APOLLO-ERA EXPLORATIONS RADICALLY ALTERED OUR VIEWS OF LUNAR ORIGIN AND THE EVOLUTION OF THE EARLY SOLAR SYSTEM. BASED ON DISTURBANCES TO U-PB AND RB-SR ISOTOPES IN HIGHLAND SAMPLES TERA ET AL. (1974 EPSL 22 1) CONCLUDED THAT THESE ROCKS HAD EXPERIENCED A SHORTLIVED IMPACT PULSE LEADING TO NEAR COMPLETE THERMAL RESETTING OF THE LUNAR SURFACE A TERMINAL CATACLYSM (LATER TERMED THE LATE HEAVY BOMBARDMENT LHB). THIS INTERPRETATION PRESENTED SOMETHING OF A CONUNDRUM AS PB-U FRACTIONATION WAS ASCRIBED TO PB VOLATILIZATION BUT THE UNDISTURBED RB-SR WHOLE ROCKS IMPLY THAT RB WAS NOT SIMILARLY AFFECTED. TERA ET AL. (1974) ACKNOWLEDGED THAT THE LACK OF A MECHANISM TO EXPLAIN THIS DIFFERENTIAL BEHAVIOR REMAINS A BASIC PROBLEM . SUBSEQUENTLY MANY RESEARCHERS ARGUED THAT 40AR/39AR AGE SPECTRA ALSO SUPPORT A THERMAL PULSE AT CA. 3.9 GA. IF THIS HYPOTHESIS IS CORRECT IT HAS TREMENDOUS IMPLICATIONS FOR LUNAR HISTORY BUT ALSO FOR EARTH HABITABILITY AND SURFACE CRATERING CHRONOLOGIES ON OTHER WORLDS. RETURNED LUNAR ROCKS TYPICALLY SAMPLE REGOLITH THAT HAS BEEN REWORKED BY BILLIONS OF YEARS OF IMPACTS. THE TRADITIONAL 40AR/39AR STEP HEATING METHOD USES SMALL AMOUNTS OF CRUSHED SAMPLE THAT NONETHELESS STILL CONTAIN DOMAINS OF VARYING PROVENANCE AS IT IS TYPICALLY NOT POSSIBLE TO ISOLATE REGIONS OF ONLY A SINGLE ROCK-FORMING AGE. RECENTLY IN SITU ANALYSIS ON LUNAR SAMPLES USING AN ION MICROPROBE OR LASERPROBE TO SPUTTER OR ABLATE TINY AMOUNTS OF SAMPLE DIRECTLY FROM THE SURFACE OF A POLISHED SECTION HAVE BEEN UNDERTAKEN. THESE STUDIES ACHIEVED UNPRECEDENTED PRECISION IN DOCUMENTING AGE TRENDS WITHIN INDIVIDUAL SAMPLES. FOR EXAMPLE MERCER ET AL. (2015) DETERMINED THAT APOLLO 17 SAMPLE 73217 CONTAINED 3 DISTINCT LITHOLOGIC DOMAINS AND DETERMINED TEXTURALLY CORRELATED AGE PEAKS AT 3.81 0.01 3.66 0.02 3.63 0.027 AND 3.273 0.02 GA. THIS ILLUSTRATES THE COMPLEXITY IN DETERMINING THE AGE OF A UNIQUE EVENT FROM A BRECCIA FORMED FROM MULTIPLE PROVENANCES. WHICH IF ANY OF THOSE AGES CAN BE DIRECTLY RELATED TO THE LHB OR ANY IMPACT EVENT? INDEED TO OUR KNOWLEDGE NO CLAIM OF CONCORDANCY AMONG MULTIPLE DATING SYSTEMS ON LUNAR MELT ROCKS HAS YET BEEN SUBSTANTIATED. AS A FIRST STEP TOWARDS TESTING THE LHB HYPOTHESIS WE PROPOSE TO DETERMINE U-PB FORMATION AGES OF ACCESSORY MINERALS IN THE SAME TEMPORALLY DEFINED REGIONS OF SAMPLES 73217 AND 77115 OF MERCER ET AL. (2015). THESE SAMPLES ARE IN OUR POSSESSION AND IN SITU ELEMENTAL MAPPING INDICATES THE PRESENCE OF NUMEROUS PHOSPHATE MINERALS AND ZIRCONS WHICH CAN BE U-PB DATED THIS INCLUDES BOTH SMALL NEOFORMED GRAINS WHICH APPEAR TO HAVE GROWN FROM THE IMPACT MELT AND FRACTURED RELICT CLASTS. U-PB FORMATION AGES OF ZIRCONS AND PHOSPHATE MINERALS WILL BE MEASURED IN THOSE PREVIOUSLY DEFINED REGIONS USING BOTH OUR CAMECA IMS1290 AND IMS1270 ION MICROPROBES. IF THE ACCESSORY MINERAL U-PB AGES MATCH THOSE PREVIOUSLY DETERMINED BY 40AR/39AR THIS WOULD PROVIDE CONFIDENCE THAT THEY DATE THE IMPACT EVENT THAT FORMED THAT PARTICULAR MELT DOMAIN. HOWEVER AGE DISCREPANCIES BETWEEN THE TWO DATING TECHNIQUES WOULD CALL INTO QUESTION THE EXTENT TO WHICH ANY SPECIFIC MEASUREMENT RELATES TO A SPECIFIC IMPACT. FOLLOWING THIS INITIAL STUDY THE RESEARCH WILL BE EXPANDED TO OTHER WELL CHARACTERIZED SAMPLES. PROF. KIP HODGES AND COLLEAGUES HAVE NINE ADDITIONAL LUNAR HIGHLAND MELT SAMPLES ON WHICH THEY ARE UNDERTAKING IN SITU 40AR/39AR ANALYSES THAT THEY WILL PROVIDE US. THESE ELEVEN SAMPLES SHOULD PROVIDE A CLEAR PICTURE OF WHETHER CONCORDANCY EXISTS BETWEEN DIFFERENT ISOTOPIC SYSTEMS IN A TEXTURALLY-CLEAR PETROGENETIC SETTING. IF SO THIS APPROACH CAN THEN BE EXTENDED TO A WIDER VARIETY OF LUNAR MELT ROCKS POTENTIALLY PERMITTING FORMATION AGES OF BRECCIAS TO BE DETERMINED AND REFINEMENTS TO BE MADE TO THE LHB HYPOTHESIS. IF NOT THEN THIS WOULD SERIOUSLY CHALLENGE THE FOUNDATION OF THE LHB HYPOTHESIS.