DOI: 10.5061/dryad.v41ns1rsn
title: Data from: Diverse communities of bacteria and archaea flourished in Palaeoarchaean (3.5-3.3 Ga) microbial mats

description: 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 characterised fossilised 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 (CH2/CH3) 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 CH2/CH3ratios
 suggesting longer, unbranched fatty acids from bacterial lipid precursors.
 Absorbance ratios of end-methyl to methylene (CH3/CH2) in Hooggenoeg,
 Josefsdal and Footbridge mats yield a range of values (0.20-0.80)
 suggesting mixed bacterial and archaeal architect communities based on
 comparison with modern examples. Higher (0.78-1.25)
 CH3/CH2 ratios in the Middle Marker mats identify Archaea. This
 exceptional preservation reflects early, rapid silicification preventing
 the alteration of biogeochemical signals inherited from biomass. Since
 silicification commenced during the lifetime of the microbial mat, FTIR
 signals estimate the affinities of the architect community and may be used
 in the reconstruction of Archaean ecosystems. Together, these results show
 that Bacteria and Archaea flourished together in Earth’s earliest
 ecosystems.
description: These files are raw data obtained using transmission Fourier
 Transform Infra-red spectroscopy (FTIR). All data were acquired using a a
 Bruker VERTEX 70 instrument equipped with a GLOBAR (silicon carbide)
 source and a deuterated triglycine sulphate (DTGS) detector with a KBr
 window. All measurements were obtaines at the Centro Interdipartimentale
 Grandi Strumenti (Università degli studi di Modena e Reggio Emilia,
 Modena, Italy). Each reported FTIR file gives the average of 16 spectra
 accumulated within the studied area within a spectral range of 7500-370
 cm<sup>–1</sup> with a 4 cm<sup>–1</sup> spectral
 resolution.
description: All files are raw numerical data obtained using transmission
 Fourier Transform Infra-red spectroscopy (FTIR). No treatment has been
 applied to these data and there are no missing values. Please see
 Hickman-Lewis et al. "Diverse communities of Bacteria and Archaea
 flourished in Palaeoarchaean (3.5-3.3 Ga) microbial mats" for the
 full interpretation of these data and explanations of the geological and
 petrographic contexts of the materials studied. The present dataset
 provides all data used in the aforementioned study.
 Addtional information is available
 in Hickman-Lewis_et_al._Palaeontology_FTIR_dataset_README.txt