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Microfossils of the Early Archean Apex Chert: New Evidence of the Antiquity of Life
Abstract
Eleven taxa (including eight heretofore undescribed species) of cellularly preserved filamentous microbes, among the oldest fossils known, have been discovered in a bedded chert unit of the Early Archean Apex Basalt of northwestern Western Australia. This prokaryotic assemblage establishes that trichomic cyanobacterium-like microorganisms were extant and morphologically diverse at least as early as approximately 3465 million years ago and suggests that oxygen-producing photoautotrophy may have already evolved by this early stage in biotic history.
... Varying chert generations may coexist where black chert dikes and lenses crosscut dark gray and whitish stratiform cherts and interlayered volcanics of the Apex Formation (Marshall et al. 2012). Carbonaceous filaments found in the Apex Chert beds, Chinaman Creek near Marble Bar, were interpreted as world's oldest fossils and as evidence for the antiquity of life on Earth (Schopf 1993). The name "Schopf locality" was given to this outcrop after J. William (Bill) Schopf, an American paleontologist and paleobiologist of the University of California, Los Angeles, who found and described these microfossils. ...
... With the development of microscopic techniques and geochemical methods, an increasing number of scientific reports on putative Archean microfossils, started to emerge in the 1980s (e.g., Awramik et al. 1983;Buick 1984). Schopf and Packer (1987) published a report on 3.5 billion years old microfossils from the Warrawoona Group in Western Australia, followed by more detailed descriptions of these then oldest fossil evidence of life on Earth (Schopf 1993). ...
... Twenty years later, an international group of researchers around the late Martin Brasier, paleontologist at Oxford University, questioned Schopf's (1993) interpretation, based on renewed microscopy of the same fossils and discredited them as "secondary artefacts formed from amorphous graphite" (Brasier et al. 2002). These claims triggered a turmoil discussion on the quality of all reports of Archean life remains and avowals that life might have developed only in the Proterozoic (Brasier et al. 2004), a view, however, which did not last for long. ...
... One of the first major geoscientific contributions came from authentic proof of plausible microfossils in the 3.4 Ga Apex chert of Western Australia reported by William J. Schopf in 1993. In 2002. ...
... Carbonaceous matter preserved in carbonaceous cherts from the Kaapvaal and Pilbara cratons have been investigated to examine morphological and geochemical signals in the search for biosignatures (Walsh and Lowe, 1985;Walsh, 1992;Schopf, 1993;Ueno et al., 2006a;. Organic material in any metasedimentary rock will have experienced burial, diagenesis and metamorphism that led to changes in the primary organic precursor (Beyssac et al., 2004;Sforna et al., 2014). ...
... Because of a sparse geological record, well preserved meta-sedimentary horizons older than ~3.5 Ga are scanty, hampering our understanding of early Earth processes. Any well-preserved, older supracrustal rock record (i.e., greenschist facies metamorphism) hold significant clues for addressing questions related to the genesis of carbonaceous rocks (e.g., cherts, and shales), which may reveal insights into potential traces of early life on Earth (Schopf, 1993;Braiser et al., 2005;Tice and Lowe, 2004;Walsh, 1985;Ueno et al., 2006;Sugitani et al., 2010Sugitani et al., , 2015a. Apart from Palaeoarchaean carbonaceous metasedimentary rocks, iron formations in particular have been investigated to understand earliest microbial processes (Smith et al., 2015;Posth et al., 2013;Kappler et al., 2005;Konhauser et al., 2002;Towe, 1991). ...
... Simple clonal filamentous modes of multicellularity are nearly as old as the fossil record of life, and clear fossil evidence of multicellular organisms exists from at least *3.5 Ga (Chapter 4.1.5). These fossils are micrometer-scale segmented filaments, interpreted as bacterial or archaeal clonally multicellular organisms (Schopf, 1993;Schopf et al., 2018). Colonies of spheroidal as well as segmented filamentous cyanobacteria are well represented from the Paleoproterozoic era (<2.5 Ga) (Schopf, 1968;Butterfield et al., 1994). ...
... The available fossil evidence demonstrates that simple multicellularity evolved relatively quickly in both prokaryotes and eukaryotes. However, it is not clear why the evolution of complex multicellularity came so late, more than 2 billion years from the oldest fossil evidence of simple multicellularity (and life) (Schopf, 1993;Schopf et al., 2018), and why it never developed in prokaryotes (Butterfield, 2009b). The tempo of multicellular evolution has been linked to transitions in global environmental conditions. ...
All organisms living on Earth descended from a single, common ancestral population of cells, known as LUCA-the last universal common ancestor. Since its emergence, the diversity and complexity of life have increased dramatically. This chapter focuses on four key biological innovations throughout Earth's history that had a significant impact on the expansion of phylogenetic diversity, organismal complexity, and ecospace habitation. First is the emergence of the last universal common ancestor, LUCA, which laid the foundation for all life-forms on Earth. Second is the evolution of oxygenic photosynthesis, which resulted in global geochemical and biological transformations. Third is the appearance of a new type of cell-the eukaryotic cell-which led to the origin of a new domain of life and the basis for complex multicellularity. Fourth is the multiple independent origins of multicellularity, resulting in the emergence of a new level of complex individuality. A discussion of these four key events will improve our understanding of the intertwined history of our planet and its inhabitants and better inform the extent to which we can expect life at different degrees of diversity and complexity elsewhere.
... In fact, some of the vintage chert beds are considered globally significant for containing the direct evidence of > 2 Ga old life forms (Awramik et al., 1983;Barghoorn & Tyler, 1965;Brasier et al., 2002;Buick, 1990;House et al., 2000;Schopf, 1993;Schopf et al., 2002). Very fine siliceous crystals in chert give high resistance to weathering, recrystallization and metamorphism. ...
... Textures are interpreted to indicate both direct crystallization of quartz from a gel and quartz precipitation as cavity fillings. Chert pseudomorphs, which are interpreted as replaced gypsum crystals, are noteworthy in the context of the disputed oldest finding of microfossils from the ~ 3.4 Ga Apex chert in the Pilbara Craton, Australia (Pinti & Altermann, 2015;Schopf, 1993;Schopf & Packer, 1987;Schopf et al., 2002). According to De Gregorio and Sharp (2003), Apex chert does not show in situ biogenic material instead having transported biogenic components interpreted as biogenicity of microfossils which came from a nearby source of microbial community in hydrothermal fluids. ...
The term ‘chert’ ideally refers to fine-grained siliceous (micro/cryptocrystalline) mineral and is also often used for rock with such siliceous mineral aggregate of chemical, biochemical, and organic origin. Petrologically, inorganic non-sedimentary origin or even volcanic derivatives formed by devitrification of metastable felsic volcanic glass can also be included within chert. A new classification scheme for Precambrian cherts is proposed, especially for field workers. Despite several worldwide studies on chert, simple comprehensive classification of chert is not available to date. There are notable differences amongst Archaean, Palaeoproterozoic and Meso-Neoproterozoic cherts. This paper reviews all the Precambrian cherts to divide them into three categories from global context. Archaean and Palaeoproterozoic cherts mostly imply precipitation from silica gel material supplied vide submarine volcanism. This paper also focuses on diagenetic chert concretion, nodules, and geodes in detail. Finally, the Mesoproterozoic Nagari Formation in Cuddapah Basin, India is shown as a case to explain the diagenetic conditions, which could favour chert development by silica supersaturation in the pores. Diagenetic sub-environments are categorized systematically as eogenetic, mesogenetic, and telogenetic types with evidences of each based on photomicrography and outcrop studies. A comprehensive analysis is attempted to understand the development of concretions, nodules and geodes due to diagenesis with respect to the Eastern Ghats Orogeny, which has played a significant role in the prominent development of diagenetic features during mesodiagenetic and telodiagenetic processes.
... Support for synsedimentary hydrothermalism presented in de Vries et al. (2010) Hooggenoeg Chert ~3.45 Microfossils (Walsh, 1992) and microbial mats (Walsh, 1992;Hickman-Lewis et al., 2020) associated with hydrothermal activity (Hofmann and Bolhar, 2007;Hickman-Lewis et al., 2020) Middle Marker Horizon ~3.47 Microbial mats and geochemical evidence for hydrothermalism Pilbara Craton, Western Australia Strelley Pool Formation ~3.43 Stromatolites (Lowe, 1980;Van Kranendonk et al., 2003;Allwood et al., 2006b;Sugitani et al., 2010;Wacey, 2010), biological sulfur isotope fractionations (Bontognali et al., 2012), functional groups associated with biology in kerogen (De Gregorio et al., 2011), carbonaceous matter of biological origin (Allwood et al., 2006a), and microfossils Alleon et al., 2018). Arguments against biogenicity via Fischer-Tropsch synthesis Lollar and McCollom, 2006;McCollom and Seewald, 2006), and arguments against biogenicity of stromatolites presented in Lowe (1994) Apex Basalt ~3.46 Microfossils (Schopf, 1983(Schopf, , 1993Schopf et al., 2007;Schopf and Kudryavtsev, 2012), microbial mats and MISS-like structures (Hickman-Lewis et al., 2016). Arguments against biogenicity of fossils and microstructures (Brasier et al., 2002García-Ruiz et al., 2003Wacey et al., 2016) Kitty's Gap Chert ~3.47 Microfossils (Westall et al., 2006b;Westall et al., 2011) (Awramik et al., 1983) Arguments for abiotic formation of carbonaceous materials (Buick, 1984(Buick, , 1990. ...
