Carbon mapping and carbon-XANES measurements on carbonate globules from ALH 84001

Details Carbon mapping and carbon-XANES measurements on carbonate globules from ALH 84001 Carbon mapping and carbon-XANES measurements on carbonate globules from ALH 84001

Mar 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997lpi....28..365f&link_type=abstract

Conference Paper, 28th Annual Lunar and Planetary Science Conference, p. 365.

Mathematics

Logic

Meteoritic Composition, Carbonates, Carbon, Energy Spectra, Absorption Spectra, Polycyclic Aromatic Hydrocarbons, Globules, Chemical Bonds, X Ray Spectroscopy, Graphite

Scientific paper

Possible evidence for ancient biological activity in carbonate globules and the rims on the carbonate globules from the ALH 84001 meteorite, believed to be from Mars, has been reported by McKay et al. (1996). The bulk of the carbon in both carbonate globules and the rims is expected to be bound in carbonates. Prior work done by the authors on interplanetary dust demonstrates that there is a strong chemical shift for the C-O bond in carbonates resulting in a peak in the C-XANES absorption spectrum at a significantly higher energy than that found for polycyclic aromatic hydrocarbons (PAHs), graphite, and other carbon-ring structures as well as most phases with C-C, C=C, or C-H bonds. A fragment of a carbonate globule, including rim material, from ALH 84001 was imbedded in elemental sulfur; an ultramicrotome thin section (about 200 nm thick) was prepared, deposited on an SiO substrate, and examined with the Scanning Transmission X-Ray Microscope (STXM). The section was mapped, with a beam spot about 50 nm in diameter, at three energies: about 280 eV (an energy where carbon has essentially no absorption), about 285 eV (an energy where PAHs and graphite absorb strongly but carbonate does not absorb), and about 300 eV (an energy where all forms of carbon absorb strongly). Carbon-XANES spectra were taken at two spots on the sample. The results are reported in this paper.

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