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Marin-Carbonne J, Remusat L, Sforna MC, Thomazo C, Cartigny P, Philippot P. Sulfur isotope's signal of nanopyrites enclosed in 2.7 Ga stromatolitic organic remains reveal microbial sulfate reduction. GEOBIOLOGY 2018; 16:121-138. [PMID: 29380506 DOI: 10.1111/gbi.12275] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2017] [Accepted: 12/18/2017] [Indexed: 06/07/2023]
Abstract
Microbial sulfate reduction (MSR) is thought to have operated very early on Earth and is often invoked to explain the occurrence of sedimentary sulfides in the rock record. Sedimentary sulfides can also form from sulfides produced abiotically during late diagenesis or metamorphism. As both biotic and abiotic processes contribute to the bulk of sedimentary sulfides, tracing back the original microbial signature from the earliest Earth record is challenging. We present in situ sulfur isotope data from nanopyrites occurring in carbonaceous remains lining the domical shape of stromatolite knobs of the 2.7-Gyr-old Tumbiana Formation (Western Australia). The analyzed nanopyrites show a large range of δ34 S values of about 84‰ (from -33.7‰ to +50.4‰). The recognition that a large δ34 S range of 80‰ is found in individual carbonaceous-rich layers support the interpretation that the nanopyrites were formed in microbial mats through MSR by a Rayleigh distillation process during early diagenesis. An active microbial cycling of sulfur during formation of the stromatolite may have facilitated the mixing of different sulfur pools (atmospheric and hydrothermal) and explain the weak mass independent signature (MIF-S) recorded in the Tumbiana Formation. These results confirm that MSR participated actively to the biogeochemical cycling of sulfur during the Neoarchean and support previous models suggesting anaerobic oxidation of methane using sulfate in the Tumbiana environment.
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Affiliation(s)
- J Marin-Carbonne
- Institut de Physique du Globe - Sorbonne Paris Cité, CNRS, Université Paris Diderot, Paris Cedex 05, France
- Univ Lyon- UJM St Etienne, Laboratoire Magmas et Volcans, UCA, CNRS, IRD, UMR 6524, Saint Etienne, France
| | - L Remusat
- Institut de Minéralogie, de Physique des Matériaux, et de Cosmochimie (IMPMC), UPMC, UMR CNRS 7590, UMR IRD 206, Sorbonne Universités - Muséum National d'Histoire Naturelle, Paris, France
| | - M C Sforna
- Institut de Physique du Globe - Sorbonne Paris Cité, CNRS, Université Paris Diderot, Paris Cedex 05, France
- Department of Geology, Palaeobiogeology-Palaeobotany-Palaeopalynology, University of Liège, Liège, Belgium
| | - C Thomazo
- UMR CNRS/uB6282 Biogéosciences, UFR Sciences Vie Terre Environnement Université de Bourgogne Franche Comté, Dijon, France
| | - P Cartigny
- Institut de Physique du Globe - Sorbonne Paris Cité, CNRS, Université Paris Diderot, Paris Cedex 05, France
| | - P Philippot
- Institut de Physique du Globe - Sorbonne Paris Cité, CNRS, Université Paris Diderot, Paris Cedex 05, France
- Géosciences Montpellier, CNRS-UMR 5243, Université de Montpellier, Montpellier Cedex 5, France
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Gallagher M, Turner EC, Kamber BS. In situ trace metal analysis of Neoarchaean--Ordovician shallow-marine microbial-carbonate-hosted pyrites. GEOBIOLOGY 2015; 13:316-339. [PMID: 25917609 DOI: 10.1111/gbi.12139] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2014] [Accepted: 03/16/2015] [Indexed: 06/04/2023]
Abstract
