Imperial College London

ProfessorMarkSephton

Faculty of EngineeringDepartment of Earth Science & Engineering

Professor of Organic Geochemistry
 
 
 
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Contact

 

+44 (0)20 7594 6542m.a.sephton Website

 
 
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Location

 

G30 (via G28)Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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236 results found

Potiszil C, Montgomery W, Sephton M, 2021, Heterogeneity within refractory organic matter from CM2 carbonaceous chondrites: evidence from Raman spectroscopy, Earth and Planetary Science Letters, ISSN: 0012-821X

CM2 chondrites experienced widespread aqueous and short term thermal alteration on their parent bodies. Whilst previous Raman spectroscopic investigations have investigated insoluble organic matter (IOM), they have not taken into account the binary nature of IOM. Studies employing mass spectrometry have indicated that IOM also known as macromolecular organic matter (MOM) is in fact composed of two distinct fractions: labile organic matter (LOM) and refractory organic matter (ROM). The ROM component represents the aromatic rich and heteroatom poor component of IOM/MOM, whilst the LOM fraction represents a more heteroatom and aliphatic rich component. Here we report Raman 2D maps and spectroscopic data for Murchison and Mighei, both before and after chemical degradation, which attacks and liberates LOM. The removal of LOM simulates the effects of aqueous alteration, where ester and ether bonds are broken and is thought to release some components to the soluble organic matter (SOM) fraction, also known as the free organic matter fraction (FOM). Raman spectroscopy can be used to reveal the nature of bonding (sp2 and sp3) within carbonaceous materials such as meteoritic organic matter, through evaluation of the D and G band peak centres and FWHM values from the recorded data. The presence of sp3 orbitals indicates that the organic materials contain aliphatic linkages and/or heteroatoms. Statistical analysis of the Raman parameters obtained here indicates that the organic matter originating the Raman response is indistinguishable between the bulk (chemically untreated) and chemically degraded (treated with KOH and HI) samples. Such an observation indicates that the ROM fraction is the major contributor to the Raman response of meteoritic organic matter and thus Raman spectroscopy is unlikely to record any aqueous alteration processes that have affected meteoritic organic matter. Therefore, studies which use Raman to probe the IOM are investigating just one of the compone

Journal article

Royle S, Watson JS, Sephton M, 2021, Transformation of cyanobacterial biomolecules by iron oxides during flash pyrolysis: Implications for Mars life detection missions, Astrobiology, ISSN: 1531-1074

Answering the question of whether life ever existed on Mars is a key goal of both NASA’s and ESA’s imminent Mars rover missions. The obfuscatory effects of oxidising salts, such as perchlorates and sulfates, on organic matter during thermal decomposition analysis techniques are well established. Less well studied are the transformative effects of iron oxides and (oxy)hydroxides, which are present in great abundances in the martian regolith. We examined the products of flash pyrolysis GC-MS, a technique analogous to the thermal techniques employed by past, current and future landed Mars missions, formed when the cyanobacteria Arthrospira platensis was heated in the presence of a variety of Mars-relevant 16iron bearing minerals. We found that iron oxides/(oxy)hydroxides have transformative effects on the pyrolytic products of cyanobacterial biomolecules. Both the abundance and variety of molecular species detected were decreased as iron substrates transformed biomolecules, by both oxidative and reductive processes, into lower fidelity alkanes, aromatic and aryl-bonded hydrocarbons. Despite the loss of fidelity, a suite containing mid-length alkanes and PAHs and/or aryl-bonded molecules in iron-rich samples subjected to pyrolysis, may allude to the transformation of cyanobacterially-derived mid-long chain length fatty acids (particularly unsaturated fatty acids) originally present in the sample. Haematite was found to be the iron-oxide with the lowest transformation potential and so, because this iron oxide has a high affinity forco-deposition of organic matter and preservation over geological timescales, sampling at Mars should target sediments/strata which have undergone a diagenetic history encouraging the dehydration, dehydroxylation and oxidation of more reactive iron-bearing phases to haematite by looking for (mineralogical) evidence of the activity of oxidising, acidic/neutral and either hot or long-lived fluids.

Journal article

Tan JSW, Sephton MA, 2021, Quantifying preservation potential: lipid degradation in a Mars-analog circumneutral iron deposit, Astrobiology, Vol: 21, Pages: 1-17, ISSN: 1531-1074

