Antiquity and Early (Precambrian) Evolution of Life When did life originate? What were the characteristics of Earth's earliest biosphere? When and how were such as photosynthesis and aerobiosis first developed, and how did they affect the early environment? When and via what mechanisms did the eukaryotic cell originate? What was the evolutionary impact of uekaryotic sexuality? What led to the advent of megascopic multicellular eukaryotes? Why and to what extent are molecular phylogenies and "molecular clocks" inconsistent with the fossil record? Why do the tempo, mode, and "normal rules" of early evolution seem to differ so significantly from those of later biologic history? In contrast with questions posed regarding many other aspects of molecular and cellular biology, evolutionary questions such as these require integrated investigation of a broad spectrum of the natural sciences. Relevant data come from virtually all the traditional biologic disciplines - molecular, cellular, organismal, populational - augmented by evidence from such seemingly disparate sources as mineralogy and geology, biochemistry and physiology, organic and isotopic geochemistry, ecology, microbiology, paleontology, and even comparative planetology. In recent years , these interdisciplinary studies have resulted in discovery of the oldest evidence of life now known, diverse types of cellular fossil prokaryotes petrified in Early Precambrian sedimentary rocks of Western Australia. This microbial assemblage established that filamentous cyanobacterium-like microoganisms were extant and morphologically diverse at least as early as ~3,465 million years ago and suggests that oxygen producing photoautotrophy may have already evolved by this very early stage in biotic history.