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Archean Microfossils Showing Cell Division from the Swaziland System of South Africa
Abstract
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 copyright holder for this preprint this version posted August 17, 2021. ; https://doi.org/10.1101/2021.08.16.456462 doi: bioRxiv preprint Spherical microfossils of different morphologies were discovered from sites within PIF (1,15,16) and BGB (4, 6,17). EM-P reproduced either by forming external or internal daughter cells (discussed in detail in accompanying manuscript). ...
... The biogenicity of Swartkoppoie formation microfossils ( fig. S32) was widely accepted among scientific community due to the discovery of microfossil morphologies in different stages of their cell-division (6). To date, a sequential 10 process by which Archean organic structures might have formed, has never been presented before. ...
... Comparison of EM-P with Swartkoppie formation microfossils.Images A-K are the images of Swartkoppie microfossils(Knoll et al., 1977) (6). Images L-R are images of EM-P exhibiting morphological similarities with Swartkoppie microfossils.Image A shows cells with membrane overhangs (red box), cells in dyads (green box) andindividual spherical cells (arrows). ...
Oldest known microfossils were known to have the most complex of morphologies among prokaryotes. Given the morphology of an organism is governed by information encoded in its genome, it was proposed that these primitive organisms most likely possessed complex molecular biological processes. Here we worked with bacterial protoplasts under environmental conditions of Archaean earth and reproduced morphologies of every known microfossil and associated structures. Contrary to the current presumption, our work suggest that complex morphologies of these microfossils could be explained not by presence but by complete absence of molecular biological mechanisms. Environmental conditions and architecture of the cell membrane are the only factors that determined the morphology of these organisms. Based on our observations we present a case for reinterpretation of Archaean microfossils as protocells that were devoid of complex molecular biological processes rather than annotating them to a particular phylogenetic group of extant bacteria.
One Sentence Summary
Microfossils reported from Archaean BIF’s most likely were liposome like protocells, which had evolved mechanisms for energy conservation, but not for regulating cell morphology and replication.
... These features clearly indicate that the microspheres are of synsedimentary origin and were not derived from contamination or artifacts (Perri and Tucker, 2007;Javaux et al., 2010). Furthermore, the spheroidal shape, paired clusters, two-layered structure, and dolomite (or carbonaceous) compositions rule out abiotic crystalline form and late diagenesis, but these same features support a biological origin (Knoll and Barghoorn, 1977;Perri and Tucker, 2007). These microspheres represent early mineralized biological bodies (Perri and Tucker, 2007). ...
... Most notably, the combination of a simple spheroidal morphology, cellular structure, binary division, and micron-scale size places these microfossils among the prokaryotic coccoidal unicellular microbes (Lengeler et al., 1999). Primitive microbes are undoubtedly simple in the present and were so in the past; many prokaryotic taxa consist entirely of smooth coccoidal unicells (Knoll and Barghoorn, 1977). Deformed carbonaceous individuals ( Fig. 1B; Fig. S3) can result from the mummification of original unicells, presumably due to dehydration and shrinkage with progressive burial. ...
... In addition, paired hemispheroids (Figs. 1F and 2G-2I) have recorded the process of cellular binary division, comparable to extant prokaryotic cells (Knoll and Barghoorn, 1977;Lengeler et al., 1999). Specifically, the distribution and division of these unicells in the semiclosed cavity of ostracod shells (Figs. ...
Methanogens are methane-producing archaea (some of the most primitive organisms on Earth), which possess great phylogenetic and ecological diversity in modern ecosystems. However, cellular fossil evidence of methanogens remains extremely scarce throughout the geological record. Here, we report a new population of spheroidal microstructures composed of dolomite observed in Permian lake deposits in northwestern China. The microspheres exhibit indicators of biological affinity and are well preserved in authigenic dolomite with cellular fidelity. Based on morphological and geochemical evidence, these microspheres are interpreted as fossilized cells of methanogenic archaea, which can be divided into three size-based taxa. These microfossils are the first fossil record of spheroidal methanogens. The microfossil-bearing dolomite exhibits extremely positive δ13C values (up to +20‰ relative to Vienna Peedee belemnite) that are attributed to microbial methanogenesis. The results suggest that methanogens were a significant component of this Permian lake biosphere. As a consequence of the metabolic activity of the methanogens, a large amount of biogenic methane was produced through methanogenesis in the anoxic lake sediments. This study not only fills a gap in the fossil record of methanogenic archaea, but it also provides new insights into methane emissions from ancient lakes.
... *[Note that these samples were collected from the same outcrops (Pflug, 1967), which were originally assigned to the Fig Tree Group, but later revised and changed to the upper Onverwacht Group (see Schopf, 1975 andKnauth, 1977)]. Simple spherical and filamentous microstructures have also been described from other Onverwacht Group cherts of the Mendon and Kromberg Formation (Engel et al., 1968;Nagy and Nagy, 1969;Brooks and Shaw, 1971;Brooks et al., 1973;Muir and Hall, 1974;Muir and Grant, 1976;Knoll and Barghoorn, 1977), however the exact stratigraphic position was often not clearly indicated, which made it challenging to put the individual findings in context to each other. In fact, the insufficient knowledge of the BGB stratigraphy at that time and the often poorly studied depositional facies, and paleoenvironmental context of the analyzed samples are central problems of most of these pioneering studies. ...
... In fact, the insufficient knowledge of the BGB stratigraphy at that time and the often poorly studied depositional facies, and paleoenvironmental context of the analyzed samples are central problems of most of these pioneering studies. Several reviewers have questioned the biogenicity of almost all of these early microfossils because of their simple morphology and wide size range, suggesting that except for the structures described by Muir and Grant (1976) and Knoll and Barghoorn (1977) all other findings should be treated as nonfossil artefacts, aggregates of amorphous carbonaceous matter or modern contaminants (Schopf, 1975;Schopf and Walter, 1983;Altermann, 2001;Wacey, 2009). In the following years, detailed sedimentological and geochronological studies, as well as extensive geological mapping helped to further establish the tectonostratigraphic context of the BGB deposits (Lowe and Knauth, 1977;Kröner et al., 1991;Lowe and Byerly, 1999;Lowe et al., 2012). ...
... None, except carbonaceous composition Possible life, but geological context and geochemistry needed to further support biogenic origin Simple morphology, and no depositional context or geochemistry reported. Could likely be non-biological (Wacey, 2009 (Knoll and Barghoorn, 1977). ...
... Although identification of compartmentalized organic material had been described in the BGB around fifty years ago (e.g., Pflug, 1966;Engel et al., 1968;Nagy and Nagy, 1969), previous reviews of reported Archean microfossils (Schopf and Walter, 1983;Schopf, 1992;Altermann, 2001) agree that all but two instances of these early reported cellular remains should be treated as nonfossils, the exceptions being those of Muir and Grant (1976) and Knoll and Barghoorn (1977). ...
... The fact that the phototrophic biofilm survived in partially exposed evaporitic conditions implies a level of halotolerancy (Kamekura, 1998). Similar styles of preservation during the silicification of EPS, microbial films, and microfossils occur in modern hot spring-type deposits (Konhauser et al., 2003;Papineau et al., 2005). Although the UV environment of the early Earth was harsh by comparison with present-day standards (Cockell and Raven, 2004;Cnossen et al., 2007), the occurrence of life occupying an emergent terrestrial niche in both Barberton (in the Josefsdal Chert and Moodies Group) and in the Pilbara (Dresser Formation: Van Kranendonk, 2006;Djokic et al., 2017) implies the existence of mechanisms to minimize cell damage due to radiation. ...
... The environment of deposition is shallow-water nearshore, as indicated by cross-stratification, oolitic textures, and flat-pebble conglomerates. Carbonaceous microspheroids within this unit were interpreted as isolated and paired unicells, exhibiting multiple phases of the cell cycle (Fig. 42.14A and B: Knoll and Barghoorn, 1977;Schopf, 2006). Interpreted as prokaryotic algae, they are small (1e4 mm), with a size frequency distribution similar to modern and ancient prokaryotic communities (Fig. 42.14G), and are morphologically varied, being flattened, wrinkled, or folded through sedimentary compaction in a fashion similar to comparable fossils in Proterozoic rocks. ...
There is much convincing evidence for early life in the Barberton greenstone belt (3.47-3.22 Ga), portraying a diverse Paleoarchean biosphere that occupied both marine and terrestrial habitats. This stands testament to the already widespread distribution and diversity of life on the early Earth. We here present an up-to-date review of fifty years of accumulated evidence for life in the Barberton greenstone belt and outline the reasoning for biogenicity in each case. Fossils of microbial life are present throughout the stratigraphy, from the oldest chert unit (the Middle Marker horizon) to the uppermost siliciclastic sediments (the Moodies Group). Although phototrophs could also develop in nutrient poor, oligotrophic areas away from hydrothermal vents, chemotrophs appear to have been strongly controlled by proximity to hydrothermally derived nutrients. The Paleoarchean was a time of surprising biological diversity, and this record is best accessed by investigating the biomes preserved in chertified horizons.
... Ancient spheroidal or coccoidal microfossil-like objects have been identified in the 3.45 Ga Hooggeoneg Formation (Walsh 1992;Glikson et al. 2008), the 3.446 Ga Kitty's Gap Chert (Westall et al. 2006(Westall et al. , 2011, the 3.35-3.43 Ga Strelley Pool Chert (Wacey et al. 2011;Sugitani et al. 2015), the 3.26 Ga Fig Tree Group (Knoll and Barghoorn 1977), and the 3.0 Ga Farrell Quartzite (Sugitani et al. 2007(Sugitani et al. , 2009) ( Fig. 10.2). Coccoidal objects exhibit substantial size variation. ...
... Spheroidal microfossil-like objects also exhibit considerable morphological differentiation: within millimeters, hollow and solid forms, both solitary and grouped, have been identified (Sugitani et al. 2007(Sugitani et al. , 2015. Compelling evidence for biogenesis has been found in certain populations of spheroidal microstructures: (i) both Knoll and Barghoorn (1977) and Westall et al. (2006Westall et al. ( , 2011 identified evidence for cell division; (ii) Walsh (1992) and Sugitani et al. (2007Sugitani et al. ( , 2015 showed that coccoidal structures can occur in pairs and groups consistent with biological cell distributions; Walsh (1992) and Sugitani et al. (2007) identified features consistent with the rupturing of cell walls; and Westall et al. (2006) noted deflated coccoid surface textures consistent with cell lysis. In this regard, coccoidal-shaped microfossils are the only ancient fossil morphotype that displays evidence for multiple stages of the cell cycle, though caution is warranted as some of the apparent "life-cycle stages" can also occur during the growth of microfossil-like minerals: silica microspheres and botryoidal oxides exhibit division-like phenomena, and many mineral species show self-organization into arrangements not dissimilar to the pairing and grouping shown by coccoidal microfossil-like objects. ...