Comparisons between the preservation potential of Mars-analog environments have historically been qualitative rather than quantitative. Recently, however, laboratory-based artificial maturation combined with kinetic modeling techniques have emerged as a potential means by which the preservation potential of solvent-soluble organic matter can be quantified in various Mars-analog environments. These methods consider how elevated temperatures, pressures, and organic–inorganic interactions influence the degradation of organic biomarkers post-burial. We used these techniques to investigate the preservation potential of deposits from a circumneutral iron-rich groundwater system. These deposits are composed of ferrihydrite (Fe5HO8 · 4H2O), an amorphous iron hydroxide mineral that is a common constituent of rocks found in ancient lacustrine environments on Mars, such as those observed in Gale Crater. Both natural and synthetic ferrihydrite samples were subjected to hydrous pyrolysis to observe the effects of long-term burial on the mineralogy and organic content of the samples. Our experiments revealed that organic–inorganic interactions in the samples are dominated by the transformation of iron minerals. As amorphous ferrihydrite transforms into more crystalline species, the decrease in surface area results in the desorption of organic matter, potentially rendering them more susceptible to degradation. We also find that circumneutral iron-rich deposits provide unfavorable conditions for the preservation of solvent-soluble organic matter. Quantitative comparisons between preservation potentials as calculated when using kinetic parameters show that circumneutral iron-rich deposits are ∼25 times less likely to preserve solvent-soluble organic matter compared with acidic, iron-rich environments. Our results suggest that circumneutral iron-rich deposits should be deprioritized in favor of acidic iron- and sulfur-rich deposits when searching for evidence o

Journal article

Royle SH, Tan J, Watson JS, Sephton MAet al., 2021, Pyrolysis of carboxylic acids in the presence of iron oxides: implications for life detection on missions to Mars, Astrobiology, Pages: 1-19, ISSN: 1531-1074

The search for, and characterization of, organic matter on Mars is central to efforts in identifying habitable environments and detecting evidence of life in the martian surface and near surface. Iron oxides are ubiquitous in the martian regolith and are known to be associated with the deposition and preservation of organic matter in certain terrestrial environments, thus iron oxide-rich sediments are potential targets for life-detection missions. The most frequently used protocol for martian organic matter characterization (also planned for use on ExoMars) has been thermal extraction for the transfer of organic matter to gas chromatography-mass spectrometry (GC-MS) detectors. For the effective use of thermal extraction for martian samples, it is necessary to explore how potential biomarker organic molecules evolve during this process in the presence of iron oxides. We have thermally decomposed iron oxides simultaneously with (z)-octadec-9-enoic and n-octadecanoic acids and analyzed the products through pyrolysis-GC-MS. We found that the thermally driven dehydration, reduction, and recrystallization of iron oxides transformed fatty acids. Overall detectability of products greatly reduced, molecular diversity decreased, unsaturated products decreased, and aromatization increased. The severity of this effect increased as reduction potential of the iron oxide and inferred free radical formation increased. Of the iron oxides tested hematite showed the least transformative effects, followed by magnetite, goethite, then ferrihydrite. It was possible to identify the saturation state of the parent carboxylic acid at high (0.5 wt %) concentrations by the distribution of n-alkylbenzenes in the pyrolysis products. When selecting life-detection targets on Mars, localities where hematite is the dominant iron oxide could be targeted preferentially, otherwise thermal analysis of carboxylic acids, or similar biomarker molecules, will lead to enhanced polymerization, aromatiz

Journal article

Tan J, Royle S, Sephton M, 2021, Artificial maturation of iron- and sulfur-rich Mars analogues: Implications for the diagenetic stability of biopolymers and their detection with pyrolysis gas chromatography–mass spectrometry, Astrobiology, Vol: 21, Pages: 199-218, ISSN: 1531-1074

Acidic iron- and sulfur-rich streams are appropriate analogues for the late Noachian and early Hesperian periods of martian history, when Mars exhibited extensive habitable environments. Any past life on Mars may have left behind diagnostic evidence of life that could be detected at the present day. For effective preservation, these remains must have avoided the harsh radiation flux at the martian surface, survived geological storage for billions of years, and remained detectable within their geochemical environment by analytical instrument suites used on Mars today, such as thermal extraction techniques.We investigated the detectability of organic matter within sulfur stream sediments that had been subjected to artificial maturation by hydrous pyrolysis. After maturation, the samples were analyzed by pyrolysis–gas chromatography–mass spectrometry (py-GC-MS) to determine whether organic matter could be detected with this commonly used technique. We find that macromolecular organic matter can survive the artificial maturation process in the presence of iron- and sulfur-rich minerals but cannot be unambiguously distinguished from abiotic organic matter. However, if jarosite and goethite are present in the sulfur stream environment, they interfere with the py-GC-MS detection of organic compounds in these samples. Clay reduces the obfuscating effect of the oxidizing minerals by providing nondeleterious adsorption sites. We also find that after a simple alkali and acid leaching process that removes oxidizing minerals such as iron sulfates, oxides, and oxyhydroxides, the sulfur stream samples exhibit much greater organic responses during py-GC-MS in terms of both abundance and diversity of organic compounds, such as the detection of hopanes in all leached samples.Our results suggest that insoluble organic matter can be preserved over billions of years of geological storage while still retaining diagnostic organic information, but sample selection strategies mu

Journal article

Tan J, Sephton M, 2020, Organic records of early life on Mars: the role of iron, burial and kinetics on preservation, Astrobiology, Vol: 20, Pages: 53-72, ISSN: 1531-1074

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.

