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Filamentous Fossil Bacteria from the Archean of Western Australia
Abstract
Four morphotypes of structurally preserved, filamentous fossil bacteria have been discovered in petrographic thin sections of laminated, carbonaceous cherts from the ∼3500 Ma-old Warrawoona Group of northwestern Australia. These tubular and septate microfossils are interpreted here as being syngenetic with Warrawoona sedimentation; as such, they are apparently the oldest such fossils now known in the geological record. The diversity of this assemblage, and the evident complexity of its individual components, suggest that the beginnings of life on Earth may have appreciably pre-dated the deposition of the Warrawoona sediments.
... Tubular carbonaceous microstructures, although rare, have been found in Meso-and Paleoarchean cherts (Awramik et al., 1983;Kiyokawa et al., 2006;Wacey et al., 2011;Sugitani et al., 2013) Tubular carbonaceous filaments, also with a highly granular appearance, have been described within cobweb-like carbonaceous textures in cherts of the ~3.4 Ga Strelley Pool Formation Schopf et al., 2017). A highly similar "cobweb macrostructure" is formed by some Paleoproterozoic microfossil assemblages (Schopf et al., 2015;Fadel et al., 2017;Barlow and van Kranendonk, 2018). ...
... Discontinuous solid threads of carbonaceous matter, commonly less than one to a few micrometers in diameter and up to several hundred micrometer long (Fig. 4C) are commonly found in Paleoarchean cherts (Awramik et al., 1983;Buick, 1984;Walsh, 1992;Ueno et al., 2001a; (Buick, 1990). They might represent filamentous microfossils that have been compressed between aligned quartz crystals (Knoll et al., 1988). ...
... Some segmented carbonaceous threads with a larger (<20 µm) diameter have been found in the 3.465 Ga Apex Chert (Figs. 4D-G) and have been considered as the oldest microfossils (Schopf, 1993;Schopf et al., 2007;Schopf and Kudryavtsev, 2012). Similar microstructures have been found in cherts of the 3.48 Ga Dresser Formation (Ueno et al., 2001b) and of the 3.47 Ga Mount Ada basalt (Awramik et al., 1983;Sugitani, 2019). The segmentation of carbonaceous matter in these structures is reminiscent of chains of barrel-shaped cells commonly found in cyanobacteria . ...
The Archean era (4 to 2.5 billion years ago, Ga) yielded rocks that include the oldest conclusive traces of life as well as many controversial occurrences. Carbonaceous matter is found in rocks as old as 3.95 Ga, but the oldest (graphitic) forms may be abiogenic. Due to the metamorphism that altered the molecular composition of all Archean organic matter, non-biological carbonaceous compounds such as those that could have formed in seafloor hydrothermal systems are difficult to rule out. Benthic microbial mats as old as 3.47 Ga are supported by the record of organic laminae in stromatolitic (layered) carbonates, in some stromatolitic siliceous sinters, and in some siliciclastic sediments. In these deposits, organic matter rarely preserved fossil cellular structures (e.g. cell walls) or ultrastructures (e.g. external sheaths) and its simple textures are difficult to attribute to either microfossils or coatings of cell-mimicking mineral templates. This distinction will require future nanoscale studies. Filamentous-sheath microfossils occur in 2.52 Ga rocks, and may have altered counterparts as old as 3.47 Ga. Surprisingly large spheres and complex organic lenses occur in rocks as old as 3.22 Ga and ~ 3.4 Ga, respectively, and represent the best candidates for the oldest microfossils. Titaniferous microtubes in volcanic or volcanoclastic rocks inferred as microbial trace fossils have been reevaluated as metamorphic or magmatic textures. Microbially-induced mineralization is supported by CaCO3 nanostructures in 2.72 Ga stromatolites. Sulfides 3.48 Ga and younger bear S-isotope ratios indicative of microbial sulfate reduction. Ferruginous conditions may have fueled primary production via anoxygenic photosynthesis–as suggested by Fe-isotope ratios–possibly as early as 3.77 Ga. Microbial methanogenesis and (likely anaerobic) methane oxidation are indicated by C-isotope ratios as early as 3.0 Ga and ~ 2.72 Ga, respectively. Photosynthetic production of O2 most likely started between 3.2 and 2.8 Ga, i.e. well before the Great Oxidation Event (2.45–2.31 Ga), as indicated by various inorganic tracers of oxidation reactions and consistent with morphology of benthic deposits and evidence for aerobic N metabolism in N-isotope ratios at ~ 2.7 Ga.
This picture of a wide diversification of the microbial biosphere during the Archean has largely been derived of bulk-rock geochemistry and petrography, supported by a recent increase in studied sample numbers and in constraints on their environments of deposition. Use of high-resolution microscopy and micro- to nanoscale analyses opens avenues to (re)assess and decipher the most ancient traces of life.
... A variety of microstructures documented in the Archean rock record are interpreted as remains of microbial life ( Knoll and Barghoorn, 1977;Schopf and Walter, 1983;Awramik, 1983;Buick, 1984;Walsh and Lowe, 1985;Awramik, 1986;Awramik et al., 1988;Walsh, 1992;Schopf, 1993;Sugitani et al., 2010Sugitani et al., , 2013Sugitani et al., , 2015aSugitani et al., , 2015bJavaux et al., 2010;Wacey et al., 2011aWacey et al., , 2012Lepot et al., 2013;Brasier et al., 2015, among others). They range morphologically from filaments ( Walsh and Lowe, 1985) to spherical structures ( Javaux et al., 2010) to spindles (Walsh, 1992;Sugitani et al., 2010Sugitani et al., , 2013Sugitani et al., , 2015aSugitani et al., , 2015b). ...
... While some of these are considered to be of biological origin ( Walsh and Lowe, 1985;Javaux et al., 2010, Wacey et al., 2011a, 2012Lepot et al., 2013;Brasier et al., 2015;Sugitani et al., 2010Sugitani et al., , 2013Sugitani et al., , 2015aSugitani et al., , 2015b, others have been identified as abiotic artefacts, e.g., volcanic tephra ( Wacey et al., 2018aWacey et al., , 2018b). Others again have been criticized for lacking appropriate geological context (Awramik et al., 1983;Schopf, 1993). Samples analyzed by Awramik (1983) lacked both the exact location and geological setting (Schopf, 1999;Brasier and Wacey, 2012). ...
... Others again have been criticized for lacking appropriate geological context (Awramik et al., 1983;Schopf, 1993). Samples analyzed by Awramik (1983) lacked both the exact location and geological setting (Schopf, 1999;Brasier and Wacey, 2012). Microstructures found in the 3.46 Ga old Apex Chert by Schopf (1993) did not stem, as was initially suggested, from an Archean beach or stream but from subsurface rocks in close association with hydrothermal veins (Brasier et al., 2002(Brasier et al., , 2004(Brasier et al., , 2005(Brasier et al., , 2011cPinti et al., 2009;Olcott Marshall et al., 2012). ...
Documenting evidence of fossil microbial life on early Earth is made difficult by the paucity of suitable Archean sedimentary rocks, their common metamorphic overprint, the small outcrop areas, and the small size of the objects of interest. Although a large number of putative microfossils dating back as far as 3700 Ma have been described, the syngeneity and biogenicity of many occurrences is debated, and some of the proposed fossils have been found to be either contaminants or abiotic artefacts. The ~3200 Ma Moodies Group of the Barberton Greenstone Belt (BGB), South Africa, contains locally abundant and remarkably well-preserved microbial mats which show indirect evidence of photosynthetic activity. They also contain microstructures which strongly resemble remains of microbial cells. Detailed morphological and geochemical analyses, however, show that these structures mostly represent fragments of volcanic tephra. Our study demonstrates that opaque microstructures within microbial mats can potentially be misidentified as microfossils even when a strict protocol is followed. It also posits the question to which degree volcanic air-borne fertilization contributed to the remarkable growth rate, high mechanical tenacity and wide extent of these oldest tidal microbial mats in siliciclastic environments.
... They must have evolved from simpler Precambrian life forms of which, however, no vestige was available. With the development of microscopic techniques and geochemical methods, an increasing number of scientific reports on putative Archean microfossils, started to emerge in the 1980s (e.g., Awramik et al. 1983;Buick 1984). Schopf and Packer (1987) published a report on 3.5 billion years old microfossils from the Warrawoona Group in Western Australia, followed by more detailed descriptions of these then oldest fossil evidence of life on Earth (Schopf 1993). ...
... The most important of such manifestations are the Dresser Formation chert (3490 Ma, stromatolites and microfossils), the Mc Phee Formation (ca. 3477 Ma) Awramik micro-fossiliferous locality (after Stanley Awramik et al. 1983), the Marble Bar Chert, and above the Apex Chert, the Strelley Pool Chert with stromatolites and microfossils, and finally the Wyman Formation stromatolitic chert (ca. 3315 Ma). ...
Apex Chert, Microfossils
Wladyslaw Altermann and Daniele L. Pinti
Keywords
Apex Chert · Apex Basalt · Biomarkers ·
Cyanobacteria · Microfossils, World’s oldest
fossils, Pseudofossils
Synonyms
Apex Chert, Apex Basalt Formation, Schopf
locality, Earth’s oldest microfossils
Definition
The Apex Chert is a lenticular and bedded, laminated,
microcrystalline silica (SiO2) deposit
interlayered with and crosscutting submarine
lavas of the Apex Basalt Formation, Pilbara Craton,
Western Australia. The Apex Basalt Formation,
Salgash Subgroup of theWarrawoona Group
dates at 3465–3458 Ma. The origin of the chert is
disputed. The rivalling interpretations: diagenetic
silicification (chertification) of clastic or
carbonate sedimentary and volcano-sedimentary
rocks versus primary silica deposition on the
ocean floor or hydrothermal chert intrusion and
replacement, do not necessarily contradict each
other. Varying chert generations may coexist
where black chert dikes and lenses crosscut dark
gray and whitish stratiform cherts and interlayered
volcanics of the Apex Formation (Marshall et al.
2012). Carbonaceous filaments found in the Apex
Chert beds, Chinaman Creek near Marble Bar,
were interpreted as world’s oldest fossils and as
evidence for the antiquity of life on Earth (Schopf
1993). The name “Schopf locality” was given to
this outcrop after J. William (Bill) Schopf, an
American paleontologist and paleobiologist of
the University of California, Los Angeles, who
found and described these microfossils......
... Gyr ago (e.g. Awramik et al., 1983;Walsh and Lowe, 1985;Walsh, 1992;Wacey et al., 2011;Sugitani et al., 2015a,b;Oehler et al., 2017;Kremer and Kazmierczak, 2017;Alleon et al., 2018;Schopf et al., 2018). Many filaments, spheroids, films, and lenses have been described in numerous Archean metasedimentary rocks, including the emblematic 3.46 Gyr-old cherts of the Strelley Pool Formation (SPF -Western Australia). ...
... Filaments are observed in a wide range of Archean rocks (Awramik et al 1983;Walsh and Lowe, 1985;Rasmussen, 2000;Ueno et al., 2001;Westall et al., 2001;Kiyokawa et al., 2006;Sugitani et al., 2007Sugitani et al., , 2010Schopf et al., 2018), and constitute the carbonaceous microstructures for which biogenicity remains a priori the most disputable (Buick, 1984, Sugitani et al., 2010. Filamentous microstructures from the SPF include both thin (< 5µm) non tubular thread and thin to relatively broad (ca. ...