Life is the outcome of a complex network of chemical reactions and molecular interactions that emerged on Earth once primitive chemical automata could self-assemble in such a way that enabled them to self-reproduce and evolve. Yet exactly how, where and when life first appeared on our planet remains unknown. In this chapter, we review the various lines of evidence from fossil and geochemical traces of early life preserved in the geological record, which provide fundamental, albeit often rudimentary, insight into early life. The oldest fossils record the nature of life more than half a billion years after it emerged on Earth and suggest that considerable metabolic diversity had already evolved by this time. Microfossils, microbial mats, stromatolites and organic and inorganic geochemical signatures have been interpreted as compelling evidence for Archean biodiversity. In spite of the chemical enigmas of the earliest life and its limited record, characterization of the various classes of biosignatures indicative of life in its geological context provides guidance as to the earliest co-evolution of the geosphere and biosphere.
... Softwares for image analysis are now used routinely to extract size or shape-describing features of objects (Adams & Otárola-Castillo, 2013;Adams, Rohlf, & Slice, 2004;Doube et al., 2010;Ferreira et al., 2014;Papadopulos et al., 2007;Rappaz et al., 2005), and such measurements have been applied to different fields: neurosciences (Bora, Fornito, Pantelis, & Yücel, 2012;Ferreira et al., 2014;Rajkowska et al., 1999), phanerozoic micropaleontology, food microstructure (Aguilera, 2005), medicine (Karakas & Kavaklı, 2005), and basin topography (Srinivasa Vittala, Govindaiah, & Honne Gowda, 2004), among others. Parameters such as size distributions have been examined for decades in the context of Precambrian life (Barghoorn & Tyler, 1965;Butterfield & Chandler, 1992;Knoll & Barghoorn, 1977;Köhler & Heubeck, 2019;Schopf & Barghoorn, 1967;Schopf et al., 2010;Sugitani et al., 2007Sugitani et al., , 2010Sugitani, Mimura, Nagaoka, Lepot, & Takeuchi, 2013;Wacey et al., 2011). ...
... Size distributions in microfossil assemblages have been used previously as a biogenicity criterion in micropaleontological studies (Barghoorn & Tyler, 1965;Butterfield & Chandler, 1992;Knoll & Barghoorn, 1977;Köhler & Heubeck, 2019;Schopf & Barghoorn, 1967;Schopf et al., 2010;Sugitani et al., 2007Sugitani et al., , 2010Sugitani et al., , 2013Wacey et al., 2011). In these studies, the absolute range of sizes and the relative width of size distributions (quantified in our study by the mean/SD parameter) were particularly discussed. ...
The identification of cellular life in the rock record is problematic, since microbial life forms, and particularly bacteria, lack sufficient morphologic complexity to be effectively distinguished from certain abiogenic features in rocks. Examples include organic pore‐fillings, hydrocarbon‐containing fluid inclusions, organic coatings on exfoliated crystals and biomimetic mineral aggregates (biomorphs). This has led to the interpretation and re‐interpretation of individual microstructures in the rock record. The morphologic description of entire populations of microstructures, however, may provide support for distinguishing between preserved micro‐organisms and abiogenic objects. Here, we present a statistical approach based on quantitative morphological description of populations of microstructures. Images of modern microbial populations were compared to images of two relevant types of abiogenic microstructures: interstitial spaces and silica–carbonate biomorphs. For the populations of these three systems, the size, circularity, and solidity of individual particles were calculated. Subsequently, the mean/SD, skewness, and kurtosis of the statistical distributions of these parameters were established. This allowed the qualitative and quantitative comparison of distributions in these three systems. In addition, the fractal dimension and lacunarity of the populations were determined. In total, 11 parameters, independent of absolute size or shape, were used to characterize each population of microstructures. Using discriminant analysis with parameter subsets, it was found that size and shape distributions are typically sufficient to discriminate populations of biologic and abiogenic microstructures. Analysis of ancient, yet unambiguously biologic, samples (1.0 Ga Angmaat Formation, Baffin Island, Canada) suggests that taphonomic effects can alter morphometric characteristics and complicate image analysis; therefore, a wider range of microfossil assemblages should be studied in the future before automated analyses can be developed. In general, however, it is clear from our results that there is great potential for morphometric descriptions of populations in the context of life recognition in rocks, either on Earth or on extraterrestrial bodies.
... In such conservation deposits, animal and plant tissues are finely preserved, often in high-quality details and occasionally at the cellular (Knoll and Barghoorn 1977;Briggs 2003a;Cohen et al. 2009;Pang et al. 2013), and sub-cellular Muscente et al. 2015b) levels. Consequently, organic structures such as internal organs (Ma et al. 2012;Maldanis et al. 2016;Hawkins et al. 2018;Pan et al. 2019), integument (Walossek et al. 1993;Müller et al. 1995;Pinheiro et al. 2012), feathers (Vinther et al. 2008;Carvalho et al. 2015), muscle fibers (Schultze 1989;Martill 1990;Osés et al. 2016), and cells with nuclei (Knoll and Barghoorn 1977;Cohen et al. 2009;Pang et al. 2013;Osés et al. 2017) can be fossilized, providing key elements for unraveling and understanding the evolution of metazoans (e.g., Butterfield 2003;Xiao et al. 2014;Carvalho et al. 2015;Martill et al. 2015;Maldanis et al. 2016;Pan et al. 2019). ...
... In such conservation deposits, animal and plant tissues are finely preserved, often in high-quality details and occasionally at the cellular (Knoll and Barghoorn 1977;Briggs 2003a;Cohen et al. 2009;Pang et al. 2013), and sub-cellular Muscente et al. 2015b) levels. Consequently, organic structures such as internal organs (Ma et al. 2012;Maldanis et al. 2016;Hawkins et al. 2018;Pan et al. 2019), integument (Walossek et al. 1993;Müller et al. 1995;Pinheiro et al. 2012), feathers (Vinther et al. 2008;Carvalho et al. 2015), muscle fibers (Schultze 1989;Martill 1990;Osés et al. 2016), and cells with nuclei (Knoll and Barghoorn 1977;Cohen et al. 2009;Pang et al. 2013;Osés et al. 2017) can be fossilized, providing key elements for unraveling and understanding the evolution of metazoans (e.g., Butterfield 2003;Xiao et al. 2014;Carvalho et al. 2015;Martill et al. 2015;Maldanis et al. 2016;Pan et al. 2019). ...
The Aptian Crato Konservat-Lagerstätte is renowned for its exceptionally preserved fossils in lacustrine laminated limestones. Although previous works on this site include numerous taxonomic studies, its taphonomy remains a subject of debate. Herein, we present new data on the taphonomy of decapod crustaceans preserved in wrinkle laminites, highlighting the role of microbial mats in enhancing fossil preservation. Our results suggest that benthic microorganisms may have promoted protection and organic mineralization of some of the allochthonous to parautochthonous organic remains within the microbial laminites of the Crato lake. Overall, this work provides the first empirical evidence that the preservational pathways of the fossils in the Crato Konservat-Lagerstätte involved microbial mats.
... The most ancient terrestrial rocks in which biomorphic microstructures are found are rocks of the Archean greenstone belts of Western Greenland, South Africa, and Australia (Knoll and Barghoorn, 1977;Schidlowski et al., 1979;Schopf, , 1993Schidlowski, 1988Schidlowski, , 2001Schidlowski, , 2005Knoll, 1994;and others). ...
... Aerobic bacteria were also registered early enough. Putative cyanobacteria are known from the sediments aged approximately 3.5 Ga (Knoll and Barghoorn, 1977;Schopf, , 1993Knoll, 1994;Bakterial'naya…, 2002). The evidence for photosynthetic life (both anoxygenic and oxygenic) dated earlier than 3.0 Ga ago, perhaps, 3.5-3.7 Ga (Rosing, 1999), was also discussed. ...
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.
... Cyanobacteria are a successful group of morphologically diverse prokaryotes that are widespread in aquatic ecosystems with different trophic statuses, where they play an important role as primary producers, nitrogen-fixing bacteria and as a food resource. Cyanobacteria are one of the most ancient organisms on the Earth: their fossils are found in the Precambrian deposits (about 3.5 billion years old) [1,2]. are used as drinking water sources and for recreation by a great number of people. ...
For the first time, microcystin-producing cyanobacteria have been detected in Khubsugul, which is ancient, pristine and one of the world’s largest lakes. The microcystin synthetase genes belonged to the genera Nostoc, Microcystis and possibly Snowella spp. No microcystins were found in the water of the lake. Using the HPLC-HRMS/TOF, five microcystin congeners were identified in biofilms from stony substrates sampled in the coastal zone. The concentration of microcystins in biofilms was low: 41.95 µg g−1 d. wt. by ELISA and 55.8 µg g−1 d. wt. using HPLC. The taxonomic composition of planktonic and benthic cyanobacterial communities was determined by means of microscopy and high-throughput sequencing of 16S rDNA amplicons. Nostocales cyanobacteria dominated benthos of Lake Khubsugul and Synechococcales—plankton. The abundance of cyanobacteria was low both in plankton and benthos; there was no mass development of cyanobacteria. Hydrochemical and microbiological analyses showed that the water in the lake was clean; the number of faecal microorganisms was significantly below the acceptable guideline values. Hydrochemical and hydrophysical parameters, and the concentration of chlorophyll a, were low and within the range of values recorded in the 1970s to 1990s, and corresponded to the oligotrophic state of the lake. There were no signs of anthropogenic eutrophication of the lake and no conditions for the cyanobacterial blooms.
... In Precambrian cherts, microfossils typically range between 10 and 100 μm in size and exhibit spheroidal or filamentous shapes (Duck et al., 2007;Glikson et al., 2008;Golubic & Hofmann, 1976;Javaux & Lepot, 2018;Knoll & Barghoorn, 1977;Rasmussen, 2000;Sugitani et al., 2007). The morphological preservation of such delicate structures may be aided by sulfide-and silica-bearing fluids causing mineral-coating or permineralization in sulfide minerals and/or chert Chert formation typically occurs in the lower temperature zones of deep-sea hydrothermal systems and is often associated with (microbial) Fe oxide formation, resulting in a characteristic jasper facies (Hannington et al., 1998). ...