Journal article

Abubakar R, Muxworthy A, Fraser A, Sephton MA, Watson JS, Heslop D, Paterson G, Southern Pet al., 2020, Mapping hydrocarbon charge-points in the Wessex Basin using seismic, geochemistry and mineral magnetics, Marine and Petroleum Geology, Vol: 111, Pages: 510-528, ISSN: 1873-4073

This study reports a multidisciplinary approach to determining hydrocarbon charge-points and migration in the Wessex Basin, southern England. Geochemical analysis of reservoir core material (Bridport Sandstone and Inferior Oolite) using gas chromatography-mass spectrometry (GC-MS), suggests that the oil in the Wessex Basin is from a single source, and that small variations in environmentally sensitive biomarkers are likely due to small differences in maturity or depositional conditions during the formation of the oil over millions of years. Using seismic data, basin modelling revealed two potential hydrocarbon migration pathways from the hanging wall of the Purbeck fault into the Sherwood Sandstone reservoir at Wytch Farm. One of these potential pathways is represented by cores termed Creech and the other Bushey Farm. To try to distinguish between the two potential pathways, cores were studied using mineral magnetic techniques. The magnetic signature was characterised using low-temperature (<50 K) magnetic measurements; this is because much of the magnetic signature was dominated by nanoparticles < 30 nm, which are thermally activated at room temperature and magnetically “transparent”. Wells that contained considerable amounts of hydrocarbons were dominated by nanometric magnetite (<30 nm). Such particles are small enough to migrate with the oil, through pore spaces, which are of the order ~100 nm. Wells located at the fringes of large hydrocarbon accumulation had enhanced pyrrhotite-dominated magnetic signals. Of the two potential migration pathways, the mineral magnetic results suggest that the oil migrated through Creech rather than through Bushey Farm.

Journal article

Royle S, Watson J, Zhang Y, Chatzitheoklitos G, Sephton Met al., 2019, Solid Phase Micro Extraction: Potential for Organic Contamination Control for Planetary Protection of Life-Detection Missions to the Icy Moons of the Outer Solar System, Astrobiology, Vol: 19, Pages: 1153-1166, ISSN: 1531-1074

Conclusively detecting, or ruling out the possibility of, life on the icy moons of the outer solar system will require spacecraft missions to undergo rigorous planetary protection and contamination control procedures to achieve extremely low levels of organic terrestrial contamination. Contamination control is necessary to avoid forward contamination of the body of interest and to avoid the detection of false positive signals which could either mask indigenous organic chemistry of interest or cause an astrobiological false alarm. Here we test a new method for rapidly and inexpensively assessing the organic cleanliness of spaceflight hardware surfaces using solid phase micro extraction (SPME) fibres to directly swab surfaces. The results suggest that the method is both time and cost efficient. The SPME-gas chromatography mass spectrometry (GC-MS) method is sensitive to common mid-weight, non-polar contaminant compounds, e.g. aliphatic and aromatic hydrocarbons, which are common contaminants in laboratory settings. While we demonstrate the potential of SPME for surface sampling, the GC-MS instrumentation restricts the SPME-GC-MS technique’s sensitivity to larger polar and non-volatile compounds. Although not used in this study, to increase the potential range of detectable compounds, SPME can also be used in conjunction with high performance liquid chromatography/liquid chromatography-mass spectrometry systems suitable for polar analytes [Kataoka et al., 2000]. Thus, our SPME method presents an opportunity to monitor organic contamination in a relatively rapid and routine way that produces information-rich data sets.

Journal article

Rettberg P, Antunes A, Brucato J, Cabezas P, Collins G, Haddaji A, Kminek G, Leuko S, McKenna-Lawlor S, Moissl-Eichinger C, Fellous J-L, Olsson-Francis K, Pearce D, Rabbow E, Royle S, Saunders M, Sephton M, Spry A, Walter N, Wimmer Schweingruber R, Treuet J-Cet al., 2019, Biological contamination prevention for outer solar system moons of astrobiological interest: What do we need to know?, Astrobiology, Vol: 19, ISSN: 1531-1074

To ensure that scientific investments in space exploration are not compromised by terrestrial contamination of celestial bodies, special care needs to be taken to preserve planetary conditions for future astrobiological exploration. Significant effort has been made and is being taken to address planetary protection in the context of inner Solar System exploration. In particular for missions to Mars, detailed internationally accepted guidelines have been established. For missions to the icy moons in the outer Solar System, Europa and Enceladus, the planetary protection requirements are so far based on a probabilistic approach and a conservative estimate of poorly known parameters. One objective of the European Commission-funded project, Planetary Protection of Outer Solar System, was to assess the existing planetary protection approach, to identify inherent knowledge gaps, and to recommend scientific investigations necessary to update the requirements for missions to the icy moons.