... The source of the Pb and other metals preserved in this hydrothermal system display unique hydrothermalism which was very different from the textbook black smoker environment. Most importantly, the synsedimentary dike complex in the study area is hosted in granitic crustal rocks whereas other hydrothermally influenced Archean paleoenvironments hosting signs of early life such as the Apex Chert (Schopf, 1983(Schopf, , 1993Schopf et al., 2007, Schopf andKudryavtsev, 2012) and the Dresser Formation (Van Kranendonk et al., 2008) were deposited on top of basaltic units. Basaltic rocks in the study area are present in the Coonterunah and Duffer Formations but are significantly distanced to the east and west of the main feeder dikes in the area from which the samples were collected (Fig. 2). ...
... Remains of biofilms could be the earliest fossil record of life forms on Earth (Schopf 1993;Mojzsis et al. 1996). They are important records in addition to conventional microfossils and macrofossils (Westall et al. 2000;Noffke et al. 2013). ...
Discoidal carbonaceous compressions are the most common type of Precambrian macrofossils with a long temporal range starting from the late Paleoproterozoic. However, their unsolved biological nature restricts our understanding of the early evolution of macroscopic life. Here we report an assemblage of well-preserved discoidal carbonaceous macrofossils from the early Mesoproterozoic Gaoyuzhuang Formation in North China, which provides insights into this problem. They are preserved in round to elliptical shapes with sizes ranging from millimeters to several centimeters. Petrographic thin sections show that the macrofossils consist of laminated structures with alternating organic matter along with clay minerals and dolomites. Neither cellular structures nor individual microfossils were identified within them, but their regular shape, internal structures, and associated mineral constituents suggest that they are probably remains of the microbial biofilms, rather than multicellular organisms. It presents a well-preserved fossil example of microbial biofilms with macroscopic size and regular overall morphology. It further implies a possible origin of microbial biofilm for some of the early carbonaceous macrofossils and calls for detailed reexaminations of those macrofossils to exclude such possibilities. Our finding is consistent with previous studies that biofilms may have played an important role in survival for early microorganisms in the Precambrian ecosystem.
Thematic collection: This article is part of the The North China Craton as a window to Earth’s middle age collection available at: https://www.lyellcollection.org/topic/collections/the-north-china-craton-as-a-window-to-earths-middle-age
... These structures were inferred from the investigations of siliceous microfossils found in layered structures belonging to the Archaean Period. These microbial structures, found in sedimentary structures with silicon dioxide composition dating back 3.5 billion years in Western Australia, are considered to be the oldest remnants of life on Earth (Schopf, 1993;Brasier et al., 2002;Konhauser, 2003;Allwood et al., 2007). ...
Due to their rarity, scientific, and aesthetic value, or being a part of an important geological process, some natural formations (like calc tufa) on Earth have to be protected. While the formation and development processes of the microbialites in Lake Van continue, the microbiolites in Adilcevaz remained outside the lake and became fossils. These structures are arranged approximately 200 m wide and 800 m long, reaching heights of 6 m in places. In this study, the area where the Adilcevaz tufa microbialites, surviving to the present day as a remnant of the level change stages of Lake Van as well as their aesthetic appearance and scientific importance, was evaluated according to the conservation approach. Phenomenology research design, one of the qualitative research designs, was used in the study. Although the research is basically a field study, secondary sources were used and face-to-face interviews were conducted. The semi-structured interview technique, one of the qualitative research techniques, was used for the interviews that were held with the participants on the basis of pre-prepared questionnaire forms. Following the interviews, the data were evaluated with descriptive and interpretive analyzes. As a result of the field observations and interviews, the area was suggested to be evaluated as a “natural monument” to protect it and carry out activities for tourism purposes. It is understood that the area has an important potential in terms of ecotourism, and should be proposed to be included in the UNESCO World Heritage List together with the Lake Van microbialites, the largest microbialites in the world.
... The evidence of oxidised biomass detected within these rock tubules suggests the presence of biological activity caused by archaea. Furthermore, 2700-million-year-old fossilised archaeon lipids have also been found in shale samples from the Pilbara Craton, Australia [75], thus providing more conclusive evidence which aids in the creation of the microbial timeline. Bacteria/Eukarya produce membrane lipids with hydrophobic fatty acid tails that are ester-bound to glycerol-3-phosphate whereas Archaea synthesize membrane lipids with hydrophobic isoprenoid lipid tails that are ether-linked to glycerol-1-phosphate with the opposite chirality [76]. ...
Mars is a focus of New Space Age exploration and colonisation, but there are significant challenges to successful colonisation by humankind. Environmental microbes play a key role in supporting the ecosystems of Earth, especially within the biodegradation and bioremediation sectors. However, the repurposed roles of microbes on Mars and their associated uses to colonists remain incompletely defined. The aim of this review was to examine the key roles of microbes on Earth and how they have been employed by humans to tackle four pivotal environmental challenges associated with the colonisation of Mars, namely the physical environment, the creation of a hospitable environment via terraforming, environmental sustainability and life support, and finally, renewable processing technologies. Some species of microbes were found to be tolerant of the ever-changing physical environment on Mars (freeze–thaw and UVC exposure) making them useful for bioremediation applications. Employing perchlorate-remediating microbes for their ability to bioremediate the soils of sodium perchlorate, which is present in Martian soils, in addition to their innate ability to cycle nutrients through the biosphere showed promise in establishing sustained crops to support colonists. The employment of terrestrial environmental microbes is a necessary part of overcoming key environmental challenges to successfully colonise Mars. Without this, future New Space exploration is unlikely to be successful.
... The presence of biomolecules is known to be necessary for the formation of welldefined structures [31]. Although science has evolved over the years, the mechanism of eggshell formation is not yet fully understood [32,33]. ...
The lack of information on structural basis where proteins are involved, as well as the biomineralization processes of different systems such as bones, diatom frustules, and eggshells, have intrigued scientists from different fields for decades. This scientific curiosity has led to the use of methodologies that help understand the mechanism involved in the formation of these complex structures. Therefore, this work focuses on the use of eggshell membranes from different species of ratites (emu and ostrich) and reptiles (two species of crocodiles) as a model to differentiate biocalcification and biosilicification by introducing calcium phosphate or silica inside the membrane fiber mantles. We performed this to obtain information about the process of eggshell formation as well as the changes that occur in the membrane during crystal formation. In order to identify and understand the early processes leading to the formation of the microstructures present in the eggshell, we decided to carry out the synthesis of silica-carbonate of calcium, barium, and strontium called biomorph in the presence of intramineral proteins. This was carried out to evaluate the influence of these proteins on the formation of specific structures. We found that the proteins on untreated membranes, present a structural growth similar to those observed in the inner part of the eggshell, while in treated membranes, the structures formed present a high similarity with those observed in the outer and intermediate part of the eggshell. Finally, a topographic and molecular analysis of the biomorphs and membranes was performed by scanning electron microscopy (SEM), Raman and Fourier-transform Infrared (FTIR) spectroscopies.
... The ability of living systems to engineer complex shapes has led us to believe in the existence of a boundary separating the realm of biology from the realm of inorganic minerals. Such a belief profoundly influences the use of morphology as a critical criterion for biogenicity in primitive life detection studies (Buick 1990;Schopf 1993). However, bizarre as it might seem, purely inorganic processes can also yield selfassembled complex structures with noncrystallographic symmetry that mimics extremely well the shape of early living organisms ( Fig. 1) (García-Ruiz 1999;Brasier and Wacey 2012). ...
... The study of past and modern microbial communities (e.g., photosynthetic cyanobacteria) is extremely important to unravel the geobiological evolution of the early Earth (Schopf, 1993;Westall et al., 2015). However, direct fossil evidence of microorganisms is only present when specific diagenetic environments allow their preservation (Noffke & Paterson, 2008;Jones, 2000;Noffke, 2021). ...
The Eastern Anti-Atlas of Morocco hosts an early Ediacaran turbiditic series (Saghro Group) (630–600 Ma) unconformably overlain by thick late Ediacaran (580–550 Ma) terrestrial volcano-clastic formations (Ouarzazate Supergroup), with thin and geographically limited paralic shallow marine sedimentary rocks.
