Signatures of early microbial life from the Archean (4 to 2.5 Ga) eon

Lepot, Kevin

doi:10.1016/j.earscirev.2020.103296

Cited by 102 publications

(58 citation statements)

References 488 publications

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“…Signatures of life on Earth have previously been identified in some of the oldest rocks on Earth, dating back to almost 4 billion years ago (reviewed by Lepot, 2020). These signatures include carbon isotope values indicative of biological CO 2 fixation (Rosing, 1999), which today plays a major role in the global carbon cycle and may have done so for most of Earth's history (Schidlowski, 2001).…”

Section: Introductionmentioning

confidence: 99%

Reconstructing Nitrogen Sources to Earth’s Earliest Biosphere at 3.7 Ga

et al. 2021

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Earth’s sedimentary record has preserved evidence of life in rocks of low metamorphic grade back to about 3.2–3.5 billion years ago (Ga). These lines of evidence include information about specific biological metabolisms, permitting the reconstruction of global biogeochemical cycles in the early Archean. Prior to 3.5 Ga, the geological record is severely compromised by pervasive physical and chemical alteration, such as amphibolite-granulite facies metamorphic overprinting. Despite this alteration, evidence of biogenic organic matter is preserved in rare localities, including meta-turbidites from the 3.8 to 3.7 Ga Isua Supracrustal Belt, Western Greenland. But detailed insights into metabolic strategies and nutrient sources during the time of deposition of these Eoarchean meta-sedimentary rocks are lacking. Here we revisit the Isua meta-turbidites and provide new data for metal abundances as well as organic carbon and nitrogen isotope values. Our results reveal mixing between authigenic and detrital nitrogen phases with the authigenic phase likely fractionated by metamorphic degassing. Rayleigh fractionation models of these 3.7 Ga samples indicate pre-metamorphic δ15N values of between −1 and −10‰. The most plausible initial values are below −5‰, in agreement with a prior study. While the upper endmember of −1‰ could indicate biological N2 fixation at 3.7 Ga, the more plausible lighter values may point toward a distinct biogeochemical nitrogen cycle at that time, relative to the rest of Earth’s history. In light of recent experimental and phylogenetic data aligned with observations from the modern atmosphere, we tentatively conclude that lightning and/or high-energy photochemical reactions in the early atmosphere may have contributed isotopically light nitrogen to surface environment(s) preserved in the Isua turbidites. In this case, recycling of Eoarchean sediments may have led to the isotopically light composition of the Earth’s upper mantle dating back to at least 3.2 Ga.

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Section: Introductionmentioning

confidence: 99%

Reconstructing Nitrogen Sources to Earth’s Earliest Biosphere at 3.7 Ga

et al. 2021

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“…On Archean Earth, however, life was already bustling and highly diverse, producing a treasure trove of carbonaceous microfossils, stromatolites, and MISS. These structures and fossils in concert with abundant chemical signals provide a large data set for the reconnaissance of potential ancient life on Mars (reviews by Hickman-Lewis et al, 2018 ; Homann, 2019 ; Grey and Awramik, 2020 ; Lepot, 2020 ). However, with respect to detectability, the old martian rocks are surprisingly superior to their terrestrial Archean counterparts.…”

Section: General Approach For the Prospection For Miss On Marsmentioning

confidence: 99%

“…Historically, life exploration on other planets is rooted in the paleontological work on early microbial life chronicled in terrestrial Archean rocks. Here, pioneering studies revealed body fossils of microbial cells and filaments, stromatolites, and a wealth of chemical signals and biomarker molecules (reviews by Hickman-Lewis et al, 2018 ; Lepot, 2020 ). Naturally, proposed search strategies for extraterrestrial life are nurtured by the large data sets on these features, already tested from all angles of perspectives (Summons et al, 2011 [for MSL]; Westall et al, 2015 ; Vago and Westall, 2017 ; and Vago et al, 2017 [for ExoMars]; McMahon et al, 2018 [for Mars2020]).…”

Section: Introductionmentioning

confidence: 99%

Microbially Induced Sedimentary Structures in Clastic Deposits: Implication for the Prospection for Fossil Life on Mars

Noffke

2021

Astrobiology

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Abundant and well-preserved fossil microbenthos occurs in siliciclastic deposits of all Earth ages, from the early Archean to today. Studies in modern settings show how microbenthos responds to sediment dynamics by baffling and trapping, binding, biostabilization, and growth. Results of this microbial-sediment interaction are microbially induced sedimentary structures (MISS). Successful prospection for rich MISS occurrences in the terrestrial lithological record requires unraveling genesis and taphonomy of MISS, both of which are defined only by a narrow range of specific conditions. These conditions have to coincide with high detectability which is a function of outcrop quality, bedding character, and rock type. Assertions on biogenicity of MISS morphologies must be based on the presence of microbially induced sedimentary textures (MIST), which are MISS-internal textures comprising replacement minerals arranged into microscopic biological morphologies, ancient carbonaceous matter, trace fossils, and geochemical signals. MISS serve as possible templates for the decryption of ancient life-processes on Mars. This article closes with a perspective on selected deposits and ancient environments in Meridiani Planum, Gale Crater, and Jezero Crater, Mars, regarding their potential for MISS occurrences. The earlier hypothesis of structures on Mars as potentially being MISS is revised.

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“…Bacteria are unicellular organisms usually a few micrometers in length which together with archaea (formerly archaebacteria) belong to the prokaryote domain of life. High-resolution microscopy and isotopic analyses of some Archaean (4-2.5 Ga) rocks show that ancestors of modern bacteria existed on earth between 3.47 and 2.7 Ga, [1][2][3] whereas studies on 1.88 Ga old stromatolites showed Fe 2 O 3 -mineralized microfossils of bacterial cells. 4 Bacteria inhabit all ecological niches including extreme environments like hydrothermal vents, 5 hot springs, 6 the deep sub-seafloor, 7 sub-polar snowpacks, 8 the Antarctic desert 9 and even nuclear waste.…”

Section: Introductionmentioning

confidence: 99%