Decorated Vesicles as Prebiont Systems (a Hypothesis).

Biogeochemical proton and base cation fluxes in a 30-year old white birch forest composed of Dystric Cambisols in northern Hokkaido, Japan were estimated using data on atmospheric deposition (AD), throughfall (TF), stemflow (SF), and discharge from soils (DS) and plant uptake (UP) from early June to November 1999. In the monitoring period, proton flux was 0.20kmolcha−1 for AD, 0.07 for TF+SF, and 0.03 for DS, indicating that atmospheric acid input was neutralized through plant and soil. Base cation flux was 1.29 for AD, 1.23 for TF+SF, and 0.99 for DS and plant base cation uptake was 2.14, indicating that the soil was the major source of base cation for plant. However, these seasonal fluxes showed various trends. Cumulative base cation flux in TF+SF showed constant increase trend during the whole period, which was similar to AD. Proton flux in AD jumped once just after a heavy rain of 255mm for 8 days at the end of July. Trends for the proton and base cation fluxes in TF plus SF were similar to that of AD. Although proton and base cation fluxes of DS were not found until middle July because of vegetation uptake and no flow, both fluxes increased suddenly after the heavy rain in July. After August, the base cation and proton fluxes in the DS increased continuously, due to the lack of plant uptake and intermittent rainfall. In this study, it is clear that plant activity and water flow are very important driving force for seasonal dynamics of biogeochemical cycling.

We propose a model whereby microscopic tunnels form in basalt glass in response to a natural proton flux from seawater into the glass. This flux is generated by the alteration of the glass as protons from water replace cations in the glass. In our proton gradient model, cells are gateways through which protons enter and alter the glass and through which cations leave the glass. In the process, tunnels are formed, and cells derive energy from the proton and ion fluxes. Proton flux from seawater into basalt glass would have occurred on Earth as soon as water accumulated on the surface and would have preceded biological redox catalysis. Tunnels in modern basalts are similar to tunnels in Archean basalts, which may be our earliest physical evidence of life. Proton gradients like those described in this paper certainly exist on other planetary bodies where silicate rocks are exposed to acidic to slightly alkaline water.

Elongate, fine tubes, approximately 1 microm wide and up to 200 microm long, extend from fractured surfaces, vesicle walls, and internal fractures into fragments of basalt glass in samples from the Hawaii Scientific Drilling Project #2 phase 1 (HSDP #2(1)) core and the Hilina slope, Hawaii. Several features indicate that these tubes are microbial endolithic microborings: the tubes resemble many described microborings from oceanic basalt glass, their formation is postdepositional but restricted to certain but different ranges of time in the two sets of samples, and they are not uniformly distributed throughout glass fragments. Microtubules record several characteristic behaviors including boring into glass, mining, seeking olivine, and avoiding plagioclase. They also are highly associated with a particular form of glass-replacing smectite. Evidence of behavior should join morphological and geochemical criteria in indicating microbial alteration of basalt glass. In some samples, steeply conical tubes, approximately 10-20 microm in diameter tapering to 1 microm and commonly filled with smectite, appear to be modifications or elaborations of the microtubules. These also curve toward olivine and are associated with replacement smectite. In HSDP #2(1) samples, microtubules initiated at margins of shards before palagonite replaced those margins and are preserved during palagonitization. In fact, microtubules appear to have provided routes that enhanced the efficiency of water's reaching of unaltered glass. In Hilina Slope samples, the microtubules appear to postdate palagonitization because they initiate at the boundary between palagonite and unaltered sideromelane. Preservation of microtubules during palagonitization in samples together with recognition of other associated characteristics representing behavior suggests that such features may be recognizable in more heavily altered ancient rocks.

Basaltic glass (BG) is an amorphous ferrous iron [Fe(II)]-containing material present in basaltic rocks, which are abundant on rocky planets such as Earth and Mars. Previous research has suggested that Fe(II) in BG can serve as an energy source for chemolithotrophic microbial metabolism, which has important ramifications for potential past and present microbial life on Mars. However, to date there has been no direct demonstration of microbially catalyzed oxidation of Fe(II) in BG. In this study, three different culture systems were used to investigate the potential for microbial oxidation of Fe(II) in BG, including (1) the chemolithoautotrophic Fe(II)-oxidizing, nitrate-reducing "Straub culture"; (2) the mixotrophic Fe(II)-oxidizing, nitrate-reducing organism Desulfitobacterium frappieri strain G2; and (3) indigenous microorganisms from a streambed Fe seep in Wisconsin. The BG employed consisted of clay and silt-sized particles of freshly quenched lava from the TEB flow in Kilauea, Hawaii. Soluble Fe(II) or chemically reduced NAu-2 smectite (RS) were employed as positive controls to verify Fe(II) oxidation activity in the culture systems. All three systems demonstrated oxidation of soluble Fe(II) and/or structural Fe(II) in RS, whereas no oxidation of Fe(II) in BG material was observed. The inability of the Straub culture to oxidize Fe(II) in BG was particularly surprising, as this culture can oxidize other insoluble Fe(II)-bearing minerals such as biotite, magnetite, and siderite. Although the reason for the resistance of the BG toward enzymatic oxidation remains unknown, it seems possible that the absence of distinct crystal faces or edge sites in the amorphous glass renders the material resistant to such attack. These findings have implications with regard to the idea that Fe(II)-Si-rich phases in basalt rocks could provide a basis for chemolithotrophic microbial life on Mars, specifically in neutral-pH environments where acid-promoted mineral dissolution and utilization of dissolved Fe(II) as an energy source is not likely to take place.

Tailoring molecular sieve properties during SDA removal via solvent extraction

Optical properties of Titan and early Earth haze laboratory analogs in the mid-visible

This study presents lithium (Li) and magnesium (Mg) isotope data from experiments designed to assess the effects of dissolution of primary phases and the formation of secondary minerals during the weathering of basalt. Basalt glass and olivine dissolution experiments were performed in mixed through-flow reactors under controlled equilibrium conditions, at low pH (2–4) in order to keep solutions undersaturated (i.e. far-from equilibrium) and inhibit the formation of secondary minerals. Combined dissolution–precipitation experiments were performed at high pH (10 and 11) increasing the saturation state of the solutions (moving the system closer to equilibrium) and thereby promoting the formation of secondary minerals. At conditions far from equilibrium saturation state modelling and solution stoichiometry suggest that little secondary mineral formation has occurred. This is supported by the similarity of the dissolution rates of basalt glass and olivine obtained here compared to those of previous experiments. The δ 7Li isotope composition of the experimental solution is indistinguishable from that of the initial basalt glass or olivine indicating that little fractionation has occurred. In contrast, the same experimental solutions have light Mg isotope compositions relative to the primary phases, and the solution becomes progressively lighter with time. In the absence of any evidence for secondary mineral formation the most likely explanation for these light Mg isotope compositions is that there has been preferential loss of light Mg during primary phase dissolution. For the experiments undertaken at close to equilibrium conditions the results of saturation state modelling and changes in solution chemistry suggest that secondary mineral formation has occurred. X-ray diffraction (XRD) measurements of the reacted mineral products from these experiments confirm that the principal secondary phase that has formed is chrysotile. Lithium isotope ratios of the experimental fluid become increasingly heavy with time, consistent with previous experimental work and natural data indicating that 6Li is preferentially incorporated into secondary minerals, leaving the solution enriched in 7Li. The behaviour of Mg isotopes is different from that anticipated or observed in natural systems. Similar to the far from equilibrium experiments initially light Mg is lost during olivine dissolution, but with time the δ 26Mg value of the solution becomes increasingly heavy. This suggests either preferential loss of light, and then heavy Mg from olivine, or that the secondary phase preferentially incorporates light Mg from solution. Assuming that the secondary phase is chrysotile, a Mg-silicate, the sense of Mg fractionation is opposite to that previously associated with silicate soils and implies that the fractionation of Mg isotopes during silicate precipitation may be mineral specific. If secondary silicates do preferentially remove light Mg from solution then this could be a possible mechanism for the relatively heavy δ 26Mg value of seawater. This study highlights the utility of experimental studies to quantify the effects of natural weathering reactions on the Li and Mg geochemical cycles.

A novel high pressure column flow reactor was used to investigate the evolution of solute chemistry along a 2.3m flow path during pure water- and CO2-charged water–basaltic glass interaction experiments at 22 and 50°C and 10−5.7 to 22bars partial pressure of CO2. Experimental results and geochemical modelling showed the pH of injected pure water evolved rapidly from 6.7 to 9–9.5 and most of the iron released to the fluid phase was subsequently consumed by secondary minerals, similar to natural meteoric water–basalt systems. In contrast to natural systems, however, the aqueous aluminium concentration remained relatively high along the entire flow path. The aqueous fluid was undersaturated with respect to basaltic glass and carbonate minerals, but supersaturated with respect to zeolites, clays, and Fe hydroxides. As CO2-charged water replaced the alkaline fluid within the column, the fluid briefly became supersaturated with respect to siderite. Basaltic glass dissolution in the column reactor, however, was insufficient to overcome the pH buffer capacity of CO2-charged water. The pH of this CO2-charged water rose from an initial 3.4 to only 4.5 in the column reactor. This acidic reactive fluid was undersaturated with respect to carbonate minerals but supersaturated with respect to clays and Fe hydroxides at 22°C, and with respect to clays and Al hydroxides at 50°C. Basaltic glass dissolution in the CO2-charged water was closer to stoichiometry than in pure water. The mobility and aqueous concentration of several metals increased significantly with the addition of CO2 to the inlet fluid, and some metals, including Mn, Cr, Al, and As exceeded the allowable drinking water limits. Iron became mobile and the aqueous Fe2+/Fe3+ ratio increased along the flow path. Although carbonate minerals did not precipitate in the column reactor in response to CO2-charged water–basaltic glass interaction, once this fluid exited the reactor, carbonates precipitated as the fluid degassed at the outlet. Substantial differences were found between the results of geochemical modelling calculations and the observed chemical evolution of the fluids during the experiments. These differences underscore the need to improve the models before they can be used to predict with confidence the fate and consequences of carbon dioxide injected into the subsurface.

The weathering and low-temperature alteration of basaltic glass was studied by geochemical modelling in order to gain an insight into the effects of temperature, acid supply and extent of reaction on the secondary mineralogy and water chemistry. Basaltic glass was dissolved in dilute water at 10–150°C in a closed system and secondary minerals commonly observed in nature allowed to precipitate when saturated. The weathering of basalts in the presence of CO$_2$ was observed to go through three stages; initially simple insoluble Al and Fe hydroxides were formed. Upon progressive basaltic glass dissolution imogolite, allophane and/or kaolinite and Ca–Mg–Fe smectites predominated, decreasing the mobility of Al, Fe, Si, Ca and Mg whereas extensive weathering and alkaline pH values resulted in the formation of smectites, zeolites, calcite and SiO$_2$ minerals. Under low-temperature geothermal conditions and in strong H$_2$ SO$_4$ acid solutions (pH\<4) amorphous silica, kaolinite, Al–Fe oxyhydroxides and sulphur-containing minerals were most important and most cations like Na, K, Ca and Mg were observed to be mobile. Under mildly acid conditions in CO$_2$ enriched waters (pH 5–7) kaolinite, chalcedony, Ca–Mg–Fe smectites and Mg–Fe–Ca carbonates predominated and Fe, Al and Si were found to be immobile, whereas Mg and Ca mobility depended on the mass of carbonate formed and water pH. Under alkaline conditions (pH\>8) that resulted from a low acid supply and/or extensive basaltic glass dissolution chalcedony, celadonite, Ca–Mg–Fe smectites, zeolites and calcite were found to form, greatly reducing the mobility of most dissolved elements. The dominant factor determining the weathering and low-temperature alteration of basaltic glass and the associated elemental mobility is the pH of the water. In turn, the pH value is determined by the input and type of acid and their ionization constant and quantity of basaltic glass dissolution and secondary minerals formed that increases with the extent of the reaction and the temperature. The weathering mineralogy observed associated with basaltic glass in Iceland is typical of low to moderate degree of alteration under low (atmospheric) CO$_2$ conditions. The low-temperature regional geothermal alteration commonly observed in Iceland is also typical for low CO$_2$ alteration and the reaction order of celadonite and chalcedony, followed by mixed clays and chlorite and eventually zeolites and calcite, indicate increased water–rock interaction at pH>8 with temperature being less important on the overall reaction path.

To evaluate the contribution of proton flux from precipitation on peat acidification in mire ecosystems, we estimated ion fluxes to peat soils from bulk deposition in Sphagnum-dominated bogs and from throughfall plus stem flow in spruce forests in three cool-temperate ombrogenous mires in the Ochiishi district, northeastern Japan. We tested the hypothesis that proton fluxes from the atmosphere to peat soils are affected by vegetation types, leading to the consequent difference in soil acidity. The proton flux in bulk deposition was higher than that in throughfall plus stem flow, but the concentration of H+ in the peat surface water in Sphagnum bogs was lower than that in spruce forests. The inverse relationship between proton flux and soil water acidity means that the soil water acidity could not be explained quantitatively by proton flux from the atmosphere to the peat surface. The ion fluxes of sea-salt components were dependent on the distance from the coast to the mires. This means that the sea-salt accumulation in the peat surface soil can be directly attributed to the high flux of sea-salt from precipitation. The flux of sea-salts deposited on the mires positively correlated with the H+ concentration of the peat surface water in each community, implying that the acidity of peat surface water depends on the cation fluxes from precipitation.

River, ground, and peat water from a basaltic catchment area, Laxa in Kjos Southwest Iceland, were sampled and analyzed for major element concentrations to define the effect of glassy versus crystalline basalt, the formation of secondary minerals, and runoff on fluxes of dissolved elements to the ocean. The proportions of the dissolved solids in the water samples derived from precipitation, air, and rock weathering were estimated. The amounts of Na, Mg, Ca, K, and S originating from precipitation were calculated from the respective solute/Cl marine ratios and the estimated aqueous Cl originated from precipitation, which was calculated using measured B content of the waters and B/Cl molal marine and rock ratios. The rock contribution from weathering ranged from 22 to 46 percent of the total dissolved solids of the waters. Iron and Al showed low mobility compared to Na. This was primarily due to consumption of these elements by ferrihydroxides, allophane, imogolite, and clay minerals. Also, Si and to a lesser degree Ca show apparent slightly lower mobility than Na. These results are in good agreement with these phases being dominant in the soils of the study area (Wada and others, 1992) and the main secondary minerals of basaltic glass in Iceland (Crovisier and others, 1992). Reaction progress calculations support these findings. According to a model interaction of basaltic glass and meteoric water Al, Fe, and Si are consumed by amorphous Fe and Al hydroxides and imogolite and allophane at low reaction progress. With increasing reaction progress, Ca-Fe-Mg smectite became the primary secondary minerals, limiting the mobility of Ca, Fe, Mg, Si, and Al. These findings suggest that the weathering in the Laxa in the Kjos catchment area has evolved into the beginning of the smectite weathering stage and that it is dominated by a relatively low reaction progress and a high water to rock ratio. In the present study the effect of runoff and rock crystallinity was quantified for dissolved elemental fluxes. Temperature, lithology (other than rock crystallinity), and rock age were similar in all of the catchment areas in this study. Silica, Ca, F, S, Al, K, Mg, and B had a very similar dependence on runoff. On the other hand, Na fluxes were found to be less dependent on runoff, and Fe fluxes were found to be independent of runoff. Basaltic glass dissolves faster than fully crystallized basaltic rocks (Gislason and Eugster, 1987a). Therefore, increased glass content of the primary rocks is thought to increase the leaching and elemental fluxes at constant runoff. However, because some of the solutes, particularly Al and Fe, were highly influenced or even controlled by the formation of secondary minerals, this increasing dissolution with increasing glass content was hidden. On the other hand, basaltic glass was observed to enhance the fluxes of more mobile elements like Na, Si, Ca, F, and S by a factor of 2 to 5 at a constant runoff of 200 cm/yr, constant vegetative cover, and 0 to 100 percent glass content of the rocks. The K and Mg fluxes were found to be independent of rock crystallinity. However, runoff alone cannot explain the fluxes of these elements, and it seems that vegetative cover and seasonal variations in biomass activities influence the K and Mg fluxes.

Earth's seasons affect a number of fundamental processes in the biosphere.These include oxygenic photosynthesis, aerobic respiration, and nitrification/denitrification, whose relative rates fluctuate over the seasonal cycle in response to changes in insolation and surface temperature [1,2].However, the implications of seasons for the co-evolution of life and its environment on early Earth remain unclear.Moreover, seasonality in the biosphere results in temporally variable atmospheric fluxes of biosignature gases like O 2 , CO 2 , and N 2 O, which may also make it a useful life detection and characterization tool for Earth-like exoplanets [3,4,5].Here, we study the effects of seasons on the biosphere to better understand their impact on nutrient availability for life on early Earth and the production of remotely detectable biosignatures on Earth-like exoplanets.We use cGENIE-PlaSim, a 3D marine biogeochemical model coupled to an atmospheric GCM, to quantify seasonality in an Earth-like biosphere under the atmospheric oxygenation conditions present over Earth's history, ranging from Archean (~10 -5 PAL) to Phanerozoic (PAL) pO 2 levels [6,7].We also vary planetary obliquity and eccentricity in our simulations to account for plausible seasonal dynamics on Earth-like exoplanets.We then describe the corresponding seasonal patterns in biologically modulated atmospheric gases such as O 2 , CO 2 , and N 2 O. Finally, we speculate on the viability of treating biospheric seasonality as an exoplanet biosignature.

The two other solar system bodies thought to be most compatible with “life as we know it” are the planet Mars and Europa, a natural satellite of the planet Jupiter. These worlds appear to harbor the potential for past and/or present-day liquid water, biologically useful energy sources, and a significant and rich organic chemistry. Such traits are under active investigation both through ongoing, targeted, solar system exploration missions and from the extensive analysis of data from previous missions and astronomical observations. And both bodies are the subject of astrobiologically inspired future missions. The nature of both Mars and Europa fuels speculation about the prospects for life, and the established facts about each of them, added to more recent observations, can explain their astrobiological interest. Nonetheless, such data can only form a circumstantial case for that interest, and further investigations of water (in all of its forms), energy, and organic chemistry are sure to be required before astrobiological investigations can be further targeted—and data from any biological observations can be properly interpreted. Most important will be a dedication to understanding both Mars and Europa for the environments that they possess—and the nature and distribution of those environments in space and time—rather than trying to understand these worlds by simple analogy to the modern Earth. It is clear that both Mars and Europa have characteristics that may be similar to those of Earth when studied over its entire history, but it is equally true that each of them have characteristics that are unlike anything presented by the Earth system at any single time in its past. The same can be said of Saturn’s moon, Titan, which presents a compelling mix of organic chemistry, water ice, and atmosphere—but must represent a significant departure from any historical Earth. This is not necessarily a disadvantage. In fact, through the study of Mars, Europa, and Titan we may come to recognize circumstances on the early Earth that are presently unknown, or at least unappreciated. Such is the promise of astrobiology—not simply a “search for life,” but a change in perspective that can shed light on established disciplines, while it allows for the pursuit of answers to some of science’s most compelling questions.

Cycling phosphorus on the Archean Earth: Part II. Phosphorus limitation on primary production in Archean ecosystems

CO2-water–basalt interaction. Low temperature experiments and implications for CO2 sequestration into basalts