This paper presents the first description of structures related to the former presence of extensive microbial mats developed in marine, fluvial, and lacustrine environments during the Ediacaran in the Eastern Anti-Atlas. These microbially induced sedimentary structures (MISS) are largely found in well-laminated fine- to coarse-grained sandstone and sandy-carbonate. They also cover vast bedding planes and occur in almost all sedimentary successions. MISS types include: gas domes, wrinkle structures, reticulate patterns, overflips and roll-ups, multidirectional linear ridges, sand cracks and biolaminated deposits. Based on morphology and petrographic macro and microfabrics, these microbially induced structures are very similar to those of modern photosynthetic cyanobacteria mats. Together with previously reported stromatolites, these newly reported microbial mat structures could have played an important ecological role in stabilizing siliciclastic sediments, as well as sustaining localized zones of high oxygen production in the Ediacaran marine and terrestrial paleoenvironments of the Anti-Atlas. The widespread geographic distribution and consistent occurrence of microbially induced sedimentary structures (MISS) in fluvial and lacustrine sediments present compelling paleontological evidence supporting the extensive greening of the land surface during the late Precambrian period.
... The evolution of metabolism from catalytic, self-replicating RNA molecules to simple, single-cell organisms that are capable of information transfer from DNA through RNA to proteins took 200-500 million years. This period was determined based on the analysis of sedimentary rocks containing traces of cellular life fossils, the age of which was estimated to be about 3.5-3.8 billion years [11,[130][131][132]. These organisms (whether it was a single organism or a group of organisms [133][134][135]) constitute a hypothetical link between the "RNA-based World" and all contemporary cells [136]. ...
Most naturally occurring nucleotides and nucleosides are N-glycosyl derivatives of β-D-ribose. These N-ribosides are involved in most metabolic processes that occur in cells. They are essential components of nucleic acids, forming the basis for genetic information storage and flow. Moreover, these compounds are involved in numerous catalytic processes, including chemical energy production and storage, in which they serve as cofactors or coribozymes. From a chemical point of view, the overall structure of nucleotides and nucleosides is very similar and simple. However, their unique chemical and structural features render these compounds versatile building blocks that are crucial for life processes in all known organisms. Notably, the universal function of these compounds in encoding genetic information and cellular catalysis strongly suggests their essential role in the origins of life. In this review, we summarize major issues related to the role of N-ribosides in biological systems, especially in the context of the origin of life and its further evolution, through the RNA-based World(s), toward the life we observe today. We also discuss possible reasons why life has arisen from derivatives of β-D-ribofuranose instead of compounds based on other sugar moieties.
... In 1993, it was reported (Schopf 1993) on the basis of paleontological studies that prokaryotic microorganisms existed on the Earth as early as at least about 3465 Mya; according to these studies, these entities emitted oxygen into environment. In 1996, the period of the bacterial life appearance at the Earth was shifted to earlier time by no less than by 350 Myr; the remains of the ancient living entities found in the Isua supracrustal belt, West Greenland, and at the nearby Akilia island were dated by the period no later than 3850 Mya (Mojzsis et al. 1996). ...
Long since, people tried to solve the mystery of the way that led to the appearance and propagation of living entities. However, no harmonious understanding of this mystery existed, because neither the scientifically grounded source minerals nor the ambient conditions were proposed and because it was groundlessly taken that the process of living matter origination is endothermal. The Life Origination Hydrate Theory (LOH-Theory) first suggests the chemical way capable of leading from the specified abundant natural minerals to origination of multitudes of multitudes of simplest living entities and gives an original explanation for the phenomena of chirality and racemization delay. The LOH-Theory covers the period up to origination of the genetic code. The LOH-Theory is grounded on the following three discoveries based on the available information and on the results of our experimental works performed using original instrumentation and computer simulations. (1) There is the only one triad of natural minerals applicable for exothermal thermodynamically possible chemical syntheses of simplest living-matter components. (2) N-base, ribose, and phosphdiester radicals and nucleic acids as whole are size-compatible with structural gas-hydrate cavities. (3) The gas-hydrate structure arises around amido-groups in cooled undisturbed systems consisting of water and highly-concentrated functional polymers with amido-groups.The natural conditions and historic periods favorable for simplest living matter origination are revealed. The LOH-Theory is supported by results of observations, biophysical and biochemical experiments, and wide application of original three-dimensional and two-dimensional computer simulations of biochemical structures within gas-hydrate matrix. The instrumentation and procedures for experimental verification of the LOH-Theory are suggested. If future experiments are successful, they, possibly, could be the first step on the way to industrial synthesis of food from minerals, i.e., to execution of the work that is performed by plants.
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... Siliceous sediments and chert deposits of soda lakes, particularly Lake Magadi and Nasikie Engida, were proposed as models to understand the deposition of Precambrian cherts (Eugster, 1967(Eugster, , 1969Eugster and Jones, 1968;Hay, 1968;Schubel and Simonson, 1990;Behr and Röhricht, 2000;Behr, 2002;Reinhardt et al., 2019) where primitive biological organisms and putative microfossils were reported (Buick, 1990;Schopf, 1993;García-Ruiz, 1994). Selfassembled silica-carbonate biomorphs were proposed as alternative explanations for these primitive organisms and putative microfossils due to morphological reminiscence and the geochemical plausibility of the chemical cocktails used for the synthesis of biomorphs and chemical gardens (García-Ruiz, 1994, 2000García-Ruiz et al., 2002, 2017, 2020. ...
... The ability of living systems to engineer complex shapes has led us to believe in the existence of a boundary separating the realm of biology from the realm of inorganic minerals. Such a belief profoundly influences the use of morphology as a critical criterion for biogenicity in primitive life detection studies (Buick 1990;Schopf 1993). However, bizarre as it might seem, purely inorganic processes can also yield selfassembled complex structures with noncrystallographic symmetry that mimics extremely well the shape of early living organisms ( Fig. 1) (García-Ruiz 1999;Brasier and Wacey 2012). ...
... 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.
... Cryptic taxa are commonly found in cyanobacteria (Zammit et al., 2012;Sciuto et al., 2017;Shalygun et al., 2017;Caires et al., 2018aCaires et al., , 2018bEngene et al., 2018), as many organisms show the same morphological features, probably as a result of convergent evolution (Dvořák et al., 2015). Their high capacity to adapt to different conditions is what allows cyanobacteria to survive and thrive in distinct environments (Casamatta, 2005;Alvarenga et al., 2015;Osorio-Santos et al., 2014;Chakraborty et al., 2019;Radzi et al., 2019), surviving for approximately 3.5 billion years (Schopf & Packer, 1987;Schopf, 1993;Whiton & Potts, 2000). ...
Brazil’s Atlantic Ocean coast is approximately 7500 km long, with several coastal and oceanic islands. The cyanoflora of this area is not commonly included in published studies, resulting in an underestimated diversity. Here, we isolated and analysed through a polyphasic approach three strains of marine benthic homocyted cyanobacteria from Brazilian coastal islands with two distinct climates: ALCB 132761 and ALCB 132774 are from the tropics, and ALCB 132760 from the subtropics. These strains presented differences in their cell morphometry and presence/absence of sheath, but were similar in apical cell shape, colour, and form of the trichome. In the 16S rRNA phylogeny, Maximum likelihood (ML) and Bayesian posterior probability (PP) analyses placed our strains in two robust clades. We propose that Microlinema tropicalium gen. et sp. nov. (ALCB 132774) is placed in the Leptolyngbyaceae, and Insularia amadoi gen. et sp. nov. (ALCB 132761) and Salileptolyngbya insularis sp. nov. (ALCB 132760) in Pseudanabaenaceae. The 16S-23S Internal Transcribed Spacer (ITS) was used to reconstruct Box B and D1-D1’ secondary structures, which were treated as autapomorphic characters. The new thin homocyted benthic cyanobacterial taxa described here from marine coastal islands of Brazil help to disentangle the Leptolyngbyaceae and Pseudanabaenaceae.
HIGHLIGHTS
• •Polyphasic description of two new Brazilian genera Insularia and Microlinema.
• •Expansion of Salileptolyngbya: recognition of one species for the Atlantic Ocean.
• •Elucidation of benthic genera in the Leptolyngbyaceae and Pseudanabaenaceae.
... [1][2][3][4] Nevertheless, the ecological conditions driving such transitions are not well understood. The first known transition to multicellularity occurred 2.5 billion years ago in cyanobacteria, [5][6][7] and today's cyanobacteria are characterized by enormous morphological diversity. They range from unicellular species; unicellular cyanobacteria with packet-like phenotypes, e.g., tetrads; and simple filamentous species to highly differentiated filamentous species. ...
