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During this work, the viability of encapsulated replicators systems as a function of the vesicle size is revisited. Now, instead of considering in detail the diffusion process, the existence of a well-mixed solution inside the vesicle was assumed. Our results corroborated previous numerical estimations about the existence of a minimal size for vesicles immersed in an extremely hostile environment. In this particular case, we found analytical expressions for the critical radius as a function of the kinetics parameters for the two different families of replicators considered during the study. Furthermore, we also reported the existence of an optimal radius of the vesicle where the replicator population reaches a maximum, a value that may change slightly according to the replicator type. On the other hand, we also found that there is not a critical radius if the conditions of the external environment are not so extreme. However, even in this case, there is an optimal radius where the replicator population within the vesicle is noticeably larger than its value in the external medium. According to our results, the size of the vesicle may determine how efficiently the process of encapsulation took place on early Earth, probably one of the key steps during the process of abiogenesis.

Potential constraints on protocell size are developed from simple entropic considerations. To do that, two new different indexes as measures of their structural and dynamic order were developed and applied to an elemental model of the heterotrophic protocell. According to our results, cell size should be a key factor determining the potential of these primitive systems to evolve and consequently to support life. Our analyses also suggest that the size of the optimal vesicles could be constrained to have radii in the interval $$ (R_{\text{S}} \le R \le R_{\text{D}} ) $$ , where the two extreme limits $$ R_{\text{S}} $$ and $$ R_{\text{D}} $$ represent the states of maximum structural order (largest accumulation of substrate inside the vesicle) and the maximum flux of entropy production, respectively. According to the above criteria, the size of the optimum vesicles falls, approximately, in the same spatial range estimated for biological living cells assuming plausible values for the second-order rate constant involved in the catabolic process. Furthermore, the existence of very small vesicles could be seriously affected by the limited efficiency, far from the theoretical limits, with which these catabolic processes may proceed in a prebiotic system.

The potential of a mass asteroid impact on Earth to disturb the chemosynthetic communities at global scale is discussed. Special emphasis is made on the potential influence on anammox communities and their implications in the nitrogen biogeochemical cycle. According to our preliminary estimates, anammox communities could be seriously affected as a consequence of global cooling and the large process of acidification usually associated with the occurrence of this kind of event. The scale of affectations could vary in a scenario like the Chicxulub as a function of the amount of soot, depth of the water column and the deposition rate for sulphates assumed in each case. The most severe affectations take place where the amount of soot and sulphates produced during the event is higher and the scale of time of settlements for sulphates is short, of the order of 10 h. In this extreme case, the activity of anammox is considerably reduced, a condition that may persist for several years after the impact. Furthermore, the impact of high levels of other chemical compounds like sulphates and nitrates associated with the occurrence of this kind of event are also discussed.

In this paper, we connect ideas of the astrobiological and ecological schools to quantify habitability. We show how habitability indexes, devised using the astrobiologically inspired Quantitative Habitability Theory (QHT), can be embedded into ecological models of trophic levels. In particular, we address the problem of spatial-temporal scales. It turns out that the versatility of QHT allows to treat spatial and temporal scales typical of ecological studies. As a habitability index, we propose a new version of our Aquatic Primary Habitability, devised by some of us and formerly applied to saltwater ecosystems (both ocean and coastal) and now applied to freshwater. Although the aim of the paper is to outline the methodology rather than realism, initial steps for parameterization are considered for lakes of South-Central Chile.

The ability to support a replicator population in an extremely hostile environment is considered in a simple model of a prebiotic cell. We explore from a classical approach how the replicator viability changes as a function of the cell radius. The model includes the interaction between two different species: a substrate that flows from the exterior and a replicator that feeds on the substrate and is readily destroyed in the environment outside the cell. According to our results, replicators in the cell only exist when the radius exceeds some critical value [Formula: see text] being, in general, a function of the substrate concentration, the diffusion constant of the replicator species, and the reproduction rate coefficient. Additionally, the influence of other parameters on the replicator population is also considered. The viability of chemical replicators under such drastic conditions could be crucial in understanding the origin of the first primitive cells and the ulterior development of life on our planet. Key Words: Prebiotic cell-Chemical replicator-Environment-Reproduction rate. Astrobiology 18, 403-411.

Some basic principles to enlarge simple ecological models and the role of nonlinearities are discussed. The inclusion of internal groups and the new dynamic possibilities associated with this procedure are considered in the context of the logistic model. According to our results, processes like the success or extinction of a particular group without affecting the global population are not necessarily linked to the impact of environmental changes or the supremacy of a determined group or subspecies. In our case, the uniformity, the success or extinction of a particular group into a global population may be seen as the possibility to achieve or not a typical symmetry-breaking process. Such possibilities arise associated with the degree of nonlinearity contributions and the specificities of the interaction network in the model. Other elements linked with the ecological interaction, the role of symmetries and the phenomenological nature of ecological modelling are also discussed.

