KEYNOTE: UNDERSTANDING THE NATURE AND EFFECTS OF LIFE ON THE EARLY EARTH

The search for evidence of the nature of life on the early Earth requires expertise in a daunting number of distantly related fields including biochemistry, condensed matter physics, crystallography, genomics, mathematics, metamorphic petrology, microbiology, mineralogy, photochemistry, physiology, proteomics, sedimentology, and isotope geochemistry. Each discipline contributes something to the study of early Earth systems but integrating the fragmentary and frequently corrupted information from the ancient rock record remains a formidable challenge. Nevertheless, important advances have been made recently in understanding the gross architecture of the tree of life and the environmental context in which life on Earth proliferated. It is the nature and attributes of early life forms, as viewed through the fossil record (sensu lato), which remain problematical. In this talk, I shall review the morphological, molecular, and geochemical evidence for the nature of early life forms and for the times of origin of major metabolic innovations that may have been responsible for, or reactions to, stepwise changes in the state of the evolving Earth system. Causal relationships of these kinds will ultimately inform searches for extraterrestrial life on habitable planets circling nearby stars.