Benthos

The Description for this book, Earth's Earliest Biosphere: Its Origin and Evolution, will be forthcoming.

@book{openalexw2026796374,
    author = "Schopf, J. William",
    title = "Earth's earliest biosphere: its origin and evolution",
    year = "1983",
    abstract = "The Description for this book, Earth's Earliest Biosphere: Its Origin and Evolution, will be forthcoming.",
    openalex = "W2026796374"
}

@incollection{walter1983archean1,
    author = "Walter, M. R",
    editor = "Schopf, J. W.",
    title = "Archean Stromatolites: Evidence of the Earth's Earliest Benthos",
    year = "1983",
    booktitle = "Earth's Earliest Biosphere",
    publisher = "Its Origin and Evolution: Princeton, Princeton University Press, p. 187-213",
    note = "talkorigins\_source = {true}; raw\_reference = {Walter, M. R., 1983, Archean Stromatolites: Evidence of the Earth's Earliest Benthos, in Schopf, J. W., ed., Earth's Earliest Biosphere: Its Origin and Evolution: Princeton, Princeton University Press, p. 187-213.}"
}

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.

@article{doi101126science2605108640,
    author = "Schopf, J. William",
    title = "Microfossils of the Early Archean Apex Chert: New Evidence of the Antiquity of Life",
    year = "1993",
    journal = "Science",
    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.",
    url = "https://doi.org/10.1126/science.260.5108.640",
    doi = "10.1126/science.260.5108.640",
    openalex = "W2163006245",
    references = "doi1010160301926888900058, doi101016030192689290074x, doi101017cbo9780511601064002, doi101038284443a0, doi101126science11539686, doi101126science1473658563, doi101126science148366627, doi1023071218353, openalexw2326083785, openalexw2336572712, vidal1985earths"
}

@incollection{tewari1998earliest,
    author = "Tewari, V. C.",
    title = "Earliest Microbes on Earth and Possible Occurrence of Stromatolites on Mars",
    year = "1998",
    booktitle = "Exobiology: Matter, Energy, and Information in the Origin and Evolution of Life in the Universe",
    url = "https://doi.org/10.1007/978-94-011-5056-9\_37",
    doi = "10.1007/978-94-011-5056-9\_37",
    openalex = "W1036388724",
    pages = "261-265",
    references = "doi1010029780470514986ch11, doi101016027311779290162q, doi101038333313a0, doi1010970000044119570700000025, doi101126science2605108640, doi101126science2735277924, openalexw1519179908, openalexw2167659733, openalexw2947283578, tewari1998earliest"
}

Stromatolites are attached, lithified sedimentary growth structures, accretionary away from a point or limited surface of initiation. Though the accretion process is commonly regarded to result from the sediment trapping or precipitation-inducing activities of microbial mats, little evidence of this process is preserved in most Precambrian stromatolites. The successful study and interpretation of stromatolites requires a process-based approach, oriented toward deconvolving the replacement textures of ancient stromatolites. The effects of diagenetic recrystallization first must be accounted for, followed by analysis of lamination textures and deduction of possible accretion mechanisms. Accretion hypotheses can be tested using numerical simulations based on modem stromatolite growth processes. Application of this approach has shown that stromatolites were originally formed largely through in situ precipitation of laminae during Archean and older Proterozoic times, but that younger Proterozoic stromatolites grew largely through the accretion of carbonate sediments, most likely through the physical process of microbial trapping and binding. This trend most likely reflects long-term evolution of the earth's environment rather than microbial communities.

@article{doi101146annurevearth271313,
    author = "Grotzinger, J. P. and Knoll, Andrew H.",
    title = "STROMATOLITES IN PRECAMBRIAN CARBONATES: Evolutionary Mileposts or Environmental Dipsticks?",
    year = "1999",
    journal = "Annual Review of Earth and Planetary Sciences",
    abstract = "Stromatolites are attached, lithified sedimentary growth structures, accretionary away from a point or limited surface of initiation. Though the accretion process is commonly regarded to result from the sediment trapping or precipitation-inducing activities of microbial mats, little evidence of this process is preserved in most Precambrian stromatolites. The successful study and interpretation of stromatolites requires a process-based approach, oriented toward deconvolving the replacement textures of ancient stromatolites. The effects of diagenetic recrystallization first must be accounted for, followed by analysis of lamination textures and deduction of possible accretion mechanisms. Accretion hypotheses can be tested using numerical simulations based on modem stromatolite growth processes. Application of this approach has shown that stromatolites were originally formed largely through in situ precipitation of laminae during Archean and older Proterozoic times, but that younger Proterozoic stromatolites grew largely through the accretion of carbonate sediments, most likely through the physical process of microbial trapping and binding. This trend most likely reflects long-term evolution of the earth's environment rather than microbial communities.",
    url = "https://doi.org/10.1146/annurev.earth.27.1.313",
    doi = "10.1146/annurev.earth.27.1.313",
    openalex = "W2142539052",
    references = "doi101007978364276884234, doi101016001670379390347y, doi101016030192688590066x, doi101016s0070457108711373, doi101016s0070457108711567, doi101016s0070457108x70451, doi101017cbo9780511599798, doi101017cbo9780511601064, doi101038324055a0, doi101038368046a0, doi101038383423a0, doi101086628623, doi101103physrevb275686, doi101103physrevlett56889, doi101126science11539686, doi101126science1585174, doi101126science1744011825, doi101139e79088, doi101146annurevecolsys281129, doi1023073514631, doi1023073514973"
}

