https://www.eurekalert.org/news-releases/1054055
Researchers study carbon in 3.9 billion year old Canadian rocks.
Scientists have found that graphite in Nunatsiavut’s ancient Saglek-Hebron iron formations, once thought to be the site of the earliest life on Earth, is likely abiotic in origin.
Early life on Earth
The isotopic composition of carbon in iron formations from the Saglek-Hebron complex in Nunatsiavut (northern Labrador) was considered evidence of the earliest traces of life on Earth. But a new study from the University of Ottawa, Carleton University and University College London suggests the opposite.
The study shows that the petrographic, geochemical and spectroscopic characteristics of the graphite (the crystalline form of carbon) found in the chemical sedimentary rocks of Saglek-Hebron are indeed “abiotic”, that is, they represent non-living physical or chemical aspects of an environment or that do not contain life.
The abiotic nature of graphite
This improves our understanding of how early biomass changed on Earth and highlights the interaction between non-biological processes and remains of ancient life. The study of graphitic materials is key to deciphering the carbon cycle on the early Earth.
This study is crucial to the search for early life on Earth and possibly on neighboring planets.
New methods in geochemical analysis
Using micro-Raman spectroscopy, the researchers examined the isotopic signatures in these rocks. Their results show that graphite could have come from liquid substances containing carbon, hydrogen and oxygen, probably resulting from the decomposition of ancient organic materials.
“Our study focuses on chemical sedimentary rocks found in the Saglek-Hebron. These rocks are among the oldest on Earth, dating back 3.9 billion years. They were formed by oceanic precipitation. They contain banded ore formations that may have been formed by the activity of bacteria,” explains co-author Jonathan O’Neil, associate professor in the Department of Earth and Environmental Sciences at the University of Ottawa.
Rethinking geological signatures
“They are ideal for studying ancient biological processes. Our study challenges the previous interpretation that the carbon isotope composition of these rocks indicates a biological origin, but their spectroscopic properties are more indicative of abiotic properties. This leads us to rethink the processes responsible for isotopic signatures and their connection to the action of microorganisms,” adds O’Neil.
Last year’s research focused on samples collected during a 2016 field campaign in Nunatsiavut. Petrological characterization was conducted in Ottawa and spectroscopic analysis of graphitic carbon was performed in London, UK.
The origins of graphite carbon
“Graphitic carbon from chemical sedimentary rock samples was studied in three sedimentary rock samples that are almost 3.9 billion years old. Spectroscopic analysis of this graphitic carbon suggests that it was formed from metamorphic fluids (at temperatures above 500OC) and not by processes involving bacteria,” says O’Neil.
Research shows that graphite in rocks may have formed in the absence of organic life, possibly through a carbon extraction process. The degree of crystallization of graphite correlates with the metamorphism of the rock, suggesting that metamorphism influences the preservation and alteration of carbon-based materials.
Reference: “Abiotic synthesis of graphitic carbons in the Eoarchean Saglek-Hebron metasedimentary rocks” by Zixiao Guo, Dominic Papineau, Jonathan O’Neil, Hanika Rizo, Zhong-Qiang Chen, Xincheng Qiu and Zhenbing She, July 6, 2024, Nature communication.
DOI: 10.1038/s41467-024-50134-1
