CO2-rich Atmosphere Research Articles

Aurora: A Generalized Retrieval Framework for Exoplanetary Transmission Spectra

Abstract Atmospheric retrievals of exoplanetary transmission spectra provide important constraints on various properties, such as chemical abundances, cloud/haze properties, and characteristic temperatures, at the day–night atmospheric terminator. To date, most spectra have been observed for giant exoplanets due to which retrievals typically assume hydrogen-rich atmospheres. However, recent observations of mini Neptunes/super-Earths, and the promise of upcoming facilities including the James Webb Space Telescope (JWST), call for a new generation of retrievals that can address a wide range of atmospheric compositions and related complexities. Here we report Aurora, a next-generation atmospheric retrieval framework that builds upon state-of-the-art architectures and incorporates the following key advancements: (a) a generalized compositional retrieval allowing for H-rich and H-poor atmospheres, (b) a generalized prescription for inhomogeneous clouds/hazes, (c) multiple Bayesian inference algorithms for high-dimensional retrievals, (d) modular considerations for refraction, forward scattering, and Mie scattering, and (e) noise modeling functionalities. We demonstrate Aurora on current and/or synthetic observations of the hot Jupiter HD 209458 b, mini Neptune K2-18b, and rocky exoplanet TRAPPIST-1 d. Using current HD 209458 b spectra, we demonstrate the robustness of our framework and cloud/haze prescription against assumptions of H-rich/H-poor atmospheres, improving on previous treatments. Using real and synthetic spectra of K2-18b, we demonstrate an agnostic approach to confidently constrain its bulk atmospheric composition and obtain precise abundance estimates. For TRAPPIST-1 d, 10 JWST-NIRSpec transits can enable identification of the main atmospheric component for cloud-free, CO2-rich, and N2-rich atmospheres and abundance constraints on trace gases, including initial indications of O3 if present at enhanced levels (∼10×–100× Earth levels).

Effects of natural and accelerated carbonation on the properties of lime-based materials

This work aims at evaluating the influence of curing conditions on the carbonation process of lime-based mortars and pastes and on the resulting mineralogical, macro- and microstructural properties. To this end, lime-based materials (mortars and pastes) were subjected to natural (0.05 % CO2) and accelerated (5 % CO2) carbonation. The influence of factors such as water/binder ratio, lime (agglomerated) particle size (surface area) and presence of admixtures on the carbonation process was also addressed. The materials cured under the CO2-rich atmosphere carbonated faster and reached a higher degree of carbonation after only 7 days than those cured naturally for 3 years, even though total carbonation was not achieved. Nevertheless, due to the high conversion rate, the evolution of the properties of the tested materials after being subjected to accelerated carbonation for 7 days is expected to be minimal (stable properties were reached). Portlandite was mostly converted into calcite that precipitated as rhombohedral and scalenohedral crystals regardless of the curing environment. The crystals appeared to be larger and better developed in the specimens subjected to accelerated carbonation, which contributed to the higher mechanical strength displayed by these mortars.

The role of planetary interior in the long-term evolution of atmospheric CO2on Earth-like exoplanets

