Paleo-Rock-Hosted Life on Earth and the Search on Mars: A Review and Strategy for Exploration
Year: 2019
Type: article
Abstract: abiotic and biotic recycling of metabolic waste products rather than on buried organic products of photosynthesis; (2) subsurface microbial cell concentrations are highest at interfaces with pronounced chemical redox gradients or permeability variations and do not correlate with bulk host rock organic carbon; (3) metabolic pathways for chemolithoautotrophic microorganisms evolved earlier in Earth's history than those of surface-dwelling phototrophic microorganisms; (4) the emergence of the former occurred at a time when Mars was habitable, whereas the emergence of the latter occurred at a time when the martian surface was not continually habitable; (5) the terrestrial rock record has biomarkers of subsurface life at least back hundreds of millions of years and likely to 3.45 Ga with several examples of excellent preservation in rock types that are quite different from those preserving the photosphere-supported biosphere. These findings suggest that rock-hosted life would have been more likely to emerge and be preserved in a martian context. Consequently, we outline a Mars exploration strategy that targets subsurface life and scales spatially, focusing initially on identifying rocks with evidence for groundwater flow and low-temperature mineralization, then identifying redox and permeability interfaces preserved within rock outcrops, and finally focusing on finding minerals associated with redox reactions and associated traces of carbon and diagnostic chemical and isotopic biosignatures. Using this strategy on Earth yields ancient rock-hosted life, preserved in the fossil record and confirmable via a suite of morphologic, organic, mineralogical, and isotopic fingerprints at micrometer scale. We expect an emphasis on rock-hosted life and this scale-dependent strategy to be crucial in the search for life on Mars.
Source: Astrobiology
Authors: T.C. Onstott, B.L. Ehlmann, H. Sapers, M. Coleman, M. Ivarsson, J.J. Marlow, A. Neubeck, P. Niles
Institutions: Princeton University, California Institute of Technology, Jet Propulsion Laboratory, University of Southern California, NASA Astrobiology Institute, University of Southern Denmark, Harvard University, Uppsala University, National Aeronautics and Space Administration, Johnson Space Center
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: hybrid
