2006, 2009, 2010; Schopf 2006), is particularly noteworthy since such distinctive structures evidently require for their formation “highly motile mat builders” such as oscillatoriacean cyanobacteria (Grotzinger and Knoll 1999, pp. 342–343). Fig. 2 Forty-eight Archean geological units reported to contain stromatolites. Data from Hofmann (2000) and Schopf (2006) hypoxia-inducible factor pathway Fig. 3 Archean-age microbially laminated stromatolites. a Domical, pseudocolumnar and branching stromatolites, overlain by rippled sediments,

and b a domical stromatolite from the ~2,723-Ma-old Tumbiana Formation (Fortescue Group) of Western Australia. c Conical stromatolite and d stratiform and conical stromatolites, from the ~2,985-Ma-old Insuzi Group, South Africa. e–g Laterally linked conical stromatolites from the ~3,388-Ma-old Strelley Pool Chert of Western Australia Cellular fossils Two principal processes preserve cellular microbial fossils: compression and permineralization. Compression-preserved microorganisms occur in fine-grained detrital sediments such as shales and siltstones, pressed and flattened along bedding planes as the sediment lithified.

Such compression-preserved microbes are poorly known from the Phanerozoic, largely neglected by Phanerozoic paleontologists who focus chiefly on megascopic remains, but they are appreciably better LY2606368 documented in the Precambrian (e.g., Butterfield 2009). The microbial fossil record is best known from microorganisms preserved by permineralization. Of all modes of fossil preservation, this process (known also as petrification) provides the most faithful representation of life-like morphology. Cyclin-dependent kinase 3 Such preservation, common for plants and fungi as well as fossilized prokaryotes, results from the pervasion of mineral-charged solutions into cells during

the early stages of diagenesis, prior to their decay and disintegration. The permeating fluids infill microscopic voids—replacing the watery milieu of the cellular components—to produce a mineral-infused inorganic–organic mix that preserves physically robust structures such as organic-rich cell walls. As a result, both the organismal morphology and cellular anatomy of such fossils can be preserved in microscopic detail. The most common such permineralizing matrix is silica, fine-grained (cryptocrystalline) quartz, the mineral that comprises the rock-type known as chert. Hundreds of microbe-preserving cherts are now known from the Precambrian when silica was abundant in the world’s oceans, well before the Phanerozoic appearance of silica-biomineralized sponges, diatoms and radiolarians that today regulate the oceanic silica budget. As shown here, such cherts can contain exquisitely preserved fossil microbes. Filamentous cyanobacteria Among the several taxonomic families of filamentous cyanobacteria, stromatolite-building members of the Oscillatoriaceae have the most extensive fossil record, represented by diverse fossils in hundreds of ancient microbial communities (e.g., Fig.