Context.The long-term carbonate silicate cycle plays an important role in the evolution of Earth’s climate and, therefore, may also be an important mechanism in the evolution of the climates of Earth-like exoplanets. However, given the large diversity in the possible interiors for Earth-like exoplanets, the ensuing evolution of the atmospheric CO2pressure may be widely different.Aims.We assess the role of the thermal evolution of the planetary interior on the long-term carbon cycle of Earth-like exoplanets. In particular, we investigate the effects of radiogenic mantle heating, core size, and planetary mass on the atmospheric partial CO2pressure, and the ability of a long-term carbon cycle driven by plate tectonics to control the atmospheric CO2pressure.Methods.We developed a box-model which connects carbon cycling to parametrized mantle convection. Processes considered in the carbon cycle are temperature-dependent continental weathering, seafloor weathering, subduction, and degassing through ridge and arc volcanism. The carbon cycle was coupled to the thermal evolution via the plate speed, which was parametrized in terms of the global Rayleigh number.Results.We find decreasing atmospheric CO2pressure with time, up to an order of magnitude over the entire main sequence lifetime of a solar-type star. High abundances of radioactive isotopes allow for more efficient mantle degassing, resulting in higher CO2pressures. Within the spread of abundances found in solar-type stars, atmospheric CO2pressures at 4.5 Gyr were found to vary from 14 Pa to 134 Pa. We find a decreasing Rayleigh number and plate speed toward planets with larger core mass fractionsfc, which leads to reduced degassing and lower atmospheric CO2pressure. In particular forfc≳ 0.8, a rapid decrease of these quantities is found. Variations in planet mass have more moderate effects. However, more massive planets may favor the development of more CO2rich atmospheres due to hotter interiors.Conclusions.The dependence of plate tectonics on mantle cooling has a significant effect on the long-term evolution of the atmospheric CO2pressure. Carbon cycling mediated by plate tectonics is efficient in regulating planetary climates for a wide range of mantle radioactive isotope abundances, planet masses and core sizes. More efficient carbon cycling on planets with a high mantle abundance of thorium or uranium highlights the importance of mapping the abundances of these elements in host stars of potentially habitable exoplanets. Inefficient carbon recycling on planets with a large core mass fraction (≳0.8) emphasizes the importance of precise mass-radius measurements of Earth-sized exoplanets.

Microalgae strategy in anoxic atmospheres with various CO2 concentrations – Environmental and (astro)biotechnological perspectives

The current study examines the survival strategy of microalgae in closed systems with anoxic atmospheres and the possibility of creating an oxygenic atmosphere through the photosynthetic management of solar radiation. The complete absence of CO2 seems to be addressed initially by the catabolism of cellular organic matter through the respiratory process (possibly by using NO2 instead of O2), which produces CO2. This CO2 supports the photosynthetic process, which produces O2, part of which is used primarily for the O2 enrichment of the atmosphere and the rest for the respiratory procedure and biomass production. Microalgae showed a tolerance to exogenously supplied extreme CO2 concentrations (1 %–40 %) in an anoxic atmosphere and displayed a significantly higher photosynthetic activity compared with that of microalgae cultures grown in an oxygenic atmosphere. This response of microalgae to extreme high CO2 concentrations under anoxic conditions enhances immediately the level of O2 in the atmosphere as well as the culture growth without any stress responses. Since this strategy of microalgae is particularly effective in converting CO2 into O2 in CO2-rich atmosphere, it could help to combat the greenhouse effect by integrating microalgae cultures into toxic gas detoxification systems with extremely high CO2 concentrations. The ability of microalgae to turn hostile atmospheres swiftly into O2-rich atmospheres could be used in the future for the continuous recycling of the atmosphere of human settlement on other planets. Additionally, the increased microalgae biomass under these conditions is an ideal module for important (astro)biotechnological applications.

The Tuning of LIPSS Wettability during Laser Machining and through Post-Processing

In this work, we investigate the fabrication of stainless-steel substrates decorated with laser-induced periodic surface structures (LIPSS) of both hydrophilic and hydrophobic wettability through different post-processing manipulation. In carrying out these experiments, we have found that while a CO2-rich atmosphere during irradiation does not affect final wettability, residence in such an atmosphere after irradiation does indeed increase hydrophobicity. Contrarily, residence in a boiling water bath will instead lead to a hydrophilic surface. Further, our experiments show the importance of removing non-sintered nanoparticles and agglomerates after laser micromachining. If they are not removed, we demonstrate that the nanoparticle agglomerates themselves become hydrophobic, creating a Cassie air-trapping layer on the surface which presents with water contact angles of 180°. However, such a surface lacks robustness; the particles are removed with the contacting water. What is left behind are LIPSS which are integral to the surface and have largely been blocked from reacting with the surrounding atmosphere. The actual surface presents with a water contact angle of approximately 80°. Finally, we show that chemical reactions on these metallic surfaces decorated with only LIPSS are comparatively slower than the reactions on metals irradiated to have hierarchical roughness. This is shown to be an important consideration to achieve the highest degree of hydro-philicity/phobicity possible. For example, repeated contact with water from goniometric measurements over the first 30 days following laser micromachining is shown to reduce the ultimate wettability of the surface to approximately 65°, compared to 135° when the surface is left undisturbed for 30 days.

