HR: 0800h
AN: V41F-1537    [Abstracts]
TI: Life on Earth before 3.83 Ga? Carbonaceous Inclusions from Akilia (West Greenland)
AU: * Mojzsis, S J
EM: mojzsis@colorado.edu
AF: University of Colorado, Department of Geological Sciences, Center for Astrobiology, 2200 Colorado Avenue UCB 399, Boulder, CO 80309-0399 United States
AU: Papineau, D
EM: dominic.papineau@colorado.edu
AF: University of Colorado, Department of Geological Sciences, Center for Astrobiology, 2200 Colorado Avenue UCB 399, Boulder, CO 80309-0399 United States
AU: Adam, J D
EM: jon.adam@colorado.edu
AF: University of Colorado, Department of Geological Sciences, Center for Astrobiology, 2200 Colorado Avenue UCB 399, Boulder, CO 80309-0399 United States
AU: Harrison, T M
EM: director.rses@anu.edu.au
AF: Australian National University, Research School of Earth Sciences, Canberra, ACT 0200 Australia
AB: The earliest records of life on Earth have been obscured by the intense metamorphism experienced by all known terranes older than ca. 3600 Ma; fragile microfossil shapes become obliterated, and chemical/isotopic biosignatures are potentially blurred, overprinted, mimicked or erased. Prior studies sought to overcome this dilemma utilizing chemofossils ~ biosignatures resistant to physical and chemical change since formation ~ in the search for possible traces of a biosphere in pre-3.8 Ga rocks. Interpreting the geology, age and origin of the oldest rocks is fraught with difficulty, yet new field- and laboratory-based techniques permit direct assessment of proposed evidence for early life in the >3.83 Ga paragneisses of the Akilia association in southern West Greenland. A comprehensive program of sampling guided by 1:100 scale mapping of these highly deformed units coupled with structural, geochemical and geochronological analyses, provides a basis for understanding of the petrogenesis of the Akilia rocks (Manning et al., in press). The new studies resolve existing controversies over this complex terrane and (i) corroborate a sedimentary rather than metasomatic origin for Fe-rich quartz pyroxene ( Aqp) units as supported by separate trace element, REE, δ¹⁸O, δ³³S/δ³⁴S and δ⁵⁶Fe isotope studies; (ii) validate a >3.83 Ga age for Aqp units on Akilia and related units in southern West Greenland as among the oldest known rocks of sedimentary origin; and (iii) verify the presence of apatite-hosted graphite in Aqp units (cf. Lepland et al., 2005; Moorbath, 2005). This growing list of results lend support to our original interpretation (Mojzsis et al., 1996) that the simplest explanation for depleted ¹³C in carbonaceous inclusions in apatite from Akilia is that life had emerged on Earth prior to 3.83 Ga. Manning, C.E., Mojzsis, S.J. and Harrison, T.M. (2005) Geology, age and origin of supracrustal rocks, Akilia, Greenland (Amer. J. Sci. in press).
DE: 1115 Radioisotope geochronology
DE: 3660 Metamorphic petrology
DE: 5225 Early environment of Earth
DE: 9350 North America
DE: 9623 Archean
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005