The biogenicity of most of the putative Archean organic-walled microfossils discussed in the literature remains debated. Here, we report morphological and geochemical characterizations of an assemblage of microfossils isolated from the 3.46 Gyr-old Strelley Pool Formation (Western Australia), thereby providing a new set of data on the oldest authentic microfossils on Earth. Isolated microstructures/microfossils were studied by combining scanning electron microscopy imaging and elemental analyses, Raman spectroscopy and nanoscale secondary ion mass spectrometry (NanoSIMS). We identified four morphological types, namely filaments, films, spheroids and lenses. A minority of spheroids, films and lenses exhibits a continuous wall cell surface and high N concentrations and substantial P contents (as suggested by ³¹P⁻/¹²C2⁻ ionic ratios), i.e. exceptionally high morphological and geochemical preservation levels. In addition to the detection of P within microfossil walls, P was also found within micrometric patches in lenses exhibiting a fusiform shape. These patches may be remains of polyphosphate granules possibly formed during sporulation, suggesting, in turn, that cellular organization appeared as soon as 3.46 Gyr ago.
... This is consistent with the appearance of cyanobacteria 3.6-3.3 Ga, long suspected from recognition of cyanobacteria-like structures (Awramik et al., 1983;Schopf, 2006), increasingly from phylogenetic studies (e.g., Boden et al., 2021), and also from a suite of additional chemical signatures for oxygen (e.g., Zhang and Shields, 2022). Our analytical data show considerable within-sample and betweensample variation, with I/(Ca + Mg) measurements ranging from nondetectable to 0.26 μmol/mol. ...
Marine oxygenation during the Archean and Paleoproterozoic is poorly constrained. Iodine in carbonate is a possible oxygen indicator. We obtained molar ratios of iodine to calcium-magnesium [I/(Ca + Mg)] for 2.93–2.31 Ga from shallow marine Ca-carbonate (limestone, dolostone) platform sediments at several locations in the southern Superior Province in Canada and the USA. Maximum I/(Ca + Mg) ratios obtained are 0.13, 0.26, 0.05 and 0.22 μmol/mol, for 2.93, 2.86, 2.80 and 2.31 Ga samples, respectively. These non-zero carbonate I/(Ca + Mg) ratios indicate localized oxygen in Archean and Paleoproterozoic shallow marine environments. These data support an early origin for biological oxygen-production and, specifically, the idea that mid-late Archean oxygenation was sufficient to facilitate Ca-carbonate precipitation in shallow marine ‘oxygen oases’ adjacent to anoxic iron-rich seas.
... The underlying basalts are transected by numerous black chert veins that terminate in the chert-barite unit. The black chert veins and associated black chert beds contain carbonaceous structures that have been compared to fossilized microbes (28)(29)(30), although their biological affinity is unclear (31)(32)(33). ...
Paleoarchean jaspilites are used to track ancient ocean chemistry and photoautotrophy because they contain hematite interpreted to have formed following biological oxidation of vent-derived Fe(II) and seawater P-scavenging. However, recent studies have triggered debate about ancient seawater Fe and P deposition. Here, we report greenalite and fluorapatite (FAP) nanoparticles in the oldest, well-preserved jaspilites from the ~3.5-billion-year Dresser Formation, Pilbara Craton, Australia. We argue that both phases are vent plume particles, whereas coexisting hematite is linked to secondary oxidation. Geochemical modeling predicts that hydrothermal alteration of seafloor basalts by anoxic, sulfate-free seawater releases Fe(II) and P that simultaneously precipitate as greenalite and FAP upon venting. The formation, transport, and preservation of FAP nanoparticles indicate that seawater P concentrations were ≥1 to 2 orders of magnitude higher than in modern deepwater. We speculate that Archean seafloor vents were nanoparticle “factories” that, on prebiotic Earth, produced countless Fe(II)- and P-rich templates available for catalysis and biosynthesis.
... In fact, some of the vintage chert beds are considered globally significant for containing the direct evidence of > 2 Ga old life forms (Awramik et al., 1983;Barghoorn & Tyler, 1965;Brasier et al., 2002;Buick, 1990;House et al., 2000;Schopf, 1993;Schopf et al., 2002). Very fine siliceous crystals in chert give high resistance to weathering, recrystallization and metamorphism. ...
The term ‘chert’ ideally refers to fine-grained siliceous (micro/cryptocrystalline) mineral and is also often used for rock with such siliceous mineral aggregate of chemical, biochemical, and organic origin. Petrologically, inorganic non-sedimentary origin or even volcanic derivatives formed by devitrification of metastable felsic volcanic glass can also be included within chert. A new classification scheme for Precambrian cherts is proposed, especially for field workers. Despite several worldwide studies on chert, simple comprehensive classification of chert is not available to date. There are notable differences amongst Archaean, Palaeoproterozoic and Meso-Neoproterozoic cherts. This paper reviews all the Precambrian cherts to divide them into three categories from global context. Archaean and Palaeoproterozoic cherts mostly imply precipitation from silica gel material supplied vide submarine volcanism. This paper also focuses on diagenetic chert concretion, nodules, and geodes in detail. Finally, the Mesoproterozoic Nagari Formation in Cuddapah Basin, India is shown as a case to explain the diagenetic conditions, which could favour chert development by silica supersaturation in the pores. Diagenetic sub-environments are categorized systematically as eogenetic, mesogenetic, and telogenetic types with evidences of each based on photomicrography and outcrop studies. A comprehensive analysis is attempted to understand the development of concretions, nodules and geodes due to diagenesis with respect to the Eastern Ghats Orogeny, which has played a significant role in the prominent development of diagenetic features during mesodiagenetic and telodiagenetic processes.
... Fossil discoveries in the Archaean as well in Ediacaran successions claim to change the evolutionary, biostratigraphy, and palaeogeographic paradigms. Because of their serious implications on our understanding of the evolution of life on the earth some of these discoveries are followed and scrutinized by some researchers (see Awramik et al., 1983;Buick, 1984;Seilacher et al., 1998;Azmi, 1998;Rai and Gautam, 1999;Kerr, 1999;Brasier, 1999;Bhatt, 1999;Bengtson et al., 2009) and a few of them, unfortunately, did not stand the test of time (Buick et al., 1981;Lowe, 1994;Grotzinger and Rothman, 1996;Brasier et al., 2002Brasier et al., , 2015Garcia-Ruiz et al., 2003;Awramik and Grey, 2005;Nutman et al., 2016;Knoll et al., 2016;Allwood et al., 2018). The Vindhyan Supergroup of India is famous for such claims and counterclaims of the fossils in the past (see Sharma et al., 1992). ...
Dickinsonia tenuis, an important Ediacaran element, reported from the Maihar Sandstone by Retallack et al. (2021) was reexamined in the field to ascertain the biogenicity of the purported fossils. Field observations, outcrop features, and laboratory analyses (XRD, Raman Spectroscopy) do not support the biogenicity and syngenecity of reported objects. Based on this discovery, the inferences drawn about the age of the Maihar Sandstone and the palaeogeographic position of India are therefore considered invalid. Indian Dickinsonia specimen described by Retallack et al. (2021) is a left-over impression of a fallen beehive which is further proved by the detailed Raman Spectroscopy and X-Ray Diffraction (XRD) analyses.
... The carbonaceous black cherts and intercalated sedimentary rocks contain purported microfossils and stromatolitic structures (8)(9)(10)(11)(12)(13)(14), as well as sulfur and carbon isotopic signatures (4,5,(15)(16)(17), consistent with the establishment of life 3.5 Ga ago. However, the robustness of the various biosignatures has been questioned, including the biological origin of the 13 C-depleted carbon (between −38.1 and −29.4‰) (5), which theoretically could have been produced by one or more abiotic processes (18,19). ...
Carbon is the key element of life, and its origin in ancient sedimentary rocks is central to questions about the emergence and early evolution of life. The oldest well-preserved carbon occurs with fossil-like structures in 3.5-billion-year-old black chert. The carbonaceous matter, which is associated with hydrothermal chert-barite vent systems originating in underlying basaltic-komatiitic lavas, is thought to be derived from microbial life. Here, we show that 3.5-billion-year-old black chert vein systems from the Pilbara Craton, Australia contain abundant residues of migrated organic carbon. Using younger analogs, we argue that the black cherts formed during precipitation from silica-rich, carbon-bearing hydrothermal fluids in vein systems and vent-proximal seafloor sediments. Given the volcanic setting and lack of organic-rich sediments, we speculate that the vent-mound systems contain carbon derived from rock-powered organic synthesis in the underlying mafic-ultramafic lavas, providing a glimpse of a prebiotic world awash in terrestrial organic compounds.
... (3) Slightly meandering tunnels terminated by mineral crystals were also rarely found (Fig. 5L). In terms of morphology they resemble Ambient Inclusion Trails (AITs) structures (Awramik et al., 1983). Typical AITs structures terminate by pyrite crystals, our examples are terminated by dolomite crystals, however. ...
Nearly 800 of Ordovician to Middle Devonian petrographic slides from the Prague Basin (Barrandian area, Czech Republic) have been inspected for the presence of microboring structures in bioclasts. Traces of microbioerosion are rare in the Ordovician to Lower Devonian of the studied area and are produced almost exclusively by bacteria and fungi on bioclast surfaces. However, a gradual increase in the abundance of microboring structures and their shift into bioclast interior is observed during the Silurian to the Early Devonian interval. This coincides with a generally ascending quantity of tunnels possibly produced by phototrophic microboring organisms (Cyanobacteria and Algae). Subsequently, the abundance of microendolithic structures notably increased from the Emsian onwards. They are not randomly distributed in relation to their palaeoenvironments, with most abundant occurrences in low-energy hemipelagic red carbonates. Although this may partially reflect the global marine evolutionary trends, the changes in microbioeroder ecosystems were more likely driven by local factors such as the drift of the Prague Basin from temperate to tropical climate zone, increased oxygen content near the sea floor or to a larger extent, the preserved shallow littoral facies.
... Filamentous fossil bacteria have been identified in thin sections of the laminated camonate cherts from the Fortescue Group, Westem Australia (Awramik et al., 1983). These are claimed, as of today, the oldest undoubted fossils known in the geological record. ...
... When growing in colonies, they can be large enough to be visible to the naked eye and they can grow into toxic or non-toxic blooms in the water column. Cyanobacterial fossil structures in the form of stromatolites have been dated back to approximately 3 500 myr and living examples of stromatolites can be seen to this day (Awramik et al. 1983). Cyanobacteria, which are also known as Cyanophyta, owe their name to the blue photosynthetic pigment phycocyanin, which gives them a characteristic blue-green colouration. ...
