The ‘Cyborg Astrobiologist’ has undergone a second geological field trial, at a site in northern Guadalajara, Spain, near Riba de Santiuste. The site at Riba de Santiuste is dominated by layered deposits of red sandstones. The Cyborg Astrobiologist is a wearable computer and video camera system that has demonstrated a capability to find uncommon interest points in geological imagery in real time in the field. In this second field trial, the computer vision system of the Cyborg Astrobiologist was tested at seven different tripod positions, on three different geological structures. The first geological structure was an outcrop of nearly homogeneous sandstone, which exhibits oxidized-iron impurities in red areas and an absence of these iron impurities in white areas. The white areas in these ‘red beds’ have turned white because the iron has been removed. The iron removal from the sandstone can proceed once the iron has been chemically reduced, perhaps by a biological agent. In one instance the computer vision system found several (iron-free) white spots to be uncommon and therefore interesting, as well as several small and dark nodules. The second geological structure was another outcrop some 600 m to the east, with white, textured mineral deposits on the surface of the sandstone, at the bottom of the outcrop. The computer vision system found these white, textured mineral deposits to be interesting. We acquired samples of the mineral deposits for geochemical analysis in the laboratory. This laboratory analysis of the crust identifies a double layer, consisting of an internal millimetre-size layering of calcite and an external centimetre-size efflorescence of gypsum. The third geological structure was a 50 cm thick palaeosol layer, with fossilized root structures of some plants. The computer vision system also found certain areas of these root structures to be interesting. A quasi-blind comparison of the Cyborg Astrobiologist's interest points for these images with the interest points determined afterwards by a human geologist shows that the Cyborg Astrobiologist concurred with the human geologist 68% of the time (true-positive rate), with a 32% false-positive rate and a 32% false-negative rate. The performance of the Cyborg Astrobiologist's computer vision system was by no means perfect, so there is plenty of room for improvement. However, these tests validate the image-segmentation and uncommon-mapping technique that we first employed at a different geological site (Rivas Vaciamadrid) with somewhat different properties for the imagery.

Despite its amazing morphological diversity, life as we know it on Earth today is remarkably similar in its basic molecular architecture and biochemistry. The assumption that all life on Earth today shares these molecular and biochemical features is part of the paradigm of modern biology. This paper examines the possibility that this assumption is false, more specifically, that the contemporary Earth contains as yet unrecognized alternative forms of microbial life. The possibility that more than one form of life arose on Earth is consistent with our current understanding of conditions on the early Earth and the biochemical and molecular possibilities for life. Arguments that microbial descendents of an alternative origin of life could not co-exist with familiar life are belied by what we know of the complexity and diversity of microbial communities. Furthermore, the tools that are currently used to explore the microbial world – microscopy (with the aid of techniques such as DAPI staining and fluorescence in situ hybridization), cultivation and PCR amplification of rRNA genes – could not detect such organisms if they existed. Thus, the fact that we have not discovered any alternative life forms cannot be taken as evidence that they do not exist.

Astrobiology harbours a number of rather diverse disciplines combining expertise in astronomy and astrophysics, biophysics and biology, chemistry and biochemistry, geophysics and geology, as well as mathematics. The need to foster advances in astrobiology are two-fold. On the one hand, there are many scientific reasons: the discoveries of extra-solar planets which contribute to our understanding of the Solar System and the formation of Earth-like planets, the realization that life can thrive under rather extreme conditions making it more probable for life to exist elsewhere in the Solar System and beyond, and the fact that major resources are being spent in developing the technology to produce artificial life, which helps us to appreciate the range of possibilities that nature may have utilized on Earth or elsewhere. On the other hand, astrobiology touches upon some fundamental questions regarding our very existence, and it is perhaps this that attracts the broad interest of scientists and the public alike. As a result, astrobiology networks and astrobiology centres have been emerging all over the world.

