Organic materials isolated from carbonaceous meteorites provide us with a record of pre-biotic chemistry in the early Solar System. Molecular, isotopic and in situ studies of these materials suggest that a number of extraterrestrial environments have contributed to the inventory of organic matter in the early Solar System including interstellar space, the Solar nebula and meteorite parent bodies.

There are several difficulties that have to be overcome in the study of the organic constituents of meteorites. Contamination by terrestrial biogenic organic matter is an ever-present concern and a wide variety of contaminant molecules have been isolated and identified including essential plant oils, derived from either biological sources or common cleaning products, and aliphatic hydrocarbons, most probably derived from petroleum-derived pollutants. Only 25% of the organic matter in carbonaceous chondrites is amenable to extraction with organic solvents; the remainder is present as a complex macromolecular aromatic network that has required the development of analytical approaches that can yield structural and isotopic information on this highly complex material.

Stable isotopic studies have been of paramount importance in understanding the origins of meteoritic organic matter and have provided evidence for the incorporation of interstellar molecules within meteoritic material. Extending isotopic studies to the molecular level is yielding new insights into both the sources of meteoritic organic matter and the processes that have modified it.

Organic matter in meteorites is intimately associated with silicate minerals and the in situ examination of the relationships between organic and inorganic components is crucial to our understanding of the role of asteroidal processes in the modification of organic matter and, in particular, the role of water as both a solvent and a reactant on meteorite parent bodies.

In the Arctic there are lenses of overcooled water brines (cryopegs) sandwiched within permafrost marine sediments 100–120 thousand years old. We have investigated the physiological properties of the pure cultures of anaerobic Clostridium sp. strain 14D1 and two strains of aerobic bacteria Psychrobacter sp. isolated from these cryopegs. The structural and physiological characteristics of new bacteria from water brines have shown their ability to survive and develop under harsh conditions, such as subzero temperatures and high salinity.

One of the current goals of Martian exploration is to find evidence for extinct (or even extant) life. Carbon (an essential ingredient of life on Earth) is known to occur on Mars as CO2 in the atmosphere and frozen in the polar caps; it is inferred to be present as carbonates in the Martian crust and soils. We are attempting to define and quantify the different carbon reservoirs on Mars, so that we can follow Mars' carbon cycle. This paper discusses a primordial magmatic component that could be the starting point of such a cycle. The nature, distribution and isotopic composition of carbon was measured in a suite of Martian meteorites, comprising Chassigny and 11 shergottites. Other Martian meteorites were not included, as they sample rocks that have been altered by fluids at Mars' surface. Our results, obtained by high-resolution stepped combustion and mass spectrometry, show that the magmatic component has a very variable abundance of 1–100 ppm, with δ13C~−20±4‰. This value is close to magmatic carbon determined for Moon and for Vesta (the parent body of the HED basaltic meteorites), but very different from that of Earth.

Mycelial fungi from cryopegs (tundra, Kolyma lowland, Russia) have been studied. The use of media with different amounts of salt and cultivation at 4 and 25 °C allowed us to isolate filamentous fungi assigned to 11 species. The micromycetes of genus Geomyces were found most often. The total amount of fungi reached 1–4×102 CFU ml−1 of water. The extreme conditions of the cryopegs – the high salinity of the water (150–200 g l−1) and the constant low temperatures (average annual temperature is from −9 to −11 °C) – might serve as a model for the conditions of interplanetary environments.

Monocyanopolyynes and dicyanopolyynes can be synthesized quite easily by the submerged electric arc. Monocyanopolyynes having the general formula H[bond](C[triple bond]C)n[bond]C[triple bond]N can be synthesized together with ordinary polyynes series H[bond](C[triple bond]C)n[bond]H by arcing graphite electrodes in acetonitrile. Dicyanopolyynes N[triple bond]C[bond](C[triple bond]C)n[bond]C[triple bond]N are produced almost pure by arcing graphite electrodes directly into liquid nitrogen. These molecules are present in the envelope of post-AGB (asymptotic giant branch), carbon-rich giant stars and also in dark molecular clouds. They are incorporated into comets and also into other primitive materials and may play a role in the prebiotic synthesis of more complex organic molecules having a biological significance. Furthermore, the cyanopolyynes are involved in the atmospheric chemistry of some bodies of the solar system. The discovery of the easy formation of these molecules under laboratory conditions may explain why these molecules are so ubiquitous in space and may also stimulate new ideas about the mechanism of their formation.