Deep- sea hydrothermal systems provide ideal conditions for prebiotic reactions and an-cient metabolic pathways and, therefore, might have played a pivotal role in the emer-gence of life. To understand this role better, it is paramount to examine fundamental interactions between hydrothermal processes, non- living matter, and microbial life in deep time. However, the distribution and diversity of microbial communities in ancient deep- sea hydrothermal systems are still poorly constrained, so evolutionary, and ecolog-ical relationships remain unclear. One important reason is an insufficient understanding of the formation of diagnostic microbial biosignatures in such settings and their preser-vation through geological time. This contribution centers around microbial biosignatures in Precambrian deep- sea hydrothermal sulfide deposits. Intending to provide a valuable resource for scientists from across the natural sciences whose research is concerned with the origins of life, we first introduce different types of biosignatures that can be preserved over geological timescales (rock fabrics and textures, microfossils, mineral precipitates, carbonaceous matter, trace metal, and isotope geochemical signatures). We then review selected reports of biosignatures from Precambrian deep- sea hydrothermal sulfide deposits and discuss their geobiological significance. Our survey highlights that Precambrian hydrothermal sulfide deposits potentially encode valuable information on environmental conditions, the presence and nature of microbial life, and the complex in-teractions between fluids, micro- organisms, and minerals. It further emphasizes that the geobiological interpretation of these records is challenging and requires the concerted application of analytical and experimental methods from various fields, including geol-ogy, mineralogy, geochemistry, and microbiology. Well- orchestrated multidisciplinary studies allow us to understand the formation and preservation of microbial biosigna-tures in deep- sea hydrothermal sulfide systems and thus help unravel the fundamental geobiology of ancient settings. This, in turn, is critical for reconstructing life's emergence and early evolution on Earth and the search for life elsewhere in the univers
... Serving as a search image in the field and in the laboratory, Gunflint-type stromatolitic cherts and microfossils soon opened the floodgates to numerous discoveries of Precambrian microfossils. Within a decade, Precambrian microfossils had been reported from many Precambrian cherts in North America and Australia, including the Neoproterozoic Bitter Springs Formation in Australia ( Fig. 1.7) (barghoorn & SchoPF, 1965;SchoPF, 1968;SchoPF & blacic, 1971), the Neoproterozoic Skillogalee Dolomite in South Australia (SchoPF & barghoorn, 1969;knoll, barghoorn, & golubic, 1975), the Neoproterozoic Beck Springs Formation in eastern California (cloud & others, 1969), the Paleoproterozoic Belcher Supergroup in Canada (hoFmann, 1974;hoFmann, 1976), Archean strata in South Africa (SchoPF & barghoorn, 1967;knoll & barghoorn, 1977), and many other units. These were followed by reports of silicified microfossils, many of which are interpreted as cyanobacteria, from Precambrian cherts around the world (see summary in SchoPF, 1983;SchoPF & klein, 1992;Sergeev, Sharma, & Shukla, 2012). ...
... 489interpreted as division point of unicells during reproduction of the life cycle of 490 unicellular microorganisms. The cell divided from this circular opening into two,491 three, and four, up to more within an envelope, and the parental envelope released the 492 enclosed daughter cells(Zhang, 1981), which is an interpretation previously invoked493 for the life cycle of some Precambrian microfossils(Knoll and Barghoorn, 1977; 494Knoll and Golubic, 1979). Although the reproduction series of a complete life cycle495 of prokaryotes is not observed in the Jixian materials, co-existence of microscopic 496 bacterial clusters and relatively large spheroids with thin envelopes indicate these 497 cell-like spheroids may have experienced similar reproduction style as part of their 498 life cycle.499 ...
Stromatolites have been widely reported from the Archean and Paleoproterozoic successions worldwide, and they could represent one of oldest life forms on Earth. Of these, a group of small stromatolites occur as microdigitate low-relief columns, and are also conspicuous in the field. However, biogenicity of these microdigitate stromatolites (MDSs) has long been disputed due to to the abundance of radial-fibrous texture and a lack of convincing microfossils. New examples of MDS are documented from the Mesoproterozoic Wumishan Formation of the Jixian area, North China. Vertically oriented fibrous fabrics are conspicuous and penetrate laminae as well as microscopic spheroids, which point to an abiotic genesis for this specific fabric. Stromatolite laminae contain abundant spheroids, typically 15–30 μm in diameter, with single or double outlines and they occur as solitary coccoid-like microfossils or in small aggregated colonies. Spheroids show strong fluorescence under both green and purple exciting lights, consistent with their composition of organic matter. Spheroids are abundant in the Wumishan stromatolites and they are categorized into two types. The first kind comprises micrite nuclei surrounded by sparitic sheaths, without nano-particle coatings. A smooth to grainy spheroidal surface defines the first kind of spheroids that also has a distinct rounded opening, which is often broken probably due to diagenesis and silicification. The second kind of spheroids is usually covered with nano-particles and lacks circular opening on surface. These spheroids possess large nuclei of single sparitic calcite coated with thin sparry sheaths. Overall, the Wumishan spheroids resemble coccoidal microorganisms reported from other Archean-Paleoproterozoic strata worldwide, but they are also better preserved. The rounded opening on spheroid surface is interpreted as division point of unicells during reproduction of the life cycle of bacteria akin to Myxococcoides grandis. Clump-like micro-particle aggregates in nuclei could represent daughter cells released from the parental envelope, similar to the reproduction process and life cycle suggested for similar spheroidal microfossils from other similar Precambrian occurrences. The Wumishan spheroids therefore may represent fossilized prokaryotes that could have contributed to construct the MDS. Moreover, filamentous microfossils are occasionally present in the coloumns of stromatolites, and they resemble filamentous cyanobacteria, but may not be major constructors of MDS due to their rarity in the buildups. Three types of nano-particles are also conspicuous: (1) putative organic relics, such as fragmented filaments and mucuslike biofilms (purported EPS), (2) organominerals, including nanoglobules, polyhedrons, and their aggregates, and (3) dumbbell-shaped nano-particle aggregates. All of these nano-particles are interpreted to be likely biogenic in origin, and many of them were found from the radial-fibrous fabrics of carbonate precipitates in the MDS, implying that some heterotrophic bacteria may have afficliated the precipitation of radial fibers in deep-time radial-fibrous carbonate precipitates. Therefore, abundant and diverse biosignatures (spheroids, tubular filaments, and nano-particles) are identified in the Wumishan MDSs, and we conclude that diverse filamentous and coccoidal micro-organismscontributed to the formation of the Wumishan stromatolites.
... The documented history of life in the rock record extends to at least *3500-3000 Ma (Knoll and Barghoorn, 1977;Moorbath, 2005;Djokic et al., 2017). The abundance of carbonate structures that contain fossilized remnants of life over 3 billion years old (Grotzinger and Knoll, 1999) indicates their importance in understanding the evolution of life and ecosystems (Foster and Green, 2011). ...
Detecting evidence of life on other planetary bodies requires a certain understanding of known biomarkers and their chemical nature, preservation potential, or biological specificity. In a planetary search for life, carbonates are of special interest due to their known association with life as we know it. On Earth, carbonates serve as an invaluable paleogeochemical archive of fossils of up to billions of years old. Here, we investigated biomarker profiles on three Chilean Triassic-Jurassic sedimentary records regarding our search for signs of past and present life over ∼200 Ma. A multianalytical platform that combines lipid-derived biomarkers, metaproteomics, and a life detector chip (LDChip) is considered in the detection of biomolecules with different perdurability and source-diagnosis potential. The combined identification of proteins with positive LDChip inmunodetections provides metabolic information and taxonomic affiliation of modern/subrecent biosignatures. Molecular and isotopic analysis of more perdurable hydrocarbon cores allows for the identification of general biosources and dominant autotrophic pathways over time, as well as recreation of prevailing redox conditions over ∼200 Ma. We demonstrate how extraterrestrial life detection can benefit from the use of different biomarkers to overcome diagnosis limitations due to a lack of specificity and/or alteration over time. Our findings have implications for future astrobiological missions to Mars.
... The rocks in question are volcanic-sedimentary sequences preserved in ancient cratonic areas of southern Africa and Western Australia dated at 3400-3500 million years (Ma) old. Silicified chemical sediments in both successions contain large populations of small (2-4 urn diameter) organic walled spheroids, some preserved in various stages of binary division (Muir and Grant, 1976;Knoll and Barghoorn, 1977;Awramik et al., 1983). These microstructures are simple in organization and, consequently, are difficult to identify unequivocally as fossils; however, the regularity of their size frequency distributions, the spatial distribution of populations along bedding planes, surface and internal diagenetic features that compare closely with those characteristic of known microfossils in younger rocks, the absence of mineral grains that could have formed templates for the organic spheroids, and the evidence for binary division collectively suggest that at least some of these Archean microstructures are most parsimoniously interpreted as the remains of once-living microorganisms. ...
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.
... Indeed, silicification occurs sufficiently early and rapidly that microfossils, microbial mats and other organo-sedimentary fabrics can be preserved in volume during life processes (e.g. Knoll and Barghoorn, 1977;Walsh, 1992;Tice and Lowe, 2006a;Westall et al., 2011Westall et al., , 2015Hickman-Lewis et al., 2017, 2018aGreco et al., 2018). This suggests that the timescale of silicification may be less than weeks to months, beginning within hours; indeed, experimental silicification of prokaryotes validates that the process begins within 24 h (Bartley, 1996;Orange et al., 2009). ...
Palaeoarchaean cherts preserve the most ancient direct traces of life, but this palaeobiological testament is rarely assimilated into ecosystem or biome models. Trace and rare earth element plus yttrium (REE+Y) compositions reliably decode the palaeodepositional settings of these cherts, and thus constrain the environments within which early microbial life flourished. Herein, we present systematic comparisons between bulk inductively coupled plasma mass spectrometry (ICP-MS) of four fossiliferous cherts from the Barberton greenstone belt, South Africa (the 3.472 Ga Middle Marker horizon, 3.45 Ga Hooggenoeg H5c chert, 3.334 Ga Footbridge Chert, and ∼3.33 Ga Josefsdal Chert), and in situ laser ablation (LA) ICP-MS transects through microbial laminations therein. Normalised bulk ICP-MS analyses generally exhibit fractionated REE+Y patterns typical of anoxic hydrogenous sedimentation, supporting previous assertions that the Palaeoarchaean habitable realm was a hydrothermally influenced ocean. Suppressed La, Eu and Y anomalies, together with supra-chondritic Y/Ho ratios, however, indicate restriction from the open ocean and influences from non-marine waters. In situ LA ICP-MS transects through fossiliferous layers yield flat, light REE-enriched REE+Y patterns and chondritic Y/Ho ratios indicating major contributions from terrigenous, riverine fluids, i.e. continental weathering. Resurgences of marine chemistry (increased Y/Ho ratios, La and Y anomalies) occur within microbial laminations themselves. Combined, these results evidence the presence of emergent, volcanic landmasses in the Palaeoarchaean, and highlight the importance of epicontinental basins atop these landmasses as loci for microbial biomes up to 250 Ma before large-scale terrestrial ecosystems. Increased riverine weathering of mafic-felsic continental material, together with periodic seawater recharge into these basins, generated disequilibrium redox conditions under which microbial life flourished. Emergent landmasses may thus have catalysed the flourishing of widespread productive photosynthetic biomes. Charting the relative dominance of biomes through time could illuminate microbial evolutionary trajectories through the lens of environmental reconstruction. Furthermore, we advocate the use of correlated bulk and in situ geochemical approaches in reconstructing ancient environments, since signals relating to small-scale palaeoenvironmental fluctuation can evidently be masked by bulk rock chemistry.
... 2.72 billion year old filamentous bacteria[108] could potentially represent one of the first multicellular cyanobacteria detected. For single celled forms, 2.56 billion year old unicellular fossils[249,250,251,248] could likely represent chroococcacean fossils, relatives of ancestral Gloeobacter violaceus orSynechococcus sp. P1 (Figure 2.7). ...