Endolithic cyanobacterial species occur in a wide range of environments including cold and hot deserts as well as marine systems where they attack biological material such as corals and the shells of molluscs including limpets, mussels and abalone. Endoliths live as parasites in mussel shells, where they erode and extract calcium carbonate leading to shell weakening, creating fracture holes that lead to shell collapse and death, but they also have positive effects when they lead to discolouration of mussel shells hence giving them the ability to reduce stressful heat gain during periods of extreme heat stress. Mussels are ecological engineers on which the abundance and diversity of associated species assemblages depend. Understanding how endolithic cyanobacteria affect mussels will not only help in predicting future patterns of mussel abundances, but also future patterns of the infauna that depend on them. Firstly, I identified endolithic species infesting mussels and assessed the prevalence of endolithic parasitism in two intertidal mussel species in South Africa, the native Perna perna and the invasive Mytilus galloprovincialis. Large-scale surveys of endolithic infestation of mussels were conducted along 2500 km of the South African coast, covering three biogeographic regions: the subtropical east coast, dominated by P. perna, the warm temperate south coast where the indigenous species coexists with M. galloprovincialis, and the cool temperate west coast which is dominated by M. galloprovincialis. The prevalence of endolithic infestation was higher in the cool temperate bioregion than in the warm temperate and subtropical bioregions which did not differ and for P. perna endolithic species assemblages revealed clear groupings by bioregion. Results for endolithic induced mortality followed the same trend, with no significant difference between the two mussel species where they coexist and these results attribute biogeography of endoliths to environmental factors rather than host identity. ii Secondly, I assessed energy budgets of infested and clean mussels, to evaluate the energetic cost of infestation. This involved measuring energy acquisition, expenditure, calculating scope for growth and lethal temperatures (LT50s). The results revealed that endolithic cyanobacteria have a negative effect on scope for growth due to increased metabolic rates for infested mussels, with no effect of endoliths on the rates or efficiency of energy acquisition through filtration and no effect on lethal temperatures. The effects of infestation were then examined in more detail through a qualitative and quantitative analysis of mussel gonads and byssal attachment strength to the substratum. Endolithic infestation was found to affect reproduction by affecting the size (mass) of gonads, but not the density of eggs within them. Attachment strength was affected by endolithic infestation with very infested mussels requiring much less force to detach them from the substratum compared to mussels with low or no infestation. These results show that endolithic infestation affects mussel fitness by directly affecting attachment strength and by reducing their reproductive output. Thirdly, endolithic succession within mussel shells was examined by assessing endolithic species composition in different regions of the shell and as a function of time. The results on the spatial distribution of endolith species within a shell supported those for temporal succession in shells deployed in the field. Endolithic species that were early colonists of clean shells were similar to those that were found in the distal edge, the new and growing region of the shell and species that arrived late in succession were similar to endolithic species found near the umbo, the oldest region of the shell. Overall, the study shows that endolithic cyanobacteria show the effects of biogeography on species distribution and clear patterns of succession within mussel shells. Cyanobacteria affect mussels negatively; they lead to low scope for growth and hence low growth rates, low reproductive output and reduced attachment strength for infested mussels. This, in turn is expected to have indirect consequences for other species that rely on mussels as ecological engineers for their survival. iii
... Recent studies showed that fully oxygenated water columns existed as early as 2.5 BY ago, thus O 2 may have accumulated in Earth's oceans well before than in the atmosphere (Ostrander et al. 2019). Photosynthetic prokaryotic organisms that produced O 2 as a waste product lived long before the first build-up of free O 2 in the atmosphere, perhaps as early as 3.5 BY ago in shallow lagoonal and peritidal environments of an ancient ocean (Awramik et al. 1983). This represents the earliest undisputed evidence of life on Earth, although life may have evolved even earlier (see Mojzsis et al. 1996). ...
... Les roches les plus anciennes ont été trouvées au nord-ouest du Canada et date de 4,00-4,03 milliards d'années (Bowring and Williams 1999), ce qui ne permet pas de déterminer la présence de vies avant cette période. Les premières traces de vie non controversées ont été trouvées en Australie et en Afrique du Sud sur des roches datant de 3,5 milliards d'années (Furnes et al. 2004 ;Awramik et al. 1983 ;Brasier et al. 2006). Ces roches présentent des structures calcaires laminées appelées stromatolites qui sont l'oeuvre de microorganismes qui précipitent et/ou piègent des minéraux en formant des couches superposées. ...
L'étude des atmosphères planétaires a fait d'immenses progrès grâce à la généralisation des modèles hydrodynamiques 3D appelés GCM (Global Climate Models). La multiplication de ces modèles spécifiques à chaque planète du système solaire est un procédé d'étude qui atteint ses limites face à la grande diversité des exoplanètes. Il est nécessaire de développer des modèles génériques dans lesquels les différents paramètres associés à la planète, tels que son atmosphère, sa rotation, son orbite et son étoile, puissent être flexibles. D'autant plus que la synergie entre ces modèles et les observations est grandissante de par l'entrée dans une nouvelle phase pour les observations d'atmosphères exoplanétaires grâce au prochain lancement du JWST suivi du lancement d'ARIEL ainsi que de la construction de l'ELT. Le LMDZ générique est un GCM développé avec cet objectif. L'objectif de cette thèse a été de contribuer à l'amélioration de ce GCM par la mise en place d'un module flexible et générique de (photo)chimie qui lui faisait jusqu'alors défaut. Celui-ci permet de suivre l'évolution d'espèces chimiques connectées par un réseau de réactions et de photodissociations. Le couplage entre la chimie, la dynamique et le transfert de rayonnement est essentiel. Par exemple, il donne lieu sur Terre à la formation d'une couche d'ozone responsable de l'inversion de température stratosphérique, ce que le LMDZ générique peut reproduire grâce aux développements apportés.Cette nouvelle fonctionnalité du code a permis deux nouvelles études réalisées dans le cadre de cette thèse. Une première étude a été de tester la stabilité de l'atmosphère terrestre dans un contexte différent, sur une planète en rotation synchrone autour d'une étoile naine rouge. En nous plaçant dans le cas spécifique de l'exoplanète tellurique tempéré Trappist-1e qui fait partie des prochaines cibles du JWST, nous avons discuté quantitativement de l'observabilité d'une telle atmosphère. Puis nous avons étudié pour la première fois en 3D le rôle de la photochimie dans l'enrichissement de l'atmosphère terrestre en oxygène, qui date d'environ 2,5 milliards d'années. La photochimie résulte en une bistabilité de la composition atmosphérique pouvant expliquer un emballement rapide de la teneur en oxygène. Le lien étroit entre la photochimie et la température de surface au cours de cet emballement est discuté permettant ainsi d'affiner la compréhension globale du phénomène.
... Irregular, thin undulating bands found in several North Pole localities have been interpreted as algal mats and stromatolites (Walter et al., 1980. They have also been shown to be associated with microstructures Awramik et al., 1983;Ueno et al., 2001) that are possibly biogenic in origin, although this interpretation remains controversial Buick and Dunlop, 1990;Schopf et al., 2002;Brasier et al., 2005). The stromatolitic structures are closely associated with layers of barite and quartz, some of which have been regarded as sedimentary beds (Walter et al., 1980;Buick et al., 1981), but some of which are clearly hydrothermal veins (Nijman et al., 1998;Runnegar et al., 2001;Ueno et al., 2001Ueno et al., , 2004Van Kranendonk et al., 2001Van Kranendonk and Pirajno, 2004). ...
Neoarchean greenstone-hosted gold deposits in the Eastern Goldfields Superterrane of the Yilgarn craton of Western Australia are diverse in style, timing with respect to magmatic activity, structural environment, host rocks, and geochemical character. Geologic constraints for the range of gold deposits indicate deposit formation synchronous with volcanism, synchronous with syn- and postvolcanic intrusion, synchronous with postvolcanic deformation in faults and shear zones, or some combination of superposed events over time. The gold deposits are distributed as clusters along linear belt-parallel fault zones internal to greenstone belts but show no association with major terrane boundary faults. World-class gold districts are associated with the thickest, internal parts of the greenstone belts identified by stratigraphic preservation and low metamorphic grades. Ore-proximal faults in those regions are more commonly associated with syn- and postvolcanic structures related to greenstone construction and deformation rather than major terrane amalgamation. Using the Kalgoorlie district as a template, the gold deposits show a predictable regional association with thicker greenstone rocks overlain unconformably by coarse clastic rock sequences in the uppermost units of the greenstone stratigraphy. At a camp scale, major gold deposits show a spatial association with unconformable epiclastic and volcaniclastic rocks located above an unconformity internal to the Black Flag Group. Distinct episodes of gold deposition in coincident locations suggest fundamental crustal structural controls provided by the fault architecture. Late penetrative deformation and metamorphism overprinted the greenstone rocks and the older components of many gold deposits and were accompanied by major gold deposition in late quartz-carbonate veins localized in crustal shear zones or their higher order fault splays.
... The light layers are partially composed of sparite, and the dark layers are dominated by micrite that is probably rich in organic matter (cp. Awramik et al. 1983). ...
The occurrence of Precambrian stromatolites is closely related to the ancient seawater composition and the evolution of life. It is also a potential oil and gas reservoir. In what kind of environment the stromatolites of the upper Ediacaran Qigebulak Formation in the Tarim Basin developed, and whether they constitute potential hydrocarbon reservoirs, remained unclear. Stromatolites occur in 1–5 m thick layers, interbedded with thrombolites and dolostones. Distinct stromatolite morphologies were observed, including columnar, sinuous, short columnar, domal, and conical shapes. The δ13C values of the stromatolites (6.1‰ on average) are slightly lighter than those of the dolostones, and the δ18O values (− 1.4‰ on average) are significantly heavier than that of the dolostones. The stromatolites have a relatively high content of rare-earth elements and a minor Ce anomaly. The geochemical results imply that the stromatolites formed in an evaporative hypersaline lagoon environment. The presence of barrier dams near the coast led to the formation of lagoons, where hypersalinity was achieved when evaporation was greater than marine or freshwater input. High salinity conditions inhibited the growth of Ediacaran metazoans, allowing the buildup of stromatolites in the restricted lagoons. The stromatolites are rich in primary fenestral pores and sheet-like cavities along the laminae, and the secondary dissolution pores and vugs are related to meteoric karstification. The stromatolites, together with dolostones and thrombolites, constitute the majority of the hydrocarbon reservoirs in the Upper Ediacaran in the Tarim Basin. The results clarify the environment where the stromatolites could still flourish and be well preserved whereas they significantly declined globally throughout the Neoproterozoic elsewhere. The results imply that extensive stromatolites in the Proterozoic strata are potentially important reservoir rocks of Precambrian petroleum systems.
... Fossil bacteria are well known throughout the rock record and are the oldest known preserved traces of life, the latter occurring as silicified remains [56][57][58] . In rare cases, fossilized in situ colonies are documented, e.g., in various Eocene vertebrate fossils with soft tissue preservation from the Messel pit 16 , in an Early Cretaceous pterosaur head crest from Brazil 59 , and in the dentine of a historic human tooth 45 . ...
Alteration of organic remains during the transition from the bio-to lithosphere is affected strongly by biotic processes of microbes influencing the potential of dead matter to become fossilized or vanish ultimately. If fossilized, bones, cartilage, and tooth dentine often display traces of bioerosion caused by destructive microbes. The causal agents, however, usually remain ambiguous. Here we present a new type of tissue alteration in fossil deep-sea shark teeth with in situ preservation of the responsible organisms embedded in a delicate filmy substance identified as extrapolymeric matter. The invading microorganisms are arranged in nest-or chain-like patterns between fluorapatite bundles of the superficial enameloid. Chemical analysis of the bacteriomorph structures indicates replacement by a phyllosilicate, which enabled in situ preservation. Our results imply that bacteria invaded the hypermineralized tissue for harvesting intra-crystalline bound organic matter, which provided nutrient supply in a nutrient depleted deep-marine environment they inhabited. We document here for the first time in situ bacteria preservation in tooth enameloid, one of the hardest mineralized tissues developed by animals. This unambiguously verifies that microbes also colonize highly mineralized dental capping tissues with only minor organic content when nutrients are scarce as in deep-marine environments.
... Fossil bacteria are well known throughout the rock record and are the oldest known preserved traces of life, the latter occurring as silicified remains [56][57][58] . In rare cases, fossilized in situ colonies are documented, e.g., in various Eocene vertebrate fossils with soft tissue preservation from the Messel pit 16 , in an Early Cretaceous pterosaur head crest from Brazil 59 , and in the dentine of a historic human tooth 45 . ...