Mass-independent isotopic signatures for delta(33)S, delta(34)S, and delta(36)S from sulfide and sulfate in Precambrian rocks indicate that a change occurred in the sulfur cycle between 2090 and 2450 million years ago (Ma). Before 2450 Ma, the cycle was influenced by gas-phase atmospheric reactions. These atmospheric reactions also played a role in determining the oxidation state of sulfur, implying that atmospheric oxygen partial pressures were low and that the roles of oxidative weathering and of microbial oxidation and reduction of sulfur were minimal. Atmospheric fractionation processes should be considered in the use of sulfur isotopes to study the onset and consequences of microbial fractionation processes in Earth's early history.

@article{doi101126science2895480756,
    author = "Farquhar, James and Bao, Huiming and Thiemens, M. H.",
    title = "Atmospheric Influence of Earth's Earliest Sulfur Cycle",
    year = "2000",
    journal = "Science",
    abstract = "Mass-independent isotopic signatures for delta(33)S, delta(34)S, and delta(36)S from sulfide and sulfate in Precambrian rocks indicate that a change occurred in the sulfur cycle between 2090 and 2450 million years ago (Ma). Before 2450 Ma, the cycle was influenced by gas-phase atmospheric reactions. These atmospheric reactions also played a role in determining the oxidation state of sulfur, implying that atmospheric oxygen partial pressures were low and that the roles of oxidative weathering and of microbial oxidation and reduction of sulfur were minimal. Atmospheric fractionation processes should be considered in the use of sulfur isotopes to study the onset and consequences of microbial fractionation processes in Earth's early history.",
    url = "https://doi.org/10.1126/science.289.5480.756",
    doi = "10.1126/science.289.5480.756",
    openalex = "W2081383679",
    references = "doi1010160016703783901515, doi1010160301926887900015, doi101016s0012821x68800597, doi101029jz070i014p03475, doi101029rg020i002p00280, doi10103835003517, doi101126science27653161217, doi101126science28253931459, doi101126science2835400341, openalexw1569598449"
}

Mass-independent fractionation (MIF) of sulfur isotopes has been reported in sediments of Archean and Early Proterozoic Age (> 2.3 Ga) but not in younger rocks. The only fractionation mechanism that is consistent with the data on all four sulfur isotopes involves atmospheric photochemical reactions such as SO2 photolysis. We have used a one-dimensional photochemical model to investigate how the isotopic fractionation produced during SO2 photolysis would have been transferred to other gaseous and particulate sulfur-bearing species in both low-O2 and high-O2 atmospheres. We show that in atmospheres with O2 concentrations or = 10(-5) PAL, all sulfur-bearing species would have passed through the oceanic sulfate reservoir before being incorporated into sediments, so any signature of MIF would have been lost. We conclude that the atmospheric O2 concentration must have been < 10(-5) PAL prior to 2.3 Ga.

@article{doi101089153110702753621321,
    author = "Pavlov, Alexander A. and Kasting, James F.",
    title = "Mass-Independent Fractionation of Sulfur Isotopes in Archean Sediments: Strong Evidence for an Anoxic Archean Atmosphere",
    year = "2002",
    journal = "Astrobiology",
    abstract = "Mass-independent fractionation (MIF) of sulfur isotopes has been reported in sediments of Archean and Early Proterozoic Age (> 2.3 Ga) but not in younger rocks. The only fractionation mechanism that is consistent with the data on all four sulfur isotopes involves atmospheric photochemical reactions such as SO2 photolysis. We have used a one-dimensional photochemical model to investigate how the isotopic fractionation produced during SO2 photolysis would have been transferred to other gaseous and particulate sulfur-bearing species in both low-O2 and high-O2 atmospheres. We show that in atmospheres with O2 concentrations or = 10(-5) PAL, all sulfur-bearing species would have passed through the oceanic sulfate reservoir before being incorporated into sediments, so any signature of MIF would have been lost. We conclude that the atmospheric O2 concentration must have been < 10(-5) PAL prior to 2.3 Ga.",
    url = "https://doi.org/10.1089/153110702753621321",
    doi = "10.1089/153110702753621321",
    openalex = "W2054861741",
    references = "doi1010160301926887900015, doi101016s0012821x03002966, doi101029jd094id13p16287, doi10103823005, doi101126science11536547, doi101126science28554301033, doi101126science2895480756, doi1015159780691220239, doi105860choice333969, openalexw1586821315"
}