The FT-Raman spectra are described of green and red snow algae, Chlamydomona, involved in the colonization of exposed surfaces of the McLeod Glacier, Jane Col, Signy Island, situated at the northern edge of the Weddell Sea, Antarctica. The protective biochemicals produced by these extremophilic algae give rise to the so-called watermelon snow of Alpine regions. The red colour of the senescent algae is shown to derive from the accumulation of carotenoids and a deficiency of chlorophyll believed to arise from UV-radiation induced breakdown into phaecophytin. A comparison of the Raman spectra of young (green) and old (red) algae is effected and possible bio-markers for spectral detection on extraterrestrial icy moons and planets are identified.

Hydrothermal gypsum deposits in the Haughton impact structure, Devon Island, Canada, contain microbial communities in an endolithic habitat within individual gypsum crystals. Cyanobacterial colonies occur as masses along cleavage planes, up to 5 cm from crystal margins. The crystals are transparent, so allow transmission of light for photosynthesis, while affording protection from dehydration and wind. The colonies appear to have modified their mineral host to provide additional space as they expanded. The colonies are black due to UV-screening pigments. The relative ease with which microbial colonization may be detected and identified in impact-generated sulphate deposits at Haughton suggests that analogous settings on other planets might merit future searches for biosignatures. The proven occurrence of sulphates on the Martian surface suggests that sulphate minerals should be a priority target in the search for life on Mars.

Chemical evolution at the primitive prebiotic level may have proceeded toward increased diversity and complexity by the adjacent possible process (originally proposed by Kauffman). Once primitive self-replicating systems evolved, they could continue evolution via Eigen's hypercycles, and by Prigogine's emergence of order at the far-from-the equilibrium, non-linear systems. We envisage a gradual transition from a complex pre-life system, which we call the transition zone. In this zone we find a mixture of complex chemical cycles that reproduce and secure energy. Small incremental changes in the structure and organization of the transition zone eventually lead to life. However, the chemical systems in this zone may or may not lead to life. It is possible that the transition to life might be the result of an algorithm. But, it is uncertain whether an algorithm could be applied to the systems in which chance plays a role.

The accomplishment of detailed geomorphological studies is a prerequisite for the location of regions in which the prevailing conditions in the past, or at present, may allow the development of possible life forms. The Atlantis basin, located in Sirenum Terrae, Southern hemisphere of Mars, is one of these astrobiologically interesting regions, where the existence of geological features such as ancient volcanic edifices, sedimentary deposits of an ancient lake and recent gullies seem to indicate the long-term presence of a thermal source and a water reservoir deep and stable enough to sustain biological processes. Here we describe the most relevant topographic and geomorphologic features in the region, highlighting the possibility for liquid water to have been present in the basin and outskirts in different moments of Mars' history. We also apply this analysis to an initial discussion of the influence of the hydrogeological evolution of the region in the putative development and/or survival of life forms in Atlantis basin.

In addition to the accepted roles of plate tectonics in regulating planetary habitability through the composition of the atmosphere and temperature, and creating continents to enhance land-based evolution and biodiversity, it has a hitherto unexplored role in influencing surface mineralogy with possible implications for early evolution. Plate tectonics creates continents through the accretion of buoyant granitic crust. Erosion of the granites yields specific minerals including quartz, radioactive (uranium-, thorium-bearing) phases and phosphates, which could play a role in early evolution. Radioactive grains could help to concentrate carbon and increase its complexity through irradiation-induced polymerization at the prebiotic stage, and possibly influence mutation rates once life was established. Weathering of phosphate minerals was an important source of phosphorus for the biochemistry that is essential to life. Quartz-rich sands provide a translucent refuge for early photosynthesizers below the harmful effects of ultra-violet irradiation at the surface. Uranium is also important to the development of nuclear power in an advanced civilization. The mineralogy that engenders these processes is distinct from that to be expected on a planet without plate tectonics, where volcanogenic sediments would predominate, and further emphasizes the importance of plate tectonics to the evolution of life.

