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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS2013

A Habitable Fluvio-Lacustrine Environment at Yellowknife Bay, Gale Crater, Mars

The Curiosity rover discovered fine-grained sedimentary rocks, which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy. This aqueous environment was characterized by neutral pH, low salinity, and variable redox states of both iron and sulfur species. Carbon, hydrogen, oxygen, sulfur, nitrogen, and phosphorus were measured directly as key biogenic elements; by inference, phosphorus is assumed to have been available. The environment probably had a minimum duration of hundreds to tens of thousands of years. These results highlight the biological viability of fluvial-lacustrine environments in the post-Noachian history of Mars.

Mars↗
NASA NTRS2016

Modeling of Sulfide Microenvironments on Mars

Yellowknife Bay (YKB; sol 124-198) is the second site that the Mars Science Laboratory Rover Curiosity investigated in detail on its mission in Gale Crater. YKB represents lake bed sediments from an overall neutral pH, low salinity environment, with a mineralogical composition which includes Ca-sulfates, Fe oxide/hydroxides, Fe-sulfides, amorphous material, and trioctahedral phyllosilicates. We investigate whether sulfide alteration could be associated with ancient habitable microenvironments in the Gale mudstones. Some textural evidence for such alteration may be pre-sent in the nodules present in the mudstone.

Schwenzer, S. P.↗
NASA NTRS2019

Long Term Biological Treatment of Space Habitation Waste Waters in a One Stage MABR: Comparison of Operation for N and C Oxidation With and Without Simultaneous Denitrification

Aerobic biological stabilization has been previously demonstrated for full size MABR?s (CoMANDR 1.0, CoMANDR 2.0, and R-CoMANDR) over operating periods of ~1 year. These systems have successfully treated a variety of possible habitation waste streams including an ISS (urine + flush and humidity condensate) and Early Planetary Base (EPB) wastewater (urine, flush water, hygiene wastewater, and laundry). Biological stabilization has a number of advantages including: 1) elimination of hazardous pre-treat chemicals; 2) production of NOx species (that can be easily rejected by evaporative or membrane systems); 3) elimination of volatile organic constituents; 4) a low pH effluent that facilitates membrane and distillation processes; and 5) a effluent that produces a better quality and less hazardous brine for water recovery. Previous work has primarily evaluated aerobic operation in which organic carbon and nitrogen is converted to CO2 and NOx-, respectively. An alternative to aerobic operation would be to include anoxic operation to promote denitrification and production of N2 gas. This allows for production of make-up gas as well as reduces the O2 demand and can increase ammonia oxidation efficiency. We evaluated the operation of a full scale (2 crew/day) MABR operated to perform oxidation of organic carbon and nitrogen with and without simultaneous reduction of oxidized N to N2 gas, simultaneous nitrification denitrification (SNDN). The system was challenged with a variety of space habitation wastewaters ranging from an ISS composition to a possible EPB waste stream under both continuous and on-production feeding modes. The system has been operated for over 2.5 years. We report on an overall comparison of aerobic oxidation and SNDN operational regimes to evaluate the system with the best overall attributes to support recycling of space habitation waste streams.

Biological water processing↗
NASA NTRS1991

The solubility of the tetragonal form of hen egg white lysozyme from pH 4.0 to 5.4

Hen egg white lysozyme solubilities in the presence of the tetragonal crystal form have been determined. Conditions investigated cover the pH range 4.0 to 5.4, varying from 2.0 to 7.0 percent NaCl concentrations and from 4 to 25 C. In all instances, the solubilities were found to increase with temperature and decrease with increasing salt concentration. The effects of pH were more complex, showing a decreasing solubility with increasing pH at low salt concentration and an increasing solubility with increasing pH at high salt concentration.