Journal article

Kminek G, Fellous J-L, Rettburg P, Moissl-Eichinger C, Sephton MA, Royle SH, Spry A, Yano H, Chujo T, Margheritis DB, Brucato JR, Haddaji AJet al., 2019, The international planetary protection handbook, Space Research Today, Vol: 205, Pages: e1-e120, ISSN: 1752-9298

Journal article

Montgomery W, Jaramillo EA, Royle S, Kounaves S, Schulze-Makuch D, Sephton MAet al., 2019, Effects of oxygen-containing salts on the detection of organic biomarkers on Mars and in terrestrial analogue soils, Astrobiology, Vol: 19, Pages: 711-721, ISSN: 1531-1074

The detection of chlorinated hydrocarbons by Curiosity on Mars has been attributed to the presence of unidentified indigenous organic matter. Similarly, oxychlorines on Earth have been proposed to be responsible for the apparent lack of organics in the Atacama Desert. The presence of perchlorate (ClO4- ) poses a unique challenge to the measurement of organic matter due to the oxidizing power of oxychlorines during commonly used pyrolysis-gas chromatography-mass spectrometry (py-GC-MS) methods. Here, we show that perchlorates and other oxyanion salts inhibit the detection of organic compounds, but that removing these problematic species prior to pyrolysis by using an optimal sample extraction duration and suitable ratios of water to sample mass enables analysis. We have characterized leached and unleached samples containing perchlorates from the Atacama Desert and have found that after leaching, the py-GC-MS chromatograms of the dried mineral residues show identifiable biomarkers associated with indigenous cyanobacteria. Samples which were pyrolyzed without leaching showed no detectable organic matter other than background siloxane and very weak or no trace of detectable polychlorinated benzenes Dried sample residues remaining after leaching, the mineral matrix and water-insoluble organic matter, showed a strong organic response in all cases when analyzed by py-GC-MS. These residues are most likely the product of the pyrolysis of water insoluble organics originally present in the samples. In addition, our results imply that previous soil analyses which contained high levels of oxyanions and concluded that organics were either not present, or at extremely low levels, should be re-examined.

Journal article

Sephton M, 2019, Using geophysics and geochemistry to find life in the solar system, First Break, Vol: 37, Pages: 79-80, ISSN: 0263-5046

Mark A. Sephton demonstrates how active missions to Mars and the icy moons of Jupiter and Saturn are using geophysics and geochemistry to detect organic matter.

Journal article

Jaramillo EA, Royle S, Claire M, Kounaves S, Sephton Met al., 2019, Indigenous organic-oxidized fluid interactions in the tissint Mars meteorite, Geophysical Research Letters, Vol: 46, Pages: 3090-3098, ISSN: 0094-8276

The observed fall and rapid recovery of the Tissint Mars meteorite has provided minimally contaminated samples of the Martian surface. We report analyses of Tissint for organic compounds by pyrolysis‐gas chromatography‐mass spectrometry and for soluble salts by ion chromatography. Pyrolysis‐gas chromatography‐mass spectrometry analysis shows the presence of organic compounds similar to those in the Mars EETA79001 and Nakhla meteorites. The organic profile is dominated by aromatic hydrocarbons, including oxygen and nitrogen‐containing aromatics, and sulfur‐containing species including thiophenes. The soluble salts in Tissint are dominated by sulfate and various oxidation states of chlorine, including perchlorate. The organic compounds and salts in the soils from the Tissint recovery strewn field differ significantly from those found in Tissint suggesting minimal terrestrial contamination. Our results support the hypothesis that the soluble inorganic components of Tissint are most likely a result of indigenous fluid inclusion, thus providing a glimpse into the composition of early Martian fluids.

Journal article

Beaty DW, Grady MM, McSween HY, Sefton-Nash E, Carrier BL, Altieri F, Amelin Y, Ammannito E, Anand M, Benning LG, Bishop JL, Borg LE, Boucher D, Brucato JR, Busemann H, Campbell KA, Czaja AD, Debaille V, Des Marais DJ, Dixon M, Ehlmann BL, Farmer JD, Fernandez-Remolar DC, Filiberto J, Fogarty J, Glavin DP, Goreva YS, Hallis LJ, Harrington AD, Hausrath EM, Herd CDK, Horgan B, Humanyun M, Kleine T, Kleinhenz J, Mackelprang R, Mangold N, Mayhew LE, McCoy JT, McCubbin FM, McLennan SM, Moser DE, Moynier F, Mustard JF, Niles PB, Ori GG, Raulin F, Rettberg P, Rucker MA, Schmitz N, Schwenzer SP, Sephton MA, Shaheen R, Sharp ZD, Schuster DL, Siljestrom S, Smith CL, Spry JA, Steele A, Swindle TD, ten Kate IL, Tosca NJ, Usui T, Van Kranendonk MJ, Wadhwa M, Weiss BP, Werner SC, Westall F, Wheeler RM, Zipfel J, Zorzano MPet al., 2019, The potential science and engineering value of samples delivered to Earth by Mars sample return, METEORITICS & PLANETARY SCIENCE, Vol: 54, Pages: 667-671, ISSN: 1086-9379

