Sulfur isotopes of organic matter preserved in 3.45-billion-year-old stromatolites reveal microbial metabolism

The 3.45-billion-year-old Strelley Pool Formation of Western Australia preserves stromatolites that are considered among the oldest evidence for life on Earth. In places of exceptional preservation, these stromatolites contain laminae rich in organic carbon, interpreted as the fossil remains of anci...

Full description

Saved in:
Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2012-09, Vol.109 (38), p.15146-15151
Main Authors: Bontognali, Tomaso R. R, Sessions, Alex L, Allwood, Abigail C, Fischer, Woodward W, Grotzinger, John P, Summons, Roger E, Eiler, John M
Format: Article
Language:English
Subjects:
Archaea - physiology
Australia
Biogeochemistry
Biological Sciences
biomass
carbon
Earth
Fossils
Fractionation
Geologic Sediments
Geology - methods
hydrogen sulfide
Hydrogen Sulfide - chemistry
Ion probes
Ions
Isotopes
Metabolism
Microbiology
Organic Chemicals - chemistry
organic matter
Physical Sciences
pyrite
Pyrites
Rocks
Stromatolites
Sulfates
Sulfides
Sulfur
Sulfur isotopes
Sulfur Isotopes - analysis
Sulfur Isotopes - chemistry
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:The 3.45-billion-year-old Strelley Pool Formation of Western Australia preserves stromatolites that are considered among the oldest evidence for life on Earth. In places of exceptional preservation, these stromatolites contain laminae rich in organic carbon, interpreted as the fossil remains of ancient microbial mats. To better understand the biogeochemistry of these rocks, we performed microscale in situ sulfur isotope measurements of the preserved organic sulfur, including both Δ ³³S and [Formula]. This approach allows us to tie physiological inference from isotope ratios directly to fossil biomass, providing a means to understand sulfur metabolism that is complimentary to, and independent from, inorganic proxies (e.g., pyrite). Δ ³³S values of the kerogen reveal mass-anomalous fractionations expected of the Archean sulfur cycle, whereas [Formula] values show large fractionations at very small spatial scales, including values below -15‰. We interpret these isotopic patterns as recording the process of sulfurization of organic matter by H ₂S in heterogeneous mat pore-waters influenced by respiratory S metabolism. Positive Δ ³³S anomalies suggest that disproportionation of elemental sulfur would have been a prominent microbial process in these communities.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.1207491109