Characterisation of the hydrospheres of TRAPPIST-1 planets

Context. Planetary mass and radius data suggest that low-mass exoplanets show a wide variety of densities. This includes sub-Neptunes, whose low densities can be explained with the presence of a volatile-rich layer. Water is one of the most abundant volatiles, which can be in the form of different phases depending on the planetary surface conditions. To constrain their composition and interior structure, models must be developed that accurately calculate the properties of water at its different phases. Aims. We present an interior structure model that includes a multiphase water layer with steam, supercritical, and condensed phases. We derive the constraints for planetary compositional parameters and their uncertainties, focusing on the multi-planetary system TRAPPIST-1, which presents both warm and temperate planets. Methods. We use a 1D steam atmosphere in radiative-convective equilibrium with an interior whose water layer is in supercritical phase self-consistently. For temperate surface conditions, we implement liquid and ice Ih to ice VII phases in the hydrosphere. We adopt a Markov chain Monte Carlo inversion scheme to derive the probability distributions of core and water compositional parameters. Results. We refine the composition of all planets and derive atmospheric parameters for planets ‘b’ and ‘c’. The latter would be in a post-runaway greenhouse state and could be extended enough to be probed by space missions such as JWST. Planets ‘d’ to ‘h’ present condensed ice phases, with maximum water mass fractions below 20%. Conclusions. The derived amounts of water for TRAPPIST-1 planets show a general increase with semi-major axis, with the exception of planet d. This deviation from the trend could be due to formation mechanisms, such as migration and an enrichment of water in the region where planet d formed, or an extended CO2-rich atmosphere.

H2SO4 and Organosulfur Compounds in Laboratory Analogue Aerosols of Warm High-metallicity Exoplanet Atmospheres

Abstract Recent transit spectra suggest organic aerosol formation in the atmosphere of sub-Neptunes. Sulfur gases are expected to be present in warm exoplanet atmospheres with high metallicity. Many aspects of the sulfur fixation process by photochemistry in planetary atmospheres are not fully understood. In this work, tholins produced in a CO2-rich atmosphere simulation experiment with H2S were analyzed with very high-resolution mass spectrometry (HRMS) that allows for searching specific molecules in addition to providing some insight on the mixture complexity. To our knowledge, this is the first experimental investigation of sulfur-bearing organic aerosol formation from irradiation of H2S at temperatures relevant to warm exoplanets. The analysis of the mass spectra shows that the soluble organic fraction of the solid particles contains over 2500 organosulfur (CHS/CHOS/CHNS/CHNOS) molecular formulas (73% of all assigned signals) within a broad mass range (from 50 to 400 u, atomic mass unit). In particular, 14 sulfuric acid derivatives were detected and 13 unique molecular formulae that could correspond to amino acid derivatives were identified. This high molecular diversity indicates a rich and active sulfur chemistry triggered by irradiation of H2S. The average elemental composition (wt%) of the soluble fraction of the particles is 40%C, 30%O, 21%S, 6%H, and 3%N, making the sulfur abundance a factor of ∼14 larger than in the initial gas composition. Our analysis of experimental simulations shows that organosulfur species are likely an important component of the haze in exoplanet atmospheres.