... 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. ...
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.
... Although several early Archean carbonaceous structures have been described and interpreted as possible remnants of microbial life (Knoll and Barghoorn, 1977;Altermann and Kaźmierczak, 2003;Brasier et al., 2006;Schopf et al., 2007;Wacey et al., 2011;Sugitani et al., 2015;Knoll et al., 2016), their biological affinities remain unclear and controversial (Brasier et al.. 2006;Knoll et al., 2016;Wacey et al., 2018). Morphological identification of microfossils embedded in, as a rule, metamorphosed early Archean rocks is difficult and problematic for many reasons. ...
... The earliest Earth's rocks enclosing biomorphic microstructures occur in the Archean green belts of western Greenland, South Africa, and Australia (Knoll and Barghoorn, 1977;Schopf, 1983Schopf, , 1993Walter, 1983;Knoll, 1994;). However, some authors cast doubts on the biological nature of Archean microfossils discovered by Schopf (Brasier et al., 2002(Brasier et al., , 2004. ...
The study of volcanogenic and volcanogenic–sedimentary rocks (Early Proterozoic pillow lava of Karelia and South Africa), where diverse fossilized bacteria (prokaryotes) and probably even eukaryotes shows that, during this early period, conditions of cooling lava flows and igneous rocks were favorable for bacterial development and colonization.
... Archean sedimentary rock successions preserve only relatively simple microfossils including filamentous, unicellular and spindle- shaped microfossils that are often found only in isolated, single populations (e.g., Czaja, Beukes, & Osterhout, 2016;Klein, Beukes, & Schopf, 1987;Knoll & Barghoorn, 1977;Kremer & Kazmierczak, 2017;Lanier, 1986;Sugitani, Grey, Nagaoka, Mimura, & Walter, 2009;Sugitani, Mimura, Nagaoka, Lepot, & Takeuchi, 2013;Sugitani, Mimura, Takeuchi, Lepot, et al., 2015;Sugitani, Mimura, Takeuchi, Yamaguchi, et al., 2015;Wacey, Kilburn, Saunders, Cliff, & Brasier, 2011;Walsh, 1992; amongst others). It is not until the c. 1.88 Ga Gunflint Iron Formation, Canada, that a variety of microbial forms with more complex morphologies are preserved, such as Kakabekia, Eoastrion and Eosphaera (Barghoorn & Tyler, 1965). ...
Eighteen microfossil morphotypes from two distinct facies of black chert from a deep‐water setting of the c. 2.4 Ga Turee Creek Group, Western Australia, are reported here. A primarily in situ, deep‐water benthic community preserved in nodular black chert occurs as a tangled network of a variety of long filamentous microfossils, unicells of one size distribution and fine filamentous rosettes, together with relatively large spherical aggregates of cells interpreted as in‐fallen, likely planktonic, forms. Bedded black cherts, in contrast, preserve microfossils primarily within, but also between, rounded clasts of organic material that are coated by thin, convoluted carbonaceous films interpreted as preserved extracellular polymeric substance (EPS). Microfossils preserved within the clasts include a wide range of unicells, both much smaller and larger than those in the nodular black chert, along with relatively short, often degraded filaments, four types of star‐shaped rosettes and umbrella‐like rosettes. Large, complexly branching filamentous microfossils are found between the clasts. The grainstone clasts in the bedded black chert are interpreted as transported from shallower water, and the contained microfossils thus likely represent a phototrophic community. Combined, the two black chert facies provide a snapshot of a microbial ecosystem spanning shallow to deeper‐water environments, and an insight into the diversity of life present during the rise in atmospheric oxygen. The preserved microfossils include two new, distinct morphologies previously unknown from the geological record, as well as a number of microfossils from the bedded black chert that are morphologically similar to—but 400–500 Ma older than—type specimens from the c. 1.88 Ga Gunflint Iron Formation. Thus, the Turee Creek Group microfossil assemblage creates a substantial reference point in the sparse fossil record of the earliest Paleoproterozoic and demonstrates that microbial life diversified quite rapidly after the end of the Archean.
... Fossil microorganisms of Archean age were discovered for the first time by Knoll and Barghoorn (1977). Later, Timofeev (1982) described the Archaean microfossils (both bacteria and eukaryotes) from Central Karelia and the Middle Dnieper. ...
Nanobacteria, buried in situ, were discovered in the Early Precambrian paraschists (Keivy, Kola Peninsula). It is suggested that occurrence of nanobacteria indicates that a biological factor played a role in the formation of enclosing rocks.
... Its stratigraphy has been examined in detail by Byerly (1999, 2007) and Hofmann (2011). Claims of varying validity for ancient life have included microbial fossils and organic remains (Barghoorn and Schopf, 1966;Pflug, 1966;Engel et al. 1968;Nagy and Nagy, 1969;Muir and Grant, 1976;Knoll and Barghoorn, 1977;Walsh and Lowe, 1985;Walsh, 1992;Westall and Gernecke, 1998;Westall et al., 2001Westall et al., , 2006Westall et al., , 2015Javaux et al., 2010;Homann et al., 2016;Oehler et al., 2017;Kremer and Kazmierczak, 2017), microbial edifices such as stromatolites (Buick et al., 1981;Byerly et al., 1986;Walsh and Westall, 2003), microbial mats or microbially induced sedimentary structures (Walsh, 1992;Walsh and Lowe, 1999;Tice andLowe, 2004, 2006;Westall et al., 2006Westall et al., , 2015Noffke et al., 2006a,b;Tice, 2009;Heubeck, 2009;Gamper et al., 2012;Homann et al., 2015), and lava-hosted microtubules (Furnes et al., 2004(Furnes et al., , 2007Banerjee et al., 2006). As with most examples of putative ancient life, the substantial weight of the burden of proof Brasier et al., 2011), together with the lack of a 'smoking gun' due to the predicament of long-term preservation (Tice and Lowe, 2006) means that most of these claims have faced criticism (see Wacey, 2009, for a recapitulation of many such claims and refutations). ...
Raman spectroscopy is a molecule-specific technique allowing the investigation of the chemical structure of organic and inorganic geological materials. Being a nobiostructures from the Barberton greenstone belt of South An-invasive analytical procedure, Raman spectroscopy is ideally suited to palaeontology. Raman spectroscopy is herein applied to the study of carbonaceous chert facies of the ~3.4 Ga old Buck Reef Chert of South Africa, which contains some of the oldest well-preserved evidence of early life. Laminated chert typically consists of microbands composed of microcrystalline quartz (chert) and an association of siderite and carbonaceous material (CM) in the form of mat-like laminations, simple carbonaceous grains, vein infills and diffuse CM. Using Raman spectroscopy, the structural characteristics of CM in mat-rich chert were investigated and compared with CM-rich grains from the same unit, which were deposited as layers that bear no evidence for mat construction. All CM retains a structural organisation consistent with the lower greenschist grade regional metamorphic imprint, however, a detailed study of the Raman signal of CM revealed some heterogeneity between different sedimentary facies, indicating the presence of different types of CM. Multiple CM precursors are indicated and may reflect different sources or different alteration chemistries of various microbial metabolic pathways. © 2010–2018 Italian Paleontological Society. All rights reserved.
... Its stratigraphy has been examined in detail by Byerly (1999, 2007) and Hofmann (2011). Claims of varying validity for ancient life have included microbial fossils and organic remains (Barghoorn and Schopf, 1966;Pflug, 1966;Engel et al. 1968;Nagy and Nagy, 1969;Muir and Grant, 1976;Knoll and Barghoorn, 1977;Walsh and Lowe, 1985;Walsh, 1992;Westall and Gernecke, 1998;Westall et al., 2001Westall et al., , 2006Westall et al., , 2015Javaux et al., 2010;Homann et al., 2016;Oehler et al., 2017;Kremer and Kazmierczak, 2017), microbial edifices such as stromatolites (Buick et al., 1981;Byerly et al., 1986;Walsh and Westall, 2003), microbial mats or microbially induced sedimentary structures (Walsh, 1992;Walsh and Lowe, 1999;Tice andLowe, 2004, 2006;Westall et al., 2006Westall et al., , 2015Noffke et al., 2006a,b;Tice, 2009;Heubeck, 2009;Gamper et al., 2012;Homann et al., 2015), and lava-hosted microtubules (Furnes et al., 2004(Furnes et al., , 2007Banerjee et al., 2006). As with most examples of putative ancient life, the substantial weight of the burden of proof Brasier et al., 2011), together with the lack of a 'smoking gun' due to the predicament of long-term preservation (Tice and Lowe, 2006) means that most of these claims have faced criticism (see Wacey, 2009, for a recapitulation of many such claims and refutations). ...
... It has been argued by many that microfossils have been discovered within carbonaceous cherts (i.e., the fine-grained silica-rich sedimentary rocks) and sandstones in Western Australia (Schopf and Packer, 1987;Schopf, 1993;Rasmussen, 2000;Ueno et al., 2001;Kiyokawa et al., 2006;Westall et al., 2006a;Glikson et al., 2008;Wacey et al., 2011;Sugitani et al., 2013;Hickman-Lewis et al., 2016), within ferruginous sedimentary rocks in Northern Quebec (Dodd et al., 2017), and within pillow lavas, siliciclastic deposits (noncarbonate, almost exclusively silica-bearing sedimentary rocks), and cherts in South Africa (Knoll and Barghoorn, 1977;Walsh and Lowe, 1985;Walsh, 1992;Westall et al., 2001Westall et al., , 2006bFurnes et al., 2004;Javaux et al., 2010) that range in diameter from *0.1 to 289 mm. The rocks in the formations hosting these possible microfossils have U-Pb dates of *3.20-3.77 ...
Estimates of the time at which life arose on Earth make use of two types of evidence. First, astrophysical and geophysical studies provide a timescale for the formation of Earth and the Moon, for large impact events on early Earth, and for the cooling of the early magma ocean. From this evidence, we can deduce a habitability boundary, which is the earliest point at which Earth became habitable. Second, biosignatures in geological samples, including microfossils, stromatolites, and chemical isotope ratios, provide evidence for when life was actually present. From these observations we can deduce a biosignature boundary, which is the earliest point at which there is clear evidence that life existed. Studies with molecular phylogenetics and records of the changing level of oxygen in the atmosphere give additional information that helps to determine the biosignature boundary. Here, we review the data from a wide range of disciplines to summarize current information on the timings of these two boundaries. The habitability boundary could be as early as 4.5 Ga, the earliest possible estimate of the time at which Earth had a stable crust and hydrosphere, or as late as 3.9 Ga, the end of the period of heavy meteorite bombardment. The lack of consensus on whether there was a late heavy meteorite bombardment that was significant enough to prevent life is the largest uncertainty in estimating the time of the habitability boundary. The biosignature boundary is more closely constrained. Evidence from carbon isotope ratios and stromatolite fossils both point to a time close to 3.7 Ga. Life must have emerged in the interval between these two boundaries. The time taken for life to appear could, therefore, be within 200 Myr or as long as 800 Myr. Key Words: Origin of life-Astrobiology-Habitability-Biosignatures-Geochemistry-Early Earth. Astrobiology 18, 343-364.
