THE ATMOSPHERES OF THE TERRESTRIAL PLANETS VENUS EARTH AND MARS HAVE EVOLVED OVER THE HISTORYOF THE SOLAR SYSTEM FROM A SIMILAR SET OF INITIAL CONDITIONS USING A COMMON SET OF PHYSICALPROCESSES. YET THEIR CURRENT STATES ARE VASTLY DIFFERENT. THE REASON FOR THE DIFFERENCES IS RELATIVELYCLEAR: AN ATMOSPHERE RESULTS FROM SOURCE AND LOSS PROCESSES ACTING ON IT OVER TIME AND THEIMPORTANCE OF THESE PROCESSES VARIES FROM PLANET TO PLANET. THEREFORE IN ORDER TO UNDERSTAND ANATMOSPHERE IT IS NECESSARY TO UNDERSTAND THE DIFFERENT PROCESSES THAT HAVE AFFECTED IT AND THEIRRELATIVE IMPORTANCE AS A FUNCTION OF TIME.IMPACTS HAVE OCCURRED ON THE PLANETS SINCE THEY FIRST FORMED AND ARE REGARDED AS BOTH A SOURCEAND SINK OF ATMOSPHERIC VOLATILES. COMETS ARE THOUGHT TO HAVE DELIVERED EARTH S WATER FROM THEOUTER SOLAR SYSTEM. AND GIANT IMPACTS ARE THOUGHT TO HAVE `SPLASHED VOLATILES OUT OF THEATMOSPHERE [MELOSH AND VICKERY 1989]. THEORETICAL CALCULATIONS OF `ATMOSPHERIC EROSION BYIMPACTS SUGGEST THAT LARGE IMPACTS COULD HAVE REMOVED AS MUCH AS 90% OF THE MARTIANATMOSPHERE [BRAIN AND JAKOSKY 1998]. OTHER MODELS SUGGEST THAT THE NET EFFECT OF IMPACTS ONTHE MARTIAN ATMOSPHERE IS LESS CLEAR WHEN SMALLER IMPACTORS ARE INCLUDED AS WELL ASCONSIDERATION OF THE VOLATILES DELIVERED BY IMPACTORS [MANNING ET AL. 2006; PHAM ET AL. 2009].TWO IMPORTANT METHODOLOGIES CAN BE USED TO VERIFY AND CONSTRAIN THE CALCULATIONS FOR MARSOUTLINED ABOVE. FIRST LARGE FLUID SIMULATIONS HAVE BEEN DEVELOPED [NEWMAN ET AL. 1999 HAMANO AND ABE 2005; SVETSOV 2007; PLESKO ET AL. 2008] THAT CAN BE USED TO VERIFY AND EXPANDUPON OLDER THEORETICAL RESULTS SO FAR WITHOUT CLEAR CONSENSUS. SECOND THE SIMULATEDCONSEQUENCES OF LARGE IMPACTS AT MARS CAN BE CONTRASTED WITH THOSE FOR OTHER TERRESTRIAL PLANETS.OUR TEAM PROPOSES TO APPLY BOTH OF THESE IDEAS TO BETTER UNDERSTAND THE ROLE THAT IMPACTS PLAYEDIN MODIFYING TERRESTRIAL ATMOSPHERIC ABUNDANCES.