Electrochemical performance and superior CO2 endurance of PrBaCo2O6–δ – PrBaCoTaO6 composite cathode for IT-SOFCs

PrBaCo2O6–δ – PrBaCoTaO6 (PBC/PBCT) composites were studied with respect to their chemical and thermomechanical compatibility with ceria electrolyte (SDC), electrical conductivity, electrochemical performance and reversibility at variations of CO2 content in the oxidizing atmosphere. The electrochemical impedance spectra of the composite electrodes were analyzed by the distribution of relaxation times technique. The best properties combination was observed for the 75/25 composite containing 25 wt% of PBCT where polarization resistance did not exceed 0.025 Ohm⋅cm2 in the air at 1073 K. Though subjected to some degradation in CO2 rich atmospheres, the 75/25 composite was shown to completely restore its electrochemical activity after annealing in the air at 973 K.

A simple experiment on global warming.

A simple experiment has been developed to demonstrate the global warming potential of carbon dioxide (CO2) gas in the Earth's atmosphere. A miniature electric resistance heating element was placed inside an inflatable balloon. The balloon was filled with either air or CO2. Whereas the CO2 partial pressure on the earth's atmosphere is approximately 4 × 10−4 atm, in this experiment, a high partial pressure of CO2 (1 atm) was used to compensate for the short radiation absorption path in the balloon. The element was heated to approximately 50°C, the power was then switched off and the element's cooling trends in air and in CO2 were monitored. It took a longer time to cool the heating element back to ambient temperature in CO2 than in air. It also took longer times to cool the element in larger size balloons and in pressurized balloons when they were filled with CO2. To the contrary, the balloon size or pressure made no difference when the balloons were filled with air. A simple mathematical model was developed, and it confirmed that the radiative heat loss from the element decreased significantly in CO2. This investigation showed that the cooling rate of an object, with surface temperature akin to temperatures found on Earth, is reduced in a CO2-rich atmosphere because of the concomitant lower heat loss to its environment.

Staphylococcus saccharolyticus: An Overlooked Human Skin Colonizer.

Coagulase-negative staphylococcal species constitute an important part of the human skin microbiota. In particular, facultative anaerobic species such as Staphylococcus epidermidis and Staphylococcus capitis can be found on the skin of virtually every human being. Here, we applied a culture-independent amplicon sequencing approach to identify staphylococcal species on the skin of healthy human individuals. While S. epidermidis and S. capitis were found as primary residents of back skin, surprisingly, the third most abundant member was Staphylococcus saccharolyticus, a relatively unstudied species. A search of skin metagenomic datasets detected sequences identical to the genome of S. saccharolyticus in diverse skin sites, including the back, forehead, and elbow pit. Although described as a slow-growing anaerobic species, a re-evaluation of its growth behavior showed that S. saccharolyticus can grow under oxic conditions, and, in particular, in a CO2-rich atmosphere. We argue here that S. saccharolyticus was largely overlooked in previous culture-dependent and -independent studies, due to its requirement for fastidious growth conditions and the lack of reference genome sequences, respectively. Future studies are needed to unravel the microbiology and host-interacting properties of S. saccharolyticus and its role as a prevalent skin colonizer.

Fluidised bed oxy-fuel gasification of coal: Interactions between volatiles and char at varying pressures and fuel feed rates

Fluidised bed gasification is a versatile technology in terms of load flexibility and ability to process various fuels. However, fluidised bed gasification processes are usually air-blown, making integration with CO2 capture difficult and expensive. Operation of a fluidised bed gasifier with O2/recycled CO2 mixtures has been proposed as a route to overcome this drawback. In this work, the effect of pressure and fuel feed rate on the extent of gasification of German lignite in a CO2 rich atmosphere has been examined in a fluidised bed reactor (FBR). A 19% decrease in carbon conversion with increasing pressure from 5 to 20 bara was observed. The higher fuel feeding rates needed to maintain the gasification agent to coal ratio in the FBR at high pressures produces a larger concentration of tars in the reactor, which seems to cause deposition, by intra and inter particle reaction, on the char and reduces its reactivity.

