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Title: Reassessing evidence of life in 3,700-million-year-old rocks of Greenland

Abstract

The Palaeoarchean supracrustal belts in Greenland contain Earth’s oldest rocks and are a prime target in the search for the earliest evidence of life on Earth. However, metamorphism has largely obliterated original rock textures and compositions, posing a challenge to the preservation of biological signatures. A recent study of 3,700-million-year-old rocks of the Isua supracrustal belt in Greenland described a rare zone in which low deformation and a closed metamorphic system allowed preservation of primary sedimentary features, including putative conical and domical stromatolites1 (laminated accretionary structures formed by microbially mediated sedimentation). The morphology, layering, mineralogy, chemistry and geological context of the structures were attributed to the formation of microbial mats in a shallow marine environment by 3,700 million years ago, at the start of Earth’s rock record. Here we report new research that shows a non-biological, post-depositional origin for the structures. Three-dimensional analysis of the morphology and orientation of the structures within the context of host rock fabrics, combined with texture-specific analyses of major and trace element chemistry, show that the ‘stromatolites’ are more plausibly interpreted as part of an assemblage of deformation structures formed in carbonate-altered metasediments long after burial. The investigation of the structures of the Isua supracrustalmore » belt serves as a cautionary tale in the search for signs of past life on Mars, highlighting the importance of three-dimensional, integrated analysis of morphology, rock fabrics and geochemistry at appropriate scales.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
Brookhaven National Lab. (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1491993
DOE Contract Number:  
SC0012704
Resource Type:
Journal Article
Journal Name:
Nature (London)
Additional Journal Information:
Journal Volume: 563; Journal Issue: 7730; Journal ID: ISSN 0028-0836
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES

Citation Formats

Allwood, Abigail C., Rosing, Minik T., Flannery, David T., Hurowitz, Joel A., and Heirwegh, Christopher M. Reassessing evidence of life in 3,700-million-year-old rocks of Greenland. United States: N. p., 2018. Web. doi:10.1038/s41586-018-0610-4.
Allwood, Abigail C., Rosing, Minik T., Flannery, David T., Hurowitz, Joel A., & Heirwegh, Christopher M. Reassessing evidence of life in 3,700-million-year-old rocks of Greenland. United States. doi:10.1038/s41586-018-0610-4.
Allwood, Abigail C., Rosing, Minik T., Flannery, David T., Hurowitz, Joel A., and Heirwegh, Christopher M. Wed . "Reassessing evidence of life in 3,700-million-year-old rocks of Greenland". United States. doi:10.1038/s41586-018-0610-4.
@article{osti_1491993,
title = {Reassessing evidence of life in 3,700-million-year-old rocks of Greenland},
author = {Allwood, Abigail C. and Rosing, Minik T. and Flannery, David T. and Hurowitz, Joel A. and Heirwegh, Christopher M.},
abstractNote = {The Palaeoarchean supracrustal belts in Greenland contain Earth’s oldest rocks and are a prime target in the search for the earliest evidence of life on Earth. However, metamorphism has largely obliterated original rock textures and compositions, posing a challenge to the preservation of biological signatures. A recent study of 3,700-million-year-old rocks of the Isua supracrustal belt in Greenland described a rare zone in which low deformation and a closed metamorphic system allowed preservation of primary sedimentary features, including putative conical and domical stromatolites1 (laminated accretionary structures formed by microbially mediated sedimentation). The morphology, layering, mineralogy, chemistry and geological context of the structures were attributed to the formation of microbial mats in a shallow marine environment by 3,700 million years ago, at the start of Earth’s rock record. Here we report new research that shows a non-biological, post-depositional origin for the structures. Three-dimensional analysis of the morphology and orientation of the structures within the context of host rock fabrics, combined with texture-specific analyses of major and trace element chemistry, show that the ‘stromatolites’ are more plausibly interpreted as part of an assemblage of deformation structures formed in carbonate-altered metasediments long after burial. The investigation of the structures of the Isua supracrustal belt serves as a cautionary tale in the search for signs of past life on Mars, highlighting the importance of three-dimensional, integrated analysis of morphology, rock fabrics and geochemistry at appropriate scales.},
doi = {10.1038/s41586-018-0610-4},
journal = {Nature (London)},
issn = {0028-0836},
number = 7730,
volume = 563,
place = {United States},
year = {2018},
month = {10}
}