins of low,
intermediate and high density. We discover new high density environment
candidates across $2.0\leq z<2.4$ and $3.1\leq z<4.2$. We analyse the quiescent
fraction, stellar mass and specific star formation rate (sSFR) of our galaxies
to understand how these vary with redshift and environment. Our results reveal
that, across $2.0\leq z<2.4$, the high density environments are the most
significant regions, which consist of elevated quiescent fractions, ${\rm
log(M_{*}/M_{\odot})}\geq10.2$ massive galaxies and suppressed star formation
activity. At $3.1\leq z<4.2$, we find that high density regions consist of
elevated stellar masses but require more complete samples of quiescent and sSFR
data to study the effects of environment in more detail at these higher
redshifts. Overall, our results suggest that well-evolved, passive galaxies are
already in place in high density environments at $z\sim2.4$, and that the
Butcher-Oemler effect and SFR-density relation may not reverse towards higher
redshifts as previously thought.
