Production of high molecular weight organic compounds on the surfaces of amorphous iron silicate catalysts: Implications for organic synthesis in the solar nebula

The high molecular weight organic products of Fischer-Tropsch/Haber-Bosch syntheses on the surfaces of Fe-silicate catalysts have been studied by GCMS

Formation of magnetic minerals at hydrocarbon-generation conditions

In this paper, we report the pyrolysis and formation of magnetic minerals in three source rock samples from the Wessex Basin in Dorset, southern England. The experimental conditions in the laboratory recreated the catagenesis environment of oil source rocks. Magnetic analysis of both the heated and the unheated samples at room temperature and at very low-temperatures (5 K), coupled with transmission electron-microscopy imaging and X-ray analysis, revealed the formation of nanometre-sized (<10 nm), magnetic particles that varied across the rock samples analysed, but more importantly across the pyrolysis temperature range. Magnetic measurements demonstrated the formation of these magnetic minerals peaked at 250 °C for all rock samples and then decreased at 300 °C before rising again at 320 °C. The newly formed magnetic minerals are suggested to be primarily pyrrhotite, though magnetite and greigite are also thought to be present. The sizes of the magnetic minerals formed suggest a propensity to migrate together with oil potentially explaining the magnetic anomalies observed above and within oil fields

Transitory Microbial Habitat in the Hyperarid Atacama Desert

Traces of life are nearly ubiquitous on Earth. However, a central unresolved question is whether these traces always indicate an active microbial community or whether, in extreme environments, such as hyperarid deserts, they instead reflect just dormant or dead cells. Although microbial biomass and diversity decrease with increasing aridity in the Atacama Desert, we provide multiple lines of evidence for the presence of an at times metabolically active, microbial community in one of the driest places on Earth. We base this observation on four major lines of evidence: a physico-chemical characterization of the soil habitability after an exceptional rain event, identified biomolecules indicative of potentially active cells [e.g., presence of ATP, phospholipid fatty acids (PLFAs), metabolites, and enzymatic activity], measurements of in situ replication rates of genomes of uncultivated bacteria reconstructed from selected samples, and microbial community patterns specific to soil parameters and depths. We infer that the microbial populations have undergone selection and adaptation in response to their specific soil microenvironment and in particular to the degree of aridity. Collectively, our results highlight that even the hyperarid Atacama Desert can provide a habitable environment for microorganisms that allows them to become metabolically active following an episodic increase in moisture and that once it decreases, so does the activity of the microbiota. These results have implications for the prospect of life on other planets such as Mars, which has transitioned from an earlier wetter environment to today's extreme hyperaridity. [Abstract copyright: Copyright © 2018 the Author(s). Published by PNAS.

Normal alkanes in meteorites: molecular δ13C values indicate an origin by terrestrial contamination

In the time period since 1961, n-alkanes (straight-chain hydrocarbons) have been detected in varying amounts in many meteorites. Proposed origins for these compounds have included extraterrestrial biotic, extraterrestrial abiotic and terrestrial contamination processes. To help establish the source of these compounds, we determined the carbon isotopic compositions of individual n-alkanes in meteorites of several different classes and terrestrial histories: Orgueil (CI1), Cold Bokkeveld (CM2), Murchison (CM2), Vigarano (CV3), Allende (CV3), Ornans (CO3), and Bishunpur (LL3). The efficiency of supercritical fluid extraction (SFE) was exploited to provide extractable non-polar organic matter from the meteorites. The n-alkanes in these extracts were then identified with gas chromatography–mass spectrometry (GC–MS) and the carbon isotopic composition of individual molecules was determined using isotope ratio monitoring–gas chromatography–mass spectrometry (irm–GC–MS). n-Alkanes were found in all but one of the meteorites analysed (Allende), but carbon number distributions varied between samples. Pristane and Phytane were also detected in five of the seven meteorites. δ13C values for the individual n-alkanes occupied a range from −25.3 to −38.7‰. The δ13C values for the meteoritic n-alkanes have a similar range as those for n-alkanes measured from petroleum in the literature. Therefore, the n-alkanes in meteorites appear to be terrestrial contaminants which may have originated from fossil hydrocarbons or petroleum products. This type of contamination is analogous to that which will be threatening future meteorite falls and the samples returned from spaceflight missions over the next two decades and beyond. For falls already contaminated, irm–GC–MS appears useful in discriminating between indigenous compounds and those introduced by terrestrial contamination

Supercritical fluid extraction of the non-polar organic compounds in meteorites

The carbonaceous chondrite meteorites contain a variety of extraterrestrial organic molecules. These organic components provide a valuable insight into the formation and evolution of the solar system. Attempts at obtaining and interpreting this information source are hampered by the small sample sizes available for study and the interferences from terrestrial contamination. Supercritical fluid extraction represents an efficient and contamination-free means of isolating extraterrestrial molecules. Gas chromatography-mass spectrometry analyses of extracts from Orgueil and Cold Bokkeveld reveal a complex mixture of free non-polar organic molecules which include normal alkanes, isoprenoid alkanes, tetrahydronaphthalenes and aromatic hydrocarbons. These organic assemblages imply contributions from both terrestrial and extraterrestrial sources

