  We explore the history and impact of galaxy mergers and interactions over
z~0.24 to 0.80, based on HST ACS, Combo-17, and Spitzer 24 mu data of ~4500
galaxies in the GEMS survey. Using visual and quantitative parameters,we
identify galaxies with strong distortions indicative of recent strong
interactions and mergers versus normal galaxies (E/S0, Sa, Sb-Sc, Sd/Irr). Our
results are: (1) The observed fraction F of strongly disturbed systems among
high mass (M>=2.5E10 Msun) galaxies is ~9% to 12% in every Gyr bin over z~0.24
to 0.80. The corresponding merger rate is a few times 10^-4 galaxies Gyr-1
Mpc-3. The fraction F shows fair agreement with the merger fraction of mass
ratio >=1:10 predicted by several LCDM-based simulations. (2) For M>=1E9 Msun
systems, the average star formation rate (SFR) of strongly disturbed systems is
only modestly enhanced with respect to normal galaxies, in agreement with
recent simulations. In fact, over z~0.24 to 0.80, strongly disturbed systems
only account for a small fraction (<~30%) of the total SFR density. This
suggests that the behaviour of the cosmic SFR density over the last seven
billion years is predominantly shaped by normal galaxies.
