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Organic records of early life on Mars: the role of iron, burial and kinetics on preservation

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Title: Organic records of early life on Mars: the role of iron, burial and kinetics on preservation
Authors: Tan, J
Sephton, M
Item Type: Journal Article
Abstract: Samples that are likely to contain evidence of past life on Mars must have been deposited when and where environments exhibited habitable conditions. Mars analogue 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 fossilised microbial organic remains and these are often-sought diagnostic evidence, but 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 post-burial 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 unfavourable conditions for the preservation of 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 post-burial 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.
Issue Date: 20-Jan-2020
Date of Acceptance: 11-Sep-2019
URI: http://hdl.handle.net/10044/1/74294
DOI: 10.1089/ast.2019.2046
ISSN: 1531-1074
Publisher: Mary Ann Liebert
Start Page: 53
End Page: 72
Journal / Book Title: Astrobiology
Volume: 20
Issue: 1
Copyright Statement: © 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.
Sponsor/Funder: Science and Technology Facilities Council (STFC)
Funder's Grant Number: ST/N000560/1
Keywords: Science & Technology
Physical Sciences
Life Sciences & Biomedicine
Astronomy & Astrophysics
Biology
Geosciences, Multidisciplinary
Life Sciences & Biomedicine - Other Topics
Geology
Mars
Biosignature
Hydrous pyrolysis
Kinetic parameters
Lipids
Artificial maturation
ISOPRENOID SULFUR-COMPOUNDS
HYDROUS PYROLYSIS
GALE CRATER
MERIDIANI-PLANUM
CLAY-MINERALS
THERMAL MATURATION
MASS-SPECTROMETRY
SEDIMENTARY-ROCKS
ISOTOPIC EVIDENCE
ABIOTIC SYNTHESIS
Artificial maturation
Biosignature
Hydrous pyrolysis
Kinetic parameters
Lipids
Mars
Astronomy & Astrophysics
0201 Astronomical and Space Sciences
0402 Geochemistry
0403 Geology
Publication Status: Published
Online Publication Date: 2019-11-22
Appears in Collections:Earth Science and Engineering
Faculty of Engineering