Diverse communities of Bacteria and Archaea flourished in Palaeoarchaean (3.5–3.3 Ga) microbial mats

Abstract

Limited taxonomic classification is possible for Archaean microbial mats and this is a fundamental limitation in constraining early ecosystems. Applying Fourier transform infrared spectroscopy (FTIR), a powerful tool for identifying vibrational motions attributable to specific functional groups, we characterized fossilized biopolymers in 3.5-3.3 Ga microbial mats from the Barberton greenstone belt (South Africa). Microbial mats from four Palaeoarchaean horizons exhibit significant differences in taxonomically informative aliphatic contents, despite high aromaticity. This reflects precursor biological heterogeneity since all horizons show equally exceptional preservation and underwent similar grades of metamorphism. Low methylene to end-methyl (CH 2 /CH 3) absorbance ratios in mats from the 3.472 Ga Middle Marker horizon signify short, highly branched n-alkanes interpreted as isoprenoid chains forming archaeal membranes. Mats from the 3.45 Ga Hooggenoeg Chert H5c, 3.334 Ga Footbridge Chert, and 3.33 Ga Josefsdal Chert exhibit higher CH 2 /CH 3

Transformation of Cyanobacterial Biomolecules by Iron Oxides During Flash Pyrolysis: Implications for Mars Life-Detection Missions

“…However, isoprenoid hydrocarbons, such as the diterpenoid neophytadiene and D-αtocopherol, detected here, along with β-carotene, inferred from the detection of α-ionene, are well used biomarkers of photosynthetic organisms (Peters et al, 2007). Isoprenoids and their unambiguous diagenetic products have been found in terrestrial sediments dating at least back to the Precambrian (Chen et al, 2018) and potentially as far back as the Palaeoarchean (Brocks et al, 2003;Hickman-Lewis et al, 2020) as they are highly recalcitrant. The repeating nature of the isoprene unit that makes up this class of organic molecules is not known to occur abiotically (Eigenbrode, 2011) with individual isoprenoids representative of specific biochemical pathways (Peters et al, 2007).…”

Chemical degradation of thermally altered silicified organic matter during acid maceration: A case study from the Lower Devonian Rhynie chert

“…In the specific context of silicified rocks -where silicification prevented migration of bitumens and favoured formation of pyrobitumen in the close vicinity of the residual kerogen -the use of in situ molecular micrometre-scale analyses offers promise in the investigation of the molecular composition of early life found within Archean silicified sediments. Indeed, the emergence of micrometre-scale in situ analyses have provided compelling evidence supporting an unexpected and wide chemical heterogeneity among Archean putative organicwalled microfossils (Delarue et al, 2017(Delarue et al, , 2020Hickman-Lewis et al, 2020). Overlooked by bulk extraction approaches, this chemical heterogeneity defines a chemically-well preserved end product among the earliest traces of life.…”

Microfossils with tail-like structures in the 3.4 Gyr old Strelley Pool Formation

“…In the specific context of silicified rocks -where silicification prevented migration of bitumens and favoured formation of pyrobitumen in the close vicinity of the residual kerogen -the use of in situ molecular micrometre-scale analyses offers promise in the investigation of the molecular composition of early life found within Archean silicified sediments. Indeed, the emergence of micrometre-scale in situ analyses have provided compelling evidence supporting an unexpected and wide chemical heterogeneity among Archean putative organicwalled microfossils Hickman-Lewis et al, 2020). Overlooked by bulk extraction approaches, this chemical heterogeneity defines a chemically-well preserved end product among the earliest traces of life.…”