Understanding the evolutionary transition to multicellularity is a key problem in biology.1,2,3,4 Nevertheless, the ecological conditions driving such transitions are not well understood. The first known transition to multicellularity occurred 2.5 billion years ago in cyanobacteria,5,6,7 and today's cyanobacteria are characterized by enormous morphological diversity. They range from unicellular species; unicellular cyanobacteria with packet-like phenotypes, e.g., tetrads; and simple filamentous species to highly differentiated filamentous species.8,9,10 The cyanobacterium Cyanothece sp. ATCC 51142, an isolate from the intertidal zone of the U.S. Gulf Coast,11 was classified as a unicellular species.12 We report a facultative life cycle of Cyanothece sp. in which multicellular filaments alternate with unicellular stages. In a series of experiments, we identified salinity and population density as environmental factors triggering the phenotypic switch between the two morphologies. Then, we used numerical models to test hypotheses regarding the nature of the environmental cues and the mechanisms underlying filament dissolution. While the results predict that the observed response is likely caused by an excreted compound in the medium, we cannot fully exclude changes in nutrient availability (as in Tuomi et al.13 and Matz and Jürgens14). The best-fit modeling results show a nonlinear effect of the compound, which is characteristic of density-dependent sensing systems.15,16 Furthermore, filament fragmentation is predicted to occur by connection cleavage rather than cell death of each alternating cell, which is supported by fluorescent and scanning electron microscopy results. The switch between unicellular and multicellular morphology constitutes an environmentally dependent life cycle that is likely an important step en route to permanent multicellularity.
... According to contemporary prevailing consensus, the emergence of life on Earth was extremely fast, stromatolites found in Apex chert deposits (the Warawoona group in Australia) suggests 2.3-3.5 billion years old traces of life, and the Greenland Isua Greenstone Belt rock formation contains samples that indicate the origin of life as 4 or even 4.2 billion years old (Griesemer 2008, p. 271). The fossils discoveries contain imprints resembling the bodies of modern cyanobacteria or blue-green algae -and the conclusion was drawn that the fossils are the remains of highly developed cells with possible photosynthesis capacity (Schopf 1993, Fry 2000. This evidence could be interpreted as a denial of a heterotrophic first life form. ...
The Oparin hypothesis from 1936 was a milestone in the origin of life research, making a model that was at least in part empirically testable, and changing the course of life studies from a long tradition of metaphysics to a scientific domain of investigation. His hypothesis is based on the idea of the prebiotic synthesis of macromolecules as a fundamental step on the road to first life. Although the Oparin hypothesis brought fresh ideas and concepts, in its description of the steps in the hypothesized transition from the inorganic to the organic world in detail, today some premises are considered unconfirmed, uncertain, or even rejected. With high respect to its metatheoretical reach and scientific impact on prebiotic chemistry, pushing the origin of first life research into an empirical context, from a contemporary viewpoint, its contribution is highly limited in the area of history of science and history of philosophy (of science). Keywords: biology, history of science, Oparin, origin of life, philosophy of science
... For example, in the 3.46 Ga Apex Chert (W. Australia), filamentous structures purported to represent fossilized bacteria, including putative cyanobacteria (Schopf 1993), were later dismissed as artifacts associated with hydrothermal emplacement of kerogen of potentially abiotic origin (Brasier et al. 2002). ...
Precambrian metasediments provide a unique archive for understanding Earth's earliest biosphere, however traces of microbial life preserved in ancient rocks are often controversial. In this study we leveraged several micro- to nano-scale techniques to study filamentous structures previously reported in clastic sediments of the 3.22 Ga Moodies Group, Barberton Greenstone Belt, S. Africa. We performed petrographic, mineralogical, electron microprobe, confocal fluorescence and electron microscopy analyses of these structures in order to evaluate their biogenicity and syngenecity. We also examined drill core samples of deep-water iron formations from the 2.46 Ga Joffre member of the Brockman Iron Formation (Hamersley Basin, W. Australia) to better understand their potential biogenicity. In both cases, we aimed to resolve primary vs. secondary mineral assemblages and their relation to filamentous or sedimentary structures. In the Moodies Group samples, filamentous structures were resolved by confocal imaging and revealed to be crosscut by later metamorphic phases, highlighting their syngenetic nature. Three-dimensional imaging reveals that while the filamentous structures are not necessarily associated with grain boundaries (e.g., as organic coatings), they form both sheets and filaments, complicating their interpretation but not ruling out a biological origin. No organic microstructures appeared to be preserved in our Dales Gorge samples. We also examined the possible application of electron paramagnetic resonance spectroscopy (EPR) to carbonaceous matter in ancient silica-rich matrices, similar to Bourbin et al. (2013), using samples from the Brockman iron formation. While resonance associated with organic matter was largely unresolvable in the Brockman iron formation samples due to their low organic matter contents, large effects on the EPR spectra were apparent stemming from the presence of magnetic iron minerals, highlighting the need to carefully consider sample composition in EPR analyses targeting ancient organic matter. Collectively, this study highlights the added value of micro- to nano-scale techniques as applied to Precambrian metasediments containing traces of ancient life, for example in revealing the pre-metamorphic emplacement and three-dimensional structure of filaments in the Moodies Group, but also the potential drawbacks and pitfalls, such as the case of strong magnetic mineral interference in EPR analysis of organic matter in trace abundance in the Dales Gorge.
For more than 3.5 billion years, life experienced dramatic environmental extremes on Earth. These include shifts from oxygen-less to over-oxygenated atmospheres and cycling between hothouse conditions and global glaciations. Meanwhile, an ecological revolution took place. The planet evolved from one dominated by microbial life to one containing the plants and animals that are most familiar today. The activities of many key cellular inventions evolved early in the history of life, collectively defining the nature of our biosphere and underpinning human survival. There is a critical need for a new disciplinary synthesis to reveal how microbes and their molecular systems survived ever changing global conditions over deep time. This review critically examines our current understanding of early microbial life and describes the foundations of an emerging area in microbiology and evolutionary synthetic biology to reconstruct the earliest microbial innovations.
Photosynthesis is a very old process on this Earth. Based on fossil discoveries and chemical evidence, cyanobacteria first appeared 2.5–2.6 billion years ago (bya). Their evolution was undoubtedly continued by a number of anaerobic, photosynthetic bacterial life forms. Carbon isotope data revealed that autotrophic carbon fixation may have begun at least a bya. It is unclear, nevertheless, what the earliest photosynthetic organisms were like. The primary elements of the photosynthetic system are the carbon fixation mechanism, electron transport complexes, antenna complexes, and reaction centers. It is most likely true that these components have not all evolved at the same point in time. Consequently, it is better to think of the photosynthetic apparatus as a mosaic made up of numerous structural components, each with its own unique evolutionary background. One early instance of a cyanobacterium’s endosymbiotic absorption by a heterotrophic organism appears to have been the source of the chloroplasts seen in yellow-green algae, glaucophytes, brown algae, cryptophytes, red algae, and other algae in the “red” line of development. The variety of species present in the algae’s “red line” is the outcome of a single secondary endo-symbiotic occurrence in which an organism resembling red algae was ingested by another eukaryote. This “red line” is further expanded by tertiary (third-level) endosymbiotic events. Photosynthetic units are found in reaction centers involving complexes for gathering light. Two of these units are necessary for oxygenic photosynthesis, which currently accounts for the majority of biological transfer of energy in the various trophic levels of the biosphere. The emergence of photosynthesis utilizing oxygen among cyanobacteria, which paved the path for the formation of complex life forms with multicellular levels of organization, had a profound influence on the biology, geology, and environment of Earth. In this review, we have discussed the early evidence of photosynthesis, the origin of reaction centers, antenna, pigments, and how oxygenic photosynthesis came into existence. The origin of the chloroplasts is a necessary event that occurred earlier and was added to the history of photosynthetic origin in this review.
Elucidating compositions of the first cell membranes requires experiments with molecules and chemical conditions representative of early Earth. The molecules used are described as ‘prebiotically plausible’, i.e., they could have formed through abiotic reactions before the emergence of biology. Similarly, the chemical properties of solutions in which these membranes are formed (e.g., pH, temperature, ionic strength) must represent early Earth environments. Here, using confocal and transmission electron microscopy combined with population morphometry, we show that prebiotically plausible molecules, in solutions representative of Hadean submarine alkaline hydrothermal vents, form microstructures with substantial morphological diversity. The microstructures hold the potential for use as analogues of prebiotic processes in the rock record. Additionally, many of the structures are morphologically similar to purported early microfossils, highlighting limitations of morphological interpretation in these studies. Detailed analyses of abiotic microstructures are essential for understanding the earliest life on Earth, and for interpretation of potential biosignatures from extra-terrestrial bodies.
