TWO EPISODES OF GLOBAL OXIDATION AT THE BEGINNING AND END OF THE PROTEROZOIC EON HAD FUNDAMENTAL IMPACTS ON THE EVOLUTION OF LIFE ON EARTH. BETWEEN 2.45-2.32 GA AGO IN THE PALEOPROTEROZOIC THE ATMOSPHERIC LEVEL OF O2 ROSE WELL ABOVE 10 5 OF PRESENT ATMOSPHERIC LEVEL UNTIL IT COLLAPSED AND STABILIZED AT A LOWER LEVEL AWAITING A SECOND RISE IN THE LATE NEOPROTEROZOIC TOWARDS MODERN LEVELS. MANY QUESTIONS REMAIN REGARDING THE TIMING AND MECHANISMS FOR THE RISE OF ATMOSPHERIC OXYGEN AND THE FEEDBACKS TO THE ENVIRONMENT AND EVOLUTION OF LIFE ON EARTH. TASK 1: THE FRANCEVILLIAN GROUP IN GABON IS ONE OF THE BEST KNOWN KEY SEDIMENTARY SEQUENCES FOR THE PALEOPROTEROZOIC CONTAINING MACROSCOPIC STRUCTURES INTERPRETED AS COLONIAL EUKARYOTIC ORGANISMS. WE WILL SYSTEMATICALLY COLLECT CARBONATE ROCKS AND BLACK SHALES FROM THE FRANCEVILLIAN GROUP AND INVESTIGATE CU AND ZN ISOTOPE COMPOSITIONS THROUGH THE STRATIGRAPHIC PROPHILES. THESE DATA WILL ALLOW US TO TRACK QUANTITATIVELY SECULAR VARIATIONS OF CU AND ZN AVAILABILITIES IN SEAWATER AND TO TEST THE HYPOTHESIS THAT THOSE MACRO-ORGANISMS MIGHT HAVE EVOLVED IN CONCERT WITH THE OXIDATION OF THE ATMOSPHERE-OCEAN SYSTEM AND INCREASES IN MARINE CU AND ZN INVENTORIES. UNLIKE MO ZN AND CU ARE CONSUMED BY EUKARYOTES REMOVING ISOTOPICALLY LIGHT CU AND ZN FROM THE SURFACE OCEAN. THEREFORE ENHANCED UPTAKE BY EUKARYOTES GENERATES ISOTOPICALLY HEAVIER MARINE ZN AND CU (PARALLEL TREND BETWEEN CU AND ZN ISOTOPES). OCEAN OXYGENATION RESULTING IN PRECIPITATION OF FE-MN OXYHYDROXIDES WOULD DRIVE TOWARDS ISOTOPICALLY HEAVY CU BUT ISOTOPICALLY LIGHT ZN IN SEAWATER. TASK 2: WE PROPOSE TO CONSTRAIN THE TIMING AND DURATION OF THE FRANCEVILLIAN GROUP WHICH RECORDS THE LOMAGUNDI EVENT THE EARLIEST AND ONE OF THE LARGEST POSITIVE D13C EXCURSIONS. THE TIMING OF THE FRANCEVILLIAN GROUP IS POORLY CONSTRAINED. WE PROPOSE TO DATE A SYENITE INTERLAYERED WITH THE SEDIMENTS AS WELL AS A WELDED TUFF NEAR THE TOP WITH OUR NEWLY DEVELOPED CHEMICAL ABRASION ISOTOPE DILUTION THERMAL IONIZATION MASS SPECTROMETRY (CA-ID-TIMS) FOR ZIRCONS. NEW HIGH-PRECISION DATA WILL ENABLE US TO CORRELATE THIS SECTION WITH OTHER PALEOPROTEROZOIC SECTIONS WORLDWIDE AND CONSTRAIN THE TERMINATION OF THE LOMAGUINDI EVENT. TASK 3: HIGH-PRECISION U-PB GEOCHRONOLOGY IS A KEY TO ADDRESS NUMEROUS FUNDAMENTAL QUESTIONS WITH REGARDS TO LATE NEOPROTEROZOIC GLACIATIONS AND THE SECOND RISE OF OXYGEN LEVELS WHICH MAY BE GENETICALLY RELATED. CURRENTLY THE MAXIMUM DURATION OF THE MARINOAN GLACIATION IS CONSTRAINED TO BE 8-20 MYR WHEREAS THE MINIMUM DURATION IS CONSTRAINED TO 0-6 MYR ON THE BASIS OF A U-PB ZIRCON DATE OF TUFF WITHIN THE POST-GLACIAL CAP CARBONATE (635.2 0.6 MA) AND A SIMS ZIRCON AGE OF 636.3 4.9 MA FOR A TUFF IN THE BASAL LAYERS OF THE SYN-GLACIAL NANTUO FORMATION. WE PROPOSE TO REVISIT THESE SAMPLES AND APPLY MODERN CA-ID-TIMS GEOCHRONOLOGY TO INVESTIGATE THE MINIMUM DURATION OF THIS GLACIATION AND THE TIMING OF THE NEOPROTEROZOIC OXIDATION EVENT. ANOTHER MAIN OPEN QUESTION IS HOW LONG IT TOOK TO DEPOSIT THE POST-GLACIAL CAP CARBONATE. CURRENT ESTIMATES RANGE FROM A FEW THOUSAND YEARS (AS SUGGESTED BY CLIMATE MODELS) TO A FEW MILLION YEARS (BASED ON MAGNETIC REVERSALS) WHICH HAVE DRASTICALLY DIFFERENT IMPLICATIONS FOR OUR UNDERSTANDING OF THE PROCESSES OF DEGLACIATION AND ENVIRONMENTAL FEEDBACKS (E.G. OCEAN MIXING WARMING AND CONTINENTAL WEATHERING). THERE ARE FOUR VOLCANIC TUFFS WITHIN THE POST-GLACIAL DOUSHANTUO CAP CARBONATE THAT WILL ALLOW DIRECT TESTING OF THESE HYPOTHESES WITH HIGH-PRECISION U-PB DATES. THE PROPOSED RESEARCH IS HIGHLY RELEVANT TO NASA S EXOBIOLOGY PROGRAM WITH AN EMPHASIS ON LARGE-SCALE ENVIRONMENTAL CHANGE AND MACROEVOLUTION. THE WORK PROPOSED HERE DIRECTLY ADDRESSES QUESTIONS REGARDING THE EVOLUTION OF THE FIRST MULTICELLULAR LIFE AND THE CONDITIONS FOR MACROSCOPIC LIFE TIED TO THE RATES OF ENVIRONMENTAL CHANGE SUCH AS GLOBAL GLACIATIONS ( SNOWBALL EARTH ) AND OXIDATION EVENTS.