Cacioppo, Elizabeth↗
NASA NTRS2009

Psychrotolerant Anaerobes from Lake Podprudnoe, Antarctica and Penguin Spheniscus demersus Colony, South Africa

The study of a sample collected from a wind-made ice sculpture near Lake Podprudnoe, Antarctica led to the isolation of the psychrotolerant strain ISLP-3. Cells of the new isolate are vibrio-shaped that measure 0.5 x 1.0-3.0 micron in size. Growth occurs within the temperature range 5-35 C with the optimum at 22 C. Salinity range for growth is 0-2 % NaCl with the optimum at 0.25 %. The new isolate grows within a pH range from 6.0 to 9.5 with the optimum at 7.5. Strain ISLP-3 is saccharolytic, growing on the following substrates: D-glucose, D-ribose, D-fructose, D-arabinose, maltose, sucrose, D-trehalose, D-mannose, D-cellobiose, lactose, starch, chitin, triethylamine, N-acetylglucosamine, and urea. The best growth occurred on D-cellobiose. An environmental sample of pond water near a colony of the endemic species of African penguins, Spheniscus demersus, was collected in February 2008 and delivered directly to the Astrobiology laboratory at NSSTC. The microbiological study of this sample led to the isolation of two psychrotolerant strains ARHSd-7G and ARHSd-9G. Both strains are strictly anaerobic bacteria and are able to grow at high pH and low temperatures. The cells of strain ARHSd-7G are motile, vibrio-shaped, spore-forming cells. Optimal growth of this strain occurs at 30 C, 3 % NaCl, and pH 8.9. The isolate ARHSd-7G combines sugarlytic and proteolytic metabolisms, growing on some proteolysis products including peptone and yeast extract and a number of sugars. The second isolate, ARHSd-9G, exhibits thin, elongated rods that measure 0.4 x 3-5 micron. The cells are motile and spore-forming. Optimal growth of strain ARHSd-9G occurs at 30 C, 1.75 % NaCl, and pH 8.5. The strain ARHSd-9G is sugarlytic, growing well on substrates such as D-glucose, sucrose, D-cellobiose, maltose, fructose, D-mannose, and trehalose (the only exception is positive growth on yeast extract). In this report, the physiological and morphological characteristics of the novel psychrotolerant, alkaliphilic, and neutrophilic isolates from the Antarctica 2008 expedition will be discussed.

Guisler, Melissa↗
NASA NTRS1999

Prebiotic Nitrogen Fixation by FeS Reduction of Nitrite Under Acidic Conditions

Theories for the origin of life require the availability of reduced nitrogen for the formation of such species as amino acid and nucleic acids. In a strongly reducing atmosphere, compounds essential to the chemical evolution of life, such as amino acids, can form by reactions between HCN, NH3, and carbonyl compounds produced in spark discharges. However, under non-reducing atmospheres, electric discharges produced NO rather than HCN or NH3. This raises the questions of; how ammonia can be formed under a neutral atmosphere, and what conditions are needed such formation to occur? On possibility is the conversion of NO into nitric and nitrous acids (through HNO) and rained into the oceans. The reduction of nitrite by aqueous Fe(II) (6 Fe(+2) + 7 H(+) + NO2(-) yields 6 Fe(III) + 2 H2O + NH3) such as was present on the early Earth could then have produced ammonia. However, this reaction does not proceed at pHs less than 7.3. An alternative is reduction by other forms of Fe(II), such as FeS. We will present results that show that FeS can reduce nitrite to ammonia at pHs as low as pH 5 under a variety of conditions.

Summers, David P.↗
NASA NTRS1994

Ecosystem and physiological controls over methane production in northern wetlands

Peat chemistry appears to exert primary control over methane production rates in the Canadian Northern Wetlands Study (NOWES) area. We determined laboratory methane production rate potentials in anaerobic slurries of samples collected from a transect of sites through the NOWES study area. We related methane production rates to indicators of resistance to microbial decay (peat C: N and lignin: N ratios) and experimentally manipulated substrate availability for methanogenesis using ethanol (EtOH) and plant litter. We also determined responses of methane production to pH and temperature. Methane production potentials declined along the gradient of sites from high rates in the coastal fens to low rates in the interior bogs and were generally highest in surface layers. Strong relationships between CH4 production potentials and peat chemistry suggested that methanogenesis was limited by fermentation rates. Methane production at ambient pH responded strongly to substrate additions in the circumneutral fens with narrow lignin: N and C: N ratios (delta CH4/delta EtOH = 0.9-2.3 mg/g) and weakly in the acidic bogs with wide C: N and lignin: N ratios (delta CH4/delta EtOH = -0.04-0.02 mg/g). Observed Q(sub 10) values ranged from 1.7 to 4.7 and generally increased with increasing substrate availability, suggesting that fermentation rates were limiting. Titration experiments generally demonstrated inhibition of methanogenesis by low pH. Our results suggest that the low rates of methane emission observed in interior bogs during NOWES likely resulted from pH and substrate quality limitation of the fermentation step in methane production and thus reflect intrinsically low methane production potentials. Low methane emission rates observed during NOWES will likely be observed in other northern wetland regions with similar vegetation chemistry.

Valentine, David W.↗
NASA NTRS2005

Fundamental Mvssbauer Parameters of Hydrous Iron Sulfates

Hydrous iron sulfates, which form as alteration products of sulfides, are rare on Earth. On Mars, the low temperature and pH found in the martian permafrost create ideal conditions for the formation of this group of minerals [1], which includes such phases as coquimbite (Fe2(SO4) 9H2O) and amarantite (FeSO4(OH) 3H2O). Viking, Mars Pathfinder, MER and OMEGA data [e.g., [2]] have all indicated the presence of high sulfur contents on the surface of Mars, but the mineralogy of the sulfur-rich phases has not been well constrained. Recent work by [3] suggests that hydrous iron sulfates might satisfy the Martian thermal emission, vis-near IR, and M ssbauer spectra. These data suggest that sulfide and sulfate minerals might be significant contributors to all types of spectra acquired on the Martian surface.

Rothstein, Y.↗
NASA NTRS2014

Elemental Geochemistry of Sedimentary Rocks at Yellowknife Bay, Gale Crater, Mars

Sedimentary rocks examined by the Curiosity rover at Yellowknife Bay, Mars, were derived from sources that evolved from an approximately average martian crustal composition to one influenced by alkaline basalts. No evidence of chemical weathering is preserved, indicating arid, possibly cold, paleoclimates and rapid erosion and deposition. The absence of predicted geochemical variations indicates that magnetite and phyllosilicates formed by diagenesis under low-temperature, circumneutral pH, rock-dominated aqueous conditions. Analyses of diagenetic features (including concretions, raised ridges, and fractures) at high spatial resolution indicate that they are composed of iron- and halogen-rich components, magnesium-iron-chlorine-rich components, and hydrated calcium sulfates, respectively. Composition of a cross-cutting dike-like feature is consistent with sedimentary intrusion. The geochemistry of these sedimentary rocks provides further evidence for diverse depositional and diagenetic sedimentary environments during the early history of Mars.

Research Support, U.S. Gov't, Non-P.H.S.↗
NASA NTRS2015

Insights into the Martian Regolith from Martian Meteorite Northwest Africa 7034

Everything we know about sedimentary processes on Mars is gleaned from remote sensing observations. Here we report insights from meteorite Northwest Africa (NWA) 7034, which is a water-rich martian regolith breccia that hosts both igneous and sedimentary clasts. The sedimentary clasts in NWA 7034 are poorly-sorted clastic siltstones that we refer to as protobreccia clasts. These protobreccia clasts record aqueous alteration process that occurred prior to breccia formation. The aqueous alteration appears to have occurred at relatively low Eh, high pH conditions based on the co-precipitation of pyrite and magnetite, and the concomitant loss of SiO2 from the system. To determine the origin of the NWA 7034 breccia, we examined the textures and grain-shape characteristics of NWA 7034 clasts. The shapes of the clasts are consistent with rock fragmentation in the absence of transport. Coupled with the clast size distribution, we interpret the protolith of NWA 7034 to have been deposited by atmospheric rainout resulting from pyroclastic eruptions and/or asteroid impacts. Cross-cutting and inclusion relationships and U-Pb data from zircon, baddelleyite, and apatite indicate NWA 7034 lithification occurred at 1.4-1.5 Ga, during a short-lived hydrothermal event at 600-700 C that was texturally imprinted upon the submicron groundmass. The hydrothermal event caused Pb-loss from apatite and U-rich metamict zircons, and it caused partial transformation of pyrite to submicron mixtures of magnetite and maghemite, indicating the fluid had higher Eh than the fluid that caused pyrite-magnetite precipitation in the protobreccia clasts. NWA 7034 also hosts ancient 4.4 Ga crustal materials in the form of baddelleyites and zircons, providing up to a 2.9 Ga record of martian geologic history. This work demonstrates the incredible value of sedimentary basins as scientific targets for Mars sample return missions, but it also highlights the importance of targeting samples that have not been overprinted by metamorphic processes, which is the case for NWA 7034.

McCubbin, Francis M.↗
NASA NTRSDate not supplied

Indigenous Organic Matter Associated with Unusual Low Temperature Aqueous Secondary Phases in the Mars Meteorite Nakhla

In freshly fractured chips of the Mars meteorite Nakhla, we found carbonaceous phases intimately associated with secondary aqueous alteration phases, both mineral and amorphous, interpreted to have formed through the low-temperature, mineral-water dissolution of the host Martian basalt.We have characterized the nature of carbonaceous matter and spatially associated secondary phases within Nakhla using a multidisciplinary suite of optical and electron beam instrumentation(Thomas-Keprta et al., 2022). Secondary Phases: The preserved secondary mineral phases are best described as ‘juvenile’ hydrated amorphous silica formed when water interacts with mafic rocks. Although amorphous silica on Earth rarely persists through geologic time due to alteration into other phases, e.g.,microcrystalline opal-CT and eventually quartz, the lack of maturation of primarily amorphous silica with embedded nano phase ferrihydrite in Nakhla infers these phases formed in a limited water environment by low temperature, circumneutral pH fluids stabilized by the presence of coexisting amorphous silica.Additionally, we report the presence of the ferrous hydroxycarbonate mineral chukanovite (Fe2(OH)2CO3)within some of the secondary mineral aggregates studied. Organic Matter:Indigenous Nakhla carbonaceous matter is present both in condensed phases and in a dispersed state spatially associated with secondary alteration phases. In the former, discrete refractory micron to submicron assemblages were identified that appear macromolecular in nature and, in several cases, associated with F and, in one case, significant N. While organically bound Fhas yet to be detected remotely on Mars, the identification of organic N within one of the carbonaceous phases is considered a prerequisite for Martian astrobiological potential. Summary: Neither the intimate association of carbonaceous matter with secondary phases nor the identification of chukanovite have been previously reported in any of the Martian meteorites.A variety of habitability-related metastable solid-phase, oxidation-reduction, and organic-molecular sample attributes in Nakhla formed hundreds of millions of years ago near Mars’ surface; these alteration products persisted on Mars until very recentlyand resemble the amorphous materials observed at Gale crater by Mars Science Laboratory CuriosityRover (Rampe et al., 2020).Similar phases may be expected to occur elsewhere on Mars (e.g., Jezerocrater). References: Rampe E. B. et al.(2020) Mineralogy and geochemistry of sedimentary rocks and eolian sediments in Gale crater, Mars: A review after six Earth years of exploration with Curiosity.Geochemistry80, 125605; Thomas-Keprta K.L. et al. (2022) Indigenous carbon-rich matter associated with unusual aqueous alteration features in Nakhla: Complex formation and preservation history. Geochim. et Cosmochim. Acta320, 41-78 (online).

Mars meteorite↗
NASA NTRSDate not supplied

Phyllosilicate Formation on Early Mars Via Open-System Acid Alteration of Basaltic Glass

Smectites are widespread on Mars, but neutral/alkaline conditions favorable for smectite formation have surprisingly not led to abundant carbonates. Smectite formation on Mars could also occur in acidic environments unfavorable for carbonate formation. Acidic smectite formation has been demonstrated in batch (closed hydrologic) systems, however, the mechanisms and octahedral composition of smectite forming in acidic flow-through (open hydrologic) systems are not fully understood. Stapafell basaltic glass was hydrothermally altered (190◦C) at two flow rates corresponding to low and high water to rock ratio (W/R) and initial pH (pH_0) values of 2, 3, 4 and 6, and a batch low W/R experiment was conducted at pH_0 2. Kaolinite, montmorillonite and chlorite formed at pH_0 2 at low W/R; no phyllosilicates formed at pH_0 2 at high W/R; and lizardite formed at pH_0 ≥3 at both W/R ratios. Lizardite, kaolinite, and montmorillonite in these experiments formed by precipitation from solution and chlorite likely formed through alteration of montmorillonite and/or basalt. Saponite formed at pH_0 2 in batch conditions by alteration of basaltic glass. Comparison of experimental data with martian phyllosilicate assemblages indicated that smectite formation on Mars likely occurred under water-limited conditions. Al-rich smectite could form in open-system low W/R subsurface environments under a narrow range of pH (pH <3) while saponite could form in closed low W/R systems under acidic to alkaline conditions. Combined open and closed hydrological regimes could be responsible for development of clay mineral stratigraphies observed on Mars. The acidic conditions required for formation of Al-rich smectite were unfavorable for carbonate precipitation, but carbonate precipitation could occur together with Fe/Mg-smectite in closed systems at pH >4. The lack of carbonates occurring together with Fe/Mg-smectite could be cause by low pCO2 in subsurface closed environments and/or by overall lack of carbonate precipitation despite significant oversaturation.

S J Ralston↗
NASA NTRS1988

Geochemistry and origin of gold mineralization in the Kolar Schist Belt

Geological, mineralogical, mineral-textural and geochemical data of the sulfide lodes in the belt indicate that the gold mineralization could be related to low temperature, low Eh and high pH rock-dominated geothermal systems set up in the submarine volcanic pile prior to amphibolite metamorphism. A relatively long-lived geothermal system produced an economic deposit, whereas short-lived ones, because of rapid burial by younger basalts throttled the geothermal system and diffused the discharge yielding low grade ore bodies. The source for gold and iron could be iron enriched tholeiites derived from source regions enriched in komatiitic melt components and komatiitic rocks derived by very low extents of melting of metasomatised mantle sources. On the other hand, the geographical restriction of the quartz-calcite lodes, their mineralogical and geochemical data and their estimated temperature of formation all seem to suggest that a major part of the hydrothermal fluids, and a significant portion of gold could have been derived from mantle derived intrusive, sanukitoid type magma sources, similar to the Champion Gneiss occurring on the eastern part of the belt. However, the possibility of some input by remobilization of a premetamorphic sulfide protore to quartz lodes cannot be ruled out completely.

Siddaiah, N. Siva↗
NASA NTRS1984

Hydrothermal alteration of CM carbonaceous chondrites: Implications of the identification of tochilinite as one type of meteoritic PCP

Poorly characterized phases (PCP's) constitute up to 30 volume percent of some CM carbonaceous chondrites, and are therefore an important key to an understanding of the physico-chemical conditions attending matrix evolution. An iron rich form of the terrestrial phase tochilinite was recently identified as a common type of PCP. Tochilinite has the general formula 6Fe(0.9)S.5(Mg,Fe)(OH)2 and consists of alternating machinawite (FeS) and brucite ((Mg,Fe)(OH)2) sheets, with iron vacancies in the sulfide sheets. In iron rich tochilinite, ferrous hydroxide, called amakinite, replaces brucite. If CM carbonaceous kchondrites have underdone hydrothermal alteration, iron rich tochilinite, at least, probably grew from aqueous solutions characterized by low FO2, high FS2, pH 10 to 12, and at a temperature at or below 170 C.

Zolensky, M. E.↗
NASA NTRS1999

Sources and sinks for ammonia and nitrite on the early Earth and the reaction of nitrite with ammonia

An analysis of sources and sinks for ammonia and nitrite on the early Earth was conducted. Rates of formation and destruction, and steady state concentrations of both species were determined by steady state kinetics. The importance of the reaction of nitrite with ammonia on the feasibility of ammonia formation from nitrite was evaluated. The analysis considered conditions such as temperature, ferrous iron concentration, and pH. For sinks we considered the reduction of nitrite to ammonia, reaction between nitrite and ammonia, photochemical destruction of both species, and destruction at hydrothermal vents. Under most environmental conditions, the primary sink for nitrite is reduction to ammonia. The reaction between ammonia and nitrite is not an important sink for either nitrite or ammonia. Destruction at hydrothermal vents is important at acidic pH's and at low ferrous iron concentrations. Photochemical destruction, even in a worst case scenario, is unimportant under many conditions except possibly under acidic, low iron concentration, or low temperature conditions. The primary sink for ammonia is photochemical destruction in the atmosphere. Under acidic conditions, more of the ammonia is tied up as ammonium (reducing its vapor pressure and keeping it in solution) and hydrothermal destruction becomes more important.

NASA Discipline Exobiology↗
NASA NTRS2015

Benefits of Microalgae for Human Space Exploration

Algae have long been known to offer a number of benefits to support long duration human space exploration. Algae contain proteins, essential amino acids, vitamins, and lipids needed for human consumption, and can be produced using waste streams, while consuming carbon dioxide, and producing oxygen. In comparison with higher plants, algae have higher growth rates, fewer environmental requirements, produce far less "waste" tissue, and are resistant to digestion and/or biodegradation. As an additional benefit, algae produce many components (fatty acids, H2, etc.) which are useful as biofuels. On Earth, micro-algae survive in many harsh environments including low humidity, extremes in temperature, pH, and as well as high salinity and solar radiation. Algae have been shown to survive inmicro-gravity, and can adapt to high and low light intensity while retaining their ability to perform nitrogen fixation and photosynthesis. Studies have demonstrated that some algae are resistant to the space radiation environment, including solar ultraviolet radiation. It remains to be experimentally demonstrated, however, that an algal-based system could fulfil the requirements for a space-based Bioregenerative Life Support System (BLSS) under comparable spaceflight power, mass, and environmental constraints. Two specific challenges facing algae cultivation in space are that (i) conventional growth platforms require large masses of water, which in turn require a large amount of propulsion fuel, and (ii) most nutrient delivery mechanisms (predominantly bubbling) are dependent on gravity. To address these challenges, we have constructed a low water biofilm based bioreactor whose operation is enabled by capillary forces. Preliminary characterization of this Surface Adhering BioReactor (SABR) suggests that it can serve as a platform for cultivating algae in space which requires about 10 times less mass than conventional reactors without sacrificing growth rate. Further work is necessary to compare the performance of microalgae-based systems, including SABR, with systems based on higher plants, as well as conventional physicochemical-based systems. Ongoing and future work in our laboratory is therefore directed determining the feasibility of using algae as a component of a BLSS in space.

Algae↗
NASA NTRS2010

Equivalent Dipole Vector Analysis for Detecting Pulmonary Hypertension

Various 12-lead ECG criteria have been established to detect right ventricular hypertrophy as a marker of pulmonary hypertension (PH). While some criteria offer good specificity they lack sensitivity because of a low prevalence of positive findings in the PH population. We hypothesized that three-dimensional equivalent dipole (ED) model could serve as a better detection tool of PH. We enrolled: 1) 17 patients (12 female, 5 male, mean age 57 years, range 19-79 years) with echocardiographically detected PH (systolic pulmonary arterial pressure greater than 35 mmHg) and no significant left ventricular disease; and 2) 19 healthy controls (7 female, 12 male, mean age 44, range 31-53 years) with no known heart disease. In each subject we recorded a 5-minute high-resolution 12-lead conventional ECG and constructed principal signals using singular value decomposition. Assuming a standard thorax dimension of an adult person with homogenous and isotropic distribution of thorax conductance, we determined moving equivalent dipoles (ED), characterized by the 3D location in the thorax, dipolar strength and the spatial orientation, in time intervals of 5 ms. We used the sum of all ED vectors in the second half of the QRS complex to derive the amplitude of the right-sided ED vector (RV), if the orientation of ED was to the right side of the thorax, and in the first half the QRS to derive the amplitude of the left-sided vector (LV), if the orientation was leftward. Finally, the parameter RV/LV ratio was determined over an average of 256 complexes. The groups differed in age and gender to some extent. There was a non-significant trend toward higher RV in patients with PH (438 units 284) than in controls (280 plus or minus 140) (p = 0.066) but the overlap was such that RV alone was not a good predictor of PH. On the other hand, the RV/LV ratio was a better predictor of PH, with 11/17 (64.7%) of PH patients but only in 1/19 (5.3%) control subjects having RV/LV ratio greater than or equal to 0.70 (p less than 0.001). The use of ED for evaluating PH shows good specificity at a reasonable sensitivity. The results are limited due to the small study groups and differences in age and gender, but further investigations are warranted, including of ED's diagnostic accuracy for PH versus that of other proposed ECG and VCG criteria.

Harlander, Matevz↗
NASA NTRS2020

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

Several lines of evidence point to low rates of net primary production (NPP) in Archean oceans. However, whether Archean NPP was limited by electron donors or nutrients, particularly phosphorus (P), and how these factors might have changed over a billion years of recorded Archean history, remains contentious. One major challenge is to understand quantitatively the biogeochemical cycling of P on the early Earth. In Part I of this series (Hao et al., 2020), we estimated the weathering flux of P to the oceans as a function of temporally increasing continental emergence and elevation through Archean time. In Part II, we conduct thermodynamic and kinetic simulations to understand key processes of P cycling within the Archean ocean, including seafloor weathering, recycling of organic P, the solubility and precipitation of secondary phosphate minerals, and the burial diagenesis of P precipitates. Our calculations suggest low solubilities of apatite minerals in Archean seawater, primarily due to nearly neutral pH and high levels of Ca. This low solubility, in turn, implies a negligible contribution of apatite dissolution to P bioavailability in Archean seawater. We also simulate the solubility limits of common secondary P-bearing minerals, showing that vivianite would have been the least soluble P mineral in ferruginous Archean seawater (0.1–0.3 µM), even at moderate supersaturation states (Ω = 100 or 1000). If vivianite precipitation was kinetically favorable by microbial activities and mineral adsorption, the sinking flux of P as vivianite in Archean seawater could have reached the modern sinking flux, implying that vivianite precipitation was a potentially major sink for P in Archean oceans. During burial diagenesis, however, vivianite in porewater would have become less stable than Ca-phosphates of lower solubility. At elevated temperatures (>100 °C) associated with burial diagenesis and low-grade metamorphism, vivianite is predicted to react irreversibly with calcite to form apatite. Optimistic assumptions about the recycling efficiency of P on the Archean Earth lead us to estimate that by the end of the eon the total flux of P (continental weathering + recycling) could have supported NPP at levels up to 7% of the modern. The total flux of P would have been much lower on the early and middle Archean Earth, whereas fluxes of electron donors could have been higher, suggesting very low productivity and P-limitation of marine ecosystems during much of the eon. Comparing our estimates of NPP as limited by P supply with the estimate by Ward et al. (2019), in which NPP was limited by electron donors and metabolic efficiency, there could have been a transition between P-limited productivity in the early to middle Archean to electron donor-limitation closer to the eon’s end (assuming no oxygenic photosynthesis). Once oxygenic photosynthesis reached ecological significance, probably near the end of the Archean, our estimated flux of P would allow rapid oxidation of atmosphere.

Vivianite↗