The Gulf of Ana Maria is located in the southeast Cuban platform and is one of the most important regions for fisheries in the country. Taking into account that marine primary production defines the areas and yields of fishery production, we develop a habitability index that quantifies the environmental suitability for phytoplankton assemblage development. The index considers light and limiting nutrient as the main environmental factors governing the phytoplankton primary production in the Gulf of Ana Maria. We considered a function of radiation described by a photosynthesis model and function of nutrient described by a eutrophication index. Quantitative estimates of habitability were made in nine stations at 1:00 PM and 4:00 PM for a typical day of October, in order to match with the available field data. Solar irradiation at sea surface was calculated by using the tropospheric ultraviolet and visible computational code TUV4.6, and we derived the data of attenuation coefficient of light from Secchi depth data. Besides, we used nutrient concentration of soluble reactive phosphorus (limiting nutrient). We obtained the first optical classification of the waters of the Gulf of Ana Maria, with a dominance of coastal water C5. It was found an intermediate potential (~50%) for phytoplankton development in the Gulf of Ana Maria, which is mainly limited by nutrients rather than by light. Further refinements in both the index and data collection are expected to reach more accurate conclusions.

The activity of anammox bacteria (AA) can be estimated based on the production of \({\text{N}}_{2}\). Known the mechanism of the catabolic reaction, three differential equations are established according to the most important substrates (\({\text{NO}}_{3}^{ - }\) and \({\text{NH}}_{4}^{ + }\)) and the pH. The solution of this system might provide a rough estimate of the activity of the anammox, since neither inhibitory effects nor efficiency of the microorganisms is considered. Anammox can be inhibited by ocean acidification, generated by the deposition of \({\text{H}}_{2} {\text{SO}}_{4}\) and \({\text{HNO}}_{3}\) during asteroid impact events such as Chicxulub. The magnitude of the inhibition depends on the amount and speed with which the \({\text{H}}_{2} {\text{SO}}_{4}\) is added fundamentally.

In this chapter, we outline general ideas to quantify habitability, starting with a general abiogenesis–biogenesis conceptual model. We connect this model with the approach of the astrobiological school of quantitative habitability, specifically with quantitative habitability theory, to devise habitability indexes. We present two indexes devised by us: the Aquatic Primary Habitability for photosynthesis-based ecosystems, and the Chemosynthetic Habitability Index for chemoautotrophy-based ones. As a case study, we present the application of the last one to hydrothermal vents. It is also mentioned the possibility of embedding parameters such as net primary productivity, calculated using habitability indexes, into greater ecological models with several trophic models, making a clear connection between the astrobiological and ecological approaches of quantitative habitability.

The Cuban archipelago has an extremely complex geology. In this chapter, an overview on its peculiarities is given. It is also presented a historical sketch of the Cuban geological heritage, and the current menaces to preserve it. Then, the current Cuban policy and practical efforts for geoconservation are described.

We perform a quantitative assessment for the potential for photosynthesis in hydrothermal vents in the deep ocean. The photosynthetically active radiation in this case is from geothermal origin: the infrared thermal radiation emitted by hot water, at temperatures ranging from 473 up to 673 K. We find that at these temperatures the photosynthetic potential is rather low in these ecosystems for most known species. However, species which a very high efficiency in the use of light and which could use infrared photons till 1300nm, could achieve good rates of photosynthesis in hydrothermal vents. These organisms might also thrive in deep hydrothermal vents in other planetary bodies, such as one of the more astrobiologically promising Jupiter satellites: Europa., Accepted for publication in Astrophysics and Space Science

The aim of this work is to study the features of a simple replicator chemical model of the relation between kinetic stability and entropy production under the action of external perturbations. We quantitatively explore the different paths leading to evolution in a toy model where two independent replicators compete for the same substrate. To do that, the same scenario described originally by Pross (J Phys Org Chem 17:312-316, 2004) is revised and new criteria to define the kinetic stability are proposed. Our results suggest that fast replicator populations are continually favored by the effects of strong stochastic environmental fluctuations capable to determine the global population, the former assumed to be the only acting evolution force. We demonstrate that the process is continually driven by strong perturbations only, and that population crashes may be useful proxies for these catastrophic environmental fluctuations. As expected, such behavior is particularly enhanced under very large scale perturbations, suggesting a likely dynamical footprint in the recovery patterns of new species after mass extinction events in the Earth's geological past. Furthermore, the hypothesis that natural selection always favors the faster processes may give theoretical support to different studies that claim the applicability of maximum principles like the Maximum Metabolic Flux (MMF) or Maximum Entropy Productions Principle (MEPP), seen as the main goal of biological evolution.