Microbiological analysis of autologous bone particles obtained by low-speed drilling and treated with different decontamination agents

The aim of this study was to compare the effectiveness of three agents – two antibiotics (amoxicillin and clindamycin) and an antiseptic (chlorhexidine) – to decontaminate bone grafts obtained by low-speed drilling. The study included 248 bone tissue samples harvested from 62 patients by low-speed drilling before dental implant placement. Each of four samples obtained from every patient was dropped, using a sterile instrument, into a sterile tube containing a 500-μl solution of 400μg/mL amoxicillin, 150μg/mL clindamycin, 0.12% chlorhexidine, or physiological saline for 1min. The number of colony-forming units (CFU) was determined at 48h of culture. The use of clindamycin, amoxicillin, or chlorhexidine as decontaminant for 1min significantly reduced the CFU count when compared to physiological saline (control agent). In both anaerobic and CO2-rich atmospheres, significant differences in CFU/mL were found between the control and chlorhexidine groups (P<0.001), control and amoxicillin groups (P<0.001), control and clindamycin groups (P<0.001), chlorhexidine and amoxicillin groups (P<0.0001), and chlorhexidine and clindamycin groups (P<0.0001). In conclusion, clindamycin had the highest decontaminating effect on bone particles obtained by low-speed drilling, followed by chlorhexidine and amoxicillin. Clindamycin may therefore be a valid alternative option for the routine decontamination of intraoral bone grafts.

Influence of the nature of the gas phase on the degradation of RNA during fossilization processes

The search for the most ancient traces of life on Earth has always been fraught with controversies because of the inevitable degradation undergone by fossilized biomolecules. Laboratory experiments may provide unique clues to achieve a better mechanistic understanding of the key processes involving (biogenic or abiotic) organic carbon during a geological history. The Earth atmosphere has changed over geological times, from a CO2-rich atmosphere during the Hadean and Archean to the O2-rich atmosphere of the present day, with a direct impact on the nature of the gas phase trapped within the sediment porosity. Yet, the influence of the nature of this gas phase on fossilization processes has almost never been investigated. Here, we conducted a series of fossilization experiments using an emblematic biomolecule (i.e. RNA) and clay minerals at 200 °C for 7 days in closed systems in equilibrium with two different gas phases (e.g. CO2 versus N2/O2). The multiscale characterization of experimental residues using a suite of advanced microscopy and spectroscopy techniques showed that the final organo-mineral assemblages strongly depend on the nature of the gas phase. In addition to the nature of the mineral phases, results showed that the nature of the gas phase impacts the chemistry of the residual N-rich organic compounds trapped within the interlayer spaces of Mg-smectites (e.g. mainly aliphatic-rich under CO2 vs dominated by heterocycles under N2/O2). Altogether, the present study demonstrates the necessity to take into account the nature of the gas phase composition when experimentally simulating fossilization processes aiming at better constraining which biosignatures may be preserved in ancient rocks. Finally, the experimental results reported here may serve to identify the potential biosignatures that should be searched for on other planetary bodies.

Sulfur-driven haze formation in warm CO2-rich exoplanet atmospheres

Sulfur gases significantly affect the photochemistry of planetary atmospheres in our Solar System, and are expected to be important components in exoplanet atmospheres. However, sulfur photochemistry in the context of exoplanets is poorly understood due to a lack of chemical-kinetics information for sulfur species under relevant conditions. Here, we study the photochemical role of hydrogen sulfide (H2S) in warm CO2-rich exoplanet atmospheres (800 K) by carrying out laboratory simulations. We find that H2S plays a significant role in photochemistry, even when present in the atmosphere at relatively low concentrations (1.6%). It participates in both gas and solid phase chemistry, leading to the formation of other sulfur gas products (CH3SH/SO, C2H4S/OCS, SO2/S2, and CS2) and to an increase in solid haze particle production and compositional complexity. Our study shows that we may expect thicker haze with small particle sizes (20 to 140 nm) for warm CO2-rich exoplanet atmospheres that possess H2S.

A New Remote Sensing-Based System for the Monitoring and Analysis of Growth and Gas Exchange Rates of Photosynthetic Microorganisms Under Simulated Non-Terrestrial Conditions.