Paleoarchean carbonates in the Pilbara Craton (Western Australia) are important archives for early life and environment on early Earth. Amongst others, carbonates occur in interstitial spaces of ca. 3.5–3.4 Ga pillow basalts (North Star-, Mount Ada-, Apex-, and Euro Basalt, Dresser Formation) and associated with bedded deposits (Dresser- and Strelley Pool Formation, Euro Basalt). This study aims to understand the formation and geobiological significance of those early Archean carbonates by investigating their temporal-spatial distribution, petrography, mineralogy, and geochemistry (e.g., trace elemental compositions, δ13C, δ18O). Three carbonate factories are recognized: (i) an oceanic crust factory, (ii) an organo-carbonate factory, and (iii) a microbial carbonate factory. The oceanic crust factory is characterized by carbonates formed in interspaces between pillowed basalts (“interstitial carbonates”). These carbonates precipitated inorganically on and within the basaltic oceanic crust from CO2-enriched seawater and seawater-derived alkaline hydrothermal fluids. The organo-carbonate factory is characterized by carbonate precipitates that are spatially associated with organic matter. The close association with organic matter suggests that the carbonates formed taphonomically via organo-mineralization, that is, linked to organic macromolecules (either biotic or abiotic) which provided nucleation sites for carbonate crystal growth. Organo-carbonate associations occur in a wide variety of hydrothermally influenced settings, ranging from shallow marine environments to terrestrial hydrothermal ponds. The microbial carbonate factory includes carbonate precipitates formed through mineralization of extracellular polymeric substances (EPS) associated with microbial mats and biofilms. It is commonly linked to shallow subaquatic environments, where (anoxygenic) photoautotrophs might have been involved in carbonate formation. In case of all three carbonates factories, hydrothermal fluids seem to play a key-role in the formation and preservation of mineral precipitates. For instance, alkaline earth metals and organic materials delivered by fluids may promote carbonate precipitation, whilst soluble silica in the fluids drives early chert formation, delicately preserving authigenic carbonate precipitates and associated features. Regardless of the formation pathway, Paleoarchean carbonates might have been major carbon sinks on the early Earth, modulating the carbon cycle and, hence, climate variability.
Microfossils, graphite and organic matter in the Archean sedimentary rocks, which are direct evidence of life on the early Earth, have been reported by previous studies. However, as the sedimentary age gets older, those evidence have been deformed, destroyed and lost, leading “mislead” with abiotic signals. In this review paper, research history about evidence of life on the early Earth are reviewed from the point of geoscience, including geology, mineralogy, isotope geochemistry, and organic geochemistry. Recent studies of microscale measurements, which are suitable for searching meager evidence in the old rocks, are also reviewed
There is a need for novel nanomaterials with properties not yet exploited in regenerative nanomedicine. Based on lessons learned from the oldest metazoan phylum, sponges, it has been recognized that two previously ignored or insufficiently recognized principles play an essential role in tissue regeneration, including biomineral formation/repair and wound healing. Firstly, the dependence on enzymes as a driving force and secondly, the availability of metabolic energy. The discovery of enzymatic synthesis and regenerative activity of amorphous biosilica that builds the mineral skeleton of siliceous sponges formed the basis for the development of successful strategies for the treatment of osteochondral impairments in humans. In addition, the elucidation of the functional significance of a second regeneratively active inorganic material, namely inorganic polyphosphate (polyP) and its amorphous nanoparticles, present from sponges to humans, has pushed forward the development of innovative materials for both soft (skin, cartilage) and hard tissue (bone) repair. This energy-rich molecule exhibits a property not shown by any other biopolymer: the delivery of metabolic energy, even extracellularly, necessary for the ATP-dependent tissue regeneration. This review summarizes the latest developments in nanobiomaterials based on these two evolutionarily old, regeneratively active materials, amorphous silica and amorphous polyP, highlighting their specific, partly unique properties and mode of action, and discussing their possible applications in human therapy. The results of initial proof-of-concept studies on patients demonstrating complete healing of chronic wounds are outlined.
To understand the origin and early evolution of life it is crucial to establish characteristics of the primordial environment that facilitated the emergence and evolution of life. One important environmental factor is the pH of the primordial environment. Here, we assessed the pH-dependent thermal stabilities of previously reconstructed ancestral nucleoside diphosphate kinases and ribosomal protein uS8s. The selected proteins were likely to be present in ancient organisms such as the last common ancestor of bacteria and that of archaea. We also assessed the thermal stability of homologous proteins from extant acidophilic, neutralophilic, and alkaliphilic microorganisms as a function of pH. Our results indicate that the reconstructed ancestral proteins are more akin to those of extant alkaliphilic bacteria, which display greater stability under alkaline conditions. These findings suggest that the common ancestors of bacterial and archaeal species thrived in an alkaline environment. Moreover, we demonstrate the reconstruction method employed in this study is a valuable technique for generating alkali-tolerant proteins that can be used in a variety of biotechnological and environmental applications.
Elucidating the most probable compositions of the first cell membranes prior to the origin of life, within a laboratory setting, requires experiments with organic molecules and chemical conditions representative of those present on the early Earth. As such, the membrane forming molecules used in these experiments are described as ‘prebiotically plausible’, i.e., they could have formed through abiotic reactions and be available for membrane formation prior to the emergence of biology. Similarly, the chemical properties of solutions in which these membranes are formed (e.g., pH, temperature, ionic strength) must represent the early Earth environmental conditions under investigation. Here, using a combined confocal and transmission electron microscopy approach, we show that prebiotically plausible organic molecules, in solutions representative of Hadean submarine alkaline hydrothermal vents, form aggregated structures with substantial morphological diversity. The structures hold the potential for use as traces of prebiotic processes in the ancient rock record. In addition, many of the structures are morphologically similar to those which are presented as early microfossils, thus highlighting the limitations of morphological interpretation in these types of studies. Detailed analyses of abiotic organic structures are essential for our understanding of the earliest living organisms on Earth, as well as for our interpretation of any potential biosignatures recovered in the future from extra-terrestrial bodies.
Up to now, research on cyanobacteria and their biologically active substances has been directed principally towards their harmful effects on humans, and little has been done to elucidate their ecological role. In order to understand better the biological success of cyanobacterial blooms, and in order to be able to compare the results of different scientific investigations, we must find and agree on a definition of the phenomenon. We propose a definition of harmful cyanobacterial blooms based on the OECD boundary system of eutrophication with the addition of phycocyanin values. We have found a direct linkage between the trophic conditions in the water-bodies and the frequency of formation of cyanobacterial blooms. Specific toxic species and their strains have been studied intensively. However, in order to elucidate the mechanisms that enable cyanobacteria to overtake eutrophic water bodies we must change our approach. Cyanobacterial blooms should not be treated merely as different species or strains but as superorganisms. It is their intraspecific diversity that permits cyanobacteria to be successful in a variable water environment. Wehere focus attention on microcystin producers and microcystins as an adaptation to the limited light conditions, which arise in cyanobacterial blooms. The conclusions are illustrated with some data from surface water-bodies in Slovenia.
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.
The Pilbara craton of northwestern Australia is known for what were, when reported, the oldest known microfossils and paleosols on Earth. Both interpretations are mired in controversy, and neither remain the oldest known. Both the microfossils and the paleosols have been considered hydrothermal artefacts: carbon films of vents and a large hydrothermal cupola, respectively. This study resampled and analyzed putative paleosols within and below the Strelley Pool Formation (3.3 Ga), at four classic locations: Strelley Pool, Steer Ridge, Trendall Ridge, and Streckfuss, and also at newly discovered outcrops near Marble Bar. The same sequence of sedimentary facies and paleosols was newly recognized unconformably above the locality for microfossils in chert of the Apex Basalt (3.5 Ga) near Marble Bar. The fossiliferous Apex chert was not a hydrothermal vein but a thick (15 m) sedimentary interbed within a sequence of pillow basalts, which form an angular unconformity capped by the same pre-Strelley paleosol and Strelley Pool Formation facies found elsewhere in the Pilbara region. Baritic alluvial paleosols within the Strelley Pool Formation include common microfossil spindles (cf. Eopoikilofusa ) distinct from marine microfossil communities with septate filaments ( Primaevifilum ) of cherts in the Apex and Mt Ada Basalts. Phosphorus and iron depletion in paleosols within and below the Strelley Pool Formation are evidence of soil communities of stable landscapes living under an atmosphere of high CO 2 (2473 ± 134 ppmv or 8.8 ± 0.5 times preindustrial atmospheric level of 280 ppm) and low O 2 (2181 ± 3018 ppmv or 0.01 ± 0.014 times modern).