On Earth, surface detritus has a quartz-rich mineralogy as a consequence of plate tectonics. Rocky planets without plate tectonics, like Mars, have surface detritus derived from volcanic rocks. There is a marked contrast in the transmission of photosynthetically active radiation (PAR) through the upper few millimetres of the two sediment types. Quartz-rich sediment allows PAR to penetrate below the level where ultraviolet (UV) radiation is cut out, so represents a potential refuge for phototrophs at an early stage of evolution before chemical defences against UV radiation are developed. Opaque volcanogenic sediment does not allow significant transmission of radiation beneath the surface. There are consequences for the expression of biosignatures from phototrophs. In the case of direct examination as proposed for Mars, techniques such as Raman spectroscopy will be applicable only to surfaces rather than penetratively into the subsurface. When spectroscopic techniques can be applied to extrasolar planets, the chance of a vegetation signature will be enhanced if the early evolution of phototrophs has been facilitated by a subsurface refuge.

The mean surface temperature on Earth and other planets with atmospheres is determined by the radiative balance between the non-reflected incoming solar radiation and the outgoing long-wave black-body radiation from the atmosphere. The surface temperature is higher than the black-body temperature due to the greenhouse warming. Balancing the ice-albedo cooling and the greenhouse warming gives rise to two stable climate states. A cold climate state with a completely ice-covered planet, called Snowball Earth, and a warm state similar to our present climate where greenhouse warming prevents the total glaciation. The warm state has dominated Earth in most of its geological history despite a 30% fainter young Sun. The warming could have been controlled by a greenhouse thermostat operating by the temperature control of the weathering process depleting CO2 from the atmosphere. This temperature control has permitted life to evolve as early as the end of the heavy bombardment 4 billion years ago.

The process of catalysis of biochemical reactions has been essential since the first organic molecules appeared on Earth. As the complexity of the ensemble of primitive biomolecules was very low, primitive catalysts had necessarily to be very simple molecules or ions. The evolution of catalysts had to be in parallel with the evolution of the molecular species reacting. An example of this parallel evolution is nucleic acid polymerization. Synthesis of primitive short oligonucleotides could have been catalysed by metal ions either in solution or on the surface of minerals such as montmorillonite clays. Some oligonucleotides could start to function as templates for the synthesis of complementary copies and there is experimental evidence supporting the role also played by metal ions in this process. In later stages of evolution, a group of enzymatic proteins, nucleic acid polymerases, has been selected to catalyse nucleic acid replication. The presence of Mg2+ in the active centre of these enzymes suggests that evolution has preserved some of the primitive catalysts, including them as cofactors of more complex molecules. However, the reasons why Mg2+ was selected among other ions that possibly were present in primitive environments are unknown. In this paper we try to approach this question by analysing the amplification efficiency of the polymerase chain reaction of a DNA fragment in the presence of different metal ions. In some cases the conditions of the reaction have been displaced from optimum (by the presence of nucleotide imbalances and a suboptimal Mg2+concentration). The results obtained permit one to draw interesting conclusions about how some metallic cations can help replication to proceed in conditions of limited substrate availability, a circumstance that could have been frequent at prebiotic stages, when nucleic acid synthesis was dependent on the physico-chemical conditions of the environment.

Escherichia coli JM109 (Gram-negative) and Bacillus subtilis (Gram-positive) were grown under hypobaric conditions for 19 days at 25 °C to study the effects of 33 and 67 kPa low pressures on selected physiological responses; growth, cytoplasmic membrane polarization (measure of cytoplasmic membrane fluidity) and total cellular fatty acids. In the first experiment, cytoplasmic membrane polarization in B. subtilis increased under both hypobaric conditions, indicating the membrane became more rigid or less fluid. This experiment was repeated and the effect of the hypobaric conditions was not evident as in the first experiment with B. subtilis. In addition, total cellular fatty acids analysis for B. subtilis showed that hypobaric conditions did not alter the ratio of saturated to unsaturated fatty acids. The cytoplasmic membrane remained in the same fluid state in hypobaric grown E. coli cell cultures as in the 101 kPa ambient control cells in both experiments. However, the saturated to unsaturated ratios were altered in E. coli under hypobaric conditions. It is important to note the ratios for E. coli were less than 1, while the ratios for Bacillus were in the 28–50 range. Growth of both species was also measured by colony forming units at the termination of the 19 day experiment. Both bacterial species were capable of growth under hypobaric conditions and no distinct trend emerged as to the effect of hypobaric pressure on bacterial growth and cytoplasmic membrane fluidity.