... Elas contêm traços químicos do que podem ser ou não fósseis químicos de formas de vida (van Zuilen et al., 2002). Existem outras evidências de células fósseis no período de 3 a 3,5 bilhões de anos (Knoll & Baghoorn, 1977, e Schopf, 1999, por exemplo, revisam as evidências). Portanto, provavelmente as células evoluíram cerca de 3,5 bilhões de anos atrás, ou um pouco depois disso. ...
Nada faz sentido em biologia exceto à luz da evolução. Essa frase, frequentemente citada, é título de um famoso trabalho de Theodosius Dobzhansky – que foi um dos biólogos evolucionistas mais eminentes do século XX - e resume bem a importância dos conceitos evolutivos para as ciências biológicas. A teoria da evolução por seleção natural é, sem dúvida alguma, a generalização mais importante até agora feita no campo das ciências naturais e pode ser testada cientificamente em todas essas áreas de conhecimento. Ela é uma das ideias mais poderosas em todas as áreas da ciência e é a única teoria que pode seriamente reivindicar a condição de unificar a biologia. Neste material irei abordar como o pensamento evolucionista foi se modificando e se aprimorando ao longo do tempo, e como essa ciência sempre foi cercada por aspectos religiosos e culturais, tanto que encontra barreiras para o seu entendimento até nos dias de hoje.
Veremos como a publicação de A Origem das Espécies por Charles Darwin, em 1859, influenciou o estudo evolucionista e os pesquisadores a partir de então, por ter feito mais do que qualquer outro indivíduo, antes ou depois dele, para modificar a atitude e a visão do homem em relação ao fenômeno da vida. Os conceitos evolutivos forneceram à biologia um arcabouço científico coerente de ideias, em vez de uma abordagem composta de mitos e superstições, fazendo com que a evolução por seleção natural se tornasse um fato inegável, compreensível como processo e abrangente como conceito. A emergência do darwinismo e o avanço tecnológico, principalmente na genética, permitiram o desenvolvimento de novas teorias e o aprimoramento de antigas. Veremos como a seleção natural, o isolamento reprodutivo e as barreiras geográficas e ecológicas são os principais mecanismos que atuam nas populações naturais, impulsionando-as a divergências evolutivas que contribuíram ao longo do tempo para a diversificação e estabelecimento da majestosa biodiversidade de nosso planeta. Uma das principais conclusões que espero é que o estudo deste módulo possa despertar em cada aluno a ideia de que somente em um contexto evolutivo o ser humano é capaz de olhar a Natureza com humildade e vislumbre, colocando-se não mais no centro de uma visão antropocêntrica para compreender a diversidade das formas de vida da atualidade. E isso só se é possível quando aplicamos os princípios das teorias evolutivas para interpretar, criticar e debater diferentes versões da origem e evolução das espécies.
Assim, os temas são aqui divididos em oito unidades que abordarão, respectivamente, (1) as principais teorias que buscam respostas sobre a origem das espécies; (2) as evidências da ação da evolução por seleção natural; (3) os princípios e perspectivas da ação da evolução; (4) os tipos de evolução; (5) a origem da Terra e da vida; (6) as vias evolutivas das plantas; (7) as vias evolutivas dos animais e, por fim, (8) a origem e evolução do ser humano. Os conteúdos dentro de cada unidade serão distribuidos em diversas lições, com a finalidade de dividir temporal e coerentemente os principais conceitos para estudo.
... Sandstones represent ancient siliciclastic environments including tidal flats, lakebeds, and sabkhas, where early benthic cyanobacterial mat communities likely thrived (Altermann 2001;Westall 2005;Noffke et al. 2006; Walsh 2010). In contrast to chemical deposits like cherts where biomaterial is preserved in situ and individual microfossils are abundant, siliciclastic sediments are susceptible to local environmental influences such as exposure to air and circulation of water throughout much of the early lithification process ( Knoll and Barghoorn 1977;Walsh 1992;Brasier et al. 2002;Westall and Folk 2003;Allwood et al. 2006; Tice and Lowe 2006; Schopf et al. 2007;Van Zuilen et al. 2007;Gamper et al. 2011;Westall et al. 2011). This means that any carbonaceous or other labile materials in the sediments are easily broken down, altered, or lost. ...
Cyanobacteria are ubiquitous in a variety of modern habitats, and siliciclastic sediments in particular are home to a wide diversity of microbial communities. Benthic microbial mats, typically established by cyanobacteria on modern Earth, were likely prevalent on Archean Earth, yet explicit traces of their ancestors in Archean siliciclastic rocks are difficult to detect. To understand the taphonomy of benthic microbial mats in sandy, subaquatic environments, cyanobacterial mats were incubated for five months under a range of temperatures representative of ambient (258C) and eogenetic conditions (378C, 708C, and 1008C). Cyanobacterial materials including trichomes, sheaths, and extracellular polymeric substances (EPS) were analyzed using scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and micro Raman spectroscopy. Textures were permineralized in all temperature regimes with phases that included mixed silicates, Na-carbonate, clays, gypsum-anhydrite, pyrrhotite, anatase, akaganeite, magnetite, natrojarosite, and ankerite. Pigments including chlorophyll, b-carotene, and scytonemin were identified in the lower temperature regimes, but were not easily detected in the samples incubated at 1008C. The morphological characteristics of trichomes and sheaths were maintained to some degree in all temperature regimes, but there was a higher relative abundance of EPS as temperatures increased. The profusion of EPS obscured the absolute differentiation between individual trichomes and sheaths at higher temperatures. The results indicate that over time, morphological, mineralogical, and carbonaceous features that formed at the end of these incubation experiments could collectively create the laminations characteristic of fossilized microbial mats found in sandstones throughout the geologic record. In Archean sandstones, where very little is preserved, these collective features may prove to be especially important in the detection of ancient life.
... Life is hypothesized to have originated on Earth between 4.2 bya and 3.8 bya [1,2]. Energy, water, and chemicals would have had to combine in perhaps precise amounts and sequences for this process to have occurred. ...
One of the key steps in the origins of life was the formation of a membrane to separate protocells from their environment. These membranes are proposed to have been formed out of single chain amphiphiles, which are less stable than the dialkyl lipids used to form modern membranes. This lack of stability, specifically for decanoate, is often used to refute ocean locations for the origins of life. This review addresses the formation of membranes in hydrothermal-vent like conditions, as well as other environmental constraints. Specifically, single chain amphiphiles can form membranes at high sea salt concentrations (150 g/L), high temperatures (65 °C), and a wide pH range (2 to 10). It additionally discusses the major challenges and advantages of membrane formation in both ocean and fresh water locations.
... Fossil record indicates that life could already exist on Earth 3.5 billion-years-ago (for review see, Altermann et al., 2006;Knoll et al., 2016) or probably even earlier (Nutman et al., 2016). The scant record of Archean rocks provide clues to the existence of life, such as (i) rare findings of spherical, lenticular, spindle-like, and filamentous carbonaceous objects interpreted as microbial remains, (ii) macroscopic stromatolites interpreted as products of microbial (most likely cyanobacterial) mats, and (iii) chemofossils (biomarkers, isotopes, minerals) believed to represent signatures of microbial activity (Knoll and Barghoorn, 1977;Walsh and Lowe, 1985;Byerly et al., 1986;Schopf, 1993Schopf, , 2004Schopf, , 2006Schopf et al., 2007;Hofmann et al., 1999;Ueno et al., 2001Ueno et al., , 2004Westall et al., 2001Westall et al., , 2006Westall et al., , 2011Kaź mierczak and Altermann, 2002;Altermann and Kaź mierczak, 2003;Altermann et al., 2006;Kaź mierczak et al., , 2016Tice and Lowe, 2004;Tice et al., 2011;Brasier et al., 2006;Kiyokawa et al., 2006;van Zuilen et al., 2007;Schiffbauer et al., 2007;Sugitani et al., 2007Sugitani et al., , 2010Sugitani et al., , 2013Sugitani et al., , 2015Glikson et al., 2008;Allwood et al., 2009;Grey and Sugitani, 2009;De Gregorio et al., 2009;Javaux et al., 2010;Oehler et al., 2010;Wacey et al., 2011;Bontognali et al., 2012;Noffke et al., 2013;Williford et al., 2013;House et al., 2013;Lepot et al., 2013;Riding et al., 2014;French et al., 2015;Foucher et al., 2015;Nutman et al., 2016). Although carbonaceous structures preserved in Archean cherts of South Africa have been described and interpreted as possible remnants of microbial life (Walsh, 1992(Walsh, , 2004Westall et al., 2001;Tice and Lowe, 2006), their univocal biological affinities remain unclear. ...
Fossil record of earliest Earth’s life is scant and restricted to simple kerogenous filaments and spheres, which origin and taxonomic affiliation are still ambiguous. Here we report clusters of cell-like bodies found in massive and weakly laminated black cherts of the ∼3.4 Ga Kromberg Formation (Onverwacht Group, Barberton greenstone belt, South Africa), known earlier for benthic microbial mats and microfossils. Morphological traits and mineralization of the Kromberg microfossils match those known from modern and fossil cyanobacteria. Micro-Raman and SEM/EDS analyses showed that the cell-like bodies fossilized mostly due to early mineralization with Al-silicates enclosing dispersed carbonaceous (kerogenous) matter derived from their thermally altered cell remains. Although in widespread opinion the early Archean life is predominantly represented by benthic microbial mats, the random (non-laminated) distribution of the studied cyanobacteria-like microfossils in the Kromberg cherts is suggestive for probably benthic-planktonic life cycle of these microbiota. The paper also discusses how the morphological similarity of the Kromberg Fm cell-like microfossils to geologically much younger and extant coccoidal cyanobacteria may influence the debate concerning the time of origin of Earth’s oxic atmosphere.
