Evaluation of meteorites as habitats for terrestrial microorganisms: Results from the Nullarbor Plain, Australia, a Mars analogue site
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Life on Mars
Troilite
Carbonate minerals
Weathering products should serve as indicators of weathering environments and may provide the best evidence of the nature of climate change on Mars. No direct mineralogical measurements of Martian regolith were performed by the Viking missions, but the biology and X-ray fluorescence experiments provided some information on the physiochemical properties of Martian regolith. Most post-Viking studies of candidate weathering products have emphasized phyllosilicates and Fe-oxides; zeolites are potentially important, but overlooked, candidate Martian minerals. Zeolites would be important on Mars for three different reasons. First, they are major sinks of atmospheric gases and, per unit mass, are stronger and more efficient sorbents than are phyllosilicates. Secondly, they can be virtually unique sorbents and shelters for organic compounds and possible catalysts for organic-based reactions. Finally, their exchangeable ions are good indicators of the chemical properties of solutions with which they have communicated. Accordingly, the search for information on past compositions of the Martian atmosphere and hydrosphere should find zeolites to be rich repositories.
Regolith
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The success of selecting future landing sites on Mars to discover extinct and/or extant extraterrestrial life is dependent on the correct approximation of available knowledge about terrestrial paleogeochemistry and life evolution to Martian (paleo) geology and geochemistry. It is well known that both Earth and Mars are Fe rich. This widespread occurrence suggests that Fe may have played a key role in early life forms, where it probably served as a key constituent in early prosthetic moieties in many proteins of ancient microbes on Earth and likely Mars. The second critical idea is the premise that Life on Mars could most likely have developed when Mars experienced tectonic activity [1] which dramatically decreased around 1 bin years after Martian creation. After that Martian life could have gone extinct or hibernated in the deep subsurface, which would be expensive to reach in contrast to the successful work of Martian surface rovers. Here we analyze the diversity of microbes in several terrestrial Fe rich surface environments in conjunction with the phylogeny and molecular timing of emergence of those microbes on Earth. Anticipated results should help evaluate future landing sites on Mars in searches for biosignatures.
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In 1996, David McKay and coworkers reported evidence suggesting the possibility of fossils in the martian meteorite ALH84001 (see PSR Discoveries article Life on Mars). This work has stimulated much discussion as to the nature and origin of organic material in ALH84001, another martian meteorite, EET79001, and other martian meteorites in general. My colleagues C. Courtney, D. A. Jeffrey, and J. W. Beck and I have been investigating the origin of the organic compounds by measuring the abundances of the isotopes of carbon (C) using accelerator mass spectrometry (AMS). Important clues to the origin of the organic material can be obtained from the amounts of 14C (frequently nicknamed radiocarbon) and the relative amounts of 13C and 12C. Our analyses indicate that at least 80% of the organic material in ALH84001 is from Earth, not Mars, casting doubt on the hypothesis the meteorite contains a record of fossil life on Mars.
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The search for life beyond Earth is the driving motivation for present and planned missions to Mars by both NASA and ESA. Water is a key ingredient and medium for life, yet the aqueous history of Mars is very poorly understood. To deepen our knowledge of Mars’ history, and aid in the search for life, it is essential to investigate secondary minerals, such as phyllosilicates, which formed by the interaction of igneous rocks with aqueous solutions.
Secondary minerals contain chemical, structural and isotopic records of their formation and alteration histories – including proxies for key environmental conditions such as temperature. A major challenge in understanding these records will be the efficient integration of data returned by lander/orbiter missions with
high-precision laboratory studies of martian meteorites and terrestrial analogues. The present study has a twofold approach: 1) Investigation of the effects of mineral heterogeneity on reflectance spectra, and 2) Investigation of clay mineral assemblages in martian meteorites, specifically the Nakhlites.
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Mariner 9 photographs of Mars indicate that significant erosion has occurred on that planet. Although several possible erosion mechanisms have been proposed, most terrestrial weathering mechanisms cannot function in the present Martian environment. Salt weathering, believed to be active in the Antarctic dry valleys, is especially suited to Mars, given the presence of salts and small amounts of water. Volcanic salts are probably available, and the association of salts and water is likely from both thermodynamic and geologic considerations.
