Aspects of the biological carbon cycle in a ca. 3.42-billion-year-old marine ecosystem

[erik simpson]

https://www.sciencedirect.com/science/article/pii/S0301926824000020?via%3Dihub

Highlights

•

Metabolic diversity in the lower platform facies of the Buck Reef
Chert.
•

Exceptional preservation of Paleoarchean carbonaceous matter also
on molecular level.
•

Different carbonaceous matter appearance (e.g., clots, laminae,
blocky aggregates).
•

Rapid silicification supported carbonaceous matter preservation.

Abstract

Microbial life on Earth was well established in the Paleoarchean, but
insight into early ecosystem diversity and thus, the complexity of the
early biological carbon cycle is limited. Here we investigated four
carbonaceous chert samples from the lower platform facies of the ca.
3.42-billion-year-old Buck Reef Chert, Barberton greenstone belt. The
analysis on multiple scales revealed exceptionally well-preserved
carbonaceous matter, even on molecular level (aliphatic and aromatic
hydrocarbons), resulting from rapid silicification. Geochemical evidence
from stable carbon and multiple sulfur isotopes supports the presence of
different microbial metabolisms in the Paleoarchean ecosystem. The local
biological carbon cycle was dominated by photoautotrophs, but
autotrophic sulfate reducers and methane- or acetate-producing microbes
were also present. In areas of microbial methane or acetate release,
methanotrophs or acetotrophs contributed to the overall biomass. These
results highlight the metabolic diversity in the lower platform
environment of the Buck Reef Chert, and underline that an advanced
biological carbon cycle already existed in the early Archean.