Since the sixties of the last century, stromatolite buildings have been successfully used for the purpose of stratigraphic dismemberment of the dumb strata of the Precambrian. The age of the stromatolites was determined on the basis of the morphology of buildings associated with a specific period of geological time. Such a formal classification made it possible to distinguish large stratigraphic divisions of erathems and suberathems in Precambrian strata, and much more fractional within stromatolite provinces. It was not possible to identify the remains of microorganisms in stromatolites for a long time. Now, with the help of an electron microscope and a special technique, it has become possible to establish numerous fossilized microfossils in these rocks. However, the reasons for the appearance of various morphological structures (stratiform stromatolites, differently branching and non-branching column-type stromatolites, etc.) and the attachment of each of them to a certain time remain unclear. Currently, it has become possible to study the role of microorganisms in this process. But the scale of stromatolite formation in the Precambrian makes it difficult to compare cyanobacteria in different stromatolite structures. Unlike the powerful Precambrian reefs stretching for kilometers, Phanerozoic stromatolites have a fairly limited distribution and are characterized by small capacities. The remains of cyanobacteria in them are preserved better, and the intensity of secondary processes affects these rocks to a lesser extent. Small incisions in the Phanerozoic make it possible to compare the role of certain cyanobacteria that took part in the construction of stromatolites of different shapes. To determine the age of rocks in the Phanerozoic, numerous remains of fauna were used, rather than rare stromatolite buildings. Therefore, they have not been practically studied before. In this work, for the first time, on the example of stromatolites from the Middle Permian, the restructuring of the organic microcosm is traced, illustrating its evolution. During the formation of the Permian stromatolite structure, three successive phases are distinguished: initial, intermediate and final. The work has established with the participation of which microfossils (coccoid, filamentous, etc.) one or another form of construction is now observed. The features of the vital activity of the cyanobacteria community are considered. The study of microorganisms in Phanerozoic stromatolites and their comparison with the Precambrian cyanobacterial community will greatly simplify the interpretation of data on ancient reef structures.
The great oxidation event (GOE), ~2.4 billion years ago, caused fundamental changes to the chemistry of Earth's surface environments. However, the effect of these changes on the biosphere is unknown, due to a worldwide lack of well-preserved fossils from this time. Here, we investigate exceptionally preserved, large spherical aggregate (SA) microfossils permineralised in chert from the c. 2.4 Ga Turee Creek Group in Western Australia. Field and petrographic observations, Raman spectroscopic mapping, and in situ carbon isotopic analyses uncover insights into the morphology, habitat, reproduction and metabolism of this unusual form, whose distinctive, SA morphology has no known counterpart in the fossil record. Comparative analysis with microfossils from before the GOE reveals the large SA microfossils represent a step-up in cellular organisation. Morphological comparison to extant micro-organisms indicates the SAs have more in common with coenobial algae than coccoidal bacteria, emphasising the complexity of this microfossil form. The remarkable preservation here provides a unique window into the biosphere, revealing an increase in the complexity of life coinciding with the GOE.
Long thought to be inaccessible to empirical inquiry, Earth's early biosphere has in recent decades become a central focus of evolutionary and paleobiological research. Knowledge of Precambrian ecosystems comes from three principal sources. The conventional fossil record consists of the compressed and permineralized remains of cyanobacteria, protists and other microorganisms (e.g., Knoll, 1996), complemented by stromatolites and oncolites, the accretionary trace fossils of microbial mat communities (Walter, 1976). Independent inferences about early evolution can be drawn from molecular phylogenies (Pace, 1997). The third principal source of information comprises biogeochemical signatures encrypted in the chemistry of ancient sedimentary rocks. Biomarker molecular fossils and distinctive isotopic compositions record the metabolic activities of organisms not necessarily preserved morphologically (Summons and Walter, 1990). In this paper, we review the inferences about early life and environments that can be drawn from the isotopic records of carbon and sulfur.
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.
Well-preserved fossil microbiotas normally present relatively high taxonomic diversity, especially if the host-rock is distributed over a large area. Estimates of taxonomic diversity, however, require proper consideration of ontogenetic, taphonomic, and ecological influences on morphological variety. Otherwise, diversity may be overestimated. Chert in the Permian Assistência Formation (Irati Subgroup, Paraná Basin, Brazil) contains an abundant, well-preserved fossil microbiota that has been studied from seven localities distributed over about 500 km. Despite the great numbers of microfossils present, morphological analysis revealed a low apparent diversity. There is no evidence of filamentous microorganisms and the chroococcacean Gloeodiniopsis lamellosa is overwhelmingly dominant, accounting for 98.6% of counted individuals. In addition to G. lamellosa, only five taxa are recognized of which four are formally described: the chroococcaceans Cyanosarcinopsis hachiroi gen. et sp. nov. and cf. Coniunctiophycus sp. and two taxa considered incertae sedis: Myxococcoides sp. A (a probable cyanobacterium) and Myxococcoides sp. B (a possible delicate eukaryote). A unique but markedly different colony was designated as unnamed form (open nomenclature). Two hypotheses may explain the enigmatic absence of filaments: (i) environmental stress associated with hypersaline conditions that severely limited diversity or (ii) long-term optimal growth conditions for coccoidal cyanobacterial blooms due to sustained basin-wide eutrophic conditions.
Earth has been habitable for 4.3 billion years, and the earliest rock record indicates the presence of a microbial biosphere by at least 3.4 billion years ago—and disputably earlier. Possible traces of life can be morphological or chemical but abiotic processes that mimic or alter them, or subsequent contamination, may challenge their interpretation. Advances in micro- and nanoscale analyses, as well as experimental approaches, are improving the characterization of these biosignatures and constraining abiotic processes, when combined with the geological context. Reassessing the evidence of early life is challenging, but essential and timely in the quest to understand the origin and evolution of life, both on Earth and beyond. Abiotic processes can mimic or alter the biogenic traces of early life but advances in micro- and nanoscale analyses provide evidence that—with geological contextualization—improves our ability to address this issue.
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.
Cambridge Core - Computational Science and Modelling - Planets and Life - edited by Woodruff T. Sullivan, III
Giant lipid vesicles resemble compartments of biological cells, mimicking them in their dimension, membrane structure and partly in their membrane composition. The spontanenous appearance of closed membranes composed of bilayers of self-assembling amphiphiles was likely a prerequisite for Darwinian competitive behavior to set in at the molecular level. Such compartments should be dynamic in their membrane composition (evolvable), sufficiently stable to harbor macromolecules (leak-free), yet semi-permeable for reactive small molecules to get across the membrane (stay away from chemical equilibrium). Here we describe bottom-up experi-ments simulating prebiotic environments that support the formation of simple amphiphilic molecules capable of self-assembling into vesicular objects on the micrometer scale. Long-chain alkyl phosphates, together with related amphiphilic compounds, were formed under simulated prebiotic phosphorylation conditions by using cyanamide, a recognized prebiotic chemical activator and precursor for several compound classes. Crude dry material of thus obtained prebiotic mixtures formed multilamellar giant vesicles once rehydrated at the appropriate pH and in the presence of plausibly prebiotic co-surfactants, as observed by optical microscopy. The size and the shape of lipid aggregates tentatively suggest that prebiotic lipid assemblies could encapsulate peptides or nucleic acids that could be formed under similar chemical prebiotic conditions. The formation of prebiotic amphiphiles was montiored by using TLC, IR, NMR and ESI-MS and UPLC-HRMS. In addition we provide a spectroscopic analysis of cyanamide under simulated prebiotic conditions in the presence of phosphate sources and specroscopic analysis of O-phosphorylethanolamine as a plausible precursor for phosphoethanolamine lipids.
Possible signs of life have been reported from eleven separate geological formations and from at least eight different lithologies in the Pilbara and Barberton regions, spanning almost the entire exposed 3–3.5 Ga stratigraphy. Evidence for life includes stromatolites, microfossils, trace fossils, biominerals, and isotopic signatures and comes from environments as diverse as a carbonate platform, sandy beach, and deep-sea hydrothermal black smoker. Putative life signals, in the form of isotopic signatures, have also been reported from rocks as old as c. 3.8 Ga in Greenland but these are particularly controversial.
It is likely that a combination of exogenous and endogenous sources contributed to the synthesis and accumulation of the building blocks of life on the early Earth. It may even have taken several starts before life surpassed the less than ideal conditions at the surface. The importance of comets for the origin of life on the Earth has been strongly advocated for several decades. We review the historical development of this idea, the collisional history of the early solar system, and the role of comets in delivering a large fraction of volatiles and intact carbon compounds onto the early planets.
The “Gaia hypothesis” which asserts that certain properties of the atmosphere are actively maintained by the biota for the biota was developed by J.E. Lovelock to explain the dynamically stable anomalous atmospheric composition, modulated alkalinities and temperatures at the Earth’s surface throughout its 3.5 billion-year-old history. Much, if not all, surface sedimentary deposition since the early Archean Aeon has been modulated by organisms. Detailed in situ characterization of microbial sedimentary communities such as that currently underway at Laguna Figueroa, Baja California, Mexico are essential for verification of the Gaia hypothesis for the atmosphere and surface sediments. A total inventory of biotic atmospheric gas emission and removal processess as well as of biomineralization potential under realistically varying environmental conditions is a sine qua non for the development of the Gaia concept. The current confused state of microbial and “botanical” systematics has precluded even the initiation of an effort that correlates biomineralization and gas exchange potential with taxon. Furthermore, geologists and paleontologists inadvertently create misunderstandings by the use of obsolete taxonomic schemes. This paper, which lists taxa along with their major biogeochemical potentials, is only a tiny first step in the clarification of the current confusion.
Five whole rocks from the Onverwacht Series give an age of 3230–3290 my by common lead and concordia interpretations. The rocks do not indicate any isotopic homogenization for the UThPb systems, other than severe loss of uranium and possibly thorium at recent times. A new graphical solution for evaluating U/Pb, Th/Pb, and Th/U ratios in rocks is described, and a preliminary framework model for understanding variations in concentration of Pb through time in basic volcanic rocks is suggested.
Bacteria isolated from the hemolymph of normal blue crabs were found to be predominantly Vibrio sp., Pseudomonas sp., Acinetobacter sp., Bacillus sp., Flavobacterium sp., and coliforms. Vibrio parahaemolyticus, a cosmopolitan facultative pathogen widely implicated in outbreaks of gastroenteritis related to the consumption of improperly processed seafood, was present in crabs collected between the months of May to November and was identified in up to 21% of the hemolymphs sampled.
A rapid, potentially clinically useful test for detection of enterotoxigenic Escherichia coli is described. Whole bacterial cultures of enterotoxigenic E. coli, when briefly exposed to Y1 adrenal cells in tissue miniculture, effect a rounding response in the tissue culture that can be discerned at 18 to 24 h. The tissue culture technique agreed with the rabbit ileal loop in all 58 enterotoxigenic and 52 non-enterotoxigenic E. coli strains tested.
A study of the ecology of Vibrio parahaemolyticus and related vibrios in the Rhode River area of Chesapeake Bay was carried out over the period December 1970 through August 1971. The incidence of V. parahaemolyticus and related vibrios was found to be correlated with water temperature. The vibrios could not be detected in the water column during the winter months, although they were present in sediment. From late spring to early summer, when water temperatures were 14 +/- 1 C, vibrios over-wintering in sediment were released from the bottom communities and attached to zooplankton, proliferating as the temperature rose. The number of vibrios in and on plankton was reflected in the water column bacterial population densities at water temperatures of ca. 19 C. Thus, temperature of the water column in the range of 14 to 19 C was found to be critical in the annual cycle of the vibrios. Interaction between sediment, water, and zooplankton was found to be essential in the natural estuarine ecosystem. Bacterial counts of zooplankton were found to be temperature dependent. The bacterial population associated with zooplankton was found to be predominantly on external surfaces and was specific, differing from that of the sediment. Vibrio spp. and related organisms comprised the total bacterial population associated with zooplankton in summer months. The ecological role of Vibrio spp., including V. parahaemolyticus, was found to be significant, with respect to their property of chitin digestion and in relation to the population dynamics of zooplankton in Chesapeake Bay.