@misc{crossref2005benthos,
    title = "Benthos",
    year = "2005",
    booktitle = "Van Nostrand's Scientific Encyclopedia",
    url = "https://doi.org/10.1002/0471743984.vse1014",
    doi = "10.1002/0471743984.vse1014"
}

Evidence for the existence of life during the Archaean segment of Earth history (more than 2500 Myr ago) is summarized. Data are presented for 48 Archaean deposits reported to contain biogenic stromatolites, for 14 such units reported to contain 40 morphotypes of putative microfossils, and for 13 especially ancient, 3200-3500 Myr old geologic units for which available organic geochemical data are also summarized. These compilations support the view that life's existence dates from more than or equal to 3500 Myr ago.

@article{doi101098rstb20061834,
    author = "Schopf, J. William",
    title = "Fossil evidence of Archaean life",
    year = "2006",
    journal = "Philosophical Transactions of the Royal Society B Biological Sciences",
    abstract = "Evidence for the existence of life during the Archaean segment of Earth history (more than 2500 Myr ago) is summarized. Data are presented for 48 Archaean deposits reported to contain biogenic stromatolites, for 14 such units reported to contain 40 morphotypes of putative microfossils, and for 13 especially ancient, 3200-3500 Myr old geologic units for which available organic geochemical data are also summarized. These compilations support the view that life's existence dates from more than or equal to 3500 Myr ago.",
    url = "https://doi.org/10.1098/rstb.2006.1834",
    doi = "10.1098/rstb.2006.1834",
    openalex = "W2159170019",
    references = "doi1010160012825273900020, doi101016030192689500018z, doi101016b0080437516071036, doi101016s014663809900145x, doi101017cbo9780511601064, doi101038416073a, doi101038416076a, doi101089ast20055333, doi101111j136530911989tb00615x, doi101126science11539686, doi101126science2605108640, doi101139e79088, doi101146annurevearth271313, doi102475ajs26791017, openalexw109813744, openalexw1552860341, openalexw624811619"
}

@misc{crossref2007benthos,
    title = "Benthos",
    year = "2007",
    booktitle = "Hawley's Condensed Chemical Dictionary",
    url = "https://doi.org/10.1002/9780470114735.hawley01649",
    doi = "10.1002/9780470114735.hawley01649",
    pages = "132-132"
}

Although cyanobacteria are the dominant primary producers in modern stromatolites and other microbialites, the oldest stromatolites pre-date geochemical evidence for oxygenic photosynthesis and cyanobacteria in the rock record. As a step towards the development of laboratory models of stromatolite growth, we tested the potential of a metabolically ancient anoxygenic photosynthetic bacterium to build stromatolites. This organism, Rhodopseudomonas palustris, stimulates the precipitation of calcite in solutions already highly saturated with respect to calcium carbonate, and greatly facilitates the incorporation of carbonate grains into proto-lamina (i.e. crusts). The appreciable stimulation of the growth of proto-lamina by a nonfilamentous anoxygenic microbe suggests that similar microbes may have played a greater role in the formation of Archean stromatolites than previously assumed.

@article{doi101111j14724669200700104x,
    author = "Bosak, Tanja and Greene, Sarah E. and Newman, Dianne K.",
    title = "A likely role for anoxygenic photosynthetic microbes in the formation of ancient stromatolites",
    year = "2007",
    journal = "Geobiology",
    abstract = "Although cyanobacteria are the dominant primary producers in modern stromatolites and other microbialites, the oldest stromatolites pre-date geochemical evidence for oxygenic photosynthesis and cyanobacteria in the rock record. As a step towards the development of laboratory models of stromatolite growth, we tested the potential of a metabolically ancient anoxygenic photosynthetic bacterium to build stromatolites. This organism, Rhodopseudomonas palustris, stimulates the precipitation of calcite in solutions already highly saturated with respect to calcium carbonate, and greatly facilitates the incorporation of carbonate grains into proto-lamina (i.e. crusts). The appreciable stimulation of the growth of proto-lamina by a nonfilamentous anoxygenic microbe suggests that similar microbes may have played a greater role in the formation of Archean stromatolites than previously assumed.",
    url = "https://doi.org/10.1111/j.1472-4669.2007.00104.x",
    doi = "10.1111/j.1472-4669.2007.00104.x",
    openalex = "W2137859535",
    references = "doi101016jtim200507008, doi10103835023158, doi101038nature04764, doi101126science1078265, doi101126science2605108640, doi101126science28554301033, doi101126science2895480756, doi101146annurevearth271313, openalexw2026796374, openalexw2738937425"
}