Pre-Cambrian atmospheric and oceanic redox evolutions are expressed in the inventory of redox-sensitive trace metals in marine sedimentary rocks. Most of the currently available information was derived from deep-water sedimentary rocks (black shale/banded iron formation). Many of the studied trace metals (e.g. Mo, U, Ni and Co) are sensitive to the composition of the exposed land surface and prevailing weathering style, and their oceanic inventory ultimately depends on the terrestrial flux. The validity of claims for increased/decreased terrestrial fluxes has remained untested as far as the shallow-marine environment is concerned. Here, the first systematic study of trace metal inventories of the shallow-marine environment by analysis of microbial carbonate-hosted pyrite, from ca. 2.65-0.52 Ga, is presented. A petrographic survey revealed a first-order difference in preservation of early diagenetic pyrite. Microbial carbonates formed before the 2.4 Ga great oxygenation event (GOE) are much richer in pyrite and contain pyrite grains of greater morphological variability but lesser chemical substitution than samples deposited after the GOE. This disparity in pyrite abundance and morphology is mirrored by the qualitative degree of preservation of organic matter (largely as kerogen). Thus, it seems that in microbial carbonates, pyrite formation and preservation were related to presence and preservation of organic C. Several redox-sensitive trace metals show interpretable temporal trends supporting earlier proposals derived from deep-water sedimentary rocks. Most notably, the shallow-water pyrite confirms a rise in the oceanic Mo inventory across the pre-Cambrian-Cambrian boundary, implying the establishment of efficient deep-ocean ventilation. The carbonate-hosted pyrite also confirms the Neoarchaean and early Palaeoproterozoic ocean had higher Ni concentration, which can now more firmly be attributed to a greater proportion of magnesian volcanic rock on land rather than a stronger hydrothermal flux of Ni. Additionally, systematic trends are reported for Co, As, and Zn, relating to terrestrial flux and oceanic productivity.
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Affiliation(s)
- M Gallagher
- Department of Geology, Trinity College Dublin, Dublin, Ireland
| | - E C Turner
- Department of Earth Sciences, Laurentian University, Sudbury, ON, Canada
| | - B S Kamber
- Department of Geology, Trinity College Dublin, Dublin, Ireland
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Abstract
Submarine hydrothermal vents above serpentinite produce chemical potential gradients of aqueous and ionic hydrogen, thus providing a very attractive venue for the origin of life. This environment was most favourable before Earth's massive CO(2) atmosphere was subducted into the mantle, which occurred tens to approximately 100 Myr after the moon-forming impact; thermophile to clement conditions persisted for several million years while atmospheric pCO(2) dropped from approximately 25 bar to below 1 bar. The ocean was weakly acid (pH ∼ 6), and a large pH gradient existed for nascent life with pH 9-11 fluids venting from serpentinite on the seafloor. Total CO(2) in water was significant so the vent environment was not carbon limited. Biologically important phosphate and Fe(II) were somewhat soluble during this period, which occurred well before the earliest record of preserved surface rocks approximately 3.8 billion years ago (Ga) when photosynthetic life teemed on the Earth and the oceanic pH was the modern value of approximately 8. Serpentinite existed by 3.9 Ga, but older rocks that might retain evidence of its presence have not been found. Earth's sequesters extensive evidence of Archaean and younger subducted biological material, but has yet to be exploited for the Hadean record.
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Affiliation(s)
- Norman H Sleep
- Department of Geophysics, Stanford University, Stanford, CA 94305, USA.
