  We introduce a system of bacteria confined to a finite 2D oil-water interface
and driven on two distinct time scales by motility and by growth. The combined
effect of activity on different time scales creates transitions between several
common collective behaviors. These transitions are observed using time-lapse
microscopy with high spatial and temporal resolution over eight hours. We
sequentially observe an initial dilute state, a clustered state, an active
turbulent state, and a glassy state, and we are able to directly observe and
characterize the transitions between these states. This system allows the
investigation of emergent effects surrounding transitions between phases,
expanding on studies that have considered them in isolation. In particular, a
peak in the velocity correlation length is observed at the turbulent-glassy
transition, suggesting that this transition significantly increases the active
turbulent length scale.