Oxygenic photosynthetic microorganisms are a focal point of research in the context of human space exploration. As part of the bioregenerative life-support systems, they could have a key role in the production of breathable O2, edible biomasses and in the regeneration of CO2 rich-atmospheres and wastewaters produced by astronauts. The test of the organism’s response to simulated physico-chemical parameters of planetary bodies could also provide important information about their habitability potential. It is believed that the success of future planetary and space missions will require innovative technologies, developed on the base of preliminary experiments in custom-made laboratory facilities. In this context, simulation chambers will play a pivotal role by allowing the growth of the microorganisms under controlled conditions and the evaluation in real-time of their biomass productivity and impact on atmosphere composition. We here present a system capable of addressing these requirements with high replicability and low costs. The setup is composed by three main parts: 1) a Star Light Simulator, able to generate different light intensities and spectra, including those of non-solar stars; 2) an Atmosphere Simulator Chamber where cultures of photosynthetic microorganisms can be exposed to different gas compositions; 3) a reflectivity detection system to measure from remote the Normalized Difference Vegetation Indexes (NDVI). Such a setup allows us to monitor photosynthetic microorganism’s growth and gas exchange performances under selected conditions of light quality and intensity, temperature, pressure, and atmospheres simulating non-terrestrial environments. All parameters are detected by remote sensing techniques, thus without interfering with the experiments and altering the environmental conditions set. We validated the setup by growing cyanobacteria liquid cultures under different light intensities of solar illumination, collecting data on their growth rate, photosynthetic activity, and gas exchange capacity. We utilized the reflectivity detection system to measure the reflection spectra of the growing cultures, obtaining their relative NDVI that was shown to correlate with optical density, chlorophyll content, and dry weight, demonstrating the potential application of this index as a proxy of growth.

Short sugarcane bagasse fibers cementitious composites for building construction

This paper presents an experimental assessment on sugarcane bagasse short fibers reinforced composites, conglomerated by Ordinary Portland Cement and Plaster and containing fine ash from rice husk combustion, for rural autonomous construction. The vegetable bagasse fibers were supplied directly from landfills of small rural sugar industries, smoked on site, washed in laboratory, treated in supersaturated calcium hydroxide at room temperature and dried before mixing. Physical and mechanical properties of components and composites were obtained. Accelerated aging of composites in CO2 rich atmosphere was done in laboratory, assessing the new properties of specimens after this aerial carbonation, in relation with the ordinary ones. Increasing of specific gravity, modulus of rupture, compressive strength, Young's Modulus, decreasing of porosity, water absorption and toughness of the aged composites was obtained. Their ability for building construction as sustainable and eco-efficient construction materials is analyzed.

Droplet combustion behavior of oxidatively degraded methyl laurate and methyl oleate in microgravity

Droplet combustion behavior of degraded and non-degraded fatty acid methyl ester (FAME) were studied under microgravity condition. Accelerated oxidation tests were conducted for methyl laurate (LME) and methyl oleate (OME) as representatives of FAME, and the changes in viscosities and compositions were evaluated. The Rancimat method was employed for oxidizing fuels at 100 °C for 6 or 24 h. The viscosities and compositions were measured with an Ubbelohde viscometer and a gas chromatography-mass spectrometer (GC–MS), respectively. Results showed that various oxidation products were formed only for OME during the oxidation test, and the amounts increased with an increase in the oxidation time. In addition, viscosities of degraded OME were higher than those of non-degraded OME, which would be attributable to the formation of oxidation products. Subsequently, the droplet combustion experiment was performed at 0.1 MPa, 750 °C in CO2-rich atmosphere under microgravity. Droplet combustion behavior was analyzed in terms of evolutions of droplet diameter squared and the instantaneous burning rate. As a result, the instantaneous burning rate of LME maintained almost constant during its combustion period as well as n-decane, which indicates that the behavior of instantaneous burning rate was not influenced by the difference in fuel properties between hydrocarbon and unsaturated FAME. In contrast, the droplet of degraded OME exhibited puffing during the evaporation and combustion periods. This indicates that oxidation products with various volatilities were formed in the degraded fuels, which resulted in puffing. As oxidation proceeded, the release rate of liquid and vapor by puffing decreased owing to the increased viscosity, which causes puffing more frequently. Furthermore, the time of bubble formation increased with an increase in the initial droplet diameter owing to an increase of the heat capacity of the droplet. On the contrary, the time of bubble formation did not vary drastically with the oxidation time, which was probably owing to a limited change in the heat capacity during the oxidation test. This study addresses the droplet burning behavior of LMEs and OMEs with an emphasis on the effects of oxidation.