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The Role of Purple Sulphur Bacteria in Carbonate Precipitation of Modern and Possibly Early Precambrian Stromatolites. ACTA ACUST UNITED AC 2010. [DOI: 10.1007/978-3-642-10415-2_9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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5
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Abstract
A sparse geological record combined with physics and molecular phylogeny constrains the environmental conditions on the early Earth. The Earth began hot after the moon-forming impact and cooled to the point where liquid water was present in approximately 10 million years. Subsequently, a few asteroid impacts may have briefly heated surface environments, leaving only thermophile survivors in kilometer-deep rocks. A warm 500 K, 100 bar CO(2) greenhouse persisted until subducted oceanic crust sequestered CO(2) into the mantle. It is not known whether the Earth's surface lingered in a approximately 70 degrees C thermophile environment well into the Archaean or cooled to clement or freezing conditions in the Hadean. Recently discovered approximately 4.3 Ga rocks near Hudson Bay may have formed during the warm greenhouse. Alkalic rocks in India indicate carbonate subduction by 4.26 Ga. The presence of 3.8 Ga black shales in Greenland indicates that S-based photosynthesis had evolved in the oceans and likely Fe-based photosynthesis and efficient chemical weathering on land. Overall, mantle derived rocks, especially kimberlites and similar CO(2)-rich magmas, preserve evidence of subducted upper oceanic crust, ancient surface environments, and biosignatures of photosynthesis.
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Affiliation(s)
- Norman H Sleep
- Department of Geophysics, Stanford University, Stanford, CA 94305, USA.
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Mentel M, Martin W. Anaerobic animals from an ancient, anoxic ecological niche. BMC Biol 2010; 8:32. [PMID: 20370917 PMCID: PMC2859860 DOI: 10.1186/1741-7007-8-32] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2010] [Accepted: 04/06/2010] [Indexed: 11/10/2022] Open
Abstract
Tiny marine animals that complete their life cycle in the total absence of light and oxygen are reported by Roberto Danovaro and colleagues in this issue of BMC Biology. These fascinating animals are new members of the phylum Loricifera and possess mitochondria that in electron micrographs look very much like hydrogenosomes, the H2-producing mitochondria found among several unicellular eukaryotic lineages. The discovery of metazoan life in a permanently anoxic and sulphidic environment provides a glimpse of what a good part of Earth's past ecology might have been like in 'Canfield oceans', before the rise of deep marine oxygen levels and the appearance of the first large animals in the fossil record roughly 550-600 million years ago. The findings underscore the evolutionary significance of anaerobic deep sea environments and the anaerobic lifestyle among mitochondrion-bearing cells. They also testify that a fuller understanding of eukaryotic and metazoan evolution will come from the study of modern anoxic and hypoxic habitats.
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Affiliation(s)
- Marek Mentel
- Department of Biochemistry, Faculty of Natural Sciences, Comenius University, Mlynská dolina CH-1, Bratislava, Slovakia
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Lake JA, Skophammer RG, Herbold CW, Servin JA. Genome beginnings: rooting the tree of life. Philos Trans R Soc Lond B Biol Sci 2009; 364:2177-85. [PMID: 19571238 DOI: 10.1098/rstb.2009.0035] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
A rooted tree of life provides a framework to answer central questions about the evolution of life. Here we review progress on rooting the tree of life and introduce a new root of life obtained through the analysis of indels, insertions and deletions, found within paralogous gene sets. Through the analysis of indels in eight paralogous gene sets, the root is localized to the branch between the clade consisting of the Actinobacteria and the double-membrane (Gram-negative) prokaryotes and one consisting of the archaebacteria and the firmicutes. This root provides a new perspective on the habitats of early life, including the evolution of methanogenesis, membranes and hyperthermophily, and the speciation of major prokaryotic taxa. Our analyses exclude methanogenesis as a primitive metabolism, in contrast to previous findings. They parsimoniously imply that the ether archaebacterial lipids are not primitive and that the cenancestral prokaryotic population consisted of organisms enclosed by a single, ester-linked lipid membrane, covered by a peptidoglycan layer. These results explain the similarities previously noted by others between the lipid synthesis pathways in eubacteria and archaebacteria. The new root also implies that the last common ancestor was not hyperthermophilic, although moderate thermophily cannot be excluded.
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Affiliation(s)
- James A Lake
- Department of Molecular, Cellular and Developmental Biology, University of California, Los Angeles, CA 90095, USA.
