Characterizing the Effect of Shock on Isotopic Ages I: Ferroan Anorthosite Major Elements

A study underway at Marshall Space Flight Center is further characterizing the effects of shock on isotopic ages. The study was inspired by the work of L. Nyquist et al. [1, 2], but goes beyond their work by investigating the spatial distribution of elements in lunar ferroan anorthosites (FANs) and magnesium-suite (Mg-suite) rocks in order to understand the processes that may influence the radioisotope ages obtained on early lunar samples. This paper discusses the first data set (major elements) obtained on FANs 62236 and 67075

Cave Biosignature Suites: Microbes, Minerals, and Mars

Earth\u27s subsurface offers one of the best possible sites to search for microbial life and the characteristic lithologies that life leaves behind. The subterrain may be equally valuable for astrobiology. Where surface conditions are particularly hostile, like on Mars, the subsurface may offer the only habitat for extant lifeforms and access to recognizable biosignatures. We have identified numerous unequivocally biogenic macroscopic, microscopic, and chemical/geochemical cave biosignatures. However, to be especially useful for astrobiology, we are looking for suites of characteristics. Ideally, biosignature suites should be both macroscopically and microscopically detectable, independently verifiable by nonmorphological means, and as independent as possible of specific details of life chemistries - demanding (and sometimes conflicting) criteria. Working in fragile, legally protected environments, we developed noninvasive and minimal impact techniques for life and biosignature detection/characterization analogous to Planetary Protection Protocols. Our difficult field conditions have shared limitations common to extraterrestrial robotic and human missions. Thus, the cave/subsurface astrobiology model addresses the most important goals from both scientific and operational points of view. We present details of cave biosignature suites involving manganese and iron oxides, calcite, and sulfur minerals. Suites include morphological fossils, mineral-coated filaments, living microbial mats and preserved biofabrics, 13C and 34S values consistent with microbial metabolism, genetic data, unusual elemental abundances and ratios, and crystallographic mineral forms

Methods to analyze metastable and microparticulate hydrated and hydrous iron sulfate minerals

We evaluate analytical methods for characterizing hydrated and hydrous iron sulfate minerals (HHIS) that are typically metastable in air or vacuum, commonly form micrometer-sized particles, and contain multi-valent and light elements (Fe2+, Fe3+, OH-, and H2O) that may be challenging to quantify. We synthesized or obtained HHIS-szomolnokite, melanterite, rhomboclase, schwertmannite, ferricopiapite, paracoquimbite, and jarosite-as well as Fe-oxides. These nominally pure samples were characterized with X-ray diffraction (XRD), and then used to evaluate bulk analyses obtained from combined inductively coupled plasma, optical emission spectroscopy (ICP-OES), ion chromatography (IC), Mössbauer spectroscopy, and mass spectrometry. Integrated bulk analyses showed excellent agreement with the nominal formulas for the minerals. Because HHIS commonly form micro-sized particles-for example, HHIS found in acid mine drainage (AMD) environments and in martian meteorites-it is necessary to develop micro-analytical techniques. Microscopic mid-infrared spectroscopy allows the analyst to successfully discriminate among HHIS with minimal sample preparation on the small scale (̃40 × 40 μm). For chemical analysis, electron probe microanalysis (EPMA) is preferred for samples that can be mounted, polished, coated, and that are stable under high vacuum; however, few HHIS meet those criteria. To characterize HHIS compositions, we show that multiple low-vacuum scanning electron microscopy (SEM) analyses of the same uncoated, unpolished mineral are required. Analysis of each mineral shows linear trends on ternary diagrams of 5×Fe-SO4-O (where oxygen is in O, OH, and H2O) that may be used to narrow down the HHIS mineralogy. Low-vacuum SEM also provides invaluable information about the geochemical and textural context of the samples. Our study provides protocols for microanalysis of these challenging, fine-grained, and metastable HHIS that may also be applied to other mineral groups

Evidence for Microbial Involvement in Pool Finger Precipitation, Hidden Cave, New Mexico