Journal article

Beaty DW, Grady MM, McSween HY, Sefton-Nash E, Carrier BL, Altieri F, Amelin Y, Ammannito E, Anand M, Benning LG, Bishop JL, Borg LE, Boucher D, Brucato JR, Busemann H, Campbell KA, Czaja AD, Debaille V, Des Marais DJ, Dixon M, Ehlmann BL, Farmer JD, Fernandez-Remolar DC, Filiberto J, Fogarty J, Glavin DP, Goreva YS, Hallis LJ, Harrington AD, Hausrath EM, Herd CDK, Horgan B, Humayun M, Kleine T, Kleinhenz J, Mackelprang R, Mangold N, Mayhew LE, McCoy JT, McCubbin FM, McLennan SM, Moser DE, Moynier F, Mustard JF, Niles PB, Ori GG, Raulin F, Rettberg P, Rucker MA, Schmitz N, Schwenzer SP, Sephton MA, Shaheen R, Sharp ZD, Shuster DL, Siljeström S, Smith CL, Spry JA, Steele A, Swindle TD, ten Kate IL, Tosca NJ, Usui T, Van Kranendonk MJ, Wadhwa M, Weiss BP, Werner SC, Westall F, Wheeler RM, Zipfel J, Zorzano MPet al., 2019, The potential science and engineering value of samples delivered to Earth by Mars sample return: International MSR Objectives and Samples Team (iMOST), Meteoritics and Planetary Science, Vol: 54, Pages: S3-S152, ISSN: 1086-9379

Executive Summary: Return of samples from the surface of Mars has been a goal of the international Mars science community for many years. Affirmation by NASA and ESA of the importance of Mars exploration led the agencies to establish the international MSR Objectives and Samples Team (iMOST). The purpose of the team is to re-evaluate and update the sample-related science and engineering objectives of a Mars Sample Return (MSR) campaign. The iMOST team has also undertaken to define the measurements and the types of samples that can best address the objectives. Seven objectives have been defined for MSR, traceable through two decades of previously published international priorities. The first two objectives are further divided into sub-objectives. Within the main part of the report, the importance to science and/or engineering of each objective is described, critical measurements that would address the objectives are specified, and the kinds of samples that would be most likely to carry key information are identified. These seven objectives provide a framework for demonstrating how the first set of returned Martian samples would impact future Martian science and exploration. They also have implications for how analogous investigations might be conducted for samples returned by future missions from other solar system bodies, especially those that may harbor biologically relevant or sensitive material, such as Ocean Worlds (Europa, Enceladus, Titan) and others. Summary of Objectives and Sub-Objectives for MSR Identified by iMOST: Objective 1 Interpret the primary geologic processes and history that formed the Martian geologic record, with an emphasis on the role of water. Intent To investigate the geologic environment(s) represented at the Mars 2020 landing site, provide definitive geologic context for collected samples, and detail any characteristics that might relate to past biologic processesThis objective is divided into five sub-objectives that would apply at differ

Journal article

Verchovsky A, Hunt S, Montgomery W, Sephton MAet al., 2019, Reaction of Q to thermal metamorphism in parent bodies: Experimental simulation, Meteoritics and Planetary Science, Vol: 54, Pages: 558-572, ISSN: 1086-9379

Planetary noble gases in chondrites are concentrated in an unidentified carrier phase, called “Q.” Phase Q oxidized at relatively low temperature in pure oxygen is a very minor part of insoluble organic matter (IOM), but has not been separated in a pure form. High‐pressure (HP) experiments have been used to test the effects of thermal metamorphism on IOM from the Orgueil (CI1) meteorite, at conditions up to 10 GPa and 700 °C. The effect of the treatment on carbon structural order was characterized by Raman spectroscopy of the carbon D and G bands. The Raman results show that the IOM becomes progressively more graphite‐like with increasing intensity and duration of the HP treatment. The carbon structural transformations are accompanied by an increase in the release temperatures for IOM carbon and 36Ar during stepped combustion (the former to a greater extent than the latter for the most HP treated sample) when compared with the original untreated Orgueil (CI1) sample. The 36Ar/C ratio also appears to vary in response to HP treatment. Since 36Ar is a part of Q, its release temperature corresponds to that for Q oxidation. Thus, the structural transformations of Q and IOM upon HP treatment are not equal. These results correspond to observations of thermal metamorphism in the meteorite parent bodies, in particular those of type 4 enstatite chondrites, e.g., Indarch (EH4), where graphitized IOM oxidized at significantly higher temperatures than Q (Verchovsky et al. 2002). Our findings imply that Q is less graphitized than most of the macromolecular carbonaceous material present during parent body metamorphism and is thus a carbonaceous phase distinct from other meteoritic IOM.

