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Organic Records of Early Life on Mars: The Role of Iron, Burial, and Kinetics on Preservation

Samples that are likely to contain evidence of past life on Mars must have been deposited when and where environments exhibited habitable conditions. Mars analog sites provide the opportunity to study how life could have exploited such habitable conditions. Acidic iron- and sulfur-rich streams are g...

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Autores principales: Tan, Jonathan, Sephton, Mark A.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Mary Ann Liebert, Inc., publishers 2020
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6987739/
https://www.ncbi.nlm.nih.gov/pubmed/31755737
http://dx.doi.org/10.1089/ast.2019.2046
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author Tan, Jonathan
Sephton, Mark A.
author_facet Tan, Jonathan
Sephton, Mark A.
author_sort Tan, Jonathan
collection PubMed
description Samples that are likely to contain evidence of past life on Mars must have been deposited when and where environments exhibited habitable conditions. Mars analog sites provide the opportunity to study how life could have exploited such habitable conditions. Acidic iron- and sulfur-rich streams are good geochemical analogues for the late Noachian and early Hesperian, periods of martian history where habitable conditions were widespread. Past life on Mars would have left behind fossilized microbial organic remains. These are often-sought diagnostic evidence, but they must be shielded from the harsh radiation flux at the martian surface and its deleterious effect on organic matter. One mechanism that promotes such preservation is burial, which raises questions about how organic biomarkers are influenced by the postburial effects of diagenesis. We investigated the kinetics of organic degradation in the subsurface of Mars. Natural mixtures of acidic iron- and sulfur-rich stream sediments and their associated microbial populations and remains were subjected to hydrous pyrolysis, which simulated the increased temperatures and pressures of burial alongside any promoted organic/mineral interactions. Calculations were made to extrapolate the observed changes over martian history. Our experiments indicate that low carbon contents, high water-to-rock ratios, and the presence of iron-rich minerals combine to provide unfavorable conditions for the preservation of soluble organic matter over the billions of years necessary to produce present-day organic records of late Noachian and early Hesperian life on Mars. Successful sample selection strategies must therefore consider the pre-, syn-, and postburial histories of sedimentary records on Mars and the balance between the production of biomass and the long-term preservation of organic biomarkers over geological time.
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spelling pubmed-69877392020-02-11 Organic Records of Early Life on Mars: The Role of Iron, Burial, and Kinetics on Preservation Tan, Jonathan Sephton, Mark A. Astrobiology Research Articles Samples that are likely to contain evidence of past life on Mars must have been deposited when and where environments exhibited habitable conditions. Mars analog sites provide the opportunity to study how life could have exploited such habitable conditions. Acidic iron- and sulfur-rich streams are good geochemical analogues for the late Noachian and early Hesperian, periods of martian history where habitable conditions were widespread. Past life on Mars would have left behind fossilized microbial organic remains. These are often-sought diagnostic evidence, but they must be shielded from the harsh radiation flux at the martian surface and its deleterious effect on organic matter. One mechanism that promotes such preservation is burial, which raises questions about how organic biomarkers are influenced by the postburial effects of diagenesis. We investigated the kinetics of organic degradation in the subsurface of Mars. Natural mixtures of acidic iron- and sulfur-rich stream sediments and their associated microbial populations and remains were subjected to hydrous pyrolysis, which simulated the increased temperatures and pressures of burial alongside any promoted organic/mineral interactions. Calculations were made to extrapolate the observed changes over martian history. Our experiments indicate that low carbon contents, high water-to-rock ratios, and the presence of iron-rich minerals combine to provide unfavorable conditions for the preservation of soluble organic matter over the billions of years necessary to produce present-day organic records of late Noachian and early Hesperian life on Mars. Successful sample selection strategies must therefore consider the pre-, syn-, and postburial histories of sedimentary records on Mars and the balance between the production of biomass and the long-term preservation of organic biomarkers over geological time. Mary Ann Liebert, Inc., publishers 2020-01-01 2020-01-20 /pmc/articles/PMC6987739/ /pubmed/31755737 http://dx.doi.org/10.1089/ast.2019.2046 Text en © Jonathan Tan and Mark A. Sephton, 2019; Published by Mary Ann Liebert, Inc. This Open Access article is distributed under the terms of the Creative Commons Attribution Noncommercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.
spellingShingle Research Articles
Tan, Jonathan
Sephton, Mark A.
Organic Records of Early Life on Mars: The Role of Iron, Burial, and Kinetics on Preservation
title Organic Records of Early Life on Mars: The Role of Iron, Burial, and Kinetics on Preservation
title_full Organic Records of Early Life on Mars: The Role of Iron, Burial, and Kinetics on Preservation
title_fullStr Organic Records of Early Life on Mars: The Role of Iron, Burial, and Kinetics on Preservation
title_full_unstemmed Organic Records of Early Life on Mars: The Role of Iron, Burial, and Kinetics on Preservation
title_short Organic Records of Early Life on Mars: The Role of Iron, Burial, and Kinetics on Preservation
title_sort organic records of early life on mars: the role of iron, burial, and kinetics on preservation
topic Research Articles
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6987739/
https://www.ncbi.nlm.nih.gov/pubmed/31755737
http://dx.doi.org/10.1089/ast.2019.2046
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