This paper looks at the possibility that the peptide bond may be more common than originally thought, leading to molecules of prebiotic interest containing heavier atoms of the second row of the periodic table. Ab initio Möller–Plesset (MP2) coupled-cluster molecular orbital methods and density functional theory have been used. A first investigation of the six-atom system [C,3H,O,N] showed that formamide, NH2[bond]CH[double bond]O, is the most stable system that can be formed. Systematic studies on this same system in which C, O and N were respectively replaced by Si, S and P were then carried out. It has been found that the peptide-like linkage is the most stable for [C,3H,S,N] and [Si,3H,O,N] where NH2[bond]CH[double bond]S and NH2[bond]SiH[double bond]O are about 10–14 kcal mol−1 more favourable than the corresponding enol tautomers and well below other isomers on the energy scale. For [C,3H,O,P], the most stable species is CH3[bond]P[double bond]O, which is found 18 kcal mol−1 below the PH2[bond]CH[double bond]O peptide analogue. By correcting the known inadequacies in the calculations with the average theoretical to experimental ratio from the benchmark molecules of the system, it is possible to obtain a best estimate of rotational constants and infrared frequencies that should be precise enough to initiate laboratory experiments and/or observations. The corrected values of B=6.0342 GHz and C=5.4921 GHz for NH2[bond]CH[double bond]S; B=9.2292 GHz and C=6.1164 GHz for NH2[bond]SiH[double bond]O; B=8.0275 GHz and C=6.4779 GHz for CH3[bond]P[double bond]O should be accurate to within a few tenths of a per cent. Theoretical infrared spectra are also provided to assist in identification of these exotic species.

The generation of organic matter from CO2 and H2O is a highly endothermic reaction. Energy for biological carbon fixation can be derived from chemical potential gradients in the environment by chemoautotrophic organisms or it can be harvested from photon energy by photosynthesis. On Earth, the plate tectonically driven carbon flux through the surface environment is of such a magnitude that the chemical free energy production within the Earth is insufficient to support conversion of any significant fraction of the carbon to organic matter through chemoautotrophy. Therefore, the chemical and isotopic fingerprints we observe in the Earth's surface environments are based on the invention of photosynthesis by life. We cannot a priori assume that life on any planet will invent photosynthesis and remote life detection should thus not be based exclusively on the expectations from our own ecosystem.

The astrobiological relevance of carbonaceous chondrites is reviewed. It is argued that the primitive meteorites called carbonaceous chondrites provide a unique source of information about the materials and conditions in the Solar System during the earliest phases of its history, and its subsequent evolution. Presolar dust grains extracted from the carbonaceous chondrites provide direct information on the previous generations of stars that provided the materials present for planet formation. The organic material found in carbonaceous chondrites consist of amino acids, carboxylic acids and sugar derivatives. Part of the amino acids found show L-enantiomeric excesses, which indicates that homochirality on Earth could be a direct result of input from meteoritic material to the early Earth.

A simulation experiment with a complex bacterial soil community in a Mars simulation chamber was performed to determine the effect of Martian conditions on community activity, stability and survival. At three different depths in the soil core short-term effects of Martian conditions with and without ultraviolet (UV) exposure corresponding to 8 Martian Sol were compared. Community metabolic activities and functional diversity, measured as glucose respiration and versatility in substrate utilization, respectively, decreased after UV exposure, whereas they remained unaffected by Martian conditions without UV exposure. In contrast, the numbers of culturable bacteria and the genetic diversity were unaffected by the simulated Martian conditions both with and without UV exposure. The genetic diversity of the soil community and of the colonies grown on agar plates were evaluated by denaturant gradient gel electrophoresis (DGGE) on DNA extracts. Desiccation of the soil prior to experimentation affected the functional diversity by decreasing the versatility in substrate utilization. The natural dominance of endospores and Gram-positive bacteria in the investigated Mars-analogue soil may explain the limited effect of the Mars incubations on the survival and community structure. Our results suggest that UV radiation and desiccation are major selecting factors on bacterial functional diversity in terrestrial bacterial communities incubated under simulated Martian conditions. Furthermore, these results suggest that forward contamination of Mars is a matter of great concern in future space missions.

The European Astrobiology Network Association (EANA) coordinates and promotes astrobiology in the 17 European countries that are member of the organization. Astrobiology includes the study of the origin, evolution and distribution of life in the Universe. It is a multi-disciplinary science that encompasses the disciplines of chemistry, biology, palaeontology, geology, atmospheric physics, planetary physics and stellar physics. The open questions to be addressed and the steps ahead in cosmochemistry, star and planet formation, the chemistry of life's origin, the study of bacterial life as a reference and the search for habitats and biosignatures beyond the Earth are presented.

Meaning and purpose can be given to life, consciousness, the laws of physics, etc. If one assumes that the Universe is endowed with some form of (strong) anthropic principle. In particular, the final anthropic principle (FAP) of Barrow and Tipler postulates that intelligent life will continue in the Universe until the far future when the computational power of descendent civilizations will be sufficient to run simulations of enormous scale and power. Tipler has claimed that it will be possible to create simulations with rendered environments and inhabitants, i.e. intelligent software constructs, which are effectively ‘people’. Proponents of this FAP claim that if both substrate independence and the pattern identity postulate hold, then these simulations would be able to contain reanimated individuals that once lived. These claims have been heavily criticized but the growing study of physical eschatology, initiated by Freeman Dyson in a seminal work, and the developments in computational theory have made some progress in showing that simulations containing intelligent information processing software constructs, which may be conscious, are not only feasible but may be a reality within the next few centuries. In this work, arguments and conservative calculations are given which concur with these latter more minimal claims. FAP-type simulations inevitably rely on cosmology type, but current observations would seem to rule appropriate models out. However, it is argued that dark energy, described in the recent forms of ‘quintessence’ cosmological models may show the current conclusions from observations to be too presumptive. In this paper some relevant physical and cosmological aspects are reviewed in the light of the recent propositions regarding the plausibility of certain simulations given by Bostrom, and the longer held postulate of finite nature – due to Fredkin – which has grown in credibility, following advances in quantum mechanics and the computational theory of cellular automata. This latter postulate supports the conclusions of Bostrom, which, under certain plausible assumptions, can imply that our Universe is itself already a simulated entity. It is demonstrated in this paper how atemporal memory connections could make efficient ancestor simulations possible, solving many of the objections faced by the FAP of Barrow and Tipler. Also, if finite nature is true then it can offer a similar vindication to this FAP. Indeed the conclusions of this postulate can be realized more easily, but only if the existence of life within the simulation/Universe is not merely incidental to the (currently unknown) purpose for which it was generated to fulfil.

Template-directed polymer assembly is a likely feature of prebiotic chemistry, but the product blocks further synthesis, preventing amplification and Darwinian selection. Nucleic acids are unusual because charge repulsion between opposing phosphates permits salt-dependent association and dissociation. It was postulated (Lathe, R. (2004). Fast tidal cycling and the origin of life. Icarus168, 18–22) that tides at ocean shores provide the driving force for amplification: evaporative concentration promoted association/assembly on drying, while charge repulsion on tidal dilution drove dissociation. This permits exponential amplification by a process termed here the tidal chain reaction (TCR). The process is not strictly contingent upon tidal ebb and flow: circadian dews and rainfalls can produce identical cycling. Ionic strength-dependent association and dissociation of nucleic acids and possible prebiotic precursors are reviewed. Polymer scavenging, chain assembly by the recruitment of pre-formed fragments, is proposed as the primary mechanism of reiterative chain assembly. Parameters determining prebiotic polymer structure and amplification by TCR are discussed, with the suggestion that Darwinian selection may have operated on families of related polymers rather than on individual molecules.

It is important for research into the origins of life to elucidate polyamino acid formation under prebiotic conditions. Only a limited set of amino acids has been reported to polymerize thermally. In this paper we demonstrate a novel thermal polymerization mechanism in a molten urea of alkylamino acids (i.e. glycine, alanine, β-alanine, α-aminobutyric acid, valine, norvaline, leucine and norleucine), which had been thought to be incapable of undergoing thermal polymerization. Also, aspartic acid was found to polymerize in molten urea at a lower temperature than that at which aspartic acid alone had previously been thermally polymerized. Individual oligomers produced in heating experiments on urea–amino acid mixtures were analysed using a liquid chromatograph mass spectrometer. Major products in the reaction mixture were three different types of polyamino acid derivatives: N-carbamoylpolyamino acids, polyamino acids containing a hydantoin ring at the N-terminal position and unidentified derivatives with molecular weights that were greater by 78 than those of the corresponding peptide forms. The polymerization reaction occurred by taking advantage of the high polarity of molten urea as well as its dehydrating ability. Under the presumed prebiotic conditions employed here, many types of amino acids were thus revealed to undergo thermal polymerization.

