The Cosmic Baryon and Metal Cycles
  Characterizing the relationship between stars, gas, and metals in galaxies is
a critical component of understanding the cosmic baryon cycle. We compile
contemporary censuses of the baryons in collapsed structures, their chemical
make-up and dust content. We show that: The H I mass density of the Universe is
well determined to redshifts z ~ 5 and shows minor evolution with time. New
observations of molecular hydrogen reveal its evolution mirrors that of the
global star formation rate density. The constant cosmic molecular gas depletion
timescale points to a universal relationship between gas reservoirs and star
formation. The metal mass density in cold gas ($T < 10^4$ K) contains virtually
all the metals produced by stars for z > 2.5. At lower redshifts, the
contributors to the total amount of metals are more diverse; at z < 1, most of
the observed metals are bound in stars. Overall there is little evidence for a
"missing metals problem" in modern censuses. We characterize the dust content
of neutral gas over cosmic time, finding the dust-to-gas and dust-to-metals
ratios fall with decreasing metallicity. We calculate the cosmological dust
mass density in the neutral gas up to z ~ 5. There is good agreement between
multiple tracers of the dust content of the Universe.