Alteration of organic remains during the transition from the bio- to lithosphere is afected strongly by biotic processes of microbes infuencing the potential of dead matter to become fossilized or vanish ultimately. If fossilized, bones, cartilage, and tooth dentine often display traces of bioerosion caused by destructive microbes. The causal agents, however, usually remain ambiguous. Here we present a new type of tissue alteration in fossil deep-sea shark teeth with in situ preservation of the responsible organisms embedded in a delicate flmy substance identifed as extrapolymeric matter. The invading microorganisms are arranged in nest- or chain-like patterns between fuorapatite bundles of the superfcial enameloid. Chemical analysis of the bacteriomorph structures indicates replacement by a phyllosilicate, which enabled in situ preservation. Our results imply that bacteria invaded the hypermineralized tissue for harvesting intra-crystalline bound organic matter, which provided nutrient supply in a nutrient depleted deep-marine environment they inhabited. We document here for the frst time in situ bacteria preservation in tooth enameloid, one of the hardest mineralized tissues developed by animals. This unambiguously verifes that microbes also colonize highly mineralized dental capping tissues with only minor organic content when nutrients are scarce as in deep-marine environments.
... At its heart are filamentous microstructures found in black cherts veins within the 3.46 Ga Apex Basalt (Pilbara Craton, Western Australia) and originally identified as fossils of photosynthetic cyanobacteria. The Apex chert "microfossils" first entered literature in 1987 (Schopf and Packer, 1987), substantiating previous reports of "microfossils" in cherts from the Warrawoona Group (e.g., Awramik et al., 1983). This discovery rapidly entered popular textbooks, even though only little attempt was made at that time to critically test the biogenic nature of these objects. ...
We still do not know when, where nor how exactly life started to exist on Earth. Despite hundreds of years of research in prebiotic chemistry, there is still no consensus on how life originated on earth, what the primordial living cells were nor how they evolved. As the unique source of direct information about past life, only the fossil record may provide answers. Yet this record is far from perfect. As a result, the search for the most ancient traces of life on Earth has always been fraught with difficulties. No absolute proof of life having existed prior to 3 Ga ago has been reported so far. Here, we review the most famous controversies of the search for traces of life in ancient rocks and use them to highlight the fundamental issues that were and still are encountered. After questioning the very existence of biosignatures, we discuss promising perspectives for decoding the most ancient fossil record.
... The majority of the bacterial fossil record is composed of filamentous, non-cyanophyte bacteria with 18 records from the Mesozoic (Awramik et al. 1983;Tazaki et al. 1992;Seckbach 1999;Gorlenko et al. 2000;Provencio and Polyak 2001;Toporski et al. 2002;Lindgren et al. 2010;Beimforde and Schmidt 2010;Schmidt et al. 2010a;Astafieva et al. 2009Astafieva et al. , 2010Astafieva et al. , 2013Chi Fru et al. 2013;Cosmidis et al. 2013;Wang et al. 2017;Keighley et al. 2018;Al-Bassam and Halodová 2018). Bacterial remains in amber have been documented resembling branched filamentous structures (Martín-González et al. 2009;Peňalver et al. 2007;Beimforde and Schmidt 2010). ...
Early endosymbiotic interactions are recorded only from a Cretaceous termite and a cockroach. Mesoblatta maxi Hinkelman, gen. et sp. nov. is the second representative of the dominant, cosmopolitan Mesozoic family Mesoblattinidae known from Cenomanian northern Myanmar amber, and the fourteenth from both amber and sedimentary rocks. Unique characters are rare (n = 19), symplesiomorphies are frequent (n = 140), and foremost is a standard maxillary palp, an irregular area between forewing veins radius and media, central ocellus, and multisegmented styli, suggesting an ancestral position with respect to Blattidae. Autapomorphies of this otherwise conservative taxon are only its large size and a short probasitarsus. Two nymphs with fecal pellets protruding from their body, Blattocoprolites mesoblattamaxi Hinkelman, ichogen. et ichnosp. nov., represent the first cockroaches with formalized coprolites (along with Blattocoprolites blattulidae Hinkelman, ichnosp. nov. established herein from Lebanese amber) and provide evidence of burial defecation. Subhomogenic consistency of coprolites with mucous components, “pseudoinclusions,” leaf, trichia, wood debris, cycad pollen, endosymbiotic protists, and epibiotic bacteria directly document pollen transfer through the digestive tract and the earliest coevolution with protists and bacteria. Other post-burial fecal bacteria at the surface are documented for the first time in the Mesozoic, directly indicating structured dung processing. Reference samples (as well as almost all Myanmar amber samples) contain numerous “pseudoinclusions,” probably representing damaged or dead cysts of Chlamydomonas hanublikanus Vršanská et Hinkelman, sp. nov. established on the basis of its reproductive stages (with an origin within the resin inside the tree). These are documented together with green algae, including Spirogyra Nees, 1820; flagellates; and flagellate amoebae, promoting massive future microbiota studies.
... Photosynthesizing prokaryotes, such as cyanobacteria probably first appeared at around 2.7-2.5 Ga (Brocks et al., 1999;Nutman et al., 2016) and multicellular algae (e.g., red algae, brown algae) also appeared at 1.2-1.0 Ga (Awramik et al., 1983;Guo et al., 2018;Qu et al., 2018). The discovery of these fossils in the black shales indicates that the aquatic algae including microbial bacteria and algae and benthic macroalgae were quite prosperous at that time. ...
The Cryogenian (720–635 Ma) is characterized by the well-known Sturtian and Marinoan glaciations which plays a key role in understanding remarkable climate and sea level changes, and oxygenation events that occurred during the Neoproterozoic Era. However, less attention has been paid to the interglacial deposits. Recently, we paid great attentions to the excellent hydrocarbon source rocks (TOC > 2%) in the Cryogenian interglacial Datangpo Formation (663 ± 4 Ma–654 ± 3.8 Ma) in South China, which mainly consists of black shales with thin manganese interbeds, making the interglacial interval a new focus. To elucidate their characteristics and depositional environments, petrological and geochemical studies were conducted on fresh rock samples collected from six sections (Gucheng, Sanlian, Xiaoxi, Gaodongyuan, Xiaochayuan, Yanglizhang) in manganese mining areas at southeastern South China. Sedimentary reconstructions suggest a transition from restricted to open ocean environment during the deposition of the Datangpo Formation. And, this formation records variations from warm and humid to dry and cold climate. Black shales were deposited in its lowest member during the warm period and showed greatest thicknesses more than 20 m at depocenters. Microscopic observations of the black shale samples exhibited abundant benthic algae with great diversities, indicating a gradual recovery of the ecosystem. Biomarker analyses further reveal that these algae combined with bacterial microorganisms prosperous in low-salinity reducing environments were the dominant organic contributors to the source rocks, which were inferred by low pristane (Pr) to phytane (Ph) ratio (Pr/Ph), low gammacerane, high tricyclic terpene and high C27 sterane contents. Trace element records combined with isotopic data suggest that the deposition of source rocks in Datangpo Formation were related to a burst in surface-water productivity due to warm climate and better preservations resulted from anoxic waters within a stratified water column. These findings indicate the Cryogenian source rocks may provide a new potential field for future explorations of shale gas and deep oil and gas.
... Значит, 3.5 млрд лет назад в отложениях, изученных Шопфом, микробиальная жизнь процветала и была широко распространена. Древнейшие ископаемые в этих породах представлены сфероидальными и нитчатыми (филаментными) микрофоссилиями (Awramik et al., 1983;Walsh, Lowe, 1985;Schopf, Packer, 1987;Walsh, 1992;Schopf, Klein, 1992;Schopf, 1993;Rasmussen, 2000;Ueno et al., 2001). Находки в Исуа с возрастом 3.8 млрд лет (Schidlowski, 1988(Schidlowski, , 2001 дискуссия Шопфа-Бразье не затронула. ...
... It means that microbial life flourished and was widespread 3.5 billion years ago in the sediments studied by Schopf. The most ancient minerals in these rocks are represented by spheroidal and filamentous microfossils (Awramik et al., 1983;Walsh and Lowe, 1985;Schopf and Packer, 1987;Walsh, 1992;Schopf and Klein, 1992;Schopf, 1993;Rasmussen, 2000;Ueno et al., 2001). The debate of Schopf and Brasier did not concern the findings in Isua, aged 3.8 billion years (Schidlowski, 1988(Schidlowski, , 2001. ...
The article discusses materials on the Archean (4.0–2.5 Ga) microfossils of the Earth (Greenland, Australia, South Africa, and Fennoscandian Shield). The main emphasis is on the description of the finds of possible members of eukaryotes. Analysis of the research by Russian paleontologists in this field has been carried out.
... Nevertheless, morphologically diverse carbonaceous microstructures, reported in Paleoarchean cherts from both the Pilbara and the Kaapvaal Cratons, were originally interpreted as fossilized filamentous and coccoidal microorganisms (e.g., Refs. [76][77][78]). Thereafter, both the age and biogenicity of these objects have yet been questioned (e.g., Ref. [79]). ...
Here we discuss the early geological record of preserved organic carbon and the criteria that must be applied to distinguish biological from non-biological origins. Sedimentary graphite, irrespective of its isotopic composition, does not constitute a reliable biosignature because the rocks in which it is found are generally metamorphosed to the point where convincing signs of life have been erased. Rather, multiple lines of evidence, including sedimentary textures, microfossils, large accumulations of organic matter and isotopic data for co-existing carbon, nitrogen and sulfur are required before biological origin can be convincingly demonstrated.
... Considéré comme des roches sédimentaires siliceuses, les cherts affleurent dans les roches datant du Précambrien à l'actuel. Ce sont des témoins de l'apparition de la vie sur Terre par la présence en leur sein des plus anciens organismes primitifs découvert à l'Archéen (Awramik et al., 1983). Ils peuvent également avoir gardé en mémoire des éléments relatifs à leurs conditions de précipitation grâce à leurs compositions isotopiques, en oxygène et en silicium et de leur mise en place. ...
Le bassin de Franceville d'âge Paléoprotérozoïque (2,2-2,0 Ga) est connu pour ses réacteurs nucléaires naturels, la richesse de son sous-sol (minéralisations uranifères et manganésifère) et ses formations sédimentaires bien préservées qui ont fourni les plus anciens macro-organismes multicellulaires déplaçant la limite de l’apparition de la vie multicellulaire précédemment fixée à 600 Ma à 2,1 Ga. Ces derniers sont retrouvés dans la formation FB dont la mise en place s'est faite durant et immédiatement après le GOE (Grand Evenement d’Oxydation de l’atmosphère terrestre). Cependant, le bassin de Franceville possède également des roches de type cherts qui appartiennent majoritairement au FC et sont le sujet de ce travail.Les observations de terrains, les études pétrographiques et géochimiques sont utilisées pour déterminer l'environnement de dépôts, le mode de formation, et la source de la silice qui compose ces cherts. L'analyse des différents affleurements met en évidence trois faciès distincts : (1) un faciès chert massif d'apparence homogène, (2) un faciès de chert béchique et (3) un faciès stromatolites. Les dômes plats, relativement peu épais, et les formes concentriques à la surface de ces dômes traduisent un milieu supratidal à intertidal. Les observations microscopiques dépeignent trois microfaciès : (1) un microfaciès homogène composé de microquarz dans lequel sont inclus de carbonates et des calcédoines ; ce microfaciès est caractéristique des affleurements de Sucaf et route de Moyabi ; (2) un microfaciès hétérogène montrant des grains qui peuvent être assimilés à des péloïdes à Bambaye, et à des intraclastes et oncoïdes à Lekouba ; (3) un microfaciès laminé (stromatolites) présent dans tous les affleurements. Ces différents microfaciès peuvent être reliés à une précipitation directe de silice, à l'exception des faciès à intraclastes comprenant des inclusions de carbonates qui résultent de la silicification d'un précurseur carbonaté. La formation FC de Francevillien du Gabon renferme les plus vieux microfossiles de Gunflint (Gunflintia, Huroniospora, Eoastrion) qui sont observés dans des stromatolites. Des observations microscopiques (microscopie optiques, microscope électronique à balayage, microscopie électronique à transmission, microscopie laser confocal à balayage et la microspectroscopie Raman) ont été utilisées pour étudier la morphologie et l'ultrastructure dans le but de mieux caractériser leur préservation, leur biogénicité et leur affinité biologique. Malgré un degré de maturation élevé de la matière organique qui les compose, les gaines et les parois des Gunflintia et Huroniospora sont préservées par une recristallisation de plusieurs générations d'opales de différentes textures. Des filaments larges (> 3 μm) à parois épaisses sont reconnus pour la première fois dans un assemblage stromatolitique de type Gunflint et montrent la préservation d'une ultra-structure de gaine épaisse souvent observée dans les cyanobactéries. Deux types de formes en étoiles (Eoastrion) sont distinguées. L'étude palynologique et ultrastructurale révèle un processus de préservation similaire à celui des Gunflintia et Huroniospora. Toutefois, les branches d'un Eoastrion traversant un cristal de chlorite diagénétique tardif sont compatibles avec la formation de branches par migration. De ce fait, leur biogénicité reste discutable.