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Blank CE. Phylogenomic dating--the relative antiquity of archaeal metabolic and physiological traits. ASTROBIOLOGY 2009; 9:193-219. [PMID: 19371161 DOI: 10.1089/ast.2008.0248] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Ancestral trait reconstruction was used to identify the relative ancestry of metabolic and physiological traits in the archaeal domain of life. First, well-resolved phylogenetic trees were inferred with multiple gene sequences obtained from whole genome sequences. Next, metabolic and physiological traits were coded into characters, and ancestral state reconstruction was used to identify ancient and derived traits. Traits inferred to be ancient included sulfur reduction, methanogenesis, and hydrogen oxidation. By using the articulation of the "oxygen age constraint," several other traits were inferred to have arisen at or after 2.32 Ga: aerobic respiration, nitrate reduction, sulfate reduction, thiosulfate reduction, sulfur oxidation, and sulfide oxidation. Complex organic metabolism appeared to be nearly as ancient as autotrophy. Hyperthermophily was ancestral, while hyperacidophily and extreme halophily likely arose after 2.32 Ga. The ancestral euryarchaeote was inferred to have been a hyperthermophilic marine methanogen that lived in a deep-sea hydrothermal vent. In contrast, the ancestral crenarchaeote was most likely a hyperthermophilic sulfur reducer that lived in a slightly acidic terrestrial environment, perhaps a fumarole. Cross-colonization of these habitats may not have occurred until after 2.32 Ga, which suggests that both archaeal lineages exhibited niche specialization on early Earth for a protracted period of time.
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Affiliation(s)
- Carrine E Blank
- Department of Geosciences, University of Montana, Missoula, Montana 59808-1296, USA.
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Evolutionary ecology during the rise of dioxygen in the Earth's atmosphere. Philos Trans R Soc Lond B Biol Sci 2008; 363:2651-64. [PMID: 18468980 PMCID: PMC2606762 DOI: 10.1098/rstb.2008.0018] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Pre-photosynthetic niches were meagre with a productivity of much less than 10(-4) of modern photosynthesis. Serpentinization, arc volcanism and ridge-axis volcanism reliably provided H(2). Methanogens and acetogens reacted CO(2) with H(2) to obtain energy and make organic matter. These skills pre-adapted a bacterium for anoxygenic photosynthesis, probably starting with H(2) in lieu of an oxygen 'acceptor'. Use of ferrous iron and sulphide followed as abundant oxygen acceptors, allowing productivity to approach modern levels. The 'photobacterium' proliferated rooting much of the bacterial tree. Land photosynthetic microbes faced a dearth of oxygen acceptors and nutrients. A consortium of photosynthetic and soil bacteria aided weathering and access to ferrous iron. Biologically enhanced weathering led to the formation of shales and, ultimately, to granitic rocks. Already oxidized iron-poor sedimentary rocks and low-iron granites provided scant oxygen acceptors, as did freshwater in their drainages. Cyanobacteria evolved dioxygen production that relieved them of these vicissitudes. They did not immediately dominate the planet. Eventually, anoxygenic and oxygenic photosynthesis oxidized much of the Earth's crust and supplied sulphate to the ocean. Anoxygenic photosynthesis remained important until there was enough O(2) in downwelling seawater to quantitatively oxidize massive sulphides at mid-ocean ridge axes.
