Confocal study of microaggregates in 2.5 billion year-old sediments
Light microscopy conducted on samples of Archean sediments reveals microaggregates (Fig. 1) which are suggestive of a biotic origin. These aggregates, typically 15 μm wide and 50 μm long, are thought to be the mineral remains of colonies of microorganisms that lived 2.5 billion years ago. Confocal microscopy is used to study the structures of these microaggregates in 3-D.Samples under study are from the lowest section 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 metamorphic conditions typically experienced by older rocks of this type. Two types of samples were prepared for study under the microscope: thin sections (~40 μm) for transmitted light microscopy to study the general rock texture and to locate the features of interest, and thick sections (3 mm) for confocal microscopy to determine the 3-D structure of the aggregates in their undisturbed state.