THE TONIAN PERIOD (CA. 1000-720 MA) FOLLOWS THE SO-CALLED "BORING BILLION" IN THE MESOPROTEROZOIC ERA AND PRECEDES THE "SNOWBALL EARTH" GLACIATIONS IN THE CRYOGENIAN PERIOD. THUS IT HOLDS TO KEY TO UNDERSTAND THE TRANSITION FROM APPARENT QUIESCENCE IN THE MESOPROTEROZOIC TO CLIMATIC CATASTROPHES IN THE CRYOGENIAN. EMERGING GEOCHEMICAL DATA INDICATE THAT THE TONIAN REPRESENTS A MAJOR TRANSITION FROM PREDOMINANTLY SULFIDIC TO FERRUGINOUS MID-DEPTH SEAWATERS ALTHOUGH ATMOSPHERIC PO2 LEVELS IN THIS GEOLOGICAL PERIOD ARE HIGHLY UNCERTAIN AND INTENSELY DEBATED. MOLECULAR CLOCK ESTIMATES SUGGEST THAT EARLY ANIMALS AND OTHER IMPORTANT EUKARYOTIC CLADES MAY HAVE DIVERGED IN THE TONIAN PERIOD RAISING THE INTRIGUING POSSIBILITY OF COUPLED ENVIRONMENTAL CHANGES AND EVOLUTIONARY INNOVATIONS. HOWEVER THE FOSSIL RECORD OF THE TONIAN PERIOD IS RATHER POOR CRITICALLY LIMITING THE CAPABILITY TO RESOLVE CURRENT DEBATE ON EARTH-LIFE EVOLUTION DURING THIS TIME PERIOD AND ITS ASTROBIOLOGICAL IMPLICATIONS. TO FILL THIS KNOWLEDGE GAP THE PI PROPOSES TO (1) ANALYZE THE GLOBAL TAXONOMIC AND MORPHOLOGICAL DIVERSITY OF TONIAN EUKARYOTES AND MULTICELLULAR ORGANISMS; AND (2) SYSTEMATICALLY INVESTIGATE PROBLEMATIC MICROFOSSILS AND MACROFOSSILS PRESERVED IN THE TONIAN HUAINAN FEISHUI AND HUAIBEI GROUPS. THE MAIN OBJECTIVES OF THE PROPOSED RESEARCH ARE (1) TO CONSTRUCT AND ANALYZE PROTEROZOIC DATABASES OF MICROSCOPIC AND MACROSCOPIC EUKARYOTIC FOSSILS (2) TO ANALYSE MICROFOSSILS AND MACROFOSSILS FROM THE HUAINAN FEISHUI AND HUAIBEI GROUPS USING A COMBINATION OF MICROANALYTICAL TOOLS; AND (3) TO INTEGRATE DATABASE-BASED AND SPECIMEN-BASED DATA TO TEST THE CO-EVOLUTION OF EUKARYOTES AND MULTICELLULAR ORGANISMS AND THE PHYSICAL ENVIRONMENTS DURING THE TONIAN AND THE PROTEROZOIC. SPECIFICALLY THE PROPOSED RESEARCH WILL TEST (1) WHETHER EUKARYOTE TAXONOMIC AND MORPHOLOGICAL DIVERSITY IN THE TONIAN PERIOD IS GREATER THAN COMPARABLE TO OR LOWER THAN IN OTHER NEOPROTEROZOIC PERIODS; AND (2) WHAT EUKARYOTIC AND MULTICELLULAR GROUPS WERE PRESENT IN THE TONIAN PERIOD AND WHETHER THEY SURVIVED THE CRYOGENIAN INTO THE EDIACARAN PERIOD. THE ULTIMATE GOAL OF THE PROPOSED RESEARCH IS TO ILLUMINATE THE CO-EVOLUTION BETWEEN LIFE AND THE PHYSICAL ENVIRONMENT BEFORE DURING AND AFTER CRYOGENIAN SNOWBALL EARTH GLACIATIONS. THE PROPOSED RESEARCH CONSISTS OF DATABASE-BASED AND SPECIMEN-BASED ANALYSES. DATABASES OF PROTEROZOIC EUKARYOTIC MICROFOSSILS AND MACROFOSSILS WILL BE ANALYZED USING A VARIETY OF STATISTICAL TOOLS TO DETECT AND TEST MAJOR EVOLUTIONARY PATTERNS AND TRENDS OF TAXONOMIC DIVERSITY AND MORPHOLOGICAL DISPARITY. FOSSIL SPECIMENS WILL BE ANALYZED USING REFLECTED AND TRANSMITTED LIGHT MICROSCOPY SCANNING AND TRANSMISSION ELECTRON MICROSCOPY FOCUSED ION BEAM ELECTRON MICROSCOPY ENERGY-DISPERSIVE X-RAY SPECTROSCOPY X-RAY MICROCT ISOTOPE RATIO MASS SPECTROMETRY AND SECOND ION MASS SPECTROSCOPY. ANALYTICAL RESULTS WILL BE INTEGRATED TO CHARACTERIZE THE CHEMICAL COMPOSITIONS AND MICROSTRUCTURES IN ORDER TO CONSTRAIN PHYLOGENETIC INTERPRETATIONS. FUNDING FOR THIS PROJECT WILL SUPPORT A POSTDOCTORAL FELLOW WHO WILL BE SUPERVISED BY THE PI TO CARRY OUT THE PROPOSED ANALYSES. THE PROPOSED RESEARCH WILL PROVIDE LONG-NEEDED DATA TO TEST COMPETING HYPOTHESES ABOUT ENVIRONMENTAL CHANGES AND EVOLUTIONARY INNOVATIONS IN THE PROTEROZOIC. IT ADDRESSES KEY QUESTIONS REGARDING THE CO-EVOLUTION OF LIFE AND THE PHYSICAL ENVIRONMENT IN EARLY EARTH HISTORY WHICH IS A MAJOR RESEARCH TOPIC IDENTIFIED IN NASAS ASTROBIOLOGY STRATEGY. IT DIRECTLY SUPPORTS TWO RESEARCH AREAS IDENTIFIED IN NASA EXOBIOLOGY PROGRAM: (1) EVOLUTION OF ADVANCED LIFE AND (2) LARGE-SCALE ENVIRONMENTAL CHANGE AND MACRO-EVOLUTION.