Journal article

Georgieva MN, Little CTS, Watson JS, Sephton MA, Ball AD, Glover AGet al., 2019, Identification of fossil worm tubes from Phanerozoic hydrothermal vents and cold seeps, Journal of Systematic Palaeontology, Vol: 17, Pages: 287-329, ISSN: 1477-2019

One of the main limitations to understanding the evolutionary history of hydrothermal vent and cold seep communities is the identification of tube fossils from ancient deposits. Tube-dwelling annelids are some of the most conspicuous inhabitants of modern vent and seep ecosystems, and ancient vent and seep tubular fossils are usually considered to have been made by annelids. However, the taxonomic affinities of many tube fossils from vents and seeps are contentious, or have remained largely undetermined due to difficulties in identification. In this study, we make a detailed chemical (Fourier-transform infrared spectroscopy and pyrolysis gas-chromatography mass-spectrometry) and morphological assessment of modern annelid tubes from six families, and fossil tubes (seven tube types from the Cenozoic, 12 Mesozoic and four Palaeozoic) from hydrothermal vent and cold seep environments. Characters identified from these investigations were used to explore for the first time the systematics of ancient vent and seep tubes within a cladistic framework. Results reveal details of the compositions and ultrastructures of modern tubes, and also suggest that two types of tubes from ancient vent localities were made by the annelid family Siboglinidae, which often dominates modern vents and seeps. Our results also highlight that several vent and seep tube fossils formerly thought to have been made by annelids cannot be assigned an annelid affiliation with any certainty. The findings overall improve the level of quality control with regard to interpretations of fossil tubes, and, most importantly, suggest that siboglinids likely occupied Mesozoic vents and seeps, greatly increasing the minimum age of the clade relative to earlier molecular estimates.

Journal article

Royle SH, Tan J, Kounaves SP, Sephton Met al., 2018, Survivability of 1-chloronapthalene during simulated early diagenesis – Implications for chlorinated hydrocarbon detection on Mars, Journal of Geophysical Research: Planets, Vol: 123, Pages: 2790-2802, ISSN: 2169-9097

All missions to Mars which have attempted to detect organic molecules have detected simple chlorohydrocarbons, the source of which has yet to be firmly established. This study assessed the likelihood of these chlorinated molecules being indigenous to the sedimentary units in which they were detected or if they were chlorinated during analysis. The survivability of 1-chloronapthalene was examined via hydrous pyrolysis experiments and its de-chlorination kinetics were determined. The results of these experiments were used to model the survivability of this simple chlorohydrocarbon under Mars-relevant diagenetic conditions using the Sheepbed mudstone unit as a case study. It was found that 1-chloronapthalene was rapidly dechlorinated under Noachian conditions and thus the detected Martian chlorohydrocarbons are unlikely to be ancient and probably formed within the rover’s sample handling chain during analysis.

Journal article

Moreno-Paz M, Gómez-Cifuentes A, Ruiz-Bermejo M, Hosftetter O, Maqueira Á, Morais S, Sephton MA, Knopp D, Parro Vet al., 2018, Detecting non-volatile life- and non-life-derived organics in a carbonaceous chondrite analogue with a new multiplex immunoassay and its relevance for planetary exploration, Astrobiology, Vol: 18, Pages: 1041-1056, ISSN: 1531-1074

Among the potential martian molecular targets are those supplied by meteoritic carbonaceous chondrites such as amino acids and polyaromatic hydrocarbons (PAHs), or true biomarkers by any hypothetical Martian biota (aromatic amino acids, steroid and triterpene molecules, peptides). Heat extraction and pyrolysis based methods currently used in planetary exploration are highly aggressive and very often modify the target molecules making a cumbersome task their identification. We have developed and validated a mild, non-destructive, multiplex competitive/inhibitory microarray immunoassay and its implementation in the SOLID (Signs of Life Detector) instrument for simultaneous detection of several organic molecules relevant for Mars exploration and environmental monitoring. A multiplex inhibitory immunoassay with a set of highly specific and sensitive antibodies capable to distinguish between D and L aromatic amino acids (Phe, Tyr, Trp), benzo[a]pyrene (BAP), pentachlorophenol or sulfone-containing aromatics, was validated in SOLID instrument for the analysis of kerogen samples as analogues of refractory organic material in carbonaceous chondrites or even Mars organics. Most of the antibodies exhibited sensitivities at 1-10 ppb level and some of them even at ppt. The multiplex immunoassay allowed the detection of BAP as well as aromatic sulfones in a water/methanol extract of an early cretaceous sample (c.a. 100 My) enriched in type IV kerogen. No L/D aromatic amino acids were detected, reflecting the high maturity and the absence of chemical groups. The results demonstrated once more the feasibility of multiplex inhibitory immunoassays and its potential use for in situ analytical instruments in planetary exploration and environmental monitoring.