@article{schopf2007earliest,
    author = "Schopf, J. William and Walter, Malcolm R. and Ruiji, Cao",
    title = "Earliest evidence of life on earth",
    year = "2007",
    journal = "Precambrian Research",
    url = "https://doi.org/10.1016/j.precamres.2007.05.001",
    doi = "10.1016/j.precamres.2007.05.001",
    number = "3-4",
    openalex = "W2070923072",
    pages = "139-140",
    volume = "158",
    references = "doi101038284441a0, doi101038284443a0, doi101038416073a, doi101038nature02888, doi101038nature04764, doi101098rstb20061834, doi101126science2605108640, doi1011300016760619991111256oogcsi23co2, doi101146annurevearth271313, openalexw566083668"
}

@article{schopf2007evidence,
    author = "Schopf, J. William and Kudryavtsev, Anatoliy B. and Czaja, Andrew D. and Tripathi, Abhishek B.",
    title = "Evidence of Archean life: Stromatolites and microfossils",
    year = "2007",
    journal = "Precambrian Research",
    url = "https://doi.org/10.1016/j.precamres.2007.04.009",
    doi = "10.1016/j.precamres.2007.04.009",
    number = "3-4",
    openalex = "W2159725055",
    pages = "141-155",
    volume = "158",
    references = "doi1010160012825273900020, doi1010160034666775900056, doi101016b0080437516071036, doi101017cbo9780511601064, doi101038416073a, doi101038416076a, doi101038nature04764, doi101111j136530911989tb00615x, doi101126science1473658563, doi101126science2605108640, doi101139e79088, doi101146annurevearth271313, openalexw1552860341, openalexw2326083785, openalexw2622880403"
}

Conditions at the surface of the young (Hadean and early Archean) Earth were suitable for the emergence and evolution of life. After an initial hot period, surface temperatures in the late Hadean may have been clement beneath an atmosphere containing greenhouse gases over an ocean-dominated planetary surface. The first crust was mafic and it internally melted repeatedly to produce the felsic rocks that crystallized the Jack Hills zircons. This crust was destabilized during late heavy bombardment. Plate tectonics probably started soon after and had produced voluminous continental crust by the mid Archean, but ocean volumes were sufficient to submerge much of this crust. In the Hadean and early Archean, hydrothermal systems around abundant komatiitic volcanism may have provided suitable sites to host the earliest living communities and for the evolution of key enzymes. Evidence from the Isua Belt, Greenland, suggests life was present by 3.8 Gya, and by the mid-Archean, the geological record both in the Pilbara in Western Australia and the Barberton Greenstone Belt in South Africa shows that microbial life was abundant, probably using anoxygenic photosynthesis. By the late Archean, oxygenic photosynthesis had evolved, transforming the atmosphere and permitting the evolution of eukaryotes.

@article{doi101146annurevearth042711105316,
    author = "Arndt, Nicholas and Nisbet, Euan",
    title = "Processes on the Young Earth and the Habitats of Early Life",
    year = "2012",
    journal = "Annual Review of Earth and Planetary Sciences",
    abstract = "Conditions at the surface of the young (Hadean and early Archean) Earth were suitable for the emergence and evolution of life. After an initial hot period, surface temperatures in the late Hadean may have been clement beneath an atmosphere containing greenhouse gases over an ocean-dominated planetary surface. The first crust was mafic and it internally melted repeatedly to produce the felsic rocks that crystallized the Jack Hills zircons. This crust was destabilized during late heavy bombardment. Plate tectonics probably started soon after and had produced voluminous continental crust by the mid Archean, but ocean volumes were sufficient to submerge much of this crust. In the Hadean and early Archean, hydrothermal systems around abundant komatiitic volcanism may have provided suitable sites to host the earliest living communities and for the evolution of key enzymes. Evidence from the Isua Belt, Greenland, suggests life was present by 3.8 Gya, and by the mid-Archean, the geological record both in the Pilbara in Western Australia and the Barberton Greenstone Belt in South Africa shows that microbial life was abundant, probably using anoxygenic photosynthesis. By the late Archean, oxygenic photosynthesis had evolved, transforming the atmosphere and permitting the evolution of eukaryotes.",
    url = "https://doi.org/10.1146/annurev-earth-042711-105316",
    doi = "10.1146/annurev-earth-042711-105316",
    openalex = "W2156233967",
    references = "doi101016jprecamres200810011, doi101038nature08793"
}

unconformably overlying 2.21-1.79 Ga Wyloo Group in the Ashburton Basin followed the Ophthalmian Orogeny, and all of these rocks were deformed by the Panhandle (c. 2 Ga) and Capricorn (c. 1.78 Ga) orogenies.