... Although there has been debate on the biogenicity of putative Archean microfossils (e.g., Awramik, Schopf, & Walter, 1988;Brasier et al., 2002;Buick, 1984Buick, , 1988Buick, , 1990Schopf, 1976;Schopf, Kudryavtsev, Agresti, Wdowiak, & Czaja, 2002;, it is now generally accepted that diverse microbes and complex ecosystems were present on the Early Archean Earth (Allwood, Walter, Kamber, Marshall, & Burch, 2006;Awramik, Schopf, & Walter, 1983;Heubeck, 2009;Homann, Heubeck, Airo, & Tice, 2015;Javaux, Marshall, & Bekker, 2010;Kremer & Kaźmierczak, 2017;Oehler et al., 2010;Rasmussen, 2000;Schopf, 1993;Schopf, Hayes, & Walter, 1983;Schopf, Kitajima, Spicuzza, Kudryavtsev, & Valley, 2017;Schopf, Kudryavtsev, Sugitani, & Walter, 2010;Sugitani, Grey, Nagaoka, Mimura, & Walter, 2009;Sugitani, Mimura, Nagaoka, Lepot, & Takeuchi, 2013;Sugitani et al., 2007, Sugitani, Mimura, Takeuchi, Lepot, et al. 2015, Sugitani, Mimura, Takeuchi, Yamaguchi, et al., 2015Tice & Lowe, 2006;Ueno, Isozaki, Yurimoto, & Maruyama, 2001;Ueno, Yamada, Yoshida, Maruyama, & Isozaki, 2006;Van Kranendonk, 2011;Wacey, Kilburn, Saunders, Cliff, & Brasier, 2011;Waldbauer, Sherman, Sumner, & Summons, 2009;Walsh, 1992;Walsh & Lowe, 1985;Westall et al., 2001Westall et al., , 2006). The morphologically diverse Archean organic microstructures include threads, hollow tubes, segmented tubes, small spheroids, large spheroids, and lenses. ...
Lenticular, and commonly flanged, microfossils in 3.0-3.4 Ga sedimentary deposits in Western Australia and South Africa are unusually large (20~80 µm across), robust, and widespread in space and time. To gain insight into the ecology of these organisms, we performed simulations of fluid dynamics of virtual cells mimicking lenticular forms of variable sizes, oblateness, flange presence, and flange thickness. Results demonstrate that 1) the flange reduces sedimentation velocity, 2) this flange function works more effectively in larger cells, and 3) modest oblateness lowers sedimentation rate. These observations support interpretations that the lenticular microbes were planktonic-a 9lifestyle that could have been advantageous in an early Earth harsh environment including violent volcanic activities, repeated asteroid impacts and relatively high UV radiation. Although the robustness of these organisms could have provided additional protection on the early Earth, this architecture may have impeded a planktonic lifestyle by increasing cell density. However, our data suggest that this disadvantage could have been compensated by enlargement of cell volume, which could have enhanced the ability of the flange to slow sedimentation rate, especially if coupled with vacuolation. The results of this simulation study may help to explain the unique morphology and unusually large size of these Archean microfossils.
Photosynthesis is a very old process on this Earth. Based on fossil discoveries and chemical evidence, cyanobacteria first appeared 2.5–2.6 billion years ago (bya). Their evolution was undoubtedly continued by a number of anaerobic, photosynthetic bacterial life forms. Carbon isotope data revealed that autotrophic carbon fixation may have begun at least a bya. It is unclear, nevertheless, what the earliest photosynthetic organisms were like. The primary elements of the photosynthetic system are the carbon fixation mechanism, electron transport complexes, antenna complexes, and reaction centers. It is most likely true that these components have not all evolved at the same point in time. Consequently, it is better to think of the photosynthetic apparatus as a mosaic made up of numerous structural components, each with its own unique evolutionary background. One early instance of a cyanobacterium’s endosymbiotic absorption by a heterotrophic organism appears to have been the source of the chloroplasts seen in yellow-green algae, glaucophytes, brown algae, cryptophytes, red algae, and other algae in the “red” line of development. The variety of species present in the algae’s “red line” is the outcome of a single secondary endo-symbiotic occurrence in which an organism resembling red algae was ingested by another eukaryote. This “red line” is further expanded by tertiary (third-level) endosymbiotic events. Photosynthetic units are found in reaction centers involving complexes for gathering light. Two of these units are necessary for oxygenic photosynthesis, which currently accounts for the majority of biological transfer of energy in the various trophic levels of the biosphere. The emergence of photosynthesis utilizing oxygen among cyanobacteria, which paved the path for the formation of complex life forms with multicellular levels of organization, had a profound influence on the biology, geology, and environment of Earth. In this review, we have discussed the early evidence of photosynthesis, the origin of reaction centers, antenna, pigments, and how oxygenic photosynthesis came into existence. The origin of the chloroplasts is a necessary event that occurred earlier and was added to the history of photosynthetic origin in this review.
The Pilbara craton of northwestern Australia is known for what were, when reported, the oldest known microfossils and paleosols on Earth. Both interpretations are mired in controversy, and neither remain the oldest known. Both the microfossils and the paleosols have been considered hydrothermal artefacts: carbon films of vents and a large hydrothermal cupola, respectively. This study resampled and analyzed putative paleosols within and below the Strelley Pool Formation (3.3 Ga), at four classic locations: Strelley Pool, Steer Ridge, Trendall Ridge, and Streckfuss, and also at newly discovered outcrops near Marble Bar. The same sequence of sedimentary facies and paleosols was newly recognized unconformably above the locality for microfossils in chert of the Apex Basalt (3.5 Ga) near Marble Bar. The fossiliferous Apex chert was not a hydrothermal vein but a thick (15 m) sedimentary interbed within a sequence of pillow basalts, which form an angular unconformity capped by the same pre-Strelley paleosol and Strelley Pool Formation facies found elsewhere in the Pilbara region. Baritic alluvial paleosols within the Strelley Pool Formation include common microfossil spindles (cf. Eopoikilofusa ) distinct from marine microfossil communities with septate filaments ( Primaevifilum ) of cherts in the Apex and Mt Ada Basalts. Phosphorus and iron depletion in paleosols within and below the Strelley Pool Formation are evidence of soil communities of stable landscapes living under an atmosphere of high CO 2 (2473 ± 134 ppmv or 8.8 ± 0.5 times preindustrial atmospheric level of 280 ppm) and low O 2 (2181 ± 3018 ppmv or 0.01 ± 0.014 times modern).
Cancer is one of the most dangerous diseases and is widely recognized as a civilization disease related to the development of our civilization. The progressive environmental pollution, improper diet, smoking, and alcohol consumption are considered risk factors for the development of cancer in humans. These factors undoubtedly increase the incidence of cancer in recent human populations. However, comparative oncology and the archaeological and paleontological record provide evidence that neoplastic diseases also affects non-human animals and have affected prehistoric human populations and even prehistoric vertebrates over millions of years of their evolution in the changing environments of our planet. This chapter traces the most important of these occurrences of them and characterizes the diagnostic features that enable the identification of various types of cancer, in particular those whose traces can be identified in the osteological record. Evolutionary perspective of tumorigenesis (e.g., Peto’s paradox) is also discussed. The chapter also characterizes other diseases that are characterized by abnormal growth, development, differentiation, and subsequent abnormal bone and cartilage structure, e.g., skeletal dysplasia, bone cysts, or hypertrophic osteoarthropathy.
The Capiru Formation records supracrustal metassedimentary rocks within the Southern Ribeira Belt. These rocks underwent heterogeneous deformation and metamorphism, resulting in an incomplete greenschist facies paragenesis. They are tectonically interbedded with strata that exhibit well-preserved primary structures. In the Morro Grande synform region, there is a continuous 150 m outcrop of metadolomites with preserved sedimentary records and was described in a stratigraphic profile (1:500) subsequently detailed (1:50). Dolomite, minor amounts of quartz, traces of ilite, graphite and zircon constitute the mineral assembly, defined by XRD, petrography and SEM-EDS. Distinct preserved facies are recognized by morphostructures: (1) lamina (parallel, discontinuous, crenulated); (2) stromatolites (homogeneous columnar, club-shaped, conical conophyton-like, pseudocolumnar, parallel-branching, divergent-branching, delicate-branching); (3) thrombolite (rugous) and (4) flat pebble conglomerate. Single-isotope data revials different microbial patterns, particularly in stromatolites (-1.57 to -0.40‰ δ13C; -8.21 to - 3.94‰ δ18O) and lamina (-1.89 to 1.29‰ δ13C; -7.32 to -3.55‰ δ18O). Facies associations suggest a shallow sea with a regressive trend. Tectonofacies are characterized by massive, venulated or brecciated carbonates. Chemostratigraphic profile is divided into two major intervals. At the bottom, the first does not exhibit a specific isotopic trend and can be subdivided in heterogeneous post-deformation venulas (Unit I, -1.75 to 0.40 δ13C; -2.34 to -8.16 δ18O), thrombolythic signals (Unit II, -1.43 to 0.40‰ δ13C; -6.35 to -4.11‰ δ18O), and facies variation, mainly supratidal (Unit III, 1.89 to 1.29‰ δ13C, -7.32 to -3.31‰ δ18O). Upwads in the profile, the second interval consists of microbial facies, displaying a more uniform signature with depleted values of δ13C and δ18O along with a slight enrichment marking the transition from intratidal to supratidal environments (Unit IV; -1.32 to -0.81‰ δ13C; - 8.17 to -6.25‰ δ18O) and supratidal lagoons (Unit V; -1.35 to -0.41‰ δ13C; -8.20 to -5.49‰ δ18O). Preserved EPS, graphite, and ilite confirm low-grade metamorphism, with clumped isotope thermometry temperatures ranging from 206.07-307.58°C. Calcite is secondary, filling porosity and present in recrystallized facies. Isotopic signature of recrystallized facies differs from microbial ones, with the most depleted values (-2.16‰ δ13C; -14.02‰ δ18O) and lower formation temperature (122.29±7.07°C), indicating a late restricted event. This dolomitic succestion within Capiru Formation provides evidence of a shallow marine paleoenvironment with diverse microbial activity during its deposition.
