We propose that nanophase iron-oxide-bearing materials provided important niches for ancient photosynthetic microbes on the Earth that ultimately led to the oxygenation of the Earth's atmosphere and the formation of iron-oxide deposits. Atmospheric oxygen and ozone attenuate ultraviolet radiation on the Earth today providing substantial protection for photosynthetic organisms. With ultraviolet radiation fluxes likely to have been even higher on the early Earth than today, accessing solar radiation was particularly risky for early organisms. Yet, we know that photosynthesis arose early and played a critical role in subsequent evolution. Of primary importance was protection below 290 nm, where peak nucleic acid (~260 nm) and protein (~280 nm) absorptions occur. Nanophase ferric oxide/oxyhydroxide minerals absorb, and thus block, the lethal ultraviolet radiation, while transmitting light through much of the visible and near-infrared regions of interest to photosynthesis (400 to 1100 nm). Furthermore, they were available in early environments, and are synthesized by many organisms. Based on experiments using nanophase ferric oxide/oxyhydroxide minerals as a sunscreen for photosynthetic microbes, we suggest that iron, an abundant element widely used in biological mechanisms, may have provided the protection that early organisms needed in order to be able to use photosynthetically active radiation while being protected from ultraviolet-induced damage. The results of this study are broadly applicable to astrobiology because of the abundance of iron in other potentially habitable bodies and the evolutionary pressure to utilize solar radiation when available as an energy source. This model could apply to a potential life form on Mars or other bodies where liquid water and ultraviolet radiation could have been present at significant levels. Based on ferric oxide/oxyhydroxide spectral properties, likely geologic processes, and the results of experiments with the photosynthetic organisms, Euglena sp. and Chlamydomonas reinhardtii, we propose a scenario where photosynthesis, and ultimately the oxygenation of the atmosphere, depended on the protection of early microbes by nanophase ferric oxides/oxyhydroxides.

A number of studies have demonstrated that bacteria and fungi are present in the stratosphere. Since the tropopause is generally regarded as a barrier to the upward movement of particles it is difficult to see how such microorganisms can reach heights above 17 km. Volcanoes provide an obvious means by which this could be achieved, but these occur infrequently and any microorganisms entering the stratosphere from this source will rapidly fall out of the stratosphere. Here, we suggest mechanisms by which microorganisms might reach the stratosphere on a more regular basis; such mechanisms are, however, likely only to explain how micrometre to submicrometre particles could be elevated into the stratosphere. Intriguingly, clumps of bacteria of size in excess of 10 μm have been found in stratospheric samples. It is difficult to understand how such clumps could be ejected from the Earth to this height, suggesting that such bacterial masses may be incoming to Earth. We suggest that the stratospheric microflora is made up of two components: (a) a mixed population of bacteria and fungi derived from Earth, which can occasionally be cultured; and (b) a population made up of clumps of, viable but non-culturable, bacteria which are too large to have originated from Earth; these, we suggest, have arrived in the stratosphere from space. Finally, we speculate on the possibility that the transfer of bacteria from the Earth to the highly mutagenic stratosphere may have played a role in bacterial evolution.

We discuss whether sulphur traces on Jupiter's moon Europa could be of biogenic origin. The compounds detected by the Galileo mission have been conjectured to be endogenic, most likely of cryovolcanic origin, due to their non-uniform distribution in patches. The Galileo space probe first detected the sulphur compounds, as well as revealing that this moon almost certainly has a volcanically heated and potentially habitable ocean hiding beneath a surface layer of ice. In planning future exploration of Europa there are options for sorting out the source of the surficial sulphur. For instance, one possibility is searching for the sulphur source in the context of the study of the Europa Microprobe In Situ Explorer (EMPIE), which has been framed within the Jovian Minisat Explorer Technology Reference Study (ESA). It is conceivable that sulphur may have come from the nearby moon Io, where sulphur and other volcanic elements are abundant. Secondly, volcanic eruptions in Europa's seafloor may have brought sulphur to the surface. Can waste products rising from bacterial colonies beneath the icy surface be a third alternative significant factor in the sulphur patches on the Europan surface? Provided that microorganisms on Europa have the same biochemical pathways as those on Earth, over geologic time it is possible that autochthonous microbes can add substantially to the sulphur deposits on the surface of Europa. We discuss possible interpretations of the non-water-ice elements (especially the sulphur compound mercaptan) in the context of the studies for future missions. To achieve reliable biosignatures it seems essential to go back to Europa. Our work highlights the type of biogenic signatures that can be searched for when probing Europa's icy and patchy surface.

A mechanism that permits the separation and concentration of particles in natural systems is proposed. According to the mechanism, the particles in an aquifer are moved by an alternating flow of ground water. The retardation factor oscillates in synchronism with the alternating water flow. The retardation factor or the flow depend on the position in the aquifer (the particle velocity is u=v/R, where v is the water velocity and R is the retardation factor). The alternating flow is induced by tides, geysers or periodic rains. The alternating water flow produces temperature and water composition oscillations in the aquifer. Moreover, the alternating flow is caused by pressure oscillations: therefore, the retardation factor (which depends on pressure, temperature and water composition) oscillates. The dependence of the retardation factor on position is due to the inhomogeneity of the aquifer medium or to the position dependence of temperature, composition or pressure. Different particles may be concentrated at different places in the aquifer or in different aquifers. The particle concentration and the time necessary for concentration are estimated. The particles may be atoms, molecules, colloids or microorganisms. Such a mechanism may have played a role in chemical evolution.

Monocyanopolyynes are formed by arcing graphite electrodes in ammonia. This work completes the parallelism existing between the polyynes formed by laser ablation experiments of graphite targets and those produced from the submerged electric arc. In both cases the same products are obtained. The products consist of hydrogen-terminated polyynes if water is present, monocyanopolyynes (mixed with hydrogen-terminated polyynes) if the carbon arc is sparked in acetonitrile or ammonia and dicyanopolyynes if the arc is struck in liquid nitrogen. The mechanism of formation of polyynes in the submerged carbon arc involves essentially neutral species; similar species and pathways may also occur in the circumstellar environment where polyynes have been detected by radioastronomy. It is shown that the relative abundances of the polyynes formed in the submerged carbon arc or in a carbon arc in vacuum decrease by a factor between three and five as the chain length increases by a C2 unit. Exactly the same trend has been observed by radioastronomy both for polyynes and cyanopolyynes in the circumstellar environment around red giants and asymptotic giant branch (AGB) stars. This fact may be a simple coincidence or may suggest that the mechanism of formation of the polyynes in the carbon arc is the same as that occurring in the surroundings of carbon-rich stars.

Spectroscopic investigations of surface mineral components, expected to exist on the surface of Mars, using multiple spectral ranges and techniques, are vital to obtain the ground truth information or reference data for Mars exploration missions. This paper presents visible, near-infrared, thermal infrared reflectance and thermal infrared transmission spectra, as well as X-ray diffraction and scanning electron microscope/energy dispersive X-ray analyses of salt crusts and sediments interleaved with cyanobacterial materials from a coastal zone of the United Arab Emirates, where sabkhas exist. The samples obtained from sabkhas were characterized because they contain minerals requiring the water for formation and they provide a possible environment for some of the earliest organisms on Earth. The surface minerals identified include gypsum, calcite, halite, aragonite and dolomite. These sediments were found to be mixed with each other and intermingled with an algal mat, which consisted of cyanobacteria. If such materials formed in similar environments on Mars, their identification would be important for understanding the geobiological conditions of the planet and the potential habitability for life.

New observations of Titan by the Cassini spacecraft suggest the presence of cryovolcanism on the surface. Cryovolcanism has important astrobiological implications, as it provides a means of exposing Titan's organics to liquid water, transforming hydrocarbons and nitriles into more evolved and oxidized prebiotic species. One possible cryovolcano – the 180 km structure Ganesa Macula – resembles the pancake domes seen on Venus by the Magellan spacecraft. To assess the potential of Ganesa Macula for prebiotic chemistry, we estimate its height using radarclinometry and other methods, and calculate the freezing timescale assuming an initially completely liquid dome. Given height constraints of ~200 m to 4 km, we find that liquid water or water–ammonia environments could be sustained in Ganesa Macula for timescales of the order of 102–105 years. These timescales open a window for prebiotic chemistry far wider than can be explored in terrestrial laboratory experiments.

EANA–European Astrobiology Network Association

10–12 October 2005

Budapest, Hungary