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This thesis investigates how increased global mean temperatures on Earth, induced by the increase in the luminosity of the Sun as it ages, change the types of habitable environments on the planet at local scales over the next 3 Gyr. Rising temperatures enhance silicate weathering rates, reducing atmospheric CO₂ levels to below the threshold for photosynthesis, while simultaneously pushing environments past the temperature tolerances of plant and animal species. This leads to the end of all plant life and animal life (due to reduced food, O₂ and H₂O availability, as well as higher temperatures) within the next 1 Gyr. The reduction in the extent of the remaining microbial biosphere due to increasing temperatures and rapid ocean evaporation is then modelled, incorporating orbital parameter changes until all known types of life become extinct; a maximum of 2.8 Gyr from the present. The biosignatures associated with these changes are determined and the analysis extended to Earth-like extrasolar planets nearing the end of their habitable lifetimes. In particular, the stages in the main sequence evolutions of Sun-like stars within 10 pc are evaluated and used to extrapolate the stage that an Earth-analogue planet would be at in its habitable evolution, to determine the best candidate systems for a far-future Earth-analogue biosphere, highlighting the Beta Canum Venaticorum system as a good target. One of the most promising biosignatures for a microbial biosphere on the far-future Earth (and similar planets) may be CH₄, which could reach levels in the atmosphere that make it more readily detectable than it is for a present-day Earth-like atmosphere. Determining these biosignatures will help expand the search for life to the wider range of environments that will be found as the habitable exoplanet inventory grows and planets are found at different stages in their habitable evolution.

<p>Modern microbialites provide the opportunity to explore the influences of biology on microbialite formation and understand how biosignatures can be preserved in these structures. In this study, we used the isotopic compositions (δ¹³C) of phospholipid fatty acids (PLFAs) and their structurally-defined profiles, in conjunction with calcium carbonate isotopic compositions and imaging to evaluate microbial autotrophic and heterotrophic processes associated with freshwater microbialites from Kelly Lake, British Columbia. This was done to determine what types of metabolism may have been influencing microbialite growth and whether a biosignature of this process was preserved. In addition, PLFA profiles from a microbialite-derived pure culture were analyzed under various growth conditions to assess environmental influences on microbial PLFA composition.</p> <p>Although the majority of the δ¹³C values of Kelly Lake microbialite surface carbonates fell within the range predicted for equilibrium precipitation, samples collected from 26 m were found to have enriched δ¹³C_carb values and are likely a biosignature of autotrophy at this depth. PLFA profiles and δ¹³C_PLFAvalues also supported the predominance of autotrophy, however, they indicated that heterotrophic organisms were also present. This data suggests that autotrophic metabolisms have influenced the local geochemistry in the past, at least at 26 m, and are likely substantial contributors to microbialite growth.</p> <p>Changes in temperature, pH, NaCl concentrations, and cell densities were found to induce variations in the PLFA profiles of the <em>Exiguobacterium</em> strain RW2. The degree of PLFA unsaturation changed in each of the different culture conditions, and was predominantly adjusted through alterations in the branched monoenoic PLFAs, particularly i-17:1Δ⁵. These results highlight the difficulties associated with applying PLFA profiles as evidence for shifts in a microbial community composition, since altered growth conditions can induce intra-specific PLFA changes.</p> / Master of Science (MSc)

abstract: The search for life on Mars is a major NASA priority. A Mars Sample Return (MSR) mission, Mars 2020, will be NASA's next step towards this goal, carrying an instrument suite that can identify samples containing potential biosignatures. Those samples will be later returned to Earth for detailed analysis. This dissertation is intended to inform strategies for fossil biosignature detection in Mars analog samples targeted for their high biosignature preservation potential (BPP) using in situ rover-based instruments. In chapter 2, I assessed the diagenesis and BPP of one relevant analog habitable Martian environment: a playa evaporite sequence within the Verde Formation, Arizona. Coupling outcrop-scale observations with laboratory analyses, results revealed four diagenetic pathways, each with distinct impacts on BPP. When MSR occurs, the sample mass returned will be restricted, highlighting the importance of developing instruments that can select the most promising samples for MSR. Raman spectroscopy is one favored technique for this purpose. Three Raman instruments will be sent onboard two upcoming Mars rover missions for the first time. In chapters 3-4, I investigated the challenges of Raman to identify samples for MSR. I examined two Raman systems, each optimized in a different way to mitigate a major problem commonly suffered by Raman instruments: background fluorescence. In Chapter 3, I focused on visible laser excitation wavelength (532 nm) gated (or time-resolved Raman, TRR) spectroscopy. Results showed occasional improvement over conventional Raman for mitigating fluorescence in samples. It was hypothesized that results were wavelength-dependent and that greater fluorescence reduction was possible with UV laser excitation. In Chapter 4, I tested this hypothesis with a time-resolved UV (266 nm) gated Raman and UV fluorescence spectroscopy capability. I acquired Raman and fluorescence data sets on samples and showed that the UV system enabled identifications of minerals and biosignatures in samples with high confidence. The results obtained in this dissertation may inform approaches for MSR by: (1) refining models for biosignature preservation in habitable Mars environments; (2) improving sample selection and caching strategies, which may increase the success of Earth-based biogenicity studies; and (3) informing the development of Raman instruments for upcoming rover-based missions. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2016