Biominerals are the product of organism activity leading to mineral formation within the cellular space or in the neighbouring environment. This chapter presents the pivotal role played by biominerals in geological and environmental processes, in addition to their physiological functions. Generalities of biomineralization processes will be described to introduce readers to the biomineral world. Then, some important examples of biominerals will be shown. The second part will focus on the interactions between bacteria, plants and the environment. We will draw attention to the critical role that biologically mediated natural processes and the formation of biominerals play when systems are perturbed by anthropogenic activities. Such a processes can be considered as a part of the resilience of the system itself. This approach will help the reader understand the sustainable application of biominerals to mine environments and industrial areas.KeywordsBiomineralsEnvironmentEnvironmental technologiesWasteSustainability
Finding the beginning of Earth's fossil record is a long-standing palaeontological challenge arising from the quest to understand the origin of life. Research in recent years has necessarily focused on determining the existence (or otherwise) of fossils in the Early Archaean rock record. Nonetheless, despite numerous reports of microfossils(?) and stromatolites, consensus on the existence of life in the Early Archaean has been elusive (e.g. Moorbath, 2005). However, new techniques and approaches are allowing more confident interpretation of the Archaean fossil record, and the nature of the earliest biosignatures can be used to inform our understanding of emergent ecosystems on Earth and perhaps on other terrestrial planets.
Evidence is mounting that microbial ecosystems may have had a firm foothold as early as ~3.5 Ga (Tice and Lowe, 2004; Schopf, 2006; Hofmann et al., 1999; Allwood et al., 2006, 2007b; Westall et al., 2006; Westall and Southam, 2006). Significantly, there is now also evidence that the Early Archaean record may not be as meager and cryptic as previously thought. For example, the 3.43 Ga Strelley Pool Chert of the Pilbara Craton of Western Australia contains kilometer-scale tracts of a fossilized stromatolite (microbial?) reef (Allwood et al., 2006, 2007b) and provides a large suite of evidence that is consistent with life's existence. Moreover, the rapidity with which the Strelley Pool reef established itself on a newly-submerged landmass suggests that life was well established by that time, waiting in the wings in planktonic form until conditions favored sessile biofilm formation. The rich vault of information in such rocks as the Strelley Pool Chert may shed light not only upon life's antiquity, but also on the nature of early organisms and ecosystems, the environments that nurtured them, the processes that aided preservation of biosignatures and the palaeontological approaches needed to interpret them. This in turn will be a valuable guide in the search for—and interpretation of—ancient microbial biosignatures in the geologic record of other planets or moons.
From the Archean toward the Proterozoic, the Earth's atmosphere underwent a major shift from anoxic to oxic conditions, around 2.4 to 2.1 Gyr, known as the Great Oxidation Event (GOE). This rapid transition may be related to an atmospheric instability caused by the formation of the ozone layer. Previous works were all based on 1D photochemical models. Here, we revisit the GOE with a 3D photochemical-climate model to investigate the possible impact of the atmospheric circulation and the coupling between the climate and the dynamics of the oxidation. We show that the diurnal, seasonal and transport variations do not bring significant changes compared to 1D models. Nevertheless, we highlight a temperature dependence for atmospheric photochemical losses. A cooling during the late Archean could then have favored the triggering of the oxygenation. In addition, we show that the Huronian glaciations, which took place during the GOE, could have introduced a fluctuation in the evolution of the oxygen level. Finally, we show that the oxygen overshoot which is expected to have occurred just after the GOE, was likely accompanied by a methane overshoot. Such high methane concentrations could have had climatic consequences and could have played a role in the dynamics of the Huronian glaciations.
From the Archean toward the Proterozoic, the Earth's atmosphere underwent a major shift from anoxic to oxic conditions, around 2.4 to 2.1 Gyr, known as the Great Oxidation Event (GOE). This rapid transition may be related to an atmospheric instability caused by the formation of the ozone layer. Previous works were all based on 1D photochemical models. Here, we revisit the GOE with a 3D photochemical-climate model to investigate the possible impact of the atmospheric circulation and the coupling between the climate and the dynamics of the oxidation. We show that the diurnal, seasonal and transport variations do not bring significant changes compared to 1D models. Nevertheless, we highlight a temperature dependence for atmospheric photochemical losses. A cooling during the late Archean could then have favored the triggering of the oxygenation. In addition, we show that the Huronian glaciations, which took place during the GOE, could have introduced a fluctuation in the evolution of the oxygen level. Finally, we show that the oxygen overshoot which is expected to have occurred just after the GOE, was likely accompanied by a methane overshoot. Such high methane concentrations could have had climatic consequences and could have played a role in the dynamics of the Huronian glaciations.
The relationship between microbes and marine sediments probably dates back to the very origin of life on Earth. This intimate association is exemplified by how the physical and geochemical environment within sediments determines which microbes dominate a certain consortium and, in turn, how microorganisms have profound effects on sediment properties through their metabolic activities at various (spatial and temporal) scales. Microbial mats, the oldest ecosystems on Earth with a fossil record dating back to 3.4 Ga, are biosedimentary structures in which microbes exploit all environmental niches that arise in relation to strong gradients in light, redox potential, the concentration of viable substrates for energy acquisition, as well as toxic compounds. In fact, microbial mats have been thought to be the environment where several metabolic pathways evolved, establishing microbial lineages and biogeochemical processes that last to this day. This chapter provides a concise summary of the evolution of those early microbial lineages, to then revisit modern, hypersaline microbial mats, and some of the microbially induced sedimentary structures (MISS) that arise from mats colonizing siliciclastic sediments. Salient ecological features and the metabolism of their microbes are briefly discussed, while emphasis is made on what can be learned from their study through the actualistic perspective of GeoBiology. Emergent properties of microbe-sediment interactions essential for the development, establishment, and preservation of microbial mats in modern and fossil settings are discussed.
Paleontological evidence indicates that terrestrial life existed at least 3500 Ma ago, and it is quite possible that the earliest cells arose well before that time. The early appearance of life on Earth suggests that under appropriate environmental conditions the probability of chemical evolution proceeding to the point of biogenesis may be reasonably high. Most of biological history has been the history of microorganisms, with tissue-grade plants and animals characterizing only the most recent 15% or so of the fossil record. Intelligent life has occupied only the latest instant in geological time. The time table of terrestrial evolution is governed more by the particulars of our planet's physical and biological history than by some universal tempo of evolutionary change. One aspect of terrestrial life that is likely to be universal is the organization of populations into efficient biogeochemical systems.
This chapter summarizes what is known about the timing of the emergence of life on Earth from the morpho- and chemo-fossil (chemical and isotopic signals remaining from the decomposition of living organisms) records. The geologic record back to ca. 3.5 billion years includes low grade sedimentary rocks in which organic residues of microbiota present during deposition have remained substantially intact. As different metabolic mechanisms variably fractionate carbon isotopes toward isotopically light values, a longstanding strategy has been to measure δ¹³C in these organic residues, or kerogens, for biologic signatures. When compared to carbon isotopes in inorganic carbonate rocks, a consistent offset is seen throughout the past 3.5 billion years with inorganic carbon averaging δ¹³C close to 0‰ and kerogens yielding δ¹³C of approximately −25‰. As the latter value is broadly characteristic of oxygenating photosynthesis, this relationship has been seen as evidence of past biologic activity. However, as metamorphic grade increases, kerogens are reacted to simpler hydrocarbons, ultimately yielding graphitic residues. The discovery of isotopically light carbon isotopes in microscopic graphite inclusions in rocks as old as ca. 3.83 billion years and in a 4.1 Ga zircon extends the possible emergence of life on this planet back into the Hadean eon. Although inorganic mechanisms exist that could potentially produce light δ¹³C signatures, these isotopic data are consistent with molecular clock calibrations of genomic mutations which suggest a lower bound for the time of life’s origin between 4.1 and 4.4 billion years.
Expanding our capabilities to unambiguously identify ancient traces of life in ancient rocks requires laboratory experiments to better constrain the evolution of biomolecules during advanced fossilization processes. Here, we submitted RNA to hydrothermal conditions in the presence of a gel of Al-smectite stoichiometry at 200 °C for 20 days. NMR and STXM-XANES investigations revealed that the organic fraction of the residues is no longer RNA, nor the quite homogeneous aromatic-rich residue obtained in the absence of clays, but rather consists of particles of various chemical composition including amide-rich compounds. Rather than the pure clays obtained in the absence of RNA, electron microscopy (SEM and TEM) and diffraction (XRD) data showed that the mineralogy of the experimental residues includes amorphous silica and aluminosilicates mixed together with nanoscales phosphates and clay minerals. In addition to the influence of clay minerals on the degradation of organic compounds, these results evidence the influence of the presence of organic compounds on the nature of the mineral assemblage, highlighting the importance of fine-scale mineralogical investigations when discussing the nature/origin of organo-mineral microstructures found in ancient rocks.
Representative Paleo- and Mesoarchean (>3.0 Ga) microfossils and possible microfossils retaining cellular structures from the Pilbara Craton, Western Australia, and the Kaapvaal Craton, South Africa, are reviewed. Rod-shaped, spheroidal, lenticular, and filamentous (and their subtypes) microfossils have been identified in those areas, and their sizes range from submicrons to 300 μm across. Depositional environments of host rocks vary from shallow marine or even terrestrial to deep-sea, with or without hydrothermal activities, providing no constraints on the geologic setting for the emergence of life. Although biological affinities such as cyanobacteria and sulfur bacteria have been proposed for a few types of Paleo- and Mesoarchean microfossils, those of most others are poorly understood.
Possible alternative habitats and life‐styles of the original metazoan are considered. It is argued from the dominance of the benthic habitat in present‐day groups that the original metazoan habitat was benthic rather than planktonic. Similarly, plesiomorphic metazoan taxa tend to be holobenthic rather than pelago‐benthic. It is therefore probable that the early Metazoa were holobenthic. The concept of plesiohabitats and apohabitats in the evolution of taxa is presented. This leads to the proposition that the early metazoans were interstitial bionts of fine sand. Finally, the controversy concerning the aerobic or anaerobic origin of the Metazoa is considered. It is shown that competition theory predicts that plesiomorphic taxa are likely to remain in plesiohabitats. Diagrams showing the possible evolution of major taxa in relation to available habitats are presented. It is concluded that the earliest Metazoa could have evolved in anaerobic marine sand and that the early Plathelminthomorpha and Aschelminthes did so.
Cambridge Core - Computational Science and Modelling - Planets and Life - edited by Woodruff T. Sullivan, III
Boring or endolithic microorgani sms discussed herein are photosynthetic cyanophytes, eucary—otic green and red algae, and heterotrophic fungi that actively penetrate carbonate substrates. Although their existence has been known since the mid-nineteenth century, new techniques for preparation and study developed within the last decade have brought about significant progress in our understanding of them. Boring microorganisms have been studied in a variety of carbonate substrates, including the shells and skeletons of living organisms or their fragmented remains, and within coastal limestones.
Recent reports have described 'yeast-like microfossils' (Isuasphaera isua Pflug) in 3,800-million year old metaquartzites from the Isua supracrustal belt of south-west Greenland. A biogenic interpretation of these objects is inconsistent with the tectonic history of the Isua region, with the petrology of the metaquartzites, and with the morphology of the microstructures themselves. The putative microfossils are indistinguishable from limonite-stained fluid inclusions: microstructures which are demonstrably inorganic and post-depositional in origin. As such, it is contended that these objects should not be regarded as evidence of early Archaean life forms.
