  We analyze a sample of ~2600 MIPS/Spitzer 24mic sources brighter than ~80muJy
and located in the Chandra Deep Field South to characterize the evolution of
the comoving infrared (IR) energy density of the Universe up to z~1. Using
published ancillary optical data we first obtain a nearly complete redshift
determination for the 24mic objects associated with R<24 counterparts at z<1.
We find that the 24mic population at 0.5<z<1 is dominated by ``Luminous
Infrared Galaxies'' (i.e., 10^11 L_sol < L_IR < 10^12 L_sol), the counterparts
of which appear to be also luminous at optical wavelengths and tend to be more
massive than the majority of optically-selected galaxies. We finally derive
15mic and total IR luminosity functions (LFs) up to z~1. In agreement with the
previous results from ISO and SCUBA and as expected from the MIPS source number
counts, we find very strong evolution of the contribution of the IR-selected
population with lookback time. Pure evolution in density is firmly excluded by
the data, but we find considerable degeneracy between strict evolution in
luminosity and a combination of increases in both density and luminosity (L*_IR
prop. to (1+z)^{3.2_{-0.2}^{+0.7}}, Phi*_IR prop. to
(1+z)^{0.7_{-0.6}^{+0.2}}). Our results imply that the comoving IR energy
density of the Universe evolves as (1+z)^(3.9+/-0.4) up to z~1 and that
galaxies luminous in the infrared (i.e., L_IR > 10^11 L_IR) are responsible for
70+/-15% of this energy density at z~1. Taking into account the contribution of
the UV luminosity evolving as (1+z)^~2.5, we infer that these IR-luminous
sources dominate the star-forming activity beyond z~0.7. The uncertainties
affecting these conclusions are largely dominated by the errors in the
k-corrections used to convert 24mic fluxes into luminosities.