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Glansdorff N, Xu Y, Labedan B. The last universal common ancestor: emergence, constitution and genetic legacy of an elusive forerunner. Biol Direct 2008; 3:29. [PMID: 18613974 PMCID: PMC2478661 DOI: 10.1186/1745-6150-3-29] [Citation(s) in RCA: 186] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2008] [Accepted: 07/09/2008] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Since the reclassification of all life forms in three Domains (Archaea, Bacteria, Eukarya), the identity of their alleged forerunner (Last Universal Common Ancestor or LUCA) has been the subject of extensive controversies: progenote or already complex organism, prokaryote or protoeukaryote, thermophile or mesophile, product of a protracted progression from simple replicators to complex cells or born in the cradle of "catalytically closed" entities? We present a critical survey of the topic and suggest a scenario. RESULTS LUCA does not appear to have been a simple, primitive, hyperthermophilic prokaryote but rather a complex community of protoeukaryotes with a RNA genome, adapted to a broad range of moderate temperatures, genetically redundant, morphologically and metabolically diverse. LUCA's genetic redundancy predicts loss of paralogous gene copies in divergent lineages to be a significant source of phylogenetic anomalies, i.e. instances where a protein tree departs from the SSU-rRNA genealogy; consequently, horizontal gene transfer may not have the rampant character assumed by many. Examining membrane lipids suggest LUCA had sn1,2 ester fatty acid lipids from which Archaea emerged from the outset as thermophilic by "thermoreduction," with a new type of membrane, composed of sn2,3 ether isoprenoid lipids; this occurred without major enzymatic reconversion. Bacteria emerged by reductive evolution from LUCA and some lineages further acquired extreme thermophily by convergent evolution. This scenario is compatible with the hypothesis that the RNA to DNA transition resulted from different viral invasions as proposed by Forterre. Beyond the controversy opposing "replication first" to metabolism first", the predictive arguments of theories on "catalytic closure" or "compositional heredity" heavily weigh in favour of LUCA's ancestors having emerged as complex, self-replicating entities from which a genetic code arose under natural selection. CONCLUSION Life was born complex and the LUCA displayed that heritage. It had the "body "of a mesophilic eukaryote well before maturing by endosymbiosis into an organism adapted to an atmosphere rich in oxygen. Abundant indications suggest reductive evolution of this complex and heterogeneous entity towards the "prokaryotic" Domains Archaea and Bacteria. The word "prokaryote" should be abandoned because epistemologically unsound. REVIEWERS This article was reviewed by Anthony Poole, Patrick Forterre, and Nicolas Galtier.
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Affiliation(s)
- Nicolas Glansdorff
- JM Wiame Research Institute for Microbiology and Vrije Universiteit Brussel, 1 ave E. Gryzon, B-1070 Brussels, Belgium.
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Kamber BS, Whitehouse MJ. Micro-scale sulphur isotope evidence for sulphur cycling in the late Archean shallow ocean. GEOBIOLOGY 2007; 5:5-17. [PMID: 36298872 DOI: 10.1111/j.1472-4669.2006.00091.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
We report in situ secondary ion mass spectrometer sulphur isotope data for sedimentary pyrite from the 2.52 Ga Upper Campbellrand Subgroup, Transvaal, South Africa. The analysed sedimentary rocks represent a transition in depositional environment from very shallow to deeper water, with strong sedimentological, facies distribution and geochemical evidence for the presence of a shallow redox chemocline. Data were obtained directly in thin section in order to preserve petrographic context. They reveal a very large extent of isotopic fractionation both in mass-independent (MIF) and in mass-dependent fractionation (MDF) on unprecedentedly small scale. In the shallow-water microbical carbonates, three types of pyrite were identified. The texturally oldest pyrite is found as small, isotopically little fractionated grains in the microbial mats. Large (several mm) spheroidal pyrite concretions, which postdate the mat pyrite, record strong evidence for an origin by bacterial sulphate reduction. Rare pyrite surrounding late fenestral calcite is inferred to have formed from recycled bacterial pyrite on account of the slope of its correlated MIF and MDF array. This latter type of pyrite was also found in an interbedded black shale and a carbonate laminite. In a deeper water chert, pyrite with very heavy sulphur indicates partial to almost complete sulphate reduction across a chemocline whose existence has been inferred independently. The combined picture from all the studied samples is that of a sulphate availability-limited environment, in which sulphur was cycled between reservoirs according to changing redox conditions established across the chemocline. Cycling apparently reduced the extent of recorded sulphur isotope fractionation relative to what is expected from projection in the correlated MIF and MDF arrays. This is consistent with regionally relatively high free oxygen concentrations in the shallow water, permitting locally strong MDF. Our new observations add to the growing evidence for a complex, fluctuating evolution of free atmospheric oxygen between c. 2.7 Ga and 2.3 Ga.