Ambient pyrites of two distinct types were described from middle Precambrian rocks of the Lake Superior area. A new class of this phenomenon is here described from middle Precambrian chert from western Australia. The newly found ambient pyrites are quite minute and characteristically occur in groups forming a "starburst" pattern. All three types of ambient pyrite may be explained in terms of pressure solution initiated by gas evolution from organic material attached to the pyrite. Thermal degradation of the kerogen produces the gases which, due to the impermeability of the encompassing chert, build up the pressures necessary to initiate solution. Pyrite appendages bear a striking resemblance to micro-organisms and, thus, constitute the smallest pseudofossils known.
The beginnings of biospheric evolution had far-reaching biogeochemical consequences for the related evolutions of atmosphere, hydrosphere, and lithosphere. Feedback to the sedimentary record from these several simultaneously interacting aspects of crustal evolution provides the evidence from which historical biogeology is reconstructed. The interpretation of that evidence, however, is beset with pitfalls. Both biogenicity and a primary origin need to be demonstrated, or confidence limits established for each supposed morphological and biochemical fossil. Relevance to biospheric or related evolutions must be critically evaluated for every geochemical and sedimentological anomaly.
Indirect evidence suggests primitive, oxygen-generating autotrophy by ∼ 3.8 × 10 ⁹ years ago (3.8 Gyr or gigayears), while free O 2 first began to accumulate only ∼ 2 Gyr ago. Various reduced substances in the atmosphere and in solution functioned as oxygen sinks, keeping photolytic and biogenic O 2 at levels tolerable by primitive anaerobic and microaerophilic procaryotes.
The oldest demonstrably biogenic and certainly primary microstructures are procaryotes from ∼ or > 2 Gyr old strata around Lake Superior. Improved biologic O 2 mediation, continued carbon segregation, and filling of O 2 sinks initiated atmospheric O 2 buildup, leading to an ozone screen ∼ or < 2 Gyr ago. Consequences were essential termination of banded iron formation, onset of red beds, and O 2 shielding of anaerobic intracellular processes, heralding the eucaryotic cell.
Probable eucaryotes appear in ∼ 1.3 Gyr old rocks in California as large unicells and large-diameter, branched, septate filaments. Likely consequences of eucaryotic evolution were increased atmospheric O 2 , increased carbonate and sulfate ion, and the rise of sexuality. Meiosis had definitely evolved > 0.7 Gyr ago and probably > 1.3 Gyr ago, perhaps simultaneously with the mitosing cell. Whatever the timing, it completed the evolution of the eucaryotic heredity mechanism and foreshadowed (given sufficient free O 2 ) the differentiation of tissues, organs, and advanced forms of life—with all their potential for biogeochemical feedback to sedimentary, diagenetic, and metallogenic processes. The first Metazoa appeared ∼ 0.7 Gyr ago. Being dependent on simple diffusion for O 2 , they lacked exoskeletons. The latter appeared, perhaps 0.6 Gyr ago, when increasing O 2 levels favored the emergence of more advanced respiratory systems.
During the last two decades the occurrence of microbial fossils in silicified Precambrian rocks has become firmly established. The significance of these early microorganisms in the bio-geo-chemical evolution has been recognized, and their frequent affiliation with. stromatolitic structures, common in Precambrian strata, has been documented (Reviewed by Schopf, 1970b; Licari and Cloud, 1972). A large number of Precambrian fossil microorganisms has been formally described (pflug, 1965, 1966; Schopf, 1968; Schopf and Blacic, 1971). Based on these descriptions and identifications oftaxonomic affmities of Precambrian microorganisms, dates have been proposed for important early evolutionary events, such as photosynthesis (Schopf et al., 1971), N2 -fixation (Cloud, 1974), Eukaryotic cell organization (Schopf, 1968, 1970b; Cloud et al., 1969) and sex (Schopf and Blacic, 1971). However, the criteria used in identification offossil microorganisms remain in many cases dubious, leaving the already generally accepted conclusions on shaky grounds..
The pre-Phanerozoic record of biotic crises and opportunities is difficult to evaluate. Life probably appeared before 3800 Ma. Terrestrial megacratering around 4200 to 3800 Ma could have (1) promoted chemical evolution and/or (2) produced ecologically harsh conditions for early life once it evolved. With the appearance of the first heterotrophs, the supply of prebiotic organic material would have become limiting. The evolution of autotrophy was a major novelty and probably resulted in the first major microbial radiation. By 3500 Ma ago microbial life was sufficiently advanced to construct stromatolites.
The pre-Phanerozoic fossil record is dominated by stromatolites and microfossils. The most ancient traces of life that are now confidently recognized are the stromatolites and filamentous microfossils from the ca.3500 Ma-old Warrawoona rocks in Western Australia. The fossil record becomes conspicous during the Proterozoic. Stromatolites are plentiful, and the variety of microfossils suggest a considerable diversity of microbial ecosystems. Phytoplankton represented by acritarchs apparently underwent a major radiation ca.1400 Ma ago. Microfossils that have been interpreted as eukaryotes have been reported from a few Proterozoic sequences and are the subject of great debate. -from Author
The siliceous geyserites of Yellowstone National Park (Wyoming, U.S.A.) are morphologically very similar to stromatolites, but are abiogenic. Geyserite is opaline silica deposited non-biogenically within and around hot springs and geysers. The deposits have a variety of shapes, each characteristic of particular environments. The shapes strikingly resemble those of stromatolites; however, the morphogenetic processes are non-biological. Columnar and spicular geyserite forms in subaerial splash zones; stratiform geyserite forms subaqueously; oolitic and pisolitic geyserites form in turbulent water, and may be continually or only intermittently submerged. Geyserite is distinguished from stromatolites by its distinctive distribution around points of water discharge, by microcrosslamination that is common but not ubiquitous, and by its banded lamination with laminae less than about 4μm thick. Spicular and columnar forms could have formed in many types of water-splash zones, such as along shorelines. The word stiriolite is introduced for geyserite-like deposits preserved in the geological record.
This chapter discusses the evolutionary process in the formation of stromatolites. To understand the evolution of stromatolite-building organisms, it is necessary to understand the processes operating in the formation of microbial mats, the precursors of stromatolites. The chapter provides background information on biological and sedimentary processes, leading to stromatolite formation and preservation. This chapter illustrates the stromatolitic habit, which is notably polyphyletic. It involves communities of microorganisms interacting with the physical environment. It is likely that the morphological conservatism of blue-green algae optimally adapted to the stromatolite-building habit is highly evolved, in the sense that stability itself is under genetic control. Blue-green algae may have been subject to rapid rates of evolution of new highly fit genotypes; but limited morphology severely limits the phenotypic information that can be deduced by studies of fossil microorganisms. It is within the blue-green algal template that other organisms have contributed to the construction of stromatolites. In view of this polyphyletic origin, evolutionary information derivable directly from stromatolites and their microbiota is intrinsically limited.
The Earth is old, and in its fabric is written a subtle and complex history. The oldest material ever discovered on Earth consists of a few crystals of a mineral called zircon. These crystals, found in Western Australia, are about 4.3 billion years old. Many of the elements that make up the Earth are roughly 4.6 billion years old, and the planet probably formed soon after that, although much of thç hydrogen in our water may be as old as the universe. For the first 300 million years that Earth existed there is no history recorded in our terrestrial rocks, although the Moon, meteorites and comets preserve earlier material. Some meteorites even preserve traces of events that took place before the formation of the Solar System.
Figure 1.1
A zircon crystal from Western Australia, 4.15 billion years old. This crystal, and others like it that range up to nearly 4.3 billion years old, formed a few million years after the accretion of the Earth. Scale bar is 100 microns long (courtesy of W. Compston).
These structurally preserved Precambrian fossils from Ontario are the most ancient organisms known.
Laguna Guerrero Negro and Ojo de Liebre are large, restricted embayments characterized by an arid climate and by a salinity ranging from that of normal seawater to the hypersalinity of sabkha environments. Intertidal microbial mats develop in some of the slightly hypersaline marshes and in many of the moderately hypersaline flats. Each major mat type corresponds to the lower, middle, or upper intertidal. In the lower intertidal mat, the photosynthetic horizon is a bilayer composed of: 1) a surface, blue‐green algal layer (about 3‐mm thick) dominated by Microcoleus chthonoplastes; and 2) an underlying purple layer (about 2‐mm thick) of photosynthetic bacteria, predominantly Chromatium sp. The mat may accrete to a thickness of 10 cm or more. It is characterized by fine laminations of alternating layers of blue‐green algae and of photosynthetic bacteria. The middle intertidal mat, dominated by Lyngbya aestuarii, is relatively thin (usually 1 or 2 cm). Only a very thin, lower horizon of purple photosynthetic bacteria develops in this mat. One‐cm tall pinnacles that resemble the Precambrian stromatolite, “Conophyton,”; occur locally in the Lyngbya mats. The upper intertidal is characterized by a crusty, wrinkled mat dominated by Calothrix crustacea; the total thickness of these mats is about 0.5 cm. None of the mats is lithified.Aragonite precipitates as uncemented grains in the mats. Non‐algal mat sediments contained only 2% CaCO3. Absolute CaCO3 content was positively correlated both with total mat thickness and with organic carbon concentration in the mat. CaCO3 content decreased with depth in the mats, which demonstrates that in a predominantly silicoclastic and slightly hypersaline environment, the CaCO3 produced in the mats is not stable. These results suggest that analogies between this modern microbial environment and ancient, marine stromatolite environments are probably limited.
Microbial contaminants may be introduced on outcrop as well as en route to or in the laboratory. Micropseudofossils may be natural or man-made. It is possible to recognize such misleading objects and important that they are not allowed to dilute the growing record of authentic pre-Phanerozoic life. Filamentous microbial contaminants from minute cracks in samples of ancient carbonate rocks from Brazil (perhaps 1 Ga old) and South Africa (∼2.3 Ga old) are similar to occurrences previously described as fossils. Published records of supposedly Archean microbial life also include microcontaminants and laboratory artifacts. Although microstructures from sedimentary rocks of the Swaziland system could be fossils, they are not demonstrably so. The oldest structurally preserved fossils yet known seem to be the filaments described by Lois Nagy from stromatolitic limestone in the ∼2.3 Ga old Malmani Dolomite of South Africa. It will be difficult to establish unequivocal older records in the absence of definitive ultrastructural or micro-chemical evidence.
A single specimen of silicified flat algal stromatolite from the late Precambrian Bitter Springs Formation, Australia, contains three distinct microbial communities: (1) an entophysalidacean mat-building community comparable to both modern members of the genus Entophysalis and 2000 Ma old algae from the Belcher Islands, Canada; (2) a filamentous assemblage composed entirely of the Phormidium or Lyngbya-like cyanophyte Eomycetopsis; and (3) a non-stromatolitic assemblage of chroococcoid unicells that may have been associated with small, quickly evaporating ponds or puddles of water. Within each community, fossil preservation varies as a function of preservational microenvironments. Recognition of degradation sequences permits an assessment of taphonomic alterations of the original biological patterns. This, in turn, allows reconstruction of community associations and diversity patterns. The paleoenvironment of this particular Bitter Springs stromatolite is considered to be the lower part of the intertidal zone bordering a shallow, perhaps somewhat restricted sea. Post-mortem degradation has acted to increase apparent diversity through the creation of diagenetic variations in morphology and to decrease the same measure by the selective destruction of less resistant taxa. Three new species are described: Eoentophysalis cumulus, Eosynnechococcus amadeus, and Gloeodiniopsis gregaria.
