  By combining the 0.12 square degree F814W Hubble Space Telescope (HST) and
Spitzer MIPS 24 micron imaging in the First Look Survey (FLS), we investigate
the properties of interacting and merging Mid-Infrared bright and faint sources
at 0.2< z <1.3. We find a marginally significant increase in the pair fraction
for MIPS 24 micron detected, optically selected close pairs, pair
fraction=0.25+/-0.10 at z~1, in contrast to 0.11+/-0.08 at z~0.4, while
galaxies below our 24 micron MIPS detection limit show a pair fraction
consistent with zero at all redshifts. Additionally, 24 micron detected
galaxies with fluxes >0.1mJy are on average five times more likely to be in a
close galaxy pair between 0.2< z <1.3 than galaxies below this flux limit.
Using the 24 micron flux to derive the total Far-IR luminosity we find that
paired galaxies (early stage mergers) are responsible for 27% +/-9% of the IR
luminosity density resulting from star formation at z~1 while morphologically
classified (late stage) mergers make up 34%+/-11%. This implies that 61%+/-14%
of the infrared luminosity density and in turn ~40% of the star formation rate
density at z~1 can be attributed to galaxies at some stage of a major merger or
interaction. We argue that, close pairs/mergers in a LIRG/ULIRG phase become
increasingly important contributers to the IR luminosity and star formation
rate density of the Universe at z>0.7.