@article{doi1018814epiiugs2012v35i1028,
    author = "Hickman, Arthur H. and Kranendonk, Martin J. Van",
    title = "Early Earth evolution: evidence from the 3.5–1.8 Ga geological history of the Pilbara region of Western Australia",
    year = "2012",
    journal = "Episodes",
    abstract = "unconformably overlying 2.21-1.79 Ga Wyloo Group in the Ashburton Basin followed the Ophthalmian Orogeny, and all of these rocks were deformed by the Panhandle (c. 2 Ga) and Capricorn (c. 1.78 Ga) orogenies.",
    url = "https://doi.org/10.18814/epiiugs/2012/v35i1/028",
    doi = "10.18814/epiiugs/2012/v35i1/028",
    openalex = "W1523338647",
    references = "doi101016s001670370200950x, doi101016s0016703781800026, doi101038416076a, doi101038nature04764, doi101089153110702753621321, doi101093petrology41121653, doi101126science1140325, doi101126science2895480756, doi1011300016760619991111256oogcsi23co2, kaufman2007late"
}

Stromatolites document microbial interactions with sediments and flowing water throughout recorded Earth history and have the potential to illuminate the long-term history of life and environments. Modern stromatolites, however, provide analogs to only a small subset of the structures preserved in Archean and Proterozoic carbonates. Thus, interpretations of secular trends in the shapes and textures of ancient columnar stromatolites require nonuniformitarian, scale-dependent models of microbial responses to nutrient availability, seawater chemistry, influx of sediment grains, shear, and burial. Models that integrate stromatolite scales, macroscopic organization, and shapes could also help test the biogenicity of the oldest stromatolites and other structures whose petrographic fabrics do not preserve direct evidence of microbial activity. An improved understanding of stromatolite morphogenesis in the presence of oxygenic and anoxygenic microbial mats may illuminate the diversity of microbial metabolisms that contributed to stromatolite growth in early oceans.

@article{doi101146annurevearth042711105327,
    author = "Bosak, Tanja and Knoll, Andrew H. and Petroff, Alexander P.",
    title = "The Meaning of Stromatolites",
    year = "2013",
    journal = "Annual Review of Earth and Planetary Sciences",
    abstract = "Stromatolites document microbial interactions with sediments and flowing water throughout recorded Earth history and have the potential to illuminate the long-term history of life and environments. Modern stromatolites, however, provide analogs to only a small subset of the structures preserved in Archean and Proterozoic carbonates. Thus, interpretations of secular trends in the shapes and textures of ancient columnar stromatolites require nonuniformitarian, scale-dependent models of microbial responses to nutrient availability, seawater chemistry, influx of sediment grains, shear, and burial. Models that integrate stromatolite scales, macroscopic organization, and shapes could also help test the biogenicity of the oldest stromatolites and other structures whose petrographic fabrics do not preserve direct evidence of microbial activity. An improved understanding of stromatolite morphogenesis in the presence of oxygenic and anoxygenic microbial mats may illuminate the diversity of microbial metabolisms that contributed to stromatolite growth in early oceans.",
    url = "https://doi.org/10.1146/annurev-earth-042711-105327",
    doi = "10.1146/annurev-earth-042711-105327",
    openalex = "W2140338234",
    references = "doi101007978364276884234, doi101007s1121400792921, doi1010160012825273900020, doi101016jtim200507008, doi101016s0070457108711567, doi101017cbo9780511599798, doi101017s0022336000030663, doi101038nature04764, doi101046j13653091200000003x, doi10106312808215, doi101103physrevlett471400, doi101103physrevlett56889, doi101111j136530911989tb00615x, doi101111j14724669200700104x, doi101139e79088, doi101146annurevearth271313, doi101680doms25844, doi1023073514674, doi102475ajs26791017, ruiji2011microbiota"
}

@incollection{crossref2014benthos,
    title = "benthos",
    year = "2014",
    booktitle = "Dictionary Geotechnical Engineering/Wörterbuch GeoTechnik",
    url = "https://doi.org/10.1007/978-3-642-41714-6\_21408",
    doi = "10.1007/978-3-642-41714-6\_21408",
    pages = "122-122"
}

@incollection{johannesson2014rare,
    author = "Johannesson, Karen H. and Telfeyan, Katherine and Chevis, Darren A. and Rosenheim, Brad E. and Leybourne, Matthew I.",
    title = "Rare Earth Elements in Stromatolites—1. Evidence that Modern Terrestrial Stromatolites Fractionate Rare Earth Elements During Incorporation from Ambient Waters",
    year = "2014",
    booktitle = "Modern Approaches in Solid Earth Sciences",
    url = "https://doi.org/10.1007/978-94-007-7615-9\_14",
    doi = "10.1007/978-94-007-7615-9\_14",
    openalex = "W140988825",
    pages = "385-411",
    references = "doi101007s004100050159, doi1010160016703764901292, doi1010160031920186900932, doi1010160301926895000879, doi101016jearscirev200810005, doi101038296214a0, doi101093petrology3251021, doi101146annurevmi49100195003431, openalexw1624806571, openalexw2508765924"
}