The microstructure in three silicified morphologically distinct and vertically intergrading stromatolites from the Aphebian (~2 Ga old) Gunflint Iron Formation of Ontario, Canada was found to be different for each stromatolite morphology studied; each in turn has a characteristic microbial composition. Non-columnar stromatolites that comprise the middle zone of the intergrading sequence contain a microstructure characterized by relatively thin laminae composed of a cyanophytic community dominated by the coccoid Huroniospora Barghoorn while the columnar stromatolites of the lower (small, frequently divergent branching columns) and upper zone (large, infrequently α- to β-parallel branching columns) have thicker laminae differing in shape and continuity, which were built by a filamentous cyanophyte-dominated community. 'Microstromatolites' referable to Frutexites Maslov are found in the middle non-columnar and occasionally in the lower parts of the upper columnar zone.In the stromatolites thus far examined from the Gunflint formation, the microbiota, microstructure, and macrostructure are all interrelated, the composition of the microbiota, the nature of the microstructure, and the resulting gross morphology of the stromatolite presumably were influenced or controlled by the microbiota.
Many naturally deformed crustal rocks contain mineral-filled extension
veins. The crystals making up the vein filling often show a fibrous
habit and seem to be built up by a succession of `crack-seal'
increments: the elastically deforming rock fails by fracture, and the
walls of the open micro-crack are sealed together by crystalline
material derived by pressure solution in the rock matrix.
The word ‘stromatolite’ should only be applied to organosedimentary structures predominantly accreted by sediment trapping, binding and/or in situ precipitation as a result of the growth and metabolic activities of benthic, principally prokaryotic, micro-organisms. Structures of uncertain origin that resemble stromatolites should be called ‘stromatoloids’. This cautious approach would eliminate the currently common assumption that structures with mesoscopic morphological similarities to microbially accreted sedimentary structures must be biogenic, a misconception that hampers investigations into the antiquity of life.A hierarchical series of meso- and microstructural attributes of stromatolites can be used to assign gradually increasing probabilities of biogenicity to stromatoloids. This method is particularly useful for interpreting ancient noncolumnar stromatoloids with poor microstructural preservation. In a range of Early Archaean pseudocolumnar, nodular and stratiform stromatoloids from North Pole studied using this method, none could be proved to be stromatolites and only a few are probable or possible stromatolites. As these stromatoloids closely resemble previously reported structures from North Pole interpreted as stromatolites, we consider that the evidence for the existence of life c. 3500 my ago at North Pole is less definitive than previously supposed.
THE oldest documented microfossils are from the ~3,300 Myr BP Onverwacht Group of South Africa6–8. Here, we discuss the occurrence of a new assemblage of microfossils from a ~3,500 Myr BP silicified shallow-water to supratidal carbonate sequence of the Warrawoona Group at North Pole, Western Australia. Five morphologies of carbonaceous spheroids are recognised, including some with splits, some with tetragonal tetrad form and others with groups of up to four individuals. Their morphology is very similar to microfossils from the Onverwacht group of South Africa, and statistical tests of size distribution support a biogenic origin. This occurrence suggests that evidence for early Archaean life may be more widespread than generally thought.
Stromatolites are the least controversial evidence of early life; they are organosedimentary structures resulting from the growth and metabolic activity of microorganisms1. Before this report, however, the oldest well established occurrence was in the 2,900–3,000 Myr Pongola Supergroup of South Africa2; five or six additional occurrences are known from the later Archean3. The only proposed example from older rocks is of a possibly stromatolitic microfabric from 3,500 Myr cherts in South Africa4; as yet that interpretation has not been supported by the discovery of macroscopic stromatolites. Here we describe stromatolites 3,400–3,500-Myr old from the Pilbara Block of Western Australia. These are the oldest firmly established biogenic deposits now known from the geological record.
Lead isotopic ages were determined for seven localities of gneissic granite and granodiorite from the Pilbara Region of Western Australia. For four of the localities Rb-Sr ages were also measured. In the lead isotopic system all localities showed some evidence of post-emplacement disturbance; lead redistribution varied from very slight effects to complete equilibration of K-feldspars during metamorphism. In one case, lead and Rb-Sr ages agreed within experimental error; in two cases, Rb-Sr mineral ages were younger than Pb-Pb ages, and in one case, the Rb-Sr age was intermediate between the primary and metamorphic ages recorded by the Pb isotopic system.Four localities show evidence of metamorphism at 2950 my. It is suggested that this represents the time of formation of the granite dome structures in the southeastern Pilbara. At least two of these localities were also affected by post-tectonic metamorphism (2600–2770 my). The other three localities show a more extended history of events starting at about 2900 my and ending between 2000 and 2250 my. The younger metamorphic ages are interpreted to record a thermal event at the time of outpouring of the Proterozoic Fortescue Group which formerly overlay the Archaean rocks.
Sedimentological studies of the dominantly volcanic, ca. 3.5 b.y. Warrawoona Group, eastern Pilbara Block, Western Australia, indicate widespread shallow-water deposition. Many cherty metasediments within the ultramafic-mafic sequence represent silicified carbonate mud, sand, breccia and conglomerate, and show cross-lamination, ripple marks, scour-and-fill structures, and evidence of reworking. At North Pole, some cherty metasediments appear to be silicified and baritized gypsiferous evaporites, and contain microfossils. Felsic volcaniclastic rocks include pyroclastic deposits, cross-laminated tuffaceous metasediments and conglomerate. Subaerial volcanism apparently increased as deposition proceeded.The depositional basin was large, volcanically active and apparently shallow with subdued marginal relief. Felsic volcanoes formed topographic highs within the basin from which sheets of volcanically derived sediments interfingered with ultramafic-mafic volcanics. The Onverwacht Group of the Barberton Mountain Land, South Africa, is of similar age to the Warrawoona Group and probably represents a similar environment, but other greenstone belts may have formed in contrasting basins, possibly under differing tectonic regimes.
Zircon U-Pb systems from a single block sample of columnar dacite from the early Archaean Warrawoona Group from the layered “greenstone” succession of the Pilbara Craton, Western Australia, indicate an age of3452 ± 16 (2σ) m.y. This is interpreted as the age of the dacite, and is the oldest age so far determined from the Archaean of Australia. This confirms the antiquity of the Warrawoona Group and suggests a close age relationship between the Warrawoona Group in the Pilbara and the Onverwacht Group in South Africa.The Rb-Sr whole rock systems of the dacite have been disturbed since emplacement and indicate apparent ages that have no direct geological significance. This is in accord with previous published accounts of resetting of Rb-Sr whole rock ages determined on acid metavolcanics.
RADIOACTIVE decay of 238U, 235U and
232Th yields 206Pb, 207Pb, and
208Pb, respectively, as daughter products. This radiogenic
lead is continually added to common lead in the source environments of
ore deposits and the lead isotopic ratios of the resulting mixture are
consequently time dependent. Because the relative proportions of these
lead isotopes are fixed when the lead, common and radiogenic together,
is separated from the parental uranium and thorium and incorporated into
a lead deposit, determination of the isotope ratios provides evidence
regarding the age of the lead ore and thus indirectly of the rock in
which the ore is contained. Generally speaking, the older the ore the
less radiogenic will be its lead. We report here analyses of extremely
primitive lead from a small lead-bearing deposit in Western Australia.
Internally laminated conical mounds characterise a regionally extensive
chert unit near the top of the 3,400-Myr old Warrawoona Group in the
Pilbara Block of Western Australia. The chert formed by silicification
of a carbonate-evaporite sequence deposited in shallow subtidal to
intertidal environments. The morphology and internal organisation of the
mounds described here suggests that they are conical stromatolites
similar but not identical to members of the common Proterozoic group
Conophyton Maslov.
A comparative statistical study has been carried out on populations of modern algae, of Precambrian algal microfossils, of the 'organized elements' of the Orgueil carbonaceous meteorite, and of the oldest microfossil-like objects now known (spheroidal bodies from the Fig Tree and Onverwacht Groups of the Swaziland Supergroup, South Africa). The distribution patterns exhibited by the greater than 3000 m.y.-old Swaziland microstructures bear considerable resemblance to those of the abiotic 'organized elements' but rather markedly differ from those exhibited by younger, assuredly biogenic, populations. Based on these comparisons it is concluded that the Swaziland spheroids could be, at least in part, of non-biologic origin; these oldest known fossil-like micro-structures should not be regarded as constituting firm evidence of Archean life.
The concept that low concentrations of atmospheric oxygen and consequent unattenuated ultraviolet irradiation limited the emergence of Phanerozoic life, the Berkner-Marshall hypothesis, is no longer tenable. Anaerobic bacteria, which probably evolved far earlier than Metazoa, were irradiated in a special chamber under strictly anaerobic conditions. Both intrinsic resistance and photoreactivation by visible light were discovered in obligately and facultatively anaeroboc microbes. Atmospheric scientists have shown that small amounts of oxygen would have limied pre-Phanerozoic surface ultraviolet irradiation to fluxes well below those used in the anaerobic experiments described. Since adequate ultraviolet protection mechanisms evolved early, the late Proterozoic appearance of Metazoa probably was not related to high fluxes of solar ultraviolet radiation.
Micropaleontological studies of carbonaceouis chert from the Fig Tree Series of South Africa (> 3.1 x 10(9) years old) revealed the presence of spheroidal microfossils, here designated Archaeosphaeroides barbertonensis, interpreted as probably representing the remnants of unicellular alga-like organisms. The presumed photosynthetic nature of these primitive microorganisms seems corroborated by organic geochemical and carbon isotopic studies of the Fig Tree organic matter, and is consistent with the geologically and mineralogically indicated Early Precambrian environment. These alga-like spheroids, together with a bacterium-like organism previously described from the Fig Tree chert, are the oldest fossil orgisms now known.
In the frigid desert of the Antarctic dry valleys there are no visible life forms on the surface of the soil or rocks. Yet in certain rock types a narrow subsurface zone has a favorable microclimate and is colonized by microorganisms. Dominant are lichens of unusual organization. They survive not by physiological adaptation to lower temperatures, but by changing their mode of growth, being able to grow between the crystals of porous rocks. Their activity results in mobilization of iron compounds and in rock weatherning with a characteristic pattern of exfoliation. This simple ecosystem lacks both higher consumers and predators.
A newly discovered population of organic walled microstructures from the Swaziland System, South Africa, is considered to be biological on the following grounds: (i) the structures are carbonaceous and occasionally have internal organic contents; (ii) the population has a narrow unimodal size frequency distribution (average diameter, 2.5 micrometers; range, 1 to 4 micrometers); (iii) the structures are not strictly spherical, but are commonly flattened and folded like younger microfossils; (iv) the sedimentary context is consistent with biogenic origins; and (v) various stages of binary division are clearly preserved.
The relationship between blue-green algae and carbonate deposits The Biology of Blue-Green Algae
- S Golubic
Golubic, S., 1973. The relationship between blue-green algae and carbonate deposits. In: N. Cart and B.A. Whitton (Editors), The Biology of Blue-Green Algae. Blackwell, London, pp. 434--472.
1:250 000 Geological Series --Explanatory Notes, Marble Bar, Western Australia
- A H Hickman
- S L Lipple
Hickman, A.H. and Lipple, S.L., 1978.1:250 000 Geological Series --Explanatory Notes, Marble Bar, Western Australia. Geol. Surv. W. Aust., Perth, 24 pp.
Precambrian organic geochemistry, preservation of the record Origin and Evolution of Earth's Earliest Biosphere: An Interdisciplincary Study
- J M Hayes
- I R Kaplan
- K W Wedeking
Hayes, J.M., Kaplan, I.R. and Wedeking, K.W., 1983. Precambrian organic geochemistry, preservation of the record. In: J.W. Schopf (Editor), Origin and Evolution of Earth's Earliest Biosphere: An Interdisciplincary Study. Princeton Univ. Press, Princeton, NJ, in press.