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Phosphate microaggregates in Archean sedimentsLight microscopy conducted on samples of Archean sediments reveals phosphate microaggregates which are suggestive of a biotic origin (Arrhenius et al., 1993). These aggregates, typically 15 micrometers wide and 50 micrometers long, are thought to be the mineral remains of colonies of microorganisms that lived during the late Archean Eon (greater than or equal to 2.5 Ga). Confocal microscopy was used to study the structures of these microaggregates in three dimensions. Samples used in this study are from the lowermost section of drill core taken from the Dales Gorge Member of the Brockman Iron-Formation (Hamersley Basin) in Western Australia. These sediments are well-preserved and escaped extensive metamorphism typically experienced by older rocks of this type. Two types of samples were prepared for study under the microscope: thin sections (30 micrometers) for transmitted light microscopy to study the general rock texture and to locate the grains of interest, and thick sections (3mm) for confocal microscopy to determine the 3-D structure of the aggregates in situ. The samples have been carefully polished so that they may be directly placed on the oil-immersion lens without the use of a cover slip. No chemical treatments of the surfaces have been performed. The aggregates often form clusters, although isolated aggregates have also been found. The clusters tend to distribute along microbands in the rocks. Electron microprobe analyses show that the phosphate grains and their inclusions, besides calcium and phosphorus, contain no major elements heavier than sodium. The proportions of calcium to phosphorus, the absence of stoichiometric amounts of other cations such as magnesium and iron, as well as optical properties suggest apatite as the mineral form.
Document ID
19950032298
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Mojzsis, S.
(Univ. of California-San Diego, La Jolla, CA US, United States)
Fan, G. Y.
(Univ. of California-San Diego, La Jolla, CA US, United States)
Arrhenius, G.
(Univ. of California-San Diego, La Jolla, CA US, United States)
Date Acquired
August 16, 2013
Publication Date
June 1, 1994
Publication Information
Publication: Origins of Life and Evolution of the Biosphere
Volume: 24
Issue: 4-Feb
ISSN: 0169-6149
Subject Category
Life Sciences (General)
Accession Number
95A63897
Funding Number(s)
CONTRACT_GRANT: NSF EAR-89-16467
CONTRACT_GRANT: NAGW-1031
CONTRACT_GRANT: NAGW-2881
Distribution Limits
Public
Copyright
Other

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