ONLY ONE HISTORY OF LIFE HAS BEEN RECORDED ON OUR PLANET AND MUCH OF THIS HISTORY IS RESOLVED AT THE ORGANISMAL POPULATION LEVEL. IN A CRITICAL SENSE THOUGH IT MAY BE ARGUED THAT THE ESSENTIAL BIOLOGICAL INTERMEDIATES THAT DROVE GLOBAL GEOCHEMICAL CYCLES IN THE EARTH S DEEP HISTORY WERE NOT ORGANISMAL BUT METABOLIC DRIVEN BY THE PRESENCE AND BEHAVIOR OF KEY ENZYMES IN MICROORGANISMS. HOW DID THESE KEY METABOLISMS EVOLVE? CAN WE RECONSTRUCT THE CONTRIBUTING METABOLIC FACTORS OF THIS BIOLOGICAL PAST? THIS PROPOSAL AIMS TO RECONSTRUCT KEY ENZYMATIC INTERMEDIATES BETWEEN BIOLOGICAL ACTIVITY AND GLOBAL GEOCHEMICAL RESERVOIRS THROUGHOUT EARTH'S DEEP HISTORY SPECIFICALLY NITROGENASE ENZYMES. NITROGEN IS A CRITICAL NUTRIENT FOR ALL LIVING ORGANISMS YET THE DEEP HISTORY OF THE GLOBAL NITROGEN CYCLE IS NOTORIOUSLY OBSCURE. NITROGEN CYCLING HAS BEEN BIOLOGICALLY CONTROLLED FOR BILLIONS OF YEARS BUT WE STILL DO NOT KNOW WHEN ORGANISMS FIRST BEGAN PULLING NITROGEN FROM THE AIR (A PROCESS CALLED NITROGEN FIXATION) IN WHAT SORT OF ENVIRONMENT NITROGEN METABOLISM EVOLVED OR HOW THE EARLIEST NITROGEN-FIXING ENZYMES FUNCTIONED. OUR INTERPRETATIONS OF THE CHEMICAL TRACES LEFT BY ANCIENT METABOLIC PROCESSES HAVE BEEN IN TERMS OF OUR KNOWLEDGE OF MODERN ENZYMES. HERE A COMPUTATION AND EXPERIMENTAL RESEARCH PROPOSAL IS PRESENTED TO RECONSTRUCT ANCIENT NITROGEN-FIXING PROTEINS TO INTERPRET THE NITROGEN RECORD IN GEOLOGIC TIME. SPECIFICALLY TOOLS DRAWN FROM PHYLOGENETICS MOLECULAR AND SYSTEMS EVOLUTION BIOCHEMISTRY AND GEOBIOLOGY WILL BE UTILIZED TO TRAVEL BACKWARDS IN EVOLUTIONARY TIME IN THE LABORATORY. WE WILL FOLLOW THE EVOLUTIONARY HISTORY OF MICROBIAL DNA TO ASSESS THE POSSIBLE ENVIRONMENTAL IMPACTS OF ANCIENT ENZYMES ON GLOBAL-SCALE SIGNATURES THAT RECORD BIOLOGICAL ACTIVITY.