Although Hadean rocks are missing, detrital zircons from Australia and India suggest that Earth’s continental crust and water existed as early as 4.4 Ga. Molecular phylogeny and the record of biogenic carbon indicate that life might have existed in the Hadean during the heavy bombardment period. The oldest crusts are exclusively Eoarchean, including the Nuvvuagittuq Craton of Canada, the Isua Craton of Greenland, the Kaapvaal Craton of South Africa, the Pilbara Craton of Australia, and the Singhbhum Craton of India. The volcano-sedimentary rocks of the greenstone facies of these five cratons have yielded a rich record of early life in hydrothermal vent environments in chemofossils, microfossils, and stromatolites. During the Eoarchean, Earth had oceans, continents, and an anoxic atmosphere. The oldest microfossils (≥4 Ga) are known from the Nuvvuagittuq Craton of Canada in the form of delicate tiny filaments and tubes in jasper-carbonate banded iron formations (BIFs) in the submarine hydrothermal vent environment, indicating an affinity toward hyperthermophilic bacteria. Isua rocks of Greenland have yielded chemofossils in the form of biogenic carbon (~3.8 Ga) and stromatolites (3.7 Ga) of possible bacterial origin. The close stratigraphic correlation between the Onverwacht Group of the Kaapvaal Craton in South Africa and the Warrawoona Group of the Pilbara Craton in Western Australia suggests that they were once part of the ancient supercontinent Vaalbara (3.6–2.8 Ga). The hydrothermal volcano-sedimentary rocks from Vaalbara have yielded the oldest and best-preserved early Archean microfossils in chert beds. The Pilbara Supergroup of Australia consists of the Warrawoona and Kelly Groups. Three sequences within the Warrawoona volcaniclastic rocks may host the evidence for Earth’s earliest life. From the oldest to the youngest, these formations represent the Dresser Formation (~3.49 Ga) at the bottom, the Apex Chert (~3.46 Ga) in the middle, and the Strelley Pool Formation (~3.43 Ga) at the top. Hyperthermophilic bacteria and archaea were the major components of ancient microbial activity, as evidenced by carbonaceous remains and fragmentary remains of cell walls from the hydrothermal black cherts of the Warrawoona. The fossil record suggests that two domains of life were already split from the last universal common ancestor (LUCA) during this time. The chemofossils from the Jack Hills of Western Australia reinforce the view that life originated on Earth at least 300 million years earlier in the Hadean Eon. The Kaapvaal Craton of South Africa is another extraordinary storehouse for the earliest record of life, such as primitive hyperthermophilic bacteria and archaea from the hydrothermal cherts sandwiched between pillow lavas. The Barberton greenstone belt of the Kaapvaal Craton of South Africa represents the oldest known volcano-sedimentary sequences that have provided critical evidence of early life. The Swaziland Supergroup is divided into three distinct units: the basal volcano-sedimentary Onverwacht Group, the middle sedimentary Fig Tree Group, and the top Moodie Group, all containing rare archives of early life (~3.5 Ga). The Iron Ore Group (IOG) of the Singhbhum Craton of eastern India has yielded spheroidal and filamentous microfossils of hyperthermophilic affinity (~3.4 Ga). Fossil records from these ancient cratons suggest that hyperthermophilic bacteria and archaea appeared in the early Archean about four billion years ago. This was followed by the evolution of anoxygenic photosynthetic bacteria and then oxygenic bacteria. The arrival of oxygenic photosynthesis allowed life to escape the hydrothermal setting and invade an utterly new environment—the broad continental shelves of the global ocean. Cyanobacteria contributed to the geological processes by providing vast amounts of carbonate sediments and stromatolitic structures in the shallow seas; they formed oxygen as a byproduct, transforming the ocean and the atmosphere around 3.2 billion years ago and triggering an explosive evolution. This development led to the origin of eukaryotes.
To understand the origin and early evolution of life it is crucial to establish characteristics of the primordial environment that facilitated the emergence and evolution of life. One importantenvironmental factor is the pH of the primordial environment. Here, we assessed the pH-dependent thermal stabilities of previously reconstructed ancestral nucleoside diphosphate kinases and ribosomal protein uS8s. The selected proteins were likely to be present in ancient organisms such as the last common ancestor of bacteria and that of archaea. We also assessed the thermal stability of homologous proteins from extant acidophilic, neutralophilic, and alkaliphilic microorganisms as a function of pH. Our results indicate that the reconstructed ancestral proteins are more akin to those of extant alkaliphilic bacteria, which display greater stability under alkaline conditions. These findings suggest that the common ancestors of bacterial and archaeal species thrived in an alkaline environment. Moreover, we demonstrate the reconstruction method employed in this study is a valuable technique for generating alkali-tolerant proteins that can be used in a variety of biotechnological and environmental applications.
Styles of mineralization in the Northern Pilbara Craton, and the size of deposits, reflect the change in tectonic processes from the Paleoarchean to the Mesoarchean. Paleoarchean magmas and hydrothermal fluids were generated during vertical recycling of continental crust, and consequently the ‘metal budget’ was limited. None of the Paleoarchean gold and base metal deposits are large by international standards. In contrast, Mesoarchean mineralization occurred during plate-tectonic processes that allowed repeated influxes of metal-charged juvenile material, either above subduction zones or along major strike-slip faults. The source of iron for the large iron ore deposits in Mesoarchean sedimentary basins of the Northern Pilbara was juvenile oceanic crust remote from the depositional sites. In contrast, Paleoarchean iron formations were deposited from local hydrothermal vents in volcanic environments and were formed as thin, low-grade, and laterally discontinuous units. The most significant mineralization in the Neoarchean Fortescue Group is conglomerate-hosted gold, although sub-economic uranium mineralization is also present in some conglomerates.
The 3530–3427 Ma Warrawoona Group is the oldest of the three groups that make up the Pilbara Supergroup. This 3530–3235 Ma supergroup comprises the Paleoarchean greenstone succession of the East Pilbara Terrane and is preserved in 20 greenstone belts. The group was erupted across the entire area of the 3800–3530 Ma Pilbara crust (Chap. 2), and its thickness varies between 10 and 15 km. Variations are partly due to local erosional unconformities that were formed from 3460 Ma onwards when granite–greenstone domes of the terrane began to rise at different rates. Apart from thin sedimentary units deposited between 3490 and 3474 Ma and between 3459 and 3450 Ma, the Warrawoona Group is volcanic. The succession is composed of successive ultramafic–mafic–felsic volcanic cycles in which felsic volcanism was contemporaneous with intrusion of tonalite–trondhjemite–granodiorite (TTG). Field exposures reveal that many of the TTG intrusions were subvolcanic to the felsic volcanic formations. The East Pilbara Terrane is now exposed across 40,000 km2 of the northeast section of the Pilbara Craton, with concealed parts estimated to occupy an additional 60,000 km2. With an interpreted total volume of volcanic rocks exceeding 1,000,000 km3, the Warrawoona Group easily meets the volume requirement for a large igneous province (LIP). The 3530–3300 Ma stratigraphic successions of the Pilbara and Kaapvaal Cratons are remarkably similar, even including a common volcanic hiatus between about 3426 and 3350 Ma. In the Pilbara, two lines of evidence indicate a magmatic event commencing abruptly at 3530 Ma: firstly, a major peak in the frequency of zircon aged between 3530 and 3490 Ma, preceded by an almost total lack of zircons dated between 3550 and 3530 Ma; and secondly, Lu–Hf isotope evidence for a surge of mantle-derived juvenile magmas between 3530 and 3490 Ma. This sudden magmatic activity is interpreted to coincide with the arrival of the first of a series of mantle plumes that had major impacts on the Paleoarchean crustal evolution of the craton.
Life's origin is an enigma. Mankind has been pondering as to how it all began for millennia, yet are we any closer to uncovering the answer to this enigma? It would seem not, but we are slowly and surely edging towards discovery of the processes and mechanics by which life emerged on Earth. There are more than a couple of dozen hypotheses which claim to have the answer, but in reality, there is no absolute front runner. We have categorised these hypotheses under the following four banners: metabolism, genetic, proteins and vesicles first. In this chapter we strive to demonstrate how they conflict with one another and to this effect we have brought into focus both the top‐down and bottom‐up approaches to the question of the origin of life in general, as well as answering the question as to which came first, chemolithoautotrophs and photolithoautotrophs? In addition, the part played by viruses (in particular the RNA ones) during the origin of life is addressed.
Determination of the time sequence in the geologic record is a logical process that involves little “guesswork.” The geologic time scale is real, not a circular argument developed to show evolution. By applying Occam's Razor and assuming continuity, it is clear that biotic succession in apparent lineages demonstrates that species are capable of giving rise to others through modification with descent and have done so through geologic time. Although the fossil record is incomplete, biotic succession on a large scale provides a clear and unambiguous outline of the history of the change in life over time.
Science seeks explanations for observations and facts that begin as hypotheses. When hypotheses successfully survive rigorous testing, they mature into accepted theories. Evolution is the theory accepted as the explanation for the facts of biotic succession. The operational processes invoked in the theory of evolution (such as mutation, natural selection, isolation, and genetic drift) have been successfully tested many times. The general pattern of biotic succession follows the path expected or predicted for the course of the evolutionary development of the biosphere.
The biotic succession is the preserved result of the operation of the processes of organic evolution. Contributions from molecular biology and cladistics make it clear that the branching processes in evolution, operating over time, have produced all the diversity preserved in the fossil record. The current diversity of life is simply the product of its three and a half billion year history.
A morphologically variable assemblage of stromatolites has been discovered in thin chert layers within the Fig Tree Group of the Swaziland Supergroup, South Africa. They are commonly low-relief, nearly stratiform, laterally linked domes. Rarer forms include pseudocolumns and crinkly stratiform stromatolites. The stromatolites grew on a substrate of altered komatiitic lava and sediments deposited on the lava surface, and in most places are covered by later komatiitic flows. Abundant fine-grained tourmaline included within the stromatolite laminae suggests that stromatolites formed in an environment dominated by boron-rich hot-spring emissions and evaporitic brines.