Journal article

Royle SH, Oberlin E, Watson JS, Montgomery W, Kounaves SP, Sephton MAet al., 2018, Perchlorate‐driven combustion of organic matter during pyrolysis‐gas chromatography‐mass spectrometry: implications for organic matter detection on earth and mars, Journal of Geophysical Research: Planets, Vol: 123, Pages: 1901-1909, ISSN: 2169-9097

The search for life on Mars targets the detection of organic matter from extant or extinct organisms. Current protocols use thermal extraction procedures to transfer organic matter to mass spectrometer detectors. Oxidizing minerals on Mars, such as perchlorate, interfere with organic detection by thermal extraction. Thermal decomposition of perchlorate releases oxygen which promotes combustion of organic carbon. We have assessed the minimum mass ratio of organic carbon to perchlorate required to detect organic matter by thermal extraction and mass spectrometry. Locations on Mars with organic carbon to perchlorate ratios above 4.7-9.6 should be targeted. Because habitability is enhanced by the presence of liquid water and because perchlorate is a water soluble salt, locations on Mars with evidence of past or recent liquid water are high priority targets.

Journal article

Sephton MA, Waite JH, Brockwell TG, 2018, How to Detect Life on Icy Moons, ASTROBIOLOGY, Vol: 18, Pages: 843-855, ISSN: 1531-1074

Journal article

Sephton MA, Waite JH, Brockwell TG, 2018, How to detect life on icy moons, Astrobiology, Vol: 18, Pages: 843-855, ISSN: 1531-1074

The icy moons of the outer solar system present the possibility of subsurface water, habitable conditions and potential abodes for life. Access to evidence that reveals the presence of life on the icy moons can be facilitated by plumes that eject material from the subsurface out into space. One instrument capable of performing life-search investigations at the icy moons is the MAss SPectrometer for Planetary EXploration/Europa (MASPEX), which constitutes a high-resolution, high sensitivity multibounce time-of-flight mass spectrometer capable of measuring trace amounts (ppb) of organic compounds. MASPEX has been selected for the NASA Europa Clipper mission and will sample any plumes and the surface-sputtered atmosphere to assess any evidence for habitability and life. MASPEX is capable of similar investigations targeted at other icy moons. Data may be forthcoming from direct sampling but also impact dissociation because of the high speed of some analytes. Impact dissociation is analogous to the dissociation provided by modern analytical pyrolysis methods. Radiolytic dissociation on the Europan surface before or during the sputtering process can also induce fragmentation similar to pyrolysis. In this study, we have compiled pyrolysis-mass spectrometry data from a variety of biological and non-biological materials to demonstrate the ability of MASPEX to recognise habitability and detect life in any plumes and atmospheres of icy moons.

Journal article

Sephton MA, Waite JH, Brockwell TG, 2018, Searching for life with mass spectrometry, ASTRONOMY & GEOPHYSICS, Vol: 59, Pages: 23-24, ISSN: 1366-8781

Journal article

Sephton MA, 2018, Back is the future: Returning samples from Mars for analysis on Earth, First Break, Vol: 36, Pages: 73-75, ISSN: 0263-5046

Seeking evidence of life in the solar system will be partly the search for organic signatures in rock matrices. The search for organic matter is common to petroleum exploration on Earth and life search missions to Mars. Despite some commonality between investigations into life records on Earth and Mars, there are also significant differences. Favourable organic concentrations in petroleum source rocks are much higher than those needed for life-search targets on Mars. Choosing samples for collection on Mars for return to Earth requires more care at earlier stages than needed for collection of samples on Earth. During and after collection, samples of Mars must be protected from organic contamination that could confuse their potentially weak and poorly understood signals. While operations on Mars provide effectively unlimited sample but with limited instrumentation, analysis on Earth involve constrained amounts of returned samples but access to the world’s best analytical capabilities. Returning samples from Mars also presents the potential for historical firsts including new technologies and important preparations for the eventual human exploration of the red planet.

Journal article

Sephton MA, Waite JH, Brockwell TG, 2018, Searching for life with mass spectrometry, Astronomy and Geophysics, Vol: 59, Pages: 3.23-3.24, ISSN: 1366-8781

Mark A Sephton, J Hunter Waite and Tim G Brockwell look at the capabilities of the Europa Clipper mission to explore one of Jupiter’s icy moons.

