HR: 1340h
AN: B53B-0987    [Abstracts]
TI: The Pilbara: one Billion Years of the Early Evolution of Earth's Surface Environments and Life
AU: * Barley, M E
EM: mbarley@segs.uwa.edu.au
AF: The University of Western Australia, 35 Stirling Highway,, Crawley, WA 6009 Australia
AB: The Pilbara contains the most complete sequence of sedimentary and volcanic rocks dating from 3.5 to 2.4 Ga. Because many of these rocks have experienced only low-grade metamorphism it is our best available natural laboratory for studying the origins and early evolution of life on Earth (and other planets) and the environments it inhabited. Indeed discoveries of the oldest possible microfossils, stromatolites and molecular fossils, as well as key mineral, geochemical and isotopic evidence of surface environments and the biosphere have all been reported from Pilbara rocks. Unfortunately complex geology and deep weathering (since the Mesozoic) makes interpretation of some of this record ambiguous leading to heated debates over evidence for life and environmental conditions. It is not surprising then that the first stages of the Astrobiology Drilling Program have been drilled in the Pilbara to obtain samples of sedimentary rocks unaffected by modern weathering. The drill cores potentially provide the best evidence yet of when and how life evolved on Earth, the nature of the environments it inhabited and a template for evaluating possible evidence of life from Mars and other planets. This talk will briefly outline the evolution of the Pilbara as one of the Earth's first continents and the interpreted environmental settings of the range of sites being drilled by the Archean Biosphere and Deep Time Drilling Programs. These include 3.52 to 2.5 Ga submarine and lacustrine black shales, 3.45 Ga deep- and shallow-marine banded cherts, 2.72 Ga stromatolite reefs, an interpreted 2.76 Ga paleosol, and banded iron formations.
DE: 9619 Precambrian
DE: 8125 Evolution of the Earth
DE: 0315 Biosphere/atmosphere interactions
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting