Basalt magma interaction with harzburgite and the formation of high-magnesium andesites

The interaction of basalt melt with mantle harzburgite at low pressure might result in silica enrichment of the melt by assimilation of orthopyroxene. Experimental tests of this hypothesis show that silica-rich liquids (56 wt %) are produced by melt-orthopyroxene reaction at 1200° to 1250°C. These silica-rich liquids are enriched in Na₂O and K₂O over that found in the starting basalt melt which indicates that the alkalis diffused against a concentration gradient into the silica-rich liquid. The liquids produced in this way are chemically similar to high-magnesium andesites or boninites

Ancient metabolisms of a thermophilic subseafloor bacterium

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Smith, A. R., Mueller, R., Fisk, M. R., & Colwell, F. S. Ancient metabolisms of a thermophilic subseafloor bacterium. Frontiers in Microbiology, 12, (2021): 764631, https://doi.org/10.3389/fmicb.2021.764631.The ancient origins of metabolism may be rooted deep in oceanic crust, and these early metabolisms may have persisted in the habitable thermal anoxic aquifer where conditions remain similar to those when they first appeared. The Wood–Ljungdahl pathway for acetogenesis is a key early biosynthetic pathway with the potential to influence ocean chemistry and productivity, but its contemporary role in oceanic crust is not well established. Here, we describe the genome of a novel acetogen from a thermal suboceanic aquifer olivine biofilm in the basaltic crust of the Juan de Fuca Ridge (JdFR) whose genome suggests it may utilize an ancient chemosynthetic lifestyle. This organism encodes the genes for the complete canonical Wood–Ljungdahl pathway, but is potentially unable to use sulfate and certain organic carbon sources such as lipids and carbohydrates to supplement its energy requirements, unlike other known acetogens. Instead, this organism may use peptides and amino acids for energy or as organic carbon sources. Additionally, genes involved in surface adhesion, the import of metallic cations found in Fe-bearing minerals, and use of molecular hydrogen, a product of serpentinization reactions between water and olivine, are prevalent within the genome. These adaptations are likely a reflection of local environmental micro-niches, where cells are adapted to life in biofilms using ancient chemosynthetic metabolisms dependent on H2 and iron minerals. Since this organism is phylogenetically distinct from a related acetogenic group of Clostridiales, we propose it as a new species, Candidatus Acetocimmeria pyornia.Metagenome sequencing was made possible by the Deep Carbon Observatory Census of Deep Life supported by the Alfred P. Sloan Foundation and was performed at the Marine Biological Laboratory (Woods Hole, MA, United States). This work was funded by NASA grant NNX08AO22G and a graduate fellowship from the NSF Center for Dark Energy Biosphere Investigations. The flow cells were funded under J0972A from the U.S. Science Support Program of Joint Oceanographic Institutions

Tectonically controlled origin of three unusual rock suites in the Woodlark basin

We propose alternative mechanisms for the origin of three unusual rock suites, high-Mg andesites, NaTi basalts, and arclike rocks, that have been dredged from the Woodlark basin, southwest Pacific Ocean. We show that the high-Mg andesites and NaTi basalts are associated with an unusually cool ridge environment. The cooling is due to increased hydrothermal circulation, stimulated by an unusually high crustal permeability. The high permeability is mainly due to cracking of the Woodlark basin lithosphere as it passes over the flexural bulge in front of the subduction zone, although local processes, such as faulting in fracture zones, may also make some contribution. This increased convective cooling affects magma dynamics and chemistry at the ridge crest. The high-Mg andesites occur where the hydrothermal circulation lowers the temperatures in the upper oceanic crust, causing the magma chamber to sit in the mantle rather than in the crust and promoting the interaction of basalt magma with harzburgite. The increased crustal cooling, which causes anomalously low degrees in partial melting of their depleted mantle source. The arclike rocks are caused by interaction with volatiles from lithosphere that was emplaced beneath the edge of the basin less than 6 m.y. ago by a now inactive subduction zone to the north of the currently active one. Simple thermal models indicate that this formerly subducting plate is still cold enough to retain volatiles and to remain seismically active. As the old plate loses volatiles, they rise into the mantle convection cell which feeds the Woodlark basin ridge crest. Because ridge subduction increases the likelihood of ophiolite obduction, these observations and explanations of Woodlark basin tectonics are potentially important for ophiolites

Sources of nutrients and energy for a deep biosphere on Mars

Hydrothermal vents appear to be the tip of the subsurface biosphere in the ocean crust. The primary prducers in this biosphere are prokaryotes that tolerate a wide variety of physical and chemical conditions and are versatile in their use of inorganic compounds to drive metabolism. A synthesis of chemical and mineralogical data from Martian meteorites and measurements of the Martian surface suggest that conditions similar to those that make life possible in Earth’s oceanic crust, namely, water, carbon, nutrients, appropriate temperatures, and gradients in redox conditions, also occur within Mars. Chemolithoautotrophic microorganisms capable of living below the seafloor on Earth would probably survive some regions of the Martian subsurface

Controllable chirality-induced geometrical Hall effect in a frustrated highly-correlated metal

A current of electrons traversing a landscape of localized spins possessing non-coplanar magnetic order gains a geometrical (Berry) phase which can lead to a Hall voltage independent of the spin-orbit coupling within the material--a geometrical Hall effect. We show that the highly-correlated metal UCu5 possesses an unusually large controllable geometrical Hall effect at T<1.2K due to its frustration-induced magnetic order. The magnitude of the Hall response exceeds 20% of the \nu=1 quantum Hall effect per atomic layer, which translates into an effective magnetic field of several hundred Tesla acting on the electrons. The existence of such a large geometric Hall response in UCu5 opens a new field of inquiry into the importance of the role of frustration in highly-correlated electron materials.Comment: article and supplemental informatio

Surface area measurements of marine basalts: Implications for the subseafloor microbial biomass

These first measurements of specific surface area (SSA) of bulk samples of subsurface marine basalts were undertaken to determine the potential area available for microbial colonization. SSA ranged from 0.3 to 52 m2/g of basalt with the lowest value coming from pillow basalt and the highest value from breccia. The average for massive and pillow basalts combined was 2.3 m2/g. The total specific surface area of the extrusive volcanic rocks of the ocean crust is estimated to be 1024 m2. This surface area could provide attachment for up to 1034 cells if cell density is the same as that of experimentally colonized basalt surfaces. Independent measures and calculations of biomass in basalts suggest that cell densities on surfaces are only 10−4 times those in laboratory experiments and, therefore, the surface area of basalt does not limit microbial biomass in the igneous ocean crust. Citation: Nielsen, M. E., and M. R. Fisk (2010), Surface area measurements of marine basalts: Implications for the subseafloor microbial biomass

Elemental abundance distributions in suboceanic basalt glass: Evidence of biogenic alteration

The alteration of subseafloor volcanic glass from three locations is qualitatively attributed to biological (biotic) or chemical (abiotic) reactions on the basis of microscopic morphology of the boundary between the unaltered and altered glass. Eleven-element composition of fresh basalt glass (sideromelane) and its alteration products were determined by electron microprobe. Principal component analysis (PCA) using these eleven elements as input (Na¹¹, Mg¹², Al¹³, Si¹⁴, P¹⁵, Cl¹⁷, K¹⁹, Ca²⁰, Ti²², Mn²⁵, and Fe²⁶) extracts three factors accounting for 80.5% of the variance in the data. These three factors can serve as inputs to a hierarchical cluster analysis (HCA) algorithm for data-driven discovery of three sample classes. This autonomous classification agrees with the petrographic microscopic classification in 14 of 15 biotic clay analyses. From a set of 34 analyses identified microscopically as abiotic clay the autonomous system identifies 4 with elemental abundance characteristics similar to the biotic clay and 4 similar to unaltered glass. PCA factors are then used as inputs to train an artificial neural network to produce a Bayesian probability of correct classification using the classes discovered by HCA. Mean Bayesian probabilities of correct classification for abiotic clays, biotic clays, and glass were 76.1 ± 8.5%, 64.9 ± 9.0%, and 77.0 ± 7.2%, respectively. Interestingly, in the 9 of 74 cases where visual and elemental analysis disagree, the Bayesian probability estimate of correct classification using only elemental abundance data is low (60.0 ± 11.7%) compared to analyses where visual and elemental data agree (75.5 ± 7.8%). To our knowledge, this is the first demonstration of a quantitative method for discrimination of biotic and abiotic alteration of subocean basalt glass. As such, the techniques make possible the systematic assessment of the impact of microbial life on subsurface basalts.Keywords: microorganisms, artificial neural networks, elemental abundances, Ocean Drilling Program, basalt, Bayesian probabilitie

Detecting Organic Compounds Released from Iron Oxidizing Bacteria using Sample Analysis at Mars (SAM) Like Instrument Protocols

Mars is a planet of great interest for Astrobiology since its past environmental conditions are thought to have been favourable for the emergence life. At present, the Red Planet is extremely cold and dry and the surface is exposed to intense UV and ionizing radiation, conditions generally considered to be incompatible with life as we know it on Earth. It was proposed that the shallow subsurface of Mars, where temperatures can be above freezing and liquid water can exist on rock surfaces, could harbor chemolithoautotrophic bacteria such as the iron oxidizing microorganism Pseudomonas sp. HerB. The Mars Science Laboratory (MSL) mission will provide the next opportunity to carry out in situ measurements for organic compounds of possible biological origin on Mars. One instrument onboard MSL, called the Sample Analysis at Mars (SAM) instrument suite, will carry out a broad and sensitive search for organic compounds in surface samples using either high temperature pyrolysis or chemical extraction followed by gas chromatography mass spectrometry. We present gas chromatograph mass spectrometer (GC/MS) data on crushed olivine rock powders that have been inoculated with Pseudomonas sp. HerB at different concentrations ranging from approx 10(exp 2) to 10(exp 7) cells per gram. The inoculated olivine samples were heated under helium carrier gas flow at 500 C and the pyrolysis products concentrated using a SAM-like hydrocarbon trap set at -20 C followed by trap heating and analysis by GC/Ms. In addition, the samples were also extracted using a low temperature "one-pot" chemical extraction technique using N-methyl, N-(tert-butyldimethylsilyl) trifluoroacetamide (MTBSTFA) as the silylating agent prior to GC/MS analysis. We identified several aldehydes, thiols, and alkene nitriles after pyrolysis GC/MS analysis of the bacteria that were not found in the olivine control samples that had not been inoculated with bacteria. The distribution of pyrolysis products extracted from the bacteria was clearly distinct from similar GC/MS analyses of the carbonaceous meteorite Murchison that was dominated by sulfur containing aromatic compounds. A similar comparison, if organic compounds are detected by SAM on Mars, could be useful to help discriminate between meteoritic or biological origins

Extent of the microbial biosphere in the oceanic crust

We estimate the depth of the 120°C isotherm by constructing crustal thermal gradients based on theoretical and observed conductive heat flux as a function of lithospheric age. We chose the 120°C isotherm because it is close to the upper limit for prokaryotic life, and therefore, the isotherm approximates the maximum depth at which life can persist in the ocean crust. The depth of the potential microbial biosphere increases with lithospheric age from approximately 0.5 to 1 km for 1 Ma lithosphere to as much as 5 km at a subduction age of 180 Ma. We use global models of oceanic plate creation to estimate the volume of crust occupied by the biosphere today and throughout geologic time. Presently, the volume of the ocean crust that is capable of containing life is similar to the volume of the oceans (∼1018 m3). Depending on the model used for the growth of continental crust, the volume of rock available to house the subsurface biosphere may have remained constant or doubled since the Archean. Although the thermal models presented here provide estimates for the potential depth and volume of rock in which microbes may live, the biomass in this volume is not well constrained. Using a previously published model, the prokaryotic biomass in the igneous ocean crust is estimated to exceed that in all aquatic and soil environments and is similar to that in the continental subsurface and in marine sediment. Most of the crustal biomass beneath the sediments is likely contained within the extrusive layer, and this has probably been the case since microbes first colonized the oceanic crust in the Archean.Keywords: Microbial biosphere, Ocean crust, Thermal structur

Genetic evidence for endolithic microbial life colonizing basaltic glass/seawater interfaces

The majority of the Earth's shallow crust is composed of basalt that erupted on the seafloor and was subsequently altered by chemical exchange with seawater. One aspect of this alteration is the replacement of glass by secondary minerals, including clays. Petrographic thin sections from ODP Holes 504B and 896A revealed characteristic patterns of pitting (channels) at the interface of fresh basalt glass and secondary clay. Fluorescent dyes that bind specifically to nucleic acids (Hoechst 33342, PO-PRO-3, and Sytol 11) were used to examine thin sections for evidence of cellular life. Independent experiments with the three dyes indicated the presence of particulate nucleic acids at the interface of altered and unaltered glass, particularly at the distal tips of channels. Organic material was extracted from crushed basalts from Holes 504B and 896A and examined for the presence of microbial DNA by a polymerase chain reaction (PCR) assay. This technique detects specific ribosomal RNA genes that are present in all cellular life-forms. The PCR assays demonstrated the presence of prokaryotic genomic DNA in the rock extracts. Among the geochemical reactions that could provide energy for biological processes are the oxidation of iron, manganese, and sulfur. Electron microprobe analyses of areas of glass that appear to be affected by microbial action have low iron relative to the fresh glass. Also, elements that are consistent with the presence of cellular life, phosphate and potassium, were elevated in the channels (P is 0.02 wt% in glass and up to 1.4 wt% in channels and K is 0.01 wt% in glass and up to 2.0 wt% in channels). These data raise the possibility that chemical transformations of basalt on the seafloor are mediated by microorganisms