@inproceedings{andwilmeth2017gas,
    author = "Wilmeth, Dylan T. and Corsetti, Frank A. and Berelson, William M. and Beukes, Nicolas J. and Awramik, Stanley M. and Petryshyn, Victoria A.",
    title = "GAS PRODUCTION WITHIN ARCHEAN STROMATOLITES: EVIDENCE FOR ANCIENT MICROBIAL METABOLISMS",
    year = "2017",
    booktitle = "Geological Society of America Abstracts with Programs",
    url = "https://doi.org/10.1130/abs/2017am-298533",
    doi = "10.1130/abs/2017am-298533",
    openalex = "W2773994121"
}

The Archean era (4 to 2.5 billion years ago, Ga) yielded rocks that include the oldest conclusive traces of life as well as many controversial occurrences. Carbonaceous matter is found in rocks as old as 3.95 Ga, but the oldest (graphitic) forms may be abiogenic. Due to the metamorphism that altered the molecular composition of all Archean organic matter, non-biological carbonaceous compounds such as those that could have formed in seafloor hydrothermal systems are difficult to rule out. Benthic microbial mats as old as 3.47 Ga are supported by the record of organic laminae in stromatolitic (layered) carbonates, in some stromatolitic siliceous sinters, and in some siliciclastic sediments. In these deposits, organic matter rarely preserved fossil cellular structures (e.g., cell walls) or ultrastructures (e.g., external sheaths) and its simple textures are difficult to attribute to either microfossils or coatings of cell-mimicking mineral templates. This distinction will require future nanoscale studies. Filamentous-sheath microfossils occur in 2.52 Ga rocks, and may have altered counterparts as old as 3.47 Ga. Surprisingly large spheres and complex organic lenses occur in rocks as old as 3.22 Ga and ~ 3.4 Ga, respectively, and represent the best candidates for the oldest microfossils. Titaniferous microtubes in volcanic or volcanoclastic rocks inferred as microbial trace fossils have been reevaluated as metamorphic or magmatic textures. Microbially-induced mineralization is supported by CaCO3 nanostructures in 2.72 Ga stromatolites. Sulfides 3.48 Ga and younger bear S-isotope ratios indicative of microbial sulfate reduction. Ferruginous conditions may have fueled primary production via anoxygenic photosynthesis–as suggested by Fe-isotope ratios–possibly as early as 3.77 Ga. Microbial methanogenesis and (likely anaerobic) methane oxidation are indicated by C-isotope ratios as early as 3.0 Ga and ~ 2.72 Ga, respectively. Photosynthetic production of O2 most likely started between 3.2 and 2.8 Ga, i.e. well before the Great Oxidation Event (2.45–2.31 Ga), as indicated by various inorganic tracers of oxidation reactions and consistent with morphology of benthic deposits and evidence for aerobic N metabolism in N-isotope ratios at ~ 2.7 Ga. This picture of a wide diversification of the microbial biosphere during the Archean has largely been derived of bulk-rock geochemistry and petrography, supported by a recent increase in studied sample numbers and in constraints on their environments of deposition. Use of high-resolution microscopy and micro- to nanoscale analyses opens avenues to (re)assess and decipher the most ancient traces of life.

