  We present the first direct and unbiased measurement of the evolution of the
dust mass function of galaxies over the past 5 billion years of cosmic history
using data from the Science Demonstration Phase of the Herschel-ATLAS. The
sample consists of galaxies selected at 250{\mu}m which have reliable
counterparts from SDSS at z < 0.5, and contains 1867 sources. Dust masses are
calculated using both a single temperature grey-body model for the spectral
energy distribution and also using a model with multiple temperature
components. The dust temperature for either model shows no trend with redshift.
Splitting the sample into bins of redshift reveals a strong evolution in the
dust properties of the most massive galaxies. At z = 0.4 - 0.5, massive
galaxies had dust masses about five times larger than in the local Universe. At
the same time, the dust-to-stellar mass ratio was about 3-4 times larger, and
the optical depth derived from fitting the UV-sub-mm data with an energy
balance model was also higher. This increase in the dust content of massive
galaxies at high redshift is difficult to explain using standard dust evolution
models and requires a rapid gas consumption timescale together with either a
more top-heavy IMF, efficient mantle growth, less dust destruction or
combinations of all three. This evolution in dust mass is likely to be
associated with a change in overall ISM mass, and points to an enhanced supply
of fuel for star formation at earlier cosmic epochs.