It is widely believed that the current DNA–RNA–protein-based life forms have evolved from preceding RNA–protein-based life forms, and these again, from mere RNA replicons. By rationale, it can be assumed that the early RNA replicons were fully heterotrophic in terms of obtaining all their building blocks from their environment. In the absence of protein catalysts, their essential life functions had to be mediated by simple functional structures and mechanisms, such as RNA secondary structures, RNA–RNA interactions and RNA-mediated catalysis, and possibly by catalytic minerals or clays. The central role of RNA catalysts in early life forms is supported by the fact that several catalytic RNAs still perform central biological functions in current life forms, and at least some of these may be derived as molecular relicts from the early RNA-based life. The RNA-catalysed metabolic reactions and molecular fossils are more conserved in the eukaryotic life forms than in the prokaryotes, suggesting that the linear eukaryote genomes may more closely resemble the structure and function of the early RNA replicons, than what do the circular prokaryote genomes. Present-day RNA viruses and viroids utilize ultimately simple life strategies, which may be similar to those used by the early RNA replicons. Thus, molecular and functional properties of viruses and viroids may be considered as examples or models of the structures and replication mechanisms, which might have been used for the replication of the early biopolymers.

We review and re-examine the arguments for the proposal that life emerged by a quantity-to-quality transition of abiotic matter. This idea was originally proposed by the dialectical materialists, who are the proponents of the materialistic approach to Hegel's laws of dialectics. We find that one of the universal features of the quantity-to-quality transitions is the change in the organization of the system, which brings about novelty. We suggest that the principle of the quantity-to-quality transition may be a part of the algorithm of life, which is not Earth-centric.

We have explored chemical weathering of probable martian materials at low temperatures based on the increasing evidence for non-hydrothermal water at or near the martian surface. Chemical weathering of minerals at low temperatures (as low as 0 °C) in aqueous environments on Mars can provide geochemical energy to support construction of potential martian organisms. Here, we examine the geochemical energy available from the interaction of the martian surface or near-surface materials with low-temperature water. We calculate the Gibbs free energy for 13 different weathering reactions that are likely to be important on Mars. The aqueous weathering of 1 kg of an ultramafic rock such as the Chassigny meteorite under present martian conditions can support the construction of ~30 g of microbes. The aqueous weathering of 1 kg of a basaltic rock on Mars can support the construction of ~26 g of biomass under present martian conditions and ~32 grams for conditions probable in the past. This means that ~1.3×1019 g of potential biomass could have been supported from weathering a global layer of rock 1 m thick. Thus, low-temperature water–rock reactions on Mars can produce abundant geochemical energy for potential martian microbes.

The differences between unidirectional and bidirectional polymerization are considered. The unidirectional case is discussed in the framework of the RNA world. Similar to earlier models of this type, where polymerization was assumed to proceed in a bidirectional fashion (presumed to be relevant to peptide nucleic acids), left- and right-handed monomers are produced via an autocatalysis from an achiral substrate. The details of the bifurcation from a racemic solution to a homochiral state of either handedness is shown to be remarkably independent of whether the polymerization is unidirectional or bidirectional. Slightly larger differences are seen when dissociation is allowed and the dissociation fragments are recycled into the achiral substrate.

Models for segregation of racemic mixtures of chiral amphiphiles and lipophiles in aqueous solutions show that the amphiphiles with active isomerization kinetics can perform a spontaneous symmetry break during the segregation and self-assemble to homochiral matter. Based on physico-chemical facts, it is argued that D-glyceraldehyde, which was synthesized from the volatiles at the hydrothermal reactors at the origin of life, could be the origin of homochirality in biological systems.