WE PROPOSE TO APPLY A GLOBAL THERMAL CRATERING MODEL DEVELOPED UNDER A PREVIOUS PGG GRANT TO EXPLORE THE EFFECTS OF SEVERAL TYPES OF IMPACT BOMBARDMENTS ON THE EARTH THE MOON MARS AND MERCURY. WE WILL MODEL TWO TYPES OF POST-ACCRETIONARY BOMBARDMENTS: (I) AN EXPONENTIAL DECAY AND (II) A SAWTOOTH TIMELINE CHARACTERIZED BY FASTER-THAN-EXPONENTIAL DECAY AND REDUCED TOTAL MASS. LIKEWISE TWO TYPES OF LATE HEAVY BOMBARDMENT (LHB) WOULD BE MODELED: (I) A BASELINE SCENARIO REPRESENTING A CLASSIC "SPIKE " CENTERED AT 3.9 GA AND LASTING 100 MYR; AND (II) A MORE RECENT CONCEPT OF A "SAWTOOTH" LHB CHARACTERIZED BY A NEAR-INSTANTANEOUS INCREASE IN THE NUMBER OF IMPACTS AT 4.1 GA OVERALL LOWER DELIVERED MASS AND A LONGER DURATION WITH EXPONENTIAL DECAY EXTENDING INTO THE ARCHEAN. HYDROCODE SIMULATIONS CONDUCTED BY COLLABORATOR MARCHI WILL BE USED TO CONSTRAIN CRATER GEOMETRIES AND TEMPERATURE DISTRIBUTIONS AND A CRATERED TERRAIN EVOLUTION MODEL (CTEM) BY CO-I RICHARDSON WILL BE USED FOR COMPARISON TO OBSERVATIONS OF HEAVILY CRATERED TERRAINS. BOMBARDMENT PARAMETERS INCLUDING DELIVERED MASS AS A FUNCTION OF TIME SIZE-FREQUENCY DISTRIBUTIONS AND IMPACTOR VELOCITIES AND COMPOSITIONS WILL BE PROVIDED BY COLLABORATOR BRASSER.