Journal article

Sephton MA, Waite JH, Brockwell TG, 2018, Searching for life with mass spectrometry, Astronomy and Geophysics, Vol: 59, Pages: 3.23-3.24, ISSN: 1366-8781

Journal article

Tan J, Lewis JMT, Sephton MA, 2018, The fate of lipid biosignatures in a Mars-analogue sulfur stream., Scientific Reports, Vol: 8, Pages: 7586-7586, ISSN: 2045-2322

Past life on Mars will have generated organic remains that may be preserved in present day Mars rocks. The most recent period in the history of Mars that retained widespread surface waters was the late Noachian and early Hesperian and thus possessed the potential to sustain the most evolved and widely distributed martian life. Guidance for investigating late Noachian and early Hesperian rocks is provided by studies of analogous acidic and sulfur-rich environments on Earth. Here we report organic responses for an acid stream containing acidophilic organisms whose post-mortem remains are entombed in iron sulphates and iron oxides. We find that, if life was present in the Hesperian, martian organic records will comprise microbial lipids. Lipids are a potential sizeable reservoir of fossil carbon on Mars, and can be used to distinguish between different domains of life. Concentrations of lipids, and particularly alkanoic or “fatty” acids, are highest in goethite layers that reflect high water-to-rock ratios and thus a greater potential for habitability. Goethite can dehydrate to hematite, which is widespread on Mars. Mars missions should seek to detect fatty acids or their diagenetic products in the oxides and hydroxides of iron associated with sulphur-rich environments.

Journal article

Gordon PR, Sephton MA, 2018, A method for choosing the best samples for Mars sample return, Astrobiology, Vol: 18, Pages: 556-570, ISSN: 1531-1074

Success of a future Mars Sample Return mission will depend on the correct choice of samples. Pyrolysis-FTIR can be employed as a triage instrument for Mars Sample Return. The technique can thermally dissociate minerals and organic matter for detection. Identification of certain mineral types can determine the habitability of the depositional environment, past or present, while detection of organic matter may suggest past or present habitation. In Mars history, the Theiikian Era represents an attractive target for life search missions and the acquisition of samples. The acidic and increasingly dry Theiikian may have been habitable and followed a lengthy neutral and wet period in Mars history during which life could have originated and proliferated to achieve relatively abundant levels of biomass with a wide distribution. Moreover, the sulfate minerals produced in the Theiikian are also known to be good preservers of organic matter. We have used pyrolysis-FTIR and samples from a Mars analogue ferrous acid stream with a thriving ecosystem to test the triage concept. Pyrolysis-FTIR identifies those samples with the greatest probability of habitability and habitation. A three tier scoring system was developed based on the detection of i) organic signals, ii) carbon dioxide and water and iii) sulfur dioxide. The presence of each component is given a score of A, B or C depending on whether the substance has been detected, tentatively detected or not detected respectively. Single-step (for greatest possible sensitivity) or multi-step (for more diagnostic data) pyrolysis-FTIR methods can inform the assignments. The system allows the highest priority samples to be categorised as AAA (or A*AA if the organic signal is complex) while the lowest priority samples can be categorised as CCC. Our methods provide a mechanism to rank samples and identify those that should take the highest priority for return to Earth during a Mars Sample Return mission.

Journal article

Lewis JMT, Najorka J, Watson JS, Sephton MAet al., 2018, The search for Hesperian organic matter on Mars: Pyrolysis studies of sediments rich in sulfur and iron, Astrobiology, Vol: 18, Pages: 454-464, ISSN: 1531-1074

Jarosite on Mars is of significant geological and astrobiological interest as it forms in acidic aqueous conditions that are potentially habitable for acidophilic organisms. Jarosite can provide environmental context and may host organic matter. The most common analytical technique used to search for organic molecules on the surface of Mars is pyrolysis. However, thermal decomposition of jarosite produces oxygen, which degrades organic signals. At pH values greater than 3 and high water to rock ratios jarosite has a close association with goethite. Hematite can form by dehydration of goethite or directly from jarosite under certain aqueous conditions. Goethite and hematite are significantly more amenable for pyrolysis experiments searching for organic matter than jarosite. Analysis of the mineralogy and organic chemistry of samples from a natural acidic stream revealed a diverse response for organic compounds during pyrolysis of goethite-rich layers but a poor response for jarosite-rich or mixed jarosite-goethite units. Goethite units that are associated with jarosite but do not contain jarosite themselves should be targeted for organic detection pyrolysis experiments on Mars. These findings are extremely timely as future exploration targets for Mars Science Laboratory include Hematite Ridge, which may have formed from goethite precursors.

Journal article

Schulze-Makuch D, Wagner D, Kounaves SP, Mangelsdorf K, Devine KG, de Vera J-P, Schmitt-Kopplin P, Grossart H-P, Parro V, Kaupenjohann M, Galy A, Schneider B, Airo A, Froesler J, Davila AF, Arens FL, Caceres L, Cornejo FS, Carrizo D, Dartnell L, DiRuggiero J, Flury M, Ganzert L, Gessner MO, Grathwohl P, Guan L, Heinz J, Hess M, Keppler F, Maus D, McKay CP, Meckenstock RU, Montgomery W, Oberlin EA, Probst AJ, Saenz JS, Sattler T, Schirmack J, Sephton MA, Schloter M, Uhl J, Valenzuela B, Vestergaard G, Woermer L, Zamorano Pet al., 2018, Transitory microbial habitat in the hyperarid Atacama Desert, PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, Vol: 115, Pages: 2670-2675, ISSN: 0027-8424

Journal article

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