Vestiges of a Beginning : Clues to the Emergent Biosphere Recorded in the Oldest Known Sedimentary Rocks

Recent explorations of the oldest known rocks of marine sedimentary origin from the southwestern coast of Greenland suggest that they preserve a biogeochemical record of early life. On the basis of the age of these rocks, the emergence of the biosphere appears to overlap with a period of intense global bombardment. This finding could also be consistent with evidence from molecular biology that places the ancestry of primitive bacteria living in extreme thermal environments near the last common ancestor of all known life. To make new advances in understanding the physical, chemical, and biological states of early environments for life through this unique Greenland record, we must fully exploit the spectrum of biosignatures available; these efforts must also be coupled with an understanding of the complex geologic history of the rocks hosting these signatures. The new methods employed here will eventually become applicable to other worlds when samples become available for study early in the 21st century.