Separation of planetary noble gas carrier from bulk carbon in enstatite chondrites during stepped combustion

The exact location of planetary noble gases in meteorites remains unknown but it is inferred to be closely associated with, if not precisely some portion of, the macromolecular organic material in carbonaceous chondrites . Herein we show that for enstatite chondrites the major carbonaceous component is not the carrier of the gases. This may also be true for other chondritic groups. Rather, these gases are all contained in a minor combustible constituent. This situation has all the hallmarks of a Russian matryoshka doll problem, as was witnessed previously in the study of meteorites prior to the understanding of the presence of presolar grains. A possible conclusion, which is in line with previous suggestions , is that planetary noble gases are also presolar and located in a new, and as yet unidentified, form of presolar material

PPOSS (PLANETARY PROTECTION OF THE OUTER SOLAR SYSTEM) – BEST PRACTICE FOR ORGANIC CONTAMINATION CONTROL

Planetary Protection of the Outer Solar System is aimed at preventing contamination between Earth and other bodies, in particular the icy moons, in the context of life detection missions. In the context of organic (rather than biological) contamination control the aim is to avoid jeopardizing the search for extraterrestrial life and its precursors and remnants through creating false positives. So far the search for life beyond the Earth has focused on Mars and so current thinking towards avoiding forward contamination of potentially habitable environments is based on our knowledge of the Martian environment. As there is now increasing evidence for the potential of life to exist on the icy moons of the outer solar system, it is necessary to think about the unique challenges for planetary protection and contamination control these environments hold. This is especially difficult, compared to Mars, due to the abundance of liquid water, both in subsurface oceans and hydrothermal plumes, which will enhance the risk of forward contamination and false positives. Due to the non-self-replicating nature of organic contaminants, unlike biological contaminants, we are mostly worried about affecting the reliability of the current mission rather than damaging the future scientific prospects of the body, although this must still be considered. While organic compounds are highly scarce on Mars and the challenge is purely to detect them, organics are likely to be plentiful on the icy moons. The complex radiation environment will create polymers and macromolecules leading to a complex and varied suite of organics. This means that the background level of indigenous abiotic organic compounds will be high and the challenge will be to distinguish between the sources of the observed organics. Planetary Protection and contamination control policy will need to be adaptable as our knowledge about the target bodies increases through future successful missions

The preservation state of organic matter in meteorites from Antarctica

The recovery of large numbers of meteorites from Antarctica has dramatically increased the amount of extraterrestrial material available for laboratory studies of solar system origin and evolution. Yet, the great age of Antarctic meteorites raises the concern that significant amounts of terrestrial weathering has corrupted their pre-terrestrial record. Organic matter found in carbonaceous chondrites is one of the components most susceptible to alteration by terrestrial processes. To assess the effects of Antarctic weathering on both non-Antarctic and Antarctic chondritic organic matter, a number of CM chondrites have been analyzed. Mössbauer spectroscopy has been used to ascertain pre-terrestrial and terrestrial oxidation levels, while pyrolysis-gas chromatography-mass spectrometry was used to determine the constitution of any organic matter present. Increased oxidation levels for iron bearing minerals within the non-Antarctic chondrites are likely to be a response to increased amounts of parent body aqueous alteration. Parent body processing also appears to remove ether bonds from organic material and alkyl side chains from its constituent units. The iron in Antarctic chondrites is generally more oxidized than that in their non-Antarctic counterparts, reflecting terrestrial weathering. Antarctic weathering of chondritic organic matter appears to proceed in a similar way to parent body aqueous alteration and simply enhances the organic responses observed in the non-Antarctic data set. Degradation of the record of preterrestrial processes in Antarctic chondrites should be taken into account when interpreting data from these meteorites

Carbon and nitrogen in carbonaceous chondrites: elemental abundances and stable isotopic compositions

We have undertaken a comprehensive study of carbon and nitrogen elemental abundances and isotopic compositions of bulk carbonaceous chondrites. A strategy of multiple analyses has enabled the investigation of hitherto unconstrained small-scale heterogeneities. No systematic differences are observed between meteorite falls and finds, suggesting that terrestrial processing has a minimal effect on bulk carbon and nitrogen chemistry. The changes in elemental abundance and isotopic composition over the petrologic range may reflect variations in primary accreted materials, but strong evidence exists of the alteration of components during secondary thermal and aqueous processing. These changes are reflected within the CM2 and CO3 groups and follow the published alteration scales for those groups. The nitrogen isotope system appears to be controlled by an organic host, which loses a 15N-rich component with progressive alteration. This study recommends caution, however, over the use of bulk carbon and nitrogen information for classification purposes; variance in relative abundance of different components in carbonaceous chondrites is significant and reflects intrameteorite heterogeneities