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Very few Archean stromatolites contain fossilized microbes, but fossilized microbes are sometimes abundant in Proterozoic stromatolites. [16] While features of some ancient apparent stromatolites are suggestive of biological activity, others possess features that are more consistent with abiotic (non-biological) precipitation. [17]
These possible biosignatures include: (a) microfossils and stromatolites; (b) molecular structures and isotopic compositions of carbon, nitrogen and hydrogen in organic matter; (c) multiple sulfur and oxygen isotope ratios of minerals; and (d) abundance relationships and isotopic compositions of redox-sensitive metals (e.g., Fe, Mo, Cr, and ...
The Pilbara region of Western Australia contains the Dresser Formation with rocks 3.48 Gya, including layered structures called stromatolites. Their modern counterparts are created by photosynthetic micro-organisms including cyanobacteria. [86] These lie within undeformed hydrothermal-sedimentary strata; their texture indicates a biogenic origin.
The stromatolites found today are almost all carbonate rocks (made of limestone), but these structures are mostly composed of the minerals gypsum and halite (rock salt), Hynek said.
The lack of many well-preserved stromatolites has been proposed as a consequence of ongoing diagenesis during formation. [5] Diagenesis is a weathering process where newly deposited sediments lies on top of the old sedimentary bed, buried and compacted, lithified and uplifted to the surface as sedimentary rocks.
Stromatolites, bioherms (domes or columns similar internally to stromatolites) and biostromes (distinct sheets of sediment) are among such microbe-influenced build-ups. [3] Other types of microbial mat have created wrinkled "elephant skin" textures in marine sediments, although it was many years before these textures were recognized as trace ...
The earliest evidence of life found in a stratigraphic unit, not just a single mineral grain, is the 3.7 Ga metasedimentary rocks containing graphite from the Isua Supracrustal Belt in Greenland. [3] The earliest direct known life on Earth are stromatolite fossils which have been found in 3.480-billion-year-old geyserite uncovered in the ...
"Spongiostromate" is also used to describe stromatolites and oncolites that do not preserve clear tubules or other cellular microstructure. Pia (1927) erected the group to contain calcareous algal fossils that contain no visible cellular structure but which he presumed represented cyanobacteria based on comparisons to modern examples.