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Affiliation(s)
- B S Kamber
- Department of Earth Sciences, Laurentian University, 935 Ramsey Lake Road, Sudbury, ON P3E 2C6, Canada
| | - M J Whitehouse
- Swedish Museum of Natural History, Box 50007, SE-104 05 Stockholm, Sweden
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Pye K, Blott SJ, Croft DJ, Carter JF. Forensic comparison of soil samples: Assessment of small-scale spatial variability in elemental composition, carbon and nitrogen isotope ratios, colour, and particle size distribution. Forensic Sci Int 2006. [DOI: 10.1016/j.forsciint.2005.11.008] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Brasier M, McLoughlin N, Green O, Wacey D. A fresh look at the fossil evidence for early Archaean cellular life. Philos Trans R Soc Lond B Biol Sci 2006; 361:887-902. [PMID: 16754605 PMCID: PMC1578727 DOI: 10.1098/rstb.2006.1835] [Citation(s) in RCA: 213] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The rock record provides us with unique evidence for testing models as to when and where cellular life first appeared on Earth. Its study, however, requires caution. The biogenicity of stromatolites and 'microfossils' older than 3.0 Gyr should not be accepted without critical analysis of morphospace and context, using multiple modern techniques, plus rejection of alternative non-biological (null) hypotheses. The previous view that the co-occurrence of biology-like morphology and carbonaceous chemistry in ancient, microfossil-like objects is a presumptive indicator of biogenicity is not enough. As with the famous Martian microfossils, we need to ask not 'what do these structures remind us of?', but 'what are these structures?' Earth's oldest putative 'microfossil' assemblages within 3.4-3.5 Gyr carbonaceous cherts, such as the Apex Chert, are likewise self-organizing structures that do not pass tests for biogenicity. There is a preservational paradox in the fossil record prior to ca 2.7 Gyr: suitable rocks (e.g. isotopically light carbonaceous cherts) are widely present, but signals of life are enigmatic and hard to decipher. One new approach includes detailed mapping of well-preserved sandstone grains in the ca 3.4 Gyr Strelley Pool Chert. These can contain endolithic microtubes showing syngenicity, grain selectivity and several levels of geochemical processing. Preliminary studies invite comparison with a class of ambient inclusion trails of putative microbial origin and with the activities of modern anaerobic proteobacteria and volcanic glass euendoliths.
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Affiliation(s)
- Martin Brasier
- Oxford University, Department of Earth Sciences, Parks Road, Oxford OX1 3PR, UK.
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Abstract
Earth is over 4,500 million years old. Massive bombardment of the planet took place for the first 500-700 million years, and the largest impacts would have been capable of sterilizing the planet. Probably until 4,000 million years ago or later, occasional impacts might have heated the ocean over 100 degrees C. Life on Earth dates from before about 3,800 million years ago, and is likely to have gone through one or more hot-ocean 'bottlenecks'. Only hyperthermophiles (organisms optimally living in water at 80-110 degrees C) would have survived. It is possible that early life diversified near hydrothermal vents, but hypotheses that life first occupied other pre-bottleneck habitats are tenable (including transfer from Mars on ejecta from impacts there). Early hyperthermophile life, probably near hydrothermal systems, may have been non-photosynthetic, and many housekeeping proteins and biochemical processes may have an original hydrothermal heritage. The development of anoxygenic and then oxygenic photosynthesis would have allowed life to escape the hydrothermal setting. By about 3,500 million years ago, most of the principal biochemical pathways that sustain the modern biosphere had evolved, and were global in scope.
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Affiliation(s)
- E G Nisbet
- Department of Geology, University of London, Egham, UK
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