Awards: G2868708944, FPDS BASE DESCRIPTION, MULTIPLE YEAR AWARD&INCREMENTAL FUNDING FOR YEARS 1 OF 5. THIS PROPOSAL IS ENTITLED, "HABITABILITY, LIFE DETECTION&THE SIGNAT, THE CURIOSITY ROVER HAS DETECTED BACKGROUND ATMOSPHERIC CH4 LEVELS OF 0.7 PPBV WITH SPIKES TO 7 PPBV [WEBSTER ET AL. 2015]. OF THE MANY MECHANISMS TO INJECT CH4 INTO THE MARTIAN ATMOSPHERE (E.G. SERPENTINIZATION UV DESTRUCTION OF ACCRETED ORGANICS ETC.) METHANOGENESIS IS THE ONLY BIOLOGICAL PROCESS PROPOSED [REID ET AL. 2006] THAT MIGHT BE ACTIVE IN THE SHALLOW SUBSURFACE ON MARS. ALSO LIQUID BRINES COMPOSED OF MG-PERCHLORATE MG-CHLORATE AND NA-PERCHLORATE HAVE BEEN DETECTED IN ACTIVE RECURRING SLOPE LINEAE (RSL) ON STEEP CRATER WALLS ON MARS [OJHA ET AL. 2015]. THE EXPERIMENTS OUTLINED HEREIN WILL ESTABLISH THE LOW-PRESSURE LOW-TEMPERATURE LOW-OXYGEN (PO2) AND HIGH PERCHLORATE AND CHLORATE SALT LIMITS FOR METABOLISM GROWTH AND CH4 PRODUCTION OF PSYCHROPHILIC METHANOGENS UNDER SIMULATED MARTIAN CONDITIONS. FURTHERMORE THE EXPERIMENTS WILL CHARACTERIZE THE TRANSCRIPTOMIC AND PROTEOMIC ALTERATIONS IN METHANOGENS WHEN GROWN UNDER CONDITIONS THAT MAY PERSIST IN SHALLOW SUBSURFACE RSL BRINES.THE RESEARCH WILL BE DIVIDED INTO TWO SECTIONS IN WHICH THE SCHUERGER LAB WILL FOCUS ON CHARACTERIZING THE LOW-PRESSURE LOWTEMPERATURE LOW-PO2 AND HIGH-SALT LIMITS OF GROWTH FOR PSYCHROPHILIC OR PSYCHROTOLERANT METHANOGENS FOR WHICH COMPLETE GENOMES EXIST (E.G. METHANOGENIUM FRIGIDIUM DSM 16458 METHANOCOCCOIDES BURTONII DSM 6242). THE ONSTOTT LAB WILL FOCUS ON CHARACTERIZING THE VARIABILITY OF THE TRANSCRIPTOMES AND PROTEOMES OF THE METHANOGENS AS FUNCTIONS OF EXPOSURE TO INCREASINGLY MARS-LIKE CONDITIONS TESTING THE LOW-PRESSURE LOW-TEMPERATURE LOW-PO2 AND HIGH PERCHLORATE/CHLORATE SALT LIMITS FOR METABOLISM AND GROWTH.A MARS SIMULATION CHAMBER (SCHUERGER LAB) WILL BE CONFIGURED WITH TWO INDEPENDENT MICROBIAL ASSAY CHAMBERS (MAC; UNITS ONHAND) IN WHICH THE BULK ATMOSPHERE OF EACH MAC UNIT CAN BE INDIVIDUALLY SAMPLED WITH A QUADRUPOLE MASS-SPEC RESIDUAL GAS ANALYZER (RGA; OPERATIONAL; MINIMUM DETECTION OF CH4 IS 0.5 PPM AT 0.7 KPA (7 MBAR)) OR GAS CHROMATOGRAPH (GC; MINIMUM DETECTION OF CH4 IS 3 PPM A 0.7 KPA). EXPERIMENTS WILL FOCUS ON THE METABOLIC RESPONSES OF THE METHANOGENS BETWEEN 5.0 KPA (THE CURRENT LOW PRESSURE GROWTH LIMIT FOR METHANOGENS [KRAL ET AL. 2011]) AND 0.7 KPA (MARTIAN SURFACE PRESSURE).WE WILL EXAMINE THE TEMPORAL EXPRESSION OF GENES USING RNA-SEQ AND PROTEOME ANALYSES USING LC-MS/MS AS THE METHANOGENS ARE SUBJECTED TO VARYING PRESSURE TEMPERATURE PO2 AND PERCHLORATE/CHLORATE SALT CONDITIONS. THE ASSEMBLED MRNA CONTIGS AND PROTEIN PEPTIDES WILL BE MAPPED TO THE HOST GENOMES AND THEIR COVERAGE AND ABUNDANCE MEASURED RESPECTIVELY. WE WILL USE A FLUORESCENT MOLECULAR BEACON TARGETING THE MCRA MRNA TO DETERMINE WHAT PROPORTION OF CELLS ARE ACTIVELY PRODUCING CH4 THEREBY PROVIDING A SPECIFIC CELLULAR CH4 PRODUCTION RATE UNDER THE DIVERSE CONDITIONS LISTED ABOVE. THE COMBINATION OF THESE TWO TOOLS WILL PROVIDE A COMPLETE PICTURE OF THE RESPONSE OF THE