Polynucleotide relationships among selected Vibrio species were examined by means of deoxyribonucleic acid (DNA) reassociation reactions and chromatography on hydroxyapatite. Relative levels of intraspecific DNA duplex formation (V. cholerae-V. cholerae and V. parahaemolyticus-V. parahaemolyticus) were found to be high at 60 C (>80%), and only minimally reduced at 75 C. Interspecific DNA duplexes between V. cholerae DNA and that of the non-cholera vibrios also exhibited high relative levels of formation at 60 C (>80%) and, with one exception, were only slightly reduced at 75 C. The thermal stability of these duplexes formed at 60 or 75 C was virtually identical to that of homologous V. cholerae DNA duplexes. The degree of reassociation and the thermal stability of V. cholerae-non-cholera vibrio DNA duplexes suggests relatively little evolutionary divergence in these organisms. In all other interspecific DNA reassociation reactions, only low levels of DNA duplex formation were noted at 60 C (<25%), and these were drastically reduced (>50%) at 75 C. The degree of nucleotide sequence divergence indicated by these reactions suggests that these Vibrio species are not significantly related to V. cholerae or V. parahaemolyticus. Reassociation reactions between V. cholerae DNA and the DNA of V. parahaemolyticus indicated these species were not significantly related to each other.
The distribution of Vibrio parahaemolyticus and related organisms in the Atlantic Ocean was determined during the summer of 1971 from samples collected at stations along four transects on the continental shelf off the South Carolina and Georgia coasts. No V. parahaemolyticus strains were isolated from any of the samples of seawater (surface and bottom), sediment, and plankton which were collected. A numerical taxonomy analysis of data on substrate utilization, including 154 organic compounds serving as single carbon sources, was carried out, and four groups of strains were observed. Each group showed well-separated distribution profiles from shore out to the continental shelf. That is, the groupings were observed to correspond to coastal, off-shore and intermediate distribution patterns for the strains. This study provides a useful example of the kind of ecological distributional analysis of bacteria which can be accomplished with numerical taxonomy.
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.
THE relatively unmetamorphosed sedimentary rocks of the Onverwacht
Group, the lowest part of the Swaziland Sequence, may contain the oldest
microfossils on Earth. The group is composed chiefly of lavas whose
composition changes upwards from ultramafic through mafic to
predominantly felsic with pyroclastics. The 17,000 m thick sequence
includes some thin cherts and limestones together with small amounts of
shale (Table 1). In the Lower Onverwacht, the cherts occur chiefly as
intercalations, sometimes of wide lateral extent and sometimes lensoid,
between the extrusives. Cherts are also found in the Upper Onverwacht in
association with limestones and shales.
The sedimentary distributions of carbon, sulfur, uranium, and ferric and ferrous iron depend greatly upon ambient oxygen pressure and should reflect any major change in proportion of oxygen in the atmosphere or hydrosphere. The similar distributions of these elements in sedimentary rocks of all ages are interpreted to indicate the existence of a Precambrian atmosphere containing much oxygen. Sedimentary pyrite is almost invariably closely associated with organic carbon, suggestive of formation by sulfate reduction, in sedimentary rocks of any age. Archean and Middle Precambrian cherty iron formations and uranium ores resemble Phanerozoic ores and probably formed similarly by diagenetic concentration. No evidence is found in the sedimentary distributions of carbon, sulfur, uranium, or iron, that an oxygen-free atmosphere has existed at any time during the span of geological history recorded in well preserved sedimentary rocks.
The Swaziland System, in the southeastern Transvaal, is one of the oldest stratified systems exposed. A brief account is given of this folded synclinal belt, and of the heterogeneous tract of migmatites. gneisses, and granites which surround it. Related geochronological work in this tract is summarized.An attempt has been made to date the system using the Rb–Sr isochron technique on (1) pegmatites that intrude it, (2) shales and graywackes of the Fig Tree Series, (3) acid lavas of the Onverwacht Series, and (4) biotite-tremolite schists associated with mineralized zones along the Onverwacht-Fig Tree contact. Essentially linear isochron plots were obtained in each case, but great caution is needed in interpreting the precise geological significance of each calculated age. The pegmatite data are interpreted as establishing a minimum age of 3.00 ±.03 b.y. for the Swaziland System, and as indicating that its deposition occurred at a significantly earlier time. The Fig Tree data yield an age of 2.98 ±.02 b.y. ...
Lead isotope ratios for the least radiogenic terrestrial leads thus far analysed, yielding model ages of 3.46 b.y., are reported. The significance of these analyses from the point of view of common lead models is discussed.
Rb-Sr age measurements have been made on total-rock samples of eight granites from Swaziland, and the results obtained broadly conform with the stratigraphic classification of the granites into G5, G4, and G1. Three samples of the G5 granite gave ages of 2200±50 m.y., 2550±50 m.y., and 2880±340 m.y., respectively. The ages of four samples of the G4 were in satisfactory agreement, and the mean age is 3070±60 m.y. Only one sample of the G1 was studied, and the age found is 3440±300 m.y. Measurements made on mineral fractions separated from some of the granites yielded discordant ages, which are interpreted as evidence of the diffusion of radiogenic Sr87 from mineral to mineral. A brief account of the petrography of the granites is included.
The microstructures show some resemblance to very simple organisms, but their morphology is poor and their size range is very great.
WE report the discovery of some complex microfossils from the Kromberg formation of the Onverwacht group of South Africa. The samples, in which the microfossils were found, were collected by D.O.H. along the banks of the Komati River in the Barberton Mountain Land, at Skaapbrug, near the old JCI mining camp. The Kromberg formation lies in the Upper part of the Onverwacht group, above the Middle Marker Horizon, which has been dated as 3.355×109yr old1. The Onverwacht group is the oldest member of the Swaziland Supergroup and lies below the 3.1×109 yr old Fig Tree group. Microfossils have been reported from the Fig Tree group2,3, and simple spherical and filamentous forms from the Onverwacht4-6. Spherical and cup-shaped carbonaceous microstructures have been reported7-9 from the Onverwacht but were not regarded as biogenic in origin.
Nagy, L. A. (Department of Geosciences, The University of Arizona, Tucson, Arizona, USA). Ellipsoidal microstructures o) narrow size range in the oldest known sediments on earth. Grana 11:91-94. Illus. 1971.-The sedimentary rocks within the Onverwacht Group, which show little or no metamorphic overprint, are the oldest known sediments on earth. Some of these sediments have been dated at ~ 3.4 × 10° years old. Microscopic examination of petrographic thin sections of these sediments has revealed round or ellipsoidal shaped microstructures of 2 μ to 6 μ size range. These microstructures show what appear to be double walls and are found individually or in chains or clusters. They are resistant to hot 6N HCl, hot 48 percent HF, ozone and organic solvents. These forms could be organic particulate matter of no chemical or biological evolutionary significance, or they could be the precursors to the first Jiving cell. Finally, they could be the oldest known microfossils on earth. Until ultramicro-chemical analyses are available on these particles, great caution is needed in the interpretation of their origin.
Fragments of the Orgueil meteorite were macerated in mineral acids (HNO3-HF-HNO3) to dissolve the mineral matrix and separate the acid-resistant organic residues; a routine procedure in the extraction of pollen and spores from terrestrial sediments. Numerous spherical hollow objects were found, optically resembling the brown amorphous residual organic matrix of the meteorite. Their morphology, size-distribution, and chemical composition, revealed by electron microprobe with reference to carbon and phosphorus, are described, and evaluated in connection with criteria of biogenicity. The intrinsic criteria are satisfactorily met, but the extrinsic requirement of a sedimentary environment is not met. A review of the literature concerning the meteoritic environment suggests an explanation of these spheres based on the environment of their formation. It is proposed that they are organic coatings on olivine microchondrules, magnetite and glass globules, the mineral component of which has been dissolved by the acid maceration. They could have initially resulted from the polymerization of dispersed small organic molecules condensing on the surface of the microchrondrules. The latter were injected from a volcanic nue ardente into the dispersed cold primordial cosmic dust of hydrated silicates and organic molecules, around the meteorite parent-body. This presumably occurred before the cosmic dust accreted as the carbonaceous chondritic outer layer of the parent-body. Upsurging reducing hot gases from the nue ardente would polymerize part of the dispersed organic matter as the insoluble brown amorphous matrix, possibly the sticking agent when the cosmic dust accreted. The spiraled form of several of the organic structures described here are suggestive of atmospheric heat microturbulences. Organic membranes and comet-form tails of spherical coatings suggest polymerization in the wake of injected microchondrules. These diverse organic structures would result in our view from the abiogenic thermal organization of organic matter in an extraterrestrial gas-solid system.Plusieurs fragments de la mtorite d''Orgueil ont t macrs dans des acides minraux (HNO3, HF, HNO3), afin de dissoudre la fraction minrale et isoler la fraction rsiduelle rsistant aux acides. C''est l un procd utilis couramment en palynologie pour extraire les grains de pollen et les spores des sdiments terrestres.De nombreux objets microscopiques, sphriques et creux, ont t mis en vidence. Ils sont optiquement similaires au rsidu organique brun, amorphe, dans lequel ils sont enrobs. Leur morphologie, leur rpartition en fonction de leur taille, et leur composition chimique lmentaire, analyse par la microsonde lectronique, qui rvle la prsence de carbone et de phosphore, sont dcrites, puis values en fonction des critres disponibles d''une ventuelle origine biologique. Les critres intrinsques aux objets sont bien satisfaits, mais non le critre extrinsque d''un environnement sdimentaire convenable.L''analyse des hypothses qui ont t avances pour dcrire l''environnement originel de la mtorite, permet de suggrer une explication de ces sphres creuses organiques, qui repose entirement sur cet environnement l''poque de leur formation. Ce sont des revtements organiques la surface de microchondrules d''olivine, de globules de verre et de magntite, minraux de haute temprature appartenant la fraction minrale de la mtorite qui a t dissoute par la macration acide.Ces coques organiques rsulteraient de la polymrisation de petites molcules organiques disperses, qui se seraient condenses la surface de gouttelettes minrales en fusion. Ces dernires ont pu tre jectes par une nue ardente volcanique issue du corps parent de la mtorite, et projetes dans la poussire cosmique primitive froide en suspension autour de ce corps parent, compose de silicates hydrats et de petites molcules organiques.C''est ensuite seulement que cette suspension de poussire primitive aurait subi l''accrtion pour former finalement la couche extrieure froide de matire toritique carbone du corps parent. En outre, des gaz rducteurs haute temprature, s''levant de la nue ardente, ont pu polymriser en partie la matire organique en suspension, pour former la matire mtoritique organique amorphe, rsistant aux acides, qui a peut-tre t l''agent agglomrant lors de l''accrtion.Les formes spirales de plusieurs des structures organiques dcrites ici suggrent des microturbulences atmosphriques des la chaleur. Des membranes organiques, et l''appendice en forme de queue de comte d''une sphrule, suggrent une polymrisation organique dans le sillage de la trajectoire de microchondrules. Selon notre opinion, ces diverses structures organiques rsultent donc de l''organisation abiognique sous l''effet de la temprature, de matire organique prexistante, plus simple, dans un systme solide-gaz extraterrestre.