@article{doi101016jearscirev2020103296,
    author = "Lepot, Kévin",
    title = "Signatures of early microbial life from the Archean (4 to 2.5 Ga) eon",
    year = "2020",
    journal = "Earth-Science Reviews",
    abstract = "The Archean era (4 to 2.5 billion years ago, Ga) yielded rocks that include the oldest conclusive traces of life as well as many controversial occurrences. Carbonaceous matter is found in rocks as old as 3.95 Ga, but the oldest (graphitic) forms may be abiogenic. Due to the metamorphism that altered the molecular composition of all Archean organic matter, non-biological carbonaceous compounds such as those that could have formed in seafloor hydrothermal systems are difficult to rule out. Benthic microbial mats as old as 3.47 Ga are supported by the record of organic laminae in stromatolitic (layered) carbonates, in some stromatolitic siliceous sinters, and in some siliciclastic sediments. In these deposits, organic matter rarely preserved fossil cellular structures (e.g., cell walls) or ultrastructures (e.g., external sheaths) and its simple textures are difficult to attribute to either microfossils or coatings of cell-mimicking mineral templates. This distinction will require future nanoscale studies. Filamentous-sheath microfossils occur in 2.52 Ga rocks, and may have altered counterparts as old as 3.47 Ga. Surprisingly large spheres and complex organic lenses occur in rocks as old as 3.22 Ga and \textasciitilde\ 3.4 Ga, respectively, and represent the best candidates for the oldest microfossils. Titaniferous microtubes in volcanic or volcanoclastic rocks inferred as microbial trace fossils have been reevaluated as metamorphic or magmatic textures. Microbially-induced mineralization is supported by CaCO3 nanostructures in 2.72 Ga stromatolites. Sulfides 3.48 Ga and younger bear S-isotope ratios indicative of microbial sulfate reduction. Ferruginous conditions may have fueled primary production via anoxygenic photosynthesis–as suggested by Fe-isotope ratios–possibly as early as 3.77 Ga. Microbial methanogenesis and (likely anaerobic) methane oxidation are indicated by C-isotope ratios as early as 3.0 Ga and \textasciitilde\ 2.72 Ga, respectively. Photosynthetic production of O2 most likely started between 3.2 and 2.8 Ga, i.e. well before the Great Oxidation Event (2.45–2.31 Ga), as indicated by various inorganic tracers of oxidation reactions and consistent with morphology of benthic deposits and evidence for aerobic N metabolism in N-isotope ratios at \textasciitilde\ 2.7 Ga. This picture of a wide diversification of the microbial biosphere during the Archean has largely been derived of bulk-rock geochemistry and petrography, supported by a recent increase in studied sample numbers and in constraints on their environments of deposition. Use of high-resolution microscopy and micro- to nanoscale analyses opens avenues to (re)assess and decipher the most ancient traces of life.",
    url = "https://doi.org/10.1016/j.earscirev.2020.103296",
    doi = "10.1016/j.earscirev.2020.103296",
    openalex = "W3043883447",
    references = "doi1010079783540775874, doi101016jearscirev200810005, doi101016jearscirev201601005, doi101016jearscirev201706012, doi101016jearscirev2019102888, doi101016jprecamres201307019, doi101016jprecamres201504018, doi101016jprecamres201804007, doi101016jprecamres2019105347, doi1010292017je005478, doi101038384055a0, doi101038nature13068, doi101038nature23261, doi101038s4158601914364, doi101098rstb20150493, doi101111j14724669200700118x, doi101126science16138451005, doi101126science2605108640, doi101126science28554301033, doi101128mr5522592871991, doi101146annurevmicro61080706093130, doi102110palo2013p13005r, doi107185geochemlet1817, openalexw1965399445, openalexw2026796374"
}

Abstract During the Noachian period, 4.1-3.7 Gys ago, the Martian environment was moderately similar to the one on present Earth. Liquid water was widespread in a neutral environment, volcanic activity and heat flow more vigorous, and atmospheric pressure and temperature were higher than today. These conditions may have favoured the spread of life on the surface of Mars. The recognition that different planets and moons share rocky material cast in space by meteoroid impact entails that life creation is not necessary for each single planetary body, but could travel through the Solar system on board of rock fragments. Studies conducted on the past forms of Martian life have already highlighted possible positive matches with microbialite-like structures, referable to the geo-environmental conditions in the Noachian and Hesperian. However, by necessity, these studies are on predominantly micro and meso-scopic scale structures and doubts arise as to their attribution to the biogenic world. We suggest that in the identification of Martian life, we are currently in a position similar to the one of Kalkowsky who in 1908, based solely on morphological and sedimentological arguments, hypothesized the (now accepted) view of the biotic origin of stromatolites. Our analysis of thousands of images from Spirit, Opportunity and Curiosity has provided a selection of images of ring-shaped, domal and coniform macrostructures that resemble terrestrial microbialites such as the ring-shaped stromatolites of Lake Thetis, and stacked cones reminiscent of the group of terrestrial Conophyton. Notably, the latter were detected by Curiosity in the mudstone known as ‘Sheepbed’, the same outcrop where past organic molecules have been detected and where the occurrence of microbial-induced sedimentary structures (MISS) and of many more microbialitic micro, meso and macrostructures has already been hypothesized. Some of the structures discussed in this work are so complex that alternative biological hypotheses can be formulated as possible algae. Alternate, non-abiotic explanations are examined but we find difficult to explain some of such structures in the context of normal sedimentary processes, both syngenetic or epigenetic.