Gamma-ray bursts (GRBs) produce a flux of radiation detectable across the observable Universe. A GRB within our own galaxy could do considerable damage to the Earth's biosphere; rate estimates suggest that a dangerously near GRB should occur on average two or more times per billion years. At least five times in the history of life, the Earth has experienced mass extinctions that eliminated a large percentage of the biota. Many possible causes have been documented, and GRBs may also have contributed. The late Ordovician mass extinction approximately 440 million years ago may be at least partly the result of a GRB. A special feature of GRBs in terms of terrestrial effects is a nearly impulsive energy input of the order of 10 s. Due to expected severe depletion of the ozone layer, intense solar ultraviolet radiation would result from a nearby GRB, and some of the patterns of extinction and survivorship at this time may be attributable to elevated levels of UV radiation reaching the Earth. In addition, a GRB could trigger the global cooling which occurs at the end of the Ordovician period that follows an interval of relatively warm climate. Intense rapid cooling and glaciation at that time, previously identified as the probable cause of this mass extinction, may have resulted from a GRB.

The importance of the search for life within the universe underpins many of the objectives of ESA and NASA. Fundamental to this objective is the recognition and understanding of the early fossil record on planet Earth. The history of study of ‘microfossils’ from the 3465 Ma Apex cherts of the Warrawoona Group in Western Australia is reviewed, as are the criteria put forward to test for for biogenicity of early microfossils. We propose that the null hypothesis of an abiotic or prebiotic origin of ancient microscopical artefacts is sustained until mutually supporting, contextural morphological and geochemical evidence for a biological origin is presented and an abiotic origin is falsified.

Chemical and microbiological studies of the impact of terrestrial contamination of the lunar surface during the Apollo missions could provide valuable data to help refine future Mars surface exploration plans and planetary protection requirements for a human mission to Mars. NASA and ESA have outlined new visions for solar system exploration that will include a series of lunar robotic missions to prepare for and support a human return to the Moon, and future human exploration of Mars and other destinations. Under the Committee on Space Research's (COSPAR's) current planetary protection policy for the Moon, no decontamination procedures are required for outbound lunar spacecraft. Nonetheless, future in situ investigations of a variety of locations on the Moon by highly sensitive instruments designed to search for biologically derived organic compounds would help assess the contamination of the Moon by lunar spacecraft and Apollo astronauts. These studies could also provide valuable ‘ground truth’ data for Mars sample return missions and help define planetary protection requirements for future Mars bound spacecraft carrying life detection experiments.

The search for extraterrestrial intelligence (SETI) at optical wavelengths counts photons from target stars. The rationale is that the number of photons received from a solar-type star in a nanosecond is typically much less than unity and that an excess number of photons may be indicative of a laser pulse from a technological civilization. Extreme magnification gravitational microlensing is a possible contaminant to optical SETI programs as it would increase the photon rate and could masquerade as an optical pulse. We show that extreme magnification gravitational microlensing is unimportant, both because the required amplifications are difficult to obtain and because the time scales are too large. This conclusion holds both for the case of background stars in the field of view of the target star and from objects (such as planets) orbiting the target star.

A prediction of panspermia is that organic material should be abundant throughout the universe. The recovery of micrometre-sized biotic particles at altitudes of around 40 km above the Earth is a key indicator of the validity of panspermia. A common criticism of experiments to capture atmospheric particles is that the particles could have originated from the Earth. Theoretical models of the variation of temperature with altitude above the Earth show that 10 μm diameter particles can withstand rapid deceleration without significant ablation. Experimental evidence shows that small particles containing bacteria can survive the temperature regimes imposed by entry into the Earth's lower atmosphere. This is an important step in demonstrating that life on Earth did not evolve in isolation from the remainder of the universe.

In the paper Biological contamination studies of lunar landing sites by D.P. Glavin et al., published online 2004, there is an error on page 4 of the paper.

On Page 4, line 5, column 1:

∼3×105 should read ∼3×107