The amounts of organic carbon and iron generally estimated to have been preserved in early Precambrian sediments suggest by implication that only the rapid, oxidative recycling of organic carbon by aerobic heterotrophy could plausibly have kept pace with the oxygen produced annually by net photosynthesis, even with a low global primary productivity of less than 1% of modern global values (Towe, 1990). A global aerobic recycling process would require at least a moderately oxygenated atmosphere to operate. The presence of such an atmosphere as far back in Earth history as 3.8 Ga ago is consistent with, but not proven by, the abundance of organic carbon and the "anomalous" distribution of rare earths in the banded iron-formations of the Isua sediments (Dymek and Klein, 1988). The absence of positive cerium anomalies and the presence of positive europium anomalies in these and other banded iron-formations (Klein and Beukes, 1989; Derry and Jacobsen, 1990) imply that iron oxidation during BIF deposition took place in waters at some depth below the zone of mixing rather than at the surface. A modified Klein-Beukes model using shallow, seasonal downwelling in an otherwise deep-water stratified basin under a moderately oxygenated atmosphere may help explain the origin of some of these enigmatic deposits.
The Proterozoic Biosphere is the first major study of the paleobiology of the Proterozoic Earth. It is a multidisciplinary work dealing with the evolution of the Earth, the environment, and life during the forty percent of Earth's history that extends from the middle of the Precambrian Eon (2500 Ma) to the beginning of the Paleozoic Era (550 Ma.). The Proterozoic Biosphere includes a vast amount of new data on Proterozoic organisms and their modern analogs. Prepared by the Precambrian Paleobiology Research Group, a multidisciplinary consortium of forty-one scientists from eight countries, this monograph will serve as a benchmark in the development of the science of the biochemistry and the organic chemistry of Proterozoic sediments. The three main goals of this study are: (1) to amass, evaluate, and synthesize the large body of paleobiologic data available from previous studies, eliminating mistakes so that future investigations will not be encumbered by them; (2) to generate new data and new analyses based on the reexamination of previous studies and on new investigations within an interdisciplinary framework; (3) to build toward the future by placing special emphasis on new or relatively neglected aspects of paleobiologic study and by highlighting major unsolved problems in the field.
The H.Y.C. Pyritic Shale Member of the Barney Creek Formation (ca 1 500 my old; northern Australia) contains several stratiform base metal sulfide deposits of economic significance. Black cherts within these mineral deposits preserve a diverse assemblage of bacterial and algal microfossils. The assemblage differs from most other Precambrian biotas so far described in that it was deposited in deep water, it is not associated with stromatolites or algal mats, and it is dominated by filamentous bacteria, most of which are pyritized. Analysis of the assemblage suggests that the depth of the depositional basin exceeded that of the photic zone, that the bacteria inhabited the basin floor where they maintained anoxic conditions through heterotrophic degradation of detrital organic matter, and that the algae inhabited overlying near surface waters. Most of the algal fossils have been assigned to the Cyanophyta, although two of the described species are potentially referable to the eukaryotic green or red algae. Differences between this assemblage and other biotas described from the McArthur Group suggest that a workable system of biostratigraphic zonation for the Group is feasible.Fossils in the H.Y.C. assemblage are here referred to 21 species and 16 genera, of which 14 species and 6 genera are new. The new taxa are: Bacteria, Biocatenoides incrustata sp. nov., B. pertenuis sp. nov., Ramacia carpentariana gen. et sp. nov., Coleobacter primus gen. et sp. nov., Ferrimonilis variabile gen. et sp. nov.; Chroococcales (Cyanophyta), Nanococcus vulgaris gen. et sp. nov., Bisacculoides tabeoviscus gen. et sp. nov., B. vacua gen. et sp. nov., B. grandis gen. et sp. nov.; Nostocales (Cyanophyta), Oscillatoriopsis schopfii sp. nov., Cyanonema inflatum sp. nov., C. minor sp. nov.; Incertae sedis, Clonophycus elegans gen. et sp. nov., Globophycus minor sp. nov. In addition, the new combination Gunflintia septata (Schopf) is proposed.
A diverse, abundant, apparently procaryotic microflora is here reported from the Tyler Fm., upper Baraga Group, Gogebic County, Michigan. In addition, numerous chains of spheroids and grains of hematite after pyrite from the Baraga Group, Baraga County, suggest a microbial presence.The Tyler microbiota occurs in spheroidal clasts and oncoids comprised of pyritic cherts along the Black River east of Ironwood. It includes nine recognizably different microbial forms, four of filaments, two of spheroids, one umbrellaform, and two stellate. Its nearest affinities are with the stratigraphically lower microbiota of the Gunflint Iron‐formation, with which it shares such distinctive fossils as Gunflintia, Metallogenium (Eoastrion), and Kakabekia cf. K. umbellata Barghoorn. The Baraga assemblage, considered as a single form of “dubiofossil,”; includes strongly curvate chains of hematized pyrite spheroids and grains arranged in configurations suggesting filamentous procaryotes. It is from a black phosphatic layer 1‐ to 9‐mm thick on the Huron River about 6.5 km south of Lake Superior.Both occurrences are from stratigraphically higher in the succession of Baraga, Animikie, and equivalent rocks of the Lake Superior region than are the previously described nannofossils of the Gunflint, Biwabik, and Pokegama strata. They are thus younger but probably not much more recent than 2 × 10years ago.
Two communities of diverse, well-preserved, fossil prokaryotic microorganisms have been discovered in petrographic thin sections of carbonaceous black chert from the ca. 1400–1500 Ma-old Gaoyuzhuang Formation at the stratotype section of the “Sinian Suberathem” near Jixian, northern China. One of these communities is preserved in bedded, essentially flat-laminated, stromatolitic chert; the other occurs in silicified conical stromatolites of the forms Conophyton cylindricum and C. garganicum. The Gaoyuzhuang cherts comprise one of the few microfossiliferous deposits now known from the Precambrian of China; the permineralized microbiotas they contain are among the first such stromatolitic assemblages to be discovered in the Sinian stratotype section.
The Fig Tree Series of the Swaziland System in South Africa is, according to radiometric data, more than 3,200 million years old. Cherts and shales, collected in the vicinity of the Sheba Gold Mine, near Barberton, have been studied for their microfossil content. Cut sections, thin sections, and macerations have yielded an assemblage of organism remains. Chemical and optical investigations have been conducted to determine whether the walls of the bodies consist of organic material. Globular-type A structures resemble cysts of flagellates, while filamentous-type C bodies are assigned to nostocalean blue-green algae. There are other structures of problematic affinity (globular-type B, filamentous-type D, and irregular-type F). Finally, a thread-like structure has been identified as a pseudo-fossil.Several of the fossil structures were chemically analysed by means of an electron probe X-ray microanalyser. The results give the impression that the algal bodies were able to precipitate metal salts (with cations such as copper, iron, calcium) from water by the action of their life processes. The observations suggest that similar biological processes could have been an important factor in the formation of the Precambrian sedimentary ore deposits. The fossil findings lead to the conclusion that life must be older than 3,200 million years. At that time, local conditions must have been present on earth which permitted the existence of photosynthetic plants.
A diverse, well-preserved microbiota has been discovered in petrographic thin sections of stromatolitic black chert of the ca. 1000–1100 Ma-old Allamoore Formation from the Van Horn region of west Texas. Geologic evidence indicates that the mat-building microbial community inhabited a shallow-water environment, probably intermittently exposed to subaerial desiccation. The microfossils occur in two interlaminated sedimentary fabrics: a flat-lying to wavy stromatolitic fabric, formed during relatively quiescent periods, and an intraclastic fabric that reflects deposition in agitated water, perhaps during storms.The carbonaceous microfossils are three-dimensionally preserved, permineralized in fine-grained chert probably of early diagenetic origin. The assemblage includes solitary and colonial unicellular cyanobacteria (Entophysalidaceae or Chroococcaceae), the tubular sheaths of at least three microbial taxa (apparently of oscillatoriacean affinities), and cellular prokaryotic filaments. The common occurrence of large spheroidal unicells, some in excess of 100 μm in diameter, suggests that fossil eukaryotes (green or red algae) may also be represented. The Allamoore cherts comprise one of only a few microfossiliferous Precambrian deposits now known from western North America.
