HR: 14:05h
AN: B52C-02 INVITED     [PDF]
TI: 3-D Raman Imagery and Atomic Force Microscopy of Ancient Microscopic Fossils
AU: * Schopf, J
EM: Schopf@ess.ucla.edu
AF: Department of Earth and Space Sciences, Institute of Geophysics and Planetary Physics (Center for the Study of Evolution and the Origin of Life), and Molecular Biology Institute, CSEOL - Geology Building University of California, Los Angeles, Los Angeles, CA 90095-1567 United States
AB: Investigations of the Precambrian (~540- to ~3,500-Ma-old) fossil record depend critically on identification of authentic microbial fossils. Combined with standard paleontologic studies (e.g., of paleoecologic setting, population structure, cellular morphology, preservational variants), two techniques recently introduced to such studies -- Raman imagery and atomic force microscopy -- can help meet this need. Laser-Raman imagery is a non-intrusive, non-destructive technique that can be used to demonstrate a micron-scale one-to-one correlation between optically discernable morphology and the organic (kerogenous) composition of individual microbial fossils(1,2), a prime indicator of biogencity. Such analyses can be used to characterize the molecular-structural makeup of organic-walled microscopic fossils both in acid-resistant residues and in petrographic thin sections, and whether the fossils analyzed are exposed at the upper surface of, or are embedded within (to depths $>$65 microns), the section studied. By providing means to map chemically, in three dimensions, whole fossils or parts of such fossils(3), Raman imagery can also show the presence of cell lumina, interior cellular cavities, another prime indicator of biogenicity. Atomic force microscopy (AFM) has been used to visualize the nanometer-scale structure of the kerogenous components of single Precambrian microscopic fossils(4). Capable of analyzing minute fragments of ancient organic matter exposed at the upper surface of thin sections (or of kerogen particles deposited on flat surfaces), such analyses hold promise not only for discriminating between biotic and abiotic micro-objects but for elucidation of the domain size -- and, thus, the degree of graphitization -- of the graphene subunits of the carbonaceous matter analyzed. These techniques -- both new to paleobiology -- can provide useful insight into the biogenicity and geochemical maturity of ancient organic matter. References: (1) Kudryavtsev, A.B. et al. (2001) Proc. Nat. Acad. Sci. USA 98: 823-826. (2) Schopf, J.W. et al. (2002) Nature 416:73-76. (3) Schopf, J.W. (2003) 7th Exobiol. PI Symp. (NASA Ames): 57. (4) Kempe, A. et al. (2002) Proc. Nat. Acad. Sci. USA 99: 9117-9120.
DE: 0400 Biogeosciences
DE: 1055 Organic geochemistry
DE: 4803 Bacteria
DE: 9619 Precambrian
DE: 9820 Techniques applicable in three or more fields
SC: Biogeosciences [B]
MN: 2003 Fall Meeting