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Abiogenesis
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Early Earth
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Abstract: The search for life on Mars: the importance of Mars-like minerals on Earth to astrobiology
In recent years, orbital and surface missions have provided a wealth of information on the Red Planet. In particular, the mineralogical composition of surface materials has helped to unravel the geological and climatic history of Mars. The ongoing accumulation of information and knowledge about Martian mineralogy, geochemical processes and climate history is helping to define search strategies for future missions that will specifically seek out traces of past life or evidence of existing life – two of the primary goals of astrobiology. This talk will give an overview of the importance of studying Mars-like minerals on Earth as an important step to addressing whether life ever existed on Mars. Spectroscopic data from Mars Global Surveyor and Mars Express, as well as from the Mars Exploration Rovers show that Ca-Mg-Fe-sulphates are abundant and diverse at various locations. The fact that these sulphates almost exclusively require liquid water to form means they are of interest to astrobiologists. The presence of the ferric sulphate jarosite within sedimentary rocks at Meridiani Planum has received particular attention because this mineral only forms at relatively low pH in Earth systems. Therefore, its presence suggests that the aqueous solutions that deposited or altered these rocks were acidic. This could potentially have important implications for the development of life on Mars or for the preservation of biosignatures of early Martian life. However, jarosite has recently been discovered within carbonate sediments on Devon Island in the Canadian High Arctic. This finding shows that jarosite can form in a well-buffered environment and likely only requires localized or transient acidic conditions in order to form. Various Ca-Mg-Fe-phyllosilicates (or clay minerals) have also been identified in some of the oldest terranes exposed at the Martian surface. Their presence suggests an early active hydrologic system, and the formation of these abundant and widespread clays would have required the presence of persistent liquid water over extended periods of time, as phyllosilicates generally form from extended periods of water-rock interaction at near circum-neutral pH. These deposits may therefore represent some of the best places to search for past habitable environments and traces of relict life on Mars. Clays are known to bind and trap organic molecules. They may also be formed by microorganisms, in some case preserving physical traces of such processes. Their catalytic properties have also been implicated in prebiotic chemistry on Earth – and perhaps Mars. However, very little work has been done on biosignature formation and preservation in clay-rich systems. It is therefore imperative that the formation and preservation of microbial biosignatures in clay minerals is studied in more detailed using analog systems on Earth in anticipation of future Mars missions.
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Recent spacecraft and lander missions to Mars have reinforced previous interpretations that Mars was a wet and warm planet in the geological past. The role of liquid water in shaping many of the surface features on Mars has long been recognized. Since the presence of liquid water is essential for survival of life, conditions on early Mars might have been more favourable for the emergence and evolution of life. Until a sample return mission to Mars, one of the ways of studying the past environmental conditions on Mars is through chemical and isotopic studies of Martian meteorites. Over 35 individual meteorite samples, believed to have originated on Mars, are now available for lab-based studies. Fe is a key element that is present in both primary and secondary minerals in the Martian meteorites. Fe-isotope ratios can be fractionated by low-temperature processes which includes biological activity. Experimental investigations of Fe reduction and oxidation by bacteria have produced large fractionation in Fe-isotope ratios. Hence, it is considered likely that if there is/were any form of life present on Mars then it might be possible to detect its signature by Fe-isotope studies of Martian meteorites. In the present study, we have analysed a number of Martian meteorites for their bulk-Fe-isotope composition. In addition, a set of terrestrial analogue material has also been analysed to compare the results and draw inferences. So far, our studies have not found any measurable Fe-isotopic fractionation in bulk Martian meteorites that can be ascribed to any low-temperature process operative on Mars.
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Atmosphere of Mars
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New developments continue in the life on Mars story, as a British team announced strong new isotopic evidence for ancient life in a Martian meteorite—while an American researcher suggested that such meteorites are marked by earthly contamination instead.
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