@article{doi101017s1473550420000026,
    author = "Rizzo, Vincenzo",
    title = "Why should geological criteria used on Earth not be valid also for Mars? Evidence of possible microbialites and algae in extinct Martian lakes",
    year = "2020",
    journal = "International Journal of Astrobiology",
    abstract = "Abstract During the Noachian period, 4.1-3.7 Gys ago, the Martian environment was moderately similar to the one on present Earth. Liquid water was widespread in a neutral environment, volcanic activity and heat flow more vigorous, and atmospheric pressure and temperature were higher than today. These conditions may have favoured the spread of life on the surface of Mars. The recognition that different planets and moons share rocky material cast in space by meteoroid impact entails that life creation is not necessary for each single planetary body, but could travel through the Solar system on board of rock fragments. Studies conducted on the past forms of Martian life have already highlighted possible positive matches with microbialite-like structures, referable to the geo-environmental conditions in the Noachian and Hesperian. However, by necessity, these studies are on predominantly micro and meso-scopic scale structures and doubts arise as to their attribution to the biogenic world. We suggest that in the identification of Martian life, we are currently in a position similar to the one of Kalkowsky who in 1908, based solely on morphological and sedimentological arguments, hypothesized the (now accepted) view of the biotic origin of stromatolites. Our analysis of thousands of images from Spirit, Opportunity and Curiosity has provided a selection of images of ring-shaped, domal and coniform macrostructures that resemble terrestrial microbialites such as the ring-shaped stromatolites of Lake Thetis, and stacked cones reminiscent of the group of terrestrial Conophyton. Notably, the latter were detected by Curiosity in the mudstone known as ‘Sheepbed’, the same outcrop where past organic molecules have been detected and where the occurrence of microbial-induced sedimentary structures (MISS) and of many more microbialitic micro, meso and macrostructures has already been hypothesized. Some of the structures discussed in this work are so complex that alternative biological hypotheses can be formulated as possible algae. Alternate, non-abiotic explanations are examined but we find difficult to explain some of such structures in the context of normal sedimentary processes, both syngenetic or epigenetic.",
    url = "https://doi.org/10.1017/s1473550420000026",
    doi = "10.1017/s1473550420000026",
    openalex = "W3009530984",
    references = "tewari1998earliest"
}

Billions of years ago, the Northern Hemisphere of Mars may have been covered by at least one ocean and thousands of lakes and rivers. These findings, based initially on telescopic observations and images by the Mariner and Viking missions, led investigators to hypothesize that stromatolite fashioning cyanobacteria may have proliferated in the surface waters, and life may have been successfully transferred between Earth and Mars via tons of debris ejected into the space following bolide impact. Studies conducted by NASA’s robotic rovers also indicate that Mars was wet and habitable and may have been inhabited in the ancient past. It has been hypothesized that Mars subsequently lost its magnetic field, oceans, and atmosphere when bolides negatively impacted its geodynamo and that the remnants of the Martian seas began to evaporate and became frozen beneath the surface. As reviewed here, twenty-five investigators have published evidence of Martian sedimentary structures that resemble microbial mats and stromatolites, which may have been constructed billions of years ago on ancient lake shores and in receding bodies of water, although if these formations are abiotic or biotic is unknown. These findings parallel the construction of the first stromatolites on Earth. The evidence reviewed here does not prove but supports the hypothesis that ancient Mars had oceans (as well as lakes) and was habitable and inhabited, and life may have been transferred between Earth and Mars billions of years ago due to powerful solar winds and life-bearing ejecta propelled into the space following the bolide impact.

@article{doi10115520206959532,
    author = "Joseph, Rhawn and Planchon, Olivier and Duxbury, N. S. and Latif, Khalid and Kidron, Giora J. and Consorti, Lorenzo and Armstrong, Richard A. and Gibson, C. H. and Schild, Rudolph E.",
    title = "Oceans, Lakes, and Stromatolites on Mars",
    year = "2020",
    journal = "Advances in Astronomy",
    abstract = "Billions of years ago, the Northern Hemisphere of Mars may have been covered by at least one ocean and thousands of lakes and rivers. These findings, based initially on telescopic observations and images by the Mariner and Viking missions, led investigators to hypothesize that stromatolite fashioning cyanobacteria may have proliferated in the surface waters, and life may have been successfully transferred between Earth and Mars via tons of debris ejected into the space following bolide impact. Studies conducted by NASA’s robotic rovers also indicate that Mars was wet and habitable and may have been inhabited in the ancient past. It has been hypothesized that Mars subsequently lost its magnetic field, oceans, and atmosphere when bolides negatively impacted its geodynamo and that the remnants of the Martian seas began to evaporate and became frozen beneath the surface. As reviewed here, twenty-five investigators have published evidence of Martian sedimentary structures that resemble microbial mats and stromatolites, which may have been constructed billions of years ago on ancient lake shores and in receding bodies of water, although if these formations are abiotic or biotic is unknown. These findings parallel the construction of the first stromatolites on Earth. The evidence reviewed here does not prove but supports the hypothesis that ancient Mars had oceans (as well as lakes) and was habitable and inhabited, and life may have been transferred between Earth and Mars billions of years ago due to powerful solar winds and life-bearing ejecta propelled into the space following the bolide impact.",
    url = "https://doi.org/10.1155/2020/6959532",
    doi = "10.1155/2020/6959532",
    openalex = "W3092861210",
    references = "tewari1998earliest"
}