Friction Performance and Mechanism of the Molybdenum Disulfide Film in Carbon Dioxide Atmosphere

In this work, the tribological properties of MoS2 films were investigated in air, vacuum and carbon dioxide environments by means of experiments and First-principles calculations. The results showed that the MoS2 film had the lowest and more stable coefficient of friction in carbon dioxide atmosphere than that in other environments. The MoS2 film usually loses some S atoms to produce S-vacancy defects during sputtering deposition, which can be filled by carbon dioxide molecules in a way of chemisorption. The strong repulsive force always existed at the interfaces of MoS2 adsorbed with carbon dioxide molecules, which was responsible for the low friction coefficient of MoS2 films in carbon dioxide. In the future, the MoS2 film is likely to be widely used on Mars that is well known for its CO2-rich atmosphere.

Comparison of the greenhouse effect between Earth and Venus using multiple atmospheric layer models

To better understand the mechanisms of global warming, we developed a one atmospheric layer model for Earth and a multiple atmospheric layer model (N = 111) for Venus. Earth’s greenhouse gas atmosphere has an average of 78.9% absorption efficiency of terrestrial radiation (f = 0.789), while we assume Venus’ atmosphere has a near 100% absorption efficiency (f = 1) due to its denser, CO2-rich atmosphere. Viewing the atmospheric layers as blackbodies, we modeled the surface temperature of Earth and Venus, both of which are able to predict the respective actual planetary temperatures. The consistency (δ &lt; 1%) between the modeled surface temperature and the observed surface temperature of these two planets suggest that the multiple layer greenhouse gas atmosphere mechanism could explain Venus’ runaway global warming and scorching temperature. The results of these two models suggest that if Earth continues to experience uncontrolled greenhouse gas emissions, global warming and its negative outcomes may be further exacerbated.

A carbonate-rich lake solution to the phosphate problem of the origin of life

Phosphate is central to the origin of life because it is a key component of nucleotides in genetic molecules, phospholipid cell membranes, and energy transfer molecules such as adenosine triphosphate. To incorporate phosphate into biomolecules, prebiotic experiments commonly use molar phosphate concentrations to overcome phosphate's poor reactivity with organics in water. However, phosphate is generally limited to micromolar levels in the environment because it precipitates with calcium as low-solubility apatite minerals. This disparity between laboratory conditions and environmental constraints is an enigma known as "the phosphate problem." Here we show that carbonate-rich lakes are a marked exception to phosphate-poor natural waters. In principle, modern carbonate-rich lakes could accumulate up to ∼0.1 molal phosphate under steady-state conditions of evaporation and stream inflow because calcium is sequestered into carbonate minerals. This prevents the loss of dissolved phosphate to apatite precipitation. Even higher phosphate concentrations (>1 molal) can form during evaporation in the absence of inflows. On the prebiotic Earth, carbonate-rich lakes were likely abundant and phosphate-rich relative to the present day because of the lack of microbial phosphate sinks and enhanced chemical weathering of phosphate minerals under relatively CO2-rich atmospheres. Furthermore, the prevailing CO2 conditions would have buffered phosphate-rich brines to moderate pH (pH 6.5 to 9). The accumulation of phosphate and other prebiotic reagents at concentration and pH levels relevant to experimental prebiotic syntheses of key biomolecules is a compelling reason to consider carbonate-rich lakes as plausible settings for the origin of life.