Shallow marine environments from the Lower Cambrian period were very different to shallow marine environments of today. Tubes of what was thought to be silica recovered from a partly dolomitized carbonate sample collected form a site near Indian Springs, Nevada could help further understand the chemistry and characteristics of such environments. The aim of this study is to present a detailed morphological description of the tubular structures found in the rock sample as well as to give a description of the environment in which they were produced. This was achieved by first studying the samples with several different analytical techniques including Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDS) and subsequent evaluation of the obtained data. This resulted in the discovery that the tubular structures have a wall mainly consisting of non-detrital silica crystals. The crystals are arranged in string-like structures which overlap to form tube walls of varying thicknesses. The observed tubular structures are typically straight and ca. 0,23 to 0,25 mm long, but slightly curved and rare bifurcating tubes were also seen. The elemental mapping of a thin section of tubes showed that the wall-forming crystals consist mainly of silica (SiO2), however, small concentrations of calcium (Ca) were found inside many of the silica crystals leading to the conclusion that positive calcium ions may have acted as a seed for the silica crystals. A comparison of the tubular structures with other tubular fossils of the same geological time period is presented as well as a discussion of whether the specimens are of biological origin, and consequently a biosignature, as these could be used in future research when studying material from other planetary bodies. / Grunda marinmiljöer i nedre Kambrium var väldigt annorlunda från grunda marinmiljöer som finns idag. Små rör av vad som hypotiserades vara kiseloxid upptäckta i en dolomitiserad kalkstenstuff från Indian Springs, Nevada skulle kunna hjälpa att förstå kemin inblandad i bildandet av dessa samt bildningsmiljön i mer detalj. Syftet med detta projekt är att presentera en detaljerad morfologisk beskrivning av dessa rör samt försöka beskriv miljön i vilken de bildades. Undersökningen gjorde genom att först studera rören med olika mikroskoperingsmetoder inklusive ett optiskt mikroskop samt med ett svepelektronmikroskop (SEM), sedan analyserades proverna med Energidispersiv röntgenspektroskopi (EDS) för att detektera och kartera de grundämnena som fanns i rören. Resultaten av dessa metoder är att rören är cylindriska eller cigarrformade samt har en väggstruktur av kiseldioxidkristaller som sitter ihop som strängar av pärlor. Rören är huvudsakligen raka och har en längd på mellan 0,23 och 0,25mm, även böjda och förgrenade rör hat hittats, dock var mer sällsynta än de raka. Den kemiska analysen av ett tunnslip på några rör visade att de består till mestadels av kiseldioxid (SiO2) men koncentrationer av kalcium (Ca) hittades som indikerar att dessa kanske agerade som små frön för kiseldioxid att växa runt. En jämförelse av dessa rör med andra liknande fossilmed samma struktur och från samma tidsperiod är presenterad samt en diskussion kring rören som biosignatur och dess potentiella biologiskt ursprung samt användning i framtida forskning inom ämnet.

In this licentiate thesis, I consider debris disks from an observational, astronomical viewpoint, but also discuss a potential astrobiological application. Debris disks are essentially disks of dust and rocks around main-sequence stars, analogue to the Kuiper- or the asteroid belt in our solar system. Their observation and theoretical modeling can help to constrain planet formation models and help in the understanding of the history of the solar system. After a general introduction into the field of debris disks and some basic debris disk physics, the thesis concentrates on the observation of gas in debris disks. The possible origins of this gas and its dynamics are discussed and it is considered what it can tell us about the physical conditions in the disk and possibly about the dust composition. In this way, the paper associated with this thesis (dealing with the gas in the β Pic debris disk) is set into context. More in detail, we observed the CII emission originating from the carbon-rich β Pic disk with Herschel HIFI and attempted to constrain the spatial distribution of the gas from the shape of the emission line. This is necessary since the gas production mechanism is currently unknown, but can be constraint by obtaining information about the spatial profile of the gas. The last part of the thesis describes our preliminary studies of the possibility of a debris disk containing biomarkers, created by a giant impact on a life-bearing exoplanet.