DIFFERENT METHANOGEN STRAINS TO DECREASING PRESSURE AND TEMPERATURE THE PRESENCE OF LOW PO2 AND TO ELEVATED PERCHLORATE/CHLORATE SALT LEVELS WHEN COMPARED TO CONTROL INCUBATIONS AT 0 DEGREE C AND 101.3 KPA IN STANDARD LIQUID MEDIA.THE PROPOSAL IS RELEVANT TO THE C.5 EXOBIOLOGY PROGRAM BASED ON: (1) THE RESEARCH WILL "..SEEK TO DETERMINE THE BIOLOGICAL AND ENVIRONMENTAL FACTORS LEADING TO-THE POTENTIAL DISTRIBUTION OF COMPLEX LIFE IN THE UNIVERSE " AND (2) THE RESEARCH WILL STUDY THE "ESTABLISHMENT OF LIFE UNDER CONDITIONS PREVAILING ON OTHER PLANETARY BODIES..;" NAMELY THE GROWTH OF A PLAUSIBLE METHANOGENIC MICROBIAL COMMUNITY IN ACTIVE RSL FEATURES ON MARS., G4762756009, THE OVERARCHING GOAL OF THIS PROPOSAL IS TO ENHANCE UNDERSTANDING OF HOW THE SURFACE AND SUBSURFACE OF MARS MAY BE IN COMMUNICATION TO BRING WATERS OF DISTINCTIVE GEOCHEMISTRIES TO THE SURFACE. GLOBAL MINERAL MAPPING BY CRISM AT HIGH RESOLUTION SHOWS THAT THE SPATIAL DISTRIBUTION OF SULFATE CHLORIDE AND CARBONATE SALTS IS HIGHLY VARIABLE. REACTIVE TRANSPORT MODELING USING PLAUSIBLE MINERAL ASSEMBLAGES IN AND AROUND THE NILI FOSSAE REGION HAS SHOWN THAT ITS CARBONATE MAY RESULT FROM REACTION OF ATMOSPHERICALLY-DERIVED GROUNDWATERS WITH THE UPPER TENS OF METERS OF HIGH-OLIVINE BEARING BASALT TO PRODUCE CARBONATE. HOWEVER WHAT IS THE SOURCE INSTEAD FOR CHLORIDE AND SULFATE DEPOSITS INCLUDING THE ACID SULFATES? A SUBSURFACE SOURCE OF ANIONS MAY BE REQUIRED. HERE WE PROPOSE A MAPPING INVESTIGATION OF THE TERRA SIRENUM REGION ON MARS SITE OF PALEOLAKE DEPOSITS HOSTING ALUNITE AND JAROSITE AND BASINS HOSTING CHLORIDES. RECENTLY LARGE SCALE FAULTS IN THE REGION HAVE ALSO BEEN MAPPED. THESE SUGGEST A MEANS FOR WATERS CIRCULATING AT DEPTH TO REACH THE SUBSURFACE. WE WILL TEST THE HYPOTHESIS THAT THE PRESENCE AND SOURCE OF UPWELLING SUBSURFACE WATERS I.E. THE PLUMBING OF MARTIAN SHALLOW OR DEEP LAKES PLAYS A CRUCIAL ROLE IN THE DEVELOPMENT OF MARTIAN PALEOLAKES WITH DISTINCTIVE GEOCHEMISTRIES AND THUS DISTINCTIVE MINERAL ASSEMBLAGES AND BIOLOGICAL POTENTIAL. OUR OBJECTIVES ARE (I) TO MAP THE DISTRIBUTIONS OF SECONDARY (WATER-RELATED) MINERALS IN THE TERRA SIRENUM REGION IN RELATION TO GEOLOGICAL FEATURES AND (II) TO CONSTRAIN THE SOURCES AND QUANTITIES OF S AND CL THAT FORM OBSERVED SALT-RICH DEPOSITS AND THUS CONTROL THE HABITABILITY AND BIOLOGICAL POTENTIAL OF WATERS. IN PARTICULAR USING OBSERVED MINERALOGY AND OBSERVED SPATIAL RELATIONSHIPS BETWEEN GEOLOGIC UNITS WE WILL EXAMINE THE PLAUSIBILITY OF (1) ATMOSPHERICALLY-SOURCED VOLATILES INTERACTING WITH SURFACE ROCKS AND SOILS TO PROVIDE S AND CL (2) WEATHERING OF SULFIDES FROM IGNEOUS ROCK (3) REMOBILIZATION OF PRIOR GENERATIONS OF BURIED SALT DEPOSITS OR (4) INTERACTION WITH MAGMATIC GASES.
OpenAlex ID: W2963995885