We do a preliminary modelling of the photosynthetic rates of phytoplankton at the very beginning of the Paleogene, just after the impact of the Chicxulub asteroid, which decisively contributed to the last known mass extinction of the Phanerozoic eon. We assume the worst possible scenario from the photobiological point of view: an already clear atmosphere with no ozone, as the timescale for soot and dust settling (years) is smaller than that of the full ozone regeneration (decades). Even in these conditions we show that most phytoplankton species would have had reasonable potential for photosynthesis in all the three main optical ocean water types. This modelling could help explain why the recovery of phytoplankton was relatively rapid after the huge environmental stress of that asteroid impact. In a more general scope, it also reminds us of the great resilience of the unicellular biosphere against huge environmental perturbations., Comment: Accepted in Astrophysics and Space Science

We examine the short-term effects that a galactic Gamma Ray Burst would cause on a planetary biosphere. The immediate environmental perturbation would arise due to the emission of an aurora like spectrum in the middle and low atmosphere, delivering at planet's surface a brief but intense ultraviolet flash. We calculated potential damages to both the photosynthetic and DNA apparatuses of unicellular organisms. We conclude that if the progenitor is 1-2 kiloparsec distant in the Milky Way, its main short-term bio-effect will be radiation damage in the photosynthetic machinery rather than in the genome.

We examine some environmental effects appearing on exoplanets in the habitable zone of red dwarfs, during the first billion years of the star evolution. We focus on the radiative perturbation that the frequent stellar flares would cause on the planet surface and down the assumed planetary ocean, with some insight on the affectation of potential life forms.

We continue former work on the modeling of potential effects of Gamma Ray Bursts on Phanerozoic Earth. We focus on global biospheric effects of ozone depletion and show a first modeling of the spectral reduction of light by NO2 formed in the stratosphere. We also illustrate the current complexities involved in the prediction of how terrestrial ecosystems would respond to this kind of burst. We conclude that more biological field and laboratory data are needed to reach even moderate accuracy in this modeling, Accepted for publication in Astrophysics & Space Science

The aim of the present work is to study the potential short-term atmospheric and biospheric influence of Gamma Ray Bursts on the Earth. We focus in the ultraviolet flash at the planet's surface, which occurs as a result of the retransmission of the $\gamma$ radiation through the atmosphere. This would be the only important short-term effect on life. We mostly consider Archean and Proterozoic eons, and for completeness we also comment on the Phanerozoic. Therefore, in our study we consider atmospheres with oxygen levels ranging from $10^{-5}$ to 1% of the present atmospheric level, representing different moments in the oxygen rise history. Ecological consequences and some strategies to estimate their importance are outlined., Comment: 13 pp., to appear in Astrophysics and Space Science

We briefly comment on a paper by Rubano and Scudellaro [Gen. Rel. Grav. 34 (2002) 307, astro-ph/0103335] where they found general exact solutions for two classes of exponential potentials in a scalar field model for quintessence. In that paper the authors were led to some interesting conclusions after a proper choice of the integration constants. By using dimensionless variables we show that the integration constants can be found explicitly without additional assumptions. In consequence we revise some results and conclusions in that paper. We also reproduce observations for Type-Ia supernovae with good accuracy.

In this work we apply a mathematical model of photosynthesis to quantify the potential for photosynthetic life in the very Early Archean oceans. We assume the presence of oceanic blockers of ultraviolet radiation, specifically ferrous ions. For this scenario, our results suggest a potential for photosynthetic life greater than or similar to that in later eras/eons, such as the Late Archean and the current Phanerozoic eon., Accepted for publication in Origins of Life and Evolution of Biospheres

In this work, we provide a tentative insight on how the solar radiation could have influenced the emergence and evolution of early photosynthetic life on Earth. An extrapolation is made for the case of other potentially habitable planets.

We continue our previous work on the potential short-term influence of a gamma ray bursts on Earth's biosphere, focusing on the only important short-term effect on life: the ultraviolet flash which occurs as a result of the retransmission of the {\gamma} radiation through the atmosphere. Thus, in this work we calculate the ultraviolet irradiances penetrating the first hundred meters of the water column, for Jerlov's ocean water types I, II and III. Then we estimate the UV flash potential for photosynthesis inhibition, showing that it can be important in a considerable part of the water column with light enough for photosynthesis to be done, the so called photic zone., Comment: Accepted for publication in Astrophysics and Space Science

Oscillating biochemical reactions are common in cell dynamics and could be closely related to the emergence of the life phenomenon itself. In this work, we study the dynamical features of some classical chemical or biochemical oscillators where the effect of cell volume changes is explicitly considered. Such analysis enables us to find some general conditions about the cell membrane to preserve such oscillatory patterns, of possible relevance to hypothetical primitive cells in which these structures first appeared.

In this work we present a model of the universe in which dark energy is modelled explicitely with both a dynamical quintessence field and a cosmological constant. Our results confirm the possibility of a future collapsing universe (for a given region of the parameter space), which is necessary for a consistent formulation of string theory and quantum field theory. We have also reproduced the measurements of modulus distance from supernovae with good accuracy., 11 pages, 4 figures, only the results for the single exponential potential are preserved. One author added. Some changes in the reference section. Submitted to Physical Review D