Although speleothems are usually considered inorganic precipitates, recent work has demonstrated hitherto unsuspected biogenic influence in some twilight areas. We have expanded this notion to the dark zone, examining pool fingers from Hidden Cave, New Mexico, to test for possible bacterial involvement. The pool fingers in Hidden Cave are pendant speleothems that formed subaqueously in paleo-pools. They are 1 to 4 cm in diameter and 5 to 50 cm long. A knobby, irregular external shape is underlaid by a layered interior on two scales, a 0.5 to 1.0 cm alternation between dense and porous layers and a mm-scale alternation between dark micritic calcite and clear dogtooth spar. The micrite is similar to microbialites identified in modern and ancient carbonates. Fossil bacteria were found in all layers. These include (1) calcified filaments 1 w m in diameter and 5–50 w m long and (2) micro-rods 0.1 w m by 1–2 w m. Most filaments are curved rods with a smooth surface but rare examples display a diamond crosshatch surface. The micro-rods occur as isolated crystals to dense meshes. We interpret the micro-rods as calcified bacilliform bacteria and the filaments as calcified filamentous bacteria. Carbon isotopic data are slightly more negative (by - 0.5 to - 1.0% in micritic layers than in dogtooth spar layers, suggesting a greater microbial influence in the micritic layers. Based on these similarities to known microbialites (e.g., petrographic fabrics, the presence of fossil bacteria, and the suggestive carbon isotopic data), we conclude that microbial activity was an intimate part of pool finger formation in Hidden Cave. The significance of such involvement goes beyond speleological contexts to wider questions of identification of biosignatures in rocks on earth and beyond

Diverse microbial communities inhabiting ferromanganese deposits in Lechuguilla and Spider Caves

Lechuguilla Cave is an ancient, deep, oligotrophic subterranean environment that contains an abundance of low‐density ferromanganese deposits, the origin of which is uncertain. To assess the possibility that biotic factors may be involved in the production of these deposits and to investigate the nature of the microbial community in these materials, we carried out culture‐independent, small subunit ribosomal RNA (SSU rRNA) sequence‐based studies from two sites and from manganese and iron enrichment cultures inoculated with ferromanganese deposits from Lechuguilla and Spider Caves. Sequence analysis showed the presence of some organisms whose closest relatives are known iron‐ and manganese‐oxidizing/reducing bacteria, including Hyphomicrobium, Pedomicrobium, Leptospirillum, Stenotrophomonas and Pantoea. The dominant clone types in one site grouped with mesophilic Archaea in both the Crenarchaeota and Euryarchaeota. The second site was dominated almost entirely by lactobacilli. Other clone sequences were most closely related to those of nitrite‐oxidizing bacteria, nitrogen‐fixing bacteria, actinomycetes and β‐ and γ‐Proteobacteria. Geochemical analyses showed a fourfold enrichment of oxidized iron and manganese from bedrock to darkest ferromanganese deposits. These data support our hypothesis that microorganisms may contribute to the formation of manganese and iron oxide‐rich deposits and a diverse microbial community is present in these unusual secondary mineral formations

Comparison of bacterial communities from lava cave microbial mats to overlying surface soils from Lava Beds National Monument, USA

<div><p>Subsurface habitats harbor novel diversity that has received little attention until recently. Accessible subsurface habitats include lava caves around the world that often support extensive microbial mats on ceilings and walls in a range of colors. Little is known about lava cave microbial diversity and how these subsurface mats differ from microbial communities in overlying surface soils. To investigate these differences, we analyzed bacterial 16S rDNA from 454 pyrosequencing from three colors of microbial mats (tan, white, and yellow) from seven lava caves in Lava Beds National Monument, CA, USA, and compared them with surface soil overlying each cave. The same phyla were represented in both surface soils and cave microbial mats, but the overlap in shared OTUs (operational taxonomic unit) was only 11.2%. Number of entrances per cave and temperature contributed to observed differences in diversity. In terms of species richness, diversity by mat color differed, but not significantly. <i>Actinobacteria</i> dominated in all cave samples, with 39% from caves and 21% from surface soils. <i>Proteobacteria</i> made up 30% of phyla from caves and 36% from surface soil. Other major phyla in caves were <i>Nitrospirae</i> (7%) followed by minor phyla (7%), compared to surface soils with <i>Bacteroidetes</i> (8%) and minor phyla (8%). Many of the most abundant sequences could not be identified to genus, indicating a high degree of novelty. Surface soil samples had more OTUs and greater diversity indices than cave samples. Although surface soil microbes immigrate into underlying caves, the environment selects for microbes able to live in the cave habitats, resulting in very different cave microbial communities. This study is the first comprehensive comparison of bacterial communities in lava caves with the overlying soil community.</p></div

NMDS (Non-Metric Dimensional Scaling).

<p>NMDS separates out lava cave mat communities at the phylum level, with <i>Proteobacteria</i> split out by class, from the overlying surface soils. Circles show the 95% confidence interval.</p

Plot of phyla and <i>Proteobacteria</i> class that were differentialy abundant between LABE surface soils and lava cave microbial mats.

<p>The band is the median, and the box delineates the upper and lower quartile. The whiskers show the maximum and minimum values. All data points are shown.</p

Characteristics of the seven study cave sites in LABE.

<p>Characteristics of the seven study cave sites in LABE.</p

Cave samples bymat color and environmental characteristics in the cave.

<p>Cave samples bymat color and environmental characteristics in the cave.</p