Small bioherms with complex conical stromatolites attributable to Thyssagetes occur at the top of the siderite orebody in the late Archean (2.75-2.70 Ga) Helen Iron-Formation at the MacLeod mine 4km northeast of Wawa. Horizontal sections show round to polygonal outlines 2-20cm across. The stromatolites are the first to be reported from siderite. They are relatively well preserved primary biosedimentary structures that provide conclusive morphologic evidence of biologic activity in the shallow-water, photic zone in the late Archean basin in which the carbonate of the Michipicoten Group accumulated. -from Authors
The word ‘stromatolite’ should only be applied to organosedimentary structures predominantly accreted by sediment trapping, binding and/or in situ precipitation as a result of the growth and metabolic activities of benthic, principally prokaryotic, micro-organisms. Structures of uncertain origin that resemble stromatolites should be called ‘stromatoloids’. This cautious approach would eliminate the currently common assumption that structures with mesoscopic morphological similarities to microbially accreted sedimentary structures must be biogenic, a misconception that hampers investigations into the antiquity of life.A hierarchical series of meso- and microstructural attributes of stromatolites can be used to assign gradually increasing probabilities of biogenicity to stromatoloids. This method is particularly useful for interpreting ancient noncolumnar stromatoloids with poor microstructural preservation. In a range of Early Archaean pseudocolumnar, nodular and stratiform stromatoloids from North Pole studied using this method, none could be proved to be stromatolites and only a few are probable or possible stromatolites. As these stromatoloids closely resemble previously reported structures from North Pole interpreted as stromatolites, we consider that the evidence for the existence of life c. 3500 my ago at North Pole is less definitive than previously supposed.
Stromatolites are the least controversial evidence of early life; they are organosedimentary structures resulting from the growth and metabolic activity of microorganisms1. Before this report, however, the oldest well established occurrence was in the 2,900–3,000 Myr Pongola Supergroup of South Africa2; five or six additional occurrences are known from the later Archean3. The only proposed example from older rocks is of a possibly stromatolitic microfabric from 3,500 Myr cherts in South Africa4; as yet that interpretation has not been supported by the discovery of macroscopic stromatolites. Here we describe stromatolites 3,400–3,500-Myr old from the Pilbara Block of Western Australia. These are the oldest firmly established biogenic deposits now known from the geological record.
Archaean supracrustal rocks that are well exposed in the Marble Bar region, Pilbara Craton, have been assigned to the Warrawoona Group and younger sequences. The predominantly volcanic Warrawoona Group, previously dated at 3300 to 3500 Ma, is largely basaltic with locally intercalated thick felsic volcanic units. The supracrustal rocks have been folded and are distributed around the margins of large, roughly circular to ovoid, “granitic-gneissic” batholiths. A UPb zircon geochronology study was undertaken to obtain precise age constraints for some of the ore deposits in the area, especially the Big Stubby, North Pole (barite), and Miralga Creek (ZnPbCuAu) deposits, in support of efforts to improve Archaean lead isotope models. The results also help significantly in interpreting stratigraphic relationships and crustal evolution in the area.
Four morphotypes of structurally preserved, filamentous fossil bacteria have been discovered in petrographic thin sections of laminated, carbonaceous cherts from the ∼3500 Ma-old Warrawoona Group of northwestern Australia. These tubular and septate microfossils are interpreted here as being syngenetic with Warrawoona sedimentation; as such, they are apparently the oldest such fossils now known in the geological record. The diversity of this assemblage, and the evident complexity of its individual components, suggest that the beginnings of life on Earth may have appreciably pre-dated the deposition of the Warrawoona sediments.
Diverse assemblages of cellularly preserved Precambrian microorganisms have been discovered in cherty stromatolitic sediments from six formations in the Soviet Union: Sukhotungusin Fm. (Middle Riphean, Siberia); Valukhtin Fm. (Middle Riphean, Siberia); Shorikha Fm. (Upper Riphean, Siberia); Minyar Fm. (Upper Riphean, Bashkiria); Olkhin Fm. (Upper Riphean, Siberia); and Chichkan Fm. (Vendian, Kazakstan). These cyanophyte-dominated microbial communities, occurring in both stratiform (cf. Stratifera) and columnar stromatolitic deposits (Baicalia hirta and Conophyton gaubitza), are the first stromatolite-building microbiotas to be reported from the Soviet Union; collectively they comprise more than one-fifth of all such Precambrian assemblages now known.
The Swaziland Supergroup, Barberton Mountain Land, South Africa, has long been regarded as a promising location for the Earth's oldest fossils because it includes some of the most ancient well-preserved sedimentary rocks, many of which contain carbonaceous matter. Although there have been numerous reports of microfossils from Swaziland Group rocks1-7, the biogenicity of most of the structures has been questioned8-10. Although some of the organic spheroids are probably biogenic10,11, the best early Archaean simple spheroids are generally regarded as `possible microfossils'10 because organic spheroids may form abiotically in several ways12. The discovery of less-simple biological morphologies is therefore important in establishing the existence of early life forms in the early Archaean. Uniformly-sized curving filaments, especially tubular ones, are difficult to explain as anything other than the fossil remains of filamentous organisms. Here we report the discovery of numerous filaments from two different stratigraphical positions in the 3,500-Myr-old Onverwacht Group of the Swaziland Supergroup. Their morphologies and abundance provide convincing evidence for the existence of bacteria- or cyanobacteria-like organisms on the Earth during the early Archaean. This supports recent reports of similar filamentous microfossils from 3,500-Myr-old rocks from Western Australia13.
Internally laminated conical mounds characterise a regionally extensive
chert unit near the top of the 3,400-Myr old Warrawoona Group in the
Pilbara Block of Western Australia. The chert formed by silicification
of a carbonate-evaporite sequence deposited in shallow subtidal to
intertidal environments. The morphology and internal organisation of the
mounds described here suggests that they are conical stromatolites
similar but not identical to members of the common Proterozoic group
Conophyton Maslov.
The Earth's atmosphere during the Archaean era (3,800-2,500 Myr ago) is generally thought to have been anoxic, with the partial pressure of atmospheric oxygen about 10(-12) times the present value. In the absence of aerobic consumption of oxygen produced by photosynthesis in the ocean, the major sink for this oxygen would have been oxidation of dissolved Fe(II). Atmospheric oxygen would also be removed by the oxidation of biogenic methane. But even very low estimates of global primary productivity, obtained from the amounts of organic carbon preserved in Archaean rocks, seem to require the sedimentation of an unrealistically large amount of iron and the oxidation of too much methane if global anoxia was to be maintained. I therefore suggest that aerobic respiration must have developed early in the Archaean to prevent a build-up of atmospheric oxygen before the Proterozoic. An atmosphere that contained a low (0.2-0.4%) but stable proportion of oxygen is required.
Two distinct generations of microfossils occur in silicified carbonates from a previously undescribed locality of the Lower Proterozoic Duck Creek Dolomite, Western Australia. The earlier generation occurs in discrete organic-rich clasts and clots characterized by microquartz anhedra; it contains a variety of filamentous and coccoidal fossils in varying states of preservation. Second generation microfossils consist almost exclusively of well-preserved Gunflintia minuta filaments that drape clasts or appear to float in clear chalcedony. These filaments appear to represent an ecologically distinct assemblage that colonized a substrate containing the partially degraded remains of the first generation community. The two assemblages differ significantly in taxonomic frequency distribution from previously described Duck Creek florules. Taken together, Duck Creek microfossils exhibit a range of assemblage variability comparable to that found in other Lower Proterozoic iron formations and ferruginous carbonates. With increasing severity of post-mortem alteration, Duck Creek microfossils appear to converge morphologically on assemblages of simple microstructures described from early Archean cherts. Two new species are described: Oscillatoriopsis majuscula and O. cuboides; the former is among the largest septate filamentous fossils described from any Proterozoic formation.
Cellularly preserved filamentous and colonial fossil microorganisms have been discovered in bedded carbonaceous cherts from
the Early Archean Apex Basalt and Towers Formation of northwestern Western Australia. The cell types detected suggest that
cyanobacteria, and therefore oxygen-producing photosynthesis, may have been extant as early as 3.3 billion to 3.5 billion
years ago. These fossils are among the oldest now known from the geologic record; their discovery substantiates previous
reports of Early Archean microfossils in Warrawoona Group strata.
There is widespread textural evidence for microbial activity in the cherts of the Early Archean Onverwacht Group. Layers with fine carbonaceous laminations resembling fossil microbial mats are abundant in the cherty metasediments of the predominantly basaltic Hooggenoeg and Kromberg Formations. In rare cases, filamentous microfossils are associated with the laminae. The morphologies of the fossils, as well as the texture of the encompassing laminae suggest an affinity to modern mat-dwelling cyanobacteria or bacteria. A variety of spheroidal and ellipsoidal structures present in cherts of the Hooggenoeg and Kromberg Formations resemble modern coccoidal bacteria and bacterial structures, including spores. The development of spores may have enabled early microorganisms to survive the relatively harsh surficial conditions, including the effects of very large meteorite impacts on the young Earth.
Several categories of biological microstructures 1.9+/- billion years old are here described, illustrated, and referred to a group of early thallophytes that includes the thread bacteria and the blue-green algae. These microstructures were almost surely autotrophic and in the line of evolution toward green-plant photosynthesis, if not themselves oxygen producers. Geochemical evidence has been interpreted by some to imply that the contemporaneous atmosphere was essentially anoxygenic (reducing), and by others to indicate an atmosphere rich in oxygen. These conflicting interpretations may be reconciled by a hypothesis, based on demonstrable fossil organisms, that calls for local centers of biologic oxygen generation.
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.
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.
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