  This paper examines how the circumgalactic medium (CGM) evolves as a function
of time by comparing results from different absorption-line surveys that have
been conducted in the vicinities of galaxies at different redshifts. Despite
very different star formation properties of the galaxies considered in these
separate studies and different intergalactic radiation fields at redshifts
between z~2.2 and z~0, I show that both the spatial extent and mean absorption
equivalent width of the CGM around galaxies of comparable mass have changed
little over this cosmic time interval.