δ13Corg and δ13Ccarb values of 58 coexisting organic carbon-carbonate pairs covering the whole Precambrian have yielded means of −24.7 ± 6.0%. [PDB] and +0.9 ± 2.7%. [PDB], respectively. Accordingly, isotopic fractionation between inorganic and organic carbon in Precambrian sediments is about the same as in geologically younger rocks (Δδ ≅ 25%.), a slight increase displayed by the Early Precambrian pairs (Δδ ≅ 28%.) being probably biassed by an over-representation in this age group of samples from one single locality (nevertheless, this value still lies within the range permitted for a possible deviation). It is reasonable to assume, therefore, that the overall isotope fractionation factor governing biological fixation of inorganic carbon has been virtually constant since some 3.3 × 109 yr ago.
Separate laminae of 1–6 mm thickness from a microcrystalline quartz-mica-calcite-bearing sedimentary rock sample from the Middle Marker Horizon of the Onverwacht Group, show concordant Rb-Sr ages within experimental error. A statistical treatment of the data gives an extrapolated value for initial87Sr/86Sr of0.7015 ± 0.0018 (2σ) and an apparent age value of3355 ± 70 (2σ) my, based on87Rbλ = 1.39 × 10−11yr−1. The low initial ratio suggests tha effect of metamorphism has been slight and that this data may be fairly close to the time of deposition of the sediments. The Onverwacht Group is of interest because it is the oldest well-preserved sedimentary-volcanic sequence known, and contains an aromatic-type kerogen and microstructures of unknown origin which morphologically resemble fossil algae.
Some rocks of the Onverwacht Group, South Africa, have been analyzed for Rb and Sr concentrations and Sr isotopie composition. These rocks include volcanic rocks, layered ultramafic differentiates and cherty sediments. Whole rock data indicate that the Rb-Sr isotopie systems in many samples were open and yield no reasonable isochron relationships. However, the data of mineral separates from a basaltic komatiite define a good isochron of t = 3.50 ± 0.20 (2δ) b.y. with an initial Sr87/Sr86 ratio of 0.70048 ± 5(2δ). The orthodox interpretation of this age is the time of the low grade metamorphism. Since the basaltic komatiite is stratigraphically lower than the Middle Marker Horizon (dated as 3.36 ± 0.07 b.y. Hurley et al., 1972), and since it is commonly found that volcanism, sedimentary deposition, metamorphism and igneous intrusion in many Archean greenstone-granite terrain all took place in a relatively short time interval (less than 100 m.y.), it is reasonable to assume that the age of 3.50 b.y. might also represent the time of initial Onverwacht volcanism and deposition. The initial Sr87/Sr86 ratio obtained above is important to an understanding of the Sr isotopic composition of the Archean upper mantle. If the komatiite represents a large degree of partial melt (40–80 per cent) of the Archean upper mantle material, then the initial ratio obtained from the metamorphic komatiite should define an upper limit for the Sr isotopic composition of the upper mantle under the African crustal segment.
A study of the incidence of Salmonella spp., Vibrio parahaemolyticus-like organisms, and clostridium botulinum in samples collected at five stations located in the Upper Chesapeake Bay, a major estuary on the Atlantic Coast of the United States, was conducted in December 1973 through December 1974. C. botulinum types B and E were detected in 12.3% of the total sediment samples examined. V. parahaemolyticus was recovered from 10.4% of a total of 86 water, sediment, and suspended sediment samples. Of 131 samples examined for the presence of Salmonella spp., approximately 3% were found to be positive for serologically confirmed Salmonella isolates. Shellfish examined during the investigation were also found to be free of enteric pathogens. The low frequency of occurrence of V. parahaemolyticus was attributed to the low salinities encountered at the sites included in the study. A low incidence of Salmonella spp. in the Upper Chesapeake Bay samples was found, whereas the distribution of C. botulinum appeared to be both random and autochthonous. A strong relationship between presence of potential pathogens and other generally accepted microbiological indicators of pollution was not observed.
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.
A Bay-wide survey of the distribution of Vibrio parahaemolyticus was carried out in Chesapeake Bay during May 1972, to determine whether the annual cycle of V. parahaemolyticus which was observed to occur in the Rhode River subestuary of Chesapeake Bay took place in other parts of Chesapeake Bay. In an earlier study, April to early June, when the water temperature rises from 14 to 19 C, was found to be a critical period in the annual cycle of the organism in the Rhode River, since this is the time period when the annual cycle is initiated. Results of this study, however, revealed that V. parahaemolyticus could not be found in the water column during May 1972. Nevertheless, several samples of sediment and plankton yielded V. parahaemolyticus isolates. Comparison of data with those for the Rhode River area examined in the earlier studies of the annual cycle of V. parahaemolyticus suggests that the time of initiation of the annual cycle of V. parahaemolyticus in the open Bay proper may be influenced by various factors such as temperature and salinity, i.e., deeper water locations may show initiation of the V. parahaemolyticus annual cycle later than shallow areas. Confirmation of the presence of the organisms in the samples studied was accomplished using numerical taxonomy with 19 reference strains also included in the analyses.
The first naturally acquired case of cholera reported in the United States since 1911 occurred in a 51-year-old resident of Port Lavaca, Texas. Extensive epidemiologic investigation of the patient's contacts and environment did not identify a cholera carrier of elucidate a pathway of transmission, but several avenues of investigation suggested possible means by which the patient may have acquired his infection. No secondary spread resulted from this case, and its occurrence did not endanger the community at large.
The usefulness of the ligated rabbit ileal loop as an experimental model of Bacillus cereus food poisoning was investigated. Positive responses, as measured by fluid accumulation in the loop, were obtained from 19 of 22 strains of B. cereus. Four of six strains of B. thuringiensis also elicited fluid accumulation, but eight strains of other Bacillus spp. failed to evoke a response. The growth medium employed markedly affected the ability of a given strain of B. cereus to provoke a response. Brain heart infusion broth (BHI) (Difco) proved to be best for this purpose. Loop fluid-inducing activity was produced by exponentially growing cells and was present in cell-free culture filtrates and associated with washed vegetative cells. Intraluminal growth of B. cereus did not elicit fluid accumulation. Cultures grown at temperatures in the range of 18 C to 43 C were loop active. When BHI cultures of selected loop positive strains were injected intraluminally into the normal ileum of rabbits, they failed to elicit diarrhea.
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.
Reduced carbon in early Precambrian cherts of the Fig Tree and upper and middle Onverwacht groups of South Africa is isotopically similar (the average value of delta(13)C(PDB) is -28.7 per mil) to photosynthetically produced organic matter of younger geological age. Reduced carbon in lower Onverwacht cherts (Theespruit formation) is anomalously heavy (the average value of delta(13)C(PDB) is -16.5 per mil). This discontinuity may reflect a major event in biological evolution.
A minute, bacterium-like, rod-shaped organism, Eobacterium isolatum, has been found organically and structurally preserved in black chert from the Fig Tree Series (3.1 x 10(9) years old) of South Africa. Filamentous organic structures of probable biological origin, and complex alkanes, which apparently contain small amounts of the isoprenoid hydrocarbons pristane and phytane, are also indigenous to this Early Precambrian sediment. These organic remnants comprise the oldest known evidence of biological organization in the geologic record.
Spheroidal and cupshaped, carbonaceous alga-like bodies, as well as filamentous structures and amorphous carbonaceous matter occur in sedimentary rocks of the Onverwacht Series (Swaziland System) in South Africa. The Onverwacht sediments are older than 3.2 eons, and they are probably the oldest, littlealtered sedimentary rocks on Earth. The basal Onverwacht sediments lie approximately 10,000 meters stratigraphically below the Fig Tree sedimentary rocks, from which similar organic microstructures have been interpreted as alga-like microfossils. The Onverwacht spheroids and filaments are best preserved in black, carbonrich cherts and siliceous argillites interlayered with thick sequences of lavas. These lifelike forms and the associated carbonaceous substances are probably biological in origin. If so, the origins of unicellular life on Earth are buried in older rocks now obliterated by igneous and metamorphic events.
- R Koch
R. Koch, Dtsch. Med. Wochenschr. 9, 743
(1883).
- J M Cameron
- K Hester
- W L Smith
- E Caviness
- F S Wolf
J. M. Cameron, K. Hester, W. L. Smith, E.
Caviness, F. S. Wolf, Morbid. Mortal. Wkly.
Rep. 26, 159 (1977).
- R A Finkelstein
R. A. Finkelstein, Crit. Rev. Microbiol. 2, 553
(1973).
- T E Lovelace
- H Tubiash
- R R Colwell
T. E. Lovelace, H. Tubiash, R. R. Colwell,
Proc. Natl. Shellfish. Assoc. 58, 82 (1968).
- R R Colwell
- T C Wicks
- H S Tubiash
- U S Natl
R. R. Colwell, T. C. Wicks, H. S. Tubiash, U.S.
Natl. Mar. Fish. Serv. Rev. 37 (Nos. 5-6), 29
(1975).
- J W Schopf
- E S Barghoorn
J. W. Schopf and E. S. Barghoorn, Science 156,
508 (1967).
- H Pflug
H. Pflug, Econ. Geol. Res. Unit Witwatersrand
Univ. Inf. Circ. 28 (1966).
- A E J Engel
- B Nagy
- L A Nagy
- C G Engel
- G O W Kremp
- C M Drew
A. E. J. Engel, B. Nagy, L. A. Nagy, C. G. Engel, G. O. W. Kremp, C. M. Drew, Science 161,
1005 (1968);
- L A Nagy
L. A. Nagy, Grana
11, 91 (1971);
- J D Brooks' M
- G Muir
- Shaw
J. Brooks' M.D. Muir, G. Shaw, Nature (London) 224, 215 (1973).
- E S Barghoorn
- J W Schopf
E. S. Barghoorn and J. W. Schopf, Science 152,
758 (1966).
- M D Muir
- D O Hall
M. D. Muir and D. O. Hall, Nature (London)
252, 376 (1974);
- P E Cloud
P. E. Cloud, Jr., Paleobiology 2, 351 (1976).
- W Schopf
W. Schopf, Annu. Rev. Earth Planet. Sci. 3, 213
(1975)].
- D J L Visser
D. J. L. Visser, S. Afr. Geol. Surv. Spec. Publ.
15 (1956);
- M J Viljoen
- R P Viljoen
M. J. Viljoen and R. P. Viljoen, Geol.
Soc. S. Afr. Spec. Pap. 2 (1969), p. 55; Spec.